| 1 | // Copyright 2024, Linaro Limited |
| 2 | // Author(s): Manos Pitsidianakis <manos.pitsidianakis@linaro.org> |
| 3 | // SPDX-License-Identifier: GPL-2.0-or-later |
| 4 | |
| 5 | //! Bindings to access QOM functionality from Rust. |
| 6 | //! |
| 7 | //! The QEMU Object Model (QOM) provides inheritance and dynamic typing for QEMU |
| 8 | //! devices. This module makes QOM's features available in Rust through three |
| 9 | //! main mechanisms: |
| 10 | //! |
| 11 | //! * Automatic creation and registration of `TypeInfo` for classes that are |
| 12 | //! written in Rust, as well as mapping between Rust traits and QOM vtables. |
| 13 | //! |
| 14 | //! * Type-safe casting between parent and child classes, through the [`IsA`] |
| 15 | //! trait and methods such as [`upcast`](ObjectCast::upcast) and |
| 16 | //! [`downcast`](ObjectCast::downcast). |
| 17 | //! |
| 18 | //! * Automatic delegation of parent class methods to child classes. When a |
| 19 | //! trait uses [`IsA`] as a bound, its contents become available to all child |
| 20 | //! classes through blanket implementations. This works both for class methods |
| 21 | //! and for instance methods accessed through references or smart pointers. |
| 22 | //! |
| 23 | //! # Structure of a class |
| 24 | //! |
| 25 | //! A leaf class only needs a struct holding instance state. The struct must |
| 26 | //! implement the [`ObjectType`] and [`IsA`] traits, as well as any `*Impl` |
| 27 | //! traits that exist for its superclasses. |
| 28 | //! |
| 29 | //! If a class has subclasses, it will also provide a struct for instance data, |
| 30 | //! with the same characteristics as for concrete classes, but it also needs |
| 31 | //! additional components to support virtual methods: |
| 32 | //! |
| 33 | //! * a struct for class data, for example `DeviceClass`. This corresponds to |
| 34 | //! the C "class struct" and holds the vtable that is used by instances of the |
| 35 | //! class and its subclasses. It must start with its parent's class struct. |
| 36 | //! |
| 37 | //! * a trait for virtual method implementations, for example `DeviceImpl`. |
| 38 | //! Child classes implement this trait to provide their own behavior for |
| 39 | //! virtual methods. The trait's methods take `&self` to access instance data. |
| 40 | //! The traits have the appropriate specialization of `IsA<>` as a supertrait, |
| 41 | //! for example `IsA<DeviceState>` for `DeviceImpl`. |
| 42 | //! |
| 43 | //! * a trait for instance methods, for example `DeviceMethods`. This trait is |
| 44 | //! automatically implemented for any reference or smart pointer to a device |
| 45 | //! instance. It calls into the vtable provides access across all subclasses |
| 46 | //! to methods defined for the class. |
| 47 | //! |
| 48 | //! * optionally, a trait for class methods, for example `DeviceClassMethods`. |
| 49 | //! This provides access to class-wide functionality that doesn't depend on |
| 50 | //! instance data. Like instance methods, these are automatically inherited by |
| 51 | //! child classes. |
| 52 | //! |
| 53 | //! # Class structures |
| 54 | //! |
| 55 | //! Each QOM class that has virtual methods describes them in a |
| 56 | //! _class struct_. Class structs include a parent field corresponding |
| 57 | //! to the vtable of the parent class, all the way up to [`ObjectClass`]. |
| 58 | //! |
| 59 | //! As mentioned above, virtual methods are defined via traits such as |
| 60 | //! `DeviceImpl`. Class structs do not define any trait but, conventionally, |
| 61 | //! all of them have a `class_init` method to initialize the virtual methods |
| 62 | //! based on the trait and then call the same method on the superclass. |
| 63 | //! |
| 64 | //! ```ignore |
| 65 | //! impl YourSubclassClass |
| 66 | //! { |
| 67 | //! pub fn class_init<T: YourSubclassImpl>(&mut self) { |
| 68 | //! ... |
| 69 | //! klass.parent_class::class_init<T>(); |
| 70 | //! } |
| 71 | //! } |
| 72 | //! ``` |
| 73 | //! |
| 74 | //! If a class implements a QOM interface. In that case, the function must |
| 75 | //! contain, for each interface, an extra forwarding call as follows: |
| 76 | //! |
| 77 | //! ```ignore |
| 78 | //! ResettableClass::cast::<Self>(self).class_init::<Self>(); |
| 79 | //! ``` |
| 80 | //! |
| 81 | //! These `class_init` functions are methods on the class rather than a trait, |
| 82 | //! because the bound on `T` (`DeviceImpl` in this case), will change for every |
| 83 | //! class struct. The functions are pointed to by the |
| 84 | //! [`ObjectImpl::CLASS_INIT`] function pointer. While there is no default |
| 85 | //! implementation, in most cases it will be enough to write it as follows: |
| 86 | //! |
| 87 | //! ```ignore |
| 88 | //! const CLASS_INIT: fn(&mut Self::Class)> = Self::Class::class_init::<Self>; |
| 89 | //! ``` |
| 90 | //! |
| 91 | //! This design incurs a small amount of code duplication but, by not using |
| 92 | //! traits, it allows the flexibility of implementing bindings in any crate, |
| 93 | //! without incurring into violations of orphan rules for traits. |
| 94 | |
| 95 | use std::{ |
| 96 | ffi::{c_void, CStr}, |
| 97 | fmt, |
| 98 | marker::PhantomData, |
| 99 | mem::{ManuallyDrop, MaybeUninit}, |
| 100 | ops::{Deref, DerefMut}, |
| 101 | ptr::NonNull, |
