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Date: Wed, 17 Jul 2002 11:51:31 -0600
Message-Id: <200207171751.g6HHpVc07197@vindaloo.ras.ucalgary.ca>
From: Richard Gooch <rgooch@ras.ucalgary.ca>
To: Andries Brouwer <aebr@win.tue.nl>
Cc: Elladan <elladan@eskimo.com>, Stevie O <stevie@qrpff.net>,
       Alan Cox <alan@lxorguk.ukuu.org.uk>,
       Zack Weinberg <zack@codesourcery.com>, linux-kernel@vger.kernel.org
Subject: Re: close return value (was Re: [ANNOUNCE] Ext3 vs Reiserfs benchmarks)
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Andries Brouwer writes:
> On Tue, Jul 16, 2002 at 09:38:53PM -0700, Elladan wrote:
> 
> > The question is, does the OS standard guarantee that the fd is closed,
> > even if close() returns EINTR or EIO?  Just going by the normal usage of
> > EINTR, one might think otherwise.  It doesn't appear to be documented
> > one way or another.
> > 
> > Alan said you could just issue close again to make sure - the example
> > shows that this is not the case.  A second close is either required or
> > forbidden in that example - and the behavior has to be well defined or
> > you won't know which to do.
> 
> No, the behaviour is not well-defined at all.
> The standard explicitly leaves undefined what happens when close
> returns EINTR or EIO.

However, the only sane thing to do is to explicitly define one way or
another. The standard is broken. Consider a threaded application,
where one thread tries to call close(), gets an error and re-tries,
because it's not sure if the fd was closed or not. If the fd *is*
closed, and the thread loops calling close(), checking for EBADF,
there is a race if another thread tries calling open()/creat()/dup().

The ambiguity in the standard thus results in the impossibility of
writing a race-free application. And no, forcing the application to
protect system calls with mutexes isn't a solution.

Linux should define explicitly what happens on error return from
close(). Let that be the new standard.

				Regards,

					Richard....
Permanent: rgooch@atnf.csiro.au
Current:   rgooch@ras.ucalgary.ca
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