Re: [PATCH v2 0/5] fix migration with bitmaps and mirror

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

19.12.2019 13:36, Peter Krempa wrote:
> On Thu, Dec 19, 2019 at 11:51:01 +0300, Vladimir Sementsov-Ogievskiy wrote:
>> Hi all!
>>
>> It's a continuation for
>> "bitmap migration bug with -drive while block mirror runs"
>> <315cff78-dcdb-a3ce-2742-da3cc9f0ca97@redhat.com>
>> https://lists.gnu.org/archive/html/qemu-devel/2019-09/msg07241.html
>>
>> The problem is that bitmaps migrated to node with same node-name or
>> blk-parent name. And currently only the latter actually work in libvirt.
>> And with mirror-top filter it doesn't work, because
>> bdrv_get_device_or_node_name don't go through filters.
> 
> I want to point out that since libvirt-5.10 we use -blockdev to
> configure the backend of storage devices with qemu-4.2 and later. This
> means unfortunately that the BlockBackend of the drive does not have a
> name any more and thus the above will not work even if you make the
> lookup code to see through filters.

Not that this series doesn't make things worse, as it loops through named
block backends when trying to use their name for migration. So with these
patches applied, qemu will just work in more possible scenarios.

> 
> As I've pointed out separately node-names are not good idea to use for
> matching either as they can be distinct on the destination of migration.
> 
> Having same node names for images during migration was not documented as
> a requiremend and even if it was the case when the mirror job is used
> the destination is a different image and thus having a different node
> name is expected.
> 
> Since it's not documented, expect the same situation as with
> autogenerated nodenames, the destination may have different node-names
> and the same node-name may refer to a different image. Implicit matching
> based on node-names is thus impossible.
> 


-- 
Best regards,
Vladimir