// SPDX-License-Identifier: GPL-2.0 //! Kernel types. use core::{ cell::UnsafeCell, marker::{PhantomData, PhantomPinned}, mem::{ManuallyDrop, MaybeUninit}, ops::{Deref, DerefMut}, ptr::NonNull,};use pin_init::{PinInit, Zeroable}; /// Used to transfer ownership to and from foreign (non-Rust) languages.////// Ownership is transferred from Rust to a foreign language by calling [`Self::into_foreign`] and/// later may be transferred back to Rust by calling [`Self::from_foreign`].////// This trait is meant to be used in cases when Rust objects are stored in C objects and/// eventually "freed" back to Rust.pub trait ForeignOwnable: Sized { /// Type used to immutably borrow a value that is currently foreign-owned. type Borrowed<'a>; /// Type used to mutably borrow a value that is currently foreign-owned. type BorrowedMut<'a>; /// Converts a Rust-owned object to a foreign-owned one. /// /// The foreign representation is a pointer to void. There are no guarantees for this pointer. /// For example, it might be invalid, dangling or pointing to uninitialized memory. Using it in /// any way except for [`from_foreign`], [`try_from_foreign`], [`borrow`], or [`borrow_mut`] can /// result in undefined behavior. /// /// [`from_foreign`]: Self::from_foreign /// [`try_from_foreign`]: Self::try_from_foreign /// [`borrow`]: Self::borrow /// [`borrow_mut`]: Self::borrow_mut fn into_foreign(self) -> *mut crate::ffi::c_void; /// Converts a foreign-owned object back to a Rust-owned one. /// /// # Safety /// /// The provided pointer must have been returned by a previous call to [`into_foreign`], and it /// must not be passed to `from_foreign` more than once. /// /// [`into_foreign`]: Self::into_foreign unsafe fn from_foreign(ptr: *mut crate::ffi::c_void) -> Self; /// Tries to convert a foreign-owned object back to a Rust-owned one. /// /// A convenience wrapper over [`ForeignOwnable::from_foreign`] that returns [`None`] if `ptr` /// is null. /// /// # Safety /// /// `ptr` must either be null or satisfy the safety requirements for [`from_foreign`]. /// /// [`from_foreign`]: Self::from_foreign unsafe fn try_from_foreign(ptr: *mut crate::ffi::c_void) -> Option<Self> { if ptr.is_null() { None } else { // SAFETY: Since `ptr` is not null here, then `ptr` satisfies the safety requirements // of `from_foreign` given the safety requirements of this function. unsafe { Some(Self::from_foreign(ptr)) } } } /// Borrows a foreign-owned object immutably. /// /// This method provides a way to access a foreign-owned value from Rust immutably. It provides /// you with exactly the same abilities as an `&Self` when the value is Rust-owned. /// /// # Safety /// /// The provided pointer must have been returned by a previous call to [`into_foreign`], and if /// the pointer is ever passed to [`from_foreign`], then that call must happen after the end of /// the lifetime `'a`. /// /// [`into_foreign`]: Self::into_foreign /// [`from_foreign`]: Self::from_foreign unsafe fn borrow<'a>(ptr: *mut crate::ffi::c_void) -> Self::Borrowed<'a>; /// Borrows a foreign-owned object mutably. /// /// This method provides a way to access a foreign-owned value from Rust mutably. It provides /// you with exactly the same abilities as an `&mut Self` when the value is Rust-owned, except /// that the address of the object must not be changed. /// /// Note that for types like [`Arc`], an `&mut Arc<T>` only gives you immutable access to the /// inner value, so this method also only provides immutable access in that case. /// /// In the case of `Box<T>`, this method gives you the ability to modify the inner `T`, but it /// does not let you change the box itself. That is, you cannot change which allocation the box /// points at. /// /// # Safety /// /// The provided pointer must have been returned by a previous call to [`into_foreign`], and if /// the pointer is ever passed to [`from_foreign`], then that call must happen after the end of /// the lifetime `'a`. /// /// The lifetime `'a` must not overlap with the lifetime of any other call to [`borrow`] or /// `borrow_mut` on the same object. /// /// [`into_foreign`]: Self::into_foreign /// [`from_foreign`]: Self::from_foreign /// [`borrow`]: Self::borrow /// [`Arc`]: crate::sync::Arc unsafe fn borrow_mut<'a>(ptr: *mut crate::ffi::c_void) -> Self::BorrowedMut<'a>;} impl ForeignOwnable for () { type Borrowed<'a> = (); type BorrowedMut<'a> = (); fn into_foreign(self) -> *mut crate::ffi::c_void { core::ptr::NonNull::dangling().as_ptr() } unsafe fn from_foreign(_: *mut crate::ffi::c_void) -> Self {} unsafe fn borrow<'a>(_: *mut crate::ffi::c_void) -> Self::Borrowed<'a> {} unsafe fn borrow_mut<'a>(_: *mut crate::ffi::c_void) -> Self::BorrowedMut<'a> {}} /// Runs a cleanup function/closure when dropped.////// The [`ScopeGuard::dismiss`] function prevents the cleanup function from running.////// # Examples////// In the example below, we have multiple exit paths and we want to log regardless of which one is/// taken:////// ```/// # use kernel::types::ScopeGuard;/// fn example1(arg: bool) {/// let _log = ScopeGuard::new(|| pr_info!("example1 completed\n"));////// if arg {/// return;/// }////// pr_info!("Do something...\n");/// }////// # example1(false);/// # example1(true);/// ```////// In the example below, we want to log the same message on all early exits but a different one on/// the main exit path:////// ```/// # use kernel::types::ScopeGuard;/// fn example2(arg: bool) {/// let log = ScopeGuard::new(|| pr_info!("example2 returned early\n"));////// if arg {/// return;/// }////// // (Other early returns...)////// log.dismiss();/// pr_info!("example2 no early return\n");/// }////// # example2(false);/// # example2(true);/// ```////// In the example below, we need a mutable object (the vector) to be accessible within the log/// function, so we wrap it in the [`ScopeGuard`]:////// ```/// # use kernel::types::ScopeGuard;/// fn example3(arg: bool) -> Result {/// let mut vec =/// ScopeGuard::new_with_data(KVec::new(), |v| pr_info!("vec had {} elements\n", v.len()));////// vec.push(10u8, GFP_KERNEL)?;/// if arg {/// return Ok(());/// }/// vec.push(20u8, GFP_KERNEL)?;/// Ok(())/// }////// # assert_eq!(example3(false), Ok(()));/// # assert_eq!(example3(true), Ok(()));/// ```////// # Invariants////// The value stored in the struct is nearly always `Some(_)`, except between/// [`ScopeGuard::dismiss`] and [`ScopeGuard::drop`]: in this case, it will be `None` as the value/// will have been returned to the caller. Since [`ScopeGuard::dismiss`] consumes the guard,/// callers won't be able to use it anymore.pub struct ScopeGuard<T, F: FnOnce(T)>(Option<(T, F)>); impl<T, F: FnOnce(T)> ScopeGuard<T, F> { /// Creates a new guarded object wrapping the given data and with the given cleanup function. pub fn new_with_data(data: T, cleanup_func: F) -> Self { // INVARIANT: The struct is being initialised with `Some(_)`. Self(Some((data, cleanup_func))) } /// Prevents the cleanup function from running and returns the guarded data. pub fn dismiss(mut self) -> T { // INVARIANT: This is the exception case in the invariant; it is not visible to callers // because this function consumes `self`. self.0.take().unwrap().0 }} impl ScopeGuard<(), fn(())> { /// Creates a new guarded object with the given cleanup function. pub fn new(cleanup: impl FnOnce()) -> ScopeGuard<(), impl FnOnce(())> { ScopeGuard::new_with_data((), move |()| cleanup()) }} impl<T, F: FnOnce(T)> Deref for ScopeGuard<T, F> { type Target = T; fn deref(&self) -> &T { // The type invariants guarantee that `unwrap` will succeed. &self.0.as_ref().unwrap().0 }} impl<T, F: FnOnce(T)> DerefMut for ScopeGuard<T, F> { fn deref_mut(&mut self) -> &mut T { // The type invariants guarantee that `unwrap` will succeed. &mut self.0.as_mut().unwrap().0 }} impl<T, F: FnOnce(T)> Drop for ScopeGuard<T, F> { fn drop(&mut self) { // Run the cleanup function if one is still present. if let Some((data, cleanup)) = self.0.take() { cleanup(data) } }} /// Stores an opaque value.////// [`Opaque<T>`] is meant to be used with FFI objects that are never interpreted by Rust code.