Network File System (NFS) Version 4 Protocol
Primary Data, Inc.4300 El Camino Real Ste 100 Los AltosCA94022United States+1 408 215 1519thomas.haynes@primarydata.comDell300 Innovative WayNashuaNH03062United States+1 781 572 8038dave_noveck@dell.com
The Network File System (NFS) version 4 protocol is a
distributed file system protocol that builds on the heritage
of NFS protocol version 2 (RFC 1094) and version 3 (RFC 1813).
Unlike earlier versions, the NFS version 4 protocol supports
traditional file access while integrating support for file
locking and the MOUNT protocol. In addition, support for
strong security (and its negotiation), COMPOUND operations,
client caching, and internationalization has been added. Of
course, attention has been applied to making NFS version 4
operate well in an Internet environment.
This document, together with the companion External Data
Representation (XDR) description document, RFC 7531, obsoletes
RFC 3530 as the definition of the NFS version 4 protocol.
The key words "MUST", "MUST NOT",
"REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED",
"MAY", and "OPTIONAL" in this document are to be
interpreted as described in RFC 2119,
except where "REQUIRED" and "RECOMMENDED" are used as qualifiers
to distinguish classes of attributes as described in Sections
and of this document.
The Network File System version 4 (NFSv4) protocol is a further
revision of the NFS protocol defined already by versions
2 and 3 .
It retains the essential
characteristics of previous versions: design for easy recovery;
independent of transport protocols, operating systems, and
file systems; simplicity; and good performance. The NFSv4
revision has the following goals:
Improved access and good performance on the Internet.
The protocol is designed to transit firewalls easily,
perform well where latency is high and bandwidth is low,
and scale to very large numbers of clients per server.
Strong security with negotiation built into the protocol.
The protocol builds on the work of the Open Network Computing
(ONC) Remote Procedure Call (RPC) working group
in supporting the RPCSEC_GSS protocol (see both
and ). Additionally, the NFSv4 protocol
provides a mechanism to allow clients and
servers the ability to negotiate security and require clients
and servers to support a minimal set of security schemes.
Good cross-platform interoperability.
The protocol features a file system model that provides a
useful, common set of features that does not unduly favor
one file system or operating system over another.
Designed for protocol extensions.
The protocol is designed to accept standard extensions that
do not compromise backward compatibility.
This document, together with the companion External Data
Representation (XDR) description document ,
obsoletes as the authoritative document
describing NFSv4. It does not introduce any over-the-wire protocol
changes, in the sense that previously valid requests remain valid.
The "Network File System (NFS) Version 4
External Data Representation Standard (XDR) Description" contains
the definitions in XDR description language of the constructs
used by the protocol. Inside this document, several
of the constructs are reproduced for purposes of explanation. The
reader is warned of the possibility of errors in the reproduced
constructs outside of .
For any part of the document that is inconsistent with
, is to be
considered authoritative.
To provide a reasonable context for the reader, the major
features of the NFSv4 protocol will be reviewed in brief.
This is done to provide an appropriate context for both
the reader who is familiar with the previous versions of the
NFS protocol and the reader who is new to the NFS protocols.
For the reader new to the NFS protocols, some fundamental
knowledge is still expected. The reader should
be familiar with the XDR and RPC protocols as described in
and .
A basic knowledge of file systems and distributed file systems
is expected as well.
As with previous versions of NFS, the XDR and RPC
mechanisms used for the NFSv4 protocol are those
defined in and
. To meet end-to-end
security requirements, the RPCSEC_GSS framework
(both version 1 in and
version 2 in )
will be used to extend the basic RPC security. With the
use of RPCSEC_GSS, various mechanisms can be provided to
offer authentication, integrity, and privacy to the
NFSv4 protocol. Kerberos V5 will be used as described
in to provide one security
framework. With the use of RPCSEC_GSS, other mechanisms
may also be specified and used for NFSv4 security.
To enable in-band security negotiation, the NFSv4
protocol has added a new operation that provides the client
with a method of querying the server about its policies regarding
which security mechanisms must be used for access to the
server's file system resources. With this, the client can
securely match the security mechanism that meets the policies
specified at both the client and server.
A significant departure from the previous versions of the
NFS protocol is the introduction of the COMPOUND procedure.
For the NFSv4 protocol, there are two RPC procedures:
NULL and COMPOUND. The COMPOUND procedure is defined in
terms of operations, and these operations correspond more
closely to the traditional NFS procedures.
With the use of the COMPOUND procedure, the client is able
to build simple or complex requests. These COMPOUND requests
allow for a reduction in the number of RPCs needed for logical
file system operations. For example, without previous contact
with a server a client will be able to read data from a file
in one request by combining LOOKUP, OPEN, and READ operations
in a single COMPOUND RPC. With previous versions of the NFS
protocol, this type of single request was not possible.
The model used for COMPOUND is very simple. There is no
logical OR or ANDing of operations. The operations combined
within a COMPOUND request are evaluated in order by the server.
Once an operation returns a failing result, the evaluation
ends and the results of all evaluated operations are returned
to the client.
The NFSv4 protocol continues to have the client refer
to a file or directory at the server by a "filehandle". The
COMPOUND procedure has a method of passing a filehandle from
one operation to another within the sequence of operations.
There is a concept of a current filehandle and a
saved filehandle. Most operations use the current filehandle
as the file system object to operate upon. The
saved filehandle is used as temporary filehandle storage within
a COMPOUND procedure as well as an additional operand for
certain operations.
The general file system model used for the NFSv4
protocol is the same as previous versions. The server
file system is hierarchical, with the regular files contained
within being treated as opaque byte streams. In a slight
departure, file and directory names are encoded with UTF-8
to deal with the basics of internationalization.
The NFSv4 protocol does not require a separate
protocol to provide for the initial mapping between pathname
and filehandle. Instead of using the older MOUNT protocol
for this mapping, the server provides a root filehandle
that represents the logical root or top of the file system
tree provided by the server. The server provides multiple
file systems by gluing them together with pseudo-file systems.
These pseudo-file systems provide for potential gaps in the
pathnames between real file systems.
In previous versions of the NFS protocol, the filehandle
provided by the server was guaranteed to be valid or
persistent for the lifetime of the file system object
to which it referred. For some server implementations,
this persistence requirement has been difficult to meet.
For the NFSv4 protocol, this requirement has been
relaxed by introducing another type of filehandle -- volatile.
With persistent and volatile filehandle types, the server
implementation can match the abilities of the file system at
the server along with the operating environment. The client
will have knowledge of the type of filehandle being provided
by the server and can be prepared to deal with the semantics
of each.
The NFSv4 protocol has a rich and extensible
file object attribute structure, which is divided
into REQUIRED, RECOMMENDED, and named attributes
(see ).
Several (but not all) of the REQUIRED attributes
are derived from the attributes of NFSv3 (see the
definition of the fattr3 data type in ). An example of a REQUIRED
attribute is the file object's type () so that regular files
can be distinguished from directories (also known
as folders in some operating environments) and
other types of objects. REQUIRED attributes are
discussed in .
An example of the RECOMMENDED attributes is
an acl (). This attribute defines
an Access Control List (ACL) on a file object. An ACL provides
file access control beyond the
model used in NFSv3. The ACL definition allows
for specification of specific sets of permissions
for individual users and groups. In addition,
ACL inheritance allows propagation of access
permissions and restriction down a directory tree
as file system objects are created. RECOMMENDED
attributes are discussed in .
A named attribute is an opaque byte stream that is associated
with a directory or file and referred to by a string name.
Named attributes are meant to be used by client applications
as a method to associate application-specific data with a
regular file or directory. NFSv4.1 modifies named attributes
relative to NFSv4.0 by tightening the allowed operations in
order to prevent the development of non&nbhy;interoperable
implementations. Named attributes are discussed
in .
A single-server namespace is the file system hierarchy that
the server presents for remote access. It is a proper
subset of all the file systems available locally.
NFSv4 contains a number of features to allow
implementation of namespaces that cross server boundaries
and that allow and facilitate a non-disruptive transfer of
support for individual file systems between servers. They
are all based upon attributes that allow one file system to
specify alternative or new locations for that file system.
That is, just as a client might traverse across local
file systems on a single server, it can now traverse to a remote
file system on a different server.
These attributes may be used together with the concept
of absent file systems, which provide specifications
for additional locations but no actual file system
content. This allows a number of important facilities:
Location attributes may be used with absent file systems
to implement referrals whereby one server may direct the
client to a file system provided by another server. This
allows extensive multi-server namespaces to be constructed.
Location attributes may be provided for present file systems
to provide the locations of alternative file system instances
or replicas to be used in the event that the current
file system instance becomes unavailable.
Location attributes may be provided when a previously
present file system becomes absent. This allows
non-disruptive migration of file systems to alternative
servers.
The NFSv4 protocol introduces OPEN and CLOSE
operations. The OPEN operation provides a single point where
file lookup, creation, and share semantics (see
) can be combined.
The CLOSE operation also provides for the release of state
accumulated by OPEN.
With the NFSv4 protocol, the support for byte-range
file locking is part of the NFS protocol. The file locking
support is structured so that an RPC callback mechanism is
not required. This is a departure from the previous versions
of the NFS file locking protocol, Network Lock Manager (NLM) .
The state associated with file locks is maintained at the
server under a lease-based model. The server defines a single
lease period for all state held by an NFS client. If the
client does not renew its lease within the defined period,
all state associated with the client's lease may be released
by the server. The client may renew its lease by use of
the RENEW operation or implicitly by use of other operations
(primarily READ).
The file, attribute, and directory caching for the NFSv4
protocol is similar to previous versions. Attributes and
directory information are cached for a duration determined by
the client. At the end of a predefined timeout, the client
will query the server to see if the related file system object
has been updated.
For file data, the client checks its cache validity when the
file is opened. A query is sent to the server to determine
if the file has been changed. Based on this information,
the client determines if the data cache for the file should be
kept or released. Also, when the file is closed, any modified
data is written to the server.
If an application wants to serialize access to file data, file
locking of the file data ranges in question should be used.
The major addition to NFSv4 in the area of caching is the
ability of the server to delegate certain responsibilities
to the client. When the server grants a delegation for a
file to a client, the client is guaranteed certain semantics
with respect to the sharing of that file with other clients.
At OPEN, the server may provide the client either a read
(OPEN_DELEGATE_READ) or a write (OPEN_DELEGATE_WRITE)
delegation for the file (see ).
If the client is granted an OPEN_DELEGATE_READ delegation,
it is assured that no other client has the ability to write
to the file for the duration of the delegation. If the
client is granted an OPEN_DELEGATE_WRITE delegation, the
client is assured that no other client has read or write
access to the file.
Delegations can be recalled by the server. If another
client requests access to the file in such a way that the
access conflicts with the granted delegation, the server is
able to notify the initial client and recall the delegation.
This requires that a callback path exist between the server and
client. If this callback path does not exist, then delegations
cannot be granted. The essence of a delegation is that it
allows the client to locally service operations such as OPEN,
CLOSE, LOCK, LOCKU, READ, or WRITE without immediate interaction
with the server.
The following definitions are provided for the purpose of providing
an appropriate context for the reader.
A file system is "absent" when a namespace component does not have a
backing file system.
The Anonymous Stateid is a special locking object and is
defined in .
In this document, a byte is an octet, i.e., a datum exactly
8 bits in length.
The client is the entity that accesses the NFS server's
resources. The client may be an application that contains
the logic to access the NFS server directly. The client
may also be the traditional operating system client that
provides remote file system services for a set of applications.
With reference to byte-range locking, the client is also the
entity that maintains a set of locks on behalf of one or more
applications. This client is responsible for crash or failure
recovery for those locks it manages.
Note that multiple clients may share the same transport and
connection, and multiple clients may exist on the same network
node.
The client ID is a 64-bit quantity used as a unique, shorthand
reference to a client-supplied verifier and ID. The server
is responsible for supplying the client ID.
The file system is the collection of objects on a server that
share the same fsid attribute (see ).
A lease is an interval of time defined by the server for which
the client is irrevocably granted a lock. At the end of a
lease period the lock may be revoked if the lease has not
been extended. The lock must be revoked if a conflicting
lock has been granted after the lease interval.
All leases granted by a server have the same fixed
duration. Note that the fixed interval duration was chosen to
alleviate the expense a server would have in maintaining
state about variable-length leases across server failures.
The term "lock" is used to refer to record (byte-range)
locks as well as share reservations unless specifically
stated otherwise.
Each byte-range lock is associated with a specific lock-owner
and an open-owner. The lock-owner consists of a
client ID and an opaque owner string.
The client presents this to the server to establish
the ownership of the byte-range lock as needed.
Each open file is associated with a specific open-owner,
which consists of a client ID and an opaque owner string.
The client presents this to the server to establish
the ownership of the open as needed.
The READ Bypass Stateid is a special locking object and is
defined in .
The "server" is the entity responsible for coordinating
client access to a set of file systems.
NFSv4 servers must be able to recover without data
loss from multiple power failures (including cascading
power failures, that is, several power failures in quick
succession), operating system failures, and hardware failure
of components other than the storage medium itself (for
example, disk, non&nbhy;volatile RAM).
Some examples of stable storage that are allowable for an
NFS server include:
Media commit of data. That is, the modified data
has been successfully written to the disk media --
for example, the disk platter.
An immediate reply disk drive with battery-backed
on-drive intermediate storage or uninterruptible
power system (UPS).
Server commit of data with battery-backed intermediate
storage and recovery software.
Cache commit with UPS and recovery software.
A stateid is a 128-bit quantity returned by a server that
uniquely identifies the open and locking states provided by the
server for a specific open-owner or lock-owner/open-owner pair for
a specific file and type of lock.
A verifier is a 64-bit quantity generated by the client that
the server can use to determine if the client has restarted and lost
all previous lock state.
The main changes from RFC 3530 are:
The XDR definition has been moved to a companion document
.
The IETF intellectual property statements were updated to the
latest version.
There is a restructured and more complete explanation of
multi-server namespace features.
The handling of domain names was updated to reflect
Internationalized Domain Names in Applications (IDNA)
.
The previously required LIPKEY and SPKM-3 security mechanisms
have been removed.
Some clarification was provided regarding a client
re-establishing callback information to the new server
if state has been migrated.
A third edge case was added for courtesy locks and network
partitions.
The definition of stateid was strengthened.
The definition of the NFSv4 protocol in
replaced and obsoleted the definition present in
. While portions of the two documents
remained the same, there were substantive changes in others.
The changes made between and
reflect implementation experience and
further review of the protocol.
The following list is not inclusive of all changes but
presents some of the most notable changes or additions made:
The state model has added an open_owner4 identifier. This
was done to accommodate POSIX-based clients and the model
they use for file locking. For POSIX clients, an open_owner4
would correspond to a file descriptor potentially shared
amongst a set of processes and the lock_owner4 identifier
would correspond to a process that is locking a file.
Added clarifications and error conditions for the
handling of the owner and group attributes. Since these
attributes are string based (as opposed to the numeric
uid/gid of previous versions of NFS), translations may not
be available and hence the changes made.
Added clarifications for the ACL and mode attributes to
address evaluation and partial support.
For identifiers that are defined as XDR opaque, set limits
on their size.
Added the mounted_on_fileid attribute to allow POSIX clients
to correctly construct local mounts.
Modified the SETCLIENTID/SETCLIENTID_CONFIRM operations to
deal correctly with confirmation details along with adding
the ability to specify new client callback information.
Also added clarification of the callback information itself.
Added a new operation RELEASE_LOCKOWNER to enable notifying
the server that a lock_owner4 will no longer be used by
the client.
Added RENEW operation changes to identify the client correctly
and allow for additional error returns.
Verified error return possibilities for all operations.
Removed use of the pathname4 data type from LOOKUP and OPEN
in favor of having the client construct a sequence of LOOKUP
operations to achieve the same effect.
The syntax and semantics to describe the data types of the
NFSv4 protocol are defined in the XDR
and RPC documents. The next sections
build upon the XDR data types to define types and structures
specific to this protocol. As a reminder, the size constants and
authoritative definitions can be found in .
lists the base NFSv4 data types.Data TypeDefinitionint32_ttypedef int int32_t;uint32_ttypedef unsigned int uint32_t;int64_ttypedef hyper int64_t;uint64_ttypedef unsigned hyper uint64_t;attrlist4typedef opaque attrlist4<>;Used for file/directory attributes.bitmap4typedef uint32_t bitmap4<>;Used in attribute array encoding.changeid4typedef uint64_t changeid4;Used in the definition of change_info4.clientid4typedef uint64_t clientid4;Shorthand reference to client identification.count4typedef uint32_t count4;Various count parameters (READ, WRITE, COMMIT).length4typedef uint64_t length4;Describes LOCK lengths.mode4typedef uint32_t mode4;Mode attribute data type.nfs_cookie4typedef uint64_t nfs_cookie4;Opaque cookie value for READDIR.nfs_fh4typedef opaque nfs_fh4<NFS4_FHSIZE>;Filehandle definition.nfs_ftype4enum nfs_ftype4;Various defined file types.nfsstat4enum nfsstat4;Return value for operations.nfs_lease4typedef uint32_t nfs_lease4;Duration of a lease in seconds.offset4typedef uint64_t offset4;Various offset designations (READ, WRITE, LOCK, COMMIT).qop4typedef uint32_t qop4;Quality of protection designation in SECINFO.sec_oid4typedef opaque sec_oid4<>;Security Object Identifier. The sec_oid4 data type is
not really opaque. Instead, it contains an ASN.1 OBJECT IDENTIFIER as used by
GSS-API in the mech_type argument to GSS_Init_sec_context. See for details.seqid4typedef uint32_t seqid4;Sequence identifier used for file locking.utf8stringtypedef opaque utf8string<>;UTF-8 encoding for strings.utf8str_cistypedef utf8string utf8str_cis;Case-insensitive UTF-8 string.utf8str_cstypedef utf8string utf8str_cs;Case-sensitive UTF-8 string.utf8str_mixedtypedef utf8string utf8str_mixed;UTF-8 strings with a case-sensitive prefix and a case-insensitive suffix.component4typedef utf8str_cs component4;Represents pathname components.linktext4typedef opaque linktext4<>;Symbolic link contents ("symbolic link" is defined in an Open Group standard).ascii_REQUIRED4typedef utf8string ascii_REQUIRED4;String is sent as ASCII and thus is automatically UTF-8.pathname4typedef component4 pathname4<>;Represents pathname for fs_locations.nfs_lockid4typedef uint64_t nfs_lockid4;verifier4typedef opaque verifier4[NFS4_VERIFIER_SIZE];Verifier used for various operations (COMMIT, CREATE, OPEN, READDIR, WRITE) NFS4_VERIFIER_SIZE is defined as 8.
struct nfstime4 {
int64_t seconds;
uint32_t nseconds;
};
The nfstime4 structure gives the number of seconds and
nanoseconds since midnight or 0 hour January 1, 1970 Coordinated
Universal Time (UTC). Values greater than zero for the seconds
field denote dates after the 0 hour January 1, 1970. Values less
than zero for the seconds field denote dates before the 0 hour
January 1, 1970. In both cases, the nseconds field is to be
added to the seconds field for the final time representation.
For example, if the time to be represented is one-half second
before 0 hour January 1, 1970, the seconds field would have a
value of negative one (-1) and the nseconds fields would have
a value of one-half second (500000000). Values greater than
999,999,999 for nseconds are considered invalid.
This data type is used to pass time and date information.
A server converts to and from its local representation of
time when processing time values, preserving as much accuracy
as possible. If the precision of timestamps stored for a
file system object is less than defined, loss of precision can
occur. An adjunct time maintenance protocol is recommended to
reduce client and server time skew.
enum time_how4 {
SET_TO_SERVER_TIME4 = 0,
SET_TO_CLIENT_TIME4 = 1
};
union settime4 switch (time_how4 set_it) {
case SET_TO_CLIENT_TIME4:
nfstime4 time;
default:
void;
};
The above definitions are used as the attribute definitions to
set time values. If set_it is SET_TO_SERVER_TIME4, then the
server uses its local representation of time for the time value.
struct specdata4 {
uint32_t specdata1; /* major device number */
uint32_t specdata2; /* minor device number */
};
This data type represents additional information for the device
file types NF4CHR and NF4BLK.
struct fsid4 {
uint64_t major;
uint64_t minor;
};
This type is the file system identifier that is used as a
REQUIRED attribute.
struct fs_location4 {
utf8str_cis server<>;
pathname4 rootpath;
};
struct fs_locations4 {
pathname4 fs_root;
fs_location4 locations<>;
};
The fs_location4 and fs_locations4 data types are used for the
fs_locations RECOMMENDED attribute, which is used for migration
and replication support.
struct fattr4 {
bitmap4 attrmask;
attrlist4 attr_vals;
};
The fattr4 structure is used to represent file and directory
attributes.
The bitmap is a counted array of 32-bit integers used to
contain bit values. The position of the integer in the array
that contains bit n can be computed from the expression
(n / 32), and its bit within that integer is (n mod 32).
0 1
+-----------+-----------+-----------+--
| count | 31 .. 0 | 63 .. 32 |
+-----------+-----------+-----------+--
struct change_info4 {
bool atomic;
changeid4 before;
changeid4 after;
};
This structure is used with the CREATE, LINK, REMOVE, and RENAME
operations to let the client know the value of the change
attribute for the directory in which the target file system
object resides.
struct clientaddr4 {
/* see struct rpcb in RFC 1833 */
string r_netid<>; /* network id */
string r_addr<>; /* universal address */
};
The clientaddr4 structure is used as part of the SETCLIENTID
operation, either (1) to specify the address of the client that is
using a client ID or (2) as part of the callback registration.
The r_netid and r_addr fields respectively contain a network
id and universal address. The network id and universal
address concepts, together with formats for TCP over IPv4
and TCP over IPv6, are defined in ,
specifically Tables 2 and 3 and Sections 5.2.3.3 and 5.2.3.4.
struct cb_client4 {
unsigned int cb_program;
clientaddr4 cb_location;
};
This structure is used by the client to inform the server of
its callback address; it includes the program number and client
address.
struct nfs_client_id4 {
verifier4 verifier;
opaque id<NFS4_OPAQUE_LIMIT>;
};
This structure is part of the arguments to the SETCLIENTID
operation.
struct open_owner4 {
clientid4 clientid;
opaque owner<NFS4_OPAQUE_LIMIT>;
};
This structure is used to identify the owner of open state.
struct lock_owner4 {
clientid4 clientid;
opaque owner<NFS4_OPAQUE_LIMIT>;
};
This structure is used to identify the owner of file locking
state.
struct open_to_lock_owner4 {
seqid4 open_seqid;
stateid4 open_stateid;
seqid4 lock_seqid;
lock_owner4 lock_owner;
};
This structure is used for the first LOCK operation done for an
open_owner4. It provides both the open_stateid and lock_owner
such that the transition is made from a valid open_stateid
sequence to that of the new lock_stateid sequence. Using this
mechanism avoids the confirmation of the lock_owner/lock_seqid
pair since it is tied to established state in the form of the
open_stateid/open_seqid.
struct stateid4 {
uint32_t seqid;
opaque other[NFS4_OTHER_SIZE];
};
This structure is used for the various state-sharing mechanisms
between the client and server. For the client, this data
structure is read-only. The server is required to increment the
seqid field monotonically at each transition of the stateid.
This is important since the client will inspect the seqid in
OPEN stateids to determine the order of OPEN processing done
by the server.
The NFSv4 protocol is an RPC application that uses RPC version 2
and the XDR as defined in
and . The RPCSEC_GSS security flavors as
defined in version 1 () and version 2
() MUST be implemented
as the mechanism to deliver stronger security for the NFSv4
protocol. However, deployment of RPCSEC_GSS is optional.
Historically, NFSv2 and NFSv3 servers have resided on
port 2049. The registered port 2049 for the NFS protocol
SHOULD be the default configuration. Using the registered port
for NFS services means the NFS client will not need to use the RPC
binding protocols as described in ; this
will allow NFS to transit firewalls.
Where an NFSv4 implementation supports operation over the IP network
protocol, the supported transport layer between NFS and IP MUST be an IETF
standardized transport protocol that is specified to avoid network
congestion; such transports include TCP and the
Stream Control Transmission Protocol (SCTP). To enhance the
possibilities for interoperability, an NFSv4 implementation MUST
support operation over the TCP transport protocol.
If TCP is used as the transport, the client and server SHOULD use
persistent connections. This will prevent the weakening of TCP's
congestion control via short-lived connections and will improve
performance for the Wide Area Network (WAN) environment by
eliminating the need for SYN handshakes.
As noted in ,
the authentication model for NFSv4 has moved from
machine-based to principal-based. However, this modification
of the authentication model does not
imply a technical requirement to move the TCP connection management
model from whole machine-based to one based on a per-user model.
In particular, NFS over TCP client implementations have traditionally
multiplexed traffic for multiple users over a common TCP connection
between an NFS client and server. This has been true, regardless of
whether the NFS client is using AUTH_SYS, AUTH_DH, RPCSEC_GSS, or
any other flavor. Similarly, NFS over TCP server implementations
have assumed such a model and thus scale the implementation of TCP
connection management in proportion to the number of expected client
machines. It is intended that NFSv4 will not modify this
connection management model. NFSv4 clients that violate
this assumption can expect scaling issues on the server and hence
reduced service.
When processing an NFSv4 request received over a reliable transport such as
TCP, the NFSv4 server MUST NOT silently drop the request,
except if the established transport connection has been broken. Given such a
contract between NFSv4 clients and servers, clients MUST NOT
retry a request unless one or both of the following are true:
The transport connection has been broken
The procedure being retried is the NULL procedure
Since reliable transports, such as TCP, do not always synchronously
inform a peer when the other peer has broken the connection (for
example, when an NFS server reboots), the NFSv4 client may
want to actively "probe" the connection to see if has been broken.
Use of the NULL procedure is one recommended way to do so. So, when
a client experiences a remote procedure call timeout (of some
arbitrary implementation-specific amount), rather than retrying the
remote procedure call, it could instead issue a NULL procedure call
to the server. If the server has died, the transport connection
break will eventually be indicated to the NFSv4 client.
The client can then reconnect, and then retry the original request.
If the NULL procedure call gets a response, the connection has
not broken. The client can decide to wait longer for the original
request's response, or it can break the transport connection and
reconnect before re&nbhy;sending the original request.
For callbacks from the server to the client, the same rules apply,
but the server doing the callback becomes the client, and the client
receiving the callback becomes the server.
Traditional RPC implementations have included AUTH_NONE, AUTH_SYS,
AUTH_DH, and AUTH_KRB4 as security flavors. With
, an additional security flavor of RPCSEC_GSS
has been introduced, which uses the functionality of GSS-API
. This allows for the
use of various security mechanisms by the RPC layer without the
additional implementation overhead of adding RPC security flavors.
For NFSv4, the RPCSEC_GSS security flavor MUST be used to
enable the mandatory-to-implement security mechanism. Other flavors,
such as AUTH_NONE, AUTH_SYS, and AUTH_DH, MAY be implemented as well.
RPCSEC_GSS, via GSS-API, supports multiple mechanisms that provide
security services. For interoperability, NFSv4 clients and servers
MUST support the Kerberos V5 security mechanism.
The use of RPCSEC_GSS requires selection of mechanism, quality of
protection (QOP), and service (authentication, integrity, privacy).
For the mandated security mechanisms, NFSv4 specifies that a QOP of
zero is used, leaving it up to the mechanism or the mechanism's
configuration to map QOP zero to an appropriate level of protection.
Each mandated mechanism specifies a minimum set of cryptographic
algorithms for implementing integrity and privacy. NFSv4 clients
and servers MUST be implemented on operating environments that comply
with the required cryptographic algorithms of each required
mechanism.
The Kerberos V5 GSS-API mechanism as described in
MUST be implemented with the
RPCSEC_GSS services as specified in
. Both client and server
MUST support each of the pseudo-flavors.
NumberNameMechanism's OIDRPCSEC_GSS service390003krb51.2.840.113554.1.2.2rpc_gss_svc_none390004krb5i1.2.840.113554.1.2.2rpc_gss_svc_integrity390005krb5p1.2.840.113554.1.2.2rpc_gss_svc_privacy
Note that the pseudo-flavor is presented here as a mapping aid to the
implementer. Because this NFS protocol includes a method to negotiate
security and it understands the GSS-API mechanism, the pseudo-flavor
is not needed. The pseudo-flavor is needed for NFSv3 since
the security negotiation is done via the MOUNT protocol as described
in .
At the time this document was specified, the Advanced Encryption Standard
(AES) with HMAC-SHA1 was a required algorithm set for Kerberos V5.
In contrast, when NFSv4.0 was first specified in
, weaker algorithm sets were
REQUIRED for Kerberos V5, and were REQUIRED in the NFSv4.0
specification, because the Kerberos V5 specification at the time did
not specify stronger algorithms. The NFSv4 specification does not
specify required algorithms for Kerberos V5, and instead, the
implementer is expected to track the evolution of the Kerberos V5
standard if and when stronger algorithms are specified.
When deploying NFSv4, the strength of the security achieved depends
on the existing Kerberos V5 infrastructure. The algorithms of
Kerberos V5 are not directly exposed to or selectable by the client
or server, so there is some due diligence required by the user of
NFSv4 to ensure that security is acceptable where needed. Guidance
is provided in as to why weak algorithms
should be disabled by default.
With the NFSv4 server potentially offering multiple security
mechanisms, the client needs a method to determine or negotiate
which mechanism is to be used for its communication with the server.
The NFS server can have multiple points within its file system
namespace that are available for use by NFS clients. In turn, the
NFS server can be configured such that each of these entry points
can have different or multiple security mechanisms in use.
The security negotiation between client and server SHOULD be done
with a secure channel to eliminate the possibility of a third party
intercepting the negotiation sequence and forcing the client and
server to choose a lower level of security than required or desired.
See for further discussion.
The SECINFO operation will allow the client to determine,
on a per-filehandle basis, what security triple (see
and )
is to be used for server access. In general, the client will not
have to use the SECINFO operation, except during initial
communication with the server or when the client encounters a
new security policy as the client navigates the namespace. Either
condition will force the client to negotiate a new security triple.
Based on the assumption that each NFSv4 client and server
MUST support a minimum set of security (i.e.,
Kerberos V5 under RPCSEC_GSS), the NFS client will start its
communication with the server with one of the minimal security triples.
During communication with the server, the client can receive an NFS
error of NFS4ERR_WRONGSEC. This error allows the server to notify the
client that the security triple currently being used is not appropriate
for access to the server's file system resources. The client is then
responsible for determining what security triples are available at the
server and choosing one that is appropriate for the client. See
for further discussion of how the
client will respond to the NFS4ERR_WRONGSEC error and use SECINFO.
Except as noted elsewhere in this section, the callback RPC (described
later) MUST mutually authenticate the NFS server to the principal
that acquired the client ID (also described later), using the security
flavor of the original SETCLIENTID operation used.
For AUTH_NONE, there are no principals, so this is a non-issue.
AUTH_SYS has no notions of mutual authentication or a server principal,
so the callback from the server simply uses the AUTH_SYS credential
that the user used when he set up the delegation.
For AUTH_DH, one commonly used convention is that the server uses
the credential corresponding to this AUTH_DH principal:
unix.host@domain
where host and domain are variables corresponding to the name of
the server host and directory services domain in which it lives,
such as a Network Information System domain or a DNS domain.
Regardless of what security mechanism under RPCSEC_GSS is
being used, the NFS server MUST identify itself in GSS-API via a
GSS_C_NT_HOSTBASED_SERVICE name type. GSS_C_NT_HOSTBASED_SERVICE names
are of the form:
service@hostname
For NFS, the "service" element is:
nfs
Implementations of security mechanisms will convert nfs@hostname to
various different forms. For Kerberos V5, the following
form is RECOMMENDED:
nfs/hostname
For Kerberos V5, nfs/hostname would be a server principal in
the Kerberos Key Distribution Center database. This is the same
principal the client acquired a GSS-API context for when it issued
the SETCLIENTID operation; therefore, the realm name for the
server principal must be the same for the callback as it was for
the SETCLIENTID.
The filehandle in the NFS protocol is a per-server unique identifier
for a file system object. The contents of the filehandle are
opaque to the client. Therefore, the server is responsible for
translating the filehandle to an internal representation of the
file system object.
The operations of the NFS protocol are defined in terms of one or
more filehandles. Therefore, the client needs a filehandle to
initiate communication with the server. With the NFSv2
protocol and the NFSv3 protocol , there
exists an ancillary protocol to obtain this first filehandle.
The MOUNT protocol, RPC program number 100005, provides the
mechanism of translating a string-based file system pathname to
a filehandle that can then be used by the NFS protocols.
The MOUNT protocol has deficiencies in the area of security
and use via firewalls. This is one reason that the use of the
public filehandle was introduced in and .
With the use of the public filehandle in combination with the
LOOKUP operation in the NFSv2 and NFSv3 protocols, it has
been demonstrated that the MOUNT protocol is unnecessary for
viable interaction between the NFS client and server.
Therefore, the NFSv4 protocol will not use an ancillary
protocol for translation from string-based pathnames to a
filehandle. Two special filehandles will be used as starting
points for the NFS client.
The first of the special filehandles is the root filehandle.
The root filehandle is the "conceptual" root of the file system
namespace at the NFS server. The client uses or starts with the
root filehandle by employing the PUTROOTFH operation. The
PUTROOTFH operation instructs the server to set the current
filehandle to the root of the server's file tree. Once this
PUTROOTFH operation is used, the client can then traverse the
entirety of the server's file tree with the LOOKUP operation.
A complete discussion of the server namespace is
in .
The second special filehandle is the public filehandle. Unlike the
root filehandle, the public filehandle may be bound or represent an
arbitrary file system object at the server. The server is responsible
for this binding. It may be that the public filehandle and the
root filehandle refer to the same file system object. However, it
is up to the administrative software at the server and the policies
of the server administrator to define the binding of the
public filehandle and server file system object. The client may not
make any assumptions about this binding. The client uses the
public filehandle via the PUTPUBFH operation.
In the NFSv2 and NFSv3 protocols, there was one type of
filehandle with a single set of semantics, of which the primary
one was that it was persistent across a server reboot. As such, this type of filehandle
is termed "persistent" in NFSv4. The semantics of a
persistent filehandle remain the same as before. A new type of
filehandle introduced in NFSv4 is the volatile filehandle,
which attempts to accommodate certain server environments.
The volatile filehandle type was introduced to address server
functionality or implementation issues that make correct
implementation of a persistent filehandle infeasible. Some server
environments do not provide a file system level invariant that
can be used to construct a persistent filehandle. The underlying
server file system may not provide the invariant, or the server's
file system programming interfaces may not provide access to the
needed invariant. Volatile filehandles may ease the implementation
of server functionality, such as hierarchical storage management
or file system reorganization or migration. However, the volatile
filehandle increases the implementation burden for the client.
Since the client will need to handle persistent and volatile
filehandles differently, a file attribute is defined that may
be used by the client to determine the filehandle types being
returned by the server.
The filehandle contains all the information the server needs to
distinguish an individual file. To the client, the filehandle is
opaque. The client stores filehandles for use in a later request and
can compare two filehandles from the same server for equality
by doing a byte-by-byte comparison. However, the client MUST
NOT otherwise interpret the contents of filehandles. If
two filehandles from the same server are equal, they MUST
refer to the same file. However, it is not required that
two different filehandles refer to different file system
objects. Servers SHOULD try to maintain a one-to-one
correspondence between filehandles and file system objects
but there may be situations in which the mapping is not
one-to-one. Clients MUST use filehandle comparisons only
to improve performance, not for correct behavior. All
clients need to be prepared for situations in which it
cannot be determined whether two different filehandles
denote the same object and in such cases need to avoid assuming
that objects denoted are different, as this might cause
incorrect behavior. Further discussion of filehandle and
attribute comparison in the context of data caching is
presented in .
As an example, in the case that two different pathnames when
traversed at the server terminate at the same file system object,
the server SHOULD return the same filehandle for each path.
This can occur if a hard link is used to create two filenames
that refer to the same underlying file object and associated data.
For example, if paths /a/b/c and /a/d/c refer to the same file,
the server SHOULD return the same filehandle for both pathname
traversals.
A persistent filehandle is defined as having a fixed value for the
lifetime of the file system object to which it refers. Once the
server creates the filehandle for a file system object, the server
MUST accept the same filehandle for the object for the lifetime of
the object. If the server restarts or reboots, the NFS server must
honor the same filehandle value as it did in the server's previous
instantiation. Similarly, if the file system is migrated, the new
NFS server must honor the same filehandle as the old NFS server.
The persistent filehandle will become stale or invalid when
the file system object is removed. When the server is presented
with a persistent filehandle that refers to a deleted object,
it MUST return an error of NFS4ERR_STALE. A filehandle may
become stale when the file system containing the object is no
longer available. The file system may become unavailable if it
exists on removable media and the media is no longer available at
the server, or if the file system in whole has been destroyed,
or if the file system has simply been removed from the server's
namespace (i.e., unmounted in a UNIX environment).
A volatile filehandle does not share the same longevity
characteristics of a persistent filehandle. The server may
determine that a volatile filehandle is no longer valid at
many different points in time. If the server can definitively
determine that a volatile filehandle refers to an object that has
been removed, the server should return NFS4ERR_STALE to the client
(as is the case for persistent filehandles). In all other cases
where the server determines that a volatile filehandle can no
longer be used, it should return an error of NFS4ERR_FHEXPIRED.
The REQUIRED attribute "fh_expire_type" is used by the client
to determine what type of filehandle the server is providing for
a particular file system. This attribute is a bitmask with the
following values:
The value of FH4_PERSISTENT is used to indicate a
persistent filehandle, which is valid until the object is
removed from the file system. The server will not return
NFS4ERR_FHEXPIRED for this filehandle. FH4_PERSISTENT is
defined as a value in which none of the bits specified
below are set.
The filehandle may expire at any time, except as
specifically excluded (i.e., FH4_NOEXPIRE_WITH_OPEN).
May only be set when FH4_VOLATILE_ANY is set. If this bit
is set, then the meaning of FH4_VOLATILE_ANY is qualified
to exclude any expiration of the filehandle when it is
open.
The filehandle will expire as a result of migration. If
FH4_VOLATILE_ANY is set, FH4_VOL_MIGRATION is redundant.
The filehandle will expire during rename. This includes a
rename by the requesting client or a rename by any other
client. If FH4_VOLATILE_ANY is set, FH4_VOL_RENAME is
redundant.
Servers that provide volatile filehandles that may expire while
open (i.e., if FH4_VOL_MIGRATION or FH4_VOL_RENAME is set or if
FH4_VOLATILE_ANY is set and FH4_NOEXPIRE_WITH_OPEN is not set)
should deny a RENAME or REMOVE that would affect an OPEN file
of any of the components leading to the OPEN file. In addition,
the server SHOULD deny all RENAME or REMOVE requests during the
grace period upon server restart.
Note that the bits FH4_VOL_MIGRATION and FH4_VOL_RENAME allow the
client to determine that expiration has occurred whenever a specific
event occurs, without an explicit filehandle expiration error from
the server. FH4_VOLATILE_ANY does not provide this form of
information. In situations where the server will expire many, but
not all, filehandles upon migration (e.g., all but those that are
open), FH4_VOLATILE_ANY (in this case, with FH4_NOEXPIRE_WITH_OPEN)
is a better choice since the client may not assume that all
filehandles will expire when migration occurs, and it is likely
that additional expirations will occur (as a result of file CLOSE)
that are separated in time from the migration event itself.
A volatile filehandle, while opaque to the client, could contain:
[volatile bit = 1 | server boot time | slot | generation number]
slot is an index in the server volatile filehandle table
generation number is the generation number for the table
entry/slot
When the client presents a volatile filehandle, the server makes the
following checks, which assume that the check for the volatile bit
has passed. If the server boot time is less than the current server
boot time, return NFS4ERR_FHEXPIRED. If slot is out of range, return
NFS4ERR_BADHANDLE. If the generation number does not match,
return NFS4ERR_FHEXPIRED.
When the server reboots, the table is gone (it is volatile).
If the volatile bit is 0, then it is a persistent filehandle with a
different structure following it.
If possible, the client should recover from the receipt of an
NFS4ERR_FHEXPIRED error. The client must take on additional
responsibility so that it may prepare itself to recover from the
expiration of a volatile filehandle. If the server returns
persistent filehandles, the client does not need these additional
steps.
For volatile filehandles, most commonly the client will need to store
the component names leading up to and including the file system object
in question. With these names, the client should be able to recover
by finding a filehandle in the namespace that is still available
or by starting at the root of the server's file system namespace.
If the expired filehandle refers to an object that has been
removed from the file system, obviously the client will not be
able to recover from the expired filehandle.
It is also possible that the expired filehandle refers to a file
that has been renamed. If the file was renamed by another client,
again it is possible that the original client will not be able to
recover. However, in the case that the client itself is renaming
the file and the file is open, it is possible that the client may
be able to recover. The client can determine the new pathname
based on the processing of the rename request. The client can
then regenerate the new filehandle based on the new pathname.
The client could also use the COMPOUND operation mechanism to
construct a set of operations like:
RENAME A B
LOOKUP B
GETFH
Note that the COMPOUND procedure does not provide atomicity.
This example only reduces the overhead of recovering from an
expired filehandle.
To meet the requirements of extensibility and increased
interoperability with non-UNIX platforms, attributes need to be handled
in a flexible manner. The NFSv3 fattr3 structure contains a
fixed list of attributes that not all clients and servers are able to
support or care about. The fattr3 structure cannot be extended as
new needs arise, and it provides no way to indicate non-support. With
the NFSv4.0 protocol, the client is able to query what attributes
the server supports and construct requests with only those supported
attributes (or a subset thereof).
To this end, attributes are divided into three groups: REQUIRED,
RECOMMENDED, and named. Both REQUIRED and RECOMMENDED attributes are
supported in the NFSv4.0 protocol by a specific and well-defined
encoding and are identified by number. They are requested by setting
a bit in the bit vector sent in the GETATTR request; the server
response includes a bit vector to list what attributes were returned
in the response. New REQUIRED or RECOMMENDED attributes may be added
to the NFSv4 protocol as part of a new minor version by publishing a
Standards Track RFC that allocates a new attribute number value and
defines the encoding for the attribute. See
for further discussion.
Named attributes are accessed by the OPENATTR operation, which
accesses a hidden directory of attributes associated with a file
system object. OPENATTR takes a filehandle for the object and returns
the filehandle for the attribute hierarchy. The filehandle for the
named attributes is a directory object accessible by LOOKUP or READDIR
and contains files whose names represent the named attributes and
whose data bytes are the value of the attribute. For example:
LOOKUP"foo"; look up fileGETATTRattrbitsOPENATTR; access foo's named attributesLOOKUP"x11icon"; look up specific attributeREAD0,4096; read stream of bytes
Named attributes are intended for data needed by applications rather
than by an NFS client implementation. NFS implementers are strongly
encouraged to define their new attributes as RECOMMENDED attributes by
bringing them to the IETF Standards Track process.
The set of attributes that are classified as REQUIRED is
deliberately small since servers need to do whatever it takes to support
them. A server should support as many of the RECOMMENDED attributes
as possible; however, by their definition, the server is not required to
support all of them. Attributes are deemed REQUIRED if the data is
both needed by a large number of clients and is not otherwise
reasonably computable by the client when support is not provided on
the server.
Note that the hidden directory returned by OPENATTR is a convenience
for protocol processing. The client should not make any assumptions
about the server's implementation of named attributes and whether or
not the underlying file system at the server has a named attribute
directory. Therefore, operations such as SETATTR and GETATTR on the
named attribute directory are undefined.
These attributes MUST be supported by every NFSv4.0 client and
server in order to ensure a minimum level of interoperability.
The server MUST store and return these attributes, and the client
MUST be able to function with an attribute set limited to these
attributes. With just the REQUIRED attributes, some client
functionality can be impaired or limited in some ways. A client
can ask for any of these attributes to be returned by setting a
bit in the GETATTR request. For each such bit set, the server
MUST return the corresponding attribute value.
These attributes are understood well enough to warrant support in the
NFSv4.0 protocol. However, they may not be supported on all
clients and servers. A client MAY ask for any of these attributes to
be returned by setting a bit in the GETATTR request but MUST handle
the case where the server does not return them. A client MAY ask for
the set of attributes the server supports and SHOULD NOT request
attributes the server does not support. A server should be tolerant
of requests for unsupported attributes and simply not return them,
rather than considering the request an error. It is expected that
servers will support all attributes they comfortably can and only fail
to support attributes that are difficult to support in their
operating environments. A server should provide attributes whenever
they don't have to "tell lies" to the client. For example, a file
modification time either should be an accurate time or should not be
supported by the server. At times this will be difficult for
clients, but a client is better positioned to decide whether and how to
fabricate or construct an attribute or whether to do without the
attribute.
These attributes are not supported by direct encoding in the NFSv4
protocol but are accessed by string names rather than
numbers and correspond to an uninterpreted stream of bytes that are
stored with the file system object. The namespace for these
attributes may be accessed by using the OPENATTR operation. The
OPENATTR operation returns a filehandle for a virtual "named attribute
directory", and further perusal and modification of the namespace may
be done using operations that work on more typical directories. In
particular, READDIR may be used to get a list of such named attributes,
and LOOKUP and OPEN may select a particular attribute. Creation of
a new named attribute may be the result of an OPEN specifying file
creation.
Once an OPEN is done, named attributes may be examined and changed
by normal READ and WRITE operations using the filehandles and stateids
returned by OPEN.
Named attributes and the named attribute directory may have
their own (non-named) attributes. Each of these objects must have all
of the REQUIRED attributes and may have additional RECOMMENDED
attributes. However, the set of attributes for named attributes
and the named attribute directory need not be, and
typically will not be, as large as that for other objects in that
file system.
Named attributes might be the target of delegations. However, since
granting of delegations is at the server's discretion, a server
need not support delegations on named attributes.
It is RECOMMENDED that servers support arbitrary named attributes. A
client should not depend on the ability to store any named attributes
in the server's file system. If a server does support named
attributes, a client that is also able to handle them should be able
to copy a file's data and metadata with complete transparency from
one location to another; this would imply that names allowed for
regular directory entries are valid for named attribute names as well.
In NFSv4.0, the structure of named attribute directories is
restricted in a number of ways, in order to prevent the development
of non-interoperable implementations in which some servers support
a fully general hierarchical directory structure for named attributes
while others support a limited but adequate structure for named
attributes. In such an environment, clients or applications might come to
depend on non-portable extensions. The restrictions are:
CREATE is not allowed in a named attribute directory. Thus, such
objects as symbolic links and special files are not allowed to
be named attributes. Further, directories may not be created
in a named attribute directory, so no hierarchical structure of
named attributes for a single object is allowed.
If OPENATTR is done on a named attribute directory or on
a named attribute, the server MUST return an error.
Doing a RENAME of a named attribute to a different named
attribute directory or to an ordinary (i.e., non-named-attribute)
directory is not allowed.
Creating hard links between named attribute directories or
between named attribute directories and ordinary directories
is not allowed.
Names of attributes will not be controlled by this document or other
IETF Standards Track documents. See
for further discussion.
Each of the attributes accessed using SETATTR and GETATTR (i.e.,
REQUIRED and RECOMMENDED attributes) can be classified
in one of three categories:
per-server attributes for which the value of the attribute
will be the same for all file objects that share the same
server.
per-file system attributes for which the value of the attribute
will be the same for some or all file objects that share the
same server and fsid attribute ().
See below for details regarding when such sharing is in effect.
per-file system object attributes.
The handling of per-file system attributes depends on the
particular attribute and the setting of the homogeneous
() attribute. The
following rules apply:
The values of the attributes supported_attrs, fsid, homogeneous,
link_support, and symlink_support are always common to all
objects within the given file system.
For other attributes, different values may be returned for
different file system objects if the attribute homogeneous
is supported within the file system in question and has
the value false.
The classification of attributes is as follows. Note that
the attributes time_access_set and time_modify_set are not
listed in this section, because they are write-only attributes
corresponding to time_access and time_modify and are used
in a special instance of SETATTR.
The per-server attribute is:
lease_time
The per-file system attributes are:
supported_attrs, fh_expire_type, link_support,
symlink_support, unique_handles, aclsupport,
cansettime, case_insensitive, case_preserving,
chown_restricted, files_avail, files_free,
files_total, fs_locations, homogeneous, maxfilesize,
maxname, maxread, maxwrite, no_trunc, space_avail,
space_free, space_total, and time_delta
The per-file system object attributes are:
type, change, size, named_attr, fsid, rdattr_error,
filehandle, acl, archive, fileid, hidden, maxlink,
mimetype, mode, numlinks, owner, owner_group, rawdev,
space_used, system, time_access, time_backup,
time_create, time_metadata, time_modify, and
mounted_on_fileid
For quota_avail_hard, quota_avail_soft, and quota_used, see their
definitions below for the appropriate classification.
Some REQUIRED and RECOMMENDED attributes are set-only; i.e., they
can be set via SETATTR but not retrieved via GETATTR. Similarly, some
REQUIRED and RECOMMENDED attributes are get-only; i.e., they
can be retrieved via GETATTR but not set via SETATTR. If a client attempts
to set a get-only attribute or get a set-only attribute, the server
MUST return NFS4ERR_INVAL.
The list of REQUIRED attributes appears in .
The meanings of the columns of the table are:
Name: The name of the attribute.ID: The number assigned to the attribute. In
the event of conflicts between the assigned number and , the latter is
authoritative, but in such an event, it should be resolved with
errata to this document and/or .
See for the errata process.Data Type: The XDR data type of the attribute.
Acc: Access allowed to the attribute. R means
read-only (GETATTR may retrieve, SETATTR may not
set). W means write-only (SETATTR may set, GETATTR
may not retrieve). R W means read/write (GETATTR
may retrieve, SETATTR may set).
Defined in: The section of this specification that describes the
attribute.NameIDData TypeAccDefined insupported_attrs0bitmap4Rtype1nfs_ftype4Rfh_expire_type2uint32_tRchange3changeid4Rsize4uint64_tR Wlink_support5boolRsymlink_support6boolRnamed_attr7boolRfsid8fsid4Runique_handles9boolRlease_time10nfs_lease4Rrdattr_error11nfsstat4Rfilehandle19nfs_fh4R
The RECOMMENDED attributes are defined in
. The meanings
of the column headers are the same as
; see for the meanings.
NameIDData TypeAccDefined inacl12nfsace4<>R Waclsupport13uint32_tRarchive14boolR Wcansettime15boolRcase_insensitive16boolRcase_preserving17boolRchown_restricted18boolRfileid20uint64_tRfiles_avail21uint64_tRfiles_free22uint64_tRfiles_total23uint64_tRfs_locations24fs_locations4Rhidden25boolR Whomogeneous26boolRmaxfilesize27uint64_tRmaxlink28uint32_tRmaxname29uint32_tRmaxread30uint64_tRmaxwrite31uint64_tRmimetype32ascii_ REQUIRED4<>R Wmode33mode4R Wmounted_on_fileid55uint64_tRno_trunc34boolRnumlinks35uint32_tRowner36utf8str_mixedR Wowner_group37utf8str_mixedR Wquota_avail_hard38uint64_tRquota_avail_soft39uint64_tRquota_used40uint64_tRrawdev41specdata4Rspace_avail42uint64_tRspace_free43uint64_tRspace_total44uint64_tRspace_used45uint64_tRsystem46boolR Wtime_access47nfstime4Rtime_access_set48settime4 Wtime_backup49nfstime4R Wtime_create50nfstime4R Wtime_delta51nfstime4Rtime_metadata52nfstime4Rtime_modify53nfstime4Rtime_modify_set54settime4 W
The bit vector that would retrieve all REQUIRED and
RECOMMENDED attributes that are supported for this object.
The scope of this attribute applies to all objects with a
matching fsid.
Designates the type of an object in terms of one of a number
of special constants:
NF4REG designates a regular file.
NF4DIR designates a directory.
NF4BLK designates a block device special file.
NF4CHR designates a character device special file.
NF4LNK designates a symbolic link.
NF4SOCK designates a named socket special file.
NF4FIFO designates a fifo special file.
NF4ATTRDIR designates a named attribute directory.
NF4NAMEDATTR designates a named attribute.
Within the explanatory text and operation descriptions, the
following phrases will be used with the meanings given below:
The phrase "is a directory" means that the object's
type attribute is NF4DIR or NF4ATTRDIR.
The phrase "is a special file" means that the object's
type attribute is NF4BLK, NF4CHR, NF4SOCK, or NF4FIFO.
The phrase "is a regular file" means that the object's
type attribute is NF4REG or NF4NAMEDATTR.
The phrase "is a symbolic link" means that the object's
type attribute is NF4LNK.
The server uses this to specify filehandle expiration behavior
to the client. See for additional
description.
A value created by the server that the client can use to
determine if file data, directory contents, or attributes of
the object have been modified. The server MAY return the
object's time_metadata attribute for this attribute's value
but only if the file system object cannot be updated more
frequently than the resolution of time_metadata.
The size of the object in bytes.
TRUE, if the object's file system supports hard links.
TRUE, if the object's file system supports symbolic links.
TRUE, if this object has named attributes. In other words,
this object has a non-empty named attribute directory.
Unique file system identifier for the file system holding this
object. The fsid attribute has major and minor components, each of
which are of data type uint64_t.
TRUE, if two distinct filehandles are guaranteed to refer to two
different file system objects.
Duration of the lease at the server in seconds.
Error returned from an attempt to retrieve attributes during a READDIR operation.
The filehandle of this object (primarily for READDIR requests).
The definitions of most of the RECOMMENDED attributes follow. Collections
that share a common category are defined in other sections.
TRUE, if this file has been archived since the time of the last
modification (deprecated in favor of time_backup).
TRUE, if the server is able to change the times for a
file system object as specified in a SETATTR operation.
TRUE, if filename comparisons on this file system are case
insensitive. This refers only to comparisons, and not to
the case in which filenames are stored.
TRUE, if the filename case on this file system is preserved.
This refers only to how filenames are stored, and not to
how they are compared. Filenames stored in mixed case
might be compared using either case-insensitive or
case-sensitive comparisons.
If TRUE, the server will reject any request to change either
the owner or the group associated with a file if the caller
is not a privileged user (for example, "root" in UNIX
operating environments or the "Take Ownership" privilege
in Windows 2000).
A number uniquely identifying the file within the file system.
File slots available to this user on the file system
containing this object -- this should be the smallest
relevant limit.
Free file slots on the file system containing this
object -- this should be the smallest relevant limit.
Total file slots on the file system containing this object.
Locations where this file system may be found. If the server
returns NFS4ERR_MOVED as an error, this attribute MUST be
supported.
The server specifies the rootpath for a given server by returning
a path consisting of zero path components.
TRUE, if the file is considered hidden with respect to
the Windows API.
TRUE, if this object's file system is homogeneous, i.e., all
objects in the file system (all objects on the server with the
same fsid) have common values for all per-file system attributes.
Maximum supported file size for the file system of this object.
Maximum number of hard links for this object.
Maximum filename size supported for this object.
Maximum amount of data the READ operation will return for this
object.
Maximum amount of data the WRITE operation will accept for this
object. This attribute SHOULD be supported if the file is writable.
Lack of this attribute can lead to the client either wasting
bandwidth or not receiving the best performance.
MIME media type/subtype of this object.
Like fileid, but if the target filehandle is the root of a
file system, this attribute represents the fileid of the underlying directory.
UNIX-based operating environments connect a file system into
the namespace by connecting (mounting) the file system onto
the existing file object (the mount point, usually a
directory) of an existing file system. When the mount point's
parent directory is read via an API such as readdir()
, the return results are
directory entries, each with a component name and
a fileid. The fileid of the mount point's directory entry will
be different from the fileid that the stat()
system call returns. The stat() system call is
returning the fileid of the root of the mounted file system,
whereas readdir() is returning the fileid that stat() would have
returned before any file systems were mounted on the mount point.
Unlike NFSv3, NFSv4.0 allows a client's LOOKUP
request to cross other file systems. The client detects the
file system crossing whenever the filehandle argument of
LOOKUP has an fsid attribute different from that of the
filehandle returned by LOOKUP. A UNIX-based client will
consider this a "mount point crossing". UNIX has a legacy
scheme for allowing a process to determine its current working
directory. This relies on readdir() of a mount point's parent
and stat() of the mount point returning fileids as previously
described. The mounted_on_fileid attribute corresponds to the
fileid that readdir() would have returned, as described
previously.
While the NFSv4.0 client could simply fabricate a fileid
corresponding to what mounted_on_fileid provides (and if the
server does not support mounted_on_fileid, the client has no
choice), there is a risk that the client will generate a
fileid that conflicts with one that is already assigned to
another object in the file system. Instead, if the server can
provide the mounted_on_fileid, the potential for client
operational problems in this area is eliminated.
