Re: [Qemu-devel] [PATCH] qcow2: Restore total_sectors value in save_vmstate

[Max Reitz <mreitz@redhat.com>]

On 2013-10-21 22:36, Eric Blake wrote:
> On 10/20/2013 07:28 PM, Max Reitz wrote:
>> Since df2a6f29a5, bdrv_co_do_writev increases the total_sectors value of
>> a growable block devices on writes after the current end. This leads to
>> the virtual disk apparently growing in qcow2_save_vmstate, which in turn
>> affects the disk size captured by the internal snapshot taken directly
>> afterwards through e.g. the HMP savevm command. Such a "grown" snapshot
>> cannot be loaded after reopening the qcow2 image, since its disk size
>> differs from the actual virtual disk size (writing a VM state does not
>> actually increase the virtual disk size).
>>
>> Fix this by restoring total_sectors at the end of qcow2_save_vmstate.
>>
>> Signed-off-by: Max Reitz <mreitz@redhat.com>
>> ---
>>   block/qcow2.c | 5 +++++
>>   1 file changed, 5 insertions(+)
>>
>> @@ -1946,6 +1947,10 @@ static int qcow2_save_vmstate(BlockDriverState *bs, QEMUIOVector *qiov,
>>       bs->growable = 1;
>>       ret = bdrv_pwritev(bs, qcow2_vm_state_offset(s) + pos, qiov);
>>       bs->growable = growable;
>> +    // bdrv_co_do_writev will have increased the total_sectors value to include
>> +    // the VM state - the VM state is however not an actual part of the block
>> +    // device, therefore, we need to restore the old value.
>> +    bs->total_sectors = total_sectors;
> It looks like // comments aren't forbidden, but also uncommon; I don't
> know if /**/ would be better.  At any rate:

Ah, right, sorry, I forgot.

Max