On Fri, Nov 30, 2018 at 01:34:56PM +0100, Igor Mammedov wrote:
> On Thu, 29 Nov 2018 15:49:00 -0200
> Eduardo Habkost <ehabk...@redhat.com> wrote:
>
> > On Tue, Nov 27, 2018 at 01:27:58PM +0400, Marc-André Lureau wrote:
> > > Let's make compatiblity properties an interface, so that objects other
> > > than QDev can benefit from having machine compatiblity properties.
> > >
> > > Signed-off-by: Marc-André Lureau <marcandre.lur...@redhat.com>
> > [...]
> > > diff --git a/hw/core/qdev.c b/hw/core/qdev.c
> > > index 3b31b2c025..b0ee05f837 100644
> > > --- a/hw/core/qdev.c
> > > +++ b/hw/core/qdev.c
> > > @@ -970,28 +970,8 @@ static void device_initfn(Object *obj)
> > > QLIST_INIT(&dev->gpios);
> > > }
> > >
> > > -static const GPtrArray *ac_compat_props;
> > > -static const GPtrArray *mc_compat_props;
> > > -
> > > -void accel_register_compat_props(const GPtrArray *props)
> > > -{
> > > - ac_compat_props = props;
> > > -}
> > > -
> > > -void machine_register_compat_props(const GPtrArray *props)
> > > -{
> > > - mc_compat_props = props;
> > > -}
> > > -
> > > static void device_post_init(Object *obj)
> > > {
> > > - if (ac_compat_props) {
> > > - object_apply_global_props(obj, ac_compat_props, &error_abort);
> > > - }
> > > - if (mc_compat_props) {
> > > - object_apply_global_props(obj, mc_compat_props, &error_abort);
> > > - }
> > > -
> > > qdev_prop_set_globals(DEVICE(obj));
> > > }
> > >
> > > @@ -1124,6 +1104,10 @@ static const TypeInfo device_type_info = {
> > > .class_init = device_class_init,
> > > .abstract = true,
> > > .class_size = sizeof(DeviceClass),
> > > + .interfaces = (InterfaceInfo[]) {
> > > + { TYPE_COMPAT_PROPS },
> > > + { }
> > > + }
> >
> > At first I thought TYPE_COMPAT_PROPS was a practical way to
> > implement this feature, but now I'm worried: the ordering between
> > compat_props_post_init() qdev_prop_set_globals() is very
> > important (user-provided globals must always be set after compat
> > props), and here the ordering is implicit and easy to break
> > accidentally.
> >
> > What if instead of a QOM interface we just provide a simple
> > object_apply_compat_props() function? e.g.:
> >
> > qdev.c:
> >
> > static void device_post_init(Object *obj)
> > {
> > object_apply_compat_props(obj);
> > apply_user_provided_globals(obj);
> > }
> >
> > object_interface.c:
> >
> > void user_creatable_complete(Object *obj, Error **errp)
> > {
> > object_apply_compat_props(obj);
> > ...
> > ucc->complete(...)
> > }
> this would work as long as nothing is happening between
> object_new() ... user_creatable_complete() but look at
> current users of user_creatable_complete() so it's
> fragile too.
You are right. This could be solved by:
void user_creatable_post_init(Object *obj)
{
object_apply_compat_props(obj);
}
>
> Reasons for compat props interface are the same as for
> instance_post_init/device_post_init.
>
> the thing we can do here is getting rid of device_post_init
> and making device override TYPE_COMPAT_PROPS::instance_post_init
> to make explicit ordering like we do everywhere else:
>
> diff --git a/hw/core/qdev.c b/hw/core/qdev.c
> index 6b3cc55..46ad6f5 100644
> --- a/hw/core/qdev.c
> +++ b/hw/core/qdev.c
> @@ -1033,11 +1033,19 @@ static void device_unparent(Object *obj)
> }
> }
>
> +device_compat_props()
> +{
> + dc->parent_compat_props()
> + apply_global_props()
> +}
> +
> static void device_class_init(ObjectClass *class, void *data)
> {
> DeviceClass *dc = DEVICE_CLASS(class);
>
> class->unparent = device_unparent;
> + dc->parent_compat_props =
> COMPAT_PROPS_GET_CLASS(class)->instance_post_init
> + COMPAT_PROPS_GET_CLASS(class)->instance_post_init = device_compat_props()
>
> /* by default all devices were considered as hotpluggable,
> * so with intent to check it in generic qdev_unplug() /
The only advantage I saw in TYPE_COMPAT_PROPS interface was to
easily allow objects to implement behavior without manually
implementing post_init. Now we can't use the interface without
an even more complex way of overriding post_init, so what's the
point?
Why not just call object_apply_compat_props() at
device_post_init()?
>
> > Most people don't understand QOM interfaces and their
> > initialization ordering rules. Everybody understands C function
> > calls.
> >
> > > [...]
> >
>
--
Eduardo
