* Greg Kurz (gr...@kaod.org) wrote:
> On Tue, 13 Jun 2017 10:00:03 +0100
> "Dr. David Alan Gilbert" <dgilb...@redhat.com> wrote:
>
> > * Greg Kurz (gr...@kaod.org) wrote:
> > > On Tue, 13 Jun 2017 16:06:31 +0800
> > > David Gibson <da...@gibson.dropbear.id.au> wrote:
> > >
> > > > On Tue, Jun 13, 2017 at 09:33:59AM +0200, Greg Kurz wrote:
> > > [...]
> > > > > > > > > +static void
> > > > > > > > > pre_2_10_vmstate_register_dummy_icp(sPAPRMachineState *spapr,
> > > > > > > > > int i)
> > > > > > > > > +{
> > > > > > > > > + bool *flag = &spapr->pre_2_10_ignore_icp[i];
> > > > > > > > > +
> > > > > > > > > + g_assert(!*flag);
> > > > > > > >
> > > > > > > > Apart from this assert(), you never seem to test the values in
> > > > > > > > the
> > > > > > > > pre_2_10_ignore_icp() array, so it seems a bit pointless.
> > > > > > > >
> > > > > > >
> > > > > > > There's the opposite check in
> > > > > > > pre_2_10_vmstate_unregister_dummy_icp().
> > > > > > > But I agree it isn't really useful... but more because of
> > > > > > > paranoia :)
> > > > > >
> > > > > > I'm all for paranoid assert()s if they can be made using data
> > > > > > readily
> > > > > > to hand. Adding a data structure just for the purpose of making an
> > > > > > assert() later, not so much.
> > > > > >
> > > > >
> > > > > It is also passed as opaque argument to vmstate_register(), where it
> > > > > is
> > > > > used as a key when calling vmstate_unregister(). I could possibly pass
> > > > > (void *) i instead, but I'm not a big fan of hijacking pointer
> > > > > arguments
> > > > > to pass numbers.
> > > >
> > > > Ah, I see your point. Creating an array, purely to generate arbitrary
> > > > pointers is also kind of ugly, though. Really the cpu_index / XICS
> > > > server number makes sense to identify the vmstate, but it looks like
> > > > vmstate_unregister() doesn't take that.
> > > >
> > >
> > > Indeed... what about adding a vmstate_unregister_by_instance_id() then ?
> > >
> > > Cc'ing Juan and David.
> >
> > So what's the problem with a (void *)i ?
>
> https://stackoverflow.com/questions/8618637/what-does-it-mean-to-convert-int-to-void-or-vice-versa
>
> > It's simple, as long as you're
> > not actually using the opaque anywhere it's easy.
> >
>
> but as you say, since the opaque isn't used anywhere, it is probably
> okay to pass (void *) i.
Yes, I don't think we're ever casting back from the (void *) to an int
so it feels pretty safe to me.
>
> > Note from a quick glance at your patch; will this work migrating
> > from this 2.10 -> 2.9 ? Are your dummy vmstate's really good enough for
> > the 2.9 ?
> >
>
> Yeah but I need to add some comments as David suggested.
>
> The idea is that 2.9 used to create a bunch of objects at machine init,
> that only get used when CPUs are plugged. With 2.10, these objects are
> now created under the CPUs. When migrating from 2.10 to 2.9, we only need
> to send the real objects. The dummy vmstate entries don't send anything
> (.needed always returns false) since the corresponding objects in 2.9 aren't
> being used and still have their default state.
>
OK, that'll probably work.
Dave
> > Dave
> >
> >
> > > --
> > > Greg
> >
> >
> > --
> > Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
>
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
