rust: qom: put class_init together from multiple ClassInitImpl<>

Parameterize the implementation of ClassInitImpl so that it is
possible to call up the chain of implementations, one superclass at
a time starting at ClassInitImpl<Self::Class>.

In order to avoid having to implement (for example)
ClassInitImpl<PL011Class>, also remove the dummy PL011Class and
PL011LuminaryClass structs and specify the same ObjectType::Class as
the superclass.  In the future this default behavior can be handled by
a procedural macro, by looking at the first field in the struct.

Note that the new trait is safe: the calls are started by
rust_class_init<>(), which is not public and can convert the class
pointer to a Rust reference.

Since CLASS_BASE_INIT applies to the type that is being defined,
and only to it, move it to ObjectImpl.

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

1 files changed, 17 insertions, 1 deletions

diff --git a/rust/qemu-api/src/sysbus.rs b/rust/qemu-api/src/sysbus.rs
index 5ee068541c..5d15b31740 100644
--- a/rust/qemu-api/src/sysbus.rs
+++ b/rust/qemu-api/src/sysbus.rs
@@ -6,7 +6,13 @@ use std::{ffi::CStr, ptr::addr_of};
 
 pub use bindings::{SysBusDevice, SysBusDeviceClass};
 
-use crate::{bindings, cell::bql_locked, irq::InterruptSource, prelude::*};
+use crate::{
+    bindings::{self, DeviceClass},
+    cell::bql_locked,
+    definitions::ClassInitImpl,
+    irq::InterruptSource,
+    prelude::*,
+};
 
 unsafe impl ObjectType for SysBusDevice {
     type Class = SysBusDeviceClass;
@@ -14,6 +20,16 @@ unsafe impl ObjectType for SysBusDevice {
         unsafe { CStr::from_bytes_with_nul_unchecked(bindings::TYPE_SYS_BUS_DEVICE) };
 }
 
+// TODO: add SysBusDeviceImpl
+impl<T> ClassInitImpl<SysBusDeviceClass> for T
+where
+    T: ClassInitImpl<DeviceClass>,
+{
+    fn class_init(sdc: &mut SysBusDeviceClass) {
+        <T as ClassInitImpl<DeviceClass>>::class_init(&mut sdc.parent_class);
+    }
+}
+
 impl SysBusDevice {
     /// Return `self` cast to a mutable pointer, for use in calls to C code.
     const fn as_mut_ptr(&self) -> *mut SysBusDevice {