| 102 | }; |
| 103 | |
| 104 | use common::Opaque; |
| 105 | use migration::{impl_vmstate_pointer, impl_vmstate_transparent}; |
| 106 | |
| 107 | use crate::bindings::{ |
| 108 | self, object_class_dynamic_cast, object_dynamic_cast, object_get_class, object_get_typename, |
| 109 | object_new, object_ref, object_unref, TypeInfo, |
| 110 | }; |
| 111 | pub use crate::bindings::{type_register_static, ObjectClass}; |
| 112 | |
| 113 | /// A safe wrapper around [`bindings::Object`]. |
| 114 | #[repr(transparent)] |
| 115 | #[derive(Debug, common::Wrapper)] |
| 116 | pub struct Object(Opaque<bindings::Object>); |
| 117 | |
| 118 | unsafe impl Send for Object {} |
| 119 | unsafe impl Sync for Object {} |
| 120 | |
| 121 | /// Marker trait: `Self` can be statically upcasted to `P` (i.e. `P` is a direct |
| 122 | /// or indirect parent of `Self`). |
| 123 | /// |
| 124 | /// # Safety |
| 125 | /// |
| 126 | /// The struct `Self` must be `#[repr(C)]` and must begin, directly or |
| 127 | /// indirectly, with a field of type `P`. This ensures that invalid casts, |
| 128 | /// which rely on `IsA<>` for static checking, are rejected at compile time. |
| 129 | pub unsafe trait IsA<P: ObjectType>: ObjectType {} |
| 130 | |
| 131 | // SAFETY: it is always safe to cast to your own type |
| 132 | unsafe impl<T: ObjectType> IsA<T> for T {} |
| 133 | |
| 134 | /// Macro to mark superclasses of QOM classes. This enables type-safe |
| 135 | /// up- and downcasting. |
| 136 | /// |
| 137 | /// # Safety |
| 138 | /// |
| 139 | /// This macro is a thin wrapper around the [`IsA`] trait and performs |
| 140 | /// no checking whatsoever of what is declared. It is the caller's |
| 141 | /// responsibility to have $struct begin, directly or indirectly, with |
| 142 | /// a field of type `$parent`. |
| 143 | #[macro_export] |
| 144 | macro_rules! qom_isa { |
| 145 | ($struct:ty : $($parent:ty),* ) => { |
| 146 | $( |
| 147 | // SAFETY: it is the caller responsibility to have $parent as the |
| 148 | // first field |
| 149 | unsafe impl $crate::IsA<$parent> for $struct {} |
| 150 | |
| 151 | impl AsRef<$parent> for $struct { |
| 152 | fn as_ref(&self) -> &$parent { |
| 153 | // SAFETY: follows the same rules as for IsA<U>, which is |
| 154 | // declared above. |
| 155 | let ptr: *const Self = self; |
| 156 | unsafe { &*ptr.cast::<$parent>() } |
| 157 | } |
| 158 | } |
| 159 | )* |
| 160 | }; |
| 161 | } |
| 162 | |
| 163 | /// This is the same as [`ManuallyDrop<T>`](std::mem::ManuallyDrop), though |
| 164 | /// it hides the standard methods of `ManuallyDrop`. |
| 165 | /// |
| 166 | /// The first field of an `ObjectType` must be of type `ParentField<T>`. |
| 167 | /// (Technically, this is only necessary if there is at least one Rust |
| 168 | /// superclass in the hierarchy). This is to ensure that the parent field is |
| 169 | /// dropped after the subclass; this drop order is enforced by the C |
| 170 | /// `object_deinit` function. |
| 171 | /// |
| 172 | /// # Examples |
| 173 | /// |
| 174 | /// ```ignore |
| 175 | /// #[repr(C)] |
| 176 | /// #[derive(qom::Object)] |
| 177 | /// pub struct MyDevice { |
| 178 | /// parent: ParentField<DeviceState>, |
| 179 | /// ... |
| 180 | /// } |
| 181 | /// ``` |
| 182 | #[derive(Debug)] |
| 183 | #[repr(transparent)] |
| 184 | pub struct ParentField<T: ObjectType>(std::mem::ManuallyDrop<T>); |
| 185 | impl_vmstate_transparent!(ParentField<T> where T: VMState + ObjectType); |
| 186 | |
| 187 | impl<T: ObjectType> Deref for ParentField<T> { |
| 188 | type Target = T; |
| 189 | |
| 190 | #[inline(always)] |
| 191 | fn deref(&self) -> &Self::Target { |
| 192 | &self.0 |
| 193 | } |
| 194 | } |
| 195 | |
| 196 | impl<T: ObjectType> DerefMut for ParentField<T> { |
| 197 | #[inline(always)] |
| 198 | fn deref_mut(&mut self) -> &mut Self::Target { |
| 199 | &mut self.0 |
| 200 | } |
| 201 | } |
| 202 | |
| 203 | impl<T: fmt::Display + ObjectType> fmt::Display for ParentField<T> { |
| 204 | #[inline(always)] |
| 205 | fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> { |
| 206 | self.0.fmt(f) |
| 207 | } |
| 208 | } |
| 209 | |
| 210 | /// This struct knows that the superclasses of the object have already been |
| 211 | /// initialized. |
| 212 | /// |
| 213 | /// The declaration of `ParentInit` is.. *"a kind of magic"*. It uses a |
| 214 | /// technique that is found in several crates, the main ones probably being |
| 215 | /// `ghost-cell` (in fact it was introduced by the [`GhostCell` paper](https://plv.mpi-sws.org/rustbelt/ghostcell/)) |
| 216 | /// and `generativity`. |
| 217 | /// |
| 218 | /// The `PhantomData` makes the `ParentInit` type *invariant* with respect to |
| 219 | /// the lifetime argument `'init`. This, together with the `for<'...>` in |
| 220 | /// `[ParentInit::with]`, block any attempt of the compiler to be creative when |
| 221 | /// operating on types of type `ParentInit` and to extend their lifetimes. In |
| 222 | /// particular, it ensures that the `ParentInit` cannot be made to outlive the |
| 223 | /// `rust_instance_init()` function that creates it, and therefore that the |
| 224 | /// `&'init T` reference is valid. |
| 225 | /// |
| 226 | /// This implementation of the same concept, without the QOM baggage, can help |
| 227 | /// understanding the effect: |
| 228 | /// |
