1 // SPDX-License-Identifier: GPL-2.0
5 use crate::init::{self, PinInit};
11 ops::{Deref, DerefMut},
15 /// Used to transfer ownership to and from foreign (non-Rust) languages.
17 /// Ownership is transferred from Rust to a foreign language by calling [`Self::into_foreign`] and
18 /// later may be transferred back to Rust by calling [`Self::from_foreign`].
20 /// This trait is meant to be used in cases when Rust objects are stored in C objects and
21 /// eventually "freed" back to Rust.
22 pub trait ForeignOwnable: Sized {
23 /// Type of values borrowed between calls to [`ForeignOwnable::into_foreign`] and
24 /// [`ForeignOwnable::from_foreign`].
27 /// Converts a Rust-owned object to a foreign-owned one.
29 /// The foreign representation is a pointer to void.
30 fn into_foreign(self) -> *const core::ffi::c_void;
32 /// Borrows a foreign-owned object.
36 /// `ptr` must have been returned by a previous call to [`ForeignOwnable::into_foreign`] for
37 /// which a previous matching [`ForeignOwnable::from_foreign`] hasn't been called yet.
38 unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> Self::Borrowed<'a>;
40 /// Converts a foreign-owned object back to a Rust-owned one.
44 /// `ptr` must have been returned by a previous call to [`ForeignOwnable::into_foreign`] for
45 /// which a previous matching [`ForeignOwnable::from_foreign`] hasn't been called yet.
46 /// Additionally, all instances (if any) of values returned by [`ForeignOwnable::borrow`] for
47 /// this object must have been dropped.
48 unsafe fn from_foreign(ptr: *const core::ffi::c_void) -> Self;
51 impl<T: 'static> ForeignOwnable for Box<T> {
52 type Borrowed<'a> = &'a T;
54 fn into_foreign(self) -> *const core::ffi::c_void {
55 Box::into_raw(self) as _
58 unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> &'a T {
59 // SAFETY: The safety requirements for this function ensure that the object is still alive,
60 // so it is safe to dereference the raw pointer.
61 // The safety requirements of `from_foreign` also ensure that the object remains alive for
62 // the lifetime of the returned value.
63 unsafe { &*ptr.cast() }
66 unsafe fn from_foreign(ptr: *const core::ffi::c_void) -> Self {
67 // SAFETY: The safety requirements of this function ensure that `ptr` comes from a previous
68 // call to `Self::into_foreign`.
69 unsafe { Box::from_raw(ptr as _) }
73 impl ForeignOwnable for () {
74 type Borrowed<'a> = ();
76 fn into_foreign(self) -> *const core::ffi::c_void {
77 core::ptr::NonNull::dangling().as_ptr()
80 unsafe fn borrow<'a>(_: *const core::ffi::c_void) -> Self::Borrowed<'a> {}
82 unsafe fn from_foreign(_: *const core::ffi::c_void) -> Self {}
85 /// Runs a cleanup function/closure when dropped.
87 /// The [`ScopeGuard::dismiss`] function prevents the cleanup function from running.
91 /// In the example below, we have multiple exit paths and we want to log regardless of which one is
94 /// # use kernel::types::ScopeGuard;
95 /// fn example1(arg: bool) {
96 /// let _log = ScopeGuard::new(|| pr_info!("example1 completed\n"));
102 /// pr_info!("Do something...\n");
105 /// # example1(false);
106 /// # example1(true);
109 /// In the example below, we want to log the same message on all early exits but a different one on
110 /// the main exit path:
112 /// # use kernel::types::ScopeGuard;
113 /// fn example2(arg: bool) {
114 /// let log = ScopeGuard::new(|| pr_info!("example2 returned early\n"));
120 /// // (Other early returns...)
123 /// pr_info!("example2 no early return\n");
126 /// # example2(false);
127 /// # example2(true);
130 /// In the example below, we need a mutable object (the vector) to be accessible within the log
131 /// function, so we wrap it in the [`ScopeGuard`]:
133 /// # use kernel::types::ScopeGuard;
134 /// fn example3(arg: bool) -> Result {
136 /// ScopeGuard::new_with_data(Vec::new(), |v| pr_info!("vec had {} elements\n", v.len()));
138 /// vec.try_push(10u8)?;
142 /// vec.try_push(20u8)?;
146 /// # assert_eq!(example3(false), Ok(()));
147 /// # assert_eq!(example3(true), Ok(()));
152 /// The value stored in the struct is nearly always `Some(_)`, except between
153 /// [`ScopeGuard::dismiss`] and [`ScopeGuard::drop`]: in this case, it will be `None` as the value
154 /// will have been returned to the caller. Since [`ScopeGuard::dismiss`] consumes the guard,
155 /// callers won't be able to use it anymore.
