Il mar 17 dic 2024, 04:39 Zhao Liu <zhao1....@intel.com> ha scritto:
> > +impl ClassInitImpl<PL011Class> for PL011State {
> > + fn class_init(klass: &mut PL011Class) {
> > + klass.device_id = DeviceId::ARM;
> > + <Self as ClassInitImpl<SysBusDeviceClass>>::class_init(&mut
> klass.parent_class);
>
> This seems a bit of a conflict with the C version of QOM semantics. In C,
> class_init is registered in TypeInfo, and then the QOM code will
> automatically call the parent's class_init without needing to explicitly
> call the parent's in the child's class_init.
>
This is the same in Rust.
The difference is that in C you have a single class_init function that sets
all members of ObjectClass, DeviceClass, etc. In Rust each class has one
trait and there is a chain of ClassInitImpl implementations—one filling in
"oc" from ObjectImpl, one filling in "dc" from DeviceImpl and so on.
But in both cases you get a chain of calls from qom/object.c.
Therefore, the call here seems valid from the code logic's perspective.
> But, when there is deeper class inheritance, it seems impossible to
> prevent class_init from being called both by the C side's QOM code and by
> this kind of recursive case on the Rust side.
>
Note that here you have two parameters: what class is being filled (the
argument C of ClassInitImpl<C>) *and* what type is being initialized
(that's Self).
The "recursion" is only on the argument C, and matches the way C code
implements class_init.
Maybe the confusion is because I implemented class_init twice instead of
using a separate trait "PL011Impl"?
Paolo
So, for devices like SysBusDevice that are registered on the C side,
> should we not implement class_init and also not call it explicitly?
>
> Or should we distinguish between two different usages of class_init? One
> is registered in TypeInfo (only as a callback in rust_class_init) - perhaps
> rename it as qom_class_init, and the other is used as a helper for
> Rust-side
> calls (similar to the recursive usage here) - maybe rename it as
> class_inter_init.
>
> > + }
> > +}
>
>