////// It is used to wrap structs from the C side, like for example `Opaque<bindings::mutex>`./// It gets rid of all the usual assumptions that Rust has for a value:////// * The value is allowed to be uninitialized (for example have invalid bit patterns: `3` for a/// [`bool`])./// * The value is allowed to be mutated, when a `&Opaque<T>` exists on the Rust side./// * No uniqueness for mutable references: it is fine to have multiple `&mut Opaque<T>` point to/// the same value./// * The value is not allowed to be shared with other threads (i.e. it is `!Sync`).////// This has to be used for all values that the C side has access to, because it can't be ensured/// that the C side is adhering to the usual constraints that Rust needs.////// Using [`Opaque<T>`] allows to continue to use references on the Rust side even for values shared/// with C.////// # Examples////// ```/// # #![expect(unreachable_pub, clippy::disallowed_names)]/// use kernel::types::Opaque;/// # // Emulate a C struct binding which is from C, maybe uninitialized or not, only the C side/// # // knows./// # mod bindings {/// # pub struct Foo {/// # pub val: u8,/// # }/// # }////// // `foo.val` is assumed to be handled on the C side, so we use `Opaque` to wrap it./// pub struct Foo {/// foo: Opaque<bindings::Foo>,/// }////// impl Foo {/// pub fn get_val(&self) -> u8 {/// let ptr = Opaque::get(&self.foo);////// // SAFETY: `Self` is valid from C side./// unsafe { (*ptr).val }/// }/// }////// // Create an instance of `Foo` with the `Opaque` wrapper./// let foo = Foo {/// foo: Opaque::new(bindings::Foo { val: 0xdb }),/// };////// assert_eq!(foo.get_val(), 0xdb);/// ```#[repr(transparent)]pub struct Opaque<T> { value: UnsafeCell<MaybeUninit<T>>, _pin: PhantomPinned,} // SAFETY: `Opaque<T>` allows the inner value to be any bit pattern, including all zeros.unsafe impl<T> Zeroable for Opaque<T> {} impl<T> Opaque<T> { /// Creates a new opaque value. pub const fn new(value: T) -> Self { Self { value: UnsafeCell::new(MaybeUninit::new(value)), _pin: PhantomPinned, } } /// Creates an uninitialised value. pub const fn uninit() -> Self { Self { value: UnsafeCell::new(MaybeUninit::uninit()), _pin: PhantomPinned, } } /// Create an opaque pin-initializer from the given pin-initializer. pub fn pin_init(slot: impl PinInit<T>) -> impl PinInit<Self> { Self::ffi_init(|ptr: *mut T| { // SAFETY: // - `ptr` is a valid pointer to uninitialized memory, // - `slot` is not accessed on error; the call is infallible, // - `slot` is pinned in memory. let _ = unsafe { PinInit::<T>::__pinned_init(slot, ptr) }; }) } /// Creates a pin-initializer from the given initializer closure. /// /// The returned initializer calls the given closure with the pointer to the inner `T` of this /// `Opaque`. Since this memory is uninitialized, the closure is not allowed to read from it. /// /// This function is safe, because the `T` inside of an `Opaque` is allowed to be /// uninitialized. Additionally, access to the inner `T` requires `unsafe`, so the caller needs /// to verify at that point that the inner value is valid. pub fn ffi_init(init_func: impl FnOnce(*mut T)) -> impl PinInit<Self> { // SAFETY: We contain a `MaybeUninit`, so it is OK for the `init_func` to not fully // initialize the `T`. unsafe { pin_init::pin_init_from_closure::<_, ::core::convert::Infallible>(move |slot| { init_func(Self::raw_get(slot)); Ok(()) }) } } /// Creates a fallible pin-initializer from the given initializer closure. /// /// The returned initializer calls the given closure with the pointer to the inner `T` of this /// `Opaque`. Since this memory is uninitialized, the closure is not allowed to read from it. /// /// This function is safe, because the `T` inside of an `Opaque` is allowed to be /// uninitialized. Additionally, access to the inner `T` requires `unsafe`, so the caller needs /// to verify at that point that the inner value is valid. pub fn try_ffi_init<E>( init_func: impl FnOnce(*mut T) -> Result<(), E>, ) -> impl PinInit<Self, E> { // SAFETY: We contain a `MaybeUninit`, so it is OK for the `init_func` to not fully // initialize the `T`. unsafe { pin_init::pin_init_from_closure::<_, E>(move |slot| init_func(Self::raw_get(slot))) } } /// Returns a raw pointer to the opaque data. pub const fn get(&self) -> *mut T { UnsafeCell::get(&self.value).cast::<T>() } /// Gets the value behind `this`. /// /// This function is useful to get access to the value without creating intermediate /// references. pub const fn raw_get(this: *const Self) -> *mut T { UnsafeCell::raw_get(this.cast::<UnsafeCell<MaybeUninit<T>>>()).cast::<T>() }} /// Types that are _always_ reference counted.////// It allows such types to define their own custom ref increment and decrement functions./// Additionally, it allows users to convert from a shared reference `&T` to an owned reference/// [`ARef<T>`].////// This is usually implemented by wrappers to existing structures on the C side of the code. For/// Rust code, the recommendation is to use [`Arc`](crate::sync::Arc) to create reference-counted/// instances of a type.////// # Safety////// Implementers must ensure that increments to the reference count keep the object alive in memory/// at least until matching decrements are performed.////// Implementers must also ensure that all instances are reference-counted. (Otherwise they/// won't be able to honour the requirement that [`AlwaysRefCounted::inc_ref`] keep the object/// alive.)pub unsafe trait AlwaysRefCounted { /// Increments the reference count on the object. fn inc_ref(&self); /// Decrements the reference count on the object. /// /// Frees the object when the count reaches zero. /// /// # Safety /// /// Callers must ensure that there was a previous matching increment to the reference count, /// and that the object is no longer used after its reference count is decremented (as it may /// result in the object being freed), unless the caller owns another increment on the refcount /// (e.g., it calls [`AlwaysRefCounted::inc_ref`] twice, then calls /// [`AlwaysRefCounted::dec_ref`] once). unsafe fn dec_ref(obj: NonNull<Self>);} /// An owned reference to an always-reference-counted object.////// The object's reference count is automatically decremented when an instance of [`ARef`] is/// dropped. It is also automatically incremented when a new instance is created via/// [`ARef::clone`].////// # Invariants////// The pointer stored in `ptr` is non-null and valid for the lifetime of the [`ARef`] instance. In/// particular, the [`ARef`] instance owns an increment on the underlying object's reference count.pub struct ARef<T: AlwaysRefCounted> { ptr: NonNull<T>, _p: PhantomData<T>,} // SAFETY: It is safe to send `ARef<T>` to another thread when the underlying `T` is `Sync` because// it effectively means sharing `&T` (which is safe because `T` is `Sync`); additionally, it needs// `T` to be `Send` because any thread that has an `ARef<T>` may ultimately access `T` using a// mutable reference, for example, when the reference count reaches zero and `T` is dropped.unsafe impl<T: AlwaysRefCounted + Sync + Send> Send for ARef<T> {} // SAFETY: It is safe to send `&ARef<T>` to another thread when the underlying `T` is `Sync`// because it effectively means sharing `&T` (which is safe because `T` is `Sync`); additionally,// it needs `T` to be `Send` because any thread that has a `&ARef<T>` may clone it and get an// `ARef<T>` on that thread, so the thread may ultimately access `T` using a mutable reference, for// example, when the reference count reaches zero and `T` is dropped.unsafe impl<T: AlwaysRefCounted + Sync + Send> Sync for ARef<T> {} impl<T: AlwaysRefCounted> ARef<T> { /// Creates a new instance of [`ARef`]. /// /// It takes over an increment of the reference count on the underlying object. /// /// # Safety /// /// Callers must ensure that the reference count was incremented at least once, and that they /// are properly relinquishing one increment. That is, if there is only one increment, callers /// must not use the underlying object anymore -- it is only safe to do so via the newly /// created [`ARef`]. pub unsafe fn from_raw(ptr: NonNull<T>) -> Self { // INVARIANT: The safety requirements guarantee that the new instance now owns the // increment on the refcount. Self { ptr, _p: PhantomData, } } /// Consumes the `ARef`, returning a raw pointer. /// /// This function does not change the refcount. After calling this function, the caller is /// responsible for the refcount previously managed by the `ARef`. /// /// # Examples /// /// ``` /// use core::ptr::NonNull; /// use kernel::types::{ARef, AlwaysRefCounted}; /// /// struct Empty {} /// /// # // SAFETY: TODO. /// unsafe impl AlwaysRefCounted for Empty { /// fn inc_ref(&self) {} /// unsafe fn dec_ref(_obj: NonNull<Self>) {} /// } /// /// let mut data = Empty {}; /// let ptr = NonNull::<Empty>::new(&mut data).unwrap(); /// # // SAFETY: TODO. /// let data_ref: ARef<Empty> = unsafe { ARef::from_raw(ptr) };Lines 1–500 of 580. Load more
// SPDX-License-Identifier: GPL-2.0 //! Kernel types. use core::{ cell::UnsafeCell, marker::{PhantomData, PhantomPinned}, mem::{ManuallyDrop, MaybeUninit}, ops::{Deref, DerefMut}, ptr::NonNull, }; use pin_init::{PinInit, Zeroable}; /// Used to transfer ownership to and from foreign (non-Rust) languages. /// /// Ownership is transferred from Rust to a foreign language by calling [`Self::into_foreign`] and /// later may be transferred back to Rust by calling [`Self::from_foreign`]. /// /// This trait is meant to be used in cases when Rust objects are stored in C objects and /// eventually "freed" back to Rust. pub trait ForeignOwnable: Sized { /// Type used to immutably borrow a value that is currently foreign-owned. type Borrowed<'a>; /// Type used to mutably borrow a value that is currently foreign-owned. type BorrowedMut<'a>; /// Converts a Rust-owned object to a foreign-owned one. /// /// The foreign representation is a pointer to void. There are no guarantees for this pointer. /// For example, it might be invalid, dangling or pointing to uninitialized memory. Using it in /// any way except for [`from_foreign`], [`try_from_foreign`], [`borrow`], or [`borrow_mut`] can /// result in undefined behavior. /// /// [`from_foreign`]: Self::from_foreign /// [`try_from_foreign`]: Self::try_from_foreign /// [`borrow`]: Self::borrow /// [`borrow_mut`]: Self::borrow_mut fn into_foreign(self) -> *mut crate::ffi::c_void; /// Converts a foreign-owned object back to a Rust-owned one. /// /// # Safety /// /// The provided pointer must have been returned by a previous call to [`into_foreign`], and it /// must not be passed to `from_foreign` more than once. /// /// [`into_foreign`]: Self::into_foreign unsafe fn from_foreign(ptr: *mut crate::ffi::c_void) -> Self; /// Tries to convert a foreign-owned object back to a Rust-owned one. /// /// A convenience wrapper over [`ForeignOwnable::from_foreign`] that returns [`None`] if `ptr` /// is null. /// /// # Safety /// /// `ptr` must either be null or satisfy the safety requirements for [`from_foreign`]. /// /// [`from_foreign`]: Self::from_foreign unsafe fn try_from_foreign(ptr: *mut crate::ffi::c_void) -> Option<Self> { if ptr.is_null() { None } else { // SAFETY: Since `ptr` is not null here, then `ptr` satisfies the safety requirements // of `from_foreign` given the safety requirements of this function. unsafe { Some(Self::from_foreign(ptr)) } } } /// Borrows a foreign-owned object immutably. /// /// This method provides a way to access a foreign-owned value from Rust immutably. It provides /// you with exactly the same abilities as an `&Self` when the value is Rust-owned. /// /// # Safety /// /// The provided pointer must have been returned by a previous call to [`into_foreign`], and if /// the pointer is ever passed to [`from_foreign`], then that call must happen after the end of /// the lifetime `'a`. /// /// [`into_foreign`]: Self::into_foreign /// [`from_foreign`]: Self::from_foreign unsafe fn borrow<'a>(ptr: *mut crate::ffi::c_void) -> Self::Borrowed<'a>; /// Borrows a foreign-owned