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Date: Wed, 23 Oct 2013 20:27:27 +0200
From: Max Reitz <mreitz@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] qcow2: Unset zero_beyond_eof in
	save_vmstate
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To: Eric Blake <eblake@redhat.com>, qemu-devel@nongnu.org
Cc: Kevin Wolf <kwolf@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>

On 2013-10-21 22:37, Eric Blake wrote:
> On 10/20/2013 08:52 PM, Max Reitz wrote:
>> Saving the VM state is done using bdrv_pwrite. This function may perform
>> a read-modify-write, which in this case results in data being read from
>> beyond the end of the virtual disk. Since we are actually trying to
>> access an area which is not a part of the virtual disk, zero_beyond_eof
>> has to be set to false before performing the partial write, otherwise
>> the VM state may become corrupted.
>>
>> Signed-off-by: Max Reitz <mreitz@redhat.com>
>> ---
>> Follow-up to (depends on):
>>   - qcow2: Restore total_sectors value in save_vmstate
> Reviewed-by: Eric Blake <eblake@redhat.com>
>
> Do you have test cases that demonstrate the corruption pre-patch?

Okay, so it is possible to test for this after all; I've just sent a 
follow-up adding such a test. Thanks for pointing that out. ;-)

Max