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From: Nick Piggin <nickpiggin@yahoo.com.au>
To: Michael Trimarchi <trimarchimichael@yahoo.it>
Subject: Re: [PATCH] VFS: make file->f_pos access atomic on 32bit arch
Date: Wed, 17 Sep 2008 11:24:14 +1000
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Cc: Hisashi Hifumi <hifumi.hisashi@oss.ntt.co.jp>, akpm@linux-foundation.org,
       linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
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On Wednesday 17 September 2008 00:57, Michael Trimarchi wrote:
> Hi,
>
> ----- Messaggio originale -----
>
> > Da: Nick Piggin <nickpiggin@yahoo.com.au>
> > A: Michael Trimarchi <trimarchimichael@yahoo.it>
>
> Cc: Hisashi Hifumi <hifumi.hisashi@oss.ntt.co.jp>;
> akpm@linux-foundation.org; linux-kernel@vger.kernel.org;
> linux-fsdevel@vger.kernel.org
>
> > Inviato: Marted́ 16 settembre 2008, 16:11:21
> > Oggetto: Re: [PATCH] VFS: make file->f_pos access atomic on 32bit arch
>
> ...
>
> > >  i was thinking about introducing a file_pos_update() not implemented
> > > using file_pos_read()/file_pos_write() and taking the seq_lock or
> > > disabling preemption only one time
> >
> > AFAIK, the only way to do an atomic 64 bit store on 32-bit x86 is
> > "cmpxchg8b" (with lock prefix on SMP). That would be far slower
> > I'm sure.
>
> Maybe it is clear with an example:

I understand and agree.