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

[Eric Blake]

On 10/07/2015 07:56 AM, Dr. David Alan Gilbert wrote:
> * Denis V. Lunev (address@hidden) wrote:
>> From: Igor Redko <address@hidden>
>>
>> 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).


>> +++ 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.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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