NFSv4.1 Server Implementation
Server support for minorversion 1 can be controlled using the
/proc/fs/nfsd/versions control file. The string output returned
by reading this file will contain either “+4.1” or “-4.1”
correspondingly.
Currently, server support for minorversion 1 is disabled by default.
It can be enabled at run time by writing the string “+4.1” to
the /proc/fs/nfsd/versions control file. Note that to write this
control file, the nfsd service must be taken down. Use your user-mode
nfs-utils to set this up; see rpc.nfsd(8)
(Warning: older servers will interpret “+4.1” and “-4.1” as “+4” and
“-4”, respectively. Therefore, code meant to work on both new and old
kernels must turn 4.1 on or off before turning support for version 4
on or off; rpc.nfsd does this correctly.)
The NFSv4 minorversion 1 (NFSv4.1) implementation in nfsd is based
on RFC 5661.
From the many new features in NFSv4.1 the current implementation
focuses on the mandatory-to-implement NFSv4.1 Sessions, providing
“exactly once” semantics and better control and throttling of the
resources allocated for each client.
Other NFSv4.1 features, Parallel NFS operations in particular,
are still under development out of tree.
See http://wiki.linux-nfs.org/wiki/index.php/PNFS_prototype_design
for more information.
The current implementation is intended for developers only: while it
does support ordinary file operations on clients we have tested against
(including the linux client), it is incomplete in ways which may limit
features unexpectedly, cause known bugs in rare cases, or cause
interoperability problems with future clients. Known issues:
- gss support is questionable: currently mounts with kerberos
from a linux client are possible, but we aren't really
conformant with the spec (for example, we don't use kerberos
on the backchannel correctly).
- no trunking support: no clients currently take advantage of
trunking, but this is a mandatory feature, and its use is
recommended to clients in a number of places. (E.g. to ensure
timely renewal in case an existing connection's retry timeouts
have gotten too long; see section 8.3 of the RFC.)
Therefore, lack of this feature may cause future clients to
fail.
- Incomplete backchannel support: incomplete backchannel gss
support and no support for BACKCHANNEL_CTL mean that
callbacks (hence delegations and layouts) may not be
available and clients confused by the incomplete
implementation may fail.
- Server reboot recovery is unsupported; if the server reboots,
clients may fail.
- We do not support SSV, which provides security for shared
client-server state (thus preventing unauthorized tampering
with locks and opens, for example). It is mandatory for
servers to support this, though no clients use it yet.
- Mandatory operations which we do not support, such as
DESTROY_CLIENTID, FREE_STATEID, SECINFO_NO_NAME, and
TEST_STATEID, are not currently used by clients, but will be
(and the spec recommends their uses in common cases), and
clients should not be expected to know how to recover from the
case where they are not supported. This will eventually cause
interoperability failures.
In addition, some limitations are inherited from the current NFSv4
implementation:
- Incomplete delegation enforcement: if a file is renamed or
unlinked, a client holding a delegation may continue to
indefinitely allow opens of the file under the old name.
The table below, taken from the NFSv4.1 document, lists
the operations that are mandatory to implement (REQ), optional
(OPT), and NFSv4.0 operations that are required not to implement (MNI)
in minor version 1. The first column indicates the operations that
are not supported yet by the linux server implementation.
The OPTIONAL features identified and their abbreviations are as follows:
pNFS Parallel NFS
FDELG File Delegations
DDELG Directory Delegations
The following abbreviations indicate the linux server implementation status.
I Implemented NFSv4.1 operations.
NS Not Supported.
NS* unimplemented optional feature.
P pNFS features implemented out of tree.
PNS pNFS features that are not supported yet (out of tree).