If the server detects that there is nothing mounted on top of
the target file object, then the value for mounted_on_fileid
that it returns is the same as that of the fileid attribute.
The mounted_on_fileid attribute is RECOMMENDED, so the server
SHOULD provide it if possible, and for a UNIX-based server,
this is straightforward. Usually, mounted_on_fileid will be
requested during a READDIR operation, in which case it is
trivial (at least for UNIX-based servers) to return
mounted_on_fileid since it is equal to the fileid of a
directory entry returned by readdir(). If mounted_on_fileid
is requested in a GETATTR operation, the server should obey an
invariant that has it returning a value that is equal to the
file object's entry in the object's parent directory,
i.e., what readdir() would have returned. Some operating
environments allow a series of two or more file systems to be
mounted onto a single mount point. In this case, for the
server to obey the aforementioned invariant, it will need to
find the base mount point, and not the intermediate mount
points.
If this attribute is TRUE, then if the client uses a filename
longer than name_max, an error will be returned instead of the
name being truncated.
Number of hard links to this object.
The string name of the owner of this object.
The string name of the group ownership of this object.
The value in bytes that represents the amount of additional
disk space beyond the current allocation that can be allocated
to this file or directory before further allocations will be
refused. It is understood that this space may be consumed by
allocations to other files or directories.
The value in bytes that represents the amount of additional
disk space that can be allocated to this file or directory
before the user may reasonably be warned. It is understood
that this space may be consumed by allocations to other files
or directories, though there may exist server-side rules as
to which other files or directories.
The value in bytes that represents the amount of disk
space used by this file or directory and possibly a
number of other similar files or directories, where the
set of "similar" meets at least the criterion that
allocating space to any file or directory in the set
will reduce the "quota_avail_hard" of every other file
or directory in the set.
Note that there may be a number of distinct but
overlapping sets of files or directories for which a
quota_used value is maintained, e.g., "all files with a
given owner", "all files with a given group owner", etc.
The server is at liberty to choose any of those sets when
providing the content of the quota_used attribute but should do
so in a repeatable way. The rule may be configured per
file system or may be "choose the set with the smallest quota".
Raw device number of file of type NF4BLK or NF4CHR. The device
number is split into major and minor numbers. If the file's type
attribute is not NF4BLK or NF4CHR, this attribute SHOULD NOT be
returned, and any value returned SHOULD NOT be considered useful.
Disk space in bytes available to this user on the file system
containing this object -- this should be the smallest
relevant limit.
Free disk space in bytes on the file system containing this
object -- this should be the smallest relevant limit.
Total disk space in bytes on the file system containing this object.
Number of file system bytes allocated to this object.
TRUE, if this file is a "system" file with respect to the
Windows operating environment.
Represents the time of last access to the object by a READ
operation sent to the server. The notion of what is
an "access" depends on the server's operating environment and/or the
server's file system semantics. For example, for servers obeying
Portable Operating System Interface (POSIX) semantics, time_access
would be updated only by the READ and READDIR operations and not any
of the operations that modify the content of the object
, ,
. Of course, setting the corresponding
time_access_set attribute is another way to modify the time_access
attribute.
Whenever the file object resides on a writable file system,
the server should make its best efforts to record time_access into
stable storage. However, to mitigate the performance effects
of doing so, and most especially whenever the server is
satisfying the read of the object's content from its cache,
the server MAY cache access time updates and lazily write them
to stable storage. It is also acceptable to give
administrators of the server the option to disable time_access
updates.
Sets the time of last access to the object. SETATTR use only.
The time of last backup of the object.
The time of creation of the object. This attribute does not
have any relation to the traditional UNIX file attribute
"ctime" ("change time").
Smallest useful server time granularity.
The time of last metadata modification of the object.
The time of last modification to the object.
Sets the time of last modification to the object. SETATTR use only.
The RECOMMENDED attributes "owner" and "owner_group" (and also users
and groups used as values of the who field within nfs4ace structures
used in the acl attribute) are represented in the form of UTF-8
strings. This format avoids the use of a representation that is tied
to a particular underlying implementation at the client or server.
Note that Section 6.1 of provides additional
rationale. It is expected that the client and server will have
their own local representation of owners and groups that is used
for local storage or presentation to the application via APIs that
expect such a representation. Therefore, the protocol requires
that when these attributes are transferred between the client and
server, the local representation is translated to a string of the
form "identifier@dns_domain". This allows clients and servers that
do not use the same local representation to effectively interoperate
since they both use a common syntax that can be interpreted by both.
Similarly, security principals may be represented in different
ways by different security mechanisms. Servers normally
translate these representations into a common format,
generally that used by local storage, to serve as a means of
identifying the users corresponding to these security
principals. When these local identifiers are translated to
the form of the owner attribute, associated with files created
by such principals, they identify, in a common format, the
users associated with each corresponding set of security
principals.
The translation used to interpret owner and group strings is
not specified as part of the protocol. This allows various
solutions to be employed. For example, a local translation
table may be consulted that maps a numeric identifier to the
user@dns_domain syntax. A name service may also be used to
accomplish the translation. A server may provide a more
general service, not limited by any particular translation
(which would only translate a limited set of possible strings)
by storing the owner and owner_group attributes in local
storage without any translation, or it may augment a
translation method by storing the entire string for attributes
for which no translation is available while using the local
representation for those cases in which a translation is
available.
Servers that do not provide support for all possible values of user
and group strings SHOULD return an error (NFS4ERR_BADOWNER) when a
string is presented that has no translation, as the value to be set
for a SETATTR of the owner or owner_group attributes or as part of
the value of the acl attribute. When a server does accept a user
or group string as valid on a SETATTR, it is promising to return
that same string (see below) when a corresponding GETATTR
is done, as long as there has been no further change in the
corresponding attribute before the GETATTR. For some
internationalization-related exceptions where this is not possible,
see below. Configuration changes (including changes from the mapping
of the string to the local representation) and ill-constructed name
translations (those that contain aliasing) may make that promise
impossible to honor. Servers should make appropriate efforts to
avoid a situation in which these attributes have their values changed
when no real change to either ownership or acls has occurred.
The "dns_domain" portion of the owner string is meant to be a
DNS domain name -- for example, "user@example.org". Servers
should accept as valid a set of users for at least one domain.
A server may treat other domains as having no valid
translations. A more general service is provided when a
server is capable of accepting users for multiple domains, or
for all domains, subject to security constraints.
As an implementation guide, both clients and servers may
provide a means to configure the "dns_domain" portion of the
owner string. For example, the DNS domain name of
the host running the NFS server might be
"lab.example.org", but the user names are defined in
"example.org". In the absence of such a configuration,
or as a default, the current DNS domain name of the server
should be the value used for the "dns_domain".
As mentioned above, it is desirable that a server, when accepting
a string of the form "user@domain" or "group@domain" in an
attribute, return this same string when that corresponding
attribute is fetched. Internationalization issues make this
impossible under certain circumstances, and the client needs
to take note of these. See for a
detailed discussion of these issues.
In the case where there is no translation available to the
client or server, the attribute value will be constructed
without the "@". Therefore, the absence of the "@" from the
owner or owner_group attribute signifies that no translation
was available at the sender and that the receiver of the
attribute should not use that string as a basis for
translation into its own internal format. Even though the
attribute value cannot be translated, it may still be useful.
In the case of a client, the attribute string may be used for
local display of ownership.
To provide a greater degree of compatibility with NFSv3, which
identified users and groups by 32-bit unsigned user identifiers
and group identifiers, owner and group strings that consist of
ASCII-encoded decimal numeric values with no leading
zeros can be given a special interpretation by clients and
servers that choose to provide such support. The receiver
may treat such a user or group string as representing the same
user as would be represented by an NFSv3 uid or gid having the
corresponding numeric value.
A server SHOULD reject such a numeric value if the security
mechanism is using Kerberos. That is, in such a scenario, the client
will already need to form "user@domain" strings. For any
other security mechanism, the server SHOULD accept such
numeric values. As an implementation note, the server could
make such an acceptance be configurable. If the server does
not support numeric values or if it is configured off, then
it MUST return an NFS4ERR_BADOWNER error. If the security
mechanism is using Kerberos and the client attempts to use the
special form, then the server SHOULD return an NFS4ERR_BADOWNER
error when there is a valid translation for the user or owner
designated in this way. In that case, the client must use
the appropriate user@domain string and not the special form
for compatibility.
The client MUST always accept numeric values if the security
mechanism is not RPCSEC_GSS. A client can determine if a server
supports numeric identifiers by first attempting to provide a
numeric identifier. If this attempt is rejected with an
NFS4ERR_BADOWNER error, then the client should only use named
identifiers of the form "user@dns_domain".
The owner string "nobody" may be used to designate an
anonymous user, which will be associated with a file created
by a security principal that cannot be mapped through normal
means to the owner attribute.
With respect to the case_insensitive and case_preserving attributes,
case-insensitive comparisons of Unicode characters SHOULD use Unicode
Default Case Folding as defined in Chapter 3 of the Unicode Standard
and MAY override that behavior for
specific selected characters with the case folding defined in
the SpecialCasing.txt file; see
Section 3.13 of the Unicode Standard.
The SpecialCasing.txt file replaces the Default Case Folding with
locale- and context-dependent case folding for specific situations.
An example of locale- and context-dependent case folding is that
LATIN CAPITAL LETTER I ("I", U+0049) is default case folded to
LATIN SMALL LETTER I ("i", U+0069). However, several languages
(e.g., Turkish) treat an "I" character with a dot as a different
letter than an "I" character without a dot; therefore, in such
languages, unless an I is before a dot_above, the "I" (U+0049)
character should be case folded to a different character,
LATIN SMALL LETTER DOTLESS I (U+0131).
The and
references in this RFC
are for version 7.0.0 of the Unicode standard, as that was
the latest version of Unicode when this RFC was published.
Implementations SHOULD always use the latest version of Unicode
(<http://www.unicode.org/versions/latest/>).
Access Control Lists (ACLs) are file attributes that specify
fine-grained access control. This section covers the
"acl", "aclsupport", and "mode"
file attributes, and their interactions. Note that file
attributes may apply to any file system object.
ACLs and modes represent two well-established models for
specifying permissions. This section specifies requirements
that attempt to meet the following goals:
If a server supports the mode attribute, it should provide
reasonable semantics to clients that only set and retrieve
the mode attribute.
If a server supports ACL attributes, it should provide
reasonable semantics to clients that only set and retrieve
those attributes.
On servers that support the mode attribute, if ACL
attributes have never been set on an object, via
inheritance or explicitly, the behavior should be
traditional UNIX-like behavior.
On servers that support the mode attribute, if the ACL
attributes have been previously set on an object, either
explicitly or via inheritance:
Setting only the mode attribute should effectively
control the traditional UNIX-like permissions of read,
write, and execute on owner, owner_group, and other.
Setting only the mode attribute should provide
reasonable security. For example, setting a mode of
000 should be enough to ensure that future opens for
read or write by any principal fail, regardless of a
previously existing or inherited ACL.
When a mode attribute is set on an object, the ACL
attributes may need to be modified so as to not conflict
with the new mode. In such cases, it is desirable that the
ACL keep as much information as possible. This includes
information about inheritance, AUDIT and ALARM
access control entries (ACEs), and permissions granted and
denied that do not conflict with the new mode.
Support for each of the ACL attributes is RECOMMENDED and not
required, since file systems accessed using NFSv4 might not
support ACLs.
The NFSv4.0 ACL attribute contains an array of ACEs that are
associated with the file system object. Although the client
can read and write the acl attribute, the server is
responsible for using the ACL to perform access control. The
client can use the OPEN or ACCESS operations to check access
without modifying or reading data or metadata.
The NFS ACE structure is defined as follows:
typedef uint32_t acetype4;
typedef uint32_t aceflag4;
typedef uint32_t acemask4;
struct nfsace4 {
acetype4 type;
aceflag4 flag;
acemask4 access_mask;
utf8str_mixed who;
};
To determine if a request succeeds, the server processes
each nfsace4 entry in order. Only ACEs that have a "who"
that matches the requester are considered. Each ACE is
processed until all of the bits of the requester's access
have been ALLOWED. Once a bit (see below) has been ALLOWED
by an ACCESS_ALLOWED_ACE, it is no longer considered in the
processing of later ACEs. If an ACCESS_DENIED_ACE is
encountered where the requester's access still has unALLOWED
bits in common with the "access_mask" of the ACE, the
request is denied. When the ACL is fully processed, if
there are bits in the requester's mask that have not been
ALLOWED or DENIED, access is denied.
Unlike the ALLOW and DENY ACE types, the ALARM and AUDIT ACE
types do not affect a requester's access and instead are
for triggering events as a result of a requester's access
attempt. Therefore, AUDIT and ALARM ACEs are processed only
after processing ALLOW and DENY ACEs.
The NFSv4.0 ACL model is quite rich. Some server
platforms may provide access control functionality that goes
beyond the UNIX-style mode attribute but that is not as
rich as the NFS ACL model. So that users can take advantage
of this more limited functionality, the server may support
the acl attributes by mapping between its ACL model and the
NFSv4.0 ACL model. Servers must ensure that the ACL
they actually store or enforce is at least as strict as the
NFSv4 ACL that was set. It is tempting to accomplish this
by rejecting any ACL that falls outside the small set that
can be represented accurately. However, such an approach
can render ACLs unusable without special client-side
knowledge of the server's mapping, which defeats the purpose
of having a common NFSv4 ACL protocol. Therefore, servers
should accept every ACL that they can without compromising
security. To help accomplish this, servers may make a
special exception, in the case of unsupported permission
bits, to the rule that bits not ALLOWED or DENIED by an ACL
must be denied. For example, a UNIX-style server might
choose to silently allow read attribute permissions even
though an ACL does not explicitly allow those permissions.
(An ACL that explicitly denies permission to read attributes
should still result in a denial.)
The situation is complicated by the fact that a server may
have multiple modules that enforce ACLs. For example, the
enforcement for NFSv4.0 access may be different from,
but not weaker than, the enforcement for local access, and
both may be different from the enforcement for access
through other protocols such as Server Message Block (SMB)
. So it may be useful for
a server to accept an ACL even if not all of its modules are
able to support it.
The guiding principle with regard to NFSv4 access is that
the server must not accept ACLs that give an appearance
of more restricted access to a file than what is actually
enforced.
The constants used for the type field (acetype4) are as
follows:
const ACE4_ACCESS_ALLOWED_ACE_TYPE = 0x00000000;
const ACE4_ACCESS_DENIED_ACE_TYPE = 0x00000001;
const ACE4_SYSTEM_AUDIT_ACE_TYPE = 0x00000002;
const ACE4_SYSTEM_ALARM_ACE_TYPE = 0x00000003;
All four bit types are permitted in the acl attribute.
ValueAbbreviationDescriptionACE4_ACCESS_ALLOWED_ACE_TYPEALLOW
Explicitly grants the access defined in acemask4 to
the file or directory.
ACE4_ACCESS_DENIED_ACE_TYPEDENY
Explicitly denies the access defined in acemask4 to
the file or directory.
ACE4_SYSTEM_AUDIT_ACE_TYPEAUDIT
LOG (in a system-dependent way) any access attempt to
a file or directory that uses any of the access
methods specified in acemask4.
ACE4_SYSTEM_ALARM_ACE_TYPEALARM
Generate a system ALARM (system dependent) when any
access attempt is made to a file or directory for the
access methods specified in acemask4.
The "Abbreviation" column denotes how the
types will be referred to throughout the rest of this
section.
A server need not support all of the above ACE types.
This attribute indicates which ACE types are supported for
the current file system. The bitmask constants used to
represent the above definitions within the aclsupport
attribute are as follows:
const ACL4_SUPPORT_ALLOW_ACL = 0x00000001;
const ACL4_SUPPORT_DENY_ACL = 0x00000002;
const ACL4_SUPPORT_AUDIT_ACL = 0x00000004;
const ACL4_SUPPORT_ALARM_ACL = 0x00000008;
Servers that support either the ALLOW or DENY ACE type
SHOULD support both ALLOW and DENY ACE types.
Clients should not attempt to set an ACE unless the server
claims support for that ACE type. If the server receives a
request to set an ACE that it cannot store, it MUST reject
the request with NFS4ERR_ATTRNOTSUPP. If the server
receives a request to set an ACE that it can store but
cannot enforce, the server SHOULD reject the request with
NFS4ERR_ATTRNOTSUPP.
The bitmask constants used for the access mask field
are as follows:
const ACE4_READ_DATA = 0x00000001;
const ACE4_LIST_DIRECTORY = 0x00000001;
const ACE4_WRITE_DATA = 0x00000002;
const ACE4_ADD_FILE = 0x00000002;
const ACE4_APPEND_DATA = 0x00000004;
const ACE4_ADD_SUBDIRECTORY = 0x00000004;
const ACE4_READ_NAMED_ATTRS = 0x00000008;
const ACE4_WRITE_NAMED_ATTRS = 0x00000010;
const ACE4_EXECUTE = 0x00000020;
const ACE4_DELETE_CHILD = 0x00000040;
const ACE4_READ_ATTRIBUTES = 0x00000080;
const ACE4_WRITE_ATTRIBUTES = 0x00000100;
const ACE4_DELETE = 0x00010000;
const ACE4_READ_ACL = 0x00020000;
const ACE4_WRITE_ACL = 0x00040000;
const ACE4_WRITE_OWNER = 0x00080000;
const ACE4_SYNCHRONIZE = 0x00100000;
Note that some masks have coincident values -- for
example, ACE4_READ_DATA and ACE4_LIST_DIRECTORY.
The mask entries ACE4_LIST_DIRECTORY,
ACE4_ADD_FILE, and ACE4_ADD_SUBDIRECTORY are
intended to be used with directory objects,
while ACE4_READ_DATA, ACE4_WRITE_DATA, and
ACE4_APPEND_DATA are intended to be used with
non-directory objects.
Permission to read the data of the file.
Servers SHOULD allow a user the ability to read the data
of the file when only the ACE4_EXECUTE access mask bit is
set.
Permission to list the contents of a directory.
Permission to modify a file's data.
Permission to add a new file in a directory.
The CREATE operation is affected when nfs_ftype4
is NF4LNK, NF4BLK, NF4CHR, NF4SOCK, or
NF4FIFO. (NF4DIR is not listed because it is
covered by ACE4_ADD_SUBDIRECTORY.) OPEN is
affected when used to create a regular file.
LINK and RENAME are always affected.
The ability to modify a file's data, but only
starting at EOF. This allows for the notion of
append-only files, by allowing ACE4_APPEND_DATA
and denying ACE4_WRITE_DATA to the same user or
group. If a file has an ACL such as the one
described above and a WRITE request is made for
somewhere other than EOF, the server SHOULD
return NFS4ERR_ACCESS.
Permission to create a subdirectory in a
directory. The CREATE operation is affected
when nfs_ftype4 is NF4DIR. The RENAME operation
is always affected.
Permission to read the named attributes of a
file or to look up the named attributes
directory. OPENATTR is affected when it is not
used to create a named attribute directory.
This is when 1) createdir is TRUE but a named
attribute directory already exists or 2)
createdir is FALSE.
Permission to write the named attributes of a
file or to create a named attribute directory.
OPENATTR is affected when it is used to create a
named attribute directory. This is when
createdir is TRUE and no named attribute
directory exists. The ability to check whether
or not a named attribute directory exists
depends on the ability to look it up; therefore,
users also need the ACE4_READ_NAMED_ATTRS
permission in order to create a named attribute
directory.
Permission to execute a file.
Servers SHOULD allow a
user the ability to read the data of the file
when only the ACE4_EXECUTE access mask bit is
set. This is because there is no way to
execute a file without reading the contents.
Though a server may treat ACE4_EXECUTE and
ACE4_READ_DATA bits identically when deciding to
permit a READ operation, it SHOULD still allow
the two bits to be set independently in ACLs
and MUST distinguish between them when replying
to ACCESS operations. In particular, servers
SHOULD NOT silently turn on one of the two bits
when the other is set, as that would make it
impossible for the client to correctly enforce
the distinction between read and execute
permissions.
As an example, following a SETATTR of the following ACL:
nfsuser:ACE4_EXECUTE:ALLOW
A subsequent GETATTR of ACL for that file SHOULD return:
nfsuser:ACE4_EXECUTE:ALLOW
Rather than:
nfsuser:ACE4_EXECUTE/ACE4_READ_DATA:ALLOW
Permission to traverse/search a directory.
Permission to delete a file or directory within
a directory.
See
for information on how ACE4_DELETE and
ACE4_DELETE_CHILD interact.
The ability to read basic attributes (non-ACLs)
of a file. On a UNIX system, basic attributes
can be thought of as the stat-level attributes.
Allowing this access mask bit would mean the
entity can execute "ls -l" and stat. If a
READDIR operation requests attributes, this mask
must be allowed for the READDIR to succeed.
Permission to change the times associated with a
file or directory to an arbitrary value. Also,
permission to change the mimetype, hidden and
system attributes. A user having
ACE4_WRITE_DATA or ACE4_WRITE_ATTRIBUTES will be
allowed to set the times associated with a file
to the current server time.
Permission to delete the file or directory.
See
for information on ACE4_DELETE and
ACE4_DELETE_CHILD interact.
Permission to read the ACL.
Permission to write the acl and mode attributes.
Permission to write the owner and owner_group
attributes. On UNIX systems, this is the
ability to execute chown() and chgrp().
Permission to use the file object as a synchronization
primitive for interprocess communication. This permission is
not enforced or interpreted by the NFSv4.0 server on behalf of
the client.
Typically, the ACE4_SYNCHRONIZE permission is only meaningful
on local file systems, i.e., file systems not accessed via
NFSv4.0. The reason that the permission bit exists is that
some operating environments, such as Windows, use
ACE4_SYNCHRONIZE.
For example, if a client copies a file that has
ACE4_SYNCHRONIZE set from a local file system to an NFSv4.0
server, and then later copies the file from the NFSv4.0 server
to a local file system, it is likely that if ACE4_SYNCHRONIZE
was set in the original file, the client will want it set in
the second copy. The first copy will not have the permission
set unless the NFSv4.0 server has the means to set the
ACE4_SYNCHRONIZE bit. The second copy will not have the
permission set unless the NFSv4.0 server has the means to
retrieve the ACE4_SYNCHRONIZE bit.
Server implementations need not provide the granularity
of control that is implied by this list of masks. For
example, POSIX-based systems might not distinguish
ACE4_APPEND_DATA (the ability to append to a file) from
ACE4_WRITE_DATA (the ability to modify existing
contents); both masks would be tied to a single "write"
permission. When such a server returns attributes to the
client, it would show both ACE4_APPEND_DATA and
ACE4_WRITE_DATA if and only if the write permission is
enabled.
If a server receives a SETATTR request that it cannot
accurately implement, it should err in the direction of
more restricted access, except in the previously
discussed cases of execute and read. For example,
suppose a server cannot distinguish overwriting data
from appending new data, as described in the previous
paragraph. If a client submits an ALLOW ACE where
ACE4_APPEND_DATA is set but ACE4_WRITE_DATA is not (or
vice versa), the server should either turn off
ACE4_APPEND_DATA or reject the request with
NFS4ERR_ATTRNOTSUPP.
Two access mask bits govern the ability to delete a
directory entry: ACE4_DELETE on the object
itself (the "target") and ACE4_DELETE_CHILD on
the containing directory (the "parent").
Many systems also take the "sticky bit" (MODE4_SVTX)
on a directory to allow unlink only to a user that
owns either the target or the parent; on some
such systems, the decision also depends on
whether the target is writable.
Servers SHOULD allow unlink if either ACE4_DELETE
is permitted on the target or ACE4_DELETE_CHILD is
permitted on the parent. (Note that this is
true even if the parent or target explicitly
denies the other of these permissions.)
If the ACLs in question neither explicitly ALLOW
nor DENY either of the above, and if MODE4_SVTX is
not set on the parent, then the server SHOULD allow
the removal if and only if ACE4_ADD_FILE is permitted.
In the case where MODE4_SVTX is set, the server
may also require the remover to own either the parent
or the target, or may require the target to be
writable.
This allows servers to support something close to
traditional UNIX-like semantics, with ACE4_ADD_FILE
taking the place of the write bit.
The bitmask constants used for the flag field are as
follows:
const ACE4_FILE_INHERIT_ACE = 0x00000001;
const ACE4_DIRECTORY_INHERIT_ACE = 0x00000002;
const ACE4_NO_PROPAGATE_INHERIT_ACE = 0x00000004;
const ACE4_INHERIT_ONLY_ACE = 0x00000008;
const ACE4_SUCCESSFUL_ACCESS_ACE_FLAG = 0x00000010;
const ACE4_FAILED_ACCESS_ACE_FLAG = 0x00000020;
const ACE4_IDENTIFIER_GROUP = 0x00000040;
A server need not support any of these flags. If the
server supports flags that are similar to, but not
exactly the same as, these flags, the implementation
may define a mapping between the protocol-defined
flags and the implementation-defined flags.
For example, suppose a client tries to set an ACE with
ACE4_FILE_INHERIT_ACE set but not
ACE4_DIRECTORY_INHERIT_ACE. If the server does not
support any form of ACL inheritance, the server should
reject the request with NFS4ERR_ATTRNOTSUPP. If the
server supports a single "inherit ACE" flag that
applies to both files and directories, the server may
reject the request (i.e., requiring the client to set
both the file and directory inheritance flags). The
server may also accept the request and silently turn
on the ACE4_DIRECTORY_INHERIT_ACE flag.
Any non-directory file in any
subdirectory will get this ACE
inherited.
Can be placed on a directory and indicates
that this ACE should be added to each new
directory created.
If this flag is set in an ACE in an ACL
attribute to be set on a non-directory
file system object, the operation
attempting to set the ACL SHOULD fail
with NFS4ERR_ATTRNOTSUPP.
Can be placed on a directory but does not
apply to the directory; ALLOW and DENY ACEs
with this bit set do not affect access to
the directory, and AUDIT and ALARM ACEs
with this bit set do not trigger log or
alarm events. Such ACEs only take effect
once they are applied (with this bit
cleared) to newly created files and
directories as specified by the above two
flags.
If this flag is present on an ACE, but
neither ACE4_DIRECTORY_INHERIT_ACE nor
ACE4_FILE_INHERIT_ACE is present, then
an operation attempting to set such an
attribute SHOULD fail with
NFS4ERR_ATTRNOTSUPP.
Can be placed on a directory. This flag
tells the server that inheritance of this
ACE should stop at newly created child
directories.
The ACE4_SUCCESSFUL_ACCESS_ACE_FLAG
(SUCCESS) and ACE4_FAILED_ACCESS_ACE_FLAG
(FAILED) flag bits may be set only on
ACE4_SYSTEM_AUDIT_ACE_TYPE (AUDIT) and
ACE4_SYSTEM_ALARM_ACE_TYPE (ALARM) ACE
types. If, during the processing of the
file's ACL, the server encounters an AUDIT
or ALARM ACE that matches the principal
attempting the OPEN, the server notes that
fact and notes the presence, if any, of the
SUCCESS and FAILED flags encountered in
the AUDIT or ALARM ACE. Once the server
completes the ACL processing, it then
notes if the operation succeeded or
failed. If the operation succeeded, and if
the SUCCESS flag was set for a matching
AUDIT or ALARM ACE, then the appropriate
AUDIT or ALARM event occurs. If the
operation failed, and if the FAILED flag
was set for the matching AUDIT or ALARM
ACE, then the appropriate AUDIT or ALARM
event occurs. Either or both of the
SUCCESS or FAILED can be set, but if
neither is set, the AUDIT or ALARM ACE is
not useful.
The previously described processing
applies to ACCESS operations even when
they return NFS4_OK. For the purposes of
AUDIT and ALARM, we consider an ACCESS
operation to be a "failure" if it fails
to return a bit that was requested and
supported.
Indicates that the "who" refers to a GROUP
as defined under UNIX or a GROUP ACCOUNT
as defined under Windows. Clients and
servers MUST ignore the
ACE4_IDENTIFIER_GROUP flag on ACEs with a
who value equal to one of the special
identifiers outlined in .
The who field of an ACE is an identifier that
specifies the principal or principals to whom the ACE
applies. It may refer to a user or a group, with the flag
bit ACE4_IDENTIFIER_GROUP specifying which.
There are several special identifiers that need to be
understood universally, rather than in the context of a
particular DNS domain. Some of these identifiers cannot be
understood when an NFS client accesses the server but
have meaning when a local process accesses the file. The
ability to display and modify these permissions is
permitted over NFS, even if none of the access methods on
the server understand the identifiers.
WhoDescriptionOWNER
The owner of the file.
GROUP
The group associated with the file.
EVERYONE
The world, including the owner and owning group.
INTERACTIVE
Accessed from an interactive terminal.
NETWORK
Accessed via the network.
DIALUP
Accessed as a dialup user to the server.
BATCH
Accessed from a batch job.
ANONYMOUS
Accessed without any authentication.
AUTHENTICATED
Any authenticated user (opposite of ANONYMOUS).
SERVICE
Access from a system service.
To avoid conflict, these special identifiers are
distinguished by an appended "@" and should appear in the
form "xxxx@" (with no domain name after the "@") -- for
example, ANONYMOUS@.
The ACE4_IDENTIFIER_GROUP flag MUST be ignored on
entries with these special identifiers. When encoding
entries with these special identifiers, the
ACE4_IDENTIFIER_GROUP flag SHOULD be set to zero.
It is important to note that "EVERYONE@" is not
equivalent to the UNIX "other" entity. This is
because, by definition, UNIX "other" does not include
the owner or owning group of a file. "EVERYONE@" means
literally everyone, including the owner or owning
group.
The NFSv4.0 mode attribute is based on the UNIX mode
bits. The following bits are defined:
const MODE4_SUID = 0x800; /* set user id on execution */
const MODE4_SGID = 0x400; /* set group id on execution */
const MODE4_SVTX = 0x200; /* save text even after use */
const MODE4_RUSR = 0x100; /* read permission: owner */
const MODE4_WUSR = 0x080; /* write permission: owner */
const MODE4_XUSR = 0x040; /* execute permission: owner */
const MODE4_RGRP = 0x020; /* read permission: group */
const MODE4_WGRP = 0x010; /* write permission: group */
const MODE4_XGRP = 0x008; /* execute permission: group */
const MODE4_ROTH = 0x004; /* read permission: other */
const MODE4_WOTH = 0x002; /* write permission: other */
const MODE4_XOTH = 0x001; /* execute permission: other */
Bits MODE4_RUSR, MODE4_WUSR, and MODE4_XUSR apply to the
principal identified in the owner attribute. Bits MODE4_RGRP,
MODE4_WGRP, and MODE4_XGRP apply to principals identified in
the owner_group attribute but who are not identified in the
owner attribute. Bits MODE4_ROTH, MODE4_WOTH, and MODE4_XOTH
apply to any principal that does not match that in the owner
attribute and does not have a group matching that of the
owner_group attribute.
Bits within the mode other than those specified above
are not defined by this protocol. A server
MUST NOT return bits other than those defined above in a
GETATTR or READDIR operation, and it MUST return NFS4ERR_INVAL
if bits other than those defined above are set in a SETATTR,
CREATE, OPEN, VERIFY, or NVERIFY operation.
The requirements in this section will be referred to in future
sections, especially .
The server uses the algorithm described in
to determine whether an ACL
allows access to an object. However, the ACL may not be
the sole determiner of access. For example:
In the case of a file system exported as read-only,
the server may deny write permissions even though
an object's ACL grants it.
Server implementations MAY grant ACE4_WRITE_ACL
and ACE4_READ_ACL permissions to prevent
a situation from arising in which there is no valid
way to ever modify the ACL.
All servers will allow a user the ability to read
the data of the file when only the execute
permission is granted (i.e., if the ACL denies the
user ACE4_READ_DATA access and allows the user
ACE4_EXECUTE, the server will allow the user to
read the data of the file).
Many servers have the notion of owner-override, in
which the owner of the object is allowed to
override accesses that are denied by the ACL.
This may be helpful, for example, to allow users
continued access to open files on which the
permissions have changed.
Many servers have the notion of a
"superuser" that has privileges beyond
an ordinary user. The superuser may be able
to read or write data or metadata in ways that would
not be permitted by the ACL.
Clients SHOULD NOT do their own access checks based on
their interpretation of the ACL but rather use the OPEN and
ACCESS operations to do access checks. This allows the
client to act on the results of having the server
determine whether or not access should be granted based on
its interpretation of the ACL.
Clients must be aware of situations in which an object's
ACL will define a certain access even though the server
will not have adequate information to enforce it. For
example, the server has no way of determining whether
a particular OPEN reflects a user's open for read access
or is done as part of executing the file in question.
In such situations, the client needs to do its part in
the enforcement of access as defined by the ACL. To
do this, the client will send the appropriate ACCESS
operation (or use a cached previous determination) prior
to servicing the request of the user or application in
order to determine whether the user or application
should be granted the access requested. For examples in
which the ACL may define accesses that the server does not
enforce, see .
The following method can be used to calculate the MODE4_R*,
MODE4_W*, and MODE4_X* bits of a mode attribute, based upon
an ACL.
First, for each of the special identifiers OWNER@, GROUP@, and
EVERYONE@, evaluate the ACL in order, considering only ALLOW
and DENY ACEs for the identifier EVERYONE@ and for the
identifier under consideration. The result of the evaluation
will be an NFSv4 ACL mask showing exactly which bits are
permitted to that identifier.
Then translate the calculated mask for OWNER@, GROUP@, and
EVERYONE@ into mode bits for the user, group, and other,
respectively, as follows:
Set the read bit (MODE4_RUSR, MODE4_RGRP, or
MODE4_ROTH) if and only if ACE4_READ_DATA is set in
the corresponding mask.
Set the write bit (MODE4_WUSR, MODE4_WGRP, or
MODE4_WOTH) if and only if ACE4_WRITE_DATA and
ACE4_APPEND_DATA are both set in the corresponding
mask.
Set the execute bit (MODE4_XUSR, MODE4_XGRP, or
MODE4_XOTH), if and only if ACE4_EXECUTE is set in the
corresponding mask.
Some server implementations also add bits permitted to
named users and groups to the group bits (MODE4_RGRP,
MODE4_WGRP, and MODE4_XGRP).
Implementations are discouraged from doing this, because
it has been found to cause confusion for users who see
members of a file's group denied access that the mode
bits appear to allow. (The presence of DENY ACEs may also
lead to such behavior, but DENY ACEs are expected to be
more rarely used.)
The same user confusion seen when fetching the mode also
results if setting the mode does not effectively control
permissions for the owner, group, and other users; this
motivates some of the requirements that follow.
The server that supports both mode and ACL must take care to
synchronize the MODE4_*USR, MODE4_*GRP, and MODE4_*OTH bits with
the ACEs that have respective who fields of "OWNER@", "GROUP@",
and "EVERYONE@" so that the client can see that semantically
equivalent access permissions exist whether the client asks
for just the ACL or any of the owner, owner_group, and mode
attributes.
Many requirements refer to ,
but note that the methods have behaviors specified with
"SHOULD". This is intentional, to avoid invalidating
existing implementations that compute the mode according to the
withdrawn POSIX ACL draft (), rather than by
actual permissions on owner, group, and other.
When any of the nine low-order mode bits
are changed because the mode
attribute was set, and no ACL attribute is explicitly
set, the acl attribute must be modified
in accordance with the updated value of those bits.
This must happen even if the value of the low-order bits
is the same after the mode is set as before.
Note that any AUDIT or ALARM ACEs
are unaffected by changes to the mode.
In cases in which the permissions bits are subject to
change, the acl attribute
MUST be modified such that the mode computed via the
method described in
yields the low-order nine bits (MODE4_R*, MODE4_W*,
MODE4_X*) of the mode attribute as modified by the
change attribute. The ACL attributes
SHOULD also be modified such that:
If MODE4_RGRP is not set, entities explicitly
listed in the ACL other than OWNER@ and EVERYONE@
SHOULD NOT be granted ACE4_READ_DATA.
If MODE4_WGRP is not set, entities explicitly
listed in the ACL other than OWNER@ and
EVERYONE@ SHOULD NOT be granted
ACE4_WRITE_DATA or ACE4_APPEND_DATA.
If MODE4_XGRP is not set, entities explicitly
listed in the ACL other than OWNER@ and EVERYONE@
SHOULD NOT be granted ACE4_EXECUTE.
Access mask bits other than those listed above, appearing
in ALLOW ACEs, MAY also be disabled.
Note that ACEs with the flag ACE4_INHERIT_ONLY_ACE set do
not affect the permissions of the ACL itself, nor do ACEs
of the types AUDIT and ALARM. As such, it is desirable to
leave these ACEs unmodified when modifying the ACL
attributes.
Also note that the requirement may be met by
discarding the acl in favor of an ACL
that represents the mode and only the mode. This is
permitted, but it is preferable for a server to
preserve as much of the ACL as possible without
violating the above requirements. Discarding the
ACL makes it effectively impossible for a file
created with a mode attribute to inherit an ACL
(see ).
When setting the acl and not setting the
mode attribute, the permission
bits of the mode need to be derived from the ACL.
In this case, the ACL attribute SHOULD be set as
given. The nine low-order bits of the mode
attribute (MODE4_R*, MODE4_W*, MODE4_X*) MUST be
modified to match the result of the method described
in . The three high-order
bits of the mode (MODE4_SUID, MODE4_SGID, MODE4_SVTX)
SHOULD remain unchanged.
When setting both the mode
and the acl attribute in the
same operation, the attributes MUST be applied in this
order: mode, then ACL. The
mode-related attribute is set as given,
then the ACL attribute is set as given, possibly changing
the final mode, as described above in
.
This section applies only to servers that support both the
mode and ACL attributes.
Some server implementations may have a concept of
"objects without ACLs", meaning that all permissions
are granted and denied according to the mode attribute, and
that no ACL attribute is stored for that object. If an ACL
attribute is requested of such a server, the server SHOULD
return an ACL that does not conflict with the mode; that is to
say, the ACL returned SHOULD represent the nine low-order bits
of the mode attribute (MODE4_R*, MODE4_W*, MODE4_X*) as
described in .
For other server implementations, the ACL attribute is always
present for every object. Such servers SHOULD store at least
the three high-order bits of the mode attribute (MODE4_SUID,
MODE4_SGID, MODE4_SVTX). The server SHOULD return a mode
attribute if one is requested, and the low-order nine bits of
the mode (MODE4_R*, MODE4_W*, MODE4_X*) MUST match the result
of applying the method in
to the ACL attribute.
If a server supports any ACL attributes, it may use the ACL
attributes on the parent directory to compute an initial ACL
attribute for a newly created object. This will be referred to
as the inherited ACL within this section. The act of adding
one or more ACEs to the inherited ACL that are based upon ACEs
in the parent directory's ACL will be referred to as
inheriting an ACE within this section.
In the presence or absence of the mode and ACL attributes, the
behavior of CREATE and OPEN SHOULD be:
If just the mode is given in the call:
In this case, inheritance
SHOULD take place, but the mode MUST be applied to the
inherited ACL as described in ,
thereby modifying the ACL.
If just the ACL is given in the call:
In this case, inheritance SHOULD NOT take place, and
the ACL as defined in the CREATE or OPEN will be set
without modification, and the mode modified as in
.
If both mode and ACL are given in the call:
In this case, inheritance
SHOULD NOT take place, and both attributes will be set
as described in .
If neither mode nor ACL is given in the call:
In the case where an object is being created without
any initial attributes at all, e.g., an OPEN operation
with an opentype4 of OPEN4_CREATE and a createmode4 of
EXCLUSIVE4, inheritance SHOULD NOT take place.
Instead, the server SHOULD set permissions to deny all
access to the newly created object. It is expected
that the appropriate client will set the desired
attributes in a subsequent SETATTR operation, and the
server SHOULD allow that operation to succeed,
regardless of what permissions the object is created
with. For example, an empty ACL denies all
permissions, but the server should allow the owner's
SETATTR to succeed even though WRITE_ACL is implicitly
denied.
In other cases, inheritance SHOULD take place, and no
modifications to the ACL will happen. The mode
attribute, if supported, MUST be as computed via the
method described in
, with the MODE4_SUID,
MODE4_SGID, and MODE4_SVTX bits clear.
If no inheritable ACEs exist on the parent directory,
the rules for creating acl attributes
are implementation defined.
If the object being created is not a directory, the
inherited ACL SHOULD NOT inherit ACEs from the parent
directory ACL unless the ACE4_FILE_INHERIT_FLAG is set.
If the object being created is a directory, the inherited
ACL should inherit all inheritable ACEs from the parent
directory, i.e., those that have the ACE4_FILE_INHERIT_ACE or
ACE4_DIRECTORY_INHERIT_ACE flag set. If the inheritable
ACE has ACE4_FILE_INHERIT_ACE set, but
ACE4_DIRECTORY_INHERIT_ACE is clear, the inherited ACE on
the newly created directory MUST have the
ACE4_INHERIT_ONLY_ACE flag set to prevent the directory
from being affected by ACEs meant for non&nbhy;directories.
When a new directory is created, the server MAY split
any inherited ACE that is both inheritable and effective
(in other words, that has neither ACE4_INHERIT_ONLY_ACE
nor ACE4_NO_PROPAGATE_INHERIT_ACE set) into two ACEs --
one with no inheritance flags, and one with
ACE4_INHERIT_ONLY_ACE set. This makes it simpler to
modify the effective permissions on the directory
without modifying the ACE that is to be inherited to the
new directory's children.
On a UNIX server, the namespace describes all the files reachable by
pathnames under the root directory or "/". On a Windows server,
the namespace constitutes all the files on disks named by mapped
disk letters. NFS server administrators rarely make the entire
server's file system namespace available to NFS clients. More often,
portions of the namespace are made available via an "export" feature.
In previous versions of the NFS protocol, the root filehandle for
each export is obtained through the MOUNT protocol; the client sends
a string that identifies an object in the exported namespace,
and the server returns the root filehandle for it. The MOUNT
protocol supports an EXPORTS procedure that will enumerate the
server's exports.
The NFSv4 protocol provides a root filehandle that clients
can use to obtain filehandles for these exports via a multi-component
LOOKUP. A common user experience is to use a graphical user interface
(perhaps a file "Open" dialog window) to find a file via progressive
browsing through a directory tree. The client must be able to move
from one export to another export via single-component, progressive
LOOKUP operations.
This style of browsing is not well supported by the NFSv2 and
NFSv3 protocols. The client expects all LOOKUP operations to remain
within a single-server file system. For example, the device attribute
will not change. This prevents a client from taking namespace
paths that span exports.
An automounter on the client can obtain a snapshot of the server's
namespace using the EXPORTS procedure of the MOUNT protocol. If it
understands the server's pathname syntax, it can create an image of
the server's namespace on the client. The parts of the namespace
that are not exported by the server are filled in with a
"pseudo-file system" that allows the user to browse from one mounted
file system to another. There is a drawback to this representation of
the server's namespace on the client: it is static. If the server
administrator adds a new export, the client will be unaware of it.
NFSv4 servers avoid this namespace inconsistency by
presenting all the exports within the framework of a single-server
namespace. An NFSv4 client uses LOOKUP and READDIR
operations to browse seamlessly from one export to another. Portions
of the server namespace that are not exported are bridged via a
"pseudo-file system" that provides a view of exported directories only.
A pseudo-file system has a unique fsid and behaves like a normal,
read-only file system.
Based on the construction of the server's namespace, it is possible
that multiple pseudo-file systems may exist. For example:
/a pseudo-file system
/a/b real file system
/a/b/c pseudo-file system
/a/b/c/d real file system
Each of the pseudo-file systems are considered separate entities and
therefore will have a unique fsid.
The DOS and Windows operating environments are sometimes described
as having "multiple roots". File systems are commonly represented
as disk letters. MacOS represents file systems as top-level names.
NFSv4 servers for these platforms can construct a
pseudo-file system above these root names so that disk letters or
volume names are simply directory names in the pseudo-root.
The nature of the server's pseudo-file system is that it is a logical
representation of file system(s) available from the server. Therefore,
the pseudo-file system is most likely constructed dynamically when
the server is first instantiated. It is expected that the
pseudo-file system may not have an on-disk counterpart from which
persistent filehandles could be constructed. Even though it is
preferable that the server provide persistent filehandles for the
pseudo-file system, the NFS client should expect that
pseudo-file system filehandles are volatile. This can be
confirmed by checking the associated "fh_expire_type" attribute
for those filehandles in question. If the filehandles are
volatile, the NFS client must be prepared to recover a
filehandle value (e.g., with a multi-component LOOKUP) when
receiving an error of NFS4ERR_FHEXPIRED.
If the server's root file system is exported, one might conclude that
a pseudo-file system is not needed. This would be wrong. Assume the
following file systems on a server:
/ disk1 (exported)
/a disk2 (not exported)
/a/b disk3 (exported)
Because disk2 is not exported, disk3 cannot be reached with simple
LOOKUPs. The server must bridge the gap with a pseudo-file system.
The server file system environment may be constructed in such a
way that one file system contains a directory that is 'covered'
or mounted upon by a second file system. For example:
/a/b (file system 1)
/a/b/c/d (file system 2)
The pseudo-file system for this server may be constructed to look like:
/ (placeholder/not exported)
/a/b (file system 1)
/a/b/c/d (file system 2)
It is the server's responsibility to present the pseudo-file system
that is complete to the client. If the client sends a LOOKUP request
for the path "/a/b/c/d", the server's response is the filehandle of
the file system "/a/b/c/d". In previous versions of the NFS protocol,
the server would respond with the filehandle of directory "/a/b/c/d"
within the file system "/a/b".
The NFS client will be able to determine if it crosses a server
mount point by a change in the value of the "fsid" attribute.
Because NFSv4 clients possess the ability to change the security
mechanisms used, after determining what is allowed, by using SECINFO
the server SHOULD NOT present a different view of
the namespace based on the security mechanism being used by a client.
Instead, it should present a consistent view and return
NFS4ERR_WRONGSEC if an attempt is made to access data with an
inappropriate security mechanism.
If security considerations make it necessary to hide the existence of
a particular file system, as opposed to all of the data within it,
the server can apply the security policy of a shared resource in the
server's namespace to components of the resource's ancestors. For
example:
/ (placeholder/not exported)
/a/b (file system 1)
/a/b/MySecretProject (file system 2)
The /a/b/MySecretProject directory is a real file system and is the
shared resource. Suppose the security policy for /a/b/
MySecretProject is Kerberos with integrity and it is desired to limit
knowledge of the existence of this file system. In this case, the
server should apply the same security policy to /a/b. This allows
for knowledge of the existence of a file system to be secured when
desirable.
For the case of the use of multiple, disjoint security mechanisms in
the server's resources, applying that sort of policy would result in
the higher-level file system not being accessible using any security
flavor. Therefore, that sort of configuration is not compatible with
hiding the existence (as opposed to the contents) from clients using
multiple disjoint sets of security flavors.
In other circumstances, a desirable policy is for the security of a
particular object in the server's namespace to include the union of
all security mechanisms of all direct descendants. A common and
convenient practice, unless strong security requirements dictate
otherwise, is to make the entire pseudo-file system accessible by
all of the valid security mechanisms.
Where there is concern about the security of data on the network,
clients should use strong security mechanisms to access the
pseudo-file system in order to prevent man-in-the-middle attacks.
NFSv4 supports attributes that allow a namespace to extend
beyond the boundaries of a single server. It is RECOMMENDED
that clients and servers support construction of such
multi-server namespaces. Use of such multi-server namespaces
is optional, however, and for many purposes,
single-server namespaces are perfectly acceptable. Use of
multi-server namespaces can provide many advantages, however, by
separating a file system's logical position in a namespace from
the (possibly changing) logistical and administrative
considerations that result in particular file systems being
located on particular servers.
NFSv4 contains RECOMMENDED attributes that allow file systems on
one server to be associated with one or more instances of that
file system on other servers. These attributes specify such
file system instances by specifying a server address
target (as either a DNS name representing one or more IP
addresses, or a literal IP address), together with the path
of that file system within the associated single-server namespace.
The fs_locations RECOMMENDED attribute allows specification of the
file system locations where the data corresponding to a given file
system may be found.
A given location in an NFSv4 namespace (typically but not necessarily
a multi-server namespace) can have a number of file system instance
locations associated with it via the fs_locations
attribute. There may also be an actual current file system at
that location, accessible via normal namespace operations (e.g.,
LOOKUP). In this case, the file system is said to be
"present" at that position in the namespace, and clients will
typically use it, reserving use of additional locations
specified via the location-related attributes to situations in
which the principal location is no longer available.
When there is no actual file system at the namespace location
in question, the file system is said to be "absent". An absent
file system contains no files or directories other than the
root. Any reference to it, except
to access a small set of attributes useful in determining
alternative locations, will result in an error, NFS4ERR_MOVED.
Note that if the server ever returns the error NFS4ERR_MOVED,
it MUST support the fs_locations attribute.
While the error name suggests that we have a case of a file system
that once was present, and has only become absent later, this is
only one possibility. A position in the namespace may be permanently
absent with the set of file system(s) designated by the location
attributes being the only realization.
The name NFS4ERR_MOVED reflects an earlier,
more limited conception of its function, but this error will be
returned whenever the referenced file system is absent, whether it
has moved or simply never existed.
Except in the case of GETATTR-type operations (to be discussed
later), when the
current filehandle at the start of an operation is within an
absent file system, that operation is not performed and the error
NFS4ERR_MOVED is returned, to indicate that the file system is
absent on the current server.
Because a GETFH cannot succeed if the current filehandle is
within an absent file system, filehandles within an absent
file system cannot be transferred to the client. When a
client does have filehandles within an absent file system, it
is the result of obtaining them when the file system was
present, and having the file system become
absent subsequently.
It should be noted that because the check for the current
filehandle being within an absent file system happens at the
start of every operation, operations that change the current
filehandle so that it is within an absent file system will not
result in an error. This allows such combinations as
PUTFH-GETATTR and LOOKUP-GETATTR to be used to get attribute
information, particularly location attribute information,
as discussed below.
When a file system is absent, most attributes are not available,
but it is necessary to allow the client access to the small
set of attributes that are available, and most particularly
that which gives information about the correct current locations
for this file system, fs_locations.
As mentioned above, an exception is made for GETATTR in that
attributes may be obtained for a filehandle within an absent
file system. This exception only applies if the attribute
mask contains at least the fs_locations attribute bit, which
indicates that the client is interested in a result regarding
an absent file system. If it is not requested, GETATTR will
result in an NFS4ERR_MOVED error.
When a GETATTR is done on an absent file system, the set of
supported attributes is very limited. Many attributes, including
those that are normally REQUIRED, will not be available on an
absent file system. In addition to the fs_locations attribute,
the following attributes SHOULD be available on absent file
systems. In the case of RECOMMENDED attributes, they should
be available at least to the same degree that they are available
on present file systems.
This attribute should be provided so that the client
can determine file system boundaries, including, in
particular, the boundary between present and absent file
systems. This value must be different from any other fsid
on the current server and need have no particular relationship
to fsids on any particular destination to which the client
might be directed.
For objects at the top of an absent
file system, this attribute needs to be available. Since
the fileid is within the present parent file
system, there should be no need to reference the absent file
system to provide this information.
Other attributes SHOULD NOT be made available for absent file
systems, even when it is possible to provide them. The server
should not assume that more information is always better and
should avoid gratuitously providing additional information.
When a GETATTR operation includes a bitmask for the
attribute fs_locations, but
where the bitmask includes attributes that are not supported,
GETATTR will not return an error but will return the mask
of the actual attributes supported with the results.
Handling of VERIFY/NVERIFY is similar to GETATTR in that if
the attribute mask does not include fs_locations
the error NFS4ERR_MOVED will result. It differs in
that any appearance in the attribute mask of an attribute not
supported for an absent file system (and note that this will
include some normally REQUIRED attributes) will also cause
an NFS4ERR_MOVED result.
A READDIR performed when the current filehandle is within an
absent file system will result in an NFS4ERR_MOVED error,
since, unlike the case of GETATTR, no such exception is
made for READDIR.
Attributes for an absent file system may be fetched via a
READDIR for a directory in a present file system, when that
directory contains the root directories of one or more absent
file systems. In this case, the handling is as follows:
If the attribute set requested includes fs_locations, then
the fetching of attributes proceeds normally, and no
NFS4ERR_MOVED indication is returned even when the
rdattr_error attribute is requested.
If the attribute set requested does not include
fs_locations, then if the
rdattr_error attribute is requested, each directory entry for
the root of an absent file system will report
NFS4ERR_MOVED as the value of the rdattr_error attribute.
If the attribute set requested does not include either of the
attributes fs_locations or rdattr_error, then the occurrence
of the root of an absent file system within the directory
will result in the READDIR failing with an NFS4ERR_MOVED error.
The unavailability of an attribute because of a file system's
absence, even one that is ordinarily REQUIRED, does not result
in any error indication. The set of attributes returned for
the root directory of the absent file system in that case is
simply restricted to those actually available.
The location-bearing attribute of fs_locations
provides, together with the possibility of absent file systems,
a number of important facilities in providing reliable, manageable,
and scalable data access.
When a file system is present, these attributes can provide
alternative locations, to be used to access the same data,
in the event of server failures, communications problems,
or other difficulties that make continued access to the current
file system impossible or otherwise impractical.
Under some circumstances, multiple alternative locations
may be used simultaneously to provide higher-performance
access to the file system in question. Provision of
such alternative locations is referred to as "replication",
although there are cases in which replicated sets of data are
not in fact present and the replicas are instead different
paths to the same data.
When a file system is present and subsequently becomes absent,
clients can be given the opportunity to have continued access
to their data, at an alternative location. Transfer of the
file system contents to the new location is referred to as
"migration". See for details.
Alternative locations may be physical replicas of the
file system data or alternative communication paths to the
same server or, in the case of various forms of server clustering,
another server providing access to the same physical file
system. The client's responsibilities in dealing with this
transition depend on the specific nature of the new access
path as well as how and whether data was in fact migrated.
These issues will be discussed in detail below.
Where a file system was not previously present, specification
of file system location provides a means by which file systems
located on one server can be associated with a namespace
defined by another server, thus allowing a general multi-server
namespace facility. A designation of such a location, in place
of an absent file system, is called a "referral".
Because client support for location-related attributes is
OPTIONAL, a server may (but is not required to) take action
to hide migration and referral events from such clients, by
acting as a proxy, for example.
The fs_locations attribute provides alternative locations,
to be used to access data in place of, or in addition to,
the current file system instance. On first access to a
file system, the client should obtain the value of the set
of alternative locations by interrogating the fs_locations
attribute.
In the event that server failures, communications problems,
or other difficulties make continued access to the current
file system impossible or otherwise impractical, the client
can use the alternative locations as a way to get continued
access to its data. Multiple locations may
be used simultaneously, to provide higher performance
through the exploitation of multiple paths between client
and target file system.
Multiple server addresses, whether they are derived from
a single entry with a DNS name representing a set of IP
addresses or from multiple entries each with its own
server address, may correspond to the same actual
server.
When a file system is present and becomes absent, clients can be
given the opportunity to have continued access to their data,
at an alternative location, as specified by the fs_locations
attribute. Typically, a client will be
accessing the file system in question, get an NFS4ERR_MOVED
error, and then use the fs_locations
attribute to determine the new location of the data.
Such migration can be helpful in providing
load balancing or general resource reallocation. The protocol
does not specify how the file system will be moved between
servers. It is anticipated that a number of different
server-to-server transfer mechanisms might be used, with the
choice left to the server implementer. The NFSv4 protocol
specifies the method used to communicate the migration
event between client and server.
When an alternative location is designated as the target for
migration, it must designate the same data.
Where file systems are writable,
a change made on the original file system must be visible on
all migration targets. Where a file system is not writable
but represents a read-only copy (possibly periodically
updated) of
a writable file system, similar requirements apply to the
propagation of updates. Any change visible in the original
file system must already be effected on all migration targets,
to avoid any
possibility that a client, in effecting a transition to
the migration target, will see any reversion in file system state.
Referrals provide a way of placing a file system in a location
within the namespace
essentially without respect to its physical location on a
given server. This allows a single server or a set of servers
to present a multi-server namespace that encompasses file systems
located on multiple servers. Some likely uses of this include
establishment of site-wide or organization-wide namespaces,
or even knitting such together into a truly global namespace.
Referrals occur when a client determines, upon first referencing
a position in the current namespace, that it is part of a new
file system and that the file system is absent. When this
occurs, typically by receiving the error NFS4ERR_MOVED, the
actual location or locations of the file system can be
determined by fetching the fs_locations attribute.
The location-related attribute may designate a single
file system location or multiple file system locations, to
be selected based on the needs of the client.
Use of multi-server namespaces is enabled by NFSv4 but is not
required. The use of multi-server namespaces and their scope
will depend on the applications used and system administration
preferences.
Multi-server namespaces can be established by a single
server providing a large set of referrals to all of the
included file systems. Alternatively, a single multi-server
namespace may be administratively segmented with separate
referral file systems (on separate servers) for each
separately administered portion of the namespace. The
top-level referral file system or any segment may use
replicated referral file systems for higher availability.
Generally, multi-server namespaces are for the most part
uniform, in that the same data made available to one client
at a given location in the namespace is made available to
all clients at that location.
As mentioned above, a single location entry may have a server
address target in the form of a DNS name that may represent
multiple
IP addresses, while multiple location entries may have their
own server address targets that reference the same server.
When multiple addresses for the same server exist, the client
may assume that for each file system in the namespace of
a given server network address, there exist
file systems at corresponding namespace locations for
each of the other server network addresses.
It may do this even in the absence of
explicit listing in fs_locations.
Such corresponding file system locations can be used as
alternative locations, just as those explicitly specified via
the fs_locations attribute.
If a single location entry designates multiple server IP addresses,
the client should choose a single one to use.
When two server addresses are designated
by a single location entry and they correspond to different
servers, this normally indicates some sort of misconfiguration,
and so the client should avoid using such location entries
when alternatives are available. When they are not,
clients should pick one of the IP addresses and use it,
without using others that are not directed to the same
server.
When clients make use of servers that implement referrals,
replication, and
migration, care should be taken that a user who mounts a given
file system that includes a referral or a relocated file system
continues to see a coherent picture of that user-side file system
despite the fact that it contains a number of server-side
file systems that may be on different servers.
One important issue is upward navigation from the root of a
server-side file system to its parent (specified as ".." in UNIX),
in the case in which it transitions to that file system as a
result of referral, migration, or a transition as a result of
replication. When the client is at such a point, and it needs to ascend to
the parent, it must go back to the parent as seen within the
multi-server namespace rather than sending a LOOKUPP operation to the
server, which would result in the parent within that server's
single-server namespace. In order to do this, the client
needs to remember the filehandles that represent such
file system roots and use these instead of issuing a
LOOKUPP operation to the current server. This will allow the client
to present to applications a consistent namespace, where
upward navigation and downward navigation are consistent.
Another issue concerns refresh of referral locations. When
referrals are used extensively, they may change as server
configurations change. It is expected that clients will cache
information related to traversing referrals so that future client-side
requests are resolved locally without server communication.
This is usually rooted in client-side name lookup caching. Clients
should periodically purge this data for referral points in order to
detect changes in location information.
A potential problem exists if a client were to allow an open-owner to
have state on multiple file systems on a server, in that it is unclear
how the sequence numbers associated with open-owners are to be dealt
with, in the event of transparent state migration. A client can avoid
such a situation if it ensures that any use of an open-owner is
confined to a single file system.
A server MAY decline to migrate state associated with open-owners that
span multiple file systems. In cases in which the server chooses not
to migrate such state, the server MUST return NFS4ERR_BAD_STATEID
when the client uses those stateids on the new server.
The server MUST return NFS4ERR_STALE_STATEID when the client
uses those stateids on the old server, regardless of whether
migration has occurred or not.
Referrals are effected when an absent file system is encountered
and one or more alternative locations are made available by the
fs_locations attribute. The client will
typically get an NFS4ERR_MOVED error, fetch the appropriate
location information, and proceed to access the file system on
a different server, even though it retains its logical position
within the original namespace. Referrals differ from migration
events in that they happen only when the client has not
previously referenced the file system in question (so there
is nothing to transition). Referrals can only come into
effect when an absent file system is encountered at its root.
The examples given in the sections below are somewhat artificial in
that an actual client will not typically do a multi-component
lookup but will have cached information regarding the upper levels
of the name hierarchy. However, these example are chosen to make
the required behavior clear and easy to put within the scope of a
small number of requests, without getting unduly into details of
how specific clients might choose to cache things.
Let us suppose that the following COMPOUND is sent in an
environment in which /this/is/the/path is absent from the
target server. This may be for a number of reasons. It may
be the case that the
file system has moved, or it may be the case that
the target server is functioning mainly, or solely, to refer
clients to the servers on which various file systems are located.
PUTROOTFH
LOOKUP "this"
LOOKUP "is"
LOOKUP "the"
LOOKUP "path"
GETFH
GETATTR(fsid, fileid, size, time_modify)
Under the given circumstances, the following will be the result:
PUTROOTFH --> NFS_OK. The current fh is now the root of
the pseudo-fs.
LOOKUP "this" --> NFS_OK. The current fh is for /this and is
within the pseudo-fs.
LOOKUP "is" --> NFS_OK. The current fh is for /this/is
and is within the pseudo-fs.
LOOKUP "the" --> NFS_OK. The current fh is for /this/is/the
and is within the pseudo-fs.
LOOKUP "path" --> NFS_OK. The current fh is for
/this/is/the/path and is within a new, absent file system,
but ... the client will never see the value of that fh.
GETFH --> NFS4ERR_MOVED.
Fails, because the current fh is in an absent file system at
the start of the operation and the specification makes
no exception for GETFH.
GETATTR(fsid, fileid, size, time_modify).
Not executed, because the failure of the GETFH stops the
processing of the COMPOUND.
Given the failure of the GETFH, the client has the job of
determining the root of the absent file system and where to find
that file system, i.e., the server and path relative to that
server's root fh. Note here that in this example, the client did
not obtain filehandles and attribute information (e.g., fsid) for
the intermediate directories, so that it would not be sure where
the absent file system starts. It could be the case, for example,
that /this/is/the is the root of the moved file system and that
the reason that the lookup of "path" succeeded is that the
file system was not absent on that operation but was moved
between the last LOOKUP and the GETFH (since COMPOUND is not
atomic). Even if we had the fsids for all of the intermediate
directories, we could have no way of knowing that /this/is/the/path
was the root of a new file system, since we don't yet have its fsid.
In order to get the necessary information, let us re-send the
chain of LOOKUPs with GETFHs and GETATTRs to at least get the
fsids so we can be sure where the appropriate file system
boundaries are. The client could choose to get fs_locations at
the same time, but in most cases the client will have a good
guess as to where the file system boundaries are (because of
where NFS4ERR_MOVED was, and was not, received), making the
fetching of fs_locations unnecessary.
PUTROOTFH --> NFS_OK
The current fh is at the root of the pseudo-fs.
GETATTR(fsid) --> NFS_OK
Just for completeness. Normally, clients will know the fsid
of the pseudo-fs as soon as they establish communication with
a server.
LOOKUP "this" --> NFS_OK
GETATTR(fsid) --> NFS_OK
Get the current fsid to see where the file system
boundaries are. The fsid will be that for the
pseudo-fs in this example, so no boundary.
GETFH --> NFS_OK
The current fh is for /this and is within the pseudo-fs.
LOOKUP "is" --> NFS_OK
The current fh is for /this/is and is within the pseudo-fs.
GETATTR(fsid) --> NFS_OK
Get the current fsid to see where the file system
boundaries are. The fsid will be that for the pseudo-fs
in this example, so no boundary.
GETFH --> NFS_OK
The current fh is for /this/is and is within the pseudo-fs.
LOOKUP "the" --> NFS_OK
The current fh is for /this/is/the and is within the pseudo-fs.
GETATTR(fsid) --> NFS_OK
Get the current fsid to see where the file system boundaries are.
The fsid will be that for the pseudo-fs in this example, so no
boundary.
GETFH --> NFS_OK
The current fh is for /this/is/the and is within the pseudo-fs.
LOOKUP "path" --> NFS_OK
The current fh is for /this/is/the/path and is within a new,
absent file system, but ...
The client will never see the value of that fh.
GETATTR(fsid, fs_locations) --> NFS_OK
We are getting the fsid to know where the file system boundaries are.
In this operation, the fsid will be different than that of the
parent directory (which in turn was retrieved in OP10).
Note that the
fsid we are given will not necessarily be preserved at the new
location. That fsid might be different, and in fact the fsid
we have for this file system might be a valid fsid of a different
file system on that new server.
In this particular case, we are pretty sure anyway that what
has moved is /this/is/the/path rather than /this/is/the
since we have the fsid of the latter and it is that of the
pseudo-fs, which presumably cannot move. However, in other
examples, we might not have this kind of information to rely
on (e.g., /this/is/the might be a non-pseudo-file system
separate from /this/is/the/path), so we need to have
other reliable source information on the boundary of the file system
that is moved. If, for example, the file system /this/is
had moved, we would have a case of migration rather than
referral, and once the boundaries of the migrated file system
were clear we could fetch fs_locations.
We are fetching fs_locations because the fact that we got an
NFS4ERR_MOVED at this point means that this is most likely a
referral and we need the destination. Even if it is the
case that /this/is/the is a file system that has migrated,
we will still need the location information for that file system.
GETFH --> NFS4ERR_MOVED
Fails because current fh is in an absent file system at the start of
the operation, and the specification makes no exception for GETFH. Note
that this means the server will never send the client a
filehandle from within an absent file system.
Given the above, the client knows where the root of the absent file
system is (/this/is/the/path) by noting where the change of fsid
occurred (between "the" and "path"). The fs_locations attribute
also gives the client the actual location of the absent
file system so that the referral can proceed. The
server gives the client the bare minimum of information about the
absent file system so that there will be very little scope for
problems of conflict between information sent by the referring
server and information of the file system's home. No filehandles
and very few attributes are present on the referring server, and the
client can treat those it receives as transient
information with the function of enabling the referral.
Another context in which a client may encounter referrals is when
it does a READDIR on a directory in which some of the subdirectories
are the roots of absent file systems.
Suppose such a directory is read as follows:
PUTROOTFH
LOOKUP "this"
LOOKUP "is"
LOOKUP "the"
READDIR(fsid, size, time_modify, mounted_on_fileid)
In this case, because rdattr_error is not requested, fs_locations
is not requested, and some of the attributes cannot be provided, the
result will be an NFS4ERR_MOVED error on the READDIR, with the
detailed results as follows:
PUTROOTFH --> NFS_OK. The current fh is at the root of the
pseudo-fs.
LOOKUP "this" --> NFS_OK. The current fh is for /this and is
within the pseudo-fs.
LOOKUP "is" --> NFS_OK. The current fh is for /this/is
and is within the pseudo-fs.
LOOKUP "the" --> NFS_OK. The current fh is for /this/is/the
and is within the pseudo-fs.
READDIR(fsid, size, time_modify, mounted_on_fileid) -->
NFS4ERR_MOVED. Note that the same error would have been
returned if /this/is/the had migrated, but it is returned because the
directory contains the root of an absent file system.
So now suppose that we re-send with rdattr_error:
PUTROOTFH
LOOKUP "this"
LOOKUP "is"
LOOKUP "the"
READDIR(rdattr_error, fsid, size, time_modify, mounted_on_fileid)
The results will be:
PUTROOTFH --> NFS_OK. The current fh is at the root of the
pseudo-fs.
LOOKUP "this" --> NFS_OK. The current fh is for /this and is
within the pseudo-fs.
LOOKUP "is" --> NFS_OK. The current fh is for /this/is
and is within the pseudo-fs.
LOOKUP "the" --> NFS_OK. The current fh is for /this/is/the
and is within the pseudo-fs.
READDIR(rdattr_error, fsid, size, time_modify, mounted_on_fileid)
--> NFS_OK. The attributes for the directory entry with the
component named "path" will only contain rdattr_error
with the value NFS4ERR_MOVED, together with an fsid
value and a value for mounted_on_fileid.
So suppose we do another READDIR to get fs_locations (although
we could have used a GETATTR directly, as in
):
PUTROOTFH
LOOKUP "this"
LOOKUP "is"
LOOKUP "the"
READDIR(rdattr_error, fs_locations, mounted_on_fileid, fsid,
size, time_modify)
The results would be:
PUTROOTFH --> NFS_OK. The current fh is at the root of the
pseudo-fs.
LOOKUP "this" --> NFS_OK. The current fh is for /this and is
within the pseudo-fs.
LOOKUP "is" --> NFS_OK. The current fh is for /this/is
and is within the pseudo-fs.
LOOKUP "the" --> NFS_OK. The current fh is for /this/is/the
and is within the pseudo-fs.
READDIR(rdattr_error, fs_locations, mounted_on_fileid, fsid,
size, time_modify) --> NFS_OK. The attributes will be as
shown below.
The attributes for the directory entry with the
component named "path" will only contain:
rdattr_error (value: NFS_OK)
fs_locations
mounted_on_fileid (value: unique fileid within referring file system)
fsid (value: unique value within referring server)
The attributes for entry "path" will not contain size or
time_modify, because these attributes are not available within an
absent file system.
The fs_locations attribute is defined by both fs_location4
() and fs_locations4
().
It is used to represent the location of a
file system by providing a server name and the path to the root
of the file system within that server's namespace.
When a set of servers have corresponding file systems at the
same path within their namespaces, an array of server names may
be provided. An entry in the server array is a UTF-8 string
and represents one of a traditional DNS host name, IPv4 address,
IPv6 address, or a zero-length string.
A zero-length string SHOULD be used to indicate the current address
being used for the RPC. It is not a requirement that all
servers that share the same rootpath be listed
in one fs_location4 instance. The array of server names is provided for
convenience. Servers that share the same rootpath may also be listed
in separate fs_location4 entries in the fs_locations attribute.
The fs_locations4 data type and fs_locations attribute contain an
array of such locations. Since the namespace of each server may be
constructed differently, the fs_root field is provided. The
path represented by the fs_root represents the location of the
file system in the current server's namespace, i.e., that of the
server from which the fs_locations attribute was obtained. The
fs_root path is meant to aid the client by clearly referencing
the root of the file system whose locations are being reported,
no matter what object within the current file system the
current filehandle designates. The fs_root is simply the
pathname the client used to reach the object on the current server
(i.e., the object to which the fs_locations attribute applies).
When the fs_locations attribute
is interrogated and there are no alternative file system locations,
the server SHOULD return a zero-length array of fs_location4
structures, together with a valid fs_root.
As an example, suppose there is a replicated file system located at two
servers (servA and servB). At servA, the file system is located at
path /a/b/c. At servB, the file system is located at path /x/y/z.
If the client were to obtain the fs_locations value for the
directory at /a/b/c/d, it might not necessarily know
that the file system's root is located in servA's namespace
at /a/b/c. When the client switches to servB, it will need
to determine that the directory it first referenced at servA is now
represented by the path /x/y/z/d on servB. To facilitate this, the
fs_locations attribute provided by servA would have an fs_root value
of /a/b/c and two entries in fs_locations. One entry in fs_locations
will be for itself (servA), and the other will be for servB with a
path of /x/y/z. With this information, the client is able to
substitute /x/y/z for /a/b/c at the beginning of its access
path and construct /x/y/z/d to use for the new server.
Note that there is no requirement that the number
of components in each rootpath be the same; there
is no relation between the number of components in the
rootpath or fs_root, and none of the components
in each rootpath and fs_root have to be the same. In
the above example, we could have had a third element
in the locations array, with server equal to "servC"
and rootpath equal to "/I/II", and a fourth element in the
locations array, with server equal to "servD" and rootpath
equal to "/aleph/beth/gimel/daleth/he".
The relationship between an fs_root and a rootpath is
that the client replaces the pathname indicated in the
fs_root for the current server for the substitute
indicated in the rootpath for the new server.
For an example of a referred or migrated file
system, suppose there is a file system located
at serv1. At serv1, the file system is located at
/az/buky/vedi/glagoli. The client finds that the object
at glagoli has migrated (or is a referral). The
client gets the fs_locations attribute, which contains
an fs_root of /az/buky/vedi/glagoli, and one element
in the locations array, with server equal to serv2,
and rootpath equal to /izhitsa/fita. The client
replaces /az/buky/vedi/glagoli with /izhitsa/fita
and uses the latter pathname on serv2.
Thus, the server MUST return an fs_root that is equal
to the path the client used to reach the object to which the
fs_locations attribute applies. Otherwise, the
client cannot determine the new path to use on the new server.
Integrating locking into the NFS protocol necessarily causes it
to be stateful. With the inclusion of share reservations, the
protocol becomes substantially more dependent on state than the
traditional combination of NFS and NLM (Network Lock Manager)
. There are three
components to making this state manageable:
clear division between client and server
ability to reliably detect inconsistency in state between
client and server
simple and robust recovery mechanisms
In this model, the server owns the state information. The client
requests changes in locks, and the server responds with the changes
made. Non-client-initiated changes in locking state are infrequent.
The client receives prompt notification of such changes and can
adjust its view of the locking state to reflect the server's changes.
Individual pieces of state created by the server and passed to the
client at its request are represented by 128-bit stateids. These
stateids may represent a particular open file, a set of byte-range
locks held by a particular owner, or a recallable delegation of
privileges to access a file in particular ways or at a particular
location.
In all cases, there is a transition from the most general information
that represents a client as a whole to the eventual lightweight
stateid used for most client and server locking interactions. The
details of this transition will vary with the type of object, but it
always starts with a client ID.
To support Win32 share reservations, it is necessary to atomically
OPEN or CREATE files and apply the appropriate locks in the same
operation. Having a separate share/unshare operation
would not allow correct implementation of the Win32 OpenFile API.
In order to correctly implement share semantics, the previous
NFS protocol mechanisms used when a file is opened or created
(LOOKUP, CREATE, ACCESS) need to be replaced. The NFSv4 protocol
has an OPEN operation that subsumes the NFSv3 methodology of
LOOKUP, CREATE, and ACCESS. However, because
many operations require a filehandle, the traditional LOOKUP is
preserved to map a filename to a filehandle without establishing
state on the server. The policy of granting access or modifying
files is managed by the server based on the client's state.
These mechanisms can implement policy ranging from advisory only
locking to full mandatory locking.
It is assumed that manipulating a byte-range lock is rare when
compared to READ and WRITE operations. It is also assumed that
server restarts and network
partitions are relatively rare. Therefore, it is important that the
READ and WRITE operations have a lightweight mechanism to indicate if
they possess a held lock. A byte-range lock request contains the
heavyweight information required to establish a lock and uniquely
define the owner of the lock.
The following sections describe the transition from the
heavyweight information to the eventual stateid used for most
client and server locking and lease interactions.
For each LOCK request, the client must identify itself to the
server. This is done in such a way as to allow for correct lock
identification and crash recovery. A sequence of a SETCLIENTID
operation followed by a SETCLIENTID_CONFIRM operation is
required to establish the identification onto the server.
Establishment of identification by a new incarnation of the
client also has the effect of immediately breaking any leased
state that a previous incarnation of the client might have had on
the server, as opposed to forcing the new client incarnation to
wait for the leases to expire. Breaking the lease state amounts
to the server removing all lock, share reservation, and, where
the server is not supporting the CLAIM_DELEGATE_PREV claim type,
all delegation state associated with the same client
with the same identity. For a discussion of delegation state
recovery, see .
Owners of opens and owners of byte-range locks are separate
entities and remain separate even if the same opaque arrays
are used to designate owners of each. The protocol distinguishes
between open-owners (represented by open_owner4 structures)
and lock-owners (represented by lock_owner4 structures).
Both sorts of owners consist of a clientid and an opaque
owner string. For each client, the set of distinct owner values
used with that client constitutes the set of owners of that type,
for the given client.
Each open is associated with a specific open-owner, while each
byte-range lock is associated with a lock-owner and an
open-owner, the latter being the open-owner associated with the
open file under which the LOCK operation was done.
Client identification is encapsulated in the following structure:
struct nfs_client_id4 {
verifier4 verifier;
opaque id<NFS4_OPAQUE_LIMIT>;
};
The first field, verifier, is a client incarnation verifier that is
used to detect client reboots. Only if the verifier is different
from that which the server has previously recorded for the client
(as identified by the second field of the structure, id) does the
server start the process of canceling the client's leased state.
The second field, id, is a variable-length string that uniquely
defines the client.
There are several considerations for how the client generates
the id string:
The string should be unique so that multiple clients do not
present the same string. The consequences of two clients
presenting the same string range from one client getting
an error to one client having its leased state abruptly and
unexpectedly canceled.
The string should be selected so the subsequent incarnations
(e.g., reboots) of the same client cause the client to present
the same string. The implementer is cautioned against an
approach that requires the string to be recorded in a local
file because this precludes the use of the implementation
in an environment where there is no local disk and all file
access is from an NFSv4 server.
The string should be different for each server network address
that the client accesses, rather than common to all server
network addresses. The reason is that it may not be possible
for the client to tell if the same server is listening on
multiple network addresses. If the client issues SETCLIENTID
with the same id string to each network address of such a
server, the server will think it is the same client, and each
successive SETCLIENTID will cause the server to begin the
process of removing the client's previous leased state.
The algorithm for generating the string should not assume that
the client's network address won't change. This includes
changes between client incarnations and even changes while
the client is still running in its current incarnation.
This means that if the client includes just the client's and
server's network address in the id string, there is a real risk,
after the client gives up the network address, that another
client, using a similar algorithm for generating the id string,
will generate a conflicting id string.
Given the above considerations, an example of a well-generated
id string is one that includes:
The server's network address.
The client's network address.
For a user-level NFSv4 client, it should contain
additional information to distinguish the client from
other user-level clients running on the same host,
such as a universally unique identifier (UUID).
Additional information that tends to be unique, such as one
or more of:
The client machine's serial number (for privacy reasons,
it is best to perform some one-way function on the serial
number).
A MAC address (for privacy reasons, it is best to perform
some one-way function on the MAC address).
The timestamp of when the NFSv4 software was
first installed on the client (though this is subject to
the previously mentioned caution about using information
that is stored in a file, because the file might only be
accessible over NFSv4).
A true random number. However, since this number ought to
be the same between client incarnations, this shares the
same problem as that of using the timestamp of the
software installation.
As a security measure, the server MUST NOT cancel a client's
leased state if the principal that established the state for a given
id string is not the same as the principal issuing the SETCLIENTID.
Note that SETCLIENTID ()
and SETCLIENTID_CONFIRM ()
have a secondary purpose of establishing the information the
server needs to make callbacks to the client for the purpose of
supporting delegations. It is permitted to change this
information via SETCLIENTID and SETCLIENTID_CONFIRM within the
same incarnation of the client without removing the client's
leased state.
Once a SETCLIENTID and SETCLIENTID_CONFIRM sequence has
successfully completed, the client uses the shorthand client
identifier, of type clientid4, instead of the longer and less
compact nfs_client_id4 structure. This shorthand client identifier
(a client ID) is assigned by the server and should be chosen so
that it will not conflict with a client ID previously assigned
by the server. This applies across server restarts or reboots.
When a client ID is presented to a server and that client ID is not
recognized, as would happen after a server reboot, the server
will reject the request with the error NFS4ERR_STALE_CLIENTID.
When this happens, the client must obtain a new client ID by
use of the SETCLIENTID operation and then proceed to any other
necessary recovery for the server reboot case (see
).
The client must also employ the SETCLIENTID operation when it
receives an NFS4ERR_STALE_STATEID error using a stateid derived
from its current client ID, since this also indicates a server
reboot, which has invalidated the existing client ID (see
for details).
See the detailed descriptions of SETCLIENTID
() and
SETCLIENTID_CONFIRM ()
for a complete specification of the operations.
If the server determines that the client holds no associated state
for its client ID, the server may choose to release the client ID.
The server may make this choice for an inactive client so that
resources are not consumed by those intermittently active clients.
If the client contacts the server after this release, the server
must ensure that the client receives the appropriate error so that
it will use the SETCLIENTID/SETCLIENTID_CONFIRM sequence to establish
a new identity. It should be clear that the server must be very
hesitant to release a client ID since the resulting work on the
client to recover from such an event will be the same burden
as if the server had failed and restarted. Typically, a server
would not release a client ID unless there had been no activity
from that client for many minutes.
Note that if the id string in a SETCLIENTID request is properly
constructed, and if the client takes care to use the same principal
for each successive use of SETCLIENTID, then, barring an active
denial-of-service attack, NFS4ERR_CLID_INUSE should never be
returned.
However, client bugs, server bugs, or perhaps a deliberate change
of the principal owner of the id string (such as the case of a
client that changes security flavors, and under the new flavor
there is no mapping to the previous owner) will in rare cases
result in NFS4ERR_CLID_INUSE.
In that event, when the server gets a SETCLIENTID for a client ID
that currently has no state, or it has state but the lease has
expired, rather than returning NFS4ERR_CLID_INUSE, the server MUST
allow the SETCLIENTID and confirm the new client ID if followed
by the appropriate SETCLIENTID_CONFIRM.
In several contexts, 32-bit sequence values called "seqids" are
used as part of managing locking state. Such values are used:
To provide an ordering of locking-related operations associated
with a particular lock-owner or open-owner. See
for a detailed explanation.
To define an ordered set of instances of a set of locks
sharing a particular set of ownership characteristics. See
for a detailed explanation.
Successive seqid values for the same object are normally arrived
at by incrementing the current value by one. This pattern continues
until the seqid is incremented past NFS4_UINT32_MAX, in which case
one (rather than zero) is to be the next seqid value.
When two seqid values are to be compared to determine which of the
two is later, the possibility of wraparound needs to be considered.
In many cases, the values are such that simple numeric comparisons
can be used. For example, if the seqid values to be compared are
both less than one million, the higher value can be considered
the later. On the other hand, if one of the values is at or near
NFS_UINT32_MAX and the other is less than one million, then
implementations can reasonably decide that the lower value has
had one more wraparound and is thus, while numerically lower,
actually later.
Implementations can compare seqids in the presence of potential
wraparound by adopting the reasonable assumption that the chain of
increments from one to the other is shorter than 2**31. So, if the
difference between the two seqids is less than 2**31, then the
lower seqid is to be treated as earlier. If, however, the
difference between the two seqids is greater than or equal to
2**31, then it can be assumed that the lower seqid has encountered
one more wraparound and can be treated as later.
When the server grants a lock of any type (including opens,
byte-range locks, and delegations), it responds with a unique
stateid that represents a set of locks (often a single lock) for the
same file, of the same type, and sharing the same ownership
characteristics. Thus, opens of the same file by different
open-owners each have an identifying stateid. Similarly, each set of
byte-range locks on a file owned by a specific lock-owner has its own
identifying stateid. Delegations also have associated
stateids by which they may be referenced. The stateid is used as a
shorthand reference to a lock or set of locks, and given a stateid,
the server can determine the associated state-owner or state-owners
(in the case of an open-owner/lock-owner pair) and the associated
filehandle. When stateids are used, the current filehandle must be
the one associated with that stateid.
All stateids associated with a given client ID are associated with a
common lease that represents the claim of those stateids and the
objects they represent to be maintained by the server. See
for a discussion of the lease.
Each stateid must be unique to the server. Many operations take
a stateid as an argument but not a clientid, so the server must
be able to infer the client from the stateid.
With the exception of special stateids
(see ), each stateid
represents locking objects of one of a set of types defined
by the NFSv4 protocol. Note that in all these cases, where
we speak of a guarantee, it is understood there are
situations such as a client restart, or lock revocation,
that allow the guarantee to be voided.
Stateids may represent opens of files.
Each stateid in this case represents the OPEN state for a
given client ID/open-owner/filehandle triple. Such
stateids are subject to change (with consequent
incrementing of the stateid's seqid) in response to OPENs that
result in upgrade and OPEN_DOWNGRADE operations.
Stateids may represent sets of byte-range locks.
All locks held on a particular file by a particular owner and all
gotten under the aegis of a particular open file
are associated with a single stateid, with the seqid
being incremented whenever LOCK and LOCKU operations affect
that set of locks.
Stateids may represent file delegations, which are
recallable guarantees by the server to the client
that other clients will not reference, or will not
modify, a particular file until the delegation is
returned.
A stateid represents a single delegation held by
a client for a particular filehandle.
Stateids are divided into two fields: a 96-bit "other" field
identifying the specific set of locks and a 32-bit "seqid" sequence
value. Except in the case of special stateids (see ), a
particular value of the "other" field denotes a set of locks of the
same type (for example, byte-range locks, opens, or delegations),
for a specific file or directory, and sharing the same ownership
characteristics. The seqid designates a specific instance
of such a set of locks, and is incremented to indicate changes in
such a set of locks, by either the addition or deletion of locks
from the set, a change in the byte-range they apply to, or
an upgrade or downgrade in the type of one or more locks.
When such a set of locks is first created, the server returns
a stateid with a seqid value of one. On subsequent operations that
modify the set of locks, the server is required to advance the
seqid field by one whenever it returns a stateid for the same
state-owner/file/type combination and the operation is one that
might make some change in the set
of locks actually designated. In this case, the server will return a
stateid with an "other" field the same as previously used for that
state-owner/file/type combination, with an incremented seqid field.
Seqids will be compared, by both the client and the server.
The client uses such comparisons to determine the order of
operations, while the server uses them to determine
whether the NFS4ERR_OLD_STATEID error is to be returned.
In all cases, the possibility of seqid wraparound needs to be
taken into account, as discussed in .
Stateid values whose "other" field is either all zeros or all
ones are reserved. They MUST NOT be assigned by the server but
have special meanings defined by the protocol. The particular
meaning depends on whether the "other" field is all zeros or
all ones and the specific value of the seqid field.
The following combinations of "other" and seqid are defined
in NFSv4:
When "other" and seqid are both zero, the
stateid is treated as a special anonymous
stateid, which can be used in READ, WRITE,
and SETATTR requests to indicate the absence
of any open state associated with the
request. When an anonymous stateid value is
used, and an existing open denies the form of
access requested, then access will be denied
to the request.
When "other" and seqid are both all ones,
the stateid is a special READ bypass stateid.
When this value is used in WRITE or SETATTR,
it is treated like the anonymous value.
When used in READ, the server MAY grant
access, even if access would normally be
denied to READ requests.
If a stateid value is used that has all zeros or all ones in the
"other" field but does not match one of the cases above, the
server MUST return the error NFS4ERR_BAD_STATEID.
Special stateids, unlike other stateids, are not associated with
individual client IDs or filehandles and can be used with all valid
client IDs and filehandles.
Stateids must remain valid until either a client restart or a
server restart, or until the client returns all of the locks
associated with the stateid by means of an operation such as
CLOSE or DELEGRETURN. If the locks are lost due to revocation,
as long as the client ID is valid, the stateid remains a
valid designation of that revoked state. Stateids associated
with byte-range locks are an exception. They remain valid even if a
LOCKU frees all remaining locks, so long as the open file with which
they are associated remains open.
It should be noted that there are situations in which the
client's locks become invalid, without the client requesting
they be returned. These include lease expiration and a number
of forms of lock revocation within the lease period. It is
important to note that in these situations, the stateid remains
valid and the client can use it to determine the disposition of
the associated lost locks.
An "other" value must never be reused for a different purpose
(i.e., different filehandle, owner, or type of locks) within the
context of a single client ID. A server may retain the "other"
value for the same purpose beyond the point where it may otherwise
be freed, but if it does so, it must maintain seqid continuity
with previous values.
One mechanism that may be used to satisfy the requirement that the
server recognize invalid and out-of-date stateids is for
the server to divide the "other" field of the stateid into two
fields:
An index into a table of locking-state structures.
A generation number that is incremented on each allocation
of a table entry for a particular use.
And then store the following in each table entry:
The client ID with which the stateid is associated.
The current generation number for the (at most one)
valid stateid sharing this index value.
The filehandle of the file on which the locks are taken.
An indication of the type of stateid (open, byte-range lock,
file delegation).
The last seqid value returned corresponding to the current
"other" value.
An indication of the current status of the locks
associated with this stateid -- in particular, whether
these have been revoked and, if so, for what reason.
With this information, an incoming stateid can be validated and
the appropriate error returned when necessary. Special and
non-special stateids are handled separately. (See
for a discussion of special
stateids.)
When a stateid is being tested,
and the "other" field is all zeros or all ones, a check that
the "other" and seqid fields match a defined combination for
a special stateid is done and the results determined as follows:
If the "other" and seqid fields do not match a defined
combination associated with a special stateid, the error
NFS4ERR_BAD_STATEID is returned.
If the combination is valid in general but is not
appropriate to the context in which the stateid is used
(e.g., an all-zero stateid is used when an open stateid
is required in a LOCK operation), the error
NFS4ERR_BAD_STATEID is also returned.
Otherwise, the check is completed and the special stateid
is accepted as valid.
When a stateid is being tested,
and the "other" field is neither all zeros nor all ones, the
following procedure could be used to
validate an incoming stateid and return an appropriate error,
when necessary, assuming that the "other" field would be divided
into a table index and an entry generation. Note that the
terms "earlier" and "later" used in connection with seqid
comparison are to be understood as explained in
.
If the table index field is outside the range of the
associated table, return NFS4ERR_BAD_STATEID.
If the selected table entry is of a different generation than
that specified in the incoming stateid, return
NFS4ERR_BAD_STATEID.
If the selected table entry does not match the current
filehandle, return NFS4ERR_BAD_STATEID.
If the stateid represents revoked state or state lost as a result
of lease expiration, then return NFS4ERR_EXPIRED,
NFS4ERR_BAD_STATEID, or NFS4ERR_ADMIN_REVOKED, as appropriate.
If the stateid type is not valid for the context in which the
stateid appears, return NFS4ERR_BAD_STATEID.
Note that a stateid may be valid in general but invalid for
a particular operation, as, for example, when a stateid
that doesn't represent byte-range locks is passed to
the non-from_open case of LOCK or to LOCKU, or when a stateid
that does not represent an open is passed to CLOSE or
OPEN_DOWNGRADE. In such cases, the server MUST return
NFS4ERR_BAD_STATEID.
If the seqid field is not zero and it is later
than the current sequence value corresponding to the
current "other" field, return NFS4ERR_BAD_STATEID.
If the seqid field is earlier than
the current sequence value corresponding to the
current "other" field, return NFS4ERR_OLD_STATEID.
Otherwise, the stateid is valid, and the table entry
should contain any additional information about the
type of stateid and information associated with that
particular type of stateid, such as the associated set
of locks (e.g., open-owner and lock-owner information),
as well as information on the specific locks themselves,
such as open modes and byte ranges.
Clients performing Input/Output (I/O) operations need to
select an appropriate stateid based on the locks (including
opens and delegations) held by the client and the various
types of state-owners sending the I/O requests. SETATTR
operations that change the file size are treated like I/O
operations in this regard.
The following rules, applied in order of decreasing priority, govern
the selection of the appropriate stateid. In following these rules,
the client will only consider locks of which it has actually received
notification by an appropriate operation response or callback.
If the client holds a delegation for the file in question, the
delegation stateid SHOULD be used.
Otherwise, if the entity corresponding to the lock-owner (e.g., a
process) sending the I/O has a byte-range lock stateid for the
associated open file, then the byte-range lock stateid for that
lock-owner and open file SHOULD be used.
If there is no byte-range lock stateid, then the OPEN stateid for
the current open-owner, i.e., the OPEN stateid for the open
file in question, SHOULD be used.
Finally, if none of the above apply, then a special stateid SHOULD
be used.
Ignoring these rules may result in situations in which the server
does not have information necessary to properly process the request.
For example, when mandatory byte-range locks are in effect, if the
stateid does not indicate the proper lock-owner, via a lock stateid,
a request might be avoidably rejected.
The server, however, should not try to enforce these ordering
rules and should use whatever information is available to
properly process I/O requests. In particular, when a client
has a delegation for a given file, it SHOULD take note of this
fact in processing a request, even if it is sent with a
special stateid.
In the case of SETATTR operations, a stateid is present. In cases
other than those that set the file size, the client may send either a
special stateid or, when a delegation is held for the file in
question, a delegation stateid. While the server SHOULD validate the
stateid and may use the stateid to optimize the determination as to
whether a delegation is held, it SHOULD note the presence of a
delegation even when a special stateid is sent, and MUST accept a
valid delegation stateid when sent.
When requesting a lock, the client must present to the server the
client ID and an identifier for the owner of the requested lock.
These two fields comprise the lock-owner and are defined as follows:
A client ID returned by the server as part of the client's use
of the SETCLIENTID operation.
A variable-length opaque array used to uniquely define the
owner of a lock managed by the client.
This may be a thread id, process id, or other unique value.
When the server grants the lock, it responds with a unique stateid.
The stateid is used as a shorthand reference to the lock-owner,
since the server will be maintaining the correspondence between
them.
All READ, WRITE, and SETATTR operations contain a stateid. For the
purposes of this section, SETATTR operations that change the
size attribute of a file are treated as if they are writing the
area between the old and new size (i.e., the range truncated or
added to the file by means of the SETATTR), even where SETATTR
is not explicitly mentioned in the text. The stateid passed to
one of these operations must be one that represents an OPEN (e.g.,
via the open-owner), a set of byte-range locks, or a
delegation, or it may be a special stateid representing anonymous
access or the READ bypass stateid.
If the state-owner performs a READ or WRITE in a situation in which
it has established a lock or share reservation on the server (any
OPEN constitutes a share reservation), the stateid (previously
returned by the server) must be used to indicate what locks,
including both byte-range locks and share reservations, are held by
the state-owner. If no state is established by the client -- either
byte-range lock or share reservation -- the anonymous stateid is used.
Regardless of whether an anonymous stateid or a stateid returned
by the server is used, if there is a conflicting share reservation
or mandatory byte-range lock held on the file, the server MUST refuse
to service the READ or WRITE operation.
Share reservations are established by OPEN operations and by
their nature are mandatory in that when the OPEN denies READ
or WRITE operations, that denial results in such operations
being rejected with error NFS4ERR_LOCKED. Byte-range locks may be
implemented by the server as either mandatory or advisory, or
the choice of mandatory or advisory behavior may be determined by
the server on the basis of the file being accessed (for example,
some UNIX-based servers support a "mandatory lock bit" on the
mode attribute such that if set, byte-range locks are required on the
file before I/O is possible). When byte-range locks are advisory,
they only prevent the granting of conflicting lock requests and
have no effect on READs or WRITEs. Mandatory byte-range locks,
however, prevent conflicting I/O operations. When they are
attempted, they are rejected with NFS4ERR_LOCKED. When the
client gets NFS4ERR_LOCKED on a file it knows it has the proper
share reservation for, it will need to issue a LOCK request on
the region of the file that includes the region the I/O was to
be performed on, with an appropriate locktype (i.e., READ*_LT
for a READ operation, WRITE*_LT for a WRITE operation).
With NFSv3, there was no notion of a stateid, so there was
no way to tell if the application process of the client sending
the READ or WRITE operation had also acquired the appropriate
byte-range lock on the file. Thus, there was no way to implement
mandatory locking. With the stateid construct, this barrier has
been removed.
Note that for UNIX environments that support mandatory file
locking, the distinction between advisory and mandatory locking is
subtle. In fact, advisory and mandatory byte-range locks are exactly
the same insofar as the APIs and requirements on implementation are
concerned.
If the mandatory lock attribute is set on the file, the server
checks to see if the lock-owner has an appropriate shared (read)
or exclusive (write) byte-range lock on the region it wishes to
read or write to. If there is no appropriate lock, the
server checks if there is a conflicting lock (which can be done
by attempting to acquire the conflicting lock on behalf of the
lock-owner and, if successful, release the lock after the
READ or WRITE is done), and if there is, the server returns
NFS4ERR_LOCKED.
For Windows environments, there are no advisory byte-range locks,
so the server always checks for byte-range locks during I/O requests.
Thus, the NFSv4 LOCK operation does not need to distinguish
between advisory and mandatory byte-range locks. It is the
NFSv4 server's processing of the READ and WRITE operations
that introduces the distinction.
Every stateid other than the special stateid values noted in this
section, whether returned by an OPEN-type operation (i.e., OPEN,
OPEN_DOWNGRADE) or by a LOCK-type operation (i.e., LOCK or LOCKU),
defines an access mode for the file (i.e., READ, WRITE, or
READ-WRITE) as established by the original OPEN that began the stateid
sequence, and as modified by subsequent OPENs and OPEN_DOWNGRADEs
within that stateid sequence. When a READ, WRITE, or SETATTR that
specifies the size attribute is done, the operation is subject to
checking against the access mode to verify that the operation is
appropriate given the OPEN with which the operation is associated.
In the case of WRITE-type operations (i.e., WRITEs and SETATTRs
that set size), the server must verify that the access mode allows
writing and return an NFS4ERR_OPENMODE error if it does not.
In the case of READ, the server may perform the corresponding
check on the access mode, or it may choose to allow READ on opens
for WRITE only, to accommodate clients whose write implementation
may unavoidably do reads (e.g., due to buffer cache constraints).
However, even if READs are allowed in these circumstances,
the server MUST still check for locks that conflict with the
READ (e.g., another open specifying denial of READs). Note that
a server that does enforce the access mode check on READs need
not explicitly check for conflicting share reservations since the
existence of OPEN for read access guarantees that no conflicting
share reservation can exist.
A READ bypass stateid MAY allow READ operations to bypass
locking checks at the server. However, WRITE operations
with a READ bypass stateid MUST NOT bypass locking checks
and are treated exactly the same as if an anonymous stateid
were used.
A lock may not be granted while a READ or WRITE operation using
one of the special stateids is being performed and the range of
the lock request conflicts with the range of the READ or WRITE
operation. For the purposes of this paragraph, a conflict occurs
when a shared lock is requested and a WRITE operation is being
performed, or an exclusive lock is requested and either a READ
or a WRITE operation is being performed. A SETATTR that sets
size is treated similarly to a WRITE as discussed above.
Locking is different than most NFS operations as it requires
"at&nbhy;most-one" semantics that are not provided by ONC RPC.
ONC RPC over a reliable transport is not sufficient because a
sequence of locking requests may span multiple TCP connections.
In the face of retransmission or reordering, lock or unlock
requests must have a well-defined and consistent behavior.
To accomplish this, each lock request contains a sequence number
that is a consecutively increasing integer. Different state-owners
have different sequences. The server maintains the last sequence
number (L) received and the response that was returned. The server
SHOULD assign a seqid value of one for the first request issued for any
given state-owner. Subsequent values are arrived at by incrementing
the seqid value, subject to wraparound as described in
.
Note that for requests that contain a sequence number, for each
state-owner, there should be no more than one outstanding request.
When a request is received, its sequence number (r)
is compared to that of the last one received (L).
Only if it has the correct next sequence,
normally L + 1, is the request processed beyond the point of
seqid checking. Given a properly functioning client, the
response to (r) must have been received before the last request (L)
was sent. If a duplicate of last request (r == L) is received,
the stored response is returned. If the sequence value received
is any other value, it is rejected with the return
of error NFS4ERR_BAD_SEQID. Sequence history is reinitialized
whenever the SETCLIENTID/SETCLIENTID_CONFIRM sequence changes
the client verifier.
It is critical that the server maintain the last response sent to the
client to provide a more reliable cache of duplicate non-idempotent
requests than that of the traditional cache described in
. The traditional duplicate request cache
uses a least recently used algorithm for removing unneeded
requests. However, the last lock request and response on a given
state-owner must be cached as long as the lock state exists on the
server.
The client MUST advance the sequence number for
the CLOSE, LOCK, LOCKU, OPEN, OPEN_CONFIRM, and OPEN_DOWNGRADE
operations. This is true even in the event that the previous
operation that used the sequence number received an error.
The only exception to this rule is if the previous operation
received one of the following errors: NFS4ERR_STALE_CLIENTID,
NFS4ERR_STALE_STATEID, NFS4ERR_BAD_STATEID, NFS4ERR_BAD_SEQID,
NFS4ERR_BADXDR, NFS4ERR_RESOURCE, NFS4ERR_NOFILEHANDLE,
or NFS4ERR_MOVED.
As described above, the sequence number is per state-owner.
As long as the server maintains the last sequence number received
and follows the methods described above, there are no risks of a
Byzantine router re-sending old requests. The server need only
maintain the (state-owner, sequence number) state as long as there
are open files or closed files with locks outstanding.
LOCK, LOCKU, OPEN, OPEN_DOWNGRADE, and CLOSE each contain a
sequence number, and therefore the risk of the replay of these
operations resulting in undesired effects is non-existent while
the server maintains the state-owner state.
Some operations may have multiple sources of data for request
sequence checking and retransmission determination. Some operations
have multiple sequence values associated with multiple types of
state-owners. In addition, such operations may also have a stateid
with its own seqid value, that will be checked for validity.
As noted above, there may be multiple sequence values to check.
The following rules should be followed by the server
in processing these multiple sequence values
within a single operation.
When a sequence value associated with a state-owner is unavailable
for checking because the state-owner is unknown to the
server, it takes no part in the comparison.
When any of the state-owner sequence values are invalid,
NFS4ERR_BAD_SEQID is returned. When a stateid sequence is checked,
NFS4ERR_BAD_STATEID or NFS4ERR_OLD_STATEID is returned as
appropriate, but NFS4ERR_BAD_SEQID has priority.
When any one of the sequence values matches a previous request,
for a state-owner, it is treated as a retransmission and not
re&nbhy;executed. When the type of the operation does not match that
originally used, NFS4ERR_BAD_SEQID is returned. When the
server can determine that the request differs from the original,
it may return NFS4ERR_BAD_SEQID.
When multiple sequence values match previous operations but the
operations are not the same, NFS4ERR_BAD_SEQID is returned.
When there are no sequence values available for comparison
and the operation is an OPEN, the server indicates
to the client that an OPEN_CONFIRM is required, unless it can
conclusively determine that confirmation is not required (e.g.,
by knowing that no open-owner state has ever been released for the
current clientid).
When a particular state-owner no longer holds open or file
locking state at the server, the server may choose to release
the sequence number state associated with the state-owner.
The server may make this choice based on lease expiration,
the reclamation of server memory, or other
implementation-specific details. Note that when this is done, a
retransmitted request, normally identified by a matching
state-owner sequence, may not be correctly recognized, so that
the client will not receive the original response that it would
have if the state-owner state was not released.
If the server were able to be sure that a given state-owner would
never again be used by a client, such an issue could not arise.
Even when the state-owner state is released and the client
subsequently uses that state-owner, retransmitted requests will be
detected as invalid and the request not executed, although the
client may have a recovery path that is more complicated than
simply getting the original response back transparently.
In any event, the server is able to safely release state-owner
state (in the sense that retransmitted requests will not be erroneously
acted upon) when the state-owner is not currently being utilized by
the client (i.e., there are no open files associated with an
open-owner and no lock stateids associated with a lock-owner).
The server may choose
to hold the state-owner state in order to simplify the recovery
path, in the case in which retransmissions of currently active
requests are received. However, the period for which it
chooses to hold this state is implementation specific.
In the case that a LOCK, LOCKU, OPEN_DOWNGRADE, or CLOSE is
retransmitted after the server has previously released the
state-owner state, the server will find that the state-owner has no
files open and an error will be returned to the client. If the
state-owner does have a file open, the stateid will not match and
again an error is returned to the client.
In the case that an OPEN is retransmitted and the open-owner is
being used for the first time or the open-owner state has been
previously released by the server, the use of the OPEN_CONFIRM
operation will prevent incorrect behavior. When the server
observes the use of the open-owner for the first time, it
will direct the client to perform the OPEN_CONFIRM for the
corresponding OPEN. This sequence establishes the use of an
open-owner and associated sequence number. Since the OPEN_CONFIRM
sequence connects a new open-owner on the server with an existing
open-owner on a client, the sequence number may have any valid
(i.e., non-zero) value. The OPEN_CONFIRM step assures the
server that the value received is the correct one.
(See for further details.)
There are a number of situations in which the requirement to
confirm an OPEN would pose difficulties for the client and
server, in that they would be prevented from acting in a timely
fashion on information received, because that information would
be provisional, subject to deletion upon non-confirmation.
Fortunately, these are situations in which the server can avoid
the need for confirmation when responding to open requests.
The two constraints are:
The server must not bestow a delegation for any open that
would require confirmation.
The server MUST NOT require confirmation on a reclaim-type
open (i.e., one specifying claim type CLAIM_PREVIOUS or
CLAIM_DELEGATE_PREV).
These constraints are related in that reclaim-type opens are the
only ones in which the server may be required to send a delegation.
For CLAIM_NULL, sending the delegation is optional, while for
CLAIM_DELEGATE_CUR, no delegation is sent.
Delegations being sent with an open requiring confirmation are
troublesome because recovering from non-confirmation adds undue
complexity to the protocol, while requiring confirmation on
reclaim-type opens poses difficulties in that the inability to
resolve the status of the reclaim until lease expiration may
make it difficult to have timely determination of the set of
locks being reclaimed (since the grace period may expire).
Requiring open confirmation on reclaim-type opens is avoidable
because of the nature of the environments in which such opens are
done. For CLAIM_PREVIOUS opens, this is immediately after server
reboot, so there should be no time for open-owners to be created,
found to be unused, and recycled. For CLAIM_DELEGATE_PREV opens, we
are dealing with either a client reboot situation or a network
partition resulting in deletion of lease state (and
returning NFS4ERR_EXPIRED). A server that supports delegations
can be sure that no open-owners for that client have been
recycled since client initialization or deletion of lease state
and thus can be confident that confirmation will not be required.
The protocol allows a lock-owner to request a lock with a byte
range and then either upgrade or unlock a sub-range of the
initial lock. It is expected that this will be an uncommon type
of request. In any case, servers or server file systems may not be
able to support sub&nbhy;range lock semantics. In the event that a
server receives a locking request that represents a sub&nbhy;range of
current locking state for the lock-owner, the server is allowed
to return the error NFS4ERR_LOCK_RANGE to signify that it does
not support sub&nbhy;range lock operations. Therefore, the client
should be prepared to receive this error and, if appropriate,
report the error to the requesting application.
The client is discouraged from combining multiple independent
locking ranges that happen to be adjacent into a single request,
since the server may not support sub-range requests, and for reasons
related to the recovery of file locking state in the event of
server failure. As discussed in
below, the server may employ certain optimizations
during recovery that work effectively only when the client's
behavior during lock recovery is similar to the client's locking
behavior prior to server failure.
If a client has a write lock on a record, it can request an
atomic downgrade of the lock to a read lock via the LOCK request,
by setting the type to READ_LT. If the server supports atomic
downgrade, the request will succeed. If not, it will return
NFS4ERR_LOCK_NOTSUPP. The client should be prepared to receive
this error and, if appropriate, report the error to the requesting
application.
If a client has a read lock on a record, it can request an
atomic upgrade of the lock to a write lock via the LOCK request
by setting the type to WRITE_LT or WRITEW_LT. If the server does
not support atomic upgrade, it will return NFS4ERR_LOCK_NOTSUPP.
If the upgrade can be achieved without an existing conflict, the
request will succeed. Otherwise, the server will return either
NFS4ERR_DENIED or NFS4ERR_DEADLOCK. The error NFS4ERR_DEADLOCK is
returned if the client issued the LOCK request with the type set
to WRITEW_LT and the server has detected a deadlock. The client
should be prepared to receive such errors and, if appropriate,
report them to the requesting application.
Some clients require the support of blocking locks. The
NFSv4 protocol must not rely on a callback mechanism and
therefore is unable to notify a client when a previously denied
lock has been granted. Clients have no choice but to continually
poll for the lock. This presents a fairness problem. Two new
lock types are added, READW and WRITEW, and are used to indicate
to the server that the client is requesting a blocking lock.
The server should maintain an ordered list of pending blocking
locks. When the conflicting lock is released, the server may
wait the lease period for the first waiting client to re-request
the lock. After the lease period expires, the next waiting client
request is allowed the lock. Clients are required to poll at
an interval sufficiently small that it is likely to acquire the
lock in a timely manner. The server is not required to maintain a
list of pending blocked locks, as it is not used to provide correct
operation but only to increase fairness. Because of the unordered
nature of crash recovery, storing of lock state to stable storage
would be required to guarantee ordered granting of blocking locks.
Servers may also note the lock types and delay returning denial
of the request to allow extra time for a conflicting lock to be
released, allowing a successful return. In this way, clients can
avoid the burden of needlessly frequent polling for blocking locks.
The server should take care with the length of delay in the event
that the client retransmits the request.
If a server receives a blocking lock request, denies it, and then
later receives a non-blocking request for the same lock, which is also
denied, then it should remove the lock in question from its list of
pending blocking locks. Clients should use such a non-blocking
request to indicate to the server that this is the last time they
intend to poll for the lock, as may happen when the process
requesting the lock is interrupted. This is a courtesy to the
server, to prevent it from unnecessarily waiting a lease period
before granting other lock requests. However, clients are not
required to perform this courtesy, and servers must not depend on
them doing so. Also, clients must be prepared for the possibility
that this final locking request will be accepted.
The purpose of a lease is to allow a server to remove stale
locks that are held by a client that has crashed or is otherwise
unreachable. It is not a mechanism for cache consistency, and
lease renewals may not be denied if the lease interval has not expired.
The client can implicitly provide a positive indication that it is
still active and that the associated state held at the server, for
the client, is still valid. Any operation made with a valid clientid
(DELEGPURGE, LOCK, LOCKT, OPEN, RELEASE_LOCKOWNER, or RENEW) or a
valid stateid (CLOSE, DELEGRETURN, LOCK, LOCKU, OPEN, OPEN_CONFIRM,
OPEN_DOWNGRADE, READ, SETATTR, or WRITE) informs the server to renew
all of the leases for that client (i.e., all those sharing a given
client ID). In the latter case, the stateid must not be one of the
special stateids (anonymous stateid or READ bypass stateid).
Note that if the client had restarted or rebooted, the
client would not be making these requests without issuing
the SETCLIENTID/SETCLIENTID_CONFIRM sequence. The use of the
SETCLIENTID/SETCLIENTID_CONFIRM sequence (one that changes the
client verifier) notifies the server to drop the locking state
associated with the client. SETCLIENTID/SETCLIENTID_CONFIRM
never renews a lease.
If the server has rebooted, the stateids (NFS4ERR_STALE_STATEID
error) or the client ID (NFS4ERR_STALE_CLIENTID error) will
not be valid, hence preventing spurious renewals.
This approach allows for low-overhead lease renewal, which scales
well. In the typical case, no extra RPCs are required for
lease renewal, and in the worst case, one RPC is required every
lease period (i.e., a RENEW operation). The number of locks held
by the client is not a factor since all state for the client is
involved with the lease renewal action.
Since all operations that create a new lease also renew existing
leases, the server must maintain a common lease expiration time
for all valid leases for a given client. This lease time can
then be easily updated upon implicit lease renewal actions.
The important requirement in crash recovery is that both the client
and the server know when the other has failed. Additionally, it
is required that a client sees a consistent view of data across
server restarts or reboots. All READ and WRITE operations that may
have been queued within the client or network buffers must wait
until the client has successfully recovered the locks protecting
the READ and WRITE operations.
In the event that a client fails, the server may recover
the client's locks when the associated leases have expired.
Conflicting locks from another client may only be granted after
this lease expiration. If the client is able to restart or
reinitialize within the lease period, the client may be forced to
wait the remainder of the lease period before obtaining new locks.
To minimize client delay upon restart, open and lock requests are
associated with an instance of the client by a client-supplied
verifier.
This verifier is part of the initial SETCLIENTID call made by
the client. The server returns a client ID as a result of the
SETCLIENTID operation. The client then confirms the use of the
client ID with SETCLIENTID_CONFIRM. The client ID in combination
with an opaque owner field is then used by the client to identify
the open-owner for OPEN. This chain of associations is then used
to identify all locks for a particular client.
Since the verifier will be changed by the client upon each
initialization, the server can compare a new verifier to the
verifier associated with currently held locks and determine that
they do not match. This signifies the client's new instantiation
and subsequent loss of locking state. As a result, the server
is free to release all locks held that are associated with the
old client ID that was derived from the old verifier.
Note that the verifier must have the same uniqueness properties
of the verifier for the COMMIT operation.
If the server loses locking state (usually as a result of a restart
or reboot), it must allow clients time to discover this fact and
re&nbhy;establish the lost locking state. The client must be able
to re&nbhy;establish the locking state without having the server deny
valid requests because the server has granted conflicting access
to another client. Likewise, if there is the possibility that
clients have not yet re&nbhy;established their locking state for a file,
the server must disallow READ and WRITE operations for that file.
The duration of this recovery period is equal to the duration of
the lease period.
A client can determine that server failure (and thus loss of
locking state) has occurred, when it receives one of two errors.
The NFS4ERR_STALE_STATEID error indicates a stateid invalidated by
a reboot or restart. The NFS4ERR_STALE_CLIENTID error indicates
a client ID invalidated by reboot or restart. When either of
these is received, the client must establish a new client ID
(see ) and re-establish the
locking state as discussed below.
The period of special handling of locking and READs and WRITEs,
equal in duration to the lease period, is referred to as the
"grace period". During the grace period, clients recover locks
and the associated state by reclaim-type locking requests (i.e.,
LOCK requests with reclaim set to TRUE and OPEN operations with
a claim type of either CLAIM_PREVIOUS or CLAIM_DELEGATE_PREV).
During the grace period, the server must reject READ and WRITE
operations and non-reclaim locking requests (i.e., other LOCK
and OPEN operations) with an error of NFS4ERR_GRACE.
