linux-kernel - Re: Finding hardlinks

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Date:	Fri, 05 Jan 2007 16:09:39 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	mikulas@...ax.karlin.mff.cuni.cz
CC:	pavel@....cz, matthew@....cx, bhalevy@...asas.com,
	arjan@...radead.org, jaharkes@...cmu.edu,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	nfsv4@...f.org
Subject: Re: Finding hardlinks

> And does it matter? If you rename a file, tar might skip it no matter of 
> hardlink detection (if readdir races with rename, you can read none of the 
> names of file, one or both --- all these are possible).
> 
> If you have "dir1/a" hardlinked to "dir1/b" and while tar runs you delete 
> both "a" and "b" and create totally new files "dir2/c" linked to "dir2/d", 
> tar might hardlink both "c" and "d" to "a" and "b".
> 
> No one guarantees you sane result of tar or cp -a while changing the tree. 
> I don't see how is_samefile() could make it worse.

There are several cases where changing the tree doesn't affect the
correctness of the tar or cp -a result.  In some of these cases using
samefile() instead of st_ino _will_ result in a corrupted result.

Generally samefile() is _weaker_ than the st_ino interface in
comparing the identity of two files without using massive amounts of
memory.  You're searching for a better solution, not one that is
broken in a different way, aren't you?

Miklos
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