object mutably. /// /// This method provides a way to access a foreign-owned value from Rust mutably. It provides /// you with exactly the same abilities as an `&mut Self` when the value is Rust-owned, except /// that the address of the object must not be changed. /// /// Note that for types like [`Arc`], an `&mut Arc<T>` only gives you immutable access to the /// inner value, so this method also only provides immutable access in that case. /// /// In the case of `Box<T>`, this method gives you the ability to modify the inner `T`, but it /// does not let you change the box itself. That is, you cannot change which allocation the box /// points at. /// /// # Safety /// /// The provided pointer must have been returned by a previous call to [`into_foreign`], and if /// the pointer is ever passed to [`from_foreign`], then that call must happen after the end of /// the lifetime `'a`. /// /// The lifetime `'a` must not overlap with the lifetime of any other call to [`borrow`] or /// `borrow_mut` on the same object. /// /// [`into_foreign`]: Self::into_foreign /// [`from_foreign`]: Self::from_foreign /// [`borrow`]: Self::borrow /// [`Arc`]: crate::sync::Arc unsafe fn borrow_mut<'a>(ptr: *mut crate::ffi::c_void) -> Self::BorrowedMut<'a>; } impl ForeignOwnable for () { type Borrowed<'a> = (); type BorrowedMut<'a> = (); fn into_foreign(self) -> *mut crate::ffi::c_void { core::ptr::NonNull::dangling().as_ptr() } unsafe fn from_foreign(_: *mut crate::ffi::c_void) -> Self {} unsafe fn borrow<'a>(_: *mut crate::ffi::c_void) -> Self::Borrowed<'a> {} unsafe fn borrow_mut<'a>(_: *mut crate::ffi::c_void) -> Self::BorrowedMut<'a> {} } /// Runs a cleanup function/closure when dropped. /// /// The [`ScopeGuard::dismiss`] function prevents the cleanup function from running. /// /// # Examples /// /// In the example below, we have multiple exit paths and we want to log regardless of which one is /// taken: /// /// ``` /// # use kernel::types::ScopeGuard; /// fn example1(arg: bool) { /// let _log = ScopeGuard::new(|| pr_info!("example1 completed\n")); /// /// if arg { /// return; /// } /// /// pr_info!("Do something...\n"); /// } /// /// # example1(false); /// # example1(true); /// ``` /// /// In the example below, we want to log the same message on all early exits but a different one on /// the main exit path: /// /// ``` /// # use kernel::types::ScopeGuard; /// fn example2(arg: bool) { /// let log = ScopeGuard::new(|| pr_info!("example2 returned early\n")); /// /// if arg { /// return; /// } /// /// // (Other early returns...) /// /// log.dismiss(); /// pr_info!("example2 no early return\n"); /// } /// /// # example2(false); /// # example2(true); /// ``` /// /// In the example below, we need a mutable object (the vector) to be accessible within the log /// function, so we wrap it in the [`ScopeGuard`]: /// /// ``` /// # use kernel::types::ScopeGuard; /// fn example3(arg: bool) -> Result { /// let mut vec = /// ScopeGuard::new_with_data(KVec::new(), |v| pr_info!("vec had {} elements\n", v.len())); /// /// vec.push(10u8, GFP_KERNEL)?; /// if arg { /// return Ok(()); /// } /// vec.push(20u8, GFP_KERNEL)?; /// Ok(()) /// } /// /// # assert_eq!(example3(false), Ok(())); /// # assert_eq!(example3(true), Ok(())); /// ``` /// /// # Invariants /// /// The value stored in the struct is nearly always `Some(_)`, except between /// [`ScopeGuard::dismiss`] and [`ScopeGuard::drop`]: in this case, it will be `None` as the value /// will have been returned to the caller. Since [`ScopeGuard::dismiss`] consumes the guard, /// callers won't be able to use it anymore. pub struct ScopeGuard<T, F: FnOnce(T)>(Option<(T, F)>); impl<T, F: FnOnce(T)> ScopeGuard<T, F> { /// Creates a new guarded object wrapping the given data and with the given cleanup function. pub fn new_with_data(data: T, cleanup_func: F) -> Self { // INVARIANT: The struct is being initialised with `Some(_)`. Self(Some((data, cleanup_func))) } /// Prevents the cleanup function from running and returns the guarded data. pub fn dismiss(mut self) -