Operations
+———————-+————+————–+—————-+
| Operation | REQ, REC, | Feature | Definition |
| | OPT, or | (REQ, REC, | |
| | MNI | or OPT) | |
+———————-+————+————–+—————-+
| ACCESS | REQ | | Section 18.1 |
NS | BACKCHANNEL_CTL | REQ | | Section 18.33 |
NS | BIND_CONN_TO_SESSION | REQ | | Section 18.34 |
| CLOSE | REQ | | Section 18.2 |
| COMMIT | REQ | | Section 18.3 |
| CREATE | REQ | | Section 18.4 |
I | CREATE_SESSION | REQ | | Section 18.36 |
NS*| DELEGPURGE | OPT | FDELG (REQ) | Section 18.5 |
| DELEGRETURN | OPT | FDELG, | Section 18.6 |
| | | DDELG, pNFS | |
| | | (REQ) | |
NS | DESTROY_CLIENTID | REQ | | Section 18.50 |
I | DESTROY_SESSION | REQ | | Section 18.37 |
I | EXCHANGE_ID | REQ | | Section 18.35 |
NS | FREE_STATEID | REQ | | Section 18.38 |
| GETATTR | REQ | | Section 18.7 |
P | GETDEVICEINFO | OPT | pNFS (REQ) | Section 18.40 |
P | GETDEVICELIST | OPT | pNFS (OPT) | Section 18.41 |
| GETFH | REQ | | Section 18.8 |
NS*| GET_DIR_DELEGATION | OPT | DDELG (REQ) | Section 18.39 |
P | LAYOUTCOMMIT | OPT | pNFS (REQ) | Section 18.42 |
P | LAYOUTGET | OPT | pNFS (REQ) | Section 18.43 |
P | LAYOUTRETURN | OPT | pNFS (REQ) | Section 18.44 |
| LINK | OPT | | Section 18.9 |
| LOCK | REQ | | Section 18.10 |
| LOCKT | REQ | | Section 18.11 |
| LOCKU | REQ | | Section 18.12 |
| LOOKUP | REQ | | Section 18.13 |
| LOOKUPP | REQ | | Section 18.14 |
| NVERIFY | REQ | | Section 18.15 |
| OPEN | REQ | | Section 18.16 |
NS*| OPENATTR | OPT | | Section 18.17 |
| OPEN_CONFIRM | MNI | | N/A |
| OPEN_DOWNGRADE | REQ | | Section 18.18 |
| PUTFH | REQ | | Section 18.19 |
| PUTPUBFH | REQ | | Section 18.20 |
| PUTROOTFH | REQ | | Section 18.21 |
| READ | REQ | | Section 18.22 |
| READDIR | REQ | | Section 18.23 |
| READLINK | OPT | | Section 18.24 |
| RECLAIM_COMPLETE | REQ | | Section 18.51 |
| RELEASE_LOCKOWNER | MNI | | N/A |
| REMOVE | REQ | | Section 18.25 |
| RENAME | REQ | | Section 18.26 |
| RENEW | MNI | | N/A |
| RESTOREFH | REQ | | Section 18.27 |
| SAVEFH | REQ | | Section 18.28 |
| SECINFO | REQ | | Section 18.29 |
NS | SECINFO_NO_NAME | REC | pNFS files | Section 18.45, |
| | | layout (REQ) | Section 13.12 |
I | SEQUENCE | REQ | | Section 18.46 |
| SETATTR | REQ | | Section 18.30 |
| SETCLIENTID | MNI | | N/A |
| SETCLIENTID_CONFIRM | MNI | | N/A |
NS | SET_SSV | REQ | | Section 18.47 |
NS | TEST_STATEID | REQ | | Section 18.48 |
| VERIFY | REQ | | Section 18.31 |
NS*| WANT_DELEGATION | OPT | FDELG (OPT) | Section 18.49 |
| WRITE | REQ | | Section 18.32 |
Callback Operations
+————————-+———–+————-+—————+
| Operation | REQ, REC, | Feature | Definition |
| | OPT, or | (REQ, REC, | |
| | MNI | or OPT) | |
+————————-+———–+————-+—————+
| CB_GETATTR | OPT | FDELG (REQ) | Section 20.1 |
P | CB_LAYOUTRECALL | OPT | pNFS (REQ) | Section 20.3 |
NS*| CB_NOTIFY | OPT | DDELG (REQ) | Section 20.4 |
P | CB_NOTIFY_DEVICEID | OPT | pNFS (OPT) | Section 20.12 |
NS*| CB_NOTIFY_LOCK | OPT | | Section 20.11 |
NS*| CB_PUSH_DELEG | OPT | FDELG (OPT) | Section 20.5 |
| CB_RECALL | OPT | FDELG, | Section 20.2 |
| | | DDELG, pNFS | |
| | | (REQ) | |
NS*| CB_RECALL_ANY | OPT | FDELG, | Section 20.6 |
| | | DDELG, pNFS | |
| | | (REQ) | |
NS | CB_RECALL_SLOT | REQ | | Section 20.8 |
NS*| CB_RECALLABLE_OBJ_AVAIL | OPT | DDELG, pNFS | Section 20.7 |
| | | (REQ) | |
I | CB_SEQUENCE | OPT | FDELG, | Section 20.9 |
| | | DDELG, pNFS | |
| | | (REQ) | |
NS*| CB_WANTS_CANCELLED | OPT | FDELG, | Section 20.10 |
| | | DDELG, pNFS | |
| | | (REQ) | |
+————————-+———–+————-+—————+
Implementation notes:
DELEGPURGE:
- mandatory only for servers that support CLAIM_DELEGATE_PREV and/or
CLAIM_DELEG_PREV_FH (which allows clients to keep delegations that
persist across client reboots). Thus we need not implement this for
now.
EXCHANGE_ID:
- only SP4_NONE state protection supported
- implementation ids are ignored
CREATE_SESSION:
- backchannel attributes are ignored
- backchannel security parameters are ignored
SEQUENCE:
- no support for dynamic slot table renegotiation (optional)
nfsv4.1 COMPOUND rules:
The following cases aren’t supported yet:
- Enforcing of NFS4ERR_NOT_ONLY_OP for: BIND_CONN_TO_SESSION, CREATE_SESSION,
DESTROY_CLIENTID, DESTROY_SESSION, EXCHANGE_ID. - DESTROY_SESSION MUST be the final operation in the COMPOUND request.
Nonstandard compound limitations:
- No support for a sessions fore channel RPC compound that requires both a
ca_maxrequestsize request and a ca_maxresponsesize reply, so we may
fail to live up to the promise we made in CREATE_SESSION fore channel
negotiation. - No more than one IO operation (read, write, readdir) allowed per
compound.
