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

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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>
This commit is contained in:
Paolo Bonzini 2024-11-29 15:19:23 +01:00
parent b1987a2547
commit 6dd818fbbb
5 changed files with 127 additions and 80 deletions
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111
rust/qemu-api/src/definitions.rs
View file

@ -26,6 +26,16 @@ unsafe extern "C" fn rust_instance_post_init<T: ObjectImpl>(obj: *mut Object) {
T::INSTANCE_POST_INIT.unwrap()(unsafe { &mut *obj.cast::<T>() })
}
unsafe extern "C" fn rust_class_init<T: ObjectType + ClassInitImpl<T::Class>>(
klass: *mut ObjectClass,
_data: *mut c_void,
) {
// SAFETY: klass is a T::Class, since rust_class_init<T>
// is called from QOM core as the class_init function
// for class T
T::class_init(unsafe { &mut *klass.cast::<T::Class>() })
}
/// Trait exposed by all structs corresponding to QOM objects.
///
/// # Safety
@ -50,7 +60,8 @@ unsafe extern "C" fn rust_instance_post_init<T: ObjectImpl>(obj: *mut Object) {
/// - likewise, the first field of the `Class` must be of the class struct
/// corresponding to the superclass, which is `ObjectImpl::ParentType::Class`.
pub unsafe trait ObjectType: Sized {
/// The QOM class object corresponding to this struct. Not used yet.
/// The QOM class object corresponding to this struct. This is used
/// to automatically generate a `class_init` method.
type Class;
/// The name of the type, which can be passed to `object_new()` to
@ -59,7 +70,7 @@ pub unsafe trait ObjectType: Sized {
}
/// Trait a type must implement to be registered with QEMU.
pub trait ObjectImpl: ObjectType + ClassInitImpl {
pub trait ObjectImpl: ObjectType + ClassInitImpl<Self::Class> {
/// The parent of the type. This should match the first field of
/// the struct that implements `ObjectImpl`:
type ParentType: ObjectType;
@ -80,6 +91,15 @@ pub trait ObjectImpl: ObjectType + ClassInitImpl {
/// `INSTANCE_INIT` functions have been called.
const INSTANCE_POST_INIT: Option<fn(&mut Self)> = None;
/// Called on descendent classes after all parent class initialization
/// has occurred, but before the class itself is initialized. This
/// is only useful if a class is not a leaf, and can be used to undo
/// the effects of copying the contents of the parent's class struct
/// to the descendants.
const CLASS_BASE_INIT: Option<
unsafe extern "C" fn(klass: *mut ObjectClass, data: *mut c_void),
> = None;
const TYPE_INFO: TypeInfo = TypeInfo {
name: Self::TYPE_NAME.as_ptr(),
parent: Self::ParentType::TYPE_NAME.as_ptr(),
@ -96,37 +116,86 @@ pub trait ObjectImpl: ObjectType + ClassInitImpl {
instance_finalize: Self::INSTANCE_FINALIZE,
abstract_: Self::ABSTRACT,
class_size: core::mem::size_of::<Self::Class>(),
class_init: <Self as ClassInitImpl>::CLASS_INIT,
class_base_init: <Self as ClassInitImpl>::CLASS_BASE_INIT,
class_init: Some(rust_class_init::<Self>),
class_base_init: Self::CLASS_BASE_INIT,
class_data: core::ptr::null_mut(),
interfaces: core::ptr::null_mut(),
};
}
/// Trait used to fill in a class struct.
/// Internal trait used to automatically fill in a class struct.
///
/// Each QOM class that has virtual methods describes them in a
/// _class struct_. Class structs include a parent field corresponding
/// to the vtable of the parent class, all the way up to [`ObjectClass`].
/// Each QOM type has one such class struct.
/// Each QOM type has one such class struct; this trait takes care of
/// initializing the `T` part of the class struct, for the type that
/// implements the trait.
///
/// The Rust implementation of methods will usually come from a trait
/// 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
/// Each struct will implement this trait with `T` equal to each
/// superclass. For example, a device should implement at least
/// `ClassInitImpl<`[`DeviceClass`](crate::bindings::DeviceClass)`>`.
/// Such implementations are made in one of two ways.
///
/// For most superclasses, `ClassInitImpl` is provided by the `qemu-api`
/// crate itself. The Rust implementation of methods will come from a
/// trait like [`ObjectImpl`] or
/// [`DeviceImpl`](crate::device_class::DeviceImpl), and `ClassInitImpl` is
/// provided by blanket implementations that operate on all implementors of the
/// `*Impl`* trait. For example:
///
/// ```ignore
/// impl<T> ClassInitImpl<DeviceClass> for T
/// where
/// T: DeviceImpl,
/// ```
///
/// The other case is when manual implementation of the trait is needed.
/// This covers the following cases:
///
/// * if a class implements a QOM interface, the Rust code _has_ to define its
/// own class struct `FooClass` and implement `ClassInitImpl<FooClass>`.
/// `ClassInitImpl<FooClass>`'s `class_init` method will then forward to
/// multiple other `class_init`s, for the interfaces as well as the
/// superclass. (Note that there is no Rust example yet for using interfaces).
///
/// * for classes implemented outside the ``qemu-api`` crate, it's not possible
/// to add blanket implementations like the above one, due to orphan rules. In
/// that case, the easiest solution is to implement
/// `ClassInitImpl<YourSuperclass>` for each subclass and not have a
/// `YourSuperclassImpl` trait at all.
///
/// ```ignore
/// impl ClassInitImpl<YourSuperclass> for YourSubclass {
/// fn class_init(klass: &mut YourSuperclass) {
/// klass.some_method = Some(Self::some_method);
/// <Self as ClassInitImpl<SysBusDeviceClass>>::class_init(&mut klass.parent_class);
/// }
/// }
/// ```
///
/// While this method incurs a small amount of code duplication,
/// it is generally limited to the recursive call on the last line.
/// This is because classes defined in Rust do not need the same
/// glue code that is needed when the classes are defined in C code.
/// You may consider using a macro if you have many subclasses.
pub trait ClassInitImpl<T> {
/// Initialize `klass` to point to the virtual method implementations
/// for `Self`. On entry, the virtual method pointers are set to
/// the default values coming from the parent classes; the function
/// can change them to override virtual methods of a parent class.
const CLASS_INIT: Option<unsafe extern "C" fn(klass: *mut ObjectClass, data: *mut c_void)>;
/// Called on descendent classes after all parent class initialization
/// has occurred, but before the class itself is initialized. This
/// is only useful if a class is not a leaf, and can be used to undo
/// the effects of copying the contents of the parent's class struct
/// to the descendants.
const CLASS_BASE_INIT: Option<
unsafe extern "C" fn(klass: *mut ObjectClass, data: *mut c_void),
>;
///
/// The virtual method implementations usually come from another
/// trait, for example [`DeviceImpl`](crate::device_class::DeviceImpl)
/// when `T` is [`DeviceClass`](crate::bindings::DeviceClass).
///
/// On entry, `klass`'s parent class is initialized, while the other fields
/// are all zero; it is therefore assumed that all fields in `T` can be
/// zeroed, otherwise it would not be possible to provide the class as a
/// `&mut T`. TODO: add a bound of [`Zeroable`](crate::zeroable::Zeroable)
/// to T; this is more easily done once Zeroable does not require a manual
/// implementation (Rust 1.75.0).
fn class_init(klass: &mut T);
}
#[macro_export]