cvs commit: src/sys/nfsclient nfs_vnops.c

[Robert Watson]

On Sat, 29 Dec 2007, Adam McDougall wrote:

> Can this be merged to 6 as well?  I've been running the patch ported to 
> 6-stable for a while with no problems.  Thanks.

Adam,

Sorry for the delay in responding -- I'll merge this to 6-STABLE after 
6.3-RELEASE is over and done with.

Robert N M Watson
Computer Laboratory
University of Cambridge

>
> On Tue, Nov 27, 2007 at 12:20:59PM +0000, Robert Watson wrote:
>
>  rwatson     2007-11-27 12:20:59 UTC
>
>    FreeBSD src repository
>
>    Modified files:        (Branch: RELENG_7)
>      sys/nfsclient        nfs_vnops.c
>    Log:
>    Merge nfs_vnops.c:1.277 from HEAD to RELENG_7:
>
>      Remove hacks from the NFSv2/3 client intended to handle a lack of a
>      server-side RPC retranmission cache for non-idempotent operations: these
>      hacks substituted 0 (success) for the expected EEXIST in the event that
>      a target name already existed for LINK, SYMLINK, and MKDIR operations,
>      under the assumption that EEXIST represented a second application of the
>      original RPC rather than a true failure.
>
>      Background: certain NFS operations (in this case, LINK, SYMLINK, and
>      MKDIR) are not idempotent, as they leave behind persisting state on the
>      server that prevents them from being replayed without an error;if an UDP
>      RPC reply is lost leading to a retransmission by theclient, the second
>      reply will return EEXIST rather than success, asthe new object has
>      already been created.  The NFS client previouslysilently mapped the
>      EEXIST return into success to paper over thisproblem.
>
>      However, in all modern NFS server implementations, a reply cache is kept
>      in order to retransmit the original reply to a retransmitted request,
>      rather than performing the operation a second time, allowing this hack
>      to be avoided.  This allows link()-based filelocking over NFS to operate
>      correctly, as an application requestingthe creation of a new link for a
>      file to tell if it succeededatomically or not.
>
>      Other NFS clients, including Solaris and Linux, generally follow this
>      behavior for the same reasons.  Most clients also now default to TCP,
>      which also helps avoid the issue of retransmitted but non-idempotent
>      requests in most cases.
>
>      Reported by:    Adam McDougall <mcdouga9 at egr dot msu dot edu>,
>                      Timo Sirainen <tss at iki dot fi>
>      Reviewed by:    mohans
>
>    Approved by:    re (kensmith)
>
>    Revision   Changes    Path
>    1.276.2.1  +4 -25     src/sys/nfsclient/nfs_vnops.c
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