diff options
Diffstat (limited to 'rust/qemu-api/src/qom.rs')
| -rw-r--r-- | rust/qemu-api/src/qom.rs | 85 |
1 files changed, 71 insertions, 14 deletions
diff --git a/rust/qemu-api/src/qom.rs b/rust/qemu-api/src/qom.rs index 7d5fbef1e1..97901fb908 100644 --- a/rust/qemu-api/src/qom.rs +++ b/rust/qemu-api/src/qom.rs @@ -55,6 +55,7 @@ use std::{ ffi::CStr, + fmt, ops::{Deref, DerefMut}, os::raw::c_void, }; @@ -105,6 +106,52 @@ macro_rules! qom_isa { }; } +/// This is the same as [`ManuallyDrop<T>`](std::mem::ManuallyDrop), though +/// it hides the standard methods of `ManuallyDrop`. +/// +/// The first field of an `ObjectType` must be of type `ParentField<T>`. +/// (Technically, this is only necessary if there is at least one Rust +/// superclass in the hierarchy). This is to ensure that the parent field is +/// dropped after the subclass; this drop order is enforced by the C +/// `object_deinit` function. +/// +/// # Examples +/// +/// ```ignore +/// #[repr(C)] +/// #[derive(qemu_api_macros::Object)] +/// pub struct MyDevice { +/// parent: ParentField<DeviceState>, +/// ... +/// } +/// ``` +#[derive(Debug)] +#[repr(transparent)] +pub struct ParentField<T: ObjectType>(std::mem::ManuallyDrop<T>); + +impl<T: ObjectType> Deref for ParentField<T> { + type Target = T; + + #[inline(always)] + fn deref(&self) -> &Self::Target { + &self.0 + } +} + +impl<T: ObjectType> DerefMut for ParentField<T> { + #[inline(always)] + fn deref_mut(&mut self) -> &mut Self::Target { + &mut self.0 + } +} + +impl<T: fmt::Display + ObjectType> fmt::Display for ParentField<T> { + #[inline(always)] + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> { + self.0.fmt(f) + } +} + 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 @@ -116,11 +163,7 @@ 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>() }) + T::INSTANCE_POST_INIT.unwrap()(unsafe { &*obj.cast::<T>() }) } unsafe extern "C" fn rust_class_init<T: ObjectType + ClassInitImpl<T::Class>>( @@ -133,6 +176,16 @@ unsafe extern "C" fn rust_class_init<T: ObjectType + ClassInitImpl<T::Class>>( T::class_init(unsafe { &mut *klass.cast::<T::Class>() }) } +unsafe extern "C" fn drop_object<T: ObjectImpl>(obj: *mut Object) { + // SAFETY: obj is an instance of T, since drop_object<T> is called + // from the QOM core function object_deinit() as the instance_finalize + // function for class T. Note that while object_deinit() will drop the + // superclass field separately after this function returns, `T` must + // implement the unsafe trait ObjectType; the safety rules for the + // trait mandate that the parent field is manually dropped. + unsafe { std::ptr::drop_in_place(obj.cast::<T>()) } +} + /// Trait exposed by all structs corresponding to QOM objects. /// /// # Safety @@ -151,11 +204,16 @@ unsafe extern "C" fn rust_class_init<T: ObjectType + ClassInitImpl<T::Class>>( /// /// - 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` +/// - the first field of the struct must be of type +/// [`ParentField<T>`](ParentField), where `T` is the parent type +/// [`ObjectImpl::ParentType`] +/// +/// - the first field of the `Class` must be of the class struct corresponding +/// to the superclass, which is `ObjectImpl::ParentType::Class`. `ParentField` +/// is not needed here. /// -/// - likewise, the first field of the `Class` must be of the class struct -/// corresponding to the superclass, which is `ObjectImpl::ParentType::Class`. +/// In both cases, having a separate class type is not necessary if the subclass +/// does not add any field. pub unsafe trait ObjectType: Sized { /// The QOM class object corresponding to this struct. This is used /// to automatically generate a `class_init` method. @@ -384,13 +442,12 @@ impl<T: ObjectType> ObjectCastMut for &mut T {} /// 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`: + /// The parent of the type. This should match the first field of the + /// struct that implements `ObjectImpl`, minus the `ParentField<_>` wrapper. 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 @@ -402,7 +459,7 @@ pub trait ObjectImpl: ObjectType + ClassInitImpl<Self::Class> { /// 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; + const INSTANCE_POST_INIT: Option<fn(&Self)> = None; /// Called on descendent classes after all parent class initialization /// has occurred, but before the class itself is initialized. This @@ -426,7 +483,7 @@ pub trait ObjectImpl: ObjectType + ClassInitImpl<Self::Class> { None => None, Some(_) => Some(rust_instance_post_init::<Self>), }, - instance_finalize: Self::INSTANCE_FINALIZE, + instance_finalize: Some(drop_object::<Self>), abstract_: Self::ABSTRACT, class_size: core::mem::size_of::<Self::Class>(), class_init: Some(rust_class_init::<Self>), |