On Fri, 16 Oct 2026 at 11:53, Daniel P. Berrangé <[email protected]> wrote:
>
> On Fri, Oct 16, 2026 at 11:14:16AM +0100, Peter Maydell wrote:
> > On Fri, 16 Oct 2026 at 10:31, Daniel P. Berrangé <[email protected]>
> > wrote:
> > > +#define qdev_realize_chain_parent(dev, dc, errp) \
> > > +
> > > DEVICE_CLASS(object_class_get_parent(OBJECT_CLASS(dc)))->realize(dev,
> > > errp)
> >
> > I'm tempted to suggest that we drop the 'dc' argument here and
> > have the macro get the class from the dev:
> >
> > DEVICE_CLASS(object_class_get_parent(object_get_class(OBJECT(dev))))->realize(dev,
> > errp)
> >
> > because I think almost all realize methods wanting to chain back up
> > won't have the class pointer to hand.
> >
> > We could maybe have an extra layer of abstraction here such that
> > you write something like:
> >
> > parent_invoke(DEVICE_CLASS, dev)->realize(dev, errp);
> >
> > Or is that trying to be too clever?
>
> This won't work if we have multiple levels in the class hierarchy
> that need chaining up, as object_class_get_parent(object_get_class(dev))
> will always just get the first level parent class of 'dev'.
Isn't that always what you want, though? In a class hierarchy
Object->Device->A->B->C, C's realize method always wants to
chain to B's realize method, and more generally "invoke the
superclass method" from C wants B's implementation, not A's
(assuming B actually implemented it).
> Somewhere/how we need to identify the current class level we're
> calling from, so we know what parent to ask for.
>
> Another option is to do what GObject does and provide a simple
> helper for getting the parent class, from OBJECT_DEFINE_TYPE*
> macros:
>
> ...
> static inline ObjectClass * \
> module_obj_name##_parent_class() { \
> return object_class_by_name(TYPE_##PARENT_MODULE_OBJ_NAME); \
> } \
> ...
>
> which would be used
>
> DeviceClass *dc = DEVICE_CLASS(pl050_kbd_parent_class());
>
> dc->realize(dev, errp);
>
> but many (most) of qdev impls don't use the relatively new
> OBJECT_DEFINE_TYPE macros. They would have to instead explicitly
> reference the parent type name:
>
> DeviceClass *dc = DEVICE_CLASS(object_class_by_name(TYPE_PL050));
> dc->realize(dev, errp);
I still don't understand why we need to get the parent's
object class by name here, rather than saying "give me
the parent class of this object's class".
thanks
-- PMM
