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Subject: Re: file offset corruption on 32-bit machines?
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Pavel Machek <pavel@ucw.cz>
Cc: Lennart Sorensen <lsorense@csclub.uwaterloo.ca>, Jan Kara <jack@suse.cz>,
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Date: Tue, 15 Apr 2008 22:28:55 +0200
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On Tue, 2008-04-15 at 22:06 +0200, Pavel Machek wrote:

> > > I'm not saying this kernel bug is likely to hit in practice. It is
> > > still a kernel bug.
> > > 
> > > Is the slowdown of lseek worth getting rid of this minor bug? Not
> > > sure, probably yes.
> > 
> > I think a slow down is the worse choice.  Adding a note to the
> > documentation saying that "By the way, on 32bit systems the seek call is
> > not atomic for 64bit file offsets, so if you happen to issue two at
> 
> That would be very wrong addition to documentation. If you really
> wanted to do something like this, you would probably want to say
> something like
> 
> "Doing concurrent seeks on one file is undefined. Kernel may end up
> with seeking to some other place."
> 
> Unfortunately, you'd have to get this addition into POSIX standard...

Is not treating the point not similar to undefined? And undefined
semantics cover pretty much anything, including the current behaviour.

FWIW I really think this issue is a non-issue; one cannot expect sane
behaviour of unsynchronized usage of a shared resource.