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Date: Wed, 07 Jan 2009 11:22:25 -0600
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: [Qemu-devel] Re: [PATCH][RESEND] qcow2: Fix cluster allocation
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To: Kevin Wolf <kwolf@suse.de>
Cc: qemu-devel@nongnu.org

Kevin Wolf wrote:
> When allocating multiple clusters at once, the qcow2 implementation
> tries to find as many physically contiguous clusters as possible to
> allow larger writes. This search includes allocated clusters which are
> in the right place and still free clusters. If the range to allocate
> spans clusters in patterns like "10 allocated, then 10 free, then again
> 10 allocated" it is only checked that the chunks of allocated clusters
> are contiguous for themselves.
>
> However, what is actually needed is to have _all_ allocated clusters
> contiguous, starting at the first cluster of the allocation and spanning
> multiple such chunks. This patch changes the check so that each offset
> is not compared to the offset of the first cluster in its own chunk but
> to the first cluster in the whole allocation.
>
> I haven't seen it happen, but without this fix data corruption on qcow2
> images is possible.
>
> Signed-off-by: Kevin Wolf <kwolf@suse.de>
> Acked-by: Gleb Natapov <gleb@redhat.com>
>   
Applied.  Thanks.

Regards,

Anthony Liguori