If the server can reliably determine that granting a non-reclaim
request will not conflict with reclamation of locks by other
clients, the NFS4ERR_GRACE error does not have to be returned
and the non&nbhy;reclaim client request can be serviced. For the
server to be able to service READ and WRITE operations during the
grace period, it must again be able to guarantee that no possible
conflict could arise between an impending reclaim locking request
and the READ or WRITE operation. If the server is unable to
offer that guarantee, the NFS4ERR_GRACE error must be returned
to the client.
For a server to provide simple, valid handling during the grace
period, the easiest method is to simply reject all non-reclaim
locking requests and READ and WRITE operations by returning the
NFS4ERR_GRACE error. However, a server may keep information
about granted locks in stable storage. With this information,
the server could determine if a regular lock or READ or WRITE
operation can be safely processed.
For example, if a count of locks on a given file is available in
stable storage, the server can track reclaimed locks for the file,
and when all reclaims have been processed, non-reclaim locking
requests may be processed. This way, the server can ensure that
non&nbhy;reclaim locking requests will not conflict with potential
reclaim requests. With respect to I/O requests, if the server is
able to determine that there are no outstanding reclaim requests
for a file by information from stable storage or another similar
mechanism, the processing of I/O requests could proceed normally
for the file.
To reiterate, for a server that allows non-reclaim lock and
I/O requests to be processed during the grace period, it MUST
determine that no lock subsequently reclaimed will be rejected
and that no lock subsequently reclaimed would have prevented any
I/O operation processed during the grace period.
Clients should be prepared for the return of NFS4ERR_GRACE errors
for non-reclaim lock and I/O requests. In this case, the client
should employ a retry mechanism for the request. A delay (on the
order of several seconds) between retries should be used to avoid
overwhelming the server. Further discussion of the general issue
is included in . The client must account
for the server that is able to perform I/O and non-reclaim
locking requests within the grace period as well as those that
cannot do so.
A reclaim-type locking request outside the server's grace period
can only succeed if the server can guarantee that no conflicting
lock or I/O request has been granted since reboot or restart.
A server may, upon restart, establish a new value for the
lease period. Therefore, clients should, once a new client ID is
established, refetch the lease_time attribute and use it as the
basis for lease renewal for the lease associated with that server.
However, the server must establish, for this restart event, a
grace period at least as long as the lease period for the previous
server instantiation. This allows the client state obtained
during the previous server instance to be reliably re-established.
If the duration of a network partition is greater than the lease
period provided by the server, the server will have not received
a lease renewal from the client. If this occurs, the server may
cancel the lease and
free all locks held for the client. As a result, all stateids
held by the client will become invalid or stale. Once the client
is able to reach the server after such a network partition,
all I/O submitted by the client with the now invalid stateids
will fail with the server returning the error NFS4ERR_EXPIRED.
Once this error is received, the client will suitably notify the
application that held the lock.
As a courtesy to the client or as an optimization, the server may
continue to hold locks, including delegations, on behalf of a client
for which recent communication has extended beyond the lease period,
delaying the cancellation of the lease. If the server receives a lock
or I/O request that conflicts with one of these courtesy locks or if it
runs out of resources, the server MAY cause lease cancellation to occur at
that time and henceforth return NFS4ERR_EXPIRED when any of the stateids
associated with the freed locks is used. If lease cancellation has not
occurred and the server receives a lock or I/O request that conflicts with
one of the courtesy locks, the requirements are as follows:
In the case of a courtesy lock that is not a delegation,
it MUST free the courtesy lock and grant the new request.
In the case of a lock or an I/O request that conflicts with a
delegation that is being held as a courtesy lock, the server
MAY delay resolution of the request but MUST NOT reject the
request and MUST free the delegation and grant the new
request eventually.
In the case of a request for a delegation that conflicts with a
delegation that is being held as a courtesy lock, the server MAY
grant the new request or not as it chooses, but if it grants the
conflicting request, the delegation held as a courtesy lock
MUST be freed.
If the server does not reboot or cancel the lease before the network
partition is healed, when the original client tries to access a courtesy
lock that was freed, the server SHOULD send back an NFS4ERR_BAD_STATEID
to the client. If the client tries to access a courtesy lock that
was not freed, then the server SHOULD mark all of the courtesy locks as
implicitly being renewed.
As a result of lease expiration, leases may be canceled, either
immediately upon expiration or subsequently, depending on the occurrence
of a conflicting lock or extension of the period of partition beyond
what the server will tolerate.
When a lease is canceled, all locking state associated with it is
freed, and the use of any of the associated stateids will result in
NFS4ERR_EXPIRED being returned. Similarly, the use of the
associated clientid will result in NFS4ERR_EXPIRED being returned.
The client should recover from this situation by using SETCLIENTID
followed by SETCLIENTID_CONFIRM, in order to establish a new
clientid. Once a lock is obtained using this clientid, a lease
will be established.
There is no way for a client to predetermine how a given server
is going to behave during a network partition. When the
partition heals, the client still has either all of its locks,
some of its locks, or none of them. The client will be able to
examine the various error return values to determine its response.
All locks have been freed as a result of a lease cancellation
that occurred during the partition. The client should use a
SETCLIENTID to recover.
The current lock has been revoked before, during, or after
the partition. The client SHOULD handle this error
as it normally would.
The current lock has been revoked/released during the
partition, and the server did not reboot. Other locks
MAY still be renewed. The client need not do a
SETCLIENTID and instead SHOULD probe via a RENEW call.
The current lock has been revoked during the partition, and
the server rebooted. The server might have no information
on the other locks. They may still be renewable.
The client's locks have been revoked during the partition, and
the server rebooted. None of the client's locks will be
renewable.
The server has not rebooted. The client SHOULD handle
this error as it normally would.
When a network partition is combined with a server reboot, then
both the server and client have responsibilities to ensure that
the client does not reclaim a lock that it should no longer
be able to access. Briefly, those are:
Client's responsibility: A client MUST NOT attempt to
reclaim any locks that it did not hold at the end of
its most recent successfully established client lease.
Server's responsibility: A server MUST NOT allow a
client to reclaim a lock unless it knows that it could
not have since granted a conflicting lock. However, in
deciding whether a conflicting lock could have been
granted, it is permitted to assume that its clients are
responsible, as above.
A server may consider a client's lease "successfully
established" once it has received an OPEN operation from that
client.
The above are directed to CLAIM_PREVIOUS reclaims and not to
CLAIM_DELEGATE_PREV reclaims, which generally do not involve
a server reboot. However, when a server persistently stores
delegation information to support CLAIM_DELEGATE_PREV across
a period in which both client and server are down at the same
time, similar strictures apply.
The next sections give examples showing what can go wrong if
these responsibilities are neglected and also provide examples of
server implementation strategies that could meet a server's
responsibilities.
The first edge condition has the following scenario:
Client A acquires a lock.
Client A and the server experience mutual network partition,
such that client A is unable to renew its lease.
Client A's lease expires, so the server releases the lock.
Client B acquires a lock that would have conflicted with
that of client A.
Client B releases the lock.
The server reboots.
The network partition between client A and the server heals.
Client A issues a RENEW operation and gets back an
NFS4ERR_STALE_CLIENTID.
Client A reclaims its lock within the server's grace period.
Thus, at the final step, the server has erroneously granted
client A's lock reclaim. If client B modified the
object the lock was protecting, client A will experience
object corruption.
The second known edge condition follows:
Client A acquires a lock.
The server reboots.
Client A and the server experience mutual network partition,
such that client A is unable to reclaim its lock within
the grace period.
The server's reclaim grace period ends. Client A has no locks
recorded on the server.
Client B acquires a lock that would have conflicted with
that of client A.
Client B releases the lock.
The server reboots a second time.
The network partition between client A and the server heals.
Client A issues a RENEW operation and gets back an
NFS4ERR_STALE_CLIENTID.
Client A reclaims its lock within the server's grace period.
As with the first edge condition, the final step of the scenario
of the second edge condition has the server erroneously granting
client A's lock reclaim.
In both of the above examples, the client attempts reclaim
of a lock that it held at the end of its most recent
successfully established lease; thus, it has fulfilled its
responsibility.
The server, however, has failed, by granting a reclaim,
despite having granted a conflicting lock since the
reclaimed lock was last held.
Solving these edge conditions requires that the
server either (1) assume after it reboots that an edge condition
occurs, and thus return NFS4ERR_NO_GRACE for all reclaim
attempts, or (2) record some information in stable storage.
The amount
of information the server records in stable storage is in inverse
proportion to how harsh the server wants to be whenever the edge
conditions occur. The server that is completely tolerant of all
edge conditions will record in stable storage every lock that
is acquired, removing the lock record from stable storage only
when the lock is unlocked by the client and the lock's owner
advances the sequence number such that the lock release is not
the last stateful event for the owner's sequence. For the two
aforementioned edge conditions, the harshest a server can be, and
still support a grace period for reclaims, requires that the server
record in stable storage some minimal information.
For example, a server implementation could, for each client,
save in stable storage a record containing:
the client's id string.
a boolean that indicates if the client's lease expired or
if there was administrative intervention (see
) to revoke a byte-range lock,
share reservation, or delegation.
a timestamp that is updated the first time after a server boot
or reboot the client acquires byte-range locking, share reservation,
or delegation state on the server. The timestamp need not be
updated on subsequent lock requests until the server reboots.
The server implementation would also record in stable storage
the timestamps from the two most recent server reboots.
Assuming the above record keeping, for the first edge condition,
after the server reboots, the record that client A's lease expired
means that another client could have acquired a conflicting record
lock, share reservation, or delegation. Hence, the server must
reject a reclaim from client A with the error NFS4ERR_NO_GRACE or
NFS4ERR_RECLAIM_BAD.
For the second edge condition, after the server reboots for a
second time, the record that the client had an unexpired record
lock, share reservation, or delegation established before the
server's previous incarnation means that the server must reject
a reclaim from client A with the error NFS4ERR_NO_GRACE or
NFS4ERR_RECLAIM_BAD.
Regardless of the level and approach to record keeping, the server
MUST implement one of the following strategies (which apply to
reclaims of share reservations, byte-range locks, and delegations):
Reject all reclaims with NFS4ERR_NO_GRACE. This is
extremely harsh but is necessary if the server does not
want to record lock state in stable storage.
Record sufficient state in stable storage to meet its
responsibilities. In doubt, the server should err on
the side of being harsh.
In the event that, after a server reboot, the server
determines that there is unrecoverable damage or corruption
to stable storage, then for all clients and/or locks
affected, the server MUST return NFS4ERR_NO_GRACE.
A third edge condition affects the client and not the server.
If the server reboots in the middle of the client reclaiming
some locks and then a network partition is established, the
client might be in the situation of having reclaimed some, but
not all, locks. In that case, a conservative client would
assume that the non-reclaimed locks were revoked.
The third known edge condition follows:
Client A acquires a lock 1.
Client A acquires a lock 2.
The server reboots.
Client A issues a RENEW operation and gets back an
NFS4ERR_STALE_CLIENTID.
Client A reclaims its lock 1 within the server's grace period.
Client A and the server experience mutual network partition,
such that client A is unable to reclaim its remaining locks
within the grace period.
The server's reclaim grace period ends.
Client B acquires a lock that would have conflicted
with client A's lock 2.
Client B releases the lock.
The server reboots a second time.
The network partition between client A and the server heals.
Client A issues a RENEW operation and gets back an
NFS4ERR_STALE_CLIENTID.
Client A reclaims both lock 1 and lock 2 within the
server's grace period.
At the last step, the client reclaims lock 2 as if it had
held that lock continuously, when in fact a conflicting lock
was granted to client B.
This occurs because the client failed its responsibility, by
attempting to reclaim lock 2 even though it had not held
that lock at the end of the lease that was established by
the SETCLIENTID after the first server reboot. (The client
did hold lock 2 on a previous lease, but it is only the most
recent lease that matters.)
A server could avoid this situation by rejecting the reclaim
of lock 2. However, to do so accurately, it would have to
ensure that additional information about individual locks
held survives a reboot. Server implementations are not
required to do that, so the client must not assume that the
server will.
Instead, a client MUST reclaim only those locks that it
successfully acquired from the previous server instance, omitting
any that it failed to reclaim before a new reboot. Thus, in the
last step above, client A should reclaim only lock 1.
A mandate for the client's handling of the NFS4ERR_NO_GRACE
and NFS4ERR_RECLAIM_BAD errors is outside the scope of this
specification, since the strategies for such handling are
very dependent on the client's operating environment.
However, one potential approach is described below.
When the client's reclaim fails, it could examine
the change attribute of the objects the client is trying
to reclaim state for, and use that to determine whether
to re-establish the state via normal OPEN or LOCK requests.
This is acceptable, provided the client's operating environment
allows it. In other words, the client implementer is advised
to document the behavior for his users. The client could also
inform the application that its byte-range lock or share
reservations (whether they were delegated or not) have been
lost, such as via a UNIX signal, a GUI pop-up window, etc.
See for a discussion of
what the client should do for dealing with unreclaimed
delegations on client state.
For further discussion of revocation of locks,
see .
In the event a lock request times out, a client may decide to
not retry the request. The client may also abort the request
when the process for which it was issued is terminated (e.g.,
in UNIX due to a signal). It is possible, though, that the server
received the request and acted upon it. This would change the
state on the server without the client being aware of the change.
It is paramount that the client resynchronize state with the server
before it attempts any other operation that takes a seqid and/or
a stateid with the same state-owner. This is straightforward to
do without a special resynchronize operation.
Since the server maintains the last lock request and response
received on the state-owner, for each state-owner, the client should
cache the last lock request it sent such that the lock request did
not receive a response. From this, the next time the client does a
lock operation for the state-owner, it can send the cached request,
if there is one, and if the request was one that established state
(e.g., a LOCK or OPEN operation), the server will return the cached
result or, if it never saw the request, perform it. The client can
follow up with a request to remove the state (e.g., a LOCKU or
CLOSE operation). With this approach, the sequencing and stateid
information on the client and server for the given state-owner
will resynchronize, and in turn the lock state will resynchronize.
At any point, the server can revoke locks held by a client and the
client must be prepared for this event. When the client detects
that its locks have been or may have been revoked, the client is
responsible for validating the state information between itself
and the server. Validating locking state for the client means
that it must verify or reclaim state for each lock currently held.
The first instance of lock revocation is upon server reboot or
re&nbhy;initialization. In this instance, the client will receive an
error (NFS4ERR_STALE_STATEID or NFS4ERR_STALE_CLIENTID) and the
client will proceed with normal crash recovery as described in
the previous section.
The second lock revocation event is the inability to renew the
lease before expiration. While this is considered a rare or
unusual event, the client must be prepared to recover. Both the
server and client will be able to detect the failure to renew
the lease and are capable of recovering without data corruption.
For the server, it tracks the last renewal event serviced for
the client and knows when the lease will expire. Similarly, the
client must track operations that will renew the lease period.
Using the time that each such request was sent and the time that
the corresponding reply was received, the client should bound the
time that the corresponding renewal could have occurred on the
server and thus determine if it is possible that a lease period
expiration could have occurred.
The third lock revocation event can occur as a result of
administrative intervention within the lease period. While this
is considered a rare event, it is possible that the server's
administrator has decided to release or revoke a particular lock
held by the client. As a result of revocation, the client will
receive an error of NFS4ERR_ADMIN_REVOKED. In this instance, the
client may assume that only the state-owner's locks have been lost.
The client notifies the lock holder appropriately. The client
cannot assume that the lease period has been renewed as a result of
a failed operation.
When the client determines the lease period may have expired,
the client must mark all locks held for the associated lease
as "unvalidated". This means the client has been unable
to re-establish or confirm the appropriate lock state with the
server. As described in ,
there are scenarios in which the server may grant conflicting
locks after the lease period has expired for a client. When it
is possible that the lease period has expired, the client must
validate each lock currently held to ensure that a conflicting
lock has not been granted. The client may accomplish this task by
issuing an I/O request; if there is no relevant I/O pending,
a zero-length read specifying the stateid associated with the lock
in question can be synthesized to trigger the renewal.
If the response to the request is success, the client has validated
all of the locks governed by that stateid and re-established the
appropriate state between itself and the server.
If the I/O request is not successful, then one or more of the
locks associated with the stateid were revoked by the server, and
the client must notify the owner.
A share reservation is a mechanism to control access to a file.
It is a separate and independent mechanism from byte-range locking.
When a client opens a file, it issues an OPEN operation to the
server specifying the type of access required (READ, WRITE, or
BOTH) and the type of access to deny others (OPEN4_SHARE_DENY_NONE,
OPEN4_SHARE_DENY_READ, OPEN4_SHARE_DENY_WRITE, or
OPEN4_SHARE_DENY_BOTH). If the OPEN fails, the client will
fail the application's open request.
Pseudo-code definition of the semantics:
if (request.access == 0)
return (NFS4ERR_INVAL)
else if ((request.access & file_state.deny) ||
(request.deny & file_state.access))
return (NFS4ERR_DENIED)
This checking of share reservations on OPEN is done with no
exception for an existing OPEN for the same open-owner.
The constants used for the OPEN and OPEN_DOWNGRADE operations
for the access and deny fields are as follows:
const OPEN4_SHARE_ACCESS_READ = 0x00000001;
const OPEN4_SHARE_ACCESS_WRITE = 0x00000002;
const OPEN4_SHARE_ACCESS_BOTH = 0x00000003;
const OPEN4_SHARE_DENY_NONE = 0x00000000;
const OPEN4_SHARE_DENY_READ = 0x00000001;
const OPEN4_SHARE_DENY_WRITE = 0x00000002;
const OPEN4_SHARE_DENY_BOTH = 0x00000003;
To provide correct share semantics, a client MUST use the OPEN
operation to obtain the initial filehandle and indicate the
desired access and what access, if any, to deny. Even if the
client intends to use one of the special stateids
(anonymous stateid or READ bypass stateid), it must
still obtain the filehandle for the regular file with the OPEN
operation so the appropriate share semantics can be applied.
Clients that do not have a deny mode built into their programming
interfaces for opening a file should request a deny mode of
OPEN4_SHARE_DENY_NONE.
The OPEN operation with the CREATE flag also subsumes the CREATE
operation for regular files as used in previous versions of the NFS
protocol. This allows a create with a share to be done atomically.
The CLOSE operation removes all share reservations held by the
open-owner on that file. If byte-range locks are held, the client
SHOULD release all locks before issuing a CLOSE. The server MAY
free all outstanding locks on CLOSE, but some servers may not
support the CLOSE of a file that still has byte-range locks held.
The server MUST return failure, NFS4ERR_LOCKS_HELD, if any locks
would exist after the CLOSE.
The LOOKUP operation will return a filehandle without establishing
any lock state on the server. Without a valid stateid, the server
will assume that the client has the least access. For example, if
one client opened a file with OPEN4_SHARE_DENY_BOTH and another
client accesses the file via a filehandle obtained through LOOKUP,
the second client could only read the file using the special READ
bypass stateid. The second client could not WRITE the file at all
because it would not have a valid stateid from OPEN and the special
anonymous stateid would not be allowed access.
Since a CLOSE operation requests deallocation of a stateid, dealing
with retransmission of the CLOSE may pose special difficulties,
since the state information, which normally would be used to
determine the state of the open file being designated, might be
deallocated, resulting in an NFS4ERR_BAD_STATEID error.
Servers may deal with this problem in a number of ways. To provide
the greatest degree of assurance that the protocol is being used
properly, a server should, rather than deallocate the stateid,
mark it as close-pending, and retain the stateid with this status,
until later deallocation. In this way, a retransmitted CLOSE can
be recognized since the stateid points to state information with
this distinctive status, so that it can be handled without error.
When adopting this strategy, a server should retain the state
information until the earliest of:
Another validly sequenced request for the same open-owner,
that is not a retransmission.
The time that an open-owner is freed by the server due to period
with no activity.
All locks for the client are freed as a result of a SETCLIENTID.
Servers may avoid this complexity, at the cost of less complete
protocol error checking, by simply responding NFS4_OK in the event
of a CLOSE for a deallocated stateid, on the assumption that this
case must be caused by a retransmitted close. When adopting this
approach, it is desirable to at least log an error when returning
a no-error indication in this situation. If the server maintains
a reply-cache mechanism, it can verify that the CLOSE is indeed a
retransmission and avoid error logging in most cases.
When an OPEN is done for a file and the open-owner for which
the open is being done already has the file open, the result
is to upgrade the open file status maintained on the server to
include the access and deny bits specified by the new OPEN as
well as those for the existing OPEN. The result is that there
is one open file, as far as the protocol is concerned, and it
includes the union of the access and deny bits for all of the OPEN
requests completed. Only a single CLOSE will be done to reset
the effects of both OPENs. Note that the client, when issuing
the OPEN, may not know that the same file is in fact being opened.
The above only applies if both OPENs result in the OPENed object
being designated by the same filehandle.
When the server chooses to export multiple filehandles
corresponding to the same file object and returns different
filehandles on two different OPENs of the same file object,
the server MUST NOT "OR" together the access and deny bits and
coalesce the two open files. Instead, the server must maintain
separate OPENs with separate stateids and will require separate
CLOSEs to free them.
When multiple open files on the client are merged into a single
open file object on the server, the close of one of the open files
(on the client) may necessitate change of the access and deny
status of the open file on the server. This is because the union
of the access and deny bits for the remaining opens may be smaller
(i.e., a proper subset) than previously. The OPEN_DOWNGRADE
operation is used to make the necessary change, and the client
should use it to update the server so that share reservation
requests by other clients are handled properly. The stateid
returned has the same "other" field as that passed to the server.
The seqid value in the returned stateid MUST be incremented (),
even in situations in which there has been no change to the access and
deny bits for the file.
When determining the time period for the server lease, the
usual lease trade-offs apply. Short leases are good for fast
server recovery at a cost of increased RENEW or READ (with
zero length) requests. Longer leases are certainly kinder and
gentler to servers trying to handle very large numbers of clients.
The number of RENEW requests drops in proportion to the lease time.
The disadvantages of long leases are slower recovery after server
failure (the server must wait for the leases to expire and the
grace period to elapse before granting new lock requests) and
increased file contention (if the client fails to transmit an unlock
request, then the server must wait for lease expiration before
granting new locks).
Long leases are usable if the server is able to store lease state
in non-volatile memory. Upon recovery, the server can reconstruct
the lease state from its non-volatile memory and continue operation
with its clients, and therefore long leases would not be an issue.
To avoid the need for synchronized clocks, lease times are granted
by the server as a time delta. However, there is a requirement
that the client and server clocks do not drift excessively over
the duration of the lock. There is also the issue of propagation
delay across the network -- which could easily be several hundred
milliseconds -- as well as the possibility that requests will be
lost and need to be retransmitted.
To take propagation delay into account, the client should subtract
it from lease times (e.g., if the client estimates the one-way
propagation delay as 200 msec, then it can assume that the lease
is already 200 msec old when it gets it). In addition, it will
take another 200 msec to get a response back to the server.
So the client must send a lock renewal or write data back to the
server 400 msec before the lease would expire.
The server's lease period configuration should take into account
the network distance of the clients that will be accessing the
server's resources. It is expected that the lease period will
take into account the network propagation delays and other network
delay factors for the client population. Since the protocol does
not allow for an automatic method to determine an appropriate
lease period, the server's administrator may have to tune the
lease period.
When responsibility for handling a given file system is transferred
to a new server (migration) or the client chooses to use an
alternative server (e.g., in response to server unresponsiveness) in
the context of file system replication, the appropriate handling of
state shared between the client and server (i.e., locks, leases,
stateids, and client IDs) is as described below. The handling
differs between migration and replication. For a related discussion
of file server state and recovery of same, see the subsections of
.
In cases in which one server is expected to accept opaque values
from the client that originated from another server, the
servers SHOULD encode the opaque values in big-endian byte
order. If this is done, the new server will be able to
parse values like stateids, directory cookies, filehandles,
etc. even if their native byte order is different from that of
other servers cooperating in the replication and migration of the
file system.
In the case of migration, the servers involved in the migration
of a file system SHOULD transfer all server state from the
original server to the new server. This must be done in a way that
is transparent to the client. This state transfer will ease the
client's transition when a file system migration occurs. If the
servers are successful in transferring all state, the client
will continue to use stateids assigned by the original server.
Therefore, the new server must recognize these stateids as valid.
This holds true for the client ID as well. Since responsibility
for an entire file system is transferred with a migration event,
there is no possibility that conflicts will arise on the new
server as a result of the transfer of locks.
As part of the transfer of information between servers, leases
would be transferred as well. The leases being transferred to
the new server will typically have a different expiration time
from those for the same client, previously on the old server.
To maintain the property that all leases on a given server for a
given client expire at the same time, the server should advance
the expiration time to the later of the leases being transferred
or the leases already present. This allows the client to maintain
lease renewal of both classes without special effort.
The servers may choose not to transfer the state information
upon migration. However, this choice is discouraged. In this
case, when the client presents state information from the
original server (e.g., in a RENEW operation or a READ operation
of zero length), the client must be prepared to receive either
NFS4ERR_STALE_CLIENTID or NFS4ERR_STALE_STATEID from the new
server. The client should then recover its state information as
it normally would in response to a server failure. The new server
must take care to allow for the recovery of state information as
it would in the event of server restart.
A client SHOULD re-establish new callback information
with the new server as soon as possible, according to
sequences described in
Sections
and .
This ensures that server operations are not blocked by
the inability to recall delegations.
Since client switch-over in the case of replication is not
under server control, the handling of state is different.
In this case, leases, stateids, and client IDs do not have validity
across a transition from one server to another. The client must
re-establish its locks on the new server. This can be compared
to the re&nbhy;establishment of locks by means of reclaim-type
requests after a server reboot. The difference is that the
server has no provision to distinguish requests reclaiming locks
from those obtaining new locks or to defer the latter. Thus,
a client re&nbhy;establishing a lock on the new server (by means of
a LOCK or OPEN request), may have the requests denied due to a
conflicting lock. Since replication is intended for read-only
use of file systems, such denial of locks should not pose large
difficulties in practice. When an attempt to re&nbhy;establish a lock
on a new server is denied, the client should treat the situation
as if its original lock had been revoked.
In the case of lease renewal, the client may not be submitting
requests for a file system that has been migrated to another server.
This can occur because of the implicit lease renewal mechanism.
The client renews leases for all file systems when submitting a
request to any one file system at the server.
In order for the client to schedule renewal of leases that may
have been relocated to the new server, the client must find out
about lease relocation before those leases expire. To accomplish
this, all operations that implicitly renew leases for a client
(such as OPEN, CLOSE, READ, WRITE, RENEW, LOCK, and others)
will return the error NFS4ERR_LEASE_MOVED if responsibility for
any of the leases to be renewed has been transferred to a new
server. This condition will continue until the client receives
an NFS4ERR_MOVED error and the server receives the subsequent
GETATTR(fs_locations) for an access to each file system for which
a lease has been moved to a new server. By convention, the compound
including the GETATTR(fs_locations) SHOULD append a RENEW operation
to permit the server to identify the client doing the access.
Upon receiving the NFS4ERR_LEASE_MOVED error, a client that supports
file system migration MUST probe all file systems from that server on
which it holds open state. Once the client has successfully probed
all those file systems that are migrated, the server MUST resume normal
handling of stateful requests from that client.
In order to support legacy clients that do not handle the
NFS4ERR_LEASE_MOVED error correctly, the server SHOULD time out after a
wait of at least two lease periods, at which time it will resume normal
handling of stateful requests from all clients. If a client attempts to
access the migrated files, the server MUST reply with NFS4ERR_MOVED.
When the client receives an NFS4ERR_MOVED error,
the client can follow the normal process to obtain the new server
information (through the fs_locations attribute) and perform
renewal of those leases on the new server.
If the server has not had state transferred to it transparently,
the client will receive either NFS4ERR_STALE_CLIENTID or NFS4ERR_STALE_STATEID
from the new server, as described above. The client can then recover
state information as it does in the event of server failure.
In order that the client may appropriately manage its leases
in the case of migration, the destination server must establish
proper values for the lease_time attribute.
When state is transferred transparently, that state should include
the correct value of the lease_time attribute. The lease_time
attribute on the destination server must never be less than that
on the source since this would result in premature expiration of
leases granted by the source server. Upon migration, in which state
is transferred transparently, the client is under no obligation
to refetch the lease_time attribute and may continue to use
the value previously fetched (on the source server).
If state has not been transferred transparently (i.e., the client
sees a real or simulated server reboot), the client should fetch
the value of lease_time on the new (i.e., destination) server
and use it for subsequent locking requests. However, the server
must respect a grace period at least as long as the lease_time on
the source server, in order to ensure that clients have ample
time to reclaim their locks before potentially conflicting
non-reclaimed locks are granted. The means by which the new
server obtains the value of lease_time on the old server is left
to the server implementations. It is not specified by the
NFSv4 protocol.
Client-side caching of data, file attributes, and filenames is
essential to providing good performance with the NFS protocol.
Providing distributed cache coherence is a difficult problem,
and previous versions of the NFS protocol have not attempted it.
Instead, several NFS client implementation techniques have been used
to reduce the problems that a lack of coherence poses for users.
These techniques have not been clearly defined by earlier protocol
specifications, and it is often unclear what is valid or invalid
client behavior.
The NFSv4 protocol uses many techniques similar to those
that have been used in previous protocol versions. The NFSv4
protocol does not provide distributed cache coherence. However,
it defines a more limited set of caching guarantees to allow locks
and share reservations to be used without destructive interference
from client-side caching.
In addition, the NFSv4 protocol introduces a delegation
mechanism that allows many decisions normally made by the server
to be made locally by clients. This mechanism provides efficient
support of the common cases where sharing is infrequent or where
sharing is read-only.
Caching techniques used in previous versions of the NFS protocol have
been successful in providing good performance. However, several
scalability challenges can arise when those techniques are used
with very large numbers of clients. This is particularly true when
clients are geographically distributed, which classically increases
the latency for cache revalidation requests.
The previous versions of the NFS protocol repeat their file data
cache validation requests at the time the file is opened. This
behavior can have serious performance drawbacks. A common case is
one in which a file is only accessed by a single client. Therefore,
sharing is infrequent.
In this case, repeated reference to the server to find that no
conflicts exist is expensive. A better option with regards to
performance is to allow a client that repeatedly opens a file to do
so without reference to the server. This is done until potentially
conflicting operations from another client actually occur.
A similar situation arises in connection with file locking. Sending
file lock and unlock requests to the server as well as the READ and
WRITE requests necessary to make data caching consistent with the
locking semantics (see )
can severely limit performance. When locking
is used to provide protection against infrequent conflicts, a large
penalty is incurred. This penalty may discourage the use of file
locking by applications.
The NFSv4 protocol provides more aggressive caching
strategies with the following design goals:
Compatibility with a large range of server semantics.
Providing the same caching benefits as previous versions of the
NFS protocol when unable to provide the more aggressive model.
Organizing requirements for aggressive caching so that a large
portion of the benefit can be obtained even when not all of the
requirements can be met.
The appropriate requirements for the server are discussed in later
sections, in which specific forms of caching are covered (see
).
Recallable delegation of server responsibilities for a file to a
client improves performance by avoiding repeated requests to the
server in the absence of inter-client conflict. With the use of a
"callback" RPC from server to client, a server recalls delegated
responsibilities when another client engages in the sharing of a
delegated file.
A delegation is passed from the server to the client, specifying the
object of the delegation and the type of delegation. There are
different types of delegations, but each type contains a stateid to be
used to represent the delegation when performing operations that
depend on the delegation. This stateid is similar to those
associated with locks and share reservations but differs in that the
stateid for a delegation is associated with a client ID and may be used
on behalf of all the open-owners for the given client. A delegation
is made to the client as a whole and not to any specific process or
thread of control within it.
Because callback RPCs may not work in all environments (due to
firewalls, for example), correct protocol operation does not depend
on them. Preliminary testing of callback functionality by means of
a CB_NULL procedure determines whether callbacks can be supported.
The CB_NULL procedure checks the continuity of the callback path.
A server makes a preliminary assessment of callback availability to
a given client and avoids delegating responsibilities until it has
determined that callbacks are supported. Because the granting of
a delegation is always conditional upon the absence of conflicting
access, clients must not assume that a delegation will be granted,
and they must always be prepared for OPENs to be processed without
any delegations being granted.
Once granted, a delegation behaves in most ways like a lock. There
is an associated lease that is subject to renewal, together with all
of the other leases held by that client.
Unlike locks, an operation by a second client to a delegated file
will cause the server to recall a delegation through a callback.
On recall, the client holding the delegation must flush modified
state (such as modified data) to the server and return the
delegation. The conflicting request will not be acted on until
the recall is complete. The recall is considered complete when
the client returns the delegation or the server times out its wait
for the delegation to be returned and revokes the delegation as
a result of the timeout. In the interim, the server will either
delay responding to conflicting requests or respond to them with
NFS4ERR_DELAY. Following the resolution of the recall, the
server has the information necessary to grant or deny the second
client's request.
At the time the client receives a delegation recall, it may have
substantial state that needs to be flushed to the server. Therefore,
the server should allow sufficient time for the delegation to be
returned since it may involve numerous RPCs to the server. If the
server is able to determine that the client is diligently flushing
state to the server as a result of the recall, the server MAY extend
the usual time allowed for a recall. However, the time allowed for
recall completion should not be unbounded.
An example of this is when responsibility to mediate opens on a given
file is delegated to a client (see ).
The server will not know what opens are in effect on the client.
Without this knowledge, the server will be unable to determine if
the access and deny state for the file allows any particular open
until the delegation for the file has been returned.
A client failure or a network partition can result in failure to
respond to a recall callback. In this case, the server will revoke
the delegation; this in turn will render useless any modified state
still on the client.
Clients need to be aware that server implementers may enforce practical
limitations on the number of delegations issued. Further, as there is
no way to determine which delegations to revoke, the server is allowed
to revoke any. If the server is implemented to revoke another delegation
held by that client, then the client may be able to determine that
a limit has been reached because each new delegation request results
in a revoke. The client could then determine which delegations it may not
need and preemptively release them.
There are three situations that delegation recovery must deal with:
Client reboot or restart
Server reboot or restart (see )
Network partition (full or callback-only)
In the event that the client reboots or restarts, the confirmation of
a SETCLIENTID done with an nfs_client_id4 with a new verifier4 value
will result in the release of byte-range locks and share reservations.
Delegations, however, may be treated a bit differently.
There will be situations in which delegations will need to be
re&nbhy;established after a client reboots or restarts. The reason for
this is the client may have file data stored locally and this data
was associated with the previously held delegations. The client will
need to re&nbhy;establish the appropriate file state on the server.
To allow for this type of client recovery, the server MAY allow
delegations to be retained after other sorts of locks are released.
This implies that requests from other clients that conflict with these
delegations will need to wait. Because the normal recall process may
require significant time for the client to flush changed state to the
server, other clients need to be prepared for delays that occur because
of a conflicting delegation. In order to give clients a chance to get
through the reboot process -- during which leases will not be
renewed -- the server MAY extend the period for delegation
recovery beyond the typical lease expiration period. For open
delegations, such delegations that are not released are reclaimed
using OPEN with a claim type of CLAIM_DELEGATE_PREV. (See
Sections
and for discussions
of open delegation and the details of OPEN, respectively.)
A server MAY support a claim type of CLAIM_DELEGATE_PREV, but if it
does, it MUST NOT remove delegations upon SETCLIENTID_CONFIRM and
instead MUST make them available for client reclaim using
CLAIM_DELEGATE_PREV. The server MUST NOT remove the delegations until
either the client does a DELEGPURGE or one lease period has
elapsed from the time -- whichever is later -- of the
SETCLIENTID_CONFIRM or the last successful CLAIM_DELEGATE_PREV
reclaim.
Note that the requirement stated above is not meant to imply that,
when the server is no longer obliged, as required above, to retain
delegation information, it should necessarily dispose of it.
Some specific cases are:
When the period is terminated by the occurrence of DELEGPURGE,
deletion of unreclaimed delegations is appropriate and desirable.
When the period is terminated by a lease period elapsing without
a successful CLAIM_DELEGATE_PREV reclaim, and that situation
appears to be the result of a network partition (i.e., lease
expiration has occurred), a server's lease expiration approach,
possibly including the use of courtesy locks, would normally
provide for the retention of unreclaimed delegations. Even in
the event that lease cancellation occurs, such delegation should
be reclaimed using CLAIM_DELEGATE_PREV as part of network partition
recovery.
When the period of non-communicating is followed by a client
reboot, unreclaimed delegations should also be reclaimable by
use of CLAIM_DELEGATE_PREV as part of client reboot recovery.
When the period is terminated by a lease period elapsing without
a successful CLAIM_DELEGATE_PREV reclaim, and lease renewal
is occurring, the server may well conclude that unreclaimed
delegations have been abandoned and consider the situation as
one in which an implied DELEGPURGE should be assumed.
A server that supports a claim type of CLAIM_DELEGATE_PREV MUST support
the DELEGPURGE operation, and similarly, a server that supports
DELEGPURGE MUST support CLAIM_DELEGATE_PREV. A server that does
not support CLAIM_DELEGATE_PREV MUST return NFS4ERR_NOTSUPP if the
client attempts to use that feature or performs a DELEGPURGE operation.
Support for a claim type of CLAIM_DELEGATE_PREV is often referred to
as providing for "client-persistent delegations" in that they allow
the use of persistent storage on the client to store data written
by the client, even across a client restart. It should be noted
that, with the optional exception noted below, this feature
requires persistent storage to be used on the client and does not
add to persistent storage requirements on the server.
One good way to think about client-persistent delegations is that for
the most part, they function like "courtesy locks", with special
semantic adjustments to allow them to be retained across a client restart,
which cause all other sorts of locks to be freed. Such locks are generally
not retained across a server restart. The one exception is the
case of simultaneous failure of the client and server and is discussed
below.
When the server indicates support of CLAIM_DELEGATE_PREV (implicitly)
by returning NFS_OK to DELEGPURGE, a client with a write delegation
can use write-back caching for data to be written to the server, deferring
the write-back until such time as the delegation is recalled, possibly
after intervening client restarts. Similarly, when the server indicates
support of CLAIM_DELEGATE_PREV, a client with a read delegation and
an open-for-write subordinate to that delegation may be sure of the
integrity of its persistently cached copy of the file after a client
restart without specific verification of the change attribute.
When the server reboots or restarts, delegations are reclaimed (using
the OPEN operation with CLAIM_PREVIOUS) in a similar fashion to byte-range
locks and share reservations. However, there is a slight
semantic difference. In the normal case, if the server decides that a
delegation should not be granted, it performs the requested action
(e.g., OPEN) without granting any delegation. For reclaim, the
server grants the delegation, but a special designation is applied so
that the client treats the delegation as having been granted but
recalled by the server. Because of this, the client has the duty to
write all modified state to the server and then return the
delegation. This process of handling delegation reclaim reconciles
three principles of the NFSv4 protocol:
Upon reclaim, a client claiming resources assigned to it by an
earlier server instance must be granted those resources.
The server has unquestionable authority to determine whether
delegations are to be granted and, once granted, whether they are
to be continued.
The use of callbacks is not to be depended upon until the client
has proven its ability to receive them.
When a client has more than a single open associated with a
delegation, state for those additional opens can be established using
OPEN operations of type CLAIM_DELEGATE_CUR. When these are used to
establish opens associated with reclaimed delegations, the server
MUST allow them when made within the grace period.
Situations in which there is a series of client and server restarts where
there is no restart of both at the same time are dealt with via a
combination of CLAIM_DELEGATE_PREV and CLAIM_PREVIOUS reclaim cycles.
Persistent storage is needed only on the client. For each server
failure, a CLAIM_PREVIOUS reclaim cycle is done, while for each client
restart, a CLAIM_DELEGATE_PREV reclaim cycle is done.
To deal with the possibility of simultaneous failure of client and
server (e.g., a data center power outage), the server MAY
persistently store delegation information so that it can respond to
a CLAIM_DELEGATE_PREV reclaim request that it receives from a
restarting client. This is the one case in which persistent
delegation state can be retained across a server restart. A server
is not required to store this information, but if it does do so, it
should do so for write delegations and for read delegations, during
the pendency of which (across multiple client and/or server
instances), some open-for-write was done as part of delegation. When
the space to persistently record such information is limited, the
server should recall delegations in this class in preference to
keeping them active without persistent storage recording.
When a network partition occurs, delegations are subject to freeing
by the server when the lease renewal period expires. This is similar
to the behavior for locks and share reservations, and as for locks
and share reservations, it may be modified by support for "courtesy
locks" in which locks are not freed in the absence of a conflicting
lock request. Whereas for locks and share reservations the freeing of
locks will occur immediately upon the appearance of a conflicting
request, for delegations, the server MAY institute a period during
which conflicting requests are held off. Eventually, the occurrence
of a conflicting request from another client will cause revocation
of the delegation.
A loss of the callback path (e.g., by a later network configuration
change) will have a similar effect in that it can also result in
revocation of a delegation. A recall request will fail, and revocation
of the delegation will result.
A client normally finds out about revocation of a delegation when it
uses a stateid associated with a delegation and receives one of the
errors NFS4ERR_EXPIRED, NFS4ERR_BAD_STATEID, or NFS4ERR_ADMIN_REVOKED
(NFS4ERR_EXPIRED indicates that all lock state associated with the
client has been lost). It also may find out about delegation revocation
after a client reboot when it attempts to reclaim a delegation and
receives NFS4ERR_EXPIRED. Note that in the case of a revoked
OPEN_DELEGATE_WRITE delegation, there are issues because data may
have been modified by the client whose delegation is revoked and,
separately, by other clients. See for
a discussion of such issues. Note also that when delegations are
revoked, information about the revoked delegation will be written
by the server to stable storage (as described
in ). This is done
to deal with the case in which a server reboots after revoking a
delegation but before the client holding the revoked delegation is
notified about the revocation.
Note that when there is a loss of a delegation, due to a network
partition in which all locks associated with the lease are lost,
the client will also receive the error NFS4ERR_EXPIRED. This case
can be distinguished from other situations in which delegations
are revoked by seeing that the associated clientid becomes invalid
so that NFS4ERR_STALE_CLIENTID is returned when it is used.
When NFS4ERR_EXPIRED is returned, the server MAY retain information
about the delegations held by the client, deleting those that are
invalidated by a conflicting request. Retaining such information
will allow the client to recover all non-invalidated delegations
using the claim type CLAIM_DELEGATE_PREV, once the
SETCLIENTID_CONFIRM is done to recover. Attempted recovery of
a delegation that the client has no record of, typically because they
were invalidated by conflicting requests, will result in the error
NFS4ERR_BAD_RECLAIM. Once a reclaim is attempted for all delegations
that the client held, it SHOULD do a DELEGPURGE to allow any remaining
server delegation information to be freed.
When applications share access to a set of files, they need to be
implemented so as to take account of the possibility of conflicting
access by another application. This is true whether the applications
in question execute on different clients or reside on the same
client.
Share reservations and byte-range locks are the facilities the
NFSv4 protocol provides to allow applications to coordinate
access by providing mutual exclusion facilities. The NFSv4
protocol's data caching must be implemented such that it does
not invalidate the assumptions that those using these facilities
depend upon.
In order to avoid invalidating the sharing assumptions that
applications rely on, NFSv4 clients should not provide cached
data to applications or modify it on behalf of an application when
it would not be valid to obtain or modify that same data via a READ
or WRITE operation.
Furthermore, in the absence of open delegation (see ), two additional rules apply. Note
that these rules are obeyed in practice by many NFSv2 and
NFSv3 clients.
First, cached data present on a client must be revalidated after
doing an OPEN. Revalidating means that the client fetches the
change attribute from the server, compares it with the cached
change attribute, and, if different, declares the cached data (as
well as the cached attributes) as invalid. This is to ensure
that the data for the OPENed file is still correctly reflected
in the client's cache. This validation must be done at least
when the client's OPEN operation includes DENY=WRITE or BOTH,
thus terminating a period in which other clients may have had
the opportunity to open the file with WRITE access. Clients may
choose to do the revalidation more often (such as at OPENs specifying
DENY=NONE) to parallel the NFSv3 protocol's practice for
the benefit of users assuming this degree of cache revalidation.
Since the change attribute is updated for data and metadata
modifications, some client implementers may be tempted to use the
time_modify attribute and not the change attribute to validate cached data, so
that metadata changes do not spuriously invalidate clean data.
The implementer is cautioned against this approach. The change
attribute is guaranteed to change for each update to the file,
whereas time_modify is guaranteed to change only at the granularity
of the time_delta attribute. Use by the client's data cache
validation logic of time_modify and not the change attribute runs the risk of
the client incorrectly marking stale data as valid.
Second, modified data must be flushed to the server before closing
a file OPENed for write. This is complementary to the first rule.
If the data is not flushed at CLOSE, the revalidation done after
the client OPENs a file is unable to achieve its purpose. The other
aspect to flushing the data before close is that the data must
be committed to stable storage, at the server, before the CLOSE
operation is requested by the client. In the case of a server
reboot or restart and a CLOSEd file, it may not be possible
to retransmit the data to be written to the file -- hence, this
requirement.
For those applications that choose to use file locking instead of
share reservations to exclude inconsistent file access, there is an
analogous set of constraints that apply to client-side data caching.
These rules are effective only if the file locking is used in a way
that matches in an equivalent way the actual READ and WRITE
operations executed. This is as opposed to file locking that is
based on pure convention. For example, it is possible to manipulate
a two-megabyte file by dividing the file into two one-megabyte
regions and protecting access to the two regions by file locks on
bytes zero and one. A lock for write on byte zero of the file would
represent the right to do READ and WRITE operations on the first
region. A lock for write on byte one of the file would represent the
right to do READ and WRITE operations on the second region. As long
as all applications manipulating the file obey this convention, they
will work on a local file system. However, they may not work with
the NFSv4 protocol unless clients refrain from data caching.
The rules for data caching in the file locking environment are:
First, when a client obtains a file lock for a particular region,
the data cache corresponding to that region (if any cached data
exists) must be revalidated. If the change attribute indicates
that the file may have been updated since the cached data was
obtained, the client must flush or invalidate the cached data for
the newly locked region. A client might choose to invalidate all
of the non-modified cached data that it has for the file,
but the only requirement for correct operation is to invalidate
all of the data in the newly locked region.
Second, before releasing a write lock for a region, all modified
data for that region must be flushed to the server. The modified
data must also be written to stable storage.
Note that flushing data to the server and the invalidation of
cached data must reflect the actual byte ranges locked or unlocked.
Rounding these up or down to reflect client cache block boundaries
will cause problems if not carefully done. For example, writing a
modified block when only half of that block is within an area being
unlocked may cause invalid modification to the region outside the
unlocked area. This, in turn, may be part of a region locked by
another client. Clients can avoid this situation by synchronously
performing portions of WRITE operations that overlap that portion
(initial or final) that is not a full block. Similarly, invalidating
a locked area that is not an integral number of full buffer blocks
would require the client to read one or two partial blocks from the
server if the revalidation procedure shows that the data that the
client possesses may not be valid.
The data that is written to the server as a prerequisite to the
unlocking of a region must be written, at the server, to stable
storage. The client may accomplish this either with synchronous
writes or by following asynchronous writes with a COMMIT operation.
This is required because retransmission of the modified data after
a server reboot might conflict with a lock held by another client.
A client implementation may choose to accommodate applications that
use byte-range locking in non-standard ways (e.g., using a byte-range lock as
a global semaphore) by flushing to the server more data upon a LOCKU
than is covered by the locked range. This may include modified data
within files other than the one for which the unlocks are being done.
In such cases, the client must not interfere with applications whose
READs and WRITEs are being done only within the bounds of record
locks that the application holds. For example, an application locks
a single byte of a file and proceeds to write that single byte. A
client that chose to handle a LOCKU by flushing all modified data to
the server could validly write that single byte in response to an
unrelated unlock. However, it would not be valid to write the entire
block in which that single written byte was located since it includes
an area that is not locked and might be locked by another client.
Client implementations can avoid this problem by dividing files
with modified data into those for which all modifications are done
to areas covered by an appropriate byte-range lock and those for which
there are modifications not covered by a byte-range lock. Any writes
done for the former class of files must not include areas not locked
and thus not modified on the client.
Client-side data caching needs to respect mandatory file locking when
it is in effect. The presence of mandatory file locking for a given
file is indicated when the client gets back NFS4ERR_LOCKED from a
READ or WRITE on a file it has an appropriate share reservation for.
When mandatory locking is in effect for a file, the client must check
for an appropriate file lock for data being read or written. If a
lock exists for the range being read or written, the client may
satisfy the request using the client's validated cache. If an
appropriate file lock is not held for the range of the READ or WRITE,
the READ or WRITE request must not be satisfied by the client's
cache and the request must be sent to the server for processing.
When a READ or WRITE request partially overlaps a locked region, the
request should be subdivided into multiple pieces with each region
(locked or not) treated appropriately.
When clients cache data, the file data needs to be organized
according to the file system object to which the data belongs. For
NFSv3 clients, the typical practice has been to assume for
the purpose of caching that distinct filehandles represent distinct
file system objects. The client then has the choice to organize and
maintain the data cache on this basis.
In the NFSv4 protocol, there is now the possibility of having
significant deviations from a "one filehandle per object"
model, because a filehandle may be constructed on the basis of the
object's pathname. Therefore, clients need a reliable method to
determine if two filehandles designate the same file system object.
If clients were simply to assume that all distinct filehandles
denote distinct objects and proceed to do data caching on this basis,
caching inconsistencies would arise between the distinct client-side
objects that mapped to the same server-side object.
By providing a method to differentiate filehandles, the NFSv4
protocol alleviates a potential functional regression in comparison
with the NFSv3 protocol. Without this method, caching
inconsistencies within the same client could occur, and this has not
been present in previous versions of the NFS protocol. Note that it
is possible to have such inconsistencies with applications executing
on multiple clients, but that is not the issue being addressed here.
For the purposes of data caching, the following steps allow an NFSv4
client to determine whether two distinct filehandles denote
the same server-side object:
If GETATTR directed to two filehandles returns different values of
the fsid attribute, then the filehandles represent distinct
objects.
If GETATTR for any file with an fsid that matches the fsid of the
two filehandles in question returns a unique_handles attribute
with a value of TRUE, then the two objects are distinct.
If GETATTR directed to the two filehandles does not return the
fileid attribute for both of the handles, then it cannot be
determined whether the two objects are the same. Therefore,
operations that depend on that knowledge (e.g., client-side data
caching) cannot be done reliably. Note that if GETATTR does not
return the fileid attribute for both filehandles, it will return
it for neither of the filehandles, since the fsid for both
filehandles is the same.
If GETATTR directed to the two filehandles returns different
values for the fileid attribute, then they are distinct objects.
Otherwise, they are the same object.
When a file is being OPENed, the server may delegate further handling
of opens and closes for that file to the opening client. Any such
delegation is recallable, since the circumstances that allowed for
the delegation are subject to change. In particular, the server may
receive a conflicting OPEN from another client; the server must recall
the delegation before deciding whether the OPEN from the other client
may be granted. Making a delegation is up to the server, and clients
should not assume that any particular OPEN either will or will not
result in an open delegation. The following is a typical set of
conditions that servers might use in deciding whether OPEN should
be delegated:
The client must be able to respond to the server's callback
requests. The server will use the CB_NULL procedure for a test
of callback ability.
The client must have responded properly to previous recalls.
There must be no current open conflicting with the requested
delegation.
There should be no current delegation that conflicts with the
delegation being requested.
The probability of future conflicting open requests should be low,
based on the recent history of the file.
The existence of any server-specific semantics of OPEN/CLOSE that
would make the required handling incompatible with the prescribed
handling that the delegated client would apply (see below).
There are two types of open delegations: OPEN_DELEGATE_READ and
OPEN_DELEGATE_WRITE. An OPEN_DELEGATE_READ delegation allows a
client to handle, on its own, requests to
open a file for reading that do not deny read access to others. It MUST,
however, continue to send all requests to open a file for writing to the
server. Multiple OPEN_DELEGATE_READ delegations may be outstanding
simultaneously and do not conflict. An OPEN_DELEGATE_WRITE
delegation allows the client to handle, on its own, all opens. Only
one OPEN_DELEGATE_WRITE delegation may exist for a given file at a
given time, and it is inconsistent with any OPEN_DELEGATE_READ
delegations.
When a single client holds an OPEN_DELEGATE_READ delegation, it is
assured that no other client may modify the contents or attributes
of the file. If more than one client holds an OPEN_DELEGATE_READ
delegation, then the contents and attributes of that file are not
allowed to change. When a client has an OPEN_DELEGATE_WRITE delegation,
it may modify the file data since no other client will be accessing
the file's data. The client holding an OPEN_DELEGATE_WRITE delegation
may only affect file attributes that are intimately connected with
the file data: size, time_modify, and change.
When a client has an open delegation, it does not send OPENs or
CLOSEs to the server but updates the appropriate status internally.
For an OPEN_DELEGATE_READ delegation, opens that cannot be handled locally
(opens for write or that deny read access) must be sent to the
server.
When an open delegation is made, the response to the OPEN contains an
open delegation structure that specifies the following:
the type of delegation (read or write)
space limitation information to control flushing of data on close
(OPEN_DELEGATE_WRITE delegation only;
see )
an nfsace4 specifying read and write permissions
a stateid to represent the delegation for READ and WRITE
The delegation stateid is separate and distinct from the stateid for
the OPEN proper. The standard stateid, unlike the delegation
stateid, is associated with a particular open-owner and will continue
to be valid after the delegation is recalled and the file remains
open.
When a request internal to the client is made to open a file and open
delegation is in effect, it will be accepted or rejected solely on
the basis of the following conditions. Any requirement for other
checks to be made by the delegate should result in open delegation
being denied so that the checks can be made by the server itself.
The access and deny bits for the request and the file, as described
in .
The read and write permissions, as determined below.
The nfsace4 passed with delegation can be used to avoid frequent
ACCESS calls. The permission check should be as follows:
If the nfsace4 indicates that the open may be done, then it should
be granted without reference to the server.
If the nfsace4 indicates that the open may not be done, then an
ACCESS request must be sent to the server to obtain the definitive
answer.
The server may return an nfsace4 that is more restrictive than the
actual ACL of the file. This includes an nfsace4 that specifies
denial of all access. Note that some common practices, such as
mapping the traditional user "root" to the user "nobody", may make
it incorrect to return the actual ACL of the file in the delegation
response.
The use of delegation, together with various other forms of caching,
creates the possibility that no server authentication will ever be
performed for a given user since all of the user's requests might
be satisfied locally. Where the client is depending on the server
for authentication, the client should be sure authentication occurs
for each user by use of the ACCESS operation. This should be the
case even if an ACCESS operation would not be required otherwise.
As mentioned before, the server may enforce frequent authentication
by returning an nfsace4 denying all access with every open delegation.
OPEN delegation allows much of the message overhead associated with
the opening and closing files to be eliminated. An open when an open
delegation is in effect does not require that a validation message be
sent to the server unless there exists a potential for conflict with the
requested share mode. The continued endurance of the "OPEN_DELEGATE_READ
delegation" provides a guarantee that no OPEN for write and thus no
write has occurred that did not originate from this client.
Similarly, when closing a file opened for write
and if OPEN_DELEGATE_WRITE delegation is in effect, the data written does
not have to be flushed to the server until the open delegation is
recalled. The continued endurance of the open delegation provides
a guarantee that no open and thus no read or write has been done by
another client.
For the purposes of open delegation, READs and WRITEs done
without an OPEN (anonymous and READ bypass stateids) are
treated as the functional equivalents of a corresponding
type of OPEN. READs and WRITEs done with an anonymous
stateid done by another client will force the server to
recall an OPEN_DELEGATE_WRITE delegation. A WRITE with an
anonymous stateid done by another client will force a recall
of OPEN_DELEGATE_READ delegations. The handling of a READ bypass
stateid is identical, except that a READ done with a READ bypass
stateid will not force a recall of an OPEN_DELEGATE_READ delegation.
With delegations, a client is able to avoid writing data to the
server when the CLOSE of a file is serviced. The file close system
call is the usual point at which the client is notified of a lack of
stable storage for the modified file data generated by the
application. At the close, file data is written to the server, and
through normal accounting the server is able to determine if the
available file system space for the data has been exceeded (i.e.,
the server returns NFS4ERR_NOSPC or NFS4ERR_DQUOT). This accounting
includes quotas. The introduction of delegations requires that an
alternative method be in place for the same type of communication
to occur between client and server.
In the delegation response, the server provides either the limit of
the size of the file or the number of modified blocks and associated
block size. The server must ensure that the client will be able to
flush to the server data of a size equal to that provided in the
original delegation. The server must make this assurance for all
outstanding delegations. Therefore, the server must be careful in
its management of available space for new or modified data, taking
into account available file system space and any applicable quotas.
