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

[Nick Piggin]

On Wednesday 17 September 2008 00:57, Michael Trimarchi wrote:
> Hi,
>
> ----- Messaggio originale -----
>
> > Da: Nick Piggin <nickpiggin@xxxxxxxxxxxx>
> > A: Michael Trimarchi <trimarchimichael@xxxxxxxx>
>
> Cc: Hisashi Hifumi <hifumi.hisashi@xxxxxxxxxxxxx>;
> akpm@xxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> linux-fsdevel@xxxxxxxxxxxxxxx
>
> > 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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