linux-kernel - Re: [PATCH] VFS: make file->f_pos access atomic on 32bit arch

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Message-Id: <200809171124.14518.nickpiggin@yahoo.com.au>
Date:	Wed, 17 Sep 2008 11:24:14 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Michael Trimarchi <trimarchimichael@...oo.it>
Cc:	Hisashi Hifumi <hifumi.hisashi@....ntt.co.jp>,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] VFS: make file->f_pos access atomic on 32bit arch

On Wednesday 17 September 2008 00:57, Michael Trimarchi wrote:
> Hi,
>
> ----- Messaggio originale -----
>
> > Da: Nick Piggin <nickpiggin@...oo.com.au>
> > A: Michael Trimarchi <trimarchimichael@...oo.it>
>
> Cc: Hisashi Hifumi <hifumi.hisashi@....ntt.co.jp>;
> akpm@...ux-foundation.org; linux-kernel@...r.kernel.org;
> linux-fsdevel@...r.kernel.org
>
> > Inviato: Martedì 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.
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