linux-kernel - fiemap is broken for sparse file in ext4?

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Date:	Fri, 11 Jun 2010 10:15:10 +0800
From:	Tao Ma <tao.ma@...cle.com>
To:	linux-ext4@...r.kernel.org, Theodore Tso <tytso@....edu>,
	linux-kernel@...r.kernel.org
Subject: fiemap is broken for sparse file in ext4?

Hi Ted and other ext4 gurus,
	I found fiemap may be broken for sparse files in ext4. Here is a simple 
example.

dd if=/dev/zero of=testfile1 bs=1M count=1
using fiemap shows that it has a delalloc extent.
Logical: 0 Ext length: 1048576	Physical: 0	flags: 7

flags 7 means FIEMAP_EXTENT_LAST, FIEMAP_EXTENT_UNKNOWN and 
FIEMAP_EXTENT_DELALLOC,

while if we create a sparse file, fiemap will not show the delalloc extent.
dd if=/dev/zero of=testfile1 bs=1M count=1 seek=1
using fiemap shows that it has no extent for the file. while we should 
have some output like:
Logical: 1048576 Ext length: 1048576	Physical: 0	flags: 7

So we have different output with sparse and non-sparse file. Is it a bug 
for ext4?

Regards,
Tao
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