Ping: [PATCH] Qemu: migration: Not bind RAM info with active migration status

[Keqian Zhu]

Hi Daniel,

Thanks for your reply :-) Please see my words below.

On 2021/1/4 19:58, Daniel P. Berrangé wrote:
> On Fri, Dec 18, 2020 at 04:38:22PM +0800, Keqian Zhu wrote:
>> Hi Daniel and Jiri,
>>
>> On 2020/12/8 18:31, Jiri Denemark wrote:
>>> On Tue, Dec 08, 2020 at 09:27:39 +0000, Daniel P. Berrangé wrote:
>>>> On Tue, Dec 08, 2020 at 10:06:25AM +0800, zhukeqian wrote:
>>>>>
>>>>> On 2020/12/7 18:38, Daniel P. Berrangé wrote:
>>>>>> On Mon, Dec 07, 2020 at 09:55:53AM +0800, zhukeqian wrote:
>>>>>>> Hi Daniel,
>> [...]
>>
>>>>>
>>>>> Hi Daniel,
>>>>>
>>>>> The purpose is to remove this failure check for QEMU v2.12.
>>>>> In QEMU commit 65ace0604551, it decoupled the RAM status from the active migration status.
>>>>>
>>>>> The usage scenario is querying migration status at destination side, which may contain
>>>>> active migration status, but without RAM status, so we will see that libvirt report error here.
>>>>
>>>> I'm confused, because AFAIK, libvirt does not need to run
>>>> query-migrate on the destination, so there shouldn't be anything
>>>> that needs fixing.
>>>
>>> Moreover, you can't even request migration statistics on the destination
>>> manually because libvirt blocks that:
>>>
>>> # virsh domjobinfo nest
>>> error: Operation not supported: migration statistics are available only
>>> on the source host
>>>
>>> Jirka
>>>
>>> .
>>>
>> Sorry for delay reply.
>>
>> The purpose of QEMU commit 65ace0604551 (migration: add postcopy total blocktime into query-migrate)
>> is to query some postcopy related information on destination side.
>>
>> We can call query-migrate on destination side *after* migration complete, thanks.
> 
> But nothing in libvirt ever tries to call query-migrate on the dest
> side. 
Yes, but the dest side does not always act as dest. After migration completion, the dest side enters
to a normal status and libvirt does not forbid us to query migration status.

Before QEMU commit 65ace0604551, we can successfully query the migration status, which is
MIGRATION_STATUS_NONE. But this commit will return valid status (MIGRATION_STATUS_COMPLETED)
without ram info, causing libvirt reports error (migration was active, but no RAM info was set).

> 
> Do you have more patches that add such calls ? If so, then please send a
> patch series that does the full job.
I do not add new feature to libvirt, but just manually execute query-migrate on dest side *after
migration completion* will trigger this problem.

Thanks,
Keqian