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Date: Tue, 30 Oct 2012 16:58:19 +0100
From: Jan Schmidt <list.btrfs@jan-o-sch.net>
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To: Hugo Mills <hugo@carfax.org.uk>,
        =?ISO-8859-1?Q?G=E1bor_Nyers?= <gnyers@suse.com>,
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Subject: Re: How to find (out if) files sharing content?
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On Tue, October 30, 2012 at 16:39 (+0100), Hugo Mills wrote:
> It should be possible to walk through the
> extents of a given file, and (I think) follow back-refs from the
> extent back to the other files that share it.

You wish :-) Backrefs are not made to walk them while the file system is online.
However "btrfs inspect logical" manages quite well, at least I haven't heard
otherwise so far. You still need to get the logical block numbers, either by
TREE_SEARCH ioctl or by filefrag.

-Jan