From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1LqWMW-0003B1-74
	for qemu-devel@nongnu.org; Sun, 05 Apr 2009 13:42:28 -0400
Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43)
	id 1LqWMR-00039O-Im
	for qemu-devel@nongnu.org; Sun, 05 Apr 2009 13:42:27 -0400
Received: from [199.232.76.173] (port=34555 helo=monty-python.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1LqWMR-00039K-7E
	for qemu-devel@nongnu.org; Sun, 05 Apr 2009 13:42:23 -0400
Received: from e39.co.us.ibm.com ([32.97.110.160]:38342)
	by monty-python.gnu.org with esmtps
	(TLS-1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.60)
	(envelope-from <aliguori@us.ibm.com>) id 1LqWMQ-0004KE-Qx
	for qemu-devel@nongnu.org; Sun, 05 Apr 2009 13:42:23 -0400
Received: from d03relay02.boulder.ibm.com (d03relay02.boulder.ibm.com
	[9.17.195.227])
	by e39.co.us.ibm.com (8.13.1/8.13.1) with ESMTP id n35HdGk1004376
	for <qemu-devel@nongnu.org>; Sun, 5 Apr 2009 11:39:16 -0600
Received: from d03av03.boulder.ibm.com (d03av03.boulder.ibm.com [9.17.195.169])
	by d03relay02.boulder.ibm.com (8.13.8/8.13.8/NCO v9.2) with ESMTP id
	n35HgLZP205602
	for <qemu-devel@nongnu.org>; Sun, 5 Apr 2009 11:42:21 -0600
Received: from d03av03.boulder.ibm.com (loopback [127.0.0.1])
	by d03av03.boulder.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id
	n35HgLAT014793
	for <qemu-devel@nongnu.org>; Sun, 5 Apr 2009 11:42:21 -0600
Received: from squirrel.codemonkey.ws (sig-9-65-213-73.mts.ibm.com
	[9.65.213.73])
	by d03av03.boulder.ibm.com (8.12.11.20060308/8.12.11) with ESMTP id
	n35HgKUj014776
	for <qemu-devel@nongnu.org>; Sun, 5 Apr 2009 11:42:20 -0600
Message-ID: <49D8ED7B.3050507@us.ibm.com>
Date: Sun, 05 Apr 2009 12:42:19 -0500
From: Anthony Liguori <aliguori@us.ibm.com>
MIME-Version: 1.0
Subject: Re: [Qemu-devel] [PATCH] Fix (at least one cause of) qcow2 corruption.
References: <1238539254.15350.554.camel@voxel>
In-Reply-To: <1238539254.15350.554.camel@voxel>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Reply-To: qemu-devel@nongnu.org
List-Id: qemu-devel.nongnu.org
List-Unsubscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.gnu.org/pipermail/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: qemu-devel@nongnu.org

Nolan wrote:
> qcow2's get_cluster_offset() scans forward in the l2 table to find other
> clusters that have the same allocation status as the first cluster.
> This is used by (among others) qcow_is_allocated().
>
> Unfortunately, it was not checking to be sure that it didn't fall off
> the end of the l2 table.  This patch adds that check.
>
> The symptom that motivated me to look into this was that
> bdrv_is_allocated() was returning false when there was in fact data
> there.  This is one of many ways this bug could lead to data corruption.
>
> I checked the other place that scans for consecutive unallocated blocks
> (alloc_cluster_offset()) and it appears to be OK:
>     nb_clusters = MIN(nb_clusters, s->l2_size - l2_index);
> appears to prevent the same problem from occurring.
>
> Signed-off-by: Nolan Leake <nolan <at> sigbus.net>
>   

Applied.  Very good work.  Thanks!

Regards,

Anthony Liguori