Re: [Qemu-devel] [PATCH 2/4] migration/savevm: use migration_is_blocked to validate

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Wei Yang (richardw.yang@linux.intel.com) wrote:
> On Wed, May 15, 2019 at 02:38:27PM +0800, Wei Yang wrote:
> >On Tue, May 14, 2019 at 04:18:14PM +0100, Dr. David Alan Gilbert wrote:
> >>* Wei Yang (richardw.yang@linux.intel.com) wrote:
> >>> 
> >>> Well, when you look into the source side of migration:
> >>> 
> >>> qmp_migrate
> >>>   migrate_prepare
> >>>     migration_is_blocked
> >>> 
> >>> This means if migration_is_blocked fails, the source will not start migration.
> >>> And it is the same as save_snapshot.
> >>> 
> >>> From my understanding, when we load a vm, it should check the same
> >>> requirement.
> >>
> >>I've been thinking about this, and I think I agree with Daniel on this.
> >>The 'migration_blockers' list tells you that something about the
> >>*current* state of a device means that it can't be migrated - e.g.
> >>a 9pfs with a mounted filesystem can't be migrated.
> >>
> >>If we're about to reload the state from a snapshot, then the saved
> >>snapshot's state must have been migratable, so that's OK.
> >>
> >
> >The situation is on a vm with 'migration_blockers' still could reload from a
> >snapshot.
> >
> >This sounds reasonable. Thanks :-)
> >
> 
> Well, this is still a little strange. The means source vm and destination vm
> could have different configuration. Is this common?

It's not different configuration that I'm worried about here; but it's different runtime state.
Items can get added/removed from migration_blockers dynamically
depending on the behaviour of the guest; e.g. a device might only
migratable in certain states.

Dave


> -- 
> Wei Yang
> Help you, Help me
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK