Re: Configuring migration

[Daniel P . Berrangé]

On Tue, Nov 14, 2023 at 10:53:20AM +0100, Markus Armbruster wrote:
> Daniel P. Berrangé <berrange@redhat.com> writes:
> 
> > On Thu, Nov 02, 2023 at 03:25:25PM +0100, Markus Armbruster wrote:
> >> Now let's try to apply this to migration.
> >>
> >> As long as we can have just one migration, we need just one QAPI object
> >> to configure it.
> >> 
> >> We could create the object with -object / object_add.  For convenience,
> >> we'd probably want to create one with default configuration
> >> automatically on demand.
> >> 
> >> We could use qom-set to change configuration.  If we're not comfortable
> >> with using qom-set for production, we could do something like
> >> blockdev-reopen instead.
> >
> > Do we even need to do this via a QAPI object ?
> 
> No.  It's merely one way to skin the cat.
> 
> > Why are we not just making the obvious design change of passing everything
> > with the 'migrate' / 'migrate-incoming' commands that kick it off:
> >
> > ie:
> >
> > { 'command': 'migrate',
> >   'data': {'uri': 'str',
> >            '*channels': [ 'MigrationChannel' ],
> >        '*capabilities': [ 'MigrateCapability' ],
> >        '*parameters': [ 'MigrateParameters' ],
> >            '*detach': 'bool', '*resume': 'bool' } }
> >
> >      (deprecated bits trimmed for clarity)
> >
> > and the counterpart:
> >
> > { 'command': 'migrate-incoming',
> >              'data': {'*uri': 'str',
> >                       '*channels': [ 'MigrationChannel' ],
> >                       '*capabilities': [ 'MigrateCapability' ],
> >                       '*parameters': [ 'MigrateParameters' ] } }
> >
> > such that the design is just like 99% of other commands which take
> > all their parameters directly. We already have 'migrate-set-parameters'
> > remaining for the runtime tunables, and can deprecate the usage of this
> > when migration is not already running, and similarly deprecate
> > migrate-set-capabilities.
> 
> We still need commands to adjust configuration while migration runs.

migrate-set-parameters will still satisfy that use case, we can allow
its usage when migration is active and deprecate its usage when migration
is not active

With regards,
Daniel
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