rust: rename qemu-api modules to follow C code a bit more

A full match would mean calling them qom::object and hw::core::qdev.  For now,
keep the names shorter but still a bit easier to find.

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

rust/qemu-api/src/qom.rs

@@ -0,0 +1,263 @@
+// Copyright 2024, Linaro Limited
+// Author(s): Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+//! Bindings to access QOM functionality from Rust.
+//!
+//! This module provides automatic creation and registration of `TypeInfo`
+//! for classes that are written in Rust, and mapping between Rust traits
+//! and QOM vtables.
+//!
+//! # Structure of a class
+//!
+//! A leaf class only needs a struct holding instance state. The struct must
+//! implement the [`ObjectType`] trait, as well as any `*Impl` traits that exist
+//! for its superclasses.
+//!
+//! If a class has subclasses, it will also provide a struct for instance data,
+//! with the same characteristics as for concrete classes, but it also needs
+//! additional components to support virtual methods:
+//!
+//! * a struct for class data, for example `DeviceClass`. This corresponds to
+//!   the C "class struct" and holds the vtable that is used by instances of the
+//!   class and its subclasses. It must start with its parent's class struct.
+//!
+//! * a trait for virtual method implementations, for example `DeviceImpl`.
+//!   Child classes implement this trait to provide their own behavior for
+//!   virtual methods. The trait's methods take `&self` to access instance data.
+//!
+//! * an implementation of [`ClassInitImpl`], for example
+//!   `ClassInitImpl<DeviceClass>`. This fills the vtable in the class struct;
+//!   the source for this is the `*Impl` trait; the associated consts and
+//!   functions if needed are wrapped to map C types into Rust types.
+
+use std::{ffi::CStr, os::raw::c_void};
+
+use crate::bindings::{self, Object, ObjectClass, TypeInfo};
+
+unsafe extern "C" fn rust_instance_init<T: ObjectImpl>(obj: *mut Object) {
+    // SAFETY: obj is an instance of T, since rust_instance_init<T>
+    // is called from QOM core as the instance_init function
+    // for class T
+    unsafe { T::INSTANCE_INIT.unwrap()(&mut *obj.cast::<T>()) }
+}
+
+unsafe extern "C" fn rust_instance_post_init<T: ObjectImpl>(obj: *mut Object) {
+    // SAFETY: obj is an instance of T, since rust_instance_post_init<T>
+    // is called from QOM core as the instance_post_init function
+    // for class T
+    //
+    // FIXME: it's not really guaranteed that there are no backpointers to
+    // obj; it's quite possible that they have been created by instance_init().
+    // The receiver should be &self, not &mut self.
+    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
+///
+/// For classes declared in C:
+///
+/// - `Class` and `TYPE` must match the data in the `TypeInfo`;
+///
+/// - the first field of the struct must be of the instance type corresponding
+///   to the superclass, as declared in the `TypeInfo`
+///
+/// - likewise, the first field of the `Class` struct must be of the class type
+///   corresponding to the superclass
+///
+/// For classes declared in Rust and implementing [`ObjectImpl`]:
+///
+/// - the struct must be `#[repr(C)]`;
+///
+/// - the first field of the struct must be of the instance struct corresponding
+///   to the superclass, which is `ObjectImpl::ParentType`
+///
+/// - 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.  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
+    /// generate an instance of this type.
+    const TYPE_NAME: &'static CStr;
+}
+
+/// Trait a type must implement to be registered with QEMU.
+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;
+
+    /// Whether the object can be instantiated
+    const ABSTRACT: bool = false;
+    const INSTANCE_FINALIZE: Option<unsafe extern "C" fn(obj: *mut Object)> = None;
+
+    /// Function that is called to initialize an object.  The parent class will
+    /// have already been initialized so the type is only responsible for
+    /// initializing its own members.
+    ///
+    /// FIXME: The argument is not really a valid reference. `&mut
+    /// MaybeUninit<Self>` would be a better description.
+    const INSTANCE_INIT: Option<unsafe fn(&mut Self)> = None;
+
+    /// Function that is called to finish initialization of an object, once
+    /// `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(),
+        instance_size: core::mem::size_of::<Self>(),
+        instance_align: core::mem::align_of::<Self>(),
+        instance_init: match Self::INSTANCE_INIT {
+            None => None,
+            Some(_) => Some(rust_instance_init::<Self>),
+        },
+        instance_post_init: match Self::INSTANCE_POST_INIT {
+            None => None,
+            Some(_) => Some(rust_instance_post_init::<Self>),
+        },
+        instance_finalize: Self::INSTANCE_FINALIZE,
+        abstract_: Self::ABSTRACT,
+        class_size: core::mem::size_of::<Self::Class>(),
+        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(),
+    };
+
+    // methods on ObjectClass
+    const UNPARENT: Option<fn(&Self)> = None;
+}
+
+/// 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; this trait takes care of
+/// initializing the `T` part of the class struct, for the type that
+/// implements the trait.
+///
+/// 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)`>` and
+/// `ClassInitImpl<`[`ObjectClass`](crate::bindings::ObjectClass)`>`.
+/// 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::qdev::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: ClassInitImpl<ObjectClass> + DeviceImpl,
+/// ```
+///
+/// The bound on `ClassInitImpl<ObjectClass>` is needed so that,
+/// after initializing the `DeviceClass` part of the class struct,
+/// the parent [`ObjectClass`] is initialized as well.
+///
+/// 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.
+    ///
+    /// The virtual method implementations usually come from another
+    /// trait, for example [`DeviceImpl`](crate::qdev::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);
+}
+
+/// # 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_unparent_fn<T: ObjectImpl>(dev: *mut Object) {
+    unsafe {
+        assert!(!dev.is_null());
+        let state = core::ptr::NonNull::new_unchecked(dev.cast::<T>());
+        T::UNPARENT.unwrap()(state.as_ref());
+    }
+}
+
+impl<T> ClassInitImpl<ObjectClass> for T
+where
+    T: ObjectImpl,
+{
+    fn class_init(oc: &mut ObjectClass) {
+        if <T as ObjectImpl>::UNPARENT.is_some() {
+            oc.unparent = Some(rust_unparent_fn::<T>);
+        }
+    }
+}
+
+unsafe impl ObjectType for Object {
+    type Class = ObjectClass;
+    const TYPE_NAME: &'static CStr =
+        unsafe { CStr::from_bytes_with_nul_unchecked(bindings::TYPE_OBJECT) };
+}