| 229 | /// ``` |
| 230 | /// use std::marker::PhantomData; |
| 231 | /// |
| 232 | /// #[derive(PartialEq, Eq)] |
| 233 | /// pub struct Jail<'closure, T: Copy>(&'closure T, PhantomData<fn(&'closure ()) -> &'closure ()>); |
| 234 | /// |
| 235 | /// impl<'closure, T: Copy> Jail<'closure, T> { |
| 236 | /// fn get(&self) -> T { |
| 237 | /// *self.0 |
| 238 | /// } |
| 239 | /// |
| 240 | /// #[inline] |
| 241 | /// fn with<U>(v: T, f: impl for<'id> FnOnce(Jail<'id, T>) -> U) -> U { |
| 242 | /// let parent_init = Jail(&v, PhantomData); |
| 243 | /// f(parent_init) |
| 244 | /// } |
| 245 | /// } |
| 246 | /// ``` |
| 247 | /// |
| 248 | /// It's impossible to escape the `Jail`; `token1` cannot be moved out of the |
| 249 | /// closure: |
| 250 | /// |
| 251 | /// ```ignore |
| 252 | /// let x = 42; |
| 253 | /// let escape = Jail::with(&x, |token1| { |
| 254 | /// println!("{}", token1.get()); |
| 255 | /// // fails to compile... |
| 256 | /// token1 |
| 257 | /// }); |
| 258 | /// // ... so you cannot do this: |
| 259 | /// println!("{}", escape.get()); |
| 260 | /// ``` |
| 261 | /// |
| 262 | /// Likewise, in the QOM case the `ParentInit` cannot be moved out of |
| 263 | /// `instance_init()`. Without this trick it would be possible to stash a |
| 264 | /// `ParentInit` and use it later to access uninitialized memory. |
| 265 | /// |
| 266 | /// Here is another example, showing how separately-created "identities" stay |
| 267 | /// isolated: |
| 268 | /// |
| 269 | /// ```ignore |
| 270 | /// impl<'closure, T: Copy> Clone for Jail<'closure, T> { |
| 271 | /// fn clone(&self) -> Jail<'closure, T> { |
| 272 | /// Jail(self.0, PhantomData) |
| 273 | /// } |
| 274 | /// } |
| 275 | /// |
| 276 | /// fn main() { |
| 277 | /// Jail::with(42, |token1| { |
| 278 | /// // this works and returns true: the clone has the same "identity" |
| 279 | /// println!("{}", token1 == token1.clone()); |
| 280 | /// Jail::with(42, |token2| { |
| 281 | /// // here the outer token remains accessible... |
| 282 | /// println!("{}", token1.get()); |
| 283 | /// // ... but the two are separate: this fails to compile: |
| 284 | /// println!("{}", token1 == token2); |
| 285 | /// }); |
| 286 | /// }); |
| 287 | /// } |
| 288 | /// ``` |
| 289 | pub struct ParentInit<'init, T>( |
| 290 | &'init mut MaybeUninit<T>, |
| 291 | PhantomData<fn(&'init ()) -> &'init ()>, |
| 292 | ); |
| 293 | |
| 294 | impl<'init, T> ParentInit<'init, T> { |
| 295 | #[inline] |
| 296 | pub fn with(obj: &'init mut MaybeUninit<T>, f: impl for<'id> FnOnce(ParentInit<'id, T>)) { |
| 297 | let parent_init = ParentInit(obj, PhantomData); |
| 298 | f(parent_init) |
| 299 | } |
| 300 | } |
| 301 | |
| 302 | impl<T: ObjectType> ParentInit<'_, T> { |
| 303 | /// Return the receiver as a mutable raw pointer to Object. |
| 304 | /// |
| 305 | /// # Safety |
| 306 | /// |
| 307 | /// Fields beyond `Object` could be uninitialized and it's your |
| 308 | /// responsibility to avoid that they're used when the pointer is |
| 309 | /// dereferenced, either directly or through a cast. |
| 310 | pub const fn as_object_mut_ptr(&self) -> *mut bindings::Object { |
| 311 | self.as_object_ptr().cast_mut() |
| 312 | } |
| 313 | |
| 314 | /// Return the receiver as a mutable raw pointer to Object. |
| 315 | /// |
| 316 | /// # Safety |
| 317 | /// |
| 318 | /// Fields beyond `Object` could be uninitialized and it's your |
| 319 | /// responsibility to avoid that they're used when the pointer is |
| 320 | /// dereferenced, either directly or through a cast. |
| 321 | pub const fn as_object_ptr(&self) -> *const bindings::Object { |
| 322 | self.0.as_ptr().cast() |
| 323 | } |
| 324 | } |
| 325 | |
| 326 | impl<'a, T: ObjectImpl> ParentInit<'a, T> { |
| 327 | /// Convert from a derived type to one of its parent types, which |
| 328 | /// have already been initialized. |
| 329 | /// |
| 330 | /// # Safety |
| 331 | /// |
| 332 | /// Structurally this is always a safe operation; the [`IsA`] trait |
| 333 | /// provides static verification trait that `Self` dereferences to `U` or |
| 334 | /// a child of `U`, and only parent types of `T` are allowed. |
| 335 | /// |
| 336 | /// However, while the fields of the resulting reference are initialized, |
| 337 | /// calls might use uninitialized fields of the subclass. It is your |
| 338 | /// responsibility to avoid this. |
| 339 | pub const unsafe fn upcast<U: ObjectType>(&self) -> &'a U |
| 340 | where |
| 341 | T::ParentType: IsA<U>, |
| 342 | { |
| 343 | // SAFETY: soundness is declared via IsA<U>, which is an unsafe trait; |
| 344 | // the parent has been initialized before `instance_init `is called |
| 345 | unsafe { &*(self.0.as_ptr().cast::<U>()) } |
| 346 | } |
| 347 | |
| 348 | /// Convert from a derived type to one of its parent types, which |
| 349 | /// have already been initialized. |
| 350 | /// |
| 351 | /// # Safety |
| 352 | /// |
| 353 | /// Structurally this is always a safe operation; the [`IsA`] trait |
| 354 | /// provides static verification trait that `Self` dereferences to `U` or |
| 355 | /// a child of `U`, and only parent types of `T` are allowed. |
| 356 | /// |
| 357 | /// However, while the fields of the resulting reference are initialized, |
| 358 | /// calls might use uninitialized fields of the subclass. It is your |