The server can recall delegations as a result of managing the
available file system space. The client should abide by the server's
state space limits for delegations. If the client exceeds the stated
limits for the delegation, the server's behavior is undefined.
Based on server conditions, quotas, or available file system space, the
server may grant OPEN_DELEGATE_WRITE delegations with very
restrictive space limitations. The limitations may be defined
in a way that will always force modified data to be flushed to the
server on close.
With respect to authentication, flushing modified data to the server
after a CLOSE has occurred may be problematic. For example, the user
of the application may have logged off the client, and unexpired
authentication credentials may not be present. In this case, the
client may need to take special care to ensure that local unexpired
credentials will in fact be available. One way that this may be
accomplished is by tracking the expiration time of credentials and
flushing data well in advance of their expiration.
When a client holds an OPEN_DELEGATE_WRITE delegation, lock operations may be
performed locally. This includes those required for mandatory file
locking. This can be done since the delegation implies that there can
be no conflicting locks. Similarly, all of the revalidations that
would normally be associated with obtaining locks and the flushing
of data associated with the releasing of locks need not be done.
When a client holds an OPEN_DELEGATE_READ delegation, lock operations are not
performed locally. All lock operations, including those requesting
non-exclusive locks, are sent to the server for resolution.
The server needs to employ special handling for a GETATTR where the
target is a file that has an OPEN_DELEGATE_WRITE delegation in effect. The
reason for this is that the client holding the OPEN_DELEGATE_WRITE delegation may
have modified the data, and the server needs to reflect this change to
the second client that submitted the GETATTR. Therefore, the client
holding the OPEN_DELEGATE_WRITE delegation needs to be interrogated. The server
will use the CB_GETATTR operation. The only attributes that the
server can reliably query via CB_GETATTR are size and change.
Since CB_GETATTR is being used to satisfy another client's GETATTR
request, the server only needs to know if the client holding the
delegation has a modified version of the file. If the client's copy
of the delegated file is not modified (data or size), the server can
satisfy the second client's GETATTR request from the attributes stored
locally at the server. If the file is modified, the server only needs
to know about this modified state. If the server determines that the
file is currently modified, it will respond to the second client's
GETATTR as if the file had been modified locally at the server.
Since the form of the change attribute is determined by the server and
is opaque to the client, the client and server need to agree on a
method of communicating the modified state of the file. For the size
attribute, the client will report its current view of the file size.
For the change attribute, the handling is more involved.
For the client, the following steps will be taken when receiving an
OPEN_DELEGATE_WRITE delegation:
The value of the change attribute will be obtained from the server and
cached. Let this value be represented by c.
The client will create a value greater than c that will be used for
communicating that modified data is held at the client. Let
this value be represented by d.
When the client is queried via CB_GETATTR for the change attribute, it
checks to see if it holds modified data. If the file is modified, the
value d is returned for the change attribute value. If this file is
not currently modified, the client returns the value c for the change
attribute.
For simplicity of implementation, the client MAY for each CB_GETATTR
return the same value d. This is true even if, between successive
CB_GETATTR operations, the client again modifies in the file's data or
metadata in its cache. The client can return the same value because
the only requirement is that the client be able to indicate to the
server that the client holds modified data. Therefore, the value of d
may always be c + 1.
While the change attribute is opaque to the client in the sense that
it has no idea what units of time, if any, the server is counting
change with, it is not opaque in that the client has to treat it as an
unsigned integer, and the server has to be able to see the results of
the client's changes to that integer. Therefore, the server MUST
encode the change attribute in network byte order when sending it
to the client. The client MUST decode it from network byte order
to its native order when receiving it, and the client MUST encode
it in network byte order when sending it to the server. For
this reason, the change attribute is defined as an unsigned integer
rather than an opaque array of bytes.
For the server, the following steps will be taken when providing an
OPEN_DELEGATE_WRITE delegation:
Upon providing an OPEN_DELEGATE_WRITE delegation, the server will cache a copy of the
change attribute in the data structure it uses to record the
delegation. Let this value be represented by sc.
When a second client sends a GETATTR operation on the same file to the
server, the server obtains the change attribute from the first client.
Let this value be cc.
If the value cc is equal to sc, the file is not modified and the
server returns the current values for change, time_metadata, and
time_modify (for example) to the second client.
If the value cc is NOT equal to sc, the file is currently modified at
the first client and most likely will be modified at the server at a
future time. The server then uses its current time to construct
attribute values for time_metadata and time_modify. A new value of
sc, which we will call nsc, is computed by the server, such that nsc
>= sc + 1. The server then returns the constructed time_metadata,
time_modify, and nsc values to the requester. The server replaces sc
in the delegation record with nsc. To prevent the possibility of
time_modify, time_metadata, and change from appearing to go backward
(which would happen if the client holding the delegation fails to
write its modified data to the server before the delegation is revoked
or returned), the server SHOULD update the file's metadata record with
the constructed attribute values. For reasons of reasonable
performance, committing the constructed attribute values to stable
storage is OPTIONAL.
As discussed earlier in this section, the client MAY return the same
cc value on subsequent CB_GETATTR calls, even if the file was modified
in the client's cache yet again between successive CB_GETATTR calls.
Therefore, the server must assume that the file has been modified yet
again and MUST take care to ensure that the new nsc it constructs and
returns is greater than the previous nsc it returned. An example
implementation's delegation record would satisfy this mandate by
including a boolean field (let us call it "modified") that is set to
FALSE when the delegation is granted, and an sc value set at the time
of grant to the change attribute value. The modified field would be
set to TRUE the first time cc != sc and would stay TRUE until the
delegation is returned or revoked. The processing for constructing
nsc, time_modify, and time_metadata would use this pseudo-code:
if (!modified) {
do CB_GETATTR for change and size;
if (cc != sc)
modified = TRUE;
} else {
do CB_GETATTR for size;
}
if (modified) {
sc = sc + 1;
time_modify = time_metadata = current_time;
update sc, time_modify, time_metadata into file's metadata;
}
This would return to the client (that sent GETATTR) the
attributes it requested but would make sure that size comes from
what CB_GETATTR returned. The server would not update the file's
metadata with the client's modified size.
In the case that the file attribute size is different than the
server's current value, the server treats this as a modification
regardless of the value of the change attribute retrieved via
CB_GETATTR and responds to the second client as in the last step.
This methodology resolves issues of clock differences between client
and server and other scenarios where the use of CB_GETATTR breaks down.
It should be noted that the server is under no obligation to use
CB_GETATTR; therefore, the server MAY simply recall the delegation
to avoid its use.
The following events necessitate the recall of an open delegation:
Potentially conflicting OPEN request (or READ/WRITE done with
"special" stateid)
SETATTR issued by another client
REMOVE request for the file
RENAME request for the file as either source or target of the
RENAME
Whether a RENAME of a directory in the path leading to the file
results in the recall of an open delegation depends on the semantics of
the server file system. If that file system denies such RENAMEs when
a file is open, the recall must be performed to determine whether
the file in question is, in fact, open.
In addition to the situations above, the server may choose to
recall open delegations at any time if resource constraints make
it advisable to do so. Clients should always be prepared for the
possibility of a recall.
When a client receives a recall for an open delegation, it needs
to update state on the server before returning the delegation.
These same updates must be done whenever a client chooses to return
a delegation voluntarily. The following items of state need to be
dealt with:
If the file associated with the delegation is no longer open and
no previous CLOSE operation has been sent to the server, a CLOSE
operation must be sent to the server.
If a file has other open references at the client, then OPEN
operations must be sent to the server. The appropriate stateids
will be provided by the server for subsequent use by the client
since the delegation stateid will not longer be valid. These OPEN
requests are done with the claim type of CLAIM_DELEGATE_CUR. This
will allow the presentation of the delegation stateid so that the
client can establish the appropriate rights to perform the OPEN.
(See for details.)
If there are granted file locks, the corresponding LOCK operations
need to be performed. This applies to the OPEN_DELEGATE_WRITE delegation
case only.
For an OPEN_DELEGATE_WRITE delegation, if at the time of
the recall the file is not open for write, all modified
data for the file must be flushed to the server. If the
delegation had not existed, the client would have done
this data flush before the CLOSE operation.
For an OPEN_DELEGATE_WRITE delegation, when a file is
still open at the time of the recall, any modified data
for the file needs to be flushed to the server.
With the OPEN_DELEGATE_WRITE delegation in place, it is possible that the
file was truncated during the duration of the delegation. For
example, the truncation could have occurred as a result of an
OPEN UNCHECKED4 with a size attribute value of zero. Therefore,
if a truncation of the file has occurred and this operation has
not been propagated to the server, the truncation must occur
before any modified data is written to the server.
In the case of an OPEN_DELEGATE_WRITE delegation, file
locking imposes some additional requirements. To precisely
maintain the associated invariant, it is required to flush
any modified data in any region for which a write lock was
released while the OPEN_DELEGATE_WRITE delegation was in
effect. However, because the OPEN_DELEGATE_WRITE delegation
implies no other locking by other clients, a simpler
implementation is to flush all modified data for the file
(as described just above) if any write lock has been released
while the OPEN_DELEGATE_WRITE delegation was in effect.
An implementation need not wait until delegation recall (or deciding
to voluntarily return a delegation) to perform any of the above
actions, if implementation considerations (e.g., resource availability
constraints) make that desirable. Generally, however, the fact that
the actual open state of the file may continue to change makes it not
worthwhile to send information about opens and closes to the server,
except as part of delegation return. Only in the case of closing the
open that resulted in obtaining the delegation would clients be likely
to do this early, since, in that case, the close once done will not
be undone. Regardless of the client's choices on scheduling these
actions, all must be performed before the delegation is returned,
including (when applicable) the close that corresponds to the open
that resulted in the delegation. These actions can be performed
either in previous requests or in previous operations in the same
COMPOUND request.
The server informs the client of a recall via a CB_RECALL. A race
case that may develop is when the delegation is immediately
recalled before the COMPOUND that established the delegation
is returned to the client. As the CB_RECALL provides both a
stateid and a filehandle for which the client has no mapping,
it cannot honor the recall attempt. At this point, the client has two
choices: either do not respond or respond with NFS4ERR_BADHANDLE.
If it does not respond, then it runs the risk of the server
deciding to not grant it further delegations.
If instead it does reply with NFS4ERR_BADHANDLE, then both the
client and the server might be able to detect that a race condition
is occurring. The client can keep a list of pending delegations.
When it receives a CB_RECALL for an unknown delegation, it can cache
the stateid and filehandle on a list of pending recalls. When it
is provided with a delegation, it would only use it if it was not
on the pending recall list. Upon the next CB_RECALL, it could
immediately return the delegation.
In turn, the server can keep track of when it issues a delegation
and assume that if a client responds to the CB_RECALL with an
NFS4ERR_BADHANDLE, then the client has yet to receive the
delegation. The server SHOULD give the client a reasonable time
both to get this delegation and to return it before revoking the
delegation. Unlike a failed callback path, the server should
periodically probe the client with CB_RECALL to see if it has
received the delegation and is ready to return it.
When the server finally determines that enough time has elapsed,
it SHOULD revoke the delegation and it SHOULD NOT revoke the lease.
During this extended recall process, the server SHOULD be
renewing the client lease. The intent here is that the client
not pay too onerous a burden for a condition caused by the server.
A client may fail to respond to a recall for various reasons, such as
a failure of the callback path from the server to the client.
The client may be unaware of a failure in the callback path.
This lack of awareness could result in the client finding out
long after the failure that its delegation has been revoked, and
another client has modified the data for which the client had
a delegation. This is especially a problem for the client that
held an OPEN_DELEGATE_WRITE delegation.
The server also has a dilemma in that the client that fails to
respond to the recall might also be sending other NFS requests,
including those that renew the lease before the lease expires.
Without returning an error for those lease-renewing operations,
the server leads the client to believe that the delegation it has
is in force.
This difficulty is solved by the following rules:
When the callback path is down, the server MUST NOT revoke the
delegation if one of the following occurs:
The client has issued a RENEW operation, and the server has
returned an NFS4ERR_CB_PATH_DOWN error. The server MUST renew
the lease for any byte-range locks and share reservations the
client has that the server has known about (as opposed to
those locks and share reservations the client has established
but not yet sent to the server, due to the delegation).
The server SHOULD give the client a reasonable time to return
its delegations to the server before revoking the client's
delegations.
The client has not issued a RENEW operation for some period of
time after the server attempted to recall the delegation.
This period of time MUST NOT be less than the value of the
lease_time attribute.
When the client holds a delegation, it cannot rely on operations,
except for RENEW, that take a stateid, to renew delegation leases
across callback path failures. The client that wants to keep
delegations in force across callback path failures must use RENEW
to do so.
At the point a delegation is revoked, if there are associated opens
on the client, the applications holding these opens need to be
notified. This notification usually occurs by returning errors for
READ/WRITE operations or when a close is attempted for the open file.
If no opens exist for the file at the point the delegation is
revoked, then notification of the revocation is unnecessary.
However, if there is modified data present at the client for
the file, the user of the application should be notified.
Unfortunately, it may not be possible to notify the user
since active applications may not be present at the client.
See for additional details.
When locks and delegations are revoked, the assumptions upon which
successful caching depend are no longer guaranteed. For any locks or
share reservations that have been revoked, the corresponding owner
needs to be notified. This notification includes applications with a
file open that has a corresponding delegation that has been revoked.
Cached data associated with the revocation must be removed from the
client. In the case of modified data existing in the client's cache,
that data must be removed from the client without it being written to
the server. As mentioned, the assumptions made by the client are no
longer valid at the point when a lock or delegation has been revoked.
For example, another client may have been granted a conflicting lock
after the revocation of the lock at the first client. Therefore, the
data within the lock range may have been modified by the other client.
Obviously, the first client is unable to guarantee to the application
what has occurred to the file in the case of revocation.
Notification to a lock-owner will in many cases consist of simply
returning an error on the next and all subsequent READs/WRITEs to the
open file or on the close. Where the methods available to a client
make such notification impossible because errors for certain
operations may not be returned, more drastic action, such as signals
or process termination, may be appropriate. The justification for
this is that an invariant on which an application depends may
be violated. Depending on how errors are typically treated for the
client operating environment, further levels of notification, including
logging, console messages, and GUI pop-ups, may be appropriate.
Revocation recovery for an OPEN_DELEGATE_WRITE delegation poses the
special issue of modified data in the client cache while the file is
not open. In this situation, any client that does not flush modified
data to the server on each close must ensure that the user receives
appropriate notification of the failure as a result of the revocation.
Since such situations may require human action to correct problems,
notification schemes in which the appropriate user or administrator
is notified may be necessary. Logging and console messages are
typical examples.
If there is modified data on the client, it must not be flushed
normally to the server. A client may attempt to provide a copy of
the file data as modified during the delegation under a different
name in the file system namespace to ease recovery. Note that when
the client can determine that the file has not been modified by any
other client, or when the client has a complete cached copy of the file
in question, such a saved copy of the client's view of the file
may be of particular value for recovery. In other cases, recovery
using a copy of the file, based partially on the client's cached
data and partially on the server copy as modified by other clients,
will be anything but straightforward, so clients may avoid saving
file contents in these situations or mark the results specially to
warn users of possible problems.
The saving of such modified data in delegation revocation situations
may be limited to files of a certain size or might be used only when
sufficient disk space is available within the target file system.
Such saving may also be restricted to situations when the client
has sufficient buffering resources to keep the cached copy available
until it is properly stored to the target file system.
The attributes discussed in this section do not include named
attributes. Individual named attributes are analogous to files, and
caching of the data for these needs to be handled just as data
caching is for regular files. Similarly, LOOKUP results from an
OPENATTR directory are to be cached on the same basis as any other
pathnames and similarly for directory contents.
Clients may cache file attributes obtained from the server and use
them to avoid subsequent GETATTR requests. This cache is
write through caching in that any modifications to the file
attributes are always done by means of requests to the server,
which means the modifications should not be done locally and should
not be cached. Exceptions to this are modifications to attributes
that are intimately connected with data caching. Therefore, extending
a file by writing data to the local data cache is reflected
immediately in the size as seen on the client without this change
being immediately reflected on the server. Normally, such changes are
not propagated directly to the server, but when the modified data is
flushed to the server, analogous attribute changes are made on the
server. When open delegation is in effect, the modified attributes
may be returned to the server in the response to a CB_GETATTR call.
The result of local caching of attributes is that the attribute
caches maintained on individual clients will not be coherent.
Changes made in one order on the server may be seen in a different
order on one client and in a third order on a different client.
The typical file system application programming interfaces do not
provide means to atomically modify or interrogate attributes for
multiple files at the same time. The following rules provide an
environment where the potential incoherency mentioned above can be
reasonably managed. These rules are derived from the practice of
previous NFS protocols.
All attributes for a given file (per-fsid attributes excepted) are
cached as a unit at the client so that no non-serializability
can arise within the context of a single file.
An upper time boundary is maintained on how long a client cache
entry can be kept without being refreshed from the server.
When operations are performed that modify attributes at the
server, the updated attribute set is requested as part of the
containing RPC. This includes directory operations that update
attributes indirectly. This is accomplished by following the
modifying operation with a GETATTR operation and then using the
results of the GETATTR to update the client's cached attributes.
Note that if the full set of attributes to be cached is requested by
READDIR, the results can be cached by the client on the same basis
as attributes obtained via GETATTR.
A client may validate its cached version of attributes for a file by
only fetching both the change and time_access attributes and assuming
that if the change attribute has the same value as it did when the
attributes were cached, then no attributes other than time_access
have changed. The time_access attribute is also fetched because
many servers operate in environments where the operation
that updates change does not update time_access. For example, POSIX
file semantics do not update access time when a file is modified by
the write system call. Therefore, the client that wants a current
time_access value should fetch it with change during the attribute
cache validation processing and update its cached time_access.
The client may maintain a cache of modified attributes for those
attributes intimately connected with data of modified regular files
(size, time_modify, and change). Other than those three attributes,
the client MUST NOT maintain a cache of modified attributes.
Instead, attribute changes are immediately sent to the server.
In some operating environments, the equivalent to time_access is
expected to be implicitly updated by each read of the content of the
file object. If an NFS client is caching the content of a file
object, whether it is a regular file, directory, or symbolic link,
the client SHOULD NOT update the time_access attribute (via SETATTR
or a small READ or READDIR request) on the server with each read that
is satisfied from cache. The reason is that this can defeat the
performance benefits of caching content, especially since an explicit
SETATTR of time_access may alter the change attribute on the server.
If the change attribute changes, clients that are caching the content
will think the content has changed and will re-read unmodified data
from the server. Nor is the client encouraged to maintain a modified
version of time_access in its cache, since this would mean that the
client either will eventually have to write the access time to the
server with bad performance effects or would never update the
server's time_access, thereby resulting in a situation where an
application that caches access time between a close and open of the
same file observes the access time oscillating between the past and
present. The time_access attribute always means the time of last
access to a file by a READ that was satisfied by the server.
This way, clients will tend to see only time_access changes that
go forward in time.
Some operating environments include the capability for an application
to map a file's content into the application's address space. Each
time the application accesses a memory location that corresponds to a
block that has not been loaded into the address space, a page
fault occurs and the file is read (or if the block does not exist
in the file, the block is allocated and then instantiated in the
application's address space).
As long as each memory-mapped access to the file requires a page
fault, the relevant attributes of the file that are used to detect
access and modification (time_access, time_metadata, time_modify,
and change) will be updated. However, in many operating environments,
when page faults are not required, these attributes will not be updated
on reads or updates to the file via memory access (regardless of whether
the file is a local file or is being accessed remotely). A client or
server MAY fail to update attributes of a file that is being accessed
via memory-mapped I/O. This has several implications:
If there is an application on the server that has memory mapped a
file that a client is also accessing, the client may not be able
to get a consistent value of the change attribute to determine
whether its cache is stale or not. A server that knows that
the file is memory mapped could always pessimistically return
updated values for change so as to force the application to
always get the most up-to-date data and metadata for the file.
However, due to the negative performance implications of this,
such behavior is OPTIONAL.
If the memory-mapped file is not being modified on the server and
instead is just being read by an application via the
memory-mapped interface, the client will not see an updated
time_access attribute. However, in many operating environments,
neither will any process running on the server. Thus, NFS
clients are at no disadvantage with respect to local processes.
If there is another client that is memory mapping the file
and if that client is holding an OPEN_DELEGATE_WRITE delegation,
the same set of issues as discussed in the previous two bullet
items apply. So, when a server does a CB_GETATTR to a file
that the client has modified in its cache, the response
from CB_GETATTR will not necessarily be accurate. As
discussed earlier, the client's obligation is to report that
the file has been modified since the delegation was granted,
not whether it has been modified again between successive
CB_GETATTR calls, and the server MUST assume that any file the
client has modified in cache has been modified again between
successive CB_GETATTR calls. Depending on the nature of the
client's memory management system, this weak obligation may not
be possible. A client MAY return stale information in CB_GETATTR
whenever the file is memory mapped.
The mixture of memory mapping and file locking on the same file is
problematic. Consider the following scenario, where the page size
on each client is 8192 bytes.
Client A memory maps first page (8192 bytes) of file X.
Client B memory maps first page (8192 bytes) of file X.
Client A write locks first 4096 bytes.
Client B write locks second 4096 bytes.
Client A, via a STORE instruction, modifies part of its
locked region.
Simultaneous to client A, client B issues a STORE on part of
its locked region.
Here, the challenge is for each client to resynchronize to get a
correct view of the first page. In many operating environments, the
virtual memory management systems on each client only know a page is
modified, not that a subset of the page corresponding to the
respective lock regions has been modified. So it is not possible
for each client to do the right thing, which is to only write to
the server that portion of the page that is locked. For example,
if client A simply writes out the page, and then client B writes
out the page, client A's data is lost.
Moreover, if mandatory locking is enabled on the file, then we have a
different problem. When clients A and B issue the STORE instructions,
the resulting page faults require a byte-range lock on the entire page.
Each client then tries to extend their locked range to the entire
page, which results in a deadlock.
Communicating the NFS4ERR_DEADLOCK error to a STORE instruction is
difficult at best.
If a client is locking the entire memory-mapped file, there is no
problem with advisory or mandatory byte-range locking, at least until
the client unlocks a region in the middle of the file.
Given the above issues, the following are permitted:
Clients and servers MAY deny memory mapping a file they know
there are byte-range locks for.
Clients and servers MAY deny a byte-range lock on a file they know is
memory mapped.
A client MAY deny memory mapping a file that it knows requires
mandatory locking for I/O. If mandatory locking is enabled after
the file is opened and mapped, the client MAY deny the application
further access to its mapped file.
The results of LOOKUP and READDIR operations may be cached to avoid
the cost of subsequent LOOKUP operations. Just as in the case of
attribute caching, inconsistencies may arise among the various client
caches. To mitigate the effects of these inconsistencies and given
the context of typical file system APIs, an upper time boundary is
maintained on how long a client name cache entry can be kept without
verifying that the entry has not been made invalid by a directory
change operation performed by another client.
When a client is not making changes to a directory for which there
exist name cache entries, the client needs to periodically fetch
attributes for that directory to ensure that it is not being
modified. After determining that no modification has occurred,
the expiration time for the associated name cache entries may be
updated to be the current time plus the name cache staleness bound.
When a client is making changes to a given directory, it needs to
determine whether there have been changes made to the directory by
other clients. It does this by using the change attribute as
reported before and after the directory operation in the associated
change_info4 value returned for the operation. The server is able to
communicate to the client whether the change_info4 data is provided
atomically with respect to the directory operation. If the change
values are provided atomically, the client is then able to compare
the pre-operation change value with the change value in the client's
name cache. If the comparison indicates that the directory was
updated by another client, the name cache associated with the modified
directory is purged from the client. If the comparison indicates
no modification, the name cache can be updated on the client to
reflect the directory operation and the associated timeout extended.
The post-operation change value needs to be saved as the basis for
future change_info4 comparisons.
As demonstrated by the scenario above, name caching requires that the
client revalidate name cache data by inspecting the change attribute
of a directory at the point when the name cache item was cached.
This requires that the server update the change attribute for
directories when the contents of the corresponding directory
are modified. For a client to use the change_info4 information
appropriately and correctly, the server must report the
pre- and post-operation change attribute values atomically. When
the server is unable to report the before and after values
atomically with respect to the directory operation, the server must
indicate that fact in the change_info4 return value. When
the information is not atomically reported, the client should not
assume that other clients have not changed the directory.
The results of READDIR operations may be used to avoid subsequent
READDIR operations. Just as in the cases of attribute and name
caching, inconsistencies may arise among the various client caches.
To mitigate the effects of these inconsistencies, and given the
context of typical file system APIs, the following rules should be
followed:
Cached READDIR information for a directory that is not obtained
in a single READDIR operation must always be a consistent snapshot
of directory contents. This is determined by using a GETATTR
before the first READDIR and after the last READDIR that
contributes to the cache.
An upper time boundary is maintained to indicate the length of
time a directory cache entry is considered valid before the client
must revalidate the cached information.
The revalidation technique parallels that discussed in the case
of name caching. When the client is not changing the directory in
question, checking the change attribute of the directory with GETATTR
is adequate. The lifetime of the cache entry can be extended at
these checkpoints. When a client is modifying the directory, the
client needs to use the change_info4 data to determine whether there
are other clients modifying the directory. If it is determined that
no other client modifications are occurring, the client may update
its directory cache to reflect its own changes.
As demonstrated previously, directory caching requires that the client
revalidate directory cache data by inspecting the change attribute of
a directory at the point when the directory was cached. This requires
that the server update the change attribute for directories when the
contents of the corresponding directory are modified. For a client
to use the change_info4 information appropriately and correctly,
the server must report the pre- and post-operation change attribute
values atomically. When the server is unable to report the before
and after values atomically with respect to the directory operation,
the server must indicate that fact in the change_info4 return value.
When the information is not atomically reported, the client should
not assume that other clients have not changed the directory.
To address the requirement of an NFS protocol that can evolve as the
need arises, the NFSv4 protocol contains the rules and
framework to allow for future minor changes or versioning.
The base assumption with respect to minor versioning is that any
future accepted minor version must follow the IETF process and be
documented in a Standards Track RFC. Therefore, each minor version
number will correspond to an RFC. Minor version 0 of the
NFSv4 protocol is represented by this RFC. The COMPOUND
and CB_COMPOUND procedures support the encoding of the minor version
being requested by the client.
Future minor versions will extend, rather than replace, the XDR
for the preceding minor version, as had been done in moving
from NFSv2 to NFSv3 and from NFSv3 to NFSv4.0.
Specification of detailed rules for the construction of minor
versions will be addressed in documents defining early minor
versions or, more desirably, in an RFC establishing a versioning
framework for NFSv4 as a whole.
Internationalization is a complex topic with its own set of
terminology (see ). The topic is
made more complex in NFSv4.0 by the tangled history and state
of NFS implementations. This section describes what we might
call "NFSv4.0 internationalization" (i.e., internationalization
as implemented by existing clients and servers) as the basis
upon which NFSv4.0 clients may implement internationalization
support.
This section is based on the behavior of existing implementations.
Note that the behaviors described are each demonstrated by a
combination of an NFSv4 server implementation proper and a
server-side physical file system. It is common for servers
and physical file systems to be configurable as to the behavior shown.
In the discussion below, each configuration that shows different
behavior is considered separately.
Note that in this section, the key words "MUST", "SHOULD", and
"MAY" retain their normal meanings. However, in deriving
this specification from implementation patterns, we document
below how the normative terms used derive from the behavior
of existing implementations, in those situations in which
existing implementation behavior patterns can be determined.
Behavior implemented by all existing clients or servers is described
using "MUST", since new implementations need to follow existing
ones to be assured of interoperability. While it is possible that
different behavior might be workable, we have found no case where
this seems reasonable.
The converse holds for "MUST NOT": if a type of behavior poses
interoperability problems, it MUST NOT be implemented by any
existing clients or servers.
Behavior implemented by most existing clients or servers, where
that behavior is more desirable than any alternative, is described
using "SHOULD", since new implementations need to follow that
existing practice unless there are strong reasons to do otherwise.
The converse holds for "SHOULD NOT".
Behavior implemented by some, but not all, existing clients or
servers is described using "MAY", indicating that new
implementations have a choice as to whether they will behave
in that way. Thus, new implementations will have the same
flexibility that existing ones do.
Behavior implemented by all existing clients or servers, so far
as is known -- but where there remains some uncertainty as to
details -- is described using "should". Such cases primarily
concern details of error returns. New implementations should
follow existing practice even though such situations generally
do not affect interoperability.
There are also cases in which certain server behaviors, while
not known to exist, cannot be reliably determined not to
exist. In part, this is a consequence of the long period of
time that has elapsed since the publication of ,
resulting in a situation in which those involved in the
implementation may no longer be involved in or aware of working
group activities.
In the case of possible server behavior that is neither known
to exist nor known not to exist, we use "SHOULD NOT" and
"MUST NOT" as follows, and similarly for "SHOULD" and "MUST".
In some cases, the potential behavior is not known to exist but is
of such a nature that, if it were in fact implemented,
interoperability difficulties would be expected and reported,
giving us cause to conclude that the potential behavior is not
implemented. For such behavior, we use "MUST NOT".
Similarly, we use "MUST" to apply to the contrary behavior.
In other cases, potential behavior is not known to exist but the
behavior, while undesirable, is not of such a nature that we are
able to draw any conclusions about its potential existence. In
such cases, we use "SHOULD NOT". Similarly, we use "SHOULD"
to apply to the contrary behavior.
In the case of a "MAY", "SHOULD", or "SHOULD NOT" that applies to
servers, clients need to be aware that there are servers that
may or may not take the specified action, and they need to
be prepared for either eventuality.
There are a number of noteworthy circumstances that limit the degree
to which internationalization-related processing can be made universal
with regard to NFSv4 clients and servers:
The NFSv4 client is part of an extensive set of client-side software
components whose design and internal interfaces are not within the
IETF's purview, limiting the degree to which a particular character
encoding may be made standard.
Server-side handling of file component names is typically
implemented within a server-side physical file system, whose
handling of character encoding and normalization is not specifiable by the IETF.
Typical implementation patterns in UNIX systems result in the
NFSv4 client having no knowledge of the character encoding being
used, which may even vary between processes on the same client
system.
Users may need access to files stored previously with non-UTF-8
encodings, or with UTF-8 encodings that do not match any particular normalization form.
As mentioned in , servers MAY
reject component name strings that are not valid UTF-8. This
leads to a number of types of valid server behavior, as
outlined below. When these are combined with
the valid normalization-related behaviors as described in ,
this leads to the combined behaviors outlined below.
Servers that limit file component names to UTF-8
strings exist with normalization-related
handling as described
in . These are best
described as "UTF-8-only servers".
Servers that do not limit file component names to UTF-8
strings are very common and are necessary to deal with
clients/applications not oriented to the use of UTF-8.
Such servers ignore normalization-related issues, and there
is no way for them to implement either normalization or
representation-independent lookups. These are best
described as "UTF-8-unaware servers", since they treat
file component names as uninterpreted strings of bytes
and have no knowledge of the characters represented.
See for details.
It is possible for a server to allow component names that
are not valid UTF-8, while still being aware of the
structure of UTF-8 strings. Such servers could implement
either normalization or representation-independent lookups
but apply those techniques only to valid UTF-8 strings.
Such servers are not common, but it is possible to configure at
least one known server to have this behavior. This behavior
SHOULD NOT be used due to the possibility that a filename
using one character set may, by coincidence, have the appearance
of a UTF-8 filename; the results of UTF-8 normalization or
representation-independent lookups are unlikely to be correct
in all cases with respect to the other character set.
Strings that potentially contain characters outside the ASCII range
are generally represented in NFSv4 using
the UTF-8 encoding of Unicode
. See for
precise encoding and decoding rules.
Some details of the protocol treatment depend on the type of string:
For strings that are component names, the preferred encoding for any
non-ASCII characters is the UTF-8 representation of Unicode.
In many cases, clients have no knowledge of the encoding
being used, with the encoding done at the user level under
the control of a per-process locale specification. As a result,
it may be impossible for the NFSv4 client to enforce the
use of UTF-8. The use of non-UTF-8 encodings can be
problematic, since it may interfere with access to files
stored using other forms of name encoding. Also,
normalization-related
processing (see ) of a string
not encoded in UTF-8 could result in inappropriate name
modification or aliasing. In cases in which one has a
non-UTF-8 encoded name that accidentally conforms to
UTF-8 rules, substitution of canonically equivalent strings
can change the non-UTF-8 encoded name drastically.
The kinds of modification and aliasing mentioned here can
lead to both false negatives and false positives, depending on
the strings in question, which can result in security
issues such as elevation of privilege and denial of service
(see for further discussion).
For strings based on domain names, non-ASCII characters MUST be
represented using the UTF-8 encoding of Unicode, and additional
string format restrictions apply.
See for details.
The contents of symbolic links (of type linktext4 in the
XDR) MUST be treated as opaque data by NFSv4 servers.
Although UTF-8 encoding is often used, it need not be.
In this respect, the contents of symbolic links are like
the contents of regular files in that their encoding is
not within the scope of this specification.
For other sorts of strings, any non-ASCII characters SHOULD be
represented using the UTF-8 encoding of Unicode.
The client and server operating environments may differ in their
policies and operational methods with respect to character
normalization (see for a discussion of
normalization forms). This difference may also exist between
applications on the
same client. This adds to the difficulty of providing a single
normalization policy for the protocol that allows for maximal
interoperability. This issue is similar to the issues of
character case where the server may or may not support
case-insensitive filename matching and may or may not preserve
the character case when storing filenames. The protocol does not
mandate a particular behavior but allows for a range of useful
behaviors.
The NFSv4 protocol does not mandate the use of a particular
normalization form at this time. A subsequent minor version of
the NFSv4 protocol might specify a particular normalization form.
Therefore, the server and client can expect that they may receive
unnormalized characters within protocol requests and responses. If
the operating environment requires normalization, then the
implementation will need to normalize the various UTF-8 encoded strings
within the protocol before presenting the information to an
application (at the client) or local file system (at the server).
Server implementations MAY normalize filenames to conform
to a particular normalization form before using the resulting
string when looking up or creating a file. Servers MAY also
perform normalization-insensitive string comparisons without
modifying the names to match a particular normalization form.
Except in cases in which component names are excluded from
normalization-related handling because they are not valid
UTF-8 strings, a server MUST make the same choice (as to
whether to normalize or not, the target form of normalization,
and whether to do normalization-insensitive string comparisons)
in the same way for all accesses to a particular file system.
Servers SHOULD NOT reject a filename because it does not
conform to a particular normalization form, as this may deny
access to clients that use a different normalization form.
There are two types of strings that NFSv4 deals with that are based
on domain names. Processing of such strings is defined by other
Internet standards, and hence the processing behavior for such
strings should be consistent across all server operating systems
and server file systems.
These are as follows:
Server names as they appear in the fs_locations attribute. Note
that for most purposes, such server names will only be sent by the
server to the client. The exception is the use of the
fs_locations attribute in a VERIFY or NVERIFY operation.
Principal suffixes that are used to denote sets of users and
groups, and are in the form of domain names.
The general rules for handling all of these domain-related strings
are similar and independent of the role of the sender or receiver as
client or server, although the consequences of failure to obey these
rules may be different for client or server. The server can report
errors when it is sent invalid strings, whereas the client will
simply ignore invalid string or use a default value in their place.
The string sent SHOULD be in the form of one or more U-labels
as defined by . If that is impractical,
it can instead be in the form of one or more LDH labels or a UTF-8 domain name that
contains labels that are not properly formatted U-labels. The receiver
needs to be able to accept domain and server names in any of
the formats allowed. The server MUST reject, using the error
NFS4ERR_INVAL, a string that is not valid UTF-8, or that
contains an ASCII label that is not a valid LDH label, or
that contains an XN&nbhy;label (begins with "xn--") for which the
characters after "xn--" are not valid output of the Punycode
algorithm .
When a domain string is part of id@domain or group@domain, there are
two possible approaches:
The server treats the domain string as a series of U-labels.
In cases where the domain string is a series of A-labels
or Non&nbhy;Reserved LDH (NR-LDH) labels, it converts them to
U-labels using the Punycode algorithm .
In cases where the domain string is a series of other sorts of
LDH labels, the server can use the ToUnicode function defined
in to convert the string to a
series of labels that generally conform to the U-label
syntax. In cases where the domain string is a UTF-8 string
that contains non-U-labels, the server can attempt to use
the ToASCII function defined in
and then the ToUnicode function on the string to convert
it to a series of labels that generally conform to the
U-label syntax. As a result, the domain string returned
within a user id on a GETATTR may not match that sent when
the user id is set using SETATTR, although when this
happens, the domain will be in the form that generally
conforms to the U-label syntax.
The server does not attempt to treat the domain string
as a series of U-labels; specifically, it does not map a
domain string that is not a U-label into a U-label using
the methods described above. As a result, the domain
string returned on a GETATTR of the user id MUST be the
same as that used when setting the user id by the SETATTR.
A server SHOULD use the first method.
For VERIFY and NVERIFY, additional string processing requirements
apply to verification of the owner and owner_group attributes;
see .
Where the client sends an invalid UTF-8 string, the server MAY
return an NFS4ERR_INVAL error. This includes cases in which
inappropriate prefixes are detected and where the count includes
trailing bytes that do not constitute a full Universal Multiple-Octet
Coded Character Set (UCS) character.
Requirements for server handling of component names that are not
valid UTF-8, when a server does not return NFS4ERR_INVAL in response
to receiving them, are described in .
Where the string supplied by the client is not rejected with
NFS4ERR_INVAL but contains characters that are not supported
by the server as a value for that string (e.g., names containing
slashes, or characters that do not fit into 16 bits when
converted from UTF-8 to a Unicode codepoint), the server
should return an NFS4ERR_BADCHAR error.
Where a UTF-8 string is used as a filename, and the file
system, while supporting all of the characters within the
name, does not allow that particular name to be used, the
server should return the error NFS4ERR_BADNAME. This includes
such situations as file system prohibitions of "." and ".."
as filenames for certain operations, and similar constraints.
As stated previously, servers MAY accept, on all or on some
subset of the physical file systems exported, component names
that are not valid UTF-8 strings. A typical pattern is for
a server to use UTF&nbhy;8-unaware physical file systems that treat
component names as uninterpreted strings of bytes, rather
than having any awareness of the character set being used.
Such servers SHOULD NOT change the stored representation of
component names from those received on the wire and SHOULD
use an octet-by-octet comparison of component name strings
to determine equivalence (as opposed to any broader notion
of string comparison). This is because the server has no
knowledge of the character encoding being used.
Nonetheless, when such a server uses a broader notion of
string equivalence than what is recommended in the
preceding paragraph, the following considerations apply:
Outside of 7-bit ASCII, string processing that changes string
contents is usually specific to a character set and hence is
generally unsafe when the character set is unknown. This
processing could change the filename in an unexpected fashion,
rendering the file inaccessible to the application or client that
created or renamed the file and to others expecting the original
filename. Hence, such processing should not be performed,
because doing so is likely to result in incorrect string
modification or aliasing.
Unicode normalization is particularly dangerous, as such
processing assumes that the string is UTF-8. When that assumption
is false because a different character set was used to create the
filename, normalization may corrupt the filename with respect to
that character set, rendering the file inaccessible to the
application that created it and others expecting the original
filename. Hence, Unicode normalization SHOULD NOT be performed,
because it may cause incorrect string modification or aliasing.
When the above recommendations are not followed, the resulting
string modification and aliasing can lead to both false negatives
and false positives, depending on the strings in question, which can
result in security issues such as elevation of privilege and
denial of service (see for further discussion).
NFS error numbers are assigned to failed operations within a
COMPOUND or CB_COMPOUND request. A COMPOUND request
contains a number of NFS operations that have their results
encoded in sequence in a COMPOUND reply. The results of successful
operations will consist of an NFS4_OK status followed by the
encoded results of the operation. If an NFS operation fails, an
error status will be entered in the reply, and the COMPOUND request
will be terminated.
ErrorNumberDescriptionNFS4_OK0NFS4ERR_ACCESS13NFS4ERR_ADMIN_REVOKED10047NFS4ERR_ATTRNOTSUPP10032NFS4ERR_BADCHAR10040NFS4ERR_BADHANDLE10001NFS4ERR_BADNAME10041NFS4ERR_BADOWNER10039NFS4ERR_BADTYPE10007NFS4ERR_BADXDR10036NFS4ERR_BAD_COOKIE10003NFS4ERR_BAD_RANGE10042NFS4ERR_BAD_SEQID10026NFS4ERR_BAD_STATEID10025NFS4ERR_CB_PATH_DOWN10048NFS4ERR_CLID_INUSE10017NFS4ERR_DEADLOCK10045NFS4ERR_DELAY10008NFS4ERR_DENIED10010NFS4ERR_DQUOT69NFS4ERR_EXIST17NFS4ERR_EXPIRED10011NFS4ERR_FBIG27NFS4ERR_FHEXPIRED10014NFS4ERR_FILE_OPEN10046NFS4ERR_GRACE10013NFS4ERR_INVAL22NFS4ERR_IO5NFS4ERR_ISDIR21NFS4ERR_LEASE_MOVED10031NFS4ERR_LOCKED10012NFS4ERR_LOCKS_HELD10037NFS4ERR_LOCK_NOTSUPP10043NFS4ERR_LOCK_RANGE10028NFS4ERR_MINOR_VERS_MISMATCH10021NFS4ERR_MLINK31NFS4ERR_MOVED10019NFS4ERR_NAMETOOLONG63NFS4ERR_NOENT2NFS4ERR_NOFILEHANDLE10020NFS4ERR_NOSPC28NFS4ERR_NOTDIR20NFS4ERR_NOTEMPTY66NFS4ERR_NOTSUPP10004NFS4ERR_NOT_SAME10027NFS4ERR_NO_GRACE10033NFS4ERR_NXIO6NFS4ERR_OLD_STATEID10024NFS4ERR_OPENMODE10038NFS4ERR_OP_ILLEGAL10044NFS4ERR_PERM1NFS4ERR_RECLAIM_BAD10034NFS4ERR_RECLAIM_CONFLICT10035NFS4ERR_RESOURCE10018NFS4ERR_RESTOREFH10030NFS4ERR_ROFS30NFS4ERR_SAME10009NFS4ERR_SERVERFAULT10006NFS4ERR_SHARE_DENIED10015NFS4ERR_STALE70NFS4ERR_STALE_CLIENTID10022NFS4ERR_STALE_STATEID10023NFS4ERR_SYMLINK10029NFS4ERR_TOOSMALL10005NFS4ERR_WRONGSEC10016NFS4ERR_XDEV18
This section deals with errors that are applicable to a broad
set of different purposes.
The arguments for this operation do not match those specified in
the XDR definition. This includes situations in which the
request ends before all the arguments have been seen. Note
that this error applies when fixed enumerations (these include
booleans) have a value within the input stream that is not
valid for the enum. A replier may pre-parse all operations for
a COMPOUND procedure before doing any operation execution
and return RPC-level XDR errors in that case.
This error is used for operations that provide a set of
information indexed by some quantity provided by the client
or cookie sent by the server for an earlier invocation.
Where the value cannot be used for its intended purpose,
this error results.
For any of a number of reasons, the replier could not
process this operation in what was deemed a reasonable
time. The client should wait and then try the request
with a new RPC transaction ID.
The following are two examples of what might lead to this situation:
A server that supports hierarchical storage receives a
request to process a file that had been migrated.
An operation requires a delegation recall to proceed,
and waiting for this delegation recall makes processing
this request in a timely fashion impossible.
The arguments for this operation are not valid for some reason, even
though they do match those specified in the XDR definition for
the request.
The operation is not supported, either because the operation is
an OPTIONAL one and is not supported by this server or
because the operation MUST NOT be implemented in
the current minor version.
An error that does not map to any of the specific legal NFSv4
protocol error values occurred on the server. The client
should translate this into an appropriate error. UNIX clients
may choose to translate this to EIO.
This error is used where an operation returns a variable amount
of data, with a limit specified by the client. Where the data
returned cannot be fitted within the limit specified by the
client, this error results.
These errors deal with the situation in which the current
or saved filehandle, or the filehandle passed to PUTFH
intended to become the current filehandle, is invalid
in some way. This includes situations in which the
filehandle is a valid filehandle in general but is not
of the appropriate object type for the current operation.
Where the error description indicates a problem with the
current or saved filehandle, it is to be understood that
filehandles are only checked for the condition if they
are implicit arguments of the operation in question.
This error is generated for an illegal NFS filehandle for the
current server. The current filehandle failed internal
consistency checks. Once accepted as valid (by PUTFH), no
subsequent status change can cause the filehandle to
generate this error.
A current or saved filehandle that is an argument to the
current operation is volatile and has expired at the server.
The current or saved filehandle designates a directory
when the current operation does not allow a directory to
be accepted as the target of this operation.
The file system that contains the current filehandle object
is not present at the server. It may have been relocated or
migrated to another server, or may have never been present.
The client may obtain the new file system location by obtaining
the "fs_locations" attribute for the current filehandle.
For further discussion, refer to .
The logical current or saved filehandle value is required by
the current operation and is not set.
This may be a result of a malformed COMPOUND
operation (i.e., no PUTFH or PUTROOTFH before an operation that
requires that the current filehandle be set).
The current (or saved) filehandle designates an object that
is not a directory for an operation in which a directory is
required.
The current or saved filehandle value designating an argument
to the current operation is invalid.
The file system object referred to by that filehandle no longer
exists, or access to it has been revoked.
The current filehandle designates a symbolic link when the
current operation does not allow a symbolic link as the
target.
This section deals with errors that relate to the overall structure
of a COMPOUND request (by which we mean to include both
COMPOUND and CB_COMPOUND), rather than to particular operations.
There are a number of basic constraints on the operations that
may appear in a COMPOUND request.
NFS_OK indicates that the operation completed successfully,
in that all of the constituent operations completed without error.
The minor version specified is not one that the current listener
supports. This value is returned in the overall status for the
COMPOUND procedure but is not associated with a specific
operation, since the results must specify a result count of zero.
The operation code is not a valid one for the current
COMPOUND procedure. The opcode
in the result stream matched with this error is the
ILLEGAL value, although the value that appears in the
request stream may be different. Where an illegal
value appears and the replier pre-parses all operations for
a COMPOUND procedure before doing any operation execution,
an RPC-level XDR error may be returned in this case.
For the processing of the COMPOUND procedure, the server may
exhaust available resources and cannot continue processing
operations within the COMPOUND procedure. This error will
be returned from the server in those instances of resource
exhaustion related to the processing of the COMPOUND procedure.
These errors describe situations that occurred in the underlying
file system implementation rather than in the protocol or any
NFSv4.x feature.
An attempt was made to create an object with an inappropriate
type specified to CREATE. This may be because the type
is undefined; because it is a type not supported by the
server; or because it is a type for which create is not
intended, such as a regular file or named attribute, for
which OPEN is used to do the file creation.
The resource (quota) hard limit has been exceeded.
The user's resource limit on the server has been exceeded.
A file system object of the specified target name (when creating,
renaming, or linking) already exists.
The file system object is too large. The operation would have caused a
file system object to grow beyond the server's limit.
The operation is not allowed because a
file system object involved in the operation is currently open.
Servers may, but are not required to, disallow linking to,
removing, or renaming open file system objects.
This indicates that an I/O error occurred for which the
file system was unable to provide recovery.
The request would have caused the server's limit for the
number of hard links a file system object may have to be exceeded.
This indicates no such file or directory. The file system object referenced by the name
specified does not exist.
This indicates no space left on the device. The operation would have
caused the server's file system to exceed its limit.
An attempt was made to remove a directory that was not empty.
This indicates an I/O error. There is no such device or address.
The RESTOREFH operation does not have a saved filehandle
(identified by SAVEFH) to operate upon.
This indicates a read-only file system. A modifying operation was
attempted on a read-only file system.
This indicates an attempt to do an operation, such as linking,
that inappropriately crosses a boundary. For example, this
may be due to a boundary between:
File systems (where the fsids are different).
Different named attribute directories, or
between a named attribute directory and an ordinary
directory.
Regions of a file system that the file system
implementation treats as separate (for example, for space
accounting purposes), and where cross-connection between
the regions is not allowed.
These errors indicate problems with the stateid (or one of
the stateids) passed to a given operation. This includes
situations in which the stateid is invalid, as well as
situations in which the stateid is valid but designates
revoked locking state. Depending on the operation, the
stateid, when valid, may designate opens, byte-range locks,
or file delegations.
A stateid designates locking state of any type that has been revoked
due to administrative interaction, possibly while the lease is valid,
or because a delegation was revoked because of failure to return it,
while the lease was valid.
A stateid generated by the current server instance was used that
either:
Does not designate any locking state (either current or superseded)
for a current (state-owner, file) pair.
Designates locking state that was freed after lease expiration but
without any lease cancellation, as may happen in the handling of
"courtesy locks".
A stateid or clientid designates locking state of any type that
has been revoked or released due to cancellation of the client's
lease, either immediately upon lease expiration, or following a later
request for a conflicting lock.
A lease being renewed is associated with a file system
that has been migrated to a new server.
A stateid is provided with a seqid value that is not the most
current.
A stateid generated by an earlier server instance was
used.
These are the various permission-related errors in NFSv4.
This indicates permission denied. The caller does
not have the correct permission to perform
the requested operation. Contrast this with
NFS4ERR_PERM (), which
restricts itself to owner or privileged user
permission failures.
This indicates that the requester is not the owner. The
operation was not allowed because the caller is neither a
privileged user (root) nor the owner of the target of the
operation.
This indicates that the security mechanism being used by the
client for the operation does not match the server's security
policy. The client should change the security mechanism being
used and re-send the operation. SECINFO can be used
to determine the appropriate mechanism.
Names in NFSv4 are UTF-8 strings. When the strings are not
of length zero, the error NFS4ERR_INVAL results. When
they are not valid UTF&nbhy;8, the error NFS4ERR_INVAL also results,
but servers may accommodate file systems with different
character formats and not return this error. Besides
this, there are a number of other errors
to indicate specific problems with names.
A UTF-8 string contains a character that is not supported
by the server in the context in which it is being used.
A name string in a request consisted of valid UTF-8
characters supported by the server, but the name is not
supported by the server as a valid name for current operation.
An example might be creating a file or directory named ".."
on a server whose file system uses that name for links to
parent directories.
This error should not be returned due to a normalization issue
in a string. When a file system keeps names in a particular
normalization form, it is the server's responsibility to
do the appropriate normalization, rather than rejecting
the name.
This is returned when the filename in an operation exceeds the
server's implementation limit.
This section deals with errors related to locking -- both
share reservations and byte-range locking. It does not deal
with errors specific to the process of reclaiming locks. Those
are dealt with in the next section.
The range for a LOCK, LOCKT, or LOCKU operation is not
appropriate to the allowable range of offsets for the
server. For example, this error results when a server
that only supports 32-bit ranges receives a range that
cannot be handled by that server. (See
.)
The sequence number (seqid) in a locking request is neither the
next expected number nor the last number processed.
The server has been able to determine a file locking
deadlock condition for a blocking lock request.
An attempt to lock a file is denied. Since this may be a
temporary condition, the client is encouraged to re-send the lock
request until the lock is accepted. See
for a discussion of the re&nbhy;send.
A READ or WRITE operation was attempted on a file where there
was a conflict between the I/O and an existing lock:
There is a share reservation inconsistent with the I/O
being done.
The range to be read or written intersects an existing
mandatory byte-range lock.
An operation was prevented by the unexpected presence of locks.
A locking request was attempted that would require the upgrade
or downgrade of a lock range already held by the owner when the
server does not support atomic upgrade or downgrade of locks.
A lock request is operating on a range that partially overlaps a
currently held lock for the current lock-owner and does not precisely
match a single such lock, where the server does not support this type
of request and thus does not implement POSIX locking semantics
. See
Sections ,
, and
for a
discussion of how this applies to LOCK, LOCKT, and LOCKU,
respectively.
The client attempted a READ, WRITE, LOCK, or other operation
not sanctioned by the stateid passed (e.g., writing to a file
opened only for read).
An attempt to OPEN a file with a share reservation has failed because
of a share conflict.
These errors relate to the process of reclaiming locks after a
server restart.
The server is in its recovery or grace period, which should
at least match the lease period of the server. A locking
request other than a reclaim could not be granted during
that period.
The server cannot guarantee that it has not granted state to
another client that may conflict with this client's state.
No further reclaims from this client will succeed.
The server cannot guarantee that it has not granted state to
another client that may conflict with the requested state.
However, this applies only to the state requested in this call;
further reclaims may succeed.
Unlike NFS4ERR_RECLAIM_CONFLICT, this can occur between
correctly functioning clients and servers: the "edge condition"
scenarios described in leave only the
server knowing whether the client's locks are still valid, and
NFS4ERR_RECLAIM_BAD is the server's way of informing the client
that they are not.
The reclaim attempted by the client conflicts with a lock
already held by another client. Unlike NFS4ERR_RECLAIM_BAD,
this can only occur if one of the clients misbehaved.
This section deals with errors associated with requests used
to create and manage client IDs.
The SETCLIENTID operation has found that a clientid is
already in use by another client.
A client ID not recognized by the server was used in a locking
or SETCLIENTID_CONFIRM request.
This section deals with errors specific to attribute handling
within NFSv4.
An attribute specified is not supported by the server. This
error MUST NOT be returned by the GETATTR operation.
This error is returned when an owner or owner_group attribute value
or the who field of an ace within an ACL attribute value cannot
be translated to a local representation.
This error is returned by the VERIFY operation to signify
that the attributes compared were not the same as those provided
in the client's request.
This error is returned by the NVERIFY operation to signify
that the attributes compared were the same as those provided
in the client's request.
There is a problem contacting the client via the callback path.
This section contains a table that gives the valid error returns
for each protocol operation. The error code NFS4_OK (indicating
no error) is not listed but should be understood to be returnable
by all operations except ILLEGAL.
