From: Christoph Hellwig <hch@lst.de>
To: qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH] Fix (at least one cause of) qcow2 corruption.
Date: Thu, 9 Apr 2009 22:44:12 +0200 [thread overview]
Message-ID: <20090409204412.GA2345@lst.de> (raw)
In-Reply-To: <1238539254.15350.554.camel@voxel>
On Tue, Mar 31, 2009 at 03:40:54PM -0700, 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.
Do you have a specific I/O patter nthat would trigger this issue?
prev parent reply other threads:[~2009-04-09 20:44 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-03-31 22:40 [Qemu-devel] [PATCH] Fix (at least one cause of) qcow2 corruption Nolan
2009-04-05 17:42 ` Anthony Liguori
2009-04-05 18:18 ` Anthony Liguori
2009-04-09 20:44 ` Christoph Hellwig [this message]
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