| 359 | /// responsibility to avoid this. |
| 360 | pub unsafe fn upcast_mut<U: ObjectType>(&mut self) -> &'a mut U |
| 361 | where |
| 362 | T::ParentType: IsA<U>, |
| 363 | { |
| 364 | // SAFETY: soundness is declared via IsA<U>, which is an unsafe trait; |
| 365 | // the parent has been initialized before `instance_init `is called |
| 366 | unsafe { &mut *(self.0.as_mut_ptr().cast::<U>()) } |
| 367 | } |
| 368 | } |
| 369 | |
| 370 | impl<T> Deref for ParentInit<'_, T> { |
| 371 | type Target = MaybeUninit<T>; |
| 372 | |
| 373 | fn deref(&self) -> &Self::Target { |
| 374 | self.0 |
| 375 | } |
| 376 | } |
| 377 | |
| 378 | impl<T> DerefMut for ParentInit<'_, T> { |
| 379 | fn deref_mut(&mut self) -> &mut Self::Target { |
| 380 | self.0 |
| 381 | } |
| 382 | } |
| 383 | |
| 384 | unsafe extern "C" fn rust_instance_init<T: ObjectImpl>(obj: *mut bindings::Object) { |
| 385 | let mut state = NonNull::new(obj).unwrap().cast::<MaybeUninit<T>>(); |
| 386 | |
| 387 | // SAFETY: obj is an instance of T, since rust_instance_init<T> |
| 388 | // is called from QOM core as the instance_init function |
| 389 | // for class T |
| 390 | unsafe { |
| 391 | ParentInit::with(state.as_mut(), |parent_init| { |
| 392 | T::INSTANCE_INIT.unwrap()(parent_init); |
| 393 | }); |
| 394 | } |
| 395 | } |
| 396 | |
| 397 | unsafe extern "C" fn rust_instance_post_init<T: ObjectImpl>(obj: *mut bindings::Object) { |
| 398 | let state = NonNull::new(obj).unwrap().cast::<T>(); |
| 399 | // SAFETY: obj is an instance of T, since rust_instance_post_init<T> |
| 400 | // is called from QOM core as the instance_post_init function |
| 401 | // for class T |
| 402 | T::INSTANCE_POST_INIT.unwrap()(unsafe { state.as_ref() }); |
| 403 | } |
| 404 | |
| 405 | unsafe extern "C" fn rust_class_init<T: ObjectType + ObjectImpl>( |
| 406 | klass: *mut ObjectClass, |
| 407 | _data: *const c_void, |
| 408 | ) { |
| 409 | let mut klass = NonNull::new(klass) |
| 410 | .unwrap() |
| 411 | .cast::<<T as ObjectType>::Class>(); |
| 412 | // SAFETY: klass is a T::Class, since rust_class_init<T> |
| 413 | // is called from QOM core as the class_init function |
| 414 | // for class T |
| 415 | <T as ObjectImpl>::CLASS_INIT(unsafe { klass.as_mut() }) |
| 416 | } |
| 417 | |
| 418 | unsafe extern "C" fn drop_object<T: ObjectImpl>(obj: *mut bindings::Object) { |
| 419 | // SAFETY: obj is an instance of T, since drop_object<T> is called |
| 420 | // from the QOM core function object_deinit() as the instance_finalize |
| 421 | // function for class T. Note that while object_deinit() will drop the |
| 422 | // superclass field separately after this function returns, `T` must |
| 423 | // implement the unsafe trait ObjectType; the safety rules for the |
| 424 | // trait mandate that the parent field is manually dropped. |
| 425 | unsafe { std::ptr::drop_in_place(obj.cast::<T>()) } |
| 426 | } |
| 427 | |
| 428 | /// Trait exposed by all structs corresponding to QOM objects. |
| 429 | /// |
| 430 | /// # Safety |
| 431 | /// |
| 432 | /// For classes declared in C: |
| 433 | /// |
| 434 | /// - `Class` and `TYPE` must match the data in the `TypeInfo`; |
| 435 | /// |
| 436 | /// - the first field of the struct must be of the instance type corresponding |
| 437 | /// to the superclass, as declared in the `TypeInfo` |
| 438 | /// |
| 439 | /// - likewise, the first field of the `Class` struct must be of the class type |
| 440 | /// corresponding to the superclass |
| 441 | /// |
| 442 | /// For classes declared in Rust and implementing [`ObjectImpl`]: |
| 443 | /// |
| 444 | /// - the struct must be `#[repr(C)]`; |
| 445 | /// |
| 446 | /// - the first field of the struct must be of type |
| 447 | /// [`ParentField<T>`](ParentField), where `T` is the parent type |
| 448 | /// [`ObjectImpl::ParentType`] |
| 449 | /// |
| 450 | /// - the first field of the `Class` must be of the class struct corresponding |
| 451 | /// to the superclass, which is `ObjectImpl::ParentType::Class`. `ParentField` |
| 452 | /// is not needed here. |
| 453 | /// |
| 454 | /// In both cases, having a separate class type is not necessary if the subclass |
| 455 | /// does not add any field. |
| 456 | pub unsafe trait ObjectType: Sized { |
| 457 | /// The QOM class object corresponding to this struct. This is used |
| 458 | /// to automatically generate a `class_init` method. |
| 459 | type Class; |
| 460 | |
| 461 | /// The name of the type, which can be passed to `object_new()` to |
| 462 | /// generate an instance of this type. |
| 463 | const TYPE_NAME: &'static CStr; |
| 464 | |
| 465 | /// Return the receiver as an Object. This is always safe, even |
| 466 | /// if this type represents an interface. |
| 467 | fn as_object(&self) -> &Object { |
| 468 | unsafe { &*self.as_ptr().cast() } |
| 469 | } |
| 470 | |
| 471 | /// Return the receiver as a const raw pointer to Object. |
| 472 | /// This is preferable to `as_object_mut_ptr()` if a C |
| 473 | /// function only needs a `const Object *`. |
| 474 | fn as_object_ptr(&self) -> *const bindings::Object { |
| 475 | self.as_object().as_ptr() |
| 476 | } |
| 477 | |
| 478 | /// Return the receiver as a mutable raw pointer to Object. |
| 479 | /// |
| 480 | /// # Safety |
| 481 | /// |
| 482 | /// This cast is always safe, but because the result is mutable |
