[PATCH 6/8] rust: qdev: move bridge for realize and reset functions out of pl011

[Paolo Bonzini]

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

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 rust/hw/char/pl011/src/device.rs       |  5 ++--
 rust/hw/char/pl011/src/device_class.rs | 26 ----------------
 rust/qemu-api/src/definitions.rs       |  2 +-
 rust/qemu-api/src/device_class.rs      | 41 ++++++++++++++++++++++----
 4 files changed, 38 insertions(+), 36 deletions(-)

diff --git a/rust/hw/char/pl011/src/device.rs b/rust/hw/char/pl011/src/device.rs
index 1906b9022bd..aeccce5186c 100644
--- a/rust/hw/char/pl011/src/device.rs
+++ b/rust/hw/char/pl011/src/device.rs
@@ -125,9 +125,8 @@ fn properties() -> &'static [Property] {
     fn vmsd() -> Option<&'static VMStateDescription> {
         Some(&device_class::VMSTATE_PL011)
     }
-    const REALIZE: Option<unsafe extern "C" fn(*mut DeviceState, *mut *mut 
Error)> =
-        Some(device_class::pl011_realize);
-    const RESET: Option<unsafe extern "C" fn(*mut DeviceState)> = 
Some(device_class::pl011_reset);
+    const REALIZE: Option<fn(&mut Self)> = Some(Self::realize);
+    const RESET: Option<fn(&mut Self)> = Some(Self::reset);
 }
 
 impl_device_class!(PL011State);
diff --git a/rust/hw/char/pl011/src/device_class.rs 
b/rust/hw/char/pl011/src/device_class.rs
index c61b6bb0258..975c3d42be7 100644
--- a/rust/hw/char/pl011/src/device_class.rs
+++ b/rust/hw/char/pl011/src/device_class.rs
@@ -92,29 +92,3 @@ extern "C" fn pl011_post_load(opaque: *mut c_void, 
version_id: c_int) -> c_int {
         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();
-    }
-}
diff --git a/rust/qemu-api/src/definitions.rs b/rust/qemu-api/src/definitions.rs
index 487712611f6..0467e6290e0 100644
--- a/rust/qemu-api/src/definitions.rs
+++ b/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
diff --git a/rust/qemu-api/src/device_class.rs 
b/rust/qemu-api/src/device_class.rs
index 72cea345f87..385f0b7a09e 100644
--- a/rust/qemu-api/src/device_class.rs
+++ b/rust/qemu-api/src/device_class.rs
@@ -8,6 +8,7 @@
     self, DeviceClass, DeviceState, Error, ObjectClass, Property, 
VMStateDescription,
 };
 
+/// Trait providing the contents of [`DeviceClass`].
 pub trait DeviceImpl {
     /// _Realization_ is the second stage of device creation. It contains
     /// all operations that depend on device properties and can fail (note:
@@ -15,14 +16,14 @@ 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
@@ -39,6 +40,30 @@ fn vmsd() -> Option<&'static VMStateDescription> {
     }
 }
 
+/// # 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
@@ -51,11 +80,11 @@ fn vmsd() -> Option<&'static VMStateDescription> {
     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 {
-            dc.realize = Some(realize_fn);
+        if <T as DeviceImpl>::REALIZE.is_some() {
+            dc.realize = Some(rust_realize_fn::<T>);
         }
-        if let Some(reset_fn) = <T as DeviceImpl>::RESET {
-            bindings::device_class_set_legacy_reset(dc, Some(reset_fn));
+        if <T as DeviceImpl>::RESET.is_some() {
+            bindings::device_class_set_legacy_reset(dc, 
Some(rust_reset_fn::<T>));
         }
         if let Some(vmsd) = <T as DeviceImpl>::vmsd() {
             dc.vmsd = vmsd;
-- 
2.47.0