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

Matthew Wilcox
2008-10-08T02:52:22Z

On Wed, Oct 08, 2008 at 01:35:44PM +1100, Nick Piggin wrote:
> Right you are. That's the fundamental question. The actual details of
> the fix and how likely the race is don't really matter until we
> answer the first question (except to say that the "fix" is never going
> to be free).
>
> We've lasted this long with the current semantics. So the natural
> reaction to anything that strengthens the semantics now is "why?". If
> we do that then we can basically never return to the weaker semantics.
> So there had better be a really good reason.

And it's worth saying that letter-of-the-standard arguments aren't
necessarily enough. Linux does not honour the POSIX guarantee that
writes are atomic (if they cross page boundaries, it's not certain).
This seems like even more of a corner case to me.

--
Matthew Wilcox Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours. We can't possibly take such
a retrograde step."