| 483 | /// and the incoming reference is not, this should only be used |
| 484 | /// for calls to C functions, and only if needed. |
| 485 | unsafe fn as_object_mut_ptr(&self) -> *mut bindings::Object { |
| 486 | self.as_object().as_mut_ptr() |
| 487 | } |
| 488 | } |
| 489 | |
| 490 | /// Trait exposed by all structs corresponding to QOM interfaces. |
| 491 | /// Unlike `ObjectType`, it is implemented on the class type (which provides |
| 492 | /// the vtable for the interfaces). |
| 493 | /// |
| 494 | /// # Safety |
| 495 | /// |
| 496 | /// `TYPE` must match the contents of the `TypeInfo` as found in the C code; |
| 497 | /// right now, interfaces can only be declared in C. |
| 498 | pub unsafe trait InterfaceType: Sized { |
| 499 | /// The name of the type, which can be passed to |
| 500 | /// `object_class_dynamic_cast()` to obtain the pointer to the vtable |
| 501 | /// for this interface. |
| 502 | const TYPE_NAME: &'static CStr; |
| 503 | |
| 504 | /// Return the vtable for the interface; `U` is the type that |
| 505 | /// lists the interface in its `TypeInfo`. |
| 506 | /// |
| 507 | /// # Examples |
| 508 | /// |
| 509 | /// This function is usually called by a `class_init` method in `U::Class`. |
| 510 | /// For example, `DeviceClass::class_init<T>` initializes its `Resettable` |
| 511 | /// interface as follows: |
| 512 | /// |
| 513 | /// ```ignore |
| 514 | /// ResettableClass::cast::<DeviceState>(self).class_init::<T>(); |
| 515 | /// ``` |
| 516 | /// |
| 517 | /// where `T` is the concrete subclass that is being initialized. |
| 518 | /// |
| 519 | /// # Panics |
| 520 | /// |
| 521 | /// Panic if the incoming argument if `T` does not implement the interface. |
| 522 | fn cast<U: ObjectType>(klass: &mut U::Class) -> &mut Self { |
| 523 | unsafe { |
| 524 | // SAFETY: upcasting to ObjectClass is always valid, and the |
| 525 | // return type is either NULL or the argument itself |
| 526 | let result: *mut Self = object_class_dynamic_cast( |
| 527 | (klass as *mut U::Class).cast(), |
| 528 | Self::TYPE_NAME.as_ptr(), |
| 529 | ) |
| 530 | .cast(); |
| 531 | result.as_mut().unwrap() |
| 532 | } |
| 533 | } |
| 534 | } |
| 535 | |
| 536 | /// This trait provides safe casting operations for QOM objects to raw pointers, |
| 537 | /// to be used for example for FFI. The trait can be applied to any kind of |
| 538 | /// reference or smart pointers, and enforces correctness through the [`IsA`] |
| 539 | /// trait. |
| 540 | pub trait ObjectDeref: Deref |
| 541 | where |
| 542 | Self::Target: ObjectType, |
| 543 | { |
| 544 | /// Convert to a const Rust pointer, to be used for example for FFI. |
| 545 | /// The target pointer type must be the type of `self` or a superclass |
| 546 | fn as_ptr<U: ObjectType>(&self) -> *const U |
| 547 | where |
| 548 | Self::Target: IsA<U>, |
| 549 | { |
| 550 | let ptr: *const Self::Target = self.deref(); |
| 551 | ptr.cast::<U>() |
| 552 | } |
| 553 | |
| 554 | /// Convert to a mutable Rust pointer, to be used for example for FFI. |
| 555 | /// The target pointer type must be the type of `self` or a superclass. |
| 556 | /// Used to implement interior mutability for objects. |
| 557 | /// |
| 558 | /// # Safety |
| 559 | /// |
| 560 | /// This method is safe because only the actual dereference of the pointer |
| 561 | /// has to be unsafe. Bindings to C APIs will use it a lot, but care has |
| 562 | /// to be taken because it overrides the const-ness of `&self`. |
| 563 | fn as_mut_ptr<U: ObjectType>(&self) -> *mut U |
| 564 | where |
| 565 | Self::Target: IsA<U>, |
| 566 | { |
| 567 | #[allow(clippy::as_ptr_cast_mut)] |
| 568 | { |
| 569 | self.as_ptr::<U>().cast_mut() |
| 570 | } |
| 571 | } |
| 572 | } |
| 573 | |
| 574 | /// Trait that adds extra functionality for `&T` where `T` is a QOM |
| 575 | /// object type. Allows conversion to/from C objects in generic code. |
| 576 | pub trait ObjectCast: ObjectDeref + Copy |
| 577 | where |
| 578 | Self::Target: ObjectType, |
| 579 | { |
| 580 | /// Safely convert from a derived type to one of its parent types. |
| 581 | /// |
| 582 | /// This is always safe; the [`IsA`] trait provides static verification |
| 583 | /// trait that `Self` dereferences to `U` or a child of `U`. |
| 584 | fn upcast<'a, U: ObjectType>(self) -> &'a U |
| 585 | where |
| 586 | Self::Target: IsA<U>, |
| 587 | Self: 'a, |
| 588 | { |
| 589 | // SAFETY: soundness is declared via IsA<U>, which is an unsafe trait |
| 590 | unsafe { self.unsafe_cast::<U>() } |
| 591 | } |
| 592 | |
| 593 | /// Attempt to convert to a derived type. |
| 594 | /// |
| 595 | /// Returns `None` if the object is not actually of type `U`. This is |
| 596 | /// verified at runtime by checking the object's type information. |
| 597 | fn downcast<'a, U: IsA<Self::Target>>(self) -> Option<&'a U> |
| 598 | where |
| 599 | Self: 'a, |
| 600 | { |
| 601 | self.dynamic_cast::<U>() |
| 602 | } |
| 603 | |
| 604 | /// Attempt to convert between any two types in the QOM hierarchy. |
| 605 | /// |
| 606 | /// Returns `None` if the object is not actually of type `U`. This is |
| 607 | /// verified at runtime by checking the object's type information. |
| 608 | fn dynamic_cast<'a, U: ObjectType>(self) -> Option<&'a U> |
| 609 | where |
| 610 | Self: 'a, |
| 611 | { |
