linux-kernel - Re: unexpected rename() behaviour

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Message-ID: <20080329011656.7c38265a@werewolf>
Date:	Sat, 29 Mar 2008 01:16:56 +0100
From:	"J.A. Magallón" <jamagallon@....com>
To:	Ketil Froyn <ketil@...yn.name>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: unexpected rename() behaviour

On Sat, 29 Mar 2008 01:07:52 +0100, Ketil Froyn <ketil@...yn.name> wrote:

> Hi,
> 
> The following behaviour was unexpected (tested on Debian/ext3):
> 
> $ echo 1 > 1
> $ ln 1 2
> $ cat 2
> 1
> $ ./rename 2 1
> $ echo $?
> 0
> $ cat 2
> 1
> 
> The code for ./rename is simple:
> 
> ---
> /* compile: gcc -o rename rename.c */
> #include <stdio.h>
> int main(int argc, char *argv[]) { return rename(argv[1], argv[2]); }
> ---
> 
> I thought this must be wrong behaviour, but I have been unable to 
> confirm what the correct result should be in this special case. rename() 
> returns success, but the source file is intact, which seems odd. The 
> "mv" command specifically checks for cases like this and calls 
> unlink("2") instead of rename("2", "1"). Are all applications meant to 
> do this? What standards describe what rename() should do in cases like this?
> 

man 2 rename:

       If  oldpath  and  newpath are existing hard links referring to the same
       file, then rename() does nothing, and returns a success status.

That's why mv checks the special case.

-- 
J.A. Magallon <jamagallon()ono!com>     \               Software is like sex:
                                         \         It's better when it's free
Mandriva Linux release 2008.1 (Cooker) for i586
Linux 2.6.23-jam05 (gcc 4.2.2 20071128 (4.2.2-2mdv2008.1)) SMP PREEMPT
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