Subject: Re: [RFC][PATCH] nfs: support legacy NFS flock behavior via mount
 option
From: Trond Myklebust <Trond.Myklebust@netapp.com>
To: Suresh Jayaraman <sjayaraman@suse.de>
Cc: Neil Brown <neilb@suse.de>,
        Linux NFS mailing list <linux-nfs@vger.kernel.org>
In-Reply-To: <4C84DFA7.7050507@suse.de>
References: <4C84DFA7.7050507@suse.de>
Content-Type: text/plain; charset="UTF-8"
Date: Tue, 07 Sep 2010 10:17:19 -0400
Message-ID: <1283869039.4291.16.camel@heimdal.trondhjem.org>
Sender: linux-nfs-owner@vger.kernel.org
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On Mon, 2010-09-06 at 18:03 +0530, Suresh Jayaraman wrote:
> NFS clients since 2.6.12 support flock()locks by emulating the
> BSD-style locks in terms of POSIX byte range locks. So the NFS client
> does not allow to lock the same file using both flock() and fcntl
> byte-range locks.
> 
> For some Windows applications which seem to use both share mode locks
> (flock()) and fcntl byte range locks sequentially on the same file,
> the locking is failing as the lock has already been acquired. i.e. the
> flock mapped as posix locks collide with actual byte range locks from
> the same process. The problem was observed on a setup with Windows
> clients accessing Excel files on a Samba exported share which is
> originally a NFS mount from a NetApp filer. Since kernels < 2.6.12 does
> not support flock, what was working (as flock locks were local) in
> older kernels is not working with newer kernels.
> 
> This could be seen as a bug in the implementation of the windows
> application or a NFS client regression, but that is debatable.
> In the spirit of not breaking existing setups, this patch adds mount
> options "flock=local" that enables older flock behavior and
> "flock=fcntl" that allows the current flock behavior.

So instead of having a special option for flock only, what say we rather
introduce an option of the form

  -olocal_lock=

which can take the values 'none', 'flock', 'fcntl' (or 'posix'?) and
'all'?

Cheers
  Trond