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

[Wenchao Xia <xiawenc@linux.vnet.ibm.com>]

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?