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Date: Wed, 06 May 2009 19:52:44 +0200
From: Kevin Wolf <kwolf@redhat.com>
MIME-Version: 1.0
Subject: Re: [Qemu-devel] Re: [PATCH] qcow2/virtio corruption: Don't allocate
	the same cluster twice
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To: Avi Kivity <avi@redhat.com>
Cc: markmc@redhat.com, qemu-devel@nongnu.org

Avi Kivity schrieb:
> Kevin Wolf wrote:
>> Avi Kivity schrieb:
>>> Also, the second request now depends on the first to update its 
>>> metadata.  But if the first request fail, it will not update its 
>>> metadata, and the second request will complete without error and also 
>>> without updating its metadata.
>>>     
>> Hm, right. Need to think about this...
>>   
> 
> I suggest retaining the part where you use inflight l2metas to layout 
> data contiguously, but change alloc_cluster_link_l2() not to rely on 
> n_start and nb_available but instead recompute them on completion. 
> m->nb_clusters should never be zeroed for this to work.

Is there even a reason why we need to copy the unmodified sectors in
alloc_cluster_link_l2() and cannot do that in alloc_cluster_offset()
before we write the new data? Then the callback wouldn't need to mess
around with figuring out which part must be overwritten and which one
mustn't.

Kevin