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

[Denis V. Lunev]

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 (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).

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.