nfsd: revise 4.1 status documentation

Some small updates, a caveat about the minorversion control interface,
and an attempt to put missing features in context.

Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
This commit is contained in:
J. Bruce Fields 2009-09-20 17:01:33 -04:00
parent cd68c374ea
commit 285a0f00c2

View File

@ -11,6 +11,11 @@ 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 the latest NFSv4.1 Internet Draft:
http://tools.ietf.org/html/draft-ietf-nfsv4-minorversion1-29
@ -25,6 +30,49 @@ 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 failure, 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 draft.)
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)
@ -142,6 +190,12 @@ NS*| CB_WANTS_CANCELLED | OPT | FDELG, | Section 20.10 |
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