| 612 | unsafe { |
| 613 | // SAFETY: upcasting to Object is always valid, and the |
| 614 | // return type is either NULL or the argument itself |
| 615 | let result: *const U = |
| 616 | object_dynamic_cast(self.as_object_mut_ptr(), U::TYPE_NAME.as_ptr()).cast(); |
| 617 | |
| 618 | result.as_ref() |
| 619 | } |
| 620 | } |
| 621 | |
| 622 | /// Convert to any QOM type without verification. |
| 623 | /// |
| 624 | /// # Safety |
| 625 | /// |
| 626 | /// What safety? You need to know yourself that the cast is correct; only |
| 627 | /// use when performance is paramount. It is still better than a raw |
| 628 | /// pointer `cast()`, which does not even check that you remain in the |
| 629 | /// realm of QOM `ObjectType`s. |
| 630 | /// |
| 631 | /// `unsafe_cast::<Object>()` is always safe. |
| 632 | unsafe fn unsafe_cast<'a, U: ObjectType>(self) -> &'a U |
| 633 | where |
| 634 | Self: 'a, |
| 635 | { |
| 636 | unsafe { &*(self.as_ptr::<Self::Target>().cast::<U>()) } |
| 637 | } |
| 638 | } |
| 639 | |
| 640 | impl<T: ObjectType> ObjectDeref for &T {} |
| 641 | impl<T: ObjectType> ObjectCast for &T {} |
| 642 | |
| 643 | impl<T: ObjectType> ObjectDeref for &mut T {} |
| 644 | |
| 645 | /// Trait a type must implement to be registered with QEMU. |
| 646 | pub trait ObjectImpl: ObjectType + IsA<Object> { |
| 647 | /// The parent of the type. This should match the first field of the |
| 648 | /// struct that implements `ObjectImpl`, minus the `ParentField<_>` wrapper. |
| 649 | type ParentType: ObjectType; |
| 650 | |
| 651 | /// Whether the object can be instantiated |
| 652 | const ABSTRACT: bool = false; |
| 653 | |
| 654 | /// Function that is called to initialize an object. The parent class will |
| 655 | /// have already been initialized so the type is only responsible for |
| 656 | /// initializing its own members. |
| 657 | /// |
| 658 | /// FIXME: The argument is not really a valid reference. `&mut |
| 659 | /// MaybeUninit<Self>` would be a better description. |
| 660 | const INSTANCE_INIT: Option<unsafe fn(ParentInit<Self>)> = None; |
| 661 | |
| 662 | /// Function that is called to finish initialization of an object, once |
| 663 | /// `INSTANCE_INIT` functions have been called. |
| 664 | const INSTANCE_POST_INIT: Option<fn(&Self)> = None; |
| 665 | |
| 666 | /// Called on descendant classes after all parent class initialization |
| 667 | /// has occurred, but before the class itself is initialized. This |
| 668 | /// is only useful if a class is not a leaf, and can be used to undo |
| 669 | /// the effects of copying the contents of the parent's class struct |
| 670 | /// to the descendants. |
| 671 | const CLASS_BASE_INIT: Option< |
| 672 | unsafe extern "C" fn(klass: *mut ObjectClass, data: *const c_void), |
| 673 | > = None; |
| 674 | |
| 675 | const TYPE_INFO: TypeInfo = TypeInfo { |
| 676 | name: Self::TYPE_NAME.as_ptr(), |
| 677 | parent: Self::ParentType::TYPE_NAME.as_ptr(), |
| 678 | instance_size: core::mem::size_of::<Self>(), |
| 679 | instance_align: core::mem::align_of::<Self>(), |
| 680 | instance_init: match Self::INSTANCE_INIT { |
| 681 | None => None, |
| 682 | Some(_) => Some(rust_instance_init::<Self>), |
| 683 | }, |
| 684 | instance_post_init: match Self::INSTANCE_POST_INIT { |
| 685 | None => None, |
| 686 | Some(_) => Some(rust_instance_post_init::<Self>), |
| 687 | }, |
| 688 | instance_finalize: Some(drop_object::<Self>), |
| 689 | abstract_: Self::ABSTRACT, |
| 690 | class_size: core::mem::size_of::<Self::Class>(), |
| 691 | class_init: Some(rust_class_init::<Self>), |
| 692 | class_base_init: Self::CLASS_BASE_INIT, |
| 693 | class_data: core::ptr::null(), |
| 694 | interfaces: core::ptr::null(), |
| 695 | }; |
| 696 | |
| 697 | // methods on ObjectClass |
| 698 | const UNPARENT: Option<fn(&Self)> = None; |
| 699 | |
| 700 | /// Store into the argument the virtual method implementations |
| 701 | /// for `Self`. On entry, the virtual method pointers are set to |
| 702 | /// the default values coming from the parent classes; the function |
| 703 | /// can change them to override virtual methods of a parent class. |
| 704 | /// |
| 705 | /// Usually defined simply as `Self::Class::class_init::<Self>`; |
| 706 | /// however a default implementation cannot be included here, because the |
| 707 | /// bounds that the `Self::Class::class_init` method places on `Self` are |
| 708 | /// not known in advance. |
| 709 | /// |
| 710 | /// # Safety |
| 711 | /// |
| 712 | /// While `klass`'s parent class is initialized on entry, the other fields |
| 713 | /// are all zero; it is therefore assumed that all fields in `T` can be |
| 714 | /// zeroed, otherwise it would not be possible to provide the class as a |
| 715 | /// `&mut T`. TODO: it may be possible to add an unsafe trait that checks |
| 716 | /// that all fields *after the parent class* (but not the parent class |
| 717 | /// itself) are Zeroable. This unsafe trait can be added via a derive |
| 718 | /// macro. |
| 719 | const CLASS_INIT: fn(&mut Self::Class); |
| 720 | } |
| 721 | |
| 722 | /// # Safety |
| 723 | /// |
| 724 | /// We expect the FFI user of this function to pass a valid pointer that |
| 725 | /// can be downcasted to type `T`. We also expect the device is |
| 726 | /// readable/writeable from one thread at any time. |
