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

[Paolo Bonzini <pbonzini@redhat.com>]

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