Re: [Qemu-devel] [PATCH 7/8] migration: new migration test mode

["Denis V. Lunev" <den@openvz.org>]

On 10/07/2015 06:08 PM, Eric Blake wrote:
> On 10/07/2015 07:56 AM, Dr. David Alan Gilbert wrote:
>> * Denis V. Lunev (den@openvz.org) wrote:
>>> From: Igor Redko <redkoi@virtuozzo.com>
>>>
>>> In this patch the ability to start a migration with test-only
>>> capability was added. It allows to gather the guest VM’s memory
>>> usage statistics avoiding time and memory overheads and real
>>> data transmission.  New MIGRATION_STATUS_TEST_COMPLETED was
>>> added to distinguish between test migration and true migration
>>> success states.
>> Why isn't this just a new transport? i.e. I could do this just by doing
>> a migrate to test:   ?
>>
>> It seems simpler and avoids some of the special casing?
> Indeed. Even if the new state can only be triggered by using a new
> option, the fact that the new state exists in introspection means
> clients have to figure out what to do with it; while a new transport
> would not require any new states ("running" to completion means that
> nothing migrated, but the existing states can then be reused to see that
> the test: transport has finished computing its numbers).
>

we need to expose calculated numbers to the caller somehow.
This could be done in MIGRATION_STATUS_COMPLETED state
even for ordinary migration. Will it be OK?

Den

>>> +++ b/qapi-schema.json
>>> @@ -432,6 +432,8 @@
>>>   #
>>>   # @completed: migration is finished.
>>>   #
>>> +# @test-completed: migration time estimation finished.
>>> +#
> If this gets added, in spite of our ideas to use a 'test:' transport
> instead of a new state, it would need a 'since 2.5' marker.
>