Re: [Qemu-devel] [PATCH] migration: notify runstate immediately before vcpu stops

[Yan Zhao <yan.y.zhao@intel.com>]

On Thu, Jul 25, 2019 at 06:39:07PM +0800, Dr. David Alan Gilbert wrote:
> * Yan Zhao (yan.y.zhao@intel.com) wrote:
> > for some devices to do live migration, it is needed to do something
> > immediately before vcpu stops. add a notification here.
> > 
> > Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
> > ---
> >  cpus.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/cpus.c b/cpus.c
> > index b09b702..d5d4abe 100644
> > --- a/cpus.c
> > +++ b/cpus.c
> > @@ -1068,6 +1068,7 @@ static int do_vm_stop(RunState state, bool send_stop)
> >      int ret = 0;
> >  
> >      if (runstate_is_running()) {
> > +        vm_state_notify(1, state);
> 
> SO that's quite interesting in that you'll end up getting a
> notificatiion like 'running=true, state=RUN_STATE_SHUTDOWN'
> that might be unexpected by existing callers.
> 
> Have you checked existing callers?  Also does this cause another event
> to be sent on the QMP - if so we need to chekc if this would confuse
> libvirt.
> 
> Dave

hi Dave
yes, this may cause problem for existing handlers as this is an
unexpected condition. like for ide's ide_restart_cb.
So, do you think it's a better that do the notification earlier, before
vm_stop_force_state() in migration.c and call notifier_list_notify(&migration_state_notifiers, s)
to notify migration state instead ?

Thanks
Yan



> 
> >          cpu_disable_ticks();
> >          pause_all_vcpus();
> >          runstate_set(state);
> > -- 
> > 2.7.4
> > 
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK