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

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Message-ID: <48EE3D84.6000003@zytor.com>
Date:	Thu, 09 Oct 2008 10:21:08 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	mtk.manpages@...il.com
CC:	Al Viro <viro@...iv.linux.org.uk>,
	Ulrich Drepper <drepper@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: dup2() vs dup3() inconsistency when

Michael Kerrisk wrote:
> Al,
> 
> your 2008-07-26 commit 6c5d0512a091480c9f981162227fdb1c9d70e555 for
> fs/fcntl.c:sys_dup3 contains
> 
> +       if (unlikely(oldfd == newfd))
> +               return -EINVAL;
> 
> This makes dup2() and dup3() differ with respect to the oldfd==newfd
> case (dup2() becomes a no-op, just returning oldfd, dup3() gives the
> EINVAL error.
> 
> Your commit log doesn't explain the rationale for this change.  What
> is it?  (I could guess that it is to error on a case that may be a
> user programming error, but I want to check this with you, so that I
> add the right text to the man page.)
> 

The dup2() behavior comes from the logical consequence of dup2()'s 
"close on reuse"; one would think it would be logical for dup3() to 
behave the same way.

	-hpa
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