GNU bug report logs - #29961
[PATCH] mv: document the missing atomicity of 'mv -n'

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Message #23 received at 29961 <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Kamil Dudka <kdudka <at> redhat.com>, Pádraig Brady
 <P <at> draigBrady.com>
Cc: 29961 <at> debbugs.gnu.org
Subject: Re: bug#29961: [PATCH] mv -n: do not overwrite the destination
Date: Thu, 4 Jan 2018 01:48:56 -0800

[Message part 1 (text/plain, inline)]

Kamil Dudka wrote:
> -      if (rename (src_name, dst_name) == 0)
> +      int flags = 0;
> +      if (x->interactive == I_ALWAYS_NO)
> +        /* do not replace DST_NAME if it was created since our last check */
> +        flags = RENAME_NOREPLACE;

By then it's too late, as multiple decisions have been made on the basis of 
stat/lstat calls that are still subject to races. It's better to try the 
renameat2 with RENAME_NOREPLACE first thing, and fall back on the existing code 
only if renameat2 fails with errno != EEXIST.

Plus, there are some other problems when combining -u and -n.

How about the attached patch instead?

[0001-mv-improve-n-atomicity.patch (text/x-patch, attachment)]

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