OperationErrorsACCESS
NFS4ERR_ACCESS,
NFS4ERR_BADHANDLE,
NFS4ERR_BADXDR,
NFS4ERR_DELAY,
NFS4ERR_FHEXPIRED,
NFS4ERR_INVAL,
NFS4ERR_IO,
NFS4ERR_MOVED,
NFS4ERR_NOFILEHANDLE,
NFS4ERR_RESOURCE,
NFS4ERR_SERVERFAULT,
NFS4ERR_STALE
CLOSE
NFS4ERR_ADMIN_REVOKED,
NFS4ERR_BADHANDLE,
NFS4ERR_BAD_SEQID,
NFS4ERR_BAD_STATEID,
NFS4ERR_BADXDR,
NFS4ERR_DELAY,
NFS4ERR_EXPIRED,
NFS4ERR_FHEXPIRED,
NFS4ERR_INVAL,
NFS4ERR_ISDIR,
NFS4ERR_LEASE_MOVED,
NFS4ERR_LOCKS_HELD,
NFS4ERR_MOVED,
NFS4ERR_NOFILEHANDLE,
NFS4ERR_OLD_STATEID,
NFS4ERR_RESOURCE,
NFS4ERR_SERVERFAULT,
NFS4ERR_STALE,
NFS4ERR_STALE_STATEID
COMMIT
NFS4ERR_ACCESS,
NFS4ERR_BADHANDLE,
NFS4ERR_BADXDR,
NFS4ERR_DELAY,
NFS4ERR_FHEXPIRED,
NFS4ERR_INVAL,
NFS4ERR_IO,
NFS4ERR_ISDIR,
NFS4ERR_MOVED,
NFS4ERR_NOFILEHANDLE,
NFS4ERR_RESOURCE,
NFS4ERR_ROFS,
NFS4ERR_SERVERFAULT,
NFS4ERR_STALE,
NFS4ERR_SYMLINK
CREATE
NFS4ERR_ACCESS,
NFS4ERR_ATTRNOTSUPP,
NFS4ERR_BADCHAR,
NFS4ERR_BADHANDLE,
NFS4ERR_BADNAME,
NFS4ERR_BADOWNER,
NFS4ERR_BADTYPE,
NFS4ERR_BADXDR,
NFS4ERR_DELAY,
NFS4ERR_DQUOT,
NFS4ERR_EXIST,
NFS4ERR_FHEXPIRED,
NFS4ERR_INVAL,
NFS4ERR_IO,
NFS4ERR_MOVED,
NFS4ERR_NAMETOOLONG,
NFS4ERR_NOFILEHANDLE,
NFS4ERR_NOSPC,
NFS4ERR_NOTDIR,
NFS4ERR_PERM,
NFS4ERR_RESOURCE,
NFS4ERR_ROFS,
NFS4ERR_SERVERFAULT,
NFS4ERR_STALE
DELEGPURGE
NFS4ERR_BADXDR,
NFS4ERR_DELAY,
NFS4ERR_LEASE_MOVED,
NFS4ERR_NOTSUPP,
NFS4ERR_RESOURCE,
NFS4ERR_SERVERFAULT,
NFS4ERR_STALE_CLIENTID
DELEGRETURN
NFS4ERR_ADMIN_REVOKED,
NFS4ERR_BAD_STATEID,
NFS4ERR_BADXDR,
NFS4ERR_DELAY,
NFS4ERR_EXPIRED,
NFS4ERR_INVAL,
NFS4ERR_LEASE_MOVED,
NFS4ERR_MOVED,
NFS4ERR_NOFILEHANDLE,
NFS4ERR_NOTSUPP,
NFS4ERR_OLD_STATEID,
NFS4ERR_RESOURCE,
NFS4ERR_SERVERFAULT,
NFS4ERR_STALE,
NFS4ERR_STALE_STATEID
GETATTR
NFS4ERR_ACCESS,
NFS4ERR_BADHANDLE,
NFS4ERR_BADXDR,
NFS4ERR_DELAY,
NFS4ERR_FHEXPIRED,
NFS4ERR_GRACE,
NFS4ERR_INVAL,
NFS4ERR_IO,
NFS4ERR_MOVED,
NFS4ERR_NOFILEHANDLE,
NFS4ERR_RESOURCE,
NFS4ERR_SERVERFAULT,
NFS4ERR_STALE
GETFH
NFS4ERR_BADHANDLE,
NFS4ERR_FHEXPIRED,
NFS4ERR_MOVED,
NFS4ERR_NOFILEHANDLE,
NFS4ERR_RESOURCE,
NFS4ERR_SERVERFAULT,
NFS4ERR_STALE
ILLEGAL
NFS4ERR_BADXDR,
NFS4ERR_OP_ILLEGAL
LINK
NFS4ERR_ACCESS,
NFS4ERR_BADCHAR,
NFS4ERR_BADHANDLE,
NFS4ERR_BADNAME,
NFS4ERR_BADXDR,
NFS4ERR_DELAY,
NFS4ERR_DQUOT,
NFS4ERR_EXIST,
NFS4ERR_FHEXPIRED,
NFS4ERR_FILE_OPEN,
NFS4ERR_INVAL,
NFS4ERR_IO,
NFS4ERR_ISDIR,
NFS4ERR_MLINK,
NFS4ERR_MOVED,
NFS4ERR_NAMETOOLONG,
NFS4ERR_NOENT,
NFS4ERR_NOFILEHANDLE,
NFS4ERR_NOSPC,
NFS4ERR_NOTDIR,
NFS4ERR_NOTSUPP,
NFS4ERR_RESOURCE,
NFS4ERR_ROFS,
NFS4ERR_SERVERFAULT,
NFS4ERR_STALE,
NFS4ERR_WRONGSEC,
NFS4ERR_XDEV
LOCK
NFS4ERR_ACCESS,
NFS4ERR_ADMIN_REVOKED,
NFS4ERR_BADHANDLE,
NFS4ERR_BAD_RANGE,
NFS4ERR_BAD_SEQID,
NFS4ERR_BAD_STATEID,
NFS4ERR_BADXDR,
NFS4ERR_DEADLOCK,
NFS4ERR_DELAY,
NFS4ERR_DENIED,
NFS4ERR_EXPIRED,
NFS4ERR_FHEXPIRED,
NFS4ERR_GRACE,
NFS4ERR_INVAL,
NFS4ERR_ISDIR,
NFS4ERR_LEASE_MOVED,
NFS4ERR_LOCK_NOTSUPP,
NFS4ERR_LOCK_RANGE,
NFS4ERR_MOVED,
NFS4ERR_NOFILEHANDLE,
NFS4ERR_NO_GRACE,
NFS4ERR_OLD_STATEID,
NFS4ERR_OPENMODE,
NFS4ERR_RECLAIM_BAD,
NFS4ERR_RECLAIM_CONFLICT,
NFS4ERR_RESOURCE,
NFS4ERR_SERVERFAULT,
NFS4ERR_STALE,
NFS4ERR_STALE_CLIENTID,
NFS4ERR_STALE_STATEID
LOCKT
NFS4ERR_ACCESS,
NFS4ERR_BADHANDLE,
NFS4ERR_BAD_RANGE,
NFS4ERR_BADXDR,
NFS4ERR_DELAY,
NFS4ERR_DENIED,
NFS4ERR_EXPIRED,
NFS4ERR_FHEXPIRED,
NFS4ERR_GRACE,
NFS4ERR_INVAL,
NFS4ERR_ISDIR,
NFS4ERR_LEASE_MOVED,
NFS4ERR_LOCK_RANGE,
NFS4ERR_MOVED,
NFS4ERR_NOFILEHANDLE,
NFS4ERR_RESOURCE,
NFS4ERR_SERVERFAULT,
NFS4ERR_STALE,
NFS4ERR_STALE_CLIENTID
LOCKU
NFS4ERR_ACCESS,
NFS4ERR_ADMIN_REVOKED,
NFS4ERR_BADHANDLE,
NFS4ERR_BAD_RANGE,
NFS4ERR_BAD_SEQID,
NFS4ERR_BAD_STATEID,
NFS4ERR_BADXDR,
NFS4ERR_DELAY,
NFS4ERR_EXPIRED,
NFS4ERR_FHEXPIRED,
NFS4ERR_GRACE,
NFS4ERR_INVAL,
NFS4ERR_ISDIR,
NFS4ERR_LEASE_MOVED,
NFS4ERR_LOCK_RANGE,
NFS4ERR_MOVED,
NFS4ERR_NOFILEHANDLE,
NFS4ERR_OLD_STATEID,
NFS4ERR_RESOURCE,
NFS4ERR_SERVERFAULT,
NFS4ERR_STALE,
NFS4ERR_STALE_STATEID
LOOKUP
NFS4ERR_ACCESS,
NFS4ERR_BADCHAR,
NFS4ERR_BADHANDLE,
NFS4ERR_BADNAME,
NFS4ERR_BADXDR,
NFS4ERR_DELAY,
NFS4ERR_FHEXPIRED,
NFS4ERR_INVAL,
NFS4ERR_IO,
NFS4ERR_MOVED,
NFS4ERR_NAMETOOLONG,
NFS4ERR_NOENT,
NFS4ERR_NOFILEHANDLE,
NFS4ERR_NOTDIR,
NFS4ERR_RESOURCE,
NFS4ERR_SERVERFAULT,
NFS4ERR_STALE,
NFS4ERR_SYMLINK,
NFS4ERR_WRONGSEC
LOOKUPP
NFS4ERR_ACCESS,
NFS4ERR_BADHANDLE,
NFS4ERR_DELAY,
NFS4ERR_FHEXPIRED,
NFS4ERR_IO,
NFS4ERR_MOVED,
NFS4ERR_NOENT,
NFS4ERR_NOFILEHANDLE,
NFS4ERR_NOTDIR,
NFS4ERR_RESOURCE,
NFS4ERR_SERVERFAULT,
NFS4ERR_STALE,
NFS4ERR_SYMLINK,
NFS4ERR_WRONGSEC
NVERIFY
NFS4ERR_ACCESS,
NFS4ERR_ATTRNOTSUPP,
NFS4ERR_BADCHAR,
NFS4ERR_BADHANDLE,
NFS4ERR_BADXDR,
NFS4ERR_DELAY,
NFS4ERR_FHEXPIRED,
NFS4ERR_GRACE,
NFS4ERR_INVAL,
NFS4ERR_IO,
NFS4ERR_MOVED,
NFS4ERR_NOFILEHANDLE,
NFS4ERR_SAME,
NFS4ERR_SERVERFAULT,
NFS4ERR_STALE
OPEN
NFS4ERR_ACCESS,
NFS4ERR_ADMIN_REVOKED,
NFS4ERR_ATTRNOTSUPP,
NFS4ERR_BADCHAR,
NFS4ERR_BADHANDLE,
NFS4ERR_BADNAME,
NFS4ERR_BADOWNER,
NFS4ERR_BAD_SEQID,
NFS4ERR_BAD_STATEID,
NFS4ERR_BADXDR,
NFS4ERR_DELAY,
NFS4ERR_DQUOT,
NFS4ERR_EXIST,
NFS4ERR_EXPIRED,
NFS4ERR_FBIG,
NFS4ERR_FHEXPIRED,
NFS4ERR_GRACE,
NFS4ERR_INVAL,
NFS4ERR_IO,
NFS4ERR_ISDIR,
NFS4ERR_MOVED,
NFS4ERR_NAMETOOLONG,
NFS4ERR_NOENT,
NFS4ERR_NOFILEHANDLE,
NFS4ERR_NO_GRACE,
NFS4ERR_NOSPC,
NFS4ERR_NOTDIR,
NFS4ERR_NOTSUPP,
NFS4ERR_OLD_STATEID,
NFS4ERR_PERM,
NFS4ERR_RECLAIM_BAD,
NFS4ERR_RECLAIM_CONFLICT,
NFS4ERR_RESOURCE,
NFS4ERR_ROFS,
NFS4ERR_SERVERFAULT,
NFS4ERR_SHARE_DENIED,
NFS4ERR_STALE,
NFS4ERR_STALE_CLIENTID,
NFS4ERR_SYMLINK,
NFS4ERR_WRONGSEC
OPENATTR
NFS4ERR_ACCESS,
NFS4ERR_BADHANDLE,
NFS4ERR_BADXDR,
NFS4ERR_DELAY,
NFS4ERR_DQUOT,
NFS4ERR_FHEXPIRED,
NFS4ERR_IO,
NFS4ERR_MOVED,
NFS4ERR_NOENT,
NFS4ERR_NOFILEHANDLE,
NFS4ERR_NOSPC,
NFS4ERR_NOTSUPP,
NFS4ERR_RESOURCE,
NFS4ERR_ROFS,
NFS4ERR_SERVERFAULT,
NFS4ERR_STALE
OPEN_CONFIRM
NFS4ERR_ADMIN_REVOKED,
NFS4ERR_BADHANDLE,
NFS4ERR_BAD_SEQID,
NFS4ERR_BAD_STATEID,
NFS4ERR_BADXDR,
NFS4ERR_EXPIRED,
NFS4ERR_FHEXPIRED,
NFS4ERR_INVAL,
NFS4ERR_ISDIR,
NFS4ERR_LEASE_MOVED,
NFS4ERR_MOVED,
NFS4ERR_NOFILEHANDLE,
NFS4ERR_OLD_STATEID,
NFS4ERR_RESOURCE,
NFS4ERR_SERVERFAULT,
NFS4ERR_STALE,
NFS4ERR_STALE_STATEID
OPEN_DOWNGRADE
NFS4ERR_ADMIN_REVOKED,
NFS4ERR_BADHANDLE,
NFS4ERR_BAD_SEQID,
NFS4ERR_BAD_STATEID,
NFS4ERR_BADXDR,
NFS4ERR_DELAY,
NFS4ERR_EXPIRED,
NFS4ERR_FHEXPIRED,
NFS4ERR_INVAL,
NFS4ERR_LEASE_MOVED,
NFS4ERR_LOCKS_HELD,
NFS4ERR_MOVED,
NFS4ERR_NOFILEHANDLE,
NFS4ERR_OLD_STATEID,
NFS4ERR_RESOURCE,
NFS4ERR_ROFS,
NFS4ERR_SERVERFAULT,
NFS4ERR_STALE,
NFS4ERR_STALE_STATEID
PUTFH
NFS4ERR_BADHANDLE,
NFS4ERR_BADXDR,
NFS4ERR_DELAY,
NFS4ERR_FHEXPIRED,
NFS4ERR_MOVED,
NFS4ERR_SERVERFAULT,
NFS4ERR_STALE,
NFS4ERR_WRONGSEC
PUTPUBFH
NFS4ERR_DELAY,
NFS4ERR_SERVERFAULT,
NFS4ERR_WRONGSEC
PUTROOTFH
NFS4ERR_DELAY,
NFS4ERR_SERVERFAULT,
NFS4ERR_WRONGSEC
READ
NFS4ERR_ACCESS,
NFS4ERR_ADMIN_REVOKED,
NFS4ERR_BADHANDLE,
NFS4ERR_BAD_STATEID,
NFS4ERR_BADXDR,
NFS4ERR_DELAY,
NFS4ERR_EXPIRED,
NFS4ERR_FHEXPIRED,
NFS4ERR_GRACE,
NFS4ERR_INVAL,
NFS4ERR_IO,
NFS4ERR_ISDIR,
NFS4ERR_LEASE_MOVED,
NFS4ERR_LOCKED,
NFS4ERR_MOVED,
NFS4ERR_NOFILEHANDLE,
NFS4ERR_OLD_STATEID,
NFS4ERR_OPENMODE,
NFS4ERR_RESOURCE,
NFS4ERR_SERVERFAULT,
NFS4ERR_STALE,
NFS4ERR_STALE_STATEID,
NFS4ERR_SYMLINK
READDIR
NFS4ERR_ACCESS,
NFS4ERR_BAD_COOKIE,
NFS4ERR_BADHANDLE,
NFS4ERR_BADXDR,
NFS4ERR_DELAY,
NFS4ERR_FHEXPIRED,
NFS4ERR_INVAL,
NFS4ERR_IO,
NFS4ERR_MOVED,
NFS4ERR_NOFILEHANDLE,
NFS4ERR_NOTDIR,
NFS4ERR_NOT_SAME,
NFS4ERR_RESOURCE,
NFS4ERR_SERVERFAULT,
NFS4ERR_STALE,
NFS4ERR_TOOSMALL
READLINK
NFS4ERR_ACCESS,
NFS4ERR_BADHANDLE,
NFS4ERR_DELAY,
NFS4ERR_FHEXPIRED,
NFS4ERR_INVAL,
NFS4ERR_IO,
NFS4ERR_ISDIR,
NFS4ERR_MOVED,
NFS4ERR_NOFILEHANDLE,
NFS4ERR_NOTSUPP,
NFS4ERR_RESOURCE,
NFS4ERR_SERVERFAULT,
NFS4ERR_STALE
RELEASE_LOCKOWNER
NFS4ERR_BADXDR,
NFS4ERR_EXPIRED,
NFS4ERR_LEASE_MOVED,
NFS4ERR_LOCKS_HELD,
NFS4ERR_RESOURCE,
NFS4ERR_SERVERFAULT,
NFS4ERR_STALE_CLIENTID
REMOVE
NFS4ERR_ACCESS,
NFS4ERR_BADCHAR,
NFS4ERR_BADHANDLE,
NFS4ERR_BADNAME,
NFS4ERR_BADXDR,
NFS4ERR_DELAY,
NFS4ERR_FHEXPIRED,
NFS4ERR_FILE_OPEN,
NFS4ERR_GRACE,
NFS4ERR_INVAL,
NFS4ERR_IO,
NFS4ERR_MOVED,
NFS4ERR_NAMETOOLONG,
NFS4ERR_NOENT,
NFS4ERR_NOFILEHANDLE,
NFS4ERR_NOTDIR,
NFS4ERR_NOTEMPTY,
NFS4ERR_RESOURCE,
NFS4ERR_ROFS,
NFS4ERR_SERVERFAULT,
NFS4ERR_STALE
RENAME
NFS4ERR_ACCESS,
NFS4ERR_BADCHAR,
NFS4ERR_BADHANDLE,
NFS4ERR_BADNAME,
NFS4ERR_BADXDR,
NFS4ERR_DELAY,
NFS4ERR_DQUOT,
NFS4ERR_EXIST,
NFS4ERR_FHEXPIRED,
NFS4ERR_FILE_OPEN,
NFS4ERR_GRACE,
NFS4ERR_INVAL,
NFS4ERR_IO,
NFS4ERR_MOVED,
NFS4ERR_NAMETOOLONG,
NFS4ERR_NOENT,
NFS4ERR_NOFILEHANDLE,
NFS4ERR_NOSPC,
NFS4ERR_NOTDIR,
NFS4ERR_NOTEMPTY,
NFS4ERR_RESOURCE,
NFS4ERR_ROFS,
NFS4ERR_SERVERFAULT,
NFS4ERR_STALE,
NFS4ERR_WRONGSEC,
NFS4ERR_XDEV
RENEW
NFS4ERR_ACCESS,
NFS4ERR_BADXDR,
NFS4ERR_CB_PATH_DOWN,
NFS4ERR_EXPIRED,
NFS4ERR_LEASE_MOVED,
NFS4ERR_RESOURCE,
NFS4ERR_SERVERFAULT,
NFS4ERR_STALE_CLIENTID
RESTOREFH
NFS4ERR_BADHANDLE,
NFS4ERR_FHEXPIRED,
NFS4ERR_MOVED,
NFS4ERR_RESOURCE,
NFS4ERR_RESTOREFH,
NFS4ERR_SERVERFAULT,
NFS4ERR_STALE,
NFS4ERR_WRONGSEC
SAVEFH
NFS4ERR_BADHANDLE,
NFS4ERR_FHEXPIRED,
NFS4ERR_MOVED,
NFS4ERR_NOFILEHANDLE,
NFS4ERR_RESOURCE,
NFS4ERR_SERVERFAULT,
NFS4ERR_STALE
SECINFO
NFS4ERR_ACCESS,
NFS4ERR_BADCHAR,
NFS4ERR_BADHANDLE,
NFS4ERR_BADNAME,
NFS4ERR_BADXDR,
NFS4ERR_DELAY,
NFS4ERR_FHEXPIRED,
NFS4ERR_INVAL,
NFS4ERR_MOVED,
NFS4ERR_NAMETOOLONG,
NFS4ERR_NOENT,
NFS4ERR_NOFILEHANDLE,
NFS4ERR_NOTDIR,
NFS4ERR_RESOURCE,
NFS4ERR_SERVERFAULT,
NFS4ERR_STALE
SETATTR
NFS4ERR_ACCESS,
NFS4ERR_ADMIN_REVOKED,
NFS4ERR_ATTRNOTSUPP,
NFS4ERR_BADCHAR,
NFS4ERR_BADHANDLE,
NFS4ERR_BADOWNER,
NFS4ERR_BAD_STATEID,
NFS4ERR_BADXDR,
NFS4ERR_DELAY,
NFS4ERR_DQUOT,
NFS4ERR_EXPIRED,
NFS4ERR_FBIG,
NFS4ERR_FHEXPIRED,
NFS4ERR_GRACE,
NFS4ERR_INVAL,
NFS4ERR_IO,
NFS4ERR_ISDIR,
NFS4ERR_LEASE_MOVED,
NFS4ERR_LOCKED,
NFS4ERR_MOVED,
NFS4ERR_NOFILEHANDLE,
NFS4ERR_NOSPC,
NFS4ERR_OLD_STATEID,
NFS4ERR_OPENMODE,
NFS4ERR_PERM,
NFS4ERR_RESOURCE,
NFS4ERR_ROFS,
NFS4ERR_SERVERFAULT,
NFS4ERR_STALE,
NFS4ERR_STALE_STATEID
SETCLIENTID
NFS4ERR_BADXDR,
NFS4ERR_CLID_INUSE,
NFS4ERR_DELAY,
NFS4ERR_INVAL,
NFS4ERR_RESOURCE,
NFS4ERR_SERVERFAULT
SETCLIENTID_CONFIRM
NFS4ERR_BADXDR,
NFS4ERR_CLID_INUSE,
NFS4ERR_DELAY,
NFS4ERR_RESOURCE,
NFS4ERR_SERVERFAULT,
NFS4ERR_STALE_CLIENTID
VERIFY
NFS4ERR_ACCESS,
NFS4ERR_ATTRNOTSUPP,
NFS4ERR_BADCHAR,
NFS4ERR_BADHANDLE,
NFS4ERR_BADXDR,
NFS4ERR_DELAY,
NFS4ERR_FHEXPIRED,
NFS4ERR_GRACE,
NFS4ERR_INVAL,
NFS4ERR_IO,
NFS4ERR_MOVED,
NFS4ERR_NOFILEHANDLE,
NFS4ERR_NOT_SAME,
NFS4ERR_RESOURCE,
NFS4ERR_SERVERFAULT,
NFS4ERR_STALE
WRITE
NFS4ERR_ACCESS,
NFS4ERR_ADMIN_REVOKED,
NFS4ERR_BADHANDLE,
NFS4ERR_BAD_STATEID,
NFS4ERR_BADXDR,
NFS4ERR_DELAY,
NFS4ERR_DQUOT,
NFS4ERR_EXPIRED,
NFS4ERR_FBIG,
NFS4ERR_FHEXPIRED,
NFS4ERR_GRACE,
NFS4ERR_INVAL,
NFS4ERR_IO,
NFS4ERR_ISDIR,
NFS4ERR_LEASE_MOVED,
NFS4ERR_LOCKED,
NFS4ERR_MOVED,
NFS4ERR_NOFILEHANDLE,
NFS4ERR_NOSPC,
NFS4ERR_NXIO,
NFS4ERR_OLD_STATEID,
NFS4ERR_OPENMODE,
NFS4ERR_RESOURCE,
NFS4ERR_ROFS,
NFS4ERR_SERVERFAULT,
NFS4ERR_STALE,
NFS4ERR_STALE_STATEID,
NFS4ERR_SYMLINK
This section contains a table that gives the valid error returns
for each callback operation. The error code NFS4_OK (indicating
no error) is not listed but should be understood to be returnable
by all callback operations, with the exception of CB_ILLEGAL.
Callback OperationErrorsCB_GETATTR
NFS4ERR_BADHANDLE,
NFS4ERR_BADXDR,
NFS4ERR_DELAY,
NFS4ERR_INVAL,
NFS4ERR_SERVERFAULT
CB_ILLEGAL
NFS4ERR_BADXDR,
NFS4ERR_OP_ILLEGAL
CB_RECALL
NFS4ERR_BADHANDLE,
NFS4ERR_BAD_STATEID,
NFS4ERR_BADXDR,
NFS4ERR_DELAY,
NFS4ERR_SERVERFAULT
ErrorOperationsNFS4ERR_ACCESS
ACCESS,
COMMIT,
CREATE,
GETATTR,
LINK,
LOCK,
LOCKT,
LOCKU,
LOOKUP,
LOOKUPP,
NVERIFY,
OPEN,
OPENATTR,
READ,
READDIR,
READLINK,
REMOVE,
RENAME,
RENEW,
SECINFO,
SETATTR,
VERIFY,
WRITE
NFS4ERR_ADMIN_REVOKED
CLOSE,
DELEGRETURN,
LOCK,
LOCKU,
OPEN,
OPEN_CONFIRM,
OPEN_DOWNGRADE,
READ,
SETATTR,
WRITE
NFS4ERR_ATTRNOTSUPP
CREATE,
NVERIFY,
OPEN,
SETATTR,
VERIFY
NFS4ERR_BADCHAR
CREATE,
LINK,
LOOKUP,
NVERIFY,
OPEN,
REMOVE,
RENAME,
SECINFO,
SETATTR,
VERIFY
NFS4ERR_BADHANDLE
ACCESS,
CB_GETATTR,
CB_RECALL,
CLOSE,
COMMIT,
CREATE,
GETATTR,
GETFH,
LINK,
LOCK,
LOCKT,
LOCKU,
LOOKUP,
LOOKUPP,
NVERIFY,
OPEN,
OPENATTR,
OPEN_CONFIRM,
OPEN_DOWNGRADE,
PUTFH,
READ,
READDIR,
READLINK,
REMOVE,
RENAME,
RESTOREFH,
SAVEFH,
SECINFO,
SETATTR,
VERIFY,
WRITE
NFS4ERR_BADNAME
CREATE,
LINK,
LOOKUP,
OPEN,
REMOVE,
RENAME,
SECINFO
NFS4ERR_BADOWNER
CREATE,
OPEN,
SETATTR
NFS4ERR_BADTYPE
CREATE
NFS4ERR_BADXDR
ACCESS,
CB_GETATTR,
CB_ILLEGAL,
CB_RECALL,
CLOSE,
COMMIT,
CREATE,
DELEGPURGE,
DELEGRETURN,
GETATTR,
ILLEGAL,
LINK,
LOCK,
LOCKT,
LOCKU,
LOOKUP,
NVERIFY,
OPEN,
OPENATTR,
OPEN_CONFIRM,
OPEN_DOWNGRADE,
PUTFH,
READ,
READDIR,
RELEASE_LOCKOWNER,
REMOVE,
RENAME,
RENEW,
SECINFO,
SETATTR,
SETCLIENTID,
SETCLIENTID_CONFIRM,
VERIFY,
WRITE
NFS4ERR_BAD_COOKIE
READDIR
NFS4ERR_BAD_RANGE
LOCK,
LOCKT,
LOCKU
NFS4ERR_BAD_SEQID
CLOSE,
LOCK,
LOCKU,
OPEN,
OPEN_CONFIRM,
OPEN_DOWNGRADE
NFS4ERR_BAD_STATEID
CB_RECALL,
CLOSE,
DELEGRETURN,
LOCK,
LOCKU,
OPEN,
OPEN_CONFIRM,
OPEN_DOWNGRADE,
READ,
SETATTR,
WRITE
NFS4ERR_CB_PATH_DOWN
RENEW
NFS4ERR_CLID_INUSE
SETCLIENTID,
SETCLIENTID_CONFIRM
NFS4ERR_DEADLOCK
LOCK
NFS4ERR_DELAY
ACCESS,
CB_GETATTR,
CB_RECALL,
CLOSE,
COMMIT,
CREATE,
DELEGPURGE,
DELEGRETURN,
GETATTR,
LINK,
LOCK,
LOCKT,
LOCKU,
LOOKUP,
LOOKUPP,
NVERIFY,
OPEN,
OPENATTR,
OPEN_DOWNGRADE,
PUTFH,
PUTPUBFH,
PUTROOTFH,
READ,
READDIR,
READLINK,
REMOVE,
RENAME,
SECINFO,
SETATTR,
SETCLIENTID,
SETCLIENTID_CONFIRM,
VERIFY,
WRITE
NFS4ERR_DENIED
LOCK,
LOCKT
NFS4ERR_DQUOT
CREATE,
LINK,
OPEN,
OPENATTR,
RENAME,
SETATTR,
WRITE
NFS4ERR_EXIST
CREATE,
LINK,
OPEN,
RENAME
NFS4ERR_EXPIRED
CLOSE,
DELEGRETURN,
LOCK,
LOCKT,
LOCKU,
OPEN,
OPEN_CONFIRM,
OPEN_DOWNGRADE,
READ,
RELEASE_LOCKOWNER,
RENEW,
SETATTR,
WRITE
NFS4ERR_FBIG
OPEN,
SETATTR,
WRITE
NFS4ERR_FHEXPIRED
ACCESS,
CLOSE,
COMMIT,
CREATE,
GETATTR,
GETFH,
LINK,
LOCK,
LOCKT,
LOCKU,
LOOKUP,
LOOKUPP,
NVERIFY,
OPEN,
OPENATTR,
OPEN_CONFIRM,
OPEN_DOWNGRADE,
PUTFH,
READ,
READDIR,
READLINK,
REMOVE,
RENAME,
RESTOREFH,
SAVEFH,
SECINFO,
SETATTR,
VERIFY,
WRITE
NFS4ERR_FILE_OPEN
LINK,
REMOVE,
RENAME
NFS4ERR_GRACE
GETATTR,
LOCK,
LOCKT,
LOCKU,
NVERIFY,
OPEN,
READ,
REMOVE,
RENAME,
SETATTR,
VERIFY,
WRITE
NFS4ERR_INVAL
ACCESS,
CB_GETATTR,
CLOSE,
COMMIT,
CREATE,
DELEGRETURN,
GETATTR,
LINK,
LOCK,
LOCKT,
LOCKU,
LOOKUP,
NVERIFY,
OPEN,
OPEN_CONFIRM,
OPEN_DOWNGRADE,
READ,
READDIR,
READLINK,
REMOVE,
RENAME,
SECINFO,
SETATTR,
SETCLIENTID,
VERIFY,
WRITE
NFS4ERR_IO
ACCESS,
COMMIT,
CREATE,
GETATTR,
LINK,
LOOKUP,
LOOKUPP,
NVERIFY,
OPEN,
OPENATTR,
READ,
READDIR,
READLINK,
REMOVE,
RENAME,
SETATTR,
VERIFY,
WRITE
NFS4ERR_ISDIR
CLOSE,
COMMIT,
LINK,
LOCK,
LOCKT,
LOCKU,
OPEN,
OPEN_CONFIRM,
READ,
READLINK,
SETATTR,
WRITE
NFS4ERR_LEASE_MOVED
CLOSE,
DELEGPURGE,
DELEGRETURN,
LOCK,
LOCKT,
LOCKU,
OPEN_CONFIRM,
OPEN_DOWNGRADE,
READ,
RELEASE_LOCKOWNER,
RENEW,
SETATTR,
WRITE
NFS4ERR_LOCKED
READ,
SETATTR,
WRITE
NFS4ERR_LOCKS_HELD
CLOSE,
OPEN_DOWNGRADE,
RELEASE_LOCKOWNER
NFS4ERR_LOCK_NOTSUPP
LOCK
NFS4ERR_LOCK_RANGE
LOCK,
LOCKT,
LOCKU
NFS4ERR_MLINK
LINK
NFS4ERR_MOVED
ACCESS,
CLOSE,
COMMIT,
CREATE,
DELEGRETURN,
GETATTR,
GETFH,
LINK,
LOCK,
LOCKT,
LOCKU,
LOOKUP,
LOOKUPP,
NVERIFY,
OPEN,
OPENATTR,
OPEN_CONFIRM,
OPEN_DOWNGRADE,
PUTFH,
READ,
READDIR,
READLINK,
REMOVE,
RENAME,
RESTOREFH,
SAVEFH,
SECINFO,
SETATTR,
VERIFY,
WRITE
NFS4ERR_NAMETOOLONG
CREATE,
LINK,
LOOKUP,
OPEN,
REMOVE,
RENAME,
SECINFO
NFS4ERR_NOENT
LINK,
LOOKUP,
LOOKUPP,
OPEN,
OPENATTR,
REMOVE,
RENAME,
SECINFO
NFS4ERR_NOFILEHANDLE
ACCESS,
CLOSE,
COMMIT,
CREATE,
DELEGRETURN,
GETATTR,
GETFH,
LINK,
LOCK,
LOCKT,
LOCKU,
LOOKUP,
LOOKUPP,
NVERIFY,
OPEN,
OPENATTR,
OPEN_CONFIRM,
OPEN_DOWNGRADE,
READ,
READDIR,
READLINK,
REMOVE,
RENAME,
SAVEFH,
SECINFO,
SETATTR,
VERIFY,
WRITE
NFS4ERR_NOSPC
CREATE,
LINK,
OPEN,
OPENATTR,
RENAME,
SETATTR,
WRITE
NFS4ERR_NOTDIR
CREATE,
LINK,
LOOKUP,
LOOKUPP,
OPEN,
READDIR,
REMOVE,
RENAME,
SECINFO
NFS4ERR_NOTEMPTY
REMOVE,
RENAME
NFS4ERR_NOTSUPP
DELEGPURGE,
DELEGRETURN,
LINK,
OPEN,
OPENATTR,
READLINK
NFS4ERR_NOT_SAME
READDIR,
VERIFY
NFS4ERR_NO_GRACE
LOCK,
OPEN
NFS4ERR_NXIO
WRITE
NFS4ERR_OLD_STATEID
CLOSE,
DELEGRETURN,
LOCK,
LOCKU,
OPEN,
OPEN_CONFIRM,
OPEN_DOWNGRADE,
READ,
SETATTR,
WRITE
NFS4ERR_OPENMODE
LOCK,
READ,
SETATTR,
WRITE
NFS4ERR_OP_ILLEGAL
CB_ILLEGAL,
ILLEGAL
NFS4ERR_PERM
CREATE,
OPEN,
SETATTR
NFS4ERR_RECLAIM_BAD
LOCK,
OPEN
NFS4ERR_RECLAIM_CONFLICT
LOCK,
OPEN
NFS4ERR_RESOURCE
ACCESS,
CLOSE,
COMMIT,
CREATE,
DELEGPURGE,
DELEGRETURN,
GETATTR,
GETFH,
LINK,
LOCK,
LOCKT,
LOCKU,
LOOKUP,
LOOKUPP,
OPEN,
OPENATTR,
OPEN_CONFIRM,
OPEN_DOWNGRADE,
READ,
READDIR,
READLINK,
RELEASE_LOCKOWNER,
REMOVE,
RENAME,
RENEW,
RESTOREFH,
SAVEFH,
SECINFO,
SETATTR,
SETCLIENTID,
SETCLIENTID_CONFIRM,
VERIFY,
WRITE
NFS4ERR_RESTOREFH
RESTOREFH
NFS4ERR_ROFS
COMMIT,
CREATE,
LINK,
OPEN,
OPENATTR,
OPEN_DOWNGRADE,
REMOVE,
RENAME,
SETATTR,
WRITE
NFS4ERR_SAME
NVERIFY
NFS4ERR_SERVERFAULT
ACCESS,
CB_GETATTR,
CB_RECALL,
CLOSE,
COMMIT,
CREATE,
DELEGPURGE,
DELEGRETURN,
GETATTR,
GETFH,
LINK,
LOCK,
LOCKT,
LOCKU,
LOOKUP,
LOOKUPP,
NVERIFY,
OPEN,
OPENATTR,
OPEN_CONFIRM,
OPEN_DOWNGRADE,
PUTFH,
PUTPUBFH,
PUTROOTFH,
READ,
READDIR,
READLINK,
RELEASE_LOCKOWNER,
REMOVE,
RENAME,
RENEW,
RESTOREFH,
SAVEFH,
SECINFO,
SETATTR,
SETCLIENTID,
SETCLIENTID_CONFIRM,
VERIFY,
WRITE
NFS4ERR_SHARE_DENIED
OPEN
NFS4ERR_STALE
ACCESS,
CLOSE,
COMMIT,
CREATE,
DELEGRETURN,
GETATTR,
GETFH,
LINK,
LOCK,
LOCKT,
LOCKU,
LOOKUP,
LOOKUPP,
NVERIFY,
OPEN,
OPENATTR,
OPEN_CONFIRM,
OPEN_DOWNGRADE,
PUTFH,
READ,
READDIR,
READLINK,
REMOVE,
RENAME,
RESTOREFH,
SAVEFH,
SECINFO,
SETATTR,
VERIFY,
WRITE
NFS4ERR_STALE_CLIENTID
DELEGPURGE,
LOCK,
LOCKT,
OPEN,
RELEASE_LOCKOWNER,
RENEW,
SETCLIENTID_CONFIRM
NFS4ERR_STALE_STATEID
CLOSE,
DELEGRETURN,
LOCK,
LOCKU,
OPEN_CONFIRM,
OPEN_DOWNGRADE,
READ,
SETATTR,
WRITE
NFS4ERR_SYMLINK
COMMIT,
LOOKUP,
LOOKUPP,
OPEN,
READ,
WRITE
NFS4ERR_TOOSMALL
READDIR
NFS4ERR_WRONGSEC
LINK,
LOOKUP,
LOOKUPP,
OPEN,
PUTFH,
PUTPUBFH,
PUTROOTFH,
RENAME,
RESTOREFH
NFS4ERR_XDEV
LINK,
RENAME
For the NFSv4 RPC program, there are two traditional RPC
procedures: NULL and COMPOUND. All other functionality is defined as
a set of operations, and these operations are defined in normal
XDR/RPC syntax and semantics. However, these operations are
encapsulated within the COMPOUND procedure. This requires that the
client combine one or more of the NFSv4 operations into a
single request.
The NFS4_CALLBACK program is used to provide server-to-client
signaling and is constructed in a fashion similar to the
NFSv4 program. The procedures CB_NULL and CB_COMPOUND are defined in
the same way as NULL and COMPOUND are within the NFS program. The
CB_COMPOUND request also encapsulates the remaining operations of the
NFS4_CALLBACK program. There is no predefined RPC program number for
the NFS4_CALLBACK program. It is up to the client to specify a
program number in the "transient" program range. The program and
port numbers of the NFS4_CALLBACK program are provided by the client
as part of the SETCLIENTID/SETCLIENTID_CONFIRM sequence. The program
and port can be changed by another SETCLIENTID/SETCLIENTID_CONFIRM
sequence, and it is possible to use the sequence to change them
within a client incarnation without removing relevant leased client
state.
The COMPOUND procedure provides the opportunity for better
performance within high-latency networks. The client can avoid
cumulative latency of multiple RPCs by combining multiple dependent
operations into a single COMPOUND procedure. A COMPOUND operation
may provide for protocol simplification by allowing the client to
combine basic procedures into a single request that is customized for
the client's environment.
The CB_COMPOUND procedure precisely parallels the features of
COMPOUND as described above.
The basic structure of the COMPOUND procedure is:
+-----+--------------+--------+-----------+-----------+-----------+--
| tag | minorversion | numops | op + args | op + args | op + args |
+-----+--------------+--------+-----------+-----------+-----------+--
and the reply's structure is:
+------------+-----+--------+-----------------------+--
|last status | tag | numres | status + op + results |
+------------+-----+--------+-----------------------+--
The numops and numres fields, used in the depiction above, represent
the count for the counted array encoding used to signify the number of
arguments or results encoded in the request and response. As per the
XDR encoding, these counts must match exactly the number of operation
arguments or results encoded.
The server will process the COMPOUND procedure by evaluating each of
the operations within the COMPOUND procedure in order. Each
component operation consists of a 32-bit operation code, followed by
the argument of length determined by the type of operation. The
results of each operation are encoded in sequence into a reply
buffer. The results of each operation are preceded by the opcode and
a status code (normally zero). If an operation results in a non-zero
status code, the status will be encoded, evaluation of the
COMPOUND sequence will halt, and the reply will be returned. Note
that evaluation stops even in the event of "non-error" conditions
such as NFS4ERR_SAME.
There are no atomicity requirements for the operations contained
within the COMPOUND procedure. The operations being evaluated as
part of a COMPOUND request may be evaluated simultaneously with other
COMPOUND requests that the server receives.
A COMPOUND is not a transaction, and it is the client's
responsibility to recover from any partially completed
COMPOUND procedure. These may occur at any point due to errors such as
NFS4ERR_RESOURCE and NFS4ERR_DELAY. Note that these errors can occur
in an otherwise valid operation string. Further, a server reboot that
occurs in the middle of processing a COMPOUND procedure may leave the
client with the difficult task of determining how far COMPOUND
processing has proceeded. Therefore, the client should avoid overly
complex COMPOUND procedures in the event of the failure of an
operation within the procedure.
Each operation assumes a current filehandle and a
saved filehandle that are available as part of the execution
context of the COMPOUND request. Operations may set, change, or
return the current filehandle. The saved filehandle is used for
temporary storage of a filehandle value and as operands for the
RENAME and LINK operations.
NFSv4 operations that modify the file system are synchronous.
When an operation is successfully completed at the server, the client
can trust that any data associated with the request is now in stable
storage (the one exception is in the case of the file data in a WRITE
operation with the UNSTABLE4 option specified).
This implies that any previous operations within the same
COMPOUND request are also reflected in stable storage. This
behavior enables the client's ability to recover from a
partially executed COMPOUND request that may have resulted
from the failure of the server. For example, if a
COMPOUND request contains operations A and B and the
server is unable to send a response to the client, then depending on
the progress the server made in servicing the request, the result of
both operations may be reflected in stable storage or just
operation A may be reflected. The server must not have
just the results of operation B in stable storage.
The operations encoded in the COMPOUND procedure are identified by
operation values. To avoid overlap with the RPC procedure numbers,
operations 0 (zero) and 1 are not defined. Operation 2 is not
defined but is reserved for future use with minor versioning.
<null>
void;
void;
Standard NULL procedure. Void argument, void response.
This procedure has no functionality associated with it.
Because of this, it is sometimes used to measure the overhead
of processing a service request. Therefore, the server
should ensure that no unnecessary work is done in servicing
this procedure.
compoundargs -> compoundres
union nfs_argop4 switch (nfs_opnum4 argop) {
case <OPCODE>: <argument>;
...
};
struct COMPOUND4args {
utf8str_cs tag;
uint32_t minorversion;
nfs_argop4 argarray<>;
};
union nfs_resop4 switch (nfs_opnum4 resop) {
case <OPCODE>: <argument>;
...
};
struct COMPOUND4res {
nfsstat4 status;
utf8str_cs tag;
nfs_resop4 resarray<>;
};
The COMPOUND procedure is used to combine one or more of
the NFS operations into a single RPC request. The main
NFS RPC program has two main procedures: NULL and COMPOUND.
All other operations use the COMPOUND procedure as a wrapper.
The COMPOUND procedure is used to combine individual operations
into a single RPC request. The server interprets each of
the operations in turn. If an operation is executed by the
server and the status of that operation is NFS4_OK, then
the next operation in the COMPOUND procedure is executed.
The server continues this process until there are no more
operations to be executed or one of the operations has a
status value other than NFS4_OK.
In the processing of the COMPOUND procedure, the server may
find that it does not have the available resources to execute
any or all of the operations within the COMPOUND sequence.
In this case, the error NFS4ERR_RESOURCE will be returned
for the particular operation within the COMPOUND procedure
where the resource exhaustion occurred. This assumes that
all previous operations within the COMPOUND sequence have
been evaluated successfully. The results for all of the
evaluated operations must be returned to the client.
The server will generally choose between two methods of
decoding the client's request. The first would be the
traditional one-pass XDR decode, in which decoding of the
entire COMPOUND precedes execution of any operation within it.
If there is an XDR decoding error in this case, an RPC XDR
decode error would be returned. The second method would be
to make an initial pass to decode the basic COMPOUND request
and then to XDR decode each of the individual operations, as
the server is ready to execute it. In this case, the server
may encounter an XDR decode error during such an operation
decode, after previous operations within the COMPOUND have
been executed. In this case, the server would return the
error NFS4ERR_BADXDR to signify the decode error.
The COMPOUND arguments contain a minorversion field.
The initial and default value for this field is 0 (zero).
This field will be used by future minor versions such that
the client can communicate to the server what minor version is
being requested. If the server receives a COMPOUND procedure
with a minorversion field value that it does not support,
the server MUST return an error of NFS4ERR_MINOR_VERS_MISMATCH
and a zero-length resultdata array.
Contained within the COMPOUND results is a status field.
If the results array length is non-zero, this status must
be equivalent to the status of the last operation that was
executed within the COMPOUND procedure. Therefore, if an
operation incurred an error, then the status value will be
the same error value as is being returned for the operation
that failed.
Note that operations 0 (zero), 1 (one), and 2 (two) are
not defined for the COMPOUND procedure. It is possible
that the server receives a request that contains an operation
that is less than the first legal operation (OP_ACCESS) or
greater than the last legal operation (OP_RELEASE_LOCKOWNER).
In this case, the server's response will encode the opcode
OP_ILLEGAL rather than the illegal opcode of the request.
The status field in the ILLEGAL return results will be set to
NFS4ERR_OP_ILLEGAL. The COMPOUND procedure's return results
will also be NFS4ERR_OP_ILLEGAL.
The definition of the "tag" in the request is left to the
implementer. It may be used to summarize the content of
the COMPOUND request for the benefit of packet sniffers and
engineers debugging implementations. However, the value of
"tag" in the response SHOULD be the same value as the value
provided in the request. This applies to the tag field of the
CB_COMPOUND procedure as well.
The current filehandle and the saved filehandle are used
throughout the protocol. Most operations implicitly use
the current filehandle as an argument, and many set
the current filehandle as part of the results.
The combination of client-specified sequences
of operations and current and saved filehandle
arguments and results allows for greater protocol
flexibility. The best or easiest example of current
filehandle usage is a sequence like the following:
PUTFH fh1 {fh1}
LOOKUP "compA" {fh2}
GETATTR {fh2}
LOOKUP "compB" {fh3}
GETATTR {fh3}
LOOKUP "compC" {fh4}
GETATTR {fh4}
GETFH
In this example, the PUTFH ()
operation explicitly sets the current filehandle value,
while the result of each LOOKUP operation sets
the current filehandle value to the resultant file system
object. Also, the client is able to insert GETATTR operations
using the current filehandle as an argument.
The PUTROOTFH () and
PUTPUBFH () operations also set the
current filehandle. The above example would replace "PUTFH fh1" with
PUTROOTFH or PUTPUBFH with no filehandle argument in order to
achieve the same effect (on the assumption that "compA" is directly
below the root of the namespace).
Along with the current filehandle, there is a saved filehandle.
While the current filehandle is set as the result of
operations like LOOKUP, the saved filehandle must be set
directly with the use of the SAVEFH operation. The SAVEFH
operation copies the current filehandle value to the saved
value. The saved filehandle value is used in combination with
the current filehandle value for the LINK and RENAME
operations. The RESTOREFH operation will copy the saved
filehandle value to the current filehandle value; as a result,
the saved filehandle value may be used as a sort of
"scratch" area for the client's series of operations.
Since an error of any type may occur after only a portion
of the operations have been evaluated, the client must be
prepared to recover from any failure. If the source of
an NFS4ERR_RESOURCE error was a complex or lengthy set of
operations, it is likely that if the number of operations were
reduced the server would be able to evaluate them successfully.
Therefore, the client is responsible for dealing with this
type of complexity in recovery.
A single compound should not contain multiple operations
that have different values for the clientid field used in
OPEN, LOCK, or RENEW. This can cause confusion in cases in
which operations that do not contain clientids have potential
interactions with operations that do. When only a single
clientid has been used, it is clear what client is being
referenced. For a particular example involving the interaction
of OPEN and GETATTR, see .
(cfh), accessreq -> supported, accessrights
const ACCESS4_READ = 0x00000001;
const ACCESS4_LOOKUP = 0x00000002;
const ACCESS4_MODIFY = 0x00000004;
const ACCESS4_EXTEND = 0x00000008;
const ACCESS4_DELETE = 0x00000010;
const ACCESS4_EXECUTE = 0x00000020;
struct ACCESS4args {
/* CURRENT_FH: object */
uint32_t access;
};
struct ACCESS4resok {
uint32_t supported;
uint32_t access;
};
union ACCESS4res switch (nfsstat4 status) {
case NFS4_OK:
ACCESS4resok resok4;
default:
void;
};
ACCESS determines the access rights that a user, as identified
by the credentials in the RPC request, has with respect to
the file system object specified by the current filehandle.
The client encodes the set of access rights that are to be
checked in the bitmask "access". The server checks the
permissions encoded in the bitmask. If a status of NFS4_OK
is returned, two bitmasks are included in the response.
The first, "supported", represents the access rights for
which the server can verify reliably. The second, "access",
represents the access rights available to the user for the
filehandle provided. On success, the current filehandle
retains its value.
Note that the supported field will contain only as many values
as were originally sent in the arguments. For example, if the
client sends an ACCESS operation with only the ACCESS4_READ
value set and the server supports this value, the server
will return only ACCESS4_READ even if it could have reliably
checked other values.
The results of this operation are necessarily advisory
in nature. A return status of NFS4_OK and the appropriate
bit set in the bitmask do not imply that such access will
be allowed to the file system object in the future. This is
because access rights can be revoked by the server at any time.
The following access permissions may be requested:
Read data from file or read a directory.
Look up a name in a directory (no meaning for
non&nbhy;directory objects).
Rewrite existing file data or modify existing directory
entries.
Write new data or add directory entries.
Delete an existing directory entry.
Execute file (no meaning for a directory).
On success, the current filehandle retains its value.
In general, it is not sufficient for the client to attempt to
deduce access permissions by inspecting the uid, gid, and mode
fields in the file attributes or by attempting to interpret
the contents of the ACL attribute. This is because the server
may perform uid or gid mapping or enforce additional access
control restrictions. It is also possible that the server
may not be in the same ID space as the client. In these cases
(and perhaps others), the client cannot reliably perform an
access check with only current file attributes.
In the NFSv2 protocol, the only reliable way to
determine whether an operation was allowed was to try it and
see if it succeeded or failed. Using the ACCESS operation in
the NFSv4 protocol, the client can ask the server to
indicate whether or not one or more classes of operations are
permitted. The ACCESS operation is provided to allow clients
to check before doing a series of operations that might result
in an access failure. The OPEN operation provides a point
where the server can verify access to the file object and the
method to return that information to the client. The ACCESS
operation is still useful for directory operations or for use
in the case where the UNIX API "access" is used on the client.
The information returned by the server in response to an ACCESS
call is not permanent. It was correct at the exact time
that the server performed the checks, but not necessarily
afterward. The server can revoke access permission at
any time.
The client should use the effective credentials of the user
to build the authentication information in the ACCESS request
used to determine access rights. It is the effective user
and group credentials that are used in subsequent READ and
WRITE operations.
Many implementations do not directly support the ACCESS4_DELETE
permission. Operating systems like UNIX will ignore
the ACCESS4_DELETE bit if set on an access request on a
non-directory object. In these systems, delete permission on a
file is determined by the access permissions on the directory
in which the file resides, instead of being determined by the
permissions of the file itself. Therefore, the mask returned
enumerating which access rights can be supported will have
the ACCESS4_DELETE value set to 0. This indicates to the
client that the server was unable to check that particular
access right. The ACCESS4_DELETE bit in the access mask
returned will then be ignored by the client.
(cfh), seqid, open_stateid -> open_stateid
struct CLOSE4args {
/* CURRENT_FH: object */
seqid4 seqid;
stateid4 open_stateid;
};
union CLOSE4res switch (nfsstat4 status) {
case NFS4_OK:
stateid4 open_stateid;
default:
void;
};
The CLOSE operation releases share reservations for the regular
or named attribute file as specified by the current filehandle.
The share reservations and other state information released at
the server as a result of this CLOSE are only associated with
the supplied stateid. The sequence id provides for the correct
ordering. State associated with other OPENs is not affected.
If byte-range locks are held, the client SHOULD release all locks
before issuing a CLOSE. The server MAY free all outstanding
locks on CLOSE, but some servers may not support the CLOSE
of a file that still has byte-range locks held. The server MUST
return failure if any locks would exist after the CLOSE.
On success, the current filehandle retains its value.
Even though CLOSE returns a stateid, this stateid is not
useful to the client and should be treated as deprecated.
CLOSE "shuts down" the state associated with all OPENs for
the file by a single open-owner. As noted above, CLOSE will
either release all file locking state or return an error.
Therefore, the stateid returned by CLOSE is not useful for
the operations that follow.
(cfh), offset, count -> verifier
struct COMMIT4args {
/* CURRENT_FH: file */
offset4 offset;
count4 count;
};
struct COMMIT4resok {
verifier4 writeverf;
};
union COMMIT4res switch (nfsstat4 status) {
case NFS4_OK:
COMMIT4resok resok4;
default:
void;
};
The COMMIT operation forces or flushes data to stable
storage for the file specified by the current filehandle.
The flushed data is that which was previously written with
a WRITE operation that had the stable field set to UNSTABLE4.
The offset specifies the position within the file where the
flush is to begin. An offset value of 0 (zero) means to
flush data starting at the beginning of the file. The count
specifies the number of bytes of data to flush. If count is 0
(zero), a flush from the offset to the end of the file is done.
The server returns a write verifier upon successful completion
of the COMMIT. The write verifier is used by the client to
determine if the server has restarted or rebooted between
the initial WRITE(s) and the COMMIT. The client does this
by comparing the write verifier returned from the initial
writes and the verifier returned by the COMMIT operation.
The server must vary the value of the write verifier at each
server event or instantiation that may lead to a loss of
uncommitted data. Most commonly, this occurs when the server
is rebooted; however, other events at the server may result
in uncommitted data loss as well.
On success, the current filehandle retains its value.
The COMMIT operation is similar in operation and semantics
to the POSIX fsync() system call that synchronizes a file's
state with the disk (file data and metadata are flushed to
disk or stable storage). COMMIT performs the same operation
for a client, flushing any unsynchronized data and metadata
on the server to the server's disk or stable storage for
the specified file. Like fsync(), it may be that there
is some modified data or no modified data to synchronize.
The data may have been synchronized by the server's normal
periodic buffer synchronization activity. COMMIT should
return NFS4_OK, unless there has been an unexpected error.
COMMIT differs from fsync() in that it is possible for the
client to flush a range of the file (most likely triggered
by a buffer-reclamation scheme on the client before the
file has been completely written).
The server implementation of COMMIT is reasonably simple.
If the server receives a full file COMMIT request that is
starting at offset 0 and count 0, it should do the equivalent
of fsync()'ing the file. Otherwise, it should arrange to
have the cached data in the range specified by offset and
count to be flushed to stable storage. In both cases, any
metadata associated with the file must be flushed to stable
storage before returning. It is not an error for there to be
nothing to flush on the server. This means that the data and
metadata that needed to be flushed have already been flushed
or lost during the last server failure.
The client implementation of COMMIT is a little more complex.
There are two reasons for wanting to commit a client buffer
to stable storage. The first is that the client wants
to reuse a buffer. In this case, the offset and count of
the buffer are sent to the server in the COMMIT request.
The server then flushes any cached data based on the offset
and count, and flushes any metadata associated with the file.
It then returns the status of the flush and the write verifier.
The other reason for the client to generate a COMMIT is for a
full file flush, such as may be done at CLOSE. In this case,
the client would gather all of the buffers for this file that
contain uncommitted data, do the COMMIT operation with an
offset of 0 and count of 0, and then free all of those buffers.
Any other dirty buffers would be sent to the server in the
normal fashion.
After a buffer is written by the client with the stable
parameter set to UNSTABLE4, the buffer must be considered
modified by the client until the buffer has been either flushed
via a COMMIT operation or written via a WRITE operation with
the stable parameter set to FILE_SYNC4 or DATA_SYNC4. This is
done to prevent the buffer from being freed and reused before the
data can be flushed to stable storage on the server.
When a response is returned from either a WRITE or a COMMIT
operation and it contains a write verifier that is different
than previously returned by the server, the client will
need to retransmit all of the buffers containing uncommitted
cached data to the server. How this is to be done is up to
the implementer. If there is only one buffer of interest,
then it should probably be sent back over in a WRITE request
with the appropriate stable parameter. If there is more
than one buffer, it might be worthwhile to retransmit all of
the buffers in WRITE requests with the stable parameter set
to UNSTABLE4 and then retransmit the COMMIT operation to flush
all of the data on the server to stable storage. The timing
of these retransmissions is left to the implementer.
The above description applies to page-cache-based systems
as well as buffer-cache-based systems. In those systems,
the virtual memory system will need to be modified instead
of the buffer cache.
(cfh), name, type, attrs -> (cfh), cinfo, attrset
union createtype4 switch (nfs_ftype4 type) {
case NF4LNK:
linktext4 linkdata;
case NF4BLK:
case NF4CHR:
specdata4 devdata;
case NF4SOCK:
case NF4FIFO:
case NF4DIR:
void;
default:
void; /* server should return NFS4ERR_BADTYPE */
};
struct CREATE4args {
/* CURRENT_FH: directory for creation */
createtype4 objtype;
component4 objname;
fattr4 createattrs;
};
struct CREATE4resok {
change_info4 cinfo;
bitmap4 attrset; /* attributes set */
};
union CREATE4res switch (nfsstat4 status) {
case NFS4_OK:
CREATE4resok resok4;
default:
void;
};
The CREATE operation creates a non-regular file object in
a directory with a given name. The OPEN operation is
used to create a regular file.
The objname specifies the name for the new object. The objtype
determines the type of object to be created: directory,
symlink, etc.
If an object of the same name already exists in the directory,
the server will return the error NFS4ERR_EXIST.
For the directory where the new file object was created, the
server returns change_info4 information in cinfo. With the
atomic field of the change_info4 struct, the server will
indicate if the before and after change attributes were
obtained atomically with respect to the file object creation.
If the objname is of zero length, NFS4ERR_INVAL will
be returned. The objname is also subject to the normal
UTF-8, character support, and name checks. See
for further discussion.
The current filehandle is replaced by that of the new object.
The createattrs field specifies the initial set of attributes for
the object. The set of attributes may include any writable
attribute valid for the object type. When the operation is
successful, the server will return to the client an attribute
mask signifying which attributes were successfully set for
the object.
If createattrs includes neither the owner attribute nor an
ACL with an ACE for the owner, and if the server's file system
both supports and requires an owner attribute (or an owner
ACE), then the server MUST derive the owner (or the owner
ACE). This would typically be from the principal indicated in
the RPC credentials of the call, but the server's operating
environment or file system semantics may dictate other methods
of derivation. Similarly, if createattrs includes neither the
group attribute nor a group ACE, and if the server's file system
both supports and requires the notion of a group attribute
(or group ACE), the server MUST derive the group attribute
(or the corresponding owner ACE) for the file. This could be
from the RPC's credentials, such as the group principal
if the credentials include it (such as with AUTH_SYS), from
the group identifier associated with the principal in the
credentials (e.g., POSIX systems have a user database
that has the group identifier for every user identifier),
inherited from the directory the object is created in, or whatever
else the server's operating environment or file system semantics
dictate. This applies to the OPEN operation too.
