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From: Robert Watson <rwatson@FreeBSD.org>
Date: Mon, 19 Nov 2007 16:03:22 +0000 (UTC)
To: src-committers@FreeBSD.org, cvs-src@FreeBSD.org, cvs-all@FreeBSD.org
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Cc: 
Subject: cvs commit: src/sys/nfsclient nfs_vnops.c
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rwatson     2007-11-19 16:03:22 UTC

  FreeBSD src repository

  Modified files:
    sys/nfsclient        nfs_vnops.c 
  Log:
  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
  MFC after:      1 week
  
  Revision  Changes    Path
  1.277     +4 -25     src/sys/nfsclient/nfs_vnops.c