rust: qdev: move bridge for realize and reset functions out of pl011

Allow the DeviceImpl trait to expose safe Rust functions.
rust_device_class_init<> adds thunks around the functions
in DeviceImpl.

Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

rust/hw/char/pl011/src/device.rs

@@ -125,9 +125,8 @@ impl DeviceImpl for PL011State {
     fn vmsd() -> Option<&'static VMStateDescription> {
         Some(&device_class::VMSTATE_PL011)
     }
-    const REALIZE: Option<unsafe extern "C" fn(*mut DeviceState, *mut *mut Error)> =
+    const REALIZE: Option<fn(&mut Self)> = Some(Self::realize);
-        Some(device_class::pl011_realize);
+    const RESET: Option<fn(&mut Self)> = Some(Self::reset);
-    const RESET: Option<unsafe extern "C" fn(*mut DeviceState)> = Some(device_class::pl011_reset);
 }
 
 impl_device_class!(PL011State);

rust/hw/char/pl011/src/device_class.rs

@@ -92,29 +92,3 @@ qemu_api::declare_properties! {
         default = true
     ),
 }
-
-/// # Safety
-///
-/// We expect the FFI user of this function to pass a valid pointer, that has
-/// the same size as [`PL011State`]. We also expect the device is
-/// readable/writeable from one thread at any time.
-pub unsafe extern "C" fn pl011_realize(dev: *mut DeviceState, _errp: *mut *mut Error) {
-    unsafe {
-        assert!(!dev.is_null());
-        let mut state = NonNull::new_unchecked(dev.cast::<PL011State>());
-        state.as_mut().realize();
-    }
-}
-
-/// # Safety
-///
-/// We expect the FFI user of this function to pass a valid pointer, that has
-/// the same size as [`PL011State`]. We also expect the device is
-/// readable/writeable from one thread at any time.
-pub unsafe extern "C" fn pl011_reset(dev: *mut DeviceState) {
-    unsafe {
-        assert!(!dev.is_null());
-        let mut state = NonNull::new_unchecked(dev.cast::<PL011State>());
-        state.as_mut().reset();
-    }
-}

rust/qemu-api/src/definitions.rs

@@ -47,7 +47,7 @@ pub trait ObjectImpl: ClassInitImpl + Sized {
 /// Each QOM type has one such class struct.
 ///
 /// The Rust implementation of methods will usually come from a trait
-/// like [`ObjectImpl`].
+/// like [`ObjectImpl`] or [`DeviceImpl`](crate::device_class::DeviceImpl).
 pub trait ClassInitImpl {
     /// Function that is called after all parent class initialization
     /// has occurred.  On entry, the virtual method pointers are set to

rust/qemu-api/src/device_class.rs

@@ -17,14 +17,14 @@ pub trait DeviceImpl {
     ///
     /// If not `None`, the parent class's `realize` method is overridden
     /// with the function pointed to by `REALIZE`.
-    const REALIZE: Option<unsafe extern "C" fn(*mut DeviceState, *mut *mut Error)> = None;
+    const REALIZE: Option<fn(&mut Self)> = None;
 
     /// If not `None`, the parent class's `reset` method is overridden
     /// with the function pointed to by `RESET`.
     ///
     /// Rust does not yet support the three-phase reset protocol; this is
     /// usually okay for leaf classes.
-    const RESET: Option<unsafe extern "C" fn(dev: *mut DeviceState)> = None;
+    const RESET: Option<fn(&mut Self)> = None;
 
     /// An array providing the properties that the user can set on the
     /// device.  Not a `const` because referencing statics in constants
@@ -41,6 +41,30 @@ pub trait DeviceImpl {
     }
 }
 
+/// # Safety
+///
+/// This function is only called through the QOM machinery and
+/// the `impl_device_class!` macro.
+/// We expect the FFI user of this function to pass a valid pointer that
+/// can be downcasted to type `T`. We also expect the device is
+/// readable/writeable from one thread at any time.
+unsafe extern "C" fn rust_realize_fn<T: DeviceImpl>(dev: *mut DeviceState, _errp: *mut *mut Error) {
+    assert!(!dev.is_null());
+    let state = dev.cast::<T>();
+    T::REALIZE.unwrap()(unsafe { &mut *state });
+}
+
+/// # Safety
+///
+/// We expect the FFI user of this function to pass a valid pointer that
+/// can be downcasted to type `T`. We also expect the device is
+/// readable/writeable from one thread at any time.
+unsafe extern "C" fn rust_reset_fn<T: DeviceImpl>(dev: *mut DeviceState) {
+    assert!(!dev.is_null());
+    let state = dev.cast::<T>();
+    T::RESET.unwrap()(unsafe { &mut *state });
+}
+
 /// # Safety
 ///
 /// We expect the FFI user of this function to pass a valid pointer that
@@ -53,11 +77,11 @@ pub unsafe extern "C" fn rust_device_class_init<T: DeviceImpl>(
     let mut dc = ::core::ptr::NonNull::new(klass.cast::<DeviceClass>()).unwrap();
     unsafe {
         let dc = dc.as_mut();
-        if let Some(realize_fn) = <T as DeviceImpl>::REALIZE {
+        if <T as DeviceImpl>::REALIZE.is_some() {
-            dc.realize = Some(realize_fn);
+            dc.realize = Some(rust_realize_fn::<T>);
         }
-        if let Some(reset_fn) = <T as DeviceImpl>::RESET {
+        if <T as DeviceImpl>::RESET.is_some() {
-            bindings::device_class_set_legacy_reset(dc, Some(reset_fn));
+            bindings::device_class_set_legacy_reset(dc, Some(rust_reset_fn::<T>));
         }
         if let Some(vmsd) = <T as DeviceImpl>::vmsd() {
             dc.vmsd = vmsd;