Conversely, it is possible the client will specify in
createattrs an owner attribute, group attribute, or ACL
that the principal indicated the RPC's credentials does
not have permissions to create files for. The error to be
returned in this instance is NFS4ERR_PERM. This applies to
the OPEN operation too.
If the client desires to set attribute values after the create,
a SETATTR operation can be added to the COMPOUND request so
that the appropriate attributes will be set.
clientid ->
struct DELEGPURGE4args {
clientid4 clientid;
};
struct DELEGPURGE4res {
nfsstat4 status;
};
DELEGPURGE purges all of the delegations awaiting recovery
for a given client. This is useful for clients that do not
commit delegation information to stable storage, to indicate
that conflicting requests need not be delayed by the server
awaiting recovery of delegation information.
This operation is provided to support clients that record delegation
information in stable storage on the client. In this case,
DELEGPURGE should be issued immediately after doing delegation
recovery (using CLAIM_DELEGATE_PREV) on all delegations known to
the client. Doing so will notify the server that no additional
delegations for the client will be recovered, allowing it to free
resources and avoid delaying other clients who make requests that
conflict with the unrecovered delegations. All clients SHOULD use
DELEGPURGE as part of recovery once it is known that no further
CLAIM_DELEGATE_PREV recovery will be done. This includes clients
that do not record delegation information in stable storage, who would
then do a DELEGPURGE immediately after SETCLIENTID_CONFIRM.
The set of delegations known to the server and the
client may be different. The reasons for this include:
A client may fail after making a request that resulted in delegation
but before it received the results and committed them to the client's
stable storage.
A client may fail after deleting its indication that a delegation exists
but before the delegation return is fully processed by the server.
In the case in which the server and the client restart, the server
may have limited persistent recording of delegations to a subset
of those in existence.
A client may have only persistently recorded information about a subset of
delegations.
The server MAY support DELEGPURGE, but its support or non-support should
match that of CLAIM_DELEGATE_PREV:
A server may support both DELEGPURGE and CLAIM_DELEGATE_PREV.
A server may support neither DELEGPURGE nor CLAIM_DELEGATE_PREV.
This fact allows a client starting up to determine if the server is prepared
to support persistent storage of delegation information and thus whether it
may use write-back caching to local persistent storage, relying on
CLAIM_DELEGATE_PREV recovery to allow such changed data to be flushed
safely to the server in the event of client restart.
(cfh), stateid ->
struct DELEGRETURN4args {
/* CURRENT_FH: delegated file */
stateid4 deleg_stateid;
};
struct DELEGRETURN4res {
nfsstat4 status;
};
DELEGRETURN returns the delegation represented by the current
filehandle and stateid.
Delegations may be returned when recalled or voluntarily
(i.e., before the server has recalled them). In either case,
the client must properly propagate state changed under the
context of the delegation to the server before returning
the delegation.
(cfh), attrbits -> attrbits, attrvals
struct GETATTR4args {
/* CURRENT_FH: directory or file */
bitmap4 attr_request;
};
struct GETATTR4resok {
fattr4 obj_attributes;
};
union GETATTR4res switch (nfsstat4 status) {
case NFS4_OK:
GETATTR4resok resok4;
default:
void;
};
The GETATTR operation will obtain attributes for the file system
object specified by the current filehandle. The client
sets a bit in the bitmap argument for each attribute value
that it would like the server to return. The server returns
an attribute bitmap that indicates the attribute values for
which it was able to return values, followed by the attribute values
ordered lowest attribute number first.
The server MUST return a value for each attribute that
the client requests if the attribute is supported by the
server. If the server does not support an attribute or
cannot approximate a useful value, then it MUST NOT return
the attribute value and MUST NOT set the attribute bit in
the result bitmap. The server MUST return an error if it
supports an attribute on the target but cannot obtain its
value. In that case, no attribute values will be returned.
File systems that are absent should be treated as having support for
a very small set of attributes as described in
-- even if previously, when
the file system was present, more attributes were supported.
All servers MUST support the REQUIRED attributes, as specified
in , for all file systems,
with the exception of absent file systems.
On success, the current filehandle retains its value.
Suppose there is an OPEN_DELEGATE_WRITE delegation held by another
client for the file in question, and size and/or change are among
the set of attributes being interrogated. The server has two choices.
First, the server can obtain the actual current value of these
attributes from the client holding the delegation by using
the CB_GETATTR callback. Second, the server, particularly when
the delegated client is unresponsive, can recall the
delegation in question. The GETATTR MUST NOT proceed
until one of the following occurs:
The requested attribute values are returned in the response to
CB_GETATTR.
The OPEN_DELEGATE_WRITE delegation is returned.
The OPEN_DELEGATE_WRITE delegation is revoked.
Unless one of the above happens very quickly,
one or more NFS4ERR_DELAY errors will be returned
while a delegation is outstanding.
(cfh) -> filehandle
/* CURRENT_FH: */
void;
struct GETFH4resok {
nfs_fh4 object;
};
union GETFH4res switch (nfsstat4 status) {
case NFS4_OK:
GETFH4resok resok4;
default:
void;
};
This operation returns the current filehandle value.
On success, the current filehandle retains its value.
Operations that change the current filehandle, like LOOKUP
or CREATE, do not automatically return the new filehandle
as a result. For instance, if a client needs to look up a
directory entry and obtain its filehandle, then the following
request is needed.
PUTFH (directory filehandle)
LOOKUP (entry name)
GETFH
(sfh), (cfh), newname -> (cfh), cinfo
struct LINK4args {
/* SAVED_FH: source object */
/* CURRENT_FH: target directory */
component4 newname;
};
struct LINK4resok {
change_info4 cinfo;
};
union LINK4res switch (nfsstat4 status) {
case NFS4_OK:
LINK4resok resok4;
default:
void;
};
The LINK operation creates an additional newname for the
file represented by the saved filehandle, as set by the
SAVEFH operation, in the directory represented by the current
filehandle. The existing file and the target directory must
reside within the same file system on the server. On success,
the current filehandle will continue to be the target
directory. If an object exists in the target directory with
the same name as newname, the server must return NFS4ERR_EXIST.
For the target directory, the server returns change_info4
information in cinfo. With the atomic field of the
change_info4 struct, the server will indicate if the before
and after change attributes were obtained atomically with
respect to the link creation.
If newname has a length of 0 (zero), or if newname does
not obey the UTF-8 definition, the error NFS4ERR_INVAL will
be returned.
Changes to any property of the "hard" linked files are
reflected in all of the linked files. When a link is made
to a file, the attributes for the file should have a value
for numlinks that is one greater than the value before the
LINK operation.
The statement "file and the target directory must reside within the
same file system on the server" means that the fsid fields in the
attributes for the objects are the same. If they reside on different
file systems, the error NFS4ERR_XDEV is returned. This error may be
returned by some servers when there is an internal partitioning of a
file system that the LINK operation would violate.
On some servers, "." and ".." are illegal values for newname, and the
error NFS4ERR_BADNAME will be returned if they are specified.
When the current filehandle designates a named attribute directory
and the object to be linked (the saved filehandle) is not a named
attribute for the same object, the error NFS4ERR_XDEV MUST be
returned. When the saved filehandle designates a named attribute and
the current filehandle is not the appropriate named attribute
directory, the error NFS4ERR_XDEV MUST also be returned.
When the current filehandle designates a named attribute directory
and the object to be linked (the saved filehandle) is a named
attribute within that directory, the server MAY return the error
NFS4ERR_NOTSUPP.
In the case that newname is already linked to the file represented by
the saved filehandle, the server will return NFS4ERR_EXIST.
Note that symbolic links are created with the CREATE operation.
(cfh) locktype, reclaim, offset, length, locker -> stateid
enum nfs_lock_type4 {
READ_LT = 1,
WRITE_LT = 2,
READW_LT = 3, /* blocking read */
WRITEW_LT = 4 /* blocking write */
};
/*
* For LOCK, transition from open_owner to new lock_owner
*/
struct open_to_lock_owner4 {
seqid4 open_seqid;
stateid4 open_stateid;
seqid4 lock_seqid;
lock_owner4 lock_owner;
};
/*
* For LOCK, existing lock_owner continues to request file locks
*/
struct exist_lock_owner4 {
stateid4 lock_stateid;
seqid4 lock_seqid;
};
union locker4 switch (bool new_lock_owner) {
case TRUE:
open_to_lock_owner4 open_owner;
case FALSE:
exist_lock_owner4 lock_owner;
};
/*
* LOCK/LOCKT/LOCKU: Record lock management
*/
struct LOCK4args {
/* CURRENT_FH: file */
nfs_lock_type4 locktype;
bool reclaim;
offset4 offset;
length4 length;
locker4 locker;
};
struct LOCK4denied {
offset4 offset;
length4 length;
nfs_lock_type4 locktype;
lock_owner4 owner;
};
struct LOCK4resok {
stateid4 lock_stateid;
};
union LOCK4res switch (nfsstat4 status) {
case NFS4_OK:
LOCK4resok resok4;
case NFS4ERR_DENIED:
LOCK4denied denied;
default:
void;
};
The LOCK operation requests a byte-range lock for the byte range
specified by the offset and length parameters. The lock type
is also specified to be one of the nfs_lock_type4s. If this
is a reclaim request, the reclaim parameter will be TRUE.
Bytes in a file may be locked even if those bytes are not
currently allocated to the file. To lock the file from a
specific offset through the end-of-file (no matter how long
the file actually is), use a length field with all bits set to
1 (one). If the length is zero, or if a length that is not
all bits set to one is specified, and the length when added to
the offset exceeds the maximum 64-bit unsigned integer value,
the error NFS4ERR_INVAL will result.
32-bit servers are servers that support locking for byte offsets that
fit within 32 bits (i.e., less than or equal to NFS4_UINT32_MAX). If
the client specifies a range that overlaps one or more bytes beyond
offset NFS4_UINT32_MAX but does not end at offset NFS4_UINT64_MAX,
then such a 32-bit server MUST return the error NFS4ERR_BAD_RANGE.
In the case that the lock is denied, the owner, offset,
and length of a conflicting lock are returned.
On success, the current filehandle retains its value.
If the server is unable to determine the exact offset and
length of the conflicting lock, the same offset and length
that were provided in the arguments should be returned in
the denied results.
contains a full
description of this and the other file locking operations.
LOCK operations are subject to permission checks and to checks
against the access type of the associated file. However, the
specific rights and modes required for various types of locks
reflect the semantics of the server-exported file system,
and are not specified by the protocol. For example, Windows
2000 allows a write lock of a file open for READ, while a
POSIX-compliant system does not.
When the client makes a lock request that corresponds to a
range that the lock-owner has locked already (with the same
or different lock type), or to a sub-region of such a range,
or to a region that includes multiple locks already granted
to that lock-owner, in whole or in part, and the server does
not support such locking operations (i.e., does not support
POSIX locking semantics), the server will return the error
NFS4ERR_LOCK_RANGE. In that case, the client may return an
error, or it may emulate the required operations, using only
LOCK for ranges that do not include any bytes already locked
by that lock-owner and LOCKU of locks held by that lock-owner
(specifying an exactly matching range and type). Similarly,
when the client makes a lock request that amounts to upgrading
(changing from a read lock to a write lock) or downgrading
(changing from a write lock to a read lock) an existing record
lock and the server does not support such a lock, the server
will return NFS4ERR_LOCK_NOTSUPP. Such operations may not
perfectly reflect the required semantics in the face of
conflicting lock requests from other clients.
When a client holds an OPEN_DELEGATE_WRITE delegation, the client
holding that delegation is assured that there are no opens by other
clients. Thus, there can be no conflicting LOCK operations from such
clients. Therefore, the client may be handling locking requests
locally, without doing LOCK operations on the server. If it does
that, it must be prepared to update the lock status on the server by
sending appropriate LOCK and LOCKU operations before returning the
delegation.
When one or more clients hold OPEN_DELEGATE_READ delegations, any
LOCK operation where the server is implementing mandatory locking
semantics MUST result in the recall of all such delegations. The
LOCK operation may not be granted until all such delegations are
returned or revoked. Except where this happens very quickly, one or
more NFS4ERR_DELAY errors will be returned to requests made while the
delegation remains outstanding.
The locker argument specifies the lock-owner that is associated with
the LOCK request. The locker4 structure is a switched union that
indicates whether the client has already created byte-range locking
state associated with the current open file and lock-owner. There
are multiple cases to be considered, corresponding to possible
combinations of whether locking state has been created for the current
open file and lock-owner, and whether the boolean new_lock_owner is set.
In all of the cases, there is a lock_seqid specified, whether the
lock-owner is specified explicitly or implicitly. This seqid value
is used
for checking lock-owner sequencing/replay issues. When the given
lock-owner is not known to the server, this establishes an initial
sequence value for the new lock-owner.
In the case in which the state has been created and the boolean is
false, the only part of the argument
other than lock_seqid is just a stateid representing
the set of locks associated with that open file and lock-owner.
In the case in which the state has been created and the boolean is
true, the server rejects the request with the error
NFS4ERR_BAD_SEQID. The only exception is where there is a
retransmission of a previous request in which the boolean was true.
In this case, the lock_seqid will match the original request, and
the response will reflect the final case, below.
In the case where no byte-range locking
state has been established and the boolean is true, the argument
contains an open_to_lock_owner structure that specifies the
stateid of the open file and the lock-owner to be used for
the lock. Note
that although the open-owner is not given explicitly, the
open_seqid associated with it is used to check for
open-owner sequencing issues. This case provides a method to
use the established state of the
open_stateid to transition to the use of a lock stateid.
(cfh) locktype, offset, length, owner -> {void, NFS4ERR_DENIED ->
owner}
struct LOCKT4args {
/* CURRENT_FH: file */
nfs_lock_type4 locktype;
offset4 offset;
length4 length;
lock_owner4 owner;
};
union LOCKT4res switch (nfsstat4 status) {
case NFS4ERR_DENIED:
LOCK4denied denied;
case NFS4_OK:
void;
default:
void;
};
The LOCKT operation tests the lock as specified in the
arguments. If a conflicting lock exists, the owner, offset,
length, and type of the conflicting lock are returned; if
no lock is held, nothing other than NFS4_OK is returned.
Lock types READ_LT and READW_LT are processed in the same
way in that a conflicting lock test is done without regard
to blocking or non-blocking. The same is true for WRITE_LT
and WRITEW_LT.
The ranges are specified as for LOCK. The NFS4ERR_INVAL
and NFS4ERR_BAD_RANGE errors are returned under the same
circumstances as for LOCK.
On success, the current filehandle retains its value.
If the server is unable to determine the exact offset and
length of the conflicting lock, the same offset and length
that were provided in the arguments should be returned in the
denied results.
contains further discussion of the file locking mechanisms.
LOCKT uses a lock_owner4, rather than a stateid4 as is used in
LOCK, to identify the owner. This is because the client does not
have to open the file to test for the existence of a lock,
so a stateid may not be available.
The test for conflicting locks SHOULD exclude locks for
the current lock-owner. Note that since such locks are
not examined the possible existence of overlapping ranges
may not affect the results of LOCKT. If the server does
examine locks that match the lock-owner for the purpose
of range checking, NFS4ERR_LOCK_RANGE may be returned.
In the event that it returns NFS4_OK, clients may do a LOCK
and receive NFS4ERR_LOCK_RANGE on the LOCK request because
of the flexibility provided to the server.
When a client holds an OPEN_DELEGATE_WRITE delegation, it may choose
(see ) to handle
LOCK requests locally. In such a
case, LOCKT requests will similarly be handled locally.
(cfh) type, seqid, stateid, offset, length -> stateid
struct LOCKU4args {
/* CURRENT_FH: file */
nfs_lock_type4 locktype;
seqid4 seqid;
stateid4 lock_stateid;
offset4 offset;
length4 length;
};
union LOCKU4res switch (nfsstat4 status) {
case NFS4_OK:
stateid4 lock_stateid;
default:
void;
};
The LOCKU operation unlocks the byte-range lock specified by
the parameters. The client may set the locktype field to any
value that is legal for the nfs_lock_type4 enumerated type,
and the server MUST accept any legal value for locktype. Any
legal value for locktype has no effect on the success or
failure of the LOCKU operation.
The ranges are specified as for LOCK. The NFS4ERR_INVAL
and NFS4ERR_BAD_RANGE errors are returned under the same
circumstances as for LOCK.
On success, the current filehandle retains its value.
If the area to be unlocked does not correspond exactly to a
lock actually held by the lock-owner, the server may return the
error NFS4ERR_LOCK_RANGE. This includes the cases where (1)
the area is not locked, (2) the area is a sub-range of the area
locked, (3) it overlaps the area locked without matching exactly,
or (4) the area specified includes multiple locks held by the
lock-owner. In all of these cases, allowed
by POSIX locking semantics, a client
receiving this error should, if it desires support for such
operations, simulate
the operation using LOCKU on ranges corresponding to locks
it actually holds, possibly followed by LOCK requests for
the sub-ranges not being unlocked.
When a client holds an OPEN_DELEGATE_WRITE delegation, it may choose
(see ) to handle
LOCK requests locally. In such a
case, LOCKU requests will similarly be handled locally.
(cfh), component -> (cfh)
struct LOOKUP4args {
/* CURRENT_FH: directory */
component4 objname;
};
struct LOOKUP4res {
/* CURRENT_FH: object */
nfsstat4 status;
};
This operation performs a LOOKUP or finds a file system object
using the directory specified by the current filehandle. LOOKUP
evaluates the component and if the object exists the current
filehandle is replaced with the component's filehandle.
If the component cannot be evaluated because either it does
not exist or the client does not have permission to evaluate
it, then an error will be returned, and the current filehandle
will be unchanged.
If the component is of zero length, NFS4ERR_INVAL will
be returned. The component is also subject to the normal
UTF-8, character support, and name checks. See
for further discussion.
If the client wants to achieve the effect of a multi-component
lookup, it may construct a COMPOUND request such as the
following (and obtain each filehandle):
PUTFH (directory filehandle)
LOOKUP "pub"
GETFH
LOOKUP "foo"
GETFH
LOOKUP "bar"
GETFH
NFSv4 servers depart from the semantics of previous
NFS versions in allowing LOOKUP requests to cross mount points
on the server. The client can detect a mount point crossing
by comparing the fsid attribute of the directory with the
fsid attribute of the directory looked up. If the fsids are
different, then the new directory is a server mount point.
UNIX clients that detect a mount point crossing will need
to mount the server's file system. This needs to be done to
maintain the file object identity-checking mechanisms common
to UNIX clients.
Servers that limit NFS access to "shares" or "exported"
file systems should provide a pseudo-file system into which
the exported file systems can be integrated, so that clients
can browse the server's namespace. The clients' view of
a pseudo-file system will be limited to paths that lead to
exported file systems.
Note: Previous versions of the protocol assigned special
semantics to the names "." and "..". NFSv4 assigns
no special semantics to these names. The LOOKUPP operator
must be used to look up a parent directory.
Note that this operation does not follow symbolic links.
The client is responsible for all parsing of filenames,
including filenames that are modified by symbolic links
encountered during the lookup process.
If the current filehandle supplied is not a directory but
a symbolic link, NFS4ERR_SYMLINK is returned as the error.
For all other non&nbhy;directory file types, the error
NFS4ERR_NOTDIR is returned.
(cfh) -> (cfh)
/* CURRENT_FH: object */
void;
struct LOOKUPP4res {
/* CURRENT_FH: directory */
nfsstat4 status;
};
The current filehandle is assumed to refer to a regular
directory or a named attribute directory. LOOKUPP assigns
the filehandle for its parent directory to be the current
filehandle. If there is no parent directory, an NFS4ERR_NOENT
error must be returned. Therefore, NFS4ERR_NOENT will be
returned by the server when the current filehandle is at the
root or top of the server's file tree.
As for LOOKUP, LOOKUPP will also cross mount points.
If the current filehandle is not a directory or named attribute
directory, the error NFS4ERR_NOTDIR is returned.
If the current filehandle is a named attribute directory that is
associated with a file system object via OPENATTR (i.e., not a
subdirectory of a named attribute directory), LOOKUPP SHOULD return the
filehandle of the associated file system object.
(cfh), fattr -> -
struct NVERIFY4args {
/* CURRENT_FH: object */
fattr4 obj_attributes;
};
struct NVERIFY4res {
nfsstat4 status;
};
This operation is used to prefix a sequence of operations
to be performed if one or more attributes have changed on
some file system object. If all the attributes match, then
the error NFS4ERR_SAME must be returned.
On success, the current filehandle retains its value.
This operation is useful as a cache validation operator.
If the object to which the attributes belong has changed,
then the following operations may obtain new data associated
with that object -- for instance, to check if a file has been
changed and obtain new data if it has:
PUTFH (public)
LOOKUP "foobar"
NVERIFY attrbits attrs
READ 0 32767
In the case that a RECOMMENDED attribute is specified in
the NVERIFY operation and the server does not support
that attribute for the file system object, the error
NFS4ERR_ATTRNOTSUPP is returned to the client.
When the attribute rdattr_error or any write-only attribute
(e.g., time_modify_set) is specified, the error NFS4ERR_INVAL
is returned to the client.
(cfh), seqid, share_access, share_deny, owner, openhow, claim ->
(cfh), stateid, cinfo, rflags, attrset, delegation
/*
* Various definitions for OPEN
*/
enum createmode4 {
UNCHECKED4 = 0,
GUARDED4 = 1,
EXCLUSIVE4 = 2
};
union createhow4 switch (createmode4 mode) {
case UNCHECKED4:
case GUARDED4:
fattr4 createattrs;
case EXCLUSIVE4:
verifier4 createverf;
};
enum opentype4 {
OPEN4_NOCREATE = 0,
OPEN4_CREATE = 1
};
union openflag4 switch (opentype4 opentype) {
case OPEN4_CREATE:
createhow4 how;
default:
void;
};
/* Next definitions used for OPEN delegation */
enum limit_by4 {
NFS_LIMIT_SIZE = 1,
NFS_LIMIT_BLOCKS = 2
/* others as needed */
};
struct nfs_modified_limit4 {
uint32_t num_blocks;
uint32_t bytes_per_block;
};
union nfs_space_limit4 switch (limit_by4 limitby) {
/* limit specified as file size */
case NFS_LIMIT_SIZE:
uint64_t filesize;
/* limit specified by number of blocks */
case NFS_LIMIT_BLOCKS:
nfs_modified_limit4 mod_blocks;
};
enum open_delegation_type4 {
OPEN_DELEGATE_NONE = 0,
OPEN_DELEGATE_READ = 1,
OPEN_DELEGATE_WRITE = 2
};
enum open_claim_type4 {
CLAIM_NULL = 0,
CLAIM_PREVIOUS = 1,
CLAIM_DELEGATE_CUR = 2,
CLAIM_DELEGATE_PREV = 3
};
struct open_claim_delegate_cur4 {
stateid4 delegate_stateid;
component4 file;
};
union open_claim4 switch (open_claim_type4 claim) {
/*
* No special rights to file.
* Ordinary OPEN of the specified file.
*/
case CLAIM_NULL:
/* CURRENT_FH: directory */
component4 file;
/*
* Right to the file established by an
* open previous to server reboot. File
* identified by filehandle obtained at
* that time rather than by name.
*/
case CLAIM_PREVIOUS:
/* CURRENT_FH: file being reclaimed */
open_delegation_type4 delegate_type;
/*
* Right to file based on a delegation
* granted by the server. File is
* specified by name.
*/
case CLAIM_DELEGATE_CUR:
/* CURRENT_FH: directory */
open_claim_delegate_cur4 delegate_cur_info;
/*
* Right to file based on a delegation
* granted to a previous boot instance
* of the client. File is specified by name.
*/
case CLAIM_DELEGATE_PREV:
/* CURRENT_FH: directory */
component4 file_delegate_prev;
};
/*
* OPEN: Open a file, potentially receiving an open delegation
*/
struct OPEN4args {
seqid4 seqid;
uint32_t share_access;
uint32_t share_deny;
open_owner4 owner;
openflag4 openhow;
open_claim4 claim;
};
struct open_read_delegation4 {
stateid4 stateid; /* Stateid for delegation */
bool recall; /* Pre-recalled flag for
delegations obtained
by reclaim (CLAIM_PREVIOUS) */
nfsace4 permissions; /* Defines users who don't
need an ACCESS call to
open for read */
};
struct open_write_delegation4 {
stateid4 stateid; /* Stateid for delegation */
bool recall; /* Pre-recalled flag for
delegations obtained
by reclaim
(CLAIM_PREVIOUS) */
nfs_space_limit4
space_limit; /* Defines condition that
the client must check to
determine whether the
file needs to be flushed
to the server on close */
nfsace4 permissions; /* Defines users who don't
need an ACCESS call as
part of a delegated
open */
};
union open_delegation4 switch
(open_delegation_type4 delegation_type) {
case OPEN_DELEGATE_NONE:
void;
case OPEN_DELEGATE_READ:
open_read_delegation4 read;
case OPEN_DELEGATE_WRITE:
open_write_delegation4 write;
};
/*
* Result flags
*/
/* Client must confirm open */
const OPEN4_RESULT_CONFIRM = 0x00000002;
/* Type of file locking behavior at the server */
const OPEN4_RESULT_LOCKTYPE_POSIX = 0x00000004;
struct OPEN4resok {
stateid4 stateid; /* Stateid for open */
change_info4 cinfo; /* Directory change info */
uint32_t rflags; /* Result flags */
bitmap4 attrset; /* attribute set for create */
open_delegation4 delegation; /* Info on any open
delegation */
};
union OPEN4res switch (nfsstat4 status) {
case NFS4_OK:
/* CURRENT_FH: opened file */
OPEN4resok resok4;
default:
void;
};
OPEN resembles LOOKUP in that it generates a filehandle for the
client to use. Unlike LOOKUP, though, OPEN creates server state
on the filehandle. In normal circumstances, the client can
only release this state with a CLOSE operation. CLOSE uses
the current filehandle to determine which file to close.
Therefore, the client MUST follow every OPEN operation with
a GETFH operation in the same COMPOUND procedure. This will
supply the client with the filehandle such that CLOSE can be
used appropriately.
Simply waiting for the lease on the file to expire is
insufficient because the server may maintain the state
indefinitely as long as another client does not attempt to
make a conflicting access to the same file.
The OPEN operation creates and/or opens a regular file in
a directory with the provided name. If the file does not
exist at the server and creation is desired, specification of
the method of creation is provided by the openhow parameter.
The client has the choice of three creation methods: UNCHECKED4,
GUARDED4, or EXCLUSIVE4.
If the current filehandle is a named attribute directory, OPEN
will then create or open a named attribute file. Note that
exclusive create of a named attribute is not supported.
If the createmode is EXCLUSIVE4 and the current filehandle
is a named attribute directory, the server will return EINVAL.
UNCHECKED4 means that the file should be created if a file
of that name does not exist and encountering an existing
regular file of that name is not an error. For this type of
create, createattrs specifies the initial set of attributes
for the file. The set of attributes may include any writable
attribute valid for regular files. When an UNCHECKED4 create
encounters an existing file, the attributes specified by
createattrs are not used, except that when a size of zero
is specified, the existing file is truncated. If GUARDED4 is
specified, the server checks for the presence of a duplicate
object by name before performing the create. If a duplicate
exists, an error of NFS4ERR_EXIST is returned as the status.
If the object does not exist, the request is performed as
described for UNCHECKED4. For each of these cases (UNCHECKED4
and GUARDED4), where the operation is successful, the server
will return to the client an attribute mask signifying which
attributes were successfully set for the object.
EXCLUSIVE4 specifies that the server is to follow exclusive
creation semantics, using the verifier to ensure exclusive
creation of the target. The server should check for the
presence of a duplicate object by name. If the object does not
exist, the server creates the object and stores the verifier
with the object. If the object does exist and the stored
verifier matches the verifier provided by the client, the server
uses the existing object as the newly created object. If the
stored verifier does not match, then an error of NFS4ERR_EXIST
is returned. No attributes may be provided in this case,
since the server may use an attribute of the target object
to store the verifier. If the server uses an attribute to
store the exclusive create verifier, it will signify which
attribute was used by setting the appropriate bit in the
attribute mask that is returned in the results.
For the target directory, the server returns change_info4
information in cinfo. With the atomic field of the
change_info4 struct, the server will indicate if the before
and after change attributes were obtained atomically with
respect to the link creation.
Upon successful creation, the current filehandle is replaced
by that of the new object.
The OPEN operation provides for Windows share reservation
capability with the use of the share_access and share_deny
fields of the OPEN arguments. The client specifies at OPEN
the required share_access and share_deny modes. For clients
that do not directly support SHAREs (i.e., UNIX), the expected
deny value is DENY_NONE. In the case that there is an existing
share reservation that conflicts with the OPEN request, the
server returns the error NFS4ERR_SHARE_DENIED. For a complete
SHARE request, the client must provide values for the owner and
seqid fields for the OPEN argument. For additional discussion
of share semantics, see .
In the case that the client is recovering state from a
server failure, the claim field of the OPEN argument is
used to signify that the request is meant to reclaim state
previously held.
The claim field of the OPEN argument is used to specify the
file to be opened and the state information that the client
claims to possess. There are four basic claim types that
cover the various situations for an OPEN. They are as follows:
For the client, this is a new OPEN request, and there is
no previous state associated with the file for the client.
The client is claiming basic OPEN state for a file that
was held previous to a server reboot. This is generally
used when a server is returning persistent filehandles; the
client may not have the filename to reclaim the OPEN.
The client is claiming a delegation for OPEN as granted by
the server. This is generally done as part of recalling
a delegation.
The client is claiming a delegation granted to a previous
client instance. This claim type is for use after a
SETCLIENTID_CONFIRM and before the corresponding DELEGPURGE
in two situations: after a client reboot and after a lease
expiration that resulted in loss of all lock state. The
server MAY support CLAIM_DELEGATE_PREV. If it does support
CLAIM_DELEGATE_PREV, SETCLIENTID_CONFIRM MUST NOT remove
the client's delegation state, and the server MUST support
the DELEGPURGE operation.
The following errors apply to use of the CLAIM_DELEGATE_PREV
claim type:
NFS4ERR_NOTSUPP is returned if the server does not support this
claim type.
NFS4ERR_INVAL is returned if the reclaim is done at an inappropriate
time, e.g., after DELEGPURGE has been done.
NFS4ERR_BAD_RECLAIM is returned if the other error conditions do not
apply and the server has no record of the delegation whose reclaim
is being attempted.
For OPEN requests whose claim type is other than CLAIM_PREVIOUS
(i.e., requests other than those devoted to reclaiming opens
after a server reboot) that reach the server during its grace
or lease expiration period, the server returns an error of
NFS4ERR_GRACE.
For any OPEN request, the server may return an open delegation,
which allows further opens and closes to be handled locally
on the client as described in .
Note that delegation is up to the server to decide.
The client should never assume that delegation will or will
not be granted in a particular instance. It should always be
prepared for either case. A partial exception is the reclaim
(CLAIM_PREVIOUS) case, in which a delegation type is claimed.
In this case, delegation will always be granted, although
the server may specify an immediate recall in the delegation
structure.
The rflags returned by a successful OPEN allow the server
to return information governing how the open file is to
be handled.
OPEN4_RESULT_CONFIRM indicates that the client MUST execute
an OPEN_CONFIRM operation before using the open file.
OPEN4_RESULT_LOCKTYPE_POSIX indicates that the server's file locking
behavior supports the complete set of POSIX locking techniques
.
From this, the client can choose to manage file locking state
in such a way as to handle a mismatch of file locking management.
If the component is of zero length, NFS4ERR_INVAL will
be returned. The component is also subject to the normal
UTF-8, character support, and name checks. See
for further discussion.
When an OPEN is done and the specified open-owner already
has the resulting filehandle open, the result is to "OR"
together the new share and deny status, together with the
existing status. In this case, only a single CLOSE need be
done, even though multiple OPENs were completed. When such
an OPEN is done, checking of share reservations for the new
OPEN proceeds normally, with no exception for the existing
OPEN held by the same owner. In this case, the stateid returned
has an "other" field that matches that of the previous open,
while the seqid field is incremented to reflect the
changed status due to the new open ().
If the underlying file system at the server is only accessible
in a read-only mode and the OPEN request has specified
OPEN4_SHARE_ACCESS_WRITE or OPEN4_SHARE_ACCESS_BOTH, the
server will return NFS4ERR_ROFS to indicate a read-only file system.
As with the CREATE operation, the server MUST derive the owner,
owner ACE, group, or group ACE if any of the four attributes
are required and supported by the server's file system. For an
OPEN with the EXCLUSIVE4 createmode, the server has no choice,
since such OPEN calls do not include the createattrs field.
Conversely, if createattrs is specified and includes owner
or group (or corresponding ACEs) that the principal in the
RPC's credentials does not have authorization to create
files for, then the server may return NFS4ERR_PERM.
In the case where an OPEN specifies a size of zero (e.g.,
truncation) and the file has named attributes, the named
attributes are left as is. They are not removed.
The OPEN operation contains support for EXCLUSIVE4 create.
The mechanism is similar to the support in NFSv3 . As in NFSv3, this mechanism
provides reliable exclusive creation. Exclusive create is
invoked when the how parameter is EXCLUSIVE4. In this case,
the client provides a verifier that can reasonably be expected
to be unique. A combination of a client identifier, perhaps
the client network address, and a unique number generated
by the client, perhaps the RPC transaction identifier, may
be appropriate.
If the object does not exist, the server creates the object
and stores the verifier in stable storage. For file systems
that do not provide a mechanism for the storage of arbitrary
file attributes, the server may use one or more elements of
the object metadata to store the verifier. The verifier must
be stored in stable storage to prevent erroneous failure
on retransmission of the request. It is assumed that an
exclusive create is being performed because exclusive
semantics are critical to the application. Because of the
expected usage, exclusive create does not rely solely on the
normally volatile duplicate request cache for storage of the
verifier. The duplicate request cache in volatile storage
does not survive a crash and may actually flush on a long
network partition, opening failure windows. In the UNIX
local file system environment, the expected storage location
for the verifier on creation is the metadata (timestamps)
of the object. For this reason, an exclusive object create
may not include initial attributes because the server would
have nowhere to store the verifier.
If the server cannot support these exclusive create semantics,
possibly because of the requirement to commit the verifier
to stable storage, it should fail the OPEN request with the
error NFS4ERR_NOTSUPP.
During an exclusive CREATE request, if the object already
exists, the server reconstructs the object's verifier and
compares it with the verifier in the request. If they match,
the server treats the request as a success. The request is
presumed to be a duplicate of an earlier, successful request
for which the reply was lost and that the server duplicate
request cache mechanism did not detect. If the verifiers
do not match, the request is rejected with the status
NFS4ERR_EXIST.
Once the client has performed a successful exclusive create,
it must issue a SETATTR to set the correct object attributes.
Until it does so, it should not rely upon any of the
object attributes, since the server implementation may
need to overload object metadata to store the verifier.
The subsequent SETATTR must not occur in the same COMPOUND
request as the OPEN. This separation will guarantee that the
exclusive create mechanism will continue to function properly
in the face of retransmission of the request.
Use of the GUARDED4 attribute does not provide "exactly-once"
semantics. In particular, if a reply is lost and the
server does not detect the retransmission of the request,
the operation can fail with NFS4ERR_EXIST, even though the
create was performed successfully. The client would use this
behavior in the case that the application has not requested
an exclusive create but has asked to have the file truncated
when the file is opened. In the case of the client timing
out and retransmitting the create request, the client can use
GUARDED4 to prevent a sequence such as create, write,
create (retransmitted) from occurring.
For share reservations (see ), the client must specify a value
for share_access that is one of OPEN4_SHARE_ACCESS_READ, OPEN4_SHARE_ACCESS_WRITE, or OPEN4_SHARE_ACCESS_BOTH.
For share_deny, the client must specify one of OPEN4_SHARE_DENY_NONE, OPEN4_SHARE_DENY_READ,
OPEN4_SHARE_DENY_WRITE, or OPEN4_SHARE_DENY_BOTH. If the client fails to do this, the server
must return NFS4ERR_INVAL.
Based on the share_access value (OPEN4_SHARE_ACCESS_READ,
OPEN4_SHARE_ACCESS_WRITE, or OPEN4_SHARE_ACCESS_BOTH),
the client should check that the requester has the proper
access rights to perform the specified operation. This would
generally be the results of applying the ACL access rules
to the file for the current requester. However, just as
with the ACCESS operation, the client should not attempt to
second-guess the server's decisions, as access rights may
change and may be subject to server administrative controls
outside the ACL framework. If the requester is not authorized
to READ or WRITE (depending on the share_access value), the
server must return NFS4ERR_ACCESS. Note that since the
NFSv4 protocol does not impose any requirement that READs
and WRITEs issued for an open file have the same credentials
as the OPEN itself, the server still must do appropriate
access checking on the READs and WRITEs themselves.
If the component provided to OPEN resolves to something
other than a regular file (or a named attribute), an error
will be returned to the
client. If it is a directory, NFS4ERR_ISDIR is returned;
otherwise, NFS4ERR_SYMLINK is returned. Note that
NFS4ERR_SYMLINK is returned for both symlinks and for special
files of other types; NFS4ERR_INVAL would be inappropriate,
since the arguments provided by the client were correct, and
the client cannot necessarily know at the time it sent the OPEN
that the component would resolve to a non-regular file.
If the current filehandle is not a directory, the error
NFS4ERR_NOTDIR will be returned.
If a COMPOUND contains an OPEN that establishes an
OPEN_DELEGATE_WRITE delegation, then subsequent GETATTRs
normally result in a CB_GETATTR being sent to the client
holding the delegation. However, in the case in which the
OPEN and GETATTR are part of the same COMPOUND, the server
SHOULD understand that the operations are for the same
client ID and avoid querying the client, which will not be
able to respond. This sequence of OPEN and GETATTR SHOULD be
understood to be the retrieval of the size and change attributes
at the time of OPEN. Further, as explained in
, the client should
not construct a COMPOUND that mixes operations for different
client IDs.
(cfh) createdir -> (cfh)
struct OPENATTR4args {
/* CURRENT_FH: object */
bool createdir;
};
struct OPENATTR4res {
/* CURRENT_FH: named attr directory */
nfsstat4 status;
};
The OPENATTR operation is used to obtain the filehandle of
the named attribute directory associated with the current
filehandle. The result of the OPENATTR will be a filehandle to
an object of type NF4ATTRDIR. From this filehandle, READDIR
and LOOKUP operations can be used to obtain filehandles for
the various named attributes associated with the original
file system object. Filehandles returned within the named
attribute directory will have a type of NF4NAMEDATTR.
The createdir argument allows the client to signify if a
named attribute directory should be created as a result of
the OPENATTR operation. Some clients may use the OPENATTR
operation with a value of FALSE for createdir to determine if
any named attributes exist for the object. If none exist, then
NFS4ERR_NOENT will be returned. If createdir has a value of
TRUE and no named attribute directory exists, one is created.
The creation of a named attribute directory assumes that
the server has implemented named attribute support in this
fashion and is not required to do so by this definition.
If the server does not support named attributes for the current
filehandle, an error of NFS4ERR_NOTSUPP will be returned to
the client.
(cfh), seqid, stateid -> stateid
struct OPEN_CONFIRM4args {
/* CURRENT_FH: opened file */
stateid4 open_stateid;
seqid4 seqid;
};
struct OPEN_CONFIRM4resok {
stateid4 open_stateid;
};
union OPEN_CONFIRM4res switch (nfsstat4 status) {
case NFS4_OK:
OPEN_CONFIRM4resok resok4;
default:
void;
};
This operation is used to confirm the sequence id usage
for the first time that an open-owner is used by a client.
The stateid returned from the OPEN operation is used as the
argument for this operation along with the next sequence id for
the open-owner. The sequence id passed to the OPEN_CONFIRM
must be 1 (one) greater than the seqid passed to the OPEN
operation ().
If the server receives an unexpected sequence id with respect
to the original OPEN, then the server assumes that the client
will not confirm the original OPEN and all state associated
with the original OPEN is released by the server.
On success, the current filehandle retains its value.
A given client might generate many open_owner4 data structures
for a given client ID. The client will periodically either
dispose of its open_owner4s or stop using them for indefinite
periods of time. The latter situation is why the NFSv4
protocol does not have an explicit operation to exit an
open_owner4: such an operation is of no use in that situation.
Instead, to avoid unbounded memory use, the server needs to
implement a strategy for disposing of open_owner4s that have
no current open state for any files and
have not been used recently. The time period used to determine
when to dispose of open_owner4s is an implementation choice.
The time period should certainly be no less than the lease
time plus any grace period the server wishes to implement
beyond a lease time. The OPEN_CONFIRM operation allows the
server to safely dispose of unused open_owner4 data structures.
In the case that a client issues an OPEN operation and the
server no longer has a record of the open_owner4, the server
needs to ensure that this is a new OPEN and not a replay
or retransmission.
Servers MUST NOT require confirmation on OPENs that grant
delegations or are doing reclaim operations. See
for details. The server can easily avoid
this by noting whether it has disposed of one open_owner4 for
the given client ID. If the server does not support delegation,
it might simply maintain a single bit that notes whether any
open_owner4 (for any client) has been disposed of.
The server must hold unconfirmed OPEN state until one of
three events occurs. First, the client sends an OPEN_CONFIRM
request with the appropriate sequence id and stateid within
the lease period. In this case, the OPEN state on the
server goes to confirmed, and the open_owner4 on the server
is fully established.
Second, the client sends another OPEN request with a sequence
id that is incorrect for the open_owner4 (out of sequence).
In this case, the server assumes the second OPEN request is
valid and the first one is a replay. The server cancels
the OPEN state of the first OPEN request, establishes an
unconfirmed OPEN state for the second OPEN request, and
responds to the second OPEN request with an indication that
an OPEN_CONFIRM is needed. The process then repeats itself.
While there is a potential for a denial-of-service attack on
the client, it is mitigated if the client and server require
the use of a security flavor based on Kerberos V5
or some other flavor that uses cryptography.
What if the server is in the unconfirmed OPEN state for a given
open_owner4, and it receives an operation on the open_owner4
that has a stateid but the operation is not OPEN, or it is
OPEN_CONFIRM but with the wrong stateid? Then, even if the
seqid is correct, the server returns NFS4ERR_BAD_STATEID,
because the server assumes the operation is a replay: if the
server has no established OPEN state, then there is no way,
for example, a LOCK operation could be valid.
Third, neither of the two aforementioned events occurs for the
open_owner4 within the lease period. In this case, the OPEN
state is canceled and disposal of the open_owner4 can occur.
(cfh), stateid, seqid, access, deny -> stateid
struct OPEN_DOWNGRADE4args {
/* CURRENT_FH: opened file */
stateid4 open_stateid;
seqid4 seqid;
uint32_t share_access;
uint32_t share_deny;
};
struct OPEN_DOWNGRADE4resok {
stateid4 open_stateid;
};
union OPEN_DOWNGRADE4res switch (nfsstat4 status) {
case NFS4_OK:
OPEN_DOWNGRADE4resok resok4;
default:
void;
};
This operation is used to adjust the share_access and
share_deny bits for a given open. This is necessary when
a given open-owner opens the same file multiple times with
different share_access and share_deny flags. In this
situation, a close of one of the opens may change the
appropriate share_access and share_deny flags to remove bits
associated with opens no longer in effect.
The share_access and share_deny bits specified in this
operation replace the current ones for the specified open file.
The share_access and share_deny bits specified must be exactly
equal to the union of the share_access and share_deny bits
specified for some subset of the OPENs in effect for the current
open-owner on the current file. If that constraint is not
respected, the error NFS4ERR_INVAL should be returned.
Since share_access and share_deny bits are subsets of those
already granted, it is not possible for this request to be
denied because of conflicting share reservations.
As the OPEN_DOWNGRADE may change a file to be not-open-for-write
and a write byte-range lock might be held, the server may have to
reject the OPEN_DOWNGRADE with an NFS4ERR_LOCKS_HELD.
On success, the current filehandle retains its value.
filehandle -> (cfh)
struct PUTFH4args {
nfs_fh4 object;
};
struct PUTFH4res {
/* CURRENT_FH: */
nfsstat4 status;
};
PUTFH replaces the current filehandle with the filehandle provided
as an argument.
If the security mechanism used by the requester does not meet
the requirements of the filehandle provided to this operation,
the server MUST return NFS4ERR_WRONGSEC.
See for more details on the
current filehandle.
PUTFH is commonly used as the first operator in an NFS request
to set the context for operations that follow it.
- -> (cfh)
void;
struct PUTPUBFH4res {
/* CURRENT_FH: public fh */
nfsstat4 status;
};
PUTPUBFH replaces the current filehandle with the filehandle that
represents the public filehandle of the server's namespace.
This filehandle may be different from the root filehandle,
which may be associated with some other directory on the
server.
The public filehandle concept was introduced in
, , and
. The intent for NFSv4 is that
the public filehandle (represented by the PUTPUBFH operation)
be used as a method of providing compatibility with the WebNFS server
of NFSv2 and NFSv3.
The public filehandle and the root filehandle (represented
by the PUTROOTFH operation) should be equivalent. If the
public and root filehandles are not equivalent, then the
public filehandle MUST be a descendant of the root filehandle.
PUTPUBFH is used as the first operator in an NFS request to set the
context for operations that follow it.
With the NFSv2 and NFSv3 public filehandle, the client is
able to specify whether the pathname provided in the LOOKUP
should be evaluated as either an absolute path relative
to the server's root or relative to the public filehandle.
contains further discussion of the
functionality.
With NFSv4, that type of specification is not directly
available in the LOOKUP operation. The reason for this is
because the component separators needed to specify absolute
versus relative are not allowed in NFSv4. Therefore, the
client is responsible for constructing its request such that
either PUTROOTFH or PUTPUBFH is used to signify absolute or
relative evaluation of an NFS URL, respectively.
Note that there are warnings mentioned in with
respect to the use of absolute evaluation and the restrictions
the server may place on that evaluation with respect to how
much of its namespace has been made available. These same
warnings apply to NFSv4. It is likely, therefore,
that because of server implementation details an NFSv3
absolute public filehandle lookup may behave differently
than an NFSv4 absolute resolution.
There is a form of security negotiation as described
in that uses the public filehandle as a
method of employing the Simple and Protected GSS-API
Negotiation Mechanism (SNEGO) . This
method is not available with NFSv4, as filehandles are not
overloaded with special meaning and therefore do not provide the
same framework as NFSv2 and NFSv3. Clients should therefore use
the security negotiation mechanisms described in this RFC.
- -> (cfh)
void;
struct PUTROOTFH4res {
/* CURRENT_FH: root fh */
nfsstat4 status;
};
PUTROOTFH replaces the current filehandle with the filehandle that
represents the root of the server's namespace. From this
filehandle, a LOOKUP operation can locate any other filehandle
on the server. This filehandle may be different from the
public filehandle, which may be associated with some other
directory on the server.
See for more details on the
current filehandle.
PUTROOTFH is commonly used as the first operator in an NFS request
to set the context for operations that follow it.
(cfh), stateid, offset, count -> eof, data
struct READ4args {
/* CURRENT_FH: file */
stateid4 stateid;
offset4 offset;
count4 count;
};
struct READ4resok {
bool eof;
opaque data<>;
};
union READ4res switch (nfsstat4 status) {
case NFS4_OK:
READ4resok resok4;
default:
void;
};
The READ operation reads data from the regular file identified
by the current filehandle.
The client provides an offset of where the READ is to start
and a count of how many bytes are to be read. An offset
of 0 (zero) means to read data starting at the beginning of
the file. If the offset is greater than or equal to the size of
the file, the status, NFS4_OK, is returned with a data length
set to 0 (zero), and eof is set to TRUE. The READ is subject
to access permissions checking.
If the client specifies a count value of 0 (zero), the READ
succeeds and returns 0 (zero) bytes of data (subject to
access permissions checking). The server may choose to
return fewer bytes than specified by the client. The client
needs to check for this condition and handle the condition
appropriately.
The stateid value for a READ request represents a value
returned from a previous byte-range lock or share reservation
request, or the stateid associated with a delegation.
The stateid is used by the server to verify that
the associated share reservation and any byte-range locks are
still valid and to update lease timeouts for the client.
If the READ ended at the end-of-file (formally, in a correctly
formed READ request, if offset + count is equal to the size of
the file), or the READ request extends beyond the size of the
file (if offset + count is greater than the size of the file),
eof is returned as TRUE; otherwise, it is FALSE. A successful
READ of an empty file will always return eof as TRUE.
If the current filehandle is not a regular file, an error
will be returned to the client. In the case where the current
filehandle represents a directory, NFS4ERR_ISDIR is returned;
otherwise, NFS4ERR_INVAL is returned.
For a READ using the special anonymous stateid, the server
MAY allow the READ to be serviced subject to mandatory file
locks or the current share_deny modes for the file. For a
READ using the special READ bypass stateid, the server MAY
allow READ operations to bypass locking checks at the server.
On success, the current filehandle retains its value.
If the server returns a "short read" (i.e., less data than requested
and eof is set to FALSE), the client should send another READ to get
the remaining data. A server may return less data than requested
under several circumstances. The file may have been truncated by
another client or perhaps on the server itself, changing the file
size from what the requesting client believes to be the case. This
would reduce the actual amount of data available to the client. It
is possible that the server reduces the transfer size and so returns a
short read result. Server resource exhaustion may also result in a
short read.
If mandatory byte-range locking is in effect for the file, and if the
byte range corresponding to the data to be read from the file is
WRITE_LT locked by an owner not associated with the stateid, the
server will return the NFS4ERR_LOCKED error. The client should try
to get the appropriate READ_LT via the LOCK operation before
re&nbhy;attempting the READ. When the READ completes, the client
should release the byte-range lock via LOCKU.
If another client has an OPEN_DELEGATE_WRITE delegation for the file
being read, the delegation must be recalled, and the operation cannot
proceed until that delegation is returned or revoked. Except where
this happens very quickly, one or more NFS4ERR_DELAY errors will be
returned to requests made while the delegation remains outstanding.
Normally, delegations will not be recalled as a result of a READ
operation, since the recall will occur as a result of an earlier OPEN.
However, since it is possible for a READ to be done with a special
stateid, the server needs to check for this case even though the
client should have done an OPEN previously.
(cfh), cookie, cookieverf, dircount, maxcount, attr_request ->
cookieverf { cookie, name, attrs }
struct READDIR4args {
/* CURRENT_FH: directory */
nfs_cookie4 cookie;
verifier4 cookieverf;
count4 dircount;
count4 maxcount;
bitmap4 attr_request;
};
struct entry4 {
nfs_cookie4 cookie;
component4 name;
fattr4 attrs;
entry4 *nextentry;
};
struct dirlist4 {
entry4 *entries;
bool eof;
};
struct READDIR4resok {
verifier4 cookieverf;
dirlist4 reply;
};
union READDIR4res switch (nfsstat4 status) {
case NFS4_OK:
READDIR4resok resok4;
default:
void;
};
The READDIR operation retrieves a variable number of entries
from a file system directory and for each entry returns
attributes that were requested by the client, along with
information to allow the client to request additional directory
entries in a subsequent READDIR.
The arguments contain a cookie value that represents where the
READDIR should start within the directory. A value of 0 (zero)
for the cookie is used to start reading at the beginning of
the directory. For subsequent READDIR requests, the client
specifies a cookie value that is provided by the server in
a previous READDIR request.
The cookieverf value should be set to 0 (zero) when the cookie
value is 0 (zero) (first directory read). On subsequent
requests, it should be a cookieverf as returned by the server.
The cookieverf must match that returned by the READDIR in
which the cookie was acquired. If the server determines
that the cookieverf is no longer valid for the directory,
the error NFS4ERR_NOT_SAME must be returned.
The dircount portion of the argument is a hint of the maximum
number of bytes of directory information that should be
returned. This value represents the length of the names of
the directory entries and the cookie value for these entries.
This length represents the XDR encoding of the data (names and
cookies) and not the length in the native format of the server.
The maxcount value of the argument is the maximum number of
bytes for the result. This maximum size represents all of
the data being returned within the READDIR4resok structure and
includes the XDR overhead. The server may return less data.
If the server is unable to return a single directory entry
within the maxcount limit, the error NFS4ERR_TOOSMALL will
be returned to the client.
Finally, attr_request represents the list of attributes to
be returned for each directory entry supplied by the server.
On successful return, the server's response will provide a
list of directory entries. Each of these entries contains the
name of the directory entry, a cookie value for that entry,
and the associated attributes as requested. The "eof" flag has
a value of TRUE if there are no more entries in the directory.
The cookie value is only meaningful to the server and is
used as a "bookmark" for the directory entry. As mentioned,
this cookie is used by the client for subsequent READDIR
operations so that it may continue reading a directory.
The cookie is similar in concept to a READ offset but should
not be interpreted as such by the client. The server SHOULD
try to accept cookie values issued with READDIR responses
even if the directory has been modified between the READDIR
calls but MAY return NFS4ERR_NOT_VALID if this is not
possible, as might be the case if the server has rebooted
in the interim.
In some cases, the server may encounter an error while
obtaining the attributes for a directory entry. Instead of
returning an error for the entire READDIR operation, the
server can instead return the attribute 'fattr4_rdattr_error'.
With this, the server is able to communicate the failure to
the client and not fail the entire operation in the instance of
what might be a transient failure. Obviously, the client must
request the fattr4_rdattr_error attribute for this method to
work properly. If the client does not request the attribute,
the server has no choice but to return failure for the entire
READDIR operation.
For some file system environments, the directory entries "." and
".." have special meaning, and in other environments, they
may not. If the server supports these special entries within
a directory, they should not be returned to the client as part
of the READDIR response. To enable some client environments,
the cookie values of 0, 1, and 2 are to be considered reserved.
Note that the UNIX client will use these values when combining
the server's response and local representations to enable a
fully formed UNIX directory presentation to the application.
For READDIR arguments, cookie values of 1 and 2 SHOULD NOT
be used, and for READDIR results, cookie values of 0, 1, and
2 MUST NOT be returned.
On success, the current filehandle retains its value.
The server's file system directory representations can differ
greatly. A client's programming interfaces may also be bound
to the local operating environment in a way that does not
translate well into the NFS protocol. Therefore, the
dircount and maxcount fields are provided to allow
the client the ability to provide guidelines to the server.
If the client is aggressive about attribute collection during
a READDIR, the server has an idea of how to limit the encoded
response. The dircount field provides a hint on the number of
entries based solely on the names of the directory entries.
Since it is a hint, it may be possible that a dircount value
is zero. In this case, the server is free to ignore the
dircount value and return directory information based on the
specified maxcount value.
As there is no way for the client to indicate that a cookie
value, once received, will not be subsequently used, server
implementations should avoid schemes that allocate memory
corresponding to a returned cookie. Such allocation can be
avoided if the server bases cookie values on a value such
as the offset within the directory where the scan is to be
resumed.
Cookies generated by such techniques should be designed to
remain valid despite modification of the associated directory.
If a server were to invalidate a cookie because of a directory
modification, READDIRs of large directories might never
finish.
If a directory is deleted after the client has carried out
one or more READDIR operations on the directory, the cookies
returned will become invalid; however, the server does not need
to be concerned, as the directory filehandle used previously
would have become stale and would be reported as such on
subsequent READDIR operations. The server would not need
to check the cookie verifier in this case.
However, certain reorganization operations on a directory
(including directory compaction) may invalidate READDIR
cookies previously given out. When such a situation occurs,
the server should modify the cookie verifier so as to disallow
the use of cookies that would otherwise no longer be valid.
The cookieverf may be used by the server to help manage
cookie values that may become stale. It should be a rare
occurrence that a server is unable to continue properly
reading a directory with the provided cookie/cookieverf pair.
The server should make every effort to avoid this condition
since the application at the client may not be able to properly
handle this type of failure.
The use of the cookieverf will also protect the client from
using READDIR cookie values that may be stale. For example,
if the file system has been migrated, the server may or may
not be able to use the same cookie values to service READDIR
as the previous server used. With the client providing the
cookieverf, the server is able to provide the appropriate
response to the client. This prevents the case where the
server may accept a cookie value but the underlying directory
has changed and the response is invalid from the client's
context of its previous READDIR.
Since some servers will not be returning "." and ".." entries
as has been done with previous versions of the NFS protocol,
the client that requires these entries be present in READDIR
responses must fabricate them.
(cfh) -> linktext
/* CURRENT_FH: symlink */
void;
struct READLINK4resok {
linktext4 link;
};
union READLINK4res switch (nfsstat4 status) {
case NFS4_OK:
READLINK4resok resok4;
default:
void;
};
READLINK reads the data associated with a symbolic link.
The data is a UTF-8 string that is opaque to the server.
That is, whether created by an NFS client or created locally
on the server, the data in a symbolic link is not interpreted
when created but is simply stored.
On success, the current filehandle retains its value.
A symbolic link is nominally a pointer to another file.
