linux-kernel - Re: dup2() vs dup3() inconsistency when

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Message-ID: <48EE703C.7070901@zytor.com>
Date:	Thu, 09 Oct 2008 13:57:32 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ulrich Drepper <drepper@...hat.com>
CC:	mtk.manpages@...il.com, Al Viro <viro@...iv.linux.org.uk>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: dup2() vs dup3() inconsistency when

Ulrich Drepper wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> H. Peter Anvin wrote:
>> The result of dup3(fd, fd, O_CLOEXEC) is to set the O_CLOEXEC flag on fd.
> 
> That's bad and disregarded by Al and myself because it is one and the
> same descriptor and therefore it changes the source descriptor.

It's not the source descriptor, per se, it is the "new" descriptor, 
which happens to have a side effect of closing the "old" descriptor.

>> Step (2) could be considered a bit dubious, but the behaviour of
>> dup2(fd, fd) is a direct consequence of the chosen semantics.
> 
> The behavior of dup2(fd,fd) is just a result of an accident in the
> original implementation.  It makes no sense and the mistake doesn't have
> to be repeated.

Inconsistency is bad, too, and one could *definitely* argue that the 
fundamental problem is the one of closing a pre-existing descriptor 
rather than forcing the user to do that explicitly if that behaviour was 
desired.

	-hpa
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