Re: [RFC 04/13] rust: add bindings for gpio_{in|out} initialization

[Paolo Bonzini <pbonzini@redhat.com>]

On 12/5/24 07:07, Zhao Liu wrote:
> The qdev_init_gpio_{in|out} are qdev interfaces, so that it's natural to
> wrap them as DeviceState's methods in Rust API, which could eliminate
> unsafe cases in the device lib.
> 
> Wrap qdev_init_gpio_{in|out} as methods in a new trait DeviceGPIOImpl.
>
> In addition, for qdev_init_gpio_in(), to convert the idiomatic Rust
> callback into a C-style callback qemu_irq_handler, add a handler pointer
> member in DeviceGPIOImpl. For any device needs to initialize GPIO in, it
> needs to define a handler. And for device which just wants to initialize
> GPIO out, it can leave the GPIO_IRQ_HANDLER as None.

This has the same issue as timers, in that you could have (especially 
once someone adds named GPIOs) multiple handlers.  So we need the same 
kind of Fn-based thing here too.

> +/// Trait that defines the irq handler for GPIO in.
> +pub trait DeviceGPIOImpl {
> +    const GPIO_IRQ_HANDLER: Option<fn(&mut Self, lines_num: u32, level: u32)> = None;

Ah, I see that you're placing the qdev_init_gpio_in here so that you
only make that accessible for devices that did implement DeviceGPIOImpl.
However you are not guaranteeing that this _is_ a DeviceState.

If the handler can be passed as a function, the problem of getting the 
GPIO_INT_HANDLER does not exist anymore.  So with the code in rust-next 
you can add these to a trait like

/// Trait for methods of [`DeviceState`] and its subclasses.
pub trait DeviceMethods: ObjectDeref
where
     Self::Target: IsA<DeviceState>,
{
     fn init_gpio_in<F: ...)(&self, lines_num: u32, f: &F) {
     }
}

impl<R: ObjectDeref> DeviceMethods for R where R::Target: 
IsA<DeviceState> {}


> +    fn init_gpio_out(&self, pins: &InterruptSource, lines_num: u32) {
> +        unsafe {
> +            qdev_init_gpio_out(addr_of!(*self) as *mut _, pins.as_ptr(), lines_num as c_int);
> +        }
> +    }
> +}

Pass a slice &[InterruptSource], and get the "len" from the length of 
the slice.

Paolo