The data is not necessarily interpreted by the server; it is just
stored in the file. It is possible for a client implementation
to store a pathname that is not meaningful to the server
operating system in a symbolic link. A READLINK operation
returns the data to the client for interpretation. If different
implementations want to share access to symbolic links,
then they must agree on the interpretation of the data in
the symbolic link.
The READLINK operation is only allowed on objects of type
NF4LNK. The server should return the error NFS4ERR_INVAL
if the object is not of type NF4LNK.
(cfh), filename -> change_info
struct REMOVE4args {
/* CURRENT_FH: directory */
component4 target;
};
struct REMOVE4resok {
change_info4 cinfo;
};
union REMOVE4res switch (nfsstat4 status) {
case NFS4_OK:
REMOVE4resok resok4;
default:
void;
};
The REMOVE operation removes (deletes) a directory entry
named by filename from the directory corresponding to the
current filehandle. If the entry in the directory was the
last reference to the corresponding file system object, the
object may be destroyed.
For the directory where the filename was removed, the server
returns change_info4 information in cinfo. With the atomic
field of the change_info4 struct, the server will indicate
if the before and after change attributes were obtained
atomically with respect to the removal.
If the target is of zero length, NFS4ERR_INVAL will
be returned. The target is also subject to the normal
UTF-8, character support, and name checks. See
for further discussion.
On success, the current filehandle retains its value.
NFSv3 required a different operator -- RMDIR -- for
directory removal, and REMOVE for non-directory removal. This
allowed clients to skip checking the file type when being
passed a non-directory delete system call
(e.g., unlink() in POSIX) to
remove a directory, as well as the converse
(e.g., a rmdir() on a non&nbhy;directory), because they knew the
server would check the file type. NFSv4 REMOVE can
be used to delete any directory entry, independent of its file
type. The implementer of an NFSv4 client's entry
points from the unlink() and rmdir() system calls should
first check the file type against the types the system call
is allowed to remove before issuing a REMOVE. Alternatively,
the implementer can produce a COMPOUND call that includes
a LOOKUP/VERIFY sequence to verify the file type before a
REMOVE operation in the same COMPOUND call.
The concept of last reference is server specific. However,
if the numlinks field in the previous attributes of the object
had the value 1, the client should not rely on referring to
the object via a filehandle. Likewise, the client should
not rely on the resources (disk space, directory entry,
and so on) formerly associated with the object becoming
immediately available. Thus, if a client needs to be able
to continue to access a file after using REMOVE to remove it,
the client should take steps to make sure that the file will
still be accessible. The usual mechanism used is to RENAME
the file from its old name to a new hidden name.
If the server finds that the file is still open when the
REMOVE arrives:
The server SHOULD NOT delete the file's directory entry
if the file was opened with OPEN4_SHARE_DENY_WRITE or
OPEN4_SHARE_DENY_BOTH.
If the file was not opened with OPEN4_SHARE_DENY_WRITE or
OPEN4_SHARE_DENY_BOTH, the server SHOULD delete the file's
directory entry. However, until the last CLOSE of the file,
the server MAY continue to allow access to the file via
its filehandle.
(sfh), oldname, (cfh), newname -> source_cinfo, target_cinfo
struct RENAME4args {
/* SAVED_FH: source directory */
component4 oldname;
/* CURRENT_FH: target directory */
component4 newname;
};
struct RENAME4resok {
change_info4 source_cinfo;
change_info4 target_cinfo;
};
union RENAME4res switch (nfsstat4 status) {
case NFS4_OK:
RENAME4resok resok4;
default:
void;
};
The RENAME operation renames the object identified by
oldname in the source directory corresponding to the saved
filehandle, as set by the SAVEFH operation, to newname in
the target directory corresponding to the current filehandle.
The operation is required to be atomic to the client. Source
and target directories must reside on the same file system on
the server. On success, the current filehandle will continue
to be the target directory.
If the target directory already contains an entry with the
name newname, the source object must be compatible with
the target: either both are non-directories, or both are
directories, and the target must be empty. If compatible,
the existing target is removed before the rename occurs (see
for client and server
actions whenever a target is removed). If they are not
compatible or if the target is a directory but not empty,
the server will return the error NFS4ERR_EXIST.
If oldname and newname both refer to the same file (they might
be hard links of each other), then RENAME should perform no
action and return success.
For both directories involved in the RENAME, the server
returns change_info4 information. With the atomic field
of the change_info4 struct, the server will indicate if the
before and after change attributes were obtained atomically
with respect to the rename.
If the oldname refers to a named attribute and the saved and
current filehandles refer to the named attribute directories
of different file system objects,
the server will return NFS4ERR_XDEV, just as if the saved
and current filehandles represented directories on different
file systems.
If the oldname or newname is of zero length, NFS4ERR_INVAL will
be returned. The oldname and newname are also subject to the
normal UTF-8, character support, and name checks. See
for further discussion.
The RENAME operation must be atomic to the client. The
statement "source and target directories must reside on the
same file system on the server" means that the fsid fields in
the attributes for the directories are the same. If they reside
on different file systems, the error NFS4ERR_XDEV is returned.
Based on the value of the fh_expire_type attribute for the
object, the filehandle may or may not expire on a RENAME.
However, server implementers are strongly encouraged to
attempt to keep filehandles from expiring in this fashion.
On some servers, the filenames "." and ".." are illegal
as either oldname or newname and will result in the error
NFS4ERR_BADNAME. In addition, on many servers the case of
oldname or newname being an alias for the source directory
will be checked for. Such servers will return the error
NFS4ERR_INVAL in these cases.
If either of the source or target filehandles are not
directories, the server will return NFS4ERR_NOTDIR.
clientid -> ()
struct RENEW4args {
clientid4 clientid;
};
struct RENEW4res {
nfsstat4 status;
};
The RENEW operation is used by the client to renew leases
that it currently holds at a server. In processing the
RENEW request, the server renews all leases associated with
the client. The associated leases are determined by the
clientid provided via the SETCLIENTID operation.
When the client holds delegations, it needs to use RENEW to
detect when the server has determined that the callback path
is down. When the server has made such a determination, only
the RENEW operation will renew the lease on delegations.
If the server determines the callback path is down, it
returns NFS4ERR_CB_PATH_DOWN. Even though it returns
NFS4ERR_CB_PATH_DOWN, the server MUST renew the lease on
the byte-range locks and share reservations that the client has
established on the server. If for some reason the lock and
share reservation lease cannot be renewed, then the server
MUST return an error other than NFS4ERR_CB_PATH_DOWN, even
if the callback path is also down. In the event that
the server has conditions such that it could return either
NFS4ERR_CB_PATH_DOWN or NFS4ERR_LEASE_MOVED,
NFS4ERR_LEASE_MOVED MUST be handled first.
The client that issues RENEW MUST choose the principal,
RPC security flavor, and, if applicable, GSS-API mechanism
and service via one of the following algorithms:
The client uses the same principal, RPC security flavor,
and -- if the flavor was RPCSEC_GSS -- the same mechanism and
service that were used when the client ID was established
via SETCLIENTID_CONFIRM.
The client uses any principal, RPC security flavor, mechanism,
and service combination that currently has an OPEN file
on the server. That is, the same principal had a successful
OPEN operation; the file is still open by that principal;
and the flavor, mechanism, and service of RENEW match that
of the previous OPEN.
The server MUST reject a RENEW that does not use one of the
aforementioned algorithms, with the error NFS4ERR_ACCESS.
(sfh) -> (cfh)
/* SAVED_FH: */
void;
struct RESTOREFH4res {
/* CURRENT_FH: value of saved fh */
nfsstat4 status;
};
Set the current filehandle to the value in the saved
filehandle. If there is no saved filehandle, then return the
error NFS4ERR_RESTOREFH.
Operations like OPEN and LOOKUP use the current filehandle to
represent a directory and replace it with a new filehandle.
Assuming that the previous filehandle was saved with a SAVEFH
operator, the previous filehandle can be restored as
the current filehandle. This is commonly used to obtain
post-operation attributes for the directory, e.g.,
PUTFH (directory filehandle)
SAVEFH
GETATTR attrbits (pre-op dir attrs)
CREATE optbits "foo" attrs
GETATTR attrbits (file attributes)
RESTOREFH
GETATTR attrbits (post-op dir attrs)
(cfh) -> (sfh)
/* CURRENT_FH: */
void;
struct SAVEFH4res {
/* SAVED_FH: value of current fh */
nfsstat4 status;
};
Save the current filehandle. If a previous filehandle was
saved, then it is no longer accessible. The saved filehandle
can be restored as the current filehandle with the RESTOREFH
operator.
On success, the current filehandle retains its value.
(cfh), name -> { secinfo }
struct SECINFO4args {
/* CURRENT_FH: directory */
component4 name;
};
/*
* From RFC 2203
*/
enum rpc_gss_svc_t {
RPC_GSS_SVC_NONE = 1,
RPC_GSS_SVC_INTEGRITY = 2,
RPC_GSS_SVC_PRIVACY = 3
};
struct rpcsec_gss_info {
sec_oid4 oid;
qop4 qop;
rpc_gss_svc_t service;
};
/* RPCSEC_GSS has a value of '6'. See RFC 2203 */
union secinfo4 switch (uint32_t flavor) {
case RPCSEC_GSS:
rpcsec_gss_info flavor_info;
default:
void;
};
typedef secinfo4 SECINFO4resok<>;
union SECINFO4res switch (nfsstat4 status) {
case NFS4_OK:
SECINFO4resok resok4;
default:
void;
};
The SECINFO operation is used by the client to obtain a list
of valid RPC authentication flavors for a specific directory
filehandle, filename pair. SECINFO should apply the same
access methodology used for LOOKUP when evaluating the name.
Therefore, if the requester does not have the appropriate
access to perform a LOOKUP for the name, then SECINFO must
behave the same way and return NFS4ERR_ACCESS.
The result will contain an array that represents the security
mechanisms available, with an order corresponding to the server's
preferences, the most preferred being first in the array. The
client is free to pick whatever security mechanism it both
desires and supports, or to pick -- in the server's preference
order -- the first one it supports. The array entries are
represented by the secinfo4 structure. The field 'flavor'
will contain a value of AUTH_NONE, AUTH_SYS (as defined in
), or RPCSEC_GSS (as defined in
).
For the flavors AUTH_NONE and AUTH_SYS, no additional security
information is returned. For a return value of RPCSEC_GSS,
a security triple is returned that contains the mechanism
object id (as defined in ), the quality
of protection (as defined in ), and the
service type (as defined in ). It
is possible for SECINFO to return multiple entries with
flavor equal to RPCSEC_GSS, with different security triple values.
On success, the current filehandle retains its value.
If the name has a length of 0 (zero), or if the name does not obey
the UTF-8 definition, the error NFS4ERR_INVAL will be returned.
The SECINFO operation is expected to be used by the NFS
client when the error value of NFS4ERR_WRONGSEC is returned
from another NFS operation. This signifies to the client
that the server's security policy is different from what
the client is currently using. At this point, the client is
expected to obtain a list of possible security flavors and
choose what best suits its policies.
As mentioned, the server's security policies will
determine when a client request receives NFS4ERR_WRONGSEC.
The operations that may receive this error are LINK,
LOOKUP, LOOKUPP, OPEN, PUTFH, PUTPUBFH, PUTROOTFH, RENAME,
RESTOREFH, and, indirectly, READDIR. LINK and RENAME will only
receive this error if the security used for the operation
is inappropriate for the saved filehandle. With the exception
of READDIR, these operations represent the point at which
the client can instantiate a filehandle into the
current filehandle at the server. The filehandle is either provided
by the client (PUTFH, PUTPUBFH, PUTROOTFH) or generated as a
result of a name-to-filehandle translation (LOOKUP and OPEN).
RESTOREFH is different because the filehandle is a result of a
previous SAVEFH. Even though the filehandle, for RESTOREFH,
might have previously passed the server's inspection for a
security match, the server will check it again on RESTOREFH
to ensure that the security policy has not changed.
If the client wants to resolve an error return of
NFS4ERR_WRONGSEC, the following will occur:
For LOOKUP and OPEN, the client will use SECINFO with the
same current filehandle and name as provided in the original
LOOKUP or OPEN to enumerate the available security triples.
For LINK, PUTFH, RENAME, and RESTOREFH, the client will
use SECINFO and provide the parent directory filehandle and
the object name that corresponds to the filehandle originally
provided by the PUTFH or RESTOREFH, or, for LINK and RENAME,
the SAVEFH.
For LOOKUPP, PUTROOTFH, and PUTPUBFH, the client will be unable
to use the SECINFO operation since SECINFO requires a
current filehandle and none exist for these three operations.
Therefore, the client must iterate through the security
triples available at the client and re&nbhy;attempt the
PUTROOTFH or PUTPUBFH operation. In the unfortunate event
that none of the MANDATORY security triples are supported by
the client and server, the client SHOULD try using others that
support integrity. Failing that, the client can try using
AUTH_NONE, but because such forms lack integrity checks,
this puts the client at risk. Nonetheless, the server
SHOULD allow the client to use whatever security form the
client requests and the server supports, since the risks
of doing so are on the client.
The READDIR operation will not directly return the
NFS4ERR_WRONGSEC error. However, if the READDIR request
included a request for attributes, it is possible that the
READDIR request's security triple does not match that of
a directory entry. If this is the case and the client has
requested the rdattr_error attribute, the server will return
the NFS4ERR_WRONGSEC error in rdattr_error for the entry.
Note that a server MAY use the AUTH_NONE flavor to signify that
the client is allowed to attempt to use authentication flavors
that are not explicitly listed in the SECINFO results.
Instead of using a listed flavor, the client might then,
for instance, opt to use an otherwise unlisted RPCSEC_GSS
mechanism instead of AUTH_NONE. It may wish to do so in order
to meet an application requirement for data integrity or privacy.
In choosing to use an unlisted flavor, the client SHOULD always
be prepared to handle a failure by falling back to using AUTH_NONE
or another listed flavor. It cannot assume that identity mapping
is supported and should be prepared for the fact that its identity
is squashed.
See for a discussion
on the recommendations for security flavors used by SECINFO.
(cfh), stateid, attrmask, attr_vals -> attrsset
struct SETATTR4args {
/* CURRENT_FH: target object */
stateid4 stateid;
fattr4 obj_attributes;
};
struct SETATTR4res {
nfsstat4 status;
bitmap4 attrsset;
};
The SETATTR operation changes one or more of the attributes of
a file system object. The new attributes are specified with a
bitmap and the attributes that follow the bitmap in bit order.
The stateid argument for SETATTR is used to provide byte-range
locking context that is necessary for SETATTR requests that
set the size attribute. Since setting the size attribute
modifies the file's data, it has the same locking requirements
as a corresponding WRITE. Any SETATTR that sets the size
attribute is incompatible with a share reservation that
specifies OPEN4_SHARE_DENY_WRITE. The area between the old end-of-file
and the new end-of-file is considered to be modified just
as would have been the case had the area in question been
specified as the target of WRITE, for the purpose of checking
conflicts with byte-range locks, for those cases in which a
server is implementing mandatory byte-range locking behavior.
A valid stateid SHOULD always be specified. When the file
size attribute is not set, the special anonymous stateid
MAY be passed.
On either success or failure of the operation, the server
will return the attrsset bitmask to represent what (if any)
attributes were successfully set. The attrsset in the response
is a subset of the bitmap4 that is part of the obj_attributes
in the argument.
On success, the current filehandle retains its value.
If the request specifies the owner attribute to be set, the
server SHOULD allow the operation to succeed if the current
owner of the object matches the value specified in the request.
Some servers may be implemented in such a way as to prohibit
the setting of the owner attribute unless the requester has the
privilege to do so. If the server is lenient in this one
case of matching owner values, the client implementation may
be simplified in cases of creation of an object
(e.g., an exclusive create via OPEN) followed by a SETATTR.
The file size attribute is used to request changes to the
size of a file. A value of zero causes the file to
be truncated, a value less than the current size of the
file causes data from the new size to the end of the file to
be discarded, and a size greater than the current size of
the file causes logically zeroed data bytes to be added to
the end of the file. Servers are free to implement this
using holes or actual zero data bytes. Clients should not
make any assumptions regarding a server's implementation of
this feature, beyond that the bytes returned will be zeroed.
Servers MUST support extending the file size via SETATTR.
SETATTR is not guaranteed atomic. A failed SETATTR may
partially change a file's attributes -- hence, the reason why
the reply always includes the status and the list of attributes
that were set.
If the object whose attributes are being changed has a file
delegation that is held by a client other than the one doing the
SETATTR, the delegation(s) must be recalled, and the operation cannot
proceed to actually change an attribute until each such delegation is
returned or revoked. In all cases in which delegations are recalled,
the server is likely to return one or more NFS4ERR_DELAY errors while
the delegation(s) remains outstanding, although it might not do that
if the delegations are returned quickly.
Changing the size of a file with SETATTR indirectly changes
the time_modify and change attributes. A client must account for
this, as size changes can result in data deletion.
The attributes time_access_set and time_modify_set are
write-only attributes constructed as a switched union so the
client can direct the server in setting the time values.
If the switched union specifies SET_TO_CLIENT_TIME4, the
client has provided an nfstime4 to be used for the operation.
If the switch union does not specify SET_TO_CLIENT_TIME4, the
server is to use its current time for the SETATTR operation.
If server and client times differ, programs that compare
client times to file times can break. A time maintenance
protocol should be used to limit client/server time skew.
Use of a COMPOUND containing a VERIFY operation specifying
only the change attribute, immediately followed by a SETATTR,
provides a means whereby a client may specify a request that
emulates the functionality of the SETATTR guard mechanism of
NFSv3. Since the function of the guard mechanism
is to avoid changes to the file attributes based on stale
information, delays between checking of the guard condition
and the setting of the attributes have the potential to
compromise this function, as would the corresponding delay in
the NFSv4 emulation. Therefore, NFSv4 servers
should take care to avoid such delays, to the degree possible,
when executing such a request.
If the server does not support an attribute as requested by
the client, the server should return NFS4ERR_ATTRNOTSUPP.
A mask of the attributes actually set is returned by SETATTR
in all cases. That mask MUST NOT include attribute bits not
requested to be set by the client. If the attribute masks in
the request and reply are equal, the status field in the reply
MUST be NFS4_OK.
client, callback, callback_ident -> clientid, setclientid_confirm
struct SETCLIENTID4args {
nfs_client_id4 client;
cb_client4 callback;
uint32_t callback_ident;
};
struct SETCLIENTID4resok {
clientid4 clientid;
verifier4 setclientid_confirm;
};
union SETCLIENTID4res switch (nfsstat4 status) {
case NFS4_OK:
SETCLIENTID4resok resok4;
case NFS4ERR_CLID_INUSE:
clientaddr4 client_using;
default:
void;
};
The client uses the SETCLIENTID operation to notify the server
of its intention to use a particular client identifier,
callback, and callback_ident for subsequent requests that
entail creating lock, share reservation, and delegation
state on the server. Upon successful completion the server
will return a shorthand client ID that, if confirmed via a
separate step, will be used in subsequent file locking and
file open requests. Confirmation of the client ID must be done
via the SETCLIENTID_CONFIRM operation to return the client ID
and setclientid_confirm values, as verifiers, to the server.
Two verifiers are necessary because it is possible to use
SETCLIENTID and SETCLIENTID_CONFIRM to modify the callback and
callback_ident information but not the shorthand client ID. In
that event, the setclientid_confirm value is effectively the
only verifier.
The callback information provided in this operation will
be used if the client is provided an open delegation at a
future point. Therefore, the client must correctly reflect
the program and port numbers for the callback program at the
time SETCLIENTID is used.
The callback_ident value is used by the server on the callback.
The client can leverage the callback_ident to eliminate the
need for more than one callback RPC program number, while
still being able to determine which server is initiating
the callback.
To understand how to implement SETCLIENTID, make the following
notations. Let:
be the value of the client.id subfield of the
SETCLIENTID4args structure.
be the value of the client.verifier subfield of the
SETCLIENTID4args structure.
be the value of the client ID field returned in the
SETCLIENTID4resok structure.
represent the value combination of the callback and
callback_ident fields of the SETCLIENTID4args structure.
be the setclientid_confirm value returned in the
SETCLIENTID4resok structure.
be a quintuple for a client record. A client
record is confirmed if there has been a SETCLIENTID_CONFIRM
operation to confirm it. Otherwise, it is unconfirmed. An
unconfirmed record is established by a SETCLIENTID call.
Since SETCLIENTID is a non-idempotent operation, let us assume
that the server is implementing the duplicate request cache (DRC).
When the server gets a SETCLIENTID { v, x, k } request,
it processes it in the following manner.
It first looks up the request in the DRC. If there is a
hit, it returns the result cached in the DRC. The server
does NOT remove client state (locks, shares, delegations),
nor does it modify any recorded callback and callback_ident
information for client { x }.
For any DRC miss, the server takes the client ID string
x, and searches for client records for x that the server
may have recorded from previous SETCLIENTID calls. For
any confirmed record with the same id string x, if the
recorded principal does not match that of the
SETCLIENTID call, then the server returns
an NFS4ERR_CLID_INUSE error.
For brevity of discussion, the remaining description of
the processing assumes that there was a DRC miss, and
that where the server has previously recorded a confirmed
record for client x, the aforementioned principal check
has successfully passed.
The server checks if it has recorded a confirmed record for
{ v, x, c, l, s }, where l may or may not equal k. If so,
and since the id verifier v of the request matches that
which is confirmed and recorded, the server treats this
as a probable callback information update and records an
unconfirmed { v, x, c, k, t } and leaves the confirmed { v,
x, c, l, s } in place, such that t != s.
It does not matter whether k equals l or not. Any
pre&nbhy;existing unconfirmed { v, x, c, *, * } is removed.
The server returns { c, t }. It is indeed returning the
old clientid4 value c, because the client apparently only
wants to update callback value k to value l. It's possible
this request is one from the Byzantine router that has
stale callback information, but this is not a problem.
The callback information update is only confirmed if
followed up by a SETCLIENTID_CONFIRM { c, t }.
The server awaits confirmation of k via SETCLIENTID_CONFIRM
{ c, t }.
The server does NOT remove client (lock/share/delegation)
state for x.
The server has previously recorded a confirmed { u, x, c,
l, s } record such that v != u, l may or may not equal k,
and has not recorded any unconfirmed { *, x, *, *, * }
record for x. The server records an unconfirmed { v, x,
d, k, t } (d != c, t != s).
The server returns { d, t }.
The server awaits confirmation of { d, k } via
SETCLIENTID_CONFIRM { d, t }.
The server does NOT remove client (lock/share/delegation)
state for x.
The server has previously recorded a confirmed { u, x, c,
l, s } record such that v != u, l may or may not equal k,
and recorded an unconfirmed { w, x, d, m, t } record such
that c != d, t != s, m may or may not equal k, m may or may
not equal l, and k may or may not equal l. Whether w == v
or w != v makes no difference. The server simply removes
the unconfirmed { w, x, d, m, t } record and replaces it
with an unconfirmed { v, x, e, k, r } record, such that e !=
d, e != c, r != t, r != s.
The server returns { e, r }.
The server awaits confirmation of { e, k } via
SETCLIENTID_CONFIRM { e, r }.
The server does NOT remove client (lock/share/delegation)
state for x.
The server has no confirmed { *, x, *, *, * } for x. It
may or may not have recorded an unconfirmed { u, x, c,
l, s }, where l may or may not equal k, and u may or may
not equal v. Any unconfirmed record { u, x, c, l, * },
regardless of whether u == v or l == k, is replaced with an
unconfirmed record { v, x, d, k, t } where d != c, t != s.
The server returns { d, t }.
The server awaits confirmation of { d, k } via
SETCLIENTID_CONFIRM { d, t }. The server does NOT remove
client (lock/share/delegation) state for x.
The server generates the clientid and setclientid_confirm
values and must take care to ensure that these values are
extremely unlikely to ever be regenerated.
clientid, setclientid_confirm -> -
struct SETCLIENTID_CONFIRM4args {
clientid4 clientid;
verifier4 setclientid_confirm;
};
struct SETCLIENTID_CONFIRM4res {
nfsstat4 status;
};
This operation is used by the client to confirm the results
from a previous call to SETCLIENTID. The client provides
the server-supplied (from a SETCLIENTID response) client ID.
The server responds with a simple status of success or failure.
The client must use the SETCLIENTID_CONFIRM operation to
confirm the following two distinct cases:
The client's use of a new shorthand client identifier (as
returned from the server in the response to SETCLIENTID),
a new callback value (as specified in the arguments
to SETCLIENTID), and a new callback_ident value (as
specified in the arguments to SETCLIENTID). The client's
use of SETCLIENTID_CONFIRM in this case also confirms
the removal of any of the client's previous relevant
leased state. Relevant leased client state includes
byte-range locks, share reservations, and -- where the
server does not support the CLAIM_DELEGATE_PREV claim type --
delegations. If the server supports CLAIM_DELEGATE_PREV,
then SETCLIENTID_CONFIRM MUST NOT remove delegations for
this client; relevant leased client state would then just
include byte-range locks and share reservations.
The client's reuse of an old, previously confirmed
shorthand client identifier; a new callback value;
and a new callback_ident value. The client's use of
SETCLIENTID_CONFIRM in this case MUST NOT result in
the removal of any previous leased state (locks, share
reservations, and delegations).
We use the same notation and definitions for v, x, c, k, s,
and unconfirmed and confirmed client records as introduced in
the description of the SETCLIENTID operation. The arguments
to SETCLIENTID_CONFIRM are indicated by the notation { c, s
}, where c is a value of type clientid4, and s is a value of
type verifier4 corresponding to the setclientid_confirm field.
As with SETCLIENTID, SETCLIENTID_CONFIRM is a non-idempotent
operation, and we assume that the server is implementing the
duplicate request cache (DRC).
When the server gets a SETCLIENTID_CONFIRM { c, s } request,
it processes it in the following manner.
It first looks up the request in the DRC. If there is a hit,
it returns the result cached in the DRC. The server does
not remove any relevant leased client state, nor does it
modify any recorded callback and callback_ident information
for client { x } as represented by the shorthand value c.
For a DRC miss, the server checks for client records that match
the shorthand value c. The processing cases are as follows:
The server has recorded an unconfirmed { v, x, c, k, s }
record and a confirmed { v, x, c, l, t } record, such
that s != t. If the principals of the records do not
match that of the SETCLIENTID_CONFIRM, the server returns
NFS4ERR_CLID_INUSE, and no relevant leased client state
is removed and no recorded callback and callback_ident
information for client { x } is changed. Otherwise, the
confirmed { v, x, c, l, t } record is removed and the
unconfirmed { v, x, c, k, s } is marked as confirmed,
thereby modifying recorded and confirmed callback and
callback_ident information for client { x }.
The server does not remove any relevant leased client state.
The server returns NFS4_OK.
The server has not recorded an unconfirmed { v, x, c, *, * }
and has recorded a confirmed { v, x, c, *, s }. If the
principals of the record and of SETCLIENTID_CONFIRM do
not match, the server returns NFS4ERR_CLID_INUSE without
removing any relevant leased client state, and without
changing recorded callback and callback_ident values for
client { x }.
If the principals match, then what has likely
happened is that the client never got the response
from the SETCLIENTID_CONFIRM, and the DRC entry has been
purged. Whatever the scenario, since the principals match,
as well as { c, s } matching a confirmed record, the server
leaves client x's relevant leased client state intact,
leaves its callback and callback_ident values unmodified,
and returns NFS4_OK.
The server has not recorded a confirmed { *, *, c, *, * }
and has recorded an unconfirmed { *, x, c, k, s }.
Even if this is a retry from the client, nonetheless the
client's first SETCLIENTID_CONFIRM attempt was not received
by the server. Retry or not, the server doesn't know, but
it processes it as if it were a first try. If the principal
of the unconfirmed { *, x, c, k, s } record mismatches
that of the SETCLIENTID_CONFIRM request, the server returns
NFS4ERR_CLID_INUSE without removing any relevant leased
client state.
Otherwise, the server records a confirmed { *, x, c, k, s }.
If there is also a confirmed { *, x, d, *, t }, the server
MUST remove client x's relevant leased client state and
overwrite the callback state with k. The confirmed
record { *, x, d, *, t } is removed.
The server returns NFS4_OK.
The server has no record of a confirmed or unconfirmed { *,
*, c, *, s }. The server returns NFS4ERR_STALE_CLIENTID.
The server does not remove any relevant leased client state,
nor does it modify any recorded callback and callback_ident
information for any client.
The server needs to cache unconfirmed { v, x, c, k, s } client
records and await for some time their confirmation. As should
be clear from the discussions of record processing for SETCLIENTID
and SETCLIENTID_CONFIRM, there are cases where the server
does not deterministically remove unconfirmed client records.
To avoid running out of resources, the server is not required
to hold unconfirmed records indefinitely. One strategy the
server might use is to set a limit on how many unconfirmed
client records it will maintain and then, when the limit
would be exceeded, remove the oldest record. Another strategy
might be to remove an unconfirmed record when some amount of
time has elapsed. The choice of the amount of time is fairly
arbitrary, but it is surely no higher than the server's lease
time period. Consider that leases need to be renewed before
the lease time expires via an operation from the client.
If the client cannot issue a SETCLIENTID_CONFIRM after a
SETCLIENTID before a period of time equal to a lease expiration
time, then the client is unlikely to be able to maintain state on
the server during steady-state operation.
If the client does send a SETCLIENTID_CONFIRM for an
unconfirmed record that the server has already deleted, the
client will get NFS4ERR_STALE_CLIENTID back. If so, the client
should then start over, and send SETCLIENTID to re-establish
an unconfirmed client record and get back an unconfirmed
client ID and setclientid_confirm verifier. The client should
then send the SETCLIENTID_CONFIRM to confirm the client ID.
SETCLIENTID_CONFIRM does not establish or renew a lease.
However, if SETCLIENTID_CONFIRM removes relevant leased client
state, and that state does not include existing delegations,
the server MUST allow the client a period of time no less
than the value of the lease_time attribute, to reclaim (via
the CLAIM_DELEGATE_PREV claim type of the OPEN operation)
its delegations before removing unreclaimed delegations.
(cfh), fattr -> -
struct VERIFY4args {
/* CURRENT_FH: object */
fattr4 obj_attributes;
};
struct VERIFY4res {
nfsstat4 status;
};
The VERIFY operation is used to verify that attributes have a
value assumed by the client before proceeding with subsequent
operations in the COMPOUND request. If any of the attributes
do not match, then the error NFS4ERR_NOT_SAME must be returned.
The current filehandle retains its value after successful
completion of the operation.
One possible use of the VERIFY operation is the following
COMPOUND sequence. With this, the client is attempting to
verify that the file being removed will match what the client
expects to be removed. This sequence can help prevent the
unintended deletion of a file.
PUTFH (directory filehandle)
LOOKUP (filename)
VERIFY (filehandle == fh)
PUTFH (directory filehandle)
REMOVE (filename)
This sequence does not prevent a second client from removing
and creating a new file in the middle of this sequence, but
it does help avoid the unintended result.
In the case that a RECOMMENDED attribute is specified in the
VERIFY operation and the server does not support that attribute
for the file system object, the error NFS4ERR_ATTRNOTSUPP is
returned to the client.
When the attribute rdattr_error or any write-only attribute
(e.g., time_modify_set) is specified, the error NFS4ERR_INVAL
is returned to the client.
(cfh), stateid, offset, stable, data -> count, committed, writeverf
enum stable_how4 {
UNSTABLE4 = 0,
DATA_SYNC4 = 1,
FILE_SYNC4 = 2
};
struct WRITE4args {
/* CURRENT_FH: file */
stateid4 stateid;
offset4 offset;
stable_how4 stable;
opaque data<>;
};
struct WRITE4resok {
count4 count;
stable_how4 committed;
verifier4 writeverf;
};
union WRITE4res switch (nfsstat4 status) {
case NFS4_OK:
WRITE4resok resok4;
default:
void;
};
The WRITE operation is used to write data to a regular file.
The target file is specified by the current filehandle.
The offset specifies the offset where the data should be
written. An offset of 0 (zero) specifies that the write should
start at the beginning of the file. The count, as encoded
as part of the opaque data parameter, represents the number
of bytes of data that are to be written. If the count is 0
(zero), the WRITE will succeed and return a count of 0 (zero)
subject to permissions checking. The server may choose to
write fewer bytes than requested by the client.
Part of the WRITE request is a specification of how the WRITE
is to be performed. The client specifies with the stable
parameter the method of how the data is to be processed
by the server. If stable is FILE_SYNC4,
the server must commit the data written plus all file system
metadata to stable storage before returning results. This
corresponds to the NFSv2 protocol semantics. Any other
behavior constitutes a protocol violation. If stable is
DATA_SYNC4, then the server must commit all of the
data to stable storage and enough of the metadata to retrieve
the data before returning. The server implementer is free to
implement DATA_SYNC4 in the same fashion as FILE_SYNC4, but
with a possible performance drop. If stable is UNSTABLE4,
the server is free to commit any part of the
data and the metadata to stable storage, including all or none,
before returning a reply to the client. There is no guarantee
whether or when any uncommitted data will subsequently be
committed to stable storage. The only guarantees made by the
server are that it will not destroy any data without changing
the value of verf and that it will not commit the data and
metadata at a level less than that requested by the client.
The stateid value for a WRITE request represents a value
returned from a previous byte-range lock or share reservation
request or the stateid associated with a delegation.
The stateid is used by the server to verify that
the associated share reservation and any byte-range locks are
still valid and to update lease timeouts for the client.
Upon successful completion, the following results are returned.
The count result is the number of bytes of data written to
the file. The server may write fewer bytes than requested. If
so, the actual number of bytes written starting at location,
offset, is returned.
The server also returns an indication of the level of
commitment of the data and metadata via committed. If the
server committed all data and metadata to stable storage,
committed should be set to FILE_SYNC4. If the level of
commitment was at least as strong as DATA_SYNC4, then
committed should be set to DATA_SYNC4. Otherwise, committed
must be returned as UNSTABLE4. If stable was FILE4_SYNC, then
committed must also be FILE_SYNC4: anything else constitutes a
protocol violation. If stable was DATA_SYNC4, then committed
may be FILE_SYNC4 or DATA_SYNC4: anything else constitutes a
protocol violation. If stable was UNSTABLE4, then committed
may be either FILE_SYNC4, DATA_SYNC4, or UNSTABLE4.
The final portion of the result is the write verifier.
The write verifier is a cookie that the client can use to
determine whether the server has changed instance (boot) state
between a call to WRITE and a subsequent call to either WRITE
or COMMIT. This cookie must be consistent during a single
instance of the NFSv4 protocol service and must be
unique between instances of the NFSv4 protocol server,
where uncommitted data may be lost.
If a client writes data to the server with the stable argument
set to UNSTABLE4 and the reply yields a committed response
of DATA_SYNC4 or UNSTABLE4, the client will follow up at some time
in the future with a COMMIT operation to synchronize
outstanding asynchronous data and metadata with the server's
stable storage, barring client error. It is possible that due
to client crash or other error a subsequent COMMIT will
not be received by the server.
For a WRITE using the special anonymous stateid, the server
MAY allow the WRITE to be serviced subject to mandatory file
locks or the current share deny modes for the file. For a
WRITE using the special READ bypass stateid, the server MUST NOT
allow the WRITE operation to bypass locking checks at the
server, and the WRITE is treated exactly the same as if the
anonymous stateid were used.
On success, the current filehandle retains its value.
It is possible for the server to write fewer bytes of data than
requested by the client. In this case, the server should not
return an error unless no data was written at all. If the
server writes less than the number of bytes specified, the
client should issue another WRITE to write the remaining data.
It is assumed that the act of writing data to a file will
cause the time_modify attribute of the file to be updated.
However, the time_modify attribute of the file should not be
changed unless the contents of the file are changed. Thus, a
WRITE request with count set to 0 should not cause the
time_modify attribute of the file to be updated.
The definition of stable storage has been historically a
point of contention. The following expected properties of
stable storage may help in resolving design issues in the
implementation. Stable storage is persistent storage that
survives:
Repeated power failures.
Hardware failures (of any board, power supply, etc.).
Repeated software crashes, including reboot cycle.
This definition does not address failure of the stable storage
module itself.
The verifier is defined to allow a client to detect different
instances of an NFSv4 protocol server over which
cached, uncommitted data may be lost. In the most likely case,
the verifier allows the client to detect server reboots. This
information is required so that the client can safely determine
whether the server could have lost cached data. If the server
fails unexpectedly and the client has uncommitted data from
previous WRITE requests (done with the stable argument set
to UNSTABLE4 and in which the result committed was returned
as UNSTABLE4 as well), it may not have flushed cached data to
stable storage. The burden of recovery is on the client, and
the client will need to retransmit the data to the server.
One suggested way to use the verifier would be to use the time that
the server was booted or the time the server was last started (if
restarting the server without a reboot results in lost buffers).
The committed field in the results allows the client to do
more effective caching. If the server is committing all
WRITE requests to stable storage, then it should return with
committed set to FILE_SYNC4, regardless of the value of the
stable field in the arguments. A server that uses an NVRAM
accelerator may choose to implement this policy. The client
can use this to increase the effectiveness of the cache by
discarding cached data that has already been committed on
the server.
Some implementations may return NFS4ERR_NOSPC instead of
NFS4ERR_DQUOT when a user's quota is exceeded. In the case
that the current filehandle is a directory, the server
will return NFS4ERR_ISDIR. If the current filehandle is
not a regular file or a directory, the server will return
NFS4ERR_INVAL.
If mandatory file locking is on for the file, and a corresponding
record of the data to be written to file is read or write locked
by an owner that is not associated with the stateid, the server
will return NFS4ERR_LOCKED. If so, the client must check if
the owner corresponding to the stateid used with the WRITE
operation has a conflicting read lock that overlaps with
the region that was to be written. If the stateid's owner
has no conflicting read lock, then the client should try to
get the appropriate write byte-range lock via the LOCK operation
before re-attempting the WRITE. When the WRITE completes,
the client should release the byte-range lock via LOCKU.
If the stateid's owner had a conflicting read lock, then
the client has no choice but to return an error to the
application that attempted the WRITE. The reason is that
since the stateid's owner had a read lock, the server either
(1) attempted to temporarily effectively upgrade this
read lock to a write lock or (2) has no upgrade
capability. If the server attempted to upgrade the read lock and
failed, it is pointless for the client to re-attempt the upgrade via
the LOCK operation, because there might be another client
also trying to upgrade. If two clients are blocked trying to
upgrade the same lock, the clients deadlock. If the server
has no upgrade capability, then it is pointless to try a LOCK
operation to upgrade.
lock-owner -> ()
struct RELEASE_LOCKOWNER4args {
lock_owner4 lock_owner;
};
struct RELEASE_LOCKOWNER4res {
nfsstat4 status;
};
This operation is used to notify the server that the lock_owner
is no longer in use by the client and that future client requests
will not reference this lock_owner. This allows the server
to release cached state related to the specified lock_owner.
If file locks associated with the lock_owner are held at
the server, the error NFS4ERR_LOCKS_HELD will be returned
and no further action will be taken.
The client may choose to use this operation to ease the
amount of server state that is held. Information that
can be released when a RELEASE_LOCKOWNER is done includes
the specified lock-owner string, the seqid associated with the
lock-owner, any saved reply for the lock-owner, and any
lock stateids associated with that lock-owner.
Depending on the behavior of applications at the client, it
may be important for the client to use this operation
since the server has certain obligations with respect to
holding a reference to lock-owner-associated state as long
as an associated file is open. Therefore, if the client
knows for certain that the lock_owner will no longer be used
to either reference existing lock stateids associated with the
lock-owner or create new ones, it should use RELEASE_LOCKOWNER.
<null> -> ()
void;
struct ILLEGAL4res {
nfsstat4 status;
};
This operation is a placeholder for encoding a result to
handle the case of the client sending an operation code within
COMPOUND that is not supported. See
for more details.
The status field of ILLEGAL4res MUST be set to
NFS4ERR_OP_ILLEGAL.
A client will probably not send an operation with code
OP_ILLEGAL, but if it does, the response will be ILLEGAL4res,
just as it would be with any other invalid operation code. Note
that if the server gets an illegal operation code that is
not OP_ILLEGAL, and if the server checks for legal operation
codes during the XDR decode phase, then the ILLEGAL4res would
not be returned.
The procedures used for callbacks are defined in the following
sections. In the interest of clarity, the terms "client" and
"server" refer to NFS clients and servers, despite the fact that
for an individual callback RPC, the sense of these terms would
be precisely the opposite.
<null>
void;
void;
Standard NULL procedure. Void argument, void response.
Even though there is no direct functionality associated with
this procedure, the server will use CB_NULL to confirm the
existence of a path for RPCs from server to client.
compoundargs -> compoundres
enum nfs_cb_opnum4 {
OP_CB_GETATTR = 3,
OP_CB_RECALL = 4,
OP_CB_ILLEGAL = 10044
};
union nfs_cb_argop4 switch (unsigned argop) {
case OP_CB_GETATTR:
CB_GETATTR4args opcbgetattr;
case OP_CB_RECALL:
CB_RECALL4args opcbrecall;
case OP_CB_ILLEGAL: void;
};
struct CB_COMPOUND4args {
utf8str_cs tag;
uint32_t minorversion;
uint32_t callback_ident;
nfs_cb_argop4 argarray<>;
};
union nfs_cb_resop4 switch (unsigned resop) {
case OP_CB_GETATTR: CB_GETATTR4res opcbgetattr;
case OP_CB_RECALL: CB_RECALL4res opcbrecall;
case OP_CB_ILLEGAL: CB_ILLEGAL4res opcbillegal;
};
struct CB_COMPOUND4res {
nfsstat4 status;
utf8str_cs tag;
nfs_cb_resop4 resarray<>;
};
The CB_COMPOUND procedure is used to combine one or more of
the callback procedures into a single RPC request. The main
callback RPC program has two main procedures: CB_NULL
and CB_COMPOUND. All other operations use the CB_COMPOUND
procedure as a wrapper.
In the processing of the CB_COMPOUND procedure, the client may
find that it does not have the available resources to execute
any or all of the operations within the CB_COMPOUND sequence.
In this case, the error NFS4ERR_RESOURCE will be returned for
the particular operation within the CB_COMPOUND procedure
where the resource exhaustion occurred. This assumes that
all previous operations within the CB_COMPOUND sequence have
been evaluated successfully.
Contained within the CB_COMPOUND results is a status field.
This status must be equivalent to the status of the last
operation that was executed within the CB_COMPOUND procedure.
Therefore, if an operation incurred an error, then the status
value will be the same error value as is being returned for
the operation that failed.
For the definition of the tag field, see .
The value of callback_ident is supplied by the client
during SETCLIENTID. The server must use the client-supplied
callback_ident during the CB_COMPOUND to allow the client to
properly identify the server.
Illegal operation codes are handled in the same way as they
are handled for the COMPOUND procedure.
The CB_COMPOUND procedure is used to combine individual
operations into a single RPC request. The client interprets
each of the operations in turn. If an operation is executed by
the client and the status of that operation is NFS4_OK, then
the next operation in the CB_COMPOUND procedure is executed.
The client continues this process until there are no more
operations to be executed or one of the operations has a
status value other than NFS4_OK.
fh, attr_request -> attrmask, attr_vals
struct CB_GETATTR4args {
nfs_fh4 fh;
bitmap4 attr_request;
};
struct CB_GETATTR4resok {
fattr4 obj_attributes;
};
union CB_GETATTR4res switch (nfsstat4 status) {
case NFS4_OK:
CB_GETATTR4resok resok4;
default:
void;
};
The CB_GETATTR operation is used by the server to obtain the
current modified state of a file that has been
OPEN_DELEGATE_WRITE delegated. The size attribute and
the change attribute are the only ones guaranteed
to be serviced by the client. See
for a full description of how the client and
server are to interact with the use of CB_GETATTR.
If the filehandle specified is not one for which the client
holds an OPEN_DELEGATE_WRITE delegation, an NFS4ERR_BADHANDLE error
is returned.
The client returns attrmask bits and the associated attribute
values only for the change attribute, and attributes that it
may change (time_modify and size).
stateid, truncate, fh -> ()
struct CB_RECALL4args {
stateid4 stateid;
bool truncate;
nfs_fh4 fh;
};
struct CB_RECALL4res {
nfsstat4 status;
};
The CB_RECALL operation is used to begin the process of
recalling an open delegation and returning it to the server.
The truncate flag is used to optimize a recall for a file
that is about to be truncated to zero. When it is set,
the client is freed of obligation to propagate modified data
for the file to the server, since this data is irrelevant.
If the handle specified is not one for which the client holds
an open delegation, an NFS4ERR_BADHANDLE error is returned.
If the stateid specified is not one corresponding to an
open delegation for the file specified by the filehandle,
an NFS4ERR_BAD_STATEID is returned.
The client should reply to the callback immediately. Replying
does not complete the recall, except when an error was returned.
The recall is not complete until the delegation is returned
using a DELEGRETURN.
<null> -> ()
void;
/*
* CB_ILLEGAL: Response for illegal operation numbers
*/
struct CB_ILLEGAL4res {
nfsstat4 status;
};
This operation is a placeholder for encoding a result to
handle the case of the client sending an operation code within
COMPOUND that is not supported. See for more details.
The status field of CB_ILLEGAL4res MUST be set to
NFS4ERR_OP_ILLEGAL.
A server will probably not send an operation with
code OP_CB_ILLEGAL, but if it does, the response will be
CB_ILLEGAL4res, just as it would be with any other invalid
operation code. Note that if the client gets an illegal
operation code that is not OP_ILLEGAL, and if the client
checks for legal operation codes during the XDR decode phase,
then the CB_ILLEGAL4res would not be returned.
NFS has historically used a model where, from an authentication
perspective, the client was the entire machine, or at least the
source IP address of the machine. The NFS server relied on the NFS
client to make the proper authentication of the end-user. The NFS
server in turn shared its files only to specific clients, as
identified by the client's source IP address. Given this model, the
AUTH_SYS RPC security flavor simply identified the end-user using the
client to the NFS server. When processing NFS responses, the client
ensured that the responses came from the same IP address and port
number that the request was sent to. While such a model is easy to
implement and simple to deploy and use, it is certainly not a safe
model. Thus, NFSv4 mandates that implementations support a security
model that uses end-to-end authentication, where an end-user on a
client mutually authenticates (via cryptographic schemes that do not
expose passwords or keys in the clear on the network) to a
principal on an NFS server. Consideration should also be given
to the integrity and privacy of NFS requests and responses.
The issues of end-to-end mutual authentication, integrity,
and privacy are discussed as part of .
When an NFSv4 mandated security model is used and a security principal or
an NFSv4 name in user@dns_domain form needs to be translated to or from a
local representation as described in
, the translation SHOULD be
done in a secure manner that preserves the integrity of the translation.
For communication with a name service such as the
Lightweight Directory Access Protocol (LDAP) (),
this means employing a security service that uses authentication
and data integrity. Kerberos and Transport Layer Security (TLS)
() are examples of such a security service.
Note that being REQUIRED to implement does not mean REQUIRED to use;
AUTH_SYS can be used by NFSv4 clients and servers. However,
AUTH_SYS is merely an OPTIONAL security flavor in NFSv4, and so
interoperability via AUTH_SYS is not assured.
For reasons of reduced administration overhead, better performance,
and/or reduction of CPU utilization, users of NFSv4
implementations may choose to not use security mechanisms that enable
integrity protection on each remote procedure call and response. The
use of mechanisms without integrity leaves the customer vulnerable to
an attacker in between the NFS client and server that modifies the
RPC request and/or the response. While implementations are free
to provide the option to use weaker security mechanisms, there
are two operations in particular that warrant the implementation
overriding user choices.
The first such operation is SECINFO. It is recommended that the
client issue the SECINFO call such that it is protected with a
security flavor that has integrity protection, such as RPCSEC_GSS
with a security triple that uses either rpc_gss_svc_integrity or
rpc_gss_svc_privacy (rpc_gss_svc_privacy includes integrity
protection) service. Without integrity protection encapsulating
SECINFO and therefore its results, an attacker in the middle could
modify results such that the client might select a weaker algorithm
in the set allowed by the server, making the client and/or server
vulnerable to further attacks.
The second operation that SHOULD use integrity protection
is any GETATTR for the fs_locations attribute. The attack has two
steps. First, the attacker modifies the unprotected results of
some operation to return NFS4ERR_MOVED. Second, when the client
follows up with a GETATTR for the fs_locations attribute, the
attacker modifies the results to cause the client to migrate its
traffic to a server controlled by the attacker.
Because the operations SETCLIENTID/SETCLIENTID_CONFIRM are
responsible for the release of client state, it is imperative
that the principal used for these operations is checked against
and matches with the previous use of these operations. See
for further discussion.
Unicode in the form of UTF-8 is used for file
component names (i.e., both directory and file components),
as well as the owner and owner_group
attributes; other character sets may also be allowed for
file component names. String processing
(e.g., Unicode normalization) raises security concerns for
string comparison. See Sections
and
for further
discussion, and see for related
identifier comparison security considerations. File component
names are identifiers with respect to the identifier comparison
discussion in because they are used to
identify the objects to which ACLs are applied;
see .
This section uses terms that are defined in .
IANA has created a registry called the "NFSv4 Named Attribute Definitions Registry"
for and . This section introduces no new
changes, but it does recap the intent.
The NFSv4 protocol supports the association of a file with zero or
more named attributes. The namespace identifiers for these attributes
are defined as string names. The protocol does not define the
specific assignment of the namespace for these file attributes.
The IANA registry promotes interoperability
where common interests exist. While application developers are
allowed to define and use attributes as needed, they are encouraged
to register the attributes with IANA.
Such registered named attributes are presumed to apply to all minor
versions of NFSv4, including those defined subsequently to the registration.
Where the named attribute is intended to be limited with regard to
the minor versions for which they are not to be used, the
assignment in the registry will clearly state the applicable
limits.
The registry is to be maintained using the Specification Required
policy as defined in Section 4.1 of .
Under the NFSv4 specification, the name of a named
attribute can in theory be up to 2^32 - 1 bytes in
length, but in practice NFSv4 clients and servers
will be unable to handle a string that long. IANA
should reject any assignment request with a named
attribute that exceeds 128 UTF-8 characters. To give
the IESG the flexibility to set up bases of assignment
of Experimental Use and Standards Action,
the prefixes of "EXPE" and "STDS" are Reserved.
The zero-length named attribute name is Reserved.
The prefix "PRIV" is allocated for Private Use. A
site that wants to make use of unregistered named
attributes without risk of conflicting with an
assignment in IANA's registry should use the prefix
"PRIV" in all of its named attributes.
Because some NFSv4 clients and servers have case-insensitive
semantics, the fifteen additional lowercase and mixed-case
permutations of each of "EXPE", "PRIV", and "STDS" are
Reserved (e.g., "expe", "expE", "exPe", etc. are Reserved).
Similarly, IANA must not allow two assignments that would conflict
if both named attributes were converted to a common case.
The registry of named attributes is a list of assignments, each
containing three fields for each assignment.
A US-ASCII string name that is the actual name of
the attribute. This name must be unique. This
string name can be 1 to 128 UTF-8 characters
long.
A reference to the specification of the named attribute.
The reference can consume up to 256 bytes (or more, if IANA
permits).
The point of contact of the registrant. The point of contact
can consume up to 256 bytes (or more, if IANA permits).
There is no initial registry.
The registrant is always permitted to update the point of contact
field. To make any other change will require Expert Review or IESG
Approval.
In addition, because this document obsoletes RFC 3530, IANA has
replaced all references to RFC 3530 in the Network Identifier (r_netid)
registry with references to this document.
replaced the reference to the nfs registration's reference to
RFC 3530 in the GSSAPI/Kerberos/SASL Service names registry
with a reference to this document.
ASCII format for network interchangeThe Unicode Standard, Version 7.0.0The Unicode ConsortiumKey words for use in RFCs to Indicate Requirement LevelsRPCSEC_GSS Protocol SpecificationGeneric Security Service Application Program Interface Version 2, Update 1Internationalizing Domain Names in Applications (IDNA)Punycode: A Bootstring encoding of Unicode for Internationalized Domain Names in Applications (IDNA)UTF-8, a transformation format of ISO 10646Guidelines for Writing an IANA Considerations Section in RFCsRPCSEC_GSS Version 2RPC: Remote Procedure Call Protocol Specification Version 2IANA Considerations for Remote Procedure Call (RPC) Network Identifiers and Universal Address FormatsInternationalized Domain Names for Applications (IDNA): Definitions and Document FrameworkInternationalized Domain Names in Applications (IDNA): ProtocolDeprecate DES, RC4-HMAC-EXP, and Other Weak Cryptographic Algorithms in KerberosNetwork File System (NFS) Version 4 External Data Representation Standard (XDR) Description
Section 3.372 of Chapter 3 of Base Definitions
of The Open Group Base Specifications Issue 7
The Open GroupSpecialCasing-7.0.0.txtThe Unicode ConsortiumNFS: Network File System Protocol specificationNFS Version 3 Protocol SpecificationBinding Protocols for ONC RPC Version 2WebNFS Client SpecificationWebNFS Server SpecificationNFS URL SchemeNFS Version 2 and Version 3 Security Issues and the NFS Protocol's Use of RPCSEC_GSS and Kerberos V5NFS Version 4 Design ConsiderationsSecurity Negotiation for WebNFSNFS version 4 ProtocolAssigned Numbers: RFC 1700 is Replaced by an On-line DatabaseNetwork File System (NFS) version 4 ProtocolThe Kerberos Version 5 Generic Security Service Application Program Interface (GSS-API) Mechanism: Version 2The Simple and Protected Generic Security Service Application Program Interface (GSS-API) Negotiation MechanismXDR: External Data Representation StandardLightweight Directory Access Protocol (LDAP): The ProtocolThe Transport Layer Security (TLS) Protocol Version 1.2Network File System (NFS) Version 4 Minor Version 1 ProtocolTerminology Used in Internationalization in the IETFIssues in Identifier Comparison for Security Purposes The Synchronization of Periodic Routing Messages Improving the Performance
and Correctness of an NFS ServerDigital Equipment Corporation Protocols for Interworking: XNFS, Version 3W, ISBN 1-85912-184-5 The Open Group IESG Processing of RFC Errata for the IETF StreamIESGSection 'read()' of System Interfaces of The Open Group Base Specifications Issue 7
The Open GroupSection 'readdir()' of System Interfaces of The Open Group Base Specifications Issue 7
The Open GroupSection 'stat()' of System Interfaces of The Open Group Base Specifications Issue 7
The Open GroupSection 'write()' of System Interfaces of The Open Group Base Specifications Issue 7
The Open Group
Section 'fcntl()' of System Interfaces of The
Open Group Base Specifications Issue 7
The Open Group
Section 'fsync()' of System Interfaces of The
Open Group Base Specifications Issue 7
The Open Group
Section 'getpwnam()' of System Interfaces of
The Open Group Base Specifications Issue 7
The Open Group
Section 'unlink()' of System Interfaces of The
Open Group Base Specifications Issue 7
The Open GroupIEEE Draft P1003.1e
Institute of Electrical and Electronics Engineers, Inc.
Server Message Block (SMB) Protocol SpecificationMicrosoft Corporation
A bis is certainly built on the shoulders of the first attempt.
Spencer Shepler, Brent Callaghan, David Robinson, Robert Thurlow,
Carl Beame, Mike Eisler, and David Noveck are responsible for a
great deal of the effort in this work.
Tom Haynes would like to thank NetApp, Inc. for its funding of
his time on this project.
Rob Thurlow clarified how a client should contact a new server
if a migration has occurred.
David Black, Nico Williams, Mike Eisler, Trond Myklebust,
James Lentini, and Mike Kupfer read many earlier draft versions
of and contributed numerous useful
suggestions, without which the necessary revision of that
section for this document would not have been possible.
Peter Staubach read almost all of the earlier draft versions of
, leading to the published result,
and his numerous comments were always useful and contributed
substantially to improving the quality of the final result.
Peter Saint-Andre was gracious enough to read the most recent draft
version of and provided some key
insight as to the concerns of the Internationalization community.
James Lentini graciously read the rewrite of
, and his comments were
vital in improving the quality of that effort.
Rob Thurlow, Sorin Faibish, James Lentini, Bruce Fields,
and Trond Myklebust were faithful attendants of the
biweekly triage meeting and accepted many an action item.
Bruce Fields was a good sounding board for both
the third edge condition and courtesy locks in general.
He was also the leading advocate of stamping out
backport issues from .
Marcel Telka was a champion of straightening out the
difference between a lock-owner and an open-owner. He
has also been diligent in reviewing the final document.
Benjamin Kaduk reminded us that DES is dead, and Nico
Williams helped us close the lid on the coffin.
Elwyn Davies provided a very thorough and engaging
Gen-ART review; thanks!