Re: [Qemu-devel] [PATCH v3 0/2] block/drive-mirror: Check for NULL backing_hd

[Max Reitz <mreitz@redhat.com>]

On 07.11.2013 03:25, Wenchao Xia wrote:
> 于 2013/11/7 2:50, Max Reitz 写道:
>> It should be possible to execute the QMP "drive-mirror" command in
>> "none" sync mode and "absolute-paths" mode even for block devices
>> lacking a backing file.
>>
>> "absolute-paths" does in fact not require a backing file to be present,
>> as can be seen from the "top" sync mode code path. "top" basically
>> states that the device should indeed have a backing file - however, the
>> current code catches the case if it doesn't and then simply treats it as
>> "full" sync mode, creating a target image without a backing file (in
>> "absolute-paths" mode). Thus, "absolute-paths" does not imply the target
>> file must indeed have a backing file.
>>
>> Therefore, the target file may be left unbacked in case of "none" sync
>> mode as well, if the specified device is not backed either. Currently,
>> qemu will crash trying to dereference the backing file pointer since it
>> assumes that it will always be non-NULL in that case ("none" with
>> "absolute-paths").
>>
>> The first patch in this series adds a check whether the specified block
>> device is backed or not (creating an unbacked target image, if required);
>> the second patch adds a test case for mirroring unbacked block devices.
>>
>> v2:
>>   - patch 1: Reuse an already existing codepath to create an unbacked
>>              target image instead of introducing a new one (based on
>>              Fam's comment).
>>   - patch 2: Incorporated test case into 041 instead of creating a new
>>              file (according to Xia's and Paolo's comments).
>>
>>
>> Max Reitz (2):
>>    block/drive-mirror: Check for NULL backing_hd
>>    qemu-iotests: Extend 041 for unbacked mirroring
>>
>>   blockdev.c                 |  4 +++-
>>   tests/qemu-iotests/041     | 25 +++++++++++++++++++++++++
>>   tests/qemu-iotests/041.out |  4 ++--
>>   3 files changed, 30 insertions(+), 3 deletions(-)
>>
> Reviewed-by: Wenchao Xia <xiawenc@linux.vnet.ibm.com>
>
> Should we change doc for NewImageMode in qapi-schema.json also?

Probably, yes. I'll send a follow-up patch.

Max