Re: [Qemu-devel] [PATCH v3 4/5] xics: directly register ICPState objects to vmstate

[Greg Kurz]

On Thu, 8 Jun 2017 13:59:21 +1000
David Gibson <address@hidden> wrote:

> On Wed, Jun 07, 2017 at 07:17:17PM +0200, Greg Kurz wrote:
> > The ICPState objects are currently registered to vmstate as qdev objects.
> > Their instance ids are hence computed automatically in the migration code,
> > and thus depends on the order the CPU cores were plugged.
> > 
> > If the destination had its CPU cores plugged in a different order than the
> > source, then ICPState objects will have different instance_ids and load
> > the wrong state.
> > 
> > Since CPU objects have a reliable cpu_index which is already used as
> > instance_id in vmstate, let's use it for ICPState as well.
> > 
> > Signed-off-by: Greg Kurz <address@hidden>
> > ---
> >  hw/intc/xics.c |    5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)  
> 
> So, this is definitely a good idea w.r.t. future compatibility.  But,
> won't it break migration compat as a once off, since the devices will
> be found under their new id instead of the qdev id?
> 

Older machine types used to allocate/realize all ICPState objects
at machine init time and never release them. The qdev ids are thus
0,1,2... nr_servers and happen to map to cpu_index.

> > 
> > diff --git a/hw/intc/xics.c b/hw/intc/xics.c
> > index 330441ff7fe8..3d76b43876c5 100644
> > --- a/hw/intc/xics.c
> > +++ b/hw/intc/xics.c
> > @@ -348,10 +348,14 @@ static void icp_realize(DeviceState *dev, Error 
> > **errp)
> >      }
> >  
> >      qemu_register_reset(icp_reset, dev);
> > +    vmstate_register(NULL, icp->cs->cpu_index, &vmstate_icp_server, icp);
> >  }
> >  
> >  static void icp_unrealize(DeviceState *dev, Error **errp)
> >  {
> > +    ICPState *icp = ICP(dev);
> > +
> > +    vmstate_unregister(NULL, &vmstate_icp_server, icp);
> >      qemu_unregister_reset(icp_reset, dev);
> >  }
> >  
> > @@ -359,7 +363,6 @@ static void icp_class_init(ObjectClass *klass, void 
> > *data)
> >  {
> >      DeviceClass *dc = DEVICE_CLASS(klass);
> >  
> > -    dc->vmsd = &vmstate_icp_server;
> >      dc->realize = icp_realize;
> >      dc->unrealize = icp_unrealize;
> >  }
> >   
>

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