| 727 | unsafe extern "C" fn rust_unparent_fn<T: ObjectImpl>(dev: *mut bindings::Object) { |
| 728 | let state = NonNull::new(dev).unwrap().cast::<T>(); |
| 729 | T::UNPARENT.unwrap()(unsafe { state.as_ref() }); |
| 730 | } |
| 731 | |
| 732 | pub trait ObjectClassExt { |
| 733 | fn class_init<T: ObjectImpl>(&mut self); |
| 734 | } |
| 735 | |
| 736 | impl ObjectClassExt for ObjectClass { |
| 737 | /// Fill in the virtual methods of `ObjectClass` based on the definitions in |
| 738 | /// the `ObjectImpl` trait. |
| 739 | fn class_init<T: ObjectImpl>(&mut self) { |
| 740 | if <T as ObjectImpl>::UNPARENT.is_some() { |
| 741 | self.unparent = Some(rust_unparent_fn::<T>); |
| 742 | } |
| 743 | } |
| 744 | } |
| 745 | |
| 746 | unsafe impl ObjectType for Object { |
| 747 | type Class = ObjectClass; |
| 748 | const TYPE_NAME: &'static CStr = |
| 749 | unsafe { CStr::from_bytes_with_nul_unchecked(bindings::TYPE_OBJECT) }; |
| 750 | } |
| 751 | |
| 752 | /// A reference-counted pointer to a QOM object. |
| 753 | /// |
| 754 | /// `Owned<T>` wraps `T` with automatic reference counting. It increases the |
| 755 | /// reference count when created via [`Owned::from`] or cloned, and decreases |
| 756 | /// it when dropped. This ensures that the reference count remains elevated |
| 757 | /// as long as any `Owned<T>` references to it exist. |
| 758 | /// |
| 759 | /// `Owned<T>` can be used for two reasons: |
| 760 | /// * because the lifetime of the QOM object is unknown and someone else could |
| 761 | /// take a reference (similar to `Arc<T>`, for example): in this case, the |
| 762 | /// object can escape and outlive the Rust struct that contains the `Owned<T>` |
| 763 | /// field; |
| 764 | /// |
| 765 | /// * to ensure that the object stays alive until after `Drop::drop` is called |
| 766 | /// on the Rust struct: in this case, the object will always die together with |
| 767 | /// the Rust struct that contains the `Owned<T>` field. |
| 768 | /// |
| 769 | /// Child properties are an example of the second case: in C, an object that |
| 770 | /// is created with `object_initialize_child` will die *before* |
| 771 | /// `instance_finalize` is called, whereas Rust expects the struct to have valid |
| 772 | /// contents when `Drop::drop` is called. Therefore Rust structs that have |
| 773 | /// child properties need to keep a reference to the child object. Right now |
| 774 | /// this can be done with `Owned<T>`; in the future one might have a separate |
| 775 | /// `Child<'parent, T>` smart pointer that keeps a reference to a `T`, like |
| 776 | /// `Owned`, but does not allow cloning. |
| 777 | /// |
| 778 | /// Note that dropping an `Owned<T>` requires the big QEMU lock to be taken. |
| 779 | #[repr(transparent)] |
| 780 | #[derive(PartialEq, Eq, Hash, PartialOrd, Ord)] |
| 781 | pub struct Owned<T: ObjectType>(NonNull<T>); |
| 782 | |
| 783 | // The following rationale for safety is taken from Linux's kernel::sync::Arc. |
| 784 | |
| 785 | // SAFETY: It is safe to send `Owned<T>` to another thread when the underlying |
| 786 | // `T` is `Sync` because it effectively means sharing `&T` (which is safe |
| 787 | // because `T` is `Sync`); additionally, it needs `T` to be `Send` because any |
| 788 | // thread that has an `Owned<T>` may ultimately access `T` using a |
| 789 | // mutable reference when the reference count reaches zero and `T` is dropped. |
| 790 | unsafe impl<T: ObjectType + Send + Sync> Send for Owned<T> {} |
| 791 | |
| 792 | // SAFETY: It is safe to send `&Owned<T>` to another thread when the underlying |
| 793 | // `T` is `Sync` because it effectively means sharing `&T` (which is safe |
| 794 | // because `T` is `Sync`); additionally, it needs `T` to be `Send` because any |
| 795 | // thread that has a `&Owned<T>` may clone it and get an `Owned<T>` on that |
| 796 | // thread, so the thread may ultimately access `T` using a mutable reference |
| 797 | // when the reference count reaches zero and `T` is dropped. |
| 798 | unsafe impl<T: ObjectType + Sync + Send> Sync for Owned<T> {} |
| 799 | |
| 800 | impl<T: ObjectType> Owned<T> { |
| 801 | /// Convert a raw C pointer into an owned reference to the QOM |
| 802 | /// object it points to. The object's reference count will be |
| 803 | /// decreased when the `Owned` is dropped. |
| 804 | /// |
| 805 | /// # Panics |
| 806 | /// |
| 807 | /// Panics if `ptr` is NULL. |
| 808 | /// |
| 809 | /// # Safety |
| 810 | /// |
| 811 | /// The caller must indeed own a reference to the QOM object. |
| 812 | /// The object must not be embedded in another unless the outer |
| 813 | /// object is guaranteed to have a longer lifetime. |
| 814 | /// |
| 815 | /// A raw pointer obtained via [`Owned::into_raw()`] can always be passed |
| 816 | /// back to `from_raw()` (assuming the original `Owned` was valid!), |
| 817 | /// since the owned reference remains there between the calls to |
| 818 | /// `into_raw()` and `from_raw()`. |
| 819 | pub unsafe fn from_raw(ptr: *const T) -> Self { |
| 820 | // SAFETY NOTE: while NonNull requires a mutable pointer, only |
| 821 | // Deref is implemented so the pointer passed to from_raw |
| 822 | // remains const |
| 823 | Owned(NonNull::new(ptr.cast_mut()).unwrap()) |
| 824 | } |
| 825 | |
| 826 | /// Obtain a raw C pointer from a reference. `src` is consumed |
