Re: [RFC][PATCH] nfs: support legacy NFS flock behavior via mount option

[Trond Myklebust <Trond.Myklebust@netapp.com>]

On Tue, 2010-09-07 at 12:08 -0400, Jeff Layton wrote:
> On Tue, 07 Sep 2010 10:17:19 -0400
> Trond Myklebust <Trond.Myklebust@netapp.com> wrote:
> 
> > 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
> 
> Another thought -- we already have "-olock" and "-onolock" and we'll
> have to keep them for compatability. Maybe this should be "-oflock" and
> "-onoflock"?
> 

No thanks. That would require us to add a -onofcntl too, since -onolock
is already defines as being equivalent to -olocal_lock=all

Trond