Re: [PATCH 09/15] rust: irq: wrap IRQState with Opaque<>

[Paolo Bonzini]

On 2/25/25 09:26, Zhao Liu wrote:
> > +/// An opaque wrapper around [`bindings::IRQState`].
> > +#[repr(transparent)]
> > +#[derive(Debug, qemu_api_macros::Wrapper)]
> > +pub struct IRQState(Opaque<bindings::IRQState>);
> > +
> >   /// Interrupt sources are used by devices to pass changes to a value 
> > (typically
> >   /// a boolean).  The interrupt sink is usually an interrupt controller or
> >   /// GPIO controller.
> > @@ -22,8 +28,7 @@
> >   /// method sends a `true` value to the sink.  If the guest has to see a
> >   /// different polarity, that change is performed by the board between the
> >   /// device and the interrupt controller.
> > -pub type IRQState = bindings::IRQState;
> > -
> > +///
> >   /// Interrupts are implemented as a pointer to the interrupt "sink", which has
> >   /// type [`IRQState`].  A device exposes its source as a QOM link property 
> > using
> >   /// a function such as [`SysBusDeviceMethods::init_irq`], and
> > @@ -41,7 +46,7 @@ pub struct InterruptSource<T = bool>
> >   where
> >       c_int: From<T>,
> >   {
> > -    cell: BqlCell<*mut IRQState>,
> > +    cell: BqlCell<*mut bindings::IRQState>,
>
> Once we've already wrapper IRQState in Opaque<>, should we still use
> bindings::IRQState?
>
> Although InterruptSource just stores a pointer. However, I think we can
> use wrapped IRQState here instead of the native binding type, since this
> item is also crossing the FFI boundary. What do you think?

Using the wrapped IRQState would be a bit more code because you have to 
cast the pointer all the time when calling C code.  As far as 
correctness is concerned, it does not really matter because as you said 
it only stores a pointer.

However, if needed, InterruptSource could have a function that converts 
from IRQState to Option<&Opaque<irq::IRQState>>.  Since the accessor is 
needed anyway, that would be a good place to put the conversion.

Paolo