| 827 | /// and the reference is leaked. |
| 828 | #[allow(clippy::missing_const_for_fn)] |
| 829 | pub fn into_raw(src: Owned<T>) -> *mut T { |
| 830 | let src = ManuallyDrop::new(src); |
| 831 | src.0.as_ptr() |
| 832 | } |
| 833 | |
| 834 | /// Increase the reference count of a QOM object and return |
| 835 | /// a new owned reference to it. |
| 836 | /// |
| 837 | /// # Safety |
| 838 | /// |
| 839 | /// The object must not be embedded in another, unless the outer |
| 840 | /// object is guaranteed to have a longer lifetime. |
| 841 | pub unsafe fn from(obj: &T) -> Self { |
| 842 | unsafe { |
| 843 | object_ref(obj.as_object_mut_ptr().cast::<c_void>()); |
| 844 | |
| 845 | // SAFETY NOTE: while NonNull requires a mutable pointer, only |
| 846 | // Deref is implemented so the reference passed to from_raw |
| 847 | // remains shared |
| 848 | Owned(NonNull::new_unchecked(obj.as_mut_ptr())) |
| 849 | } |
| 850 | } |
| 851 | } |
| 852 | |
| 853 | impl<T: ObjectType> Clone for Owned<T> { |
| 854 | fn clone(&self) -> Self { |
| 855 | // SAFETY: creation method is unsafe; whoever calls it has |
| 856 | // responsibility that the pointer is valid, and remains valid |
| 857 | // throughout the lifetime of the `Owned<T>` and its clones. |
| 858 | unsafe { Owned::from(self.deref()) } |
| 859 | } |
| 860 | } |
| 861 | |
| 862 | impl<T: ObjectType> Deref for Owned<T> { |
| 863 | type Target = T; |
| 864 | |
| 865 | fn deref(&self) -> &Self::Target { |
| 866 | // SAFETY: creation method is unsafe; whoever calls it has |
| 867 | // responsibility that the pointer is valid, and remains valid |
| 868 | // throughout the lifetime of the `Owned<T>` and its clones. |
| 869 | // With that guarantee, reference counting ensures that |
| 870 | // the object remains alive. |
| 871 | unsafe { &*self.0.as_ptr() } |
| 872 | } |
| 873 | } |
| 874 | impl<T: ObjectType> ObjectDeref for Owned<T> {} |
| 875 | |
| 876 | impl<T: ObjectType> Drop for Owned<T> { |
| 877 | fn drop(&mut self) { |
| 878 | assert!(bql::is_locked()); |
| 879 | // SAFETY: creation method is unsafe, and whoever calls it has |
| 880 | // responsibility that the pointer is valid, and remains valid |
| 881 | // throughout the lifetime of the `Owned<T>` and its clones. |
| 882 | unsafe { |
| 883 | object_unref(self.as_object_mut_ptr().cast::<c_void>()); |
| 884 | } |
| 885 | } |
| 886 | } |
| 887 | |
| 888 | impl<T: IsA<Object>> fmt::Debug for Owned<T> { |
| 889 | fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { |
| 890 | self.deref().debug_fmt(f) |
| 891 | } |
| 892 | } |
| 893 | |
| 894 | /// Trait for class methods exposed by the Object class. The methods can be |
| 895 | /// called on all objects that have the trait `IsA<Object>`. |
| 896 | /// |
| 897 | /// The trait should only be used through the blanket implementation, |
| 898 | /// which guarantees safety via `IsA` |
| 899 | pub trait ObjectClassMethods: IsA<Object> { |
| 900 | /// Return a new reference counted instance of this class |
| 901 | fn new() -> Owned<Self> { |
| 902 | assert!(bql::is_locked()); |
| 903 | // SAFETY: the object created by object_new is allocated on |
| 904 | // the heap and has a reference count of 1 |
| 905 | unsafe { |
| 906 | let raw_obj = object_new(Self::TYPE_NAME.as_ptr()); |
| 907 | let obj = Object::from_raw(raw_obj).unsafe_cast::<Self>(); |
| 908 | Owned::from_raw(obj) |
| 909 | } |
| 910 | } |
| 911 | } |
| 912 | |
| 913 | /// Trait for methods exposed by the Object class. The methods can be |
| 914 | /// called on all objects that have the trait `IsA<Object>`. |
| 915 | /// |
| 916 | /// The trait should only be used through the blanket implementation, |
| 917 | /// which guarantees safety via `IsA` |
| 918 | pub trait ObjectMethods: ObjectDeref |
| 919 | where |
| 920 | Self::Target: IsA<Object>, |
| 921 | { |
| 922 | /// Return the name of the type of `self` |
| 923 | fn typename(&self) -> std::borrow::Cow<'_, str> { |
| 924 | let obj = self.upcast::<Object>(); |
| 925 | // SAFETY: safety of this is the requirement for implementing IsA |
| 926 | // The result of the C API has static lifetime |
| 927 | unsafe { |
| 928 | let p = object_get_typename(obj.as_mut_ptr()); |
| 929 | CStr::from_ptr(p).to_string_lossy() |
| 930 | } |
| 931 | } |
| 932 | |
| 933 | fn get_class(&self) -> &'static <Self::Target as ObjectType>::Class { |
| 934 | let obj = self.upcast::<Object>(); |
| 935 | |
| 936 | // SAFETY: all objects can call object_get_class; the actual class |
| 937 | // type is guaranteed by the implementation of `ObjectType` and |
| 938 | // `ObjectImpl`. |
| 939 | let klass: &'static <Self::Target as ObjectType>::Class = |
| 940 | unsafe { &*object_get_class(obj.as_mut_ptr()).cast() }; |
| 941 | |
| 942 | klass |
| 943 | } |
| 944 | |
| 945 | /// Convenience function for implementing the Debug trait |
| 946 | fn debug_fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { |
| 947 | f.debug_tuple(&self.typename()) |
| 948 | .field(&(self as *const Self)) |
| 949 | .finish() |
| 950 | } |
| 951 | } |
| 952 | |
| 953 | impl<T> ObjectClassMethods for T where T: IsA<Object> {} |
| 954 | impl<R: ObjectDeref> ObjectMethods for R where R::Target: IsA<Object> {} |
| 955 | |
| 956 | impl_vmstate_pointer!(Owned<T> where T: VMState + ObjectType); |