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Date: Tue, 26 Feb 2002 11:55:48 -0700
From: Andreas Dilger <adilger@turbolabs.com>
To: linux-kernel@vger.kernel.org
Subject: Re: ext3 and undeletion
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On Feb 26, 2002  19:14 +0100, Andreas Ferber wrote:
> On Tue, Feb 26, 2002 at 09:38:22AM -0800, Mike Fedyk wrote:
> > Basically, it would only move the files to the undelete area if the link
> > count == 1.  If you just decremented the link, then unlink() in glibc would
> > work as it does now.
> 
> Always racy if done in userspace, unless you introduce a centralised
> "unlink daemon" (hope no glibc developer reads that, they might be
> tempted to implement such an abomination...):
> 
>      proc1       proc2
>    --------------------
>     stat()
>                 stat()
>     unlink()
>                 unlink()
> 
> *kaboom*, blackhole opens, file is gone.

I had previously suggested to Mike (but he seems to have missed it) that
you should _always_ move files to the undelete area, regardless of how
many links there are.  This avoids all of the races, doesn't increase
space usage at all (because the undelete area is always in the same fs),
and is actually better for the users (because "rm <file>", "unrm <file>"
will always work even if <file> has multiple links).

Cheers, Andreas
--
Andreas Dilger
http://sourceforge.net/projects/ext2resize/
http://www-mddsp.enel.ucalgary.ca/People/adilger/

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