linux-ext4 - [RFC] FIEMAP on ext3

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Message-ID: <20080416191030.GE15668@unused.rdu.redhat.com>
Date:	Wed, 16 Apr 2008 15:10:30 -0400
From:	Josef Bacik <jbacik@...hat.com>
To:	linux-ext4@...r.kernel.org
Subject: [RFC] FIEMAP on ext3

Hello,

Obviously ext3 doesn't have extents, however it would still be usefull to use it
on sparse files in order to find data/holes within a file.  What I'm thinking is
treat contigous allocated blocks as an extent, and contiguous non-allocated
blocks as extents.  So for example, with Eric's fiemap test program, on a normal
non-sparse file you would only see one large extent for the entire file.  In the
case of a file that has data, hole and then data you would see 3 extents, two
for the two spans of data and one for the span of holes.
FIEMAP_FLAG_NUM_EXTENTS would in that case return 3.  Does this sound like an
acceptable thing to do?  If not, are there any other suggestions on how to do
fiemap in ext3?  Thanks much,

Josef
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