156 pub struct ScopeGuard<T, F: FnOnce(T)>(Option<(T, F)>);
158 impl<T, F: FnOnce(T)> ScopeGuard<T, F> {
159 /// Creates a new guarded object wrapping the given data and with the given cleanup function.
160 pub fn new_with_data(data: T, cleanup_func: F) -> Self {
161 // INVARIANT: The struct is being initialised with `Some(_)`.
162 Self(Some((data, cleanup_func)))
165 /// Prevents the cleanup function from running and returns the guarded data.
166 pub fn dismiss(mut self) -> T {
167 // INVARIANT: This is the exception case in the invariant; it is not visible to callers
168 // because this function consumes `self`.
169 self.0.take().unwrap().0
173 impl ScopeGuard<(), fn(())> {
174 /// Creates a new guarded object with the given cleanup function.
175 pub fn new(cleanup: impl FnOnce()) -> ScopeGuard<(), impl FnOnce(())> {
176 ScopeGuard::new_with_data((), move |_| cleanup())
180 impl<T, F: FnOnce(T)> Deref for ScopeGuard<T, F> {
183 fn deref(&self) -> &T {
184 // The type invariants guarantee that `unwrap` will succeed.
185 &self.0.as_ref().unwrap().0
189 impl<T, F: FnOnce(T)> DerefMut for ScopeGuard<T, F> {
190 fn deref_mut(&mut self) -> &mut T {
191 // The type invariants guarantee that `unwrap` will succeed.
192 &mut self.0.as_mut().unwrap().0
196 impl<T, F: FnOnce(T)> Drop for ScopeGuard<T, F> {
198 // Run the cleanup function if one is still present.
199 if let Some((data, cleanup)) = self.0.take() {
205 /// Stores an opaque value.
207 /// This is meant to be used with FFI objects that are never interpreted by Rust code.
209 pub struct Opaque<T>(MaybeUninit<UnsafeCell<T>>);
212 /// Creates a new opaque value.
213 pub const fn new(value: T) -> Self {
214 Self(MaybeUninit::new(UnsafeCell::new(value)))
217 /// Creates an uninitialised value.
218 pub const fn uninit() -> Self {
219 Self(MaybeUninit::uninit())
222 /// Creates a pin-initializer from the given initializer closure.
224 /// The returned initializer calls the given closure with the pointer to the inner `T` of this
225 /// `Opaque`. Since this memory is uninitialized, the closure is not allowed to read from it.
227 /// This function is safe, because the `T` inside of an `Opaque` is allowed to be
228 /// uninitialized. Additionally, access to the inner `T` requires `unsafe`, so the caller needs
229 /// to verify at that point that the inner value is valid.
230 pub fn ffi_init(init_func: impl FnOnce(*mut T)) -> impl PinInit<Self> {
231 // SAFETY: We contain a `MaybeUninit`, so it is OK for the `init_func` to not fully
232 // initialize the `T`.
234 init::pin_init_from_closure::<_, ::core::convert::Infallible>(move |slot| {
235 init_func(Self::raw_get(slot));
241 /// Returns a raw pointer to the opaque data.
242 pub fn get(&self) -> *mut T {
243 UnsafeCell::raw_get(self.0.as_ptr())
246 /// Gets the value behind `this`.
248 /// This function is useful to get access to the value without creating intermediate
250 pub const fn raw_get(this: *const Self) -> *mut T {
251 UnsafeCell::raw_get(this.cast::<UnsafeCell<T>>())
255 /// Types that are _always_ reference counted.
257 /// It allows such types to define their own custom ref increment and decrement functions.
258 /// Additionally, it allows users to convert from a shared reference `&T` to an owned reference
261 /// This is usually implemented by wrappers to existing structures on the C side of the code. For
262 /// Rust code, the recommendation is to use [`Arc`](crate::sync::Arc) to create reference-counted
263 /// instances of a type.
267 /// Implementers must ensure that increments to the reference count keep the object alive in memory
268 /// at least until matching decrements are performed.
270 /// Implementers must also ensure that all instances are reference-counted. (Otherwise they
271 /// won't be able to honour the requirement that [`AlwaysRefCounted::inc_ref`] keep the object
273 pub unsafe trait AlwaysRefCounted {
274 /// Increments the reference count on the object.
277 /// Decrements the reference count on the object.
279 /// Frees the object when the count reaches zero.
283 /// Callers must ensure that there was a previous matching increment to the reference count,
284 /// and that the object is no longer used after its reference count is decremented (as it may
285 /// result in the object being freed), unless the caller owns another increment on the refcount
286 /// (e.g., it calls [`AlwaysRefCounted::inc_ref`] twice, then calls
287 /// [`AlwaysRefCounted::dec_ref`] once).
288 unsafe fn dec_ref(obj: NonNull<Self>);
291 /// An owned reference to an always-reference-counted object.
293 /// The object's reference count is automatically decremented when an instance of [`ARef`] is
294 /// dropped. It is also automatically incremented when a new instance is created via
299 /// The pointer stored in `ptr` is non-null and valid for the lifetime of the [`ARef`] instance. In
300 /// particular, the [`ARef`] instance owns an increment on the underlying object's reference count.
301 pub struct ARef<T: AlwaysRefCounted> {
306 // SAFETY: It is safe to send `ARef<T>` to another thread when the underlying `T` is `Sync` because
307 // it effectively means sharing `&T` (which is safe because `T` is `Sync`); additionally, it needs
308 // `T` to be `Send` because any thread that has an `ARef<T>` may ultimately access `T` using a
309 // mutable reference, for example, when the reference count reaches zero and `T` is dropped.
310 unsafe impl<T: AlwaysRefCounted + Sync + Send> Send for ARef<T> {}
312 // SAFETY: It is safe to send `&ARef<T>` to another thread when the underlying `T` is `Sync`
313 // because it effectively means sharing `&T` (which is safe because `T` is `Sync`); additionally,
314 // it needs `T` to be `Send` because any thread that has a `&ARef<T>` may clone it and get an
315 // `ARef<T>` on that thread, so the thread may ultimately access `T` using a mutable reference, for
316 // example, when the reference count reaches zero and `T` is dropped.
317 unsafe impl<T: AlwaysRefCounted + Sync + Send> Sync for ARef<T> {}
319 impl<T: AlwaysRefCounted> ARef<T> {
320 /// Creates a new instance of [`ARef`].
322 /// It takes over an increment of the reference count on the underlying object.
326 /// Callers must ensure that the reference count was incremented at least once, and that they
327 /// are properly relinquishing one increment. That is, if there is only one increment, callers
328 /// must not use the underlying object anymore -- it is only safe to do so via the newly
329 /// created [`ARef`].
330 pub unsafe fn from_raw(ptr: NonNull<T>) -> Self {
331 // INVARIANT: The safety requirements guarantee that the new instance now owns the
332 // increment on the refcount.
340 impl<T: AlwaysRefCounted> Clone for ARef<T> {
341 fn clone(&self) -> Self {
343 // SAFETY: We just incremented the refcount above.
344 unsafe { Self::from_raw(self.ptr) }
348 impl<T: AlwaysRefCounted> Deref for ARef<T> {
351 fn deref(&self) -> &Self::Target {
352 // SAFETY: The type invariants guarantee that the object is valid.
353 unsafe { self.ptr.as_ref() }
357 impl<T: AlwaysRefCounted> From<&T> for ARef<T> {
358 fn from(b: &T) -> Self {
360 // SAFETY: We just incremented the refcount above.
361 unsafe { Self::from_raw(NonNull::from(b)) }
365 impl<T: AlwaysRefCounted> Drop for ARef<T> {
367 // SAFETY: The type invariants guarantee that the `ARef` owns the reference we're about to
369 unsafe { T::dec_ref(self.ptr) };
373 /// A sum type that always holds either a value of type `L` or `R`.
374 pub enum Either<L, R> {
375 /// Constructs an instance of [`Either`] containing a value of type `L`.
378 /// Constructs an instance of [`Either`] containing a value of type `R`.