linux-kernel - ext4_fiemap gives 0 extents for files smaller than a block (patch included)

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Date:	Wed, 04 Nov 2009 19:42:41 +0100
From:	Leonard Michlmayr <leonard.michlmayr@...il.com>
To:	Andreas Dilger <adilger@....com>
Cc:	Theodore Ts'o <tytso@....edu>, linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: ext4_fiemap gives 0 extents for files smaller than a block (patch
 included)

Fiemap (ioctl) does not return any extents for small files on ext4.
(fm_start=0, fm_length=filesize)

File affected: fs/ext4/extents.c

I found the reason of the bug: wrong rounding. It will not only affect
small files, but any request that overlaps an extent boundary by less
that blocksize.

The attached patch is against 2.6.32-rc5.

Leonard Michlmayr

View attachment "ext4_fiemap_fix.patch" of type "text/x-patch" (746 bytes)