linux-kernel - Re: [RESEND] [PATCH] VFS: make file->f

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Message-ID: <20081009122319.GC1623@ucw.cz>
Date:	Thu, 9 Oct 2008 14:23:19 +0200
From:	Pavel Machek <pavel@...e.cz>
To:	Matthew Wilcox <matthew@....cx>
Cc:	Nick Piggin <nickpiggin@...oo.com.au>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	torvalds@...ux-foundation.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Hisashi Hifumi <hifumi.hisashi@....ntt.co.jp>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Theodore Ts'o <tytso@....edu>
Subject: Re: [RESEND] [PATCH] VFS: make file->f_pos access atomic on 32bit
	arch

On Tue 2008-10-07 20:52:09, Matthew Wilcox wrote:
> 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.

We have append-only files, and normal users should not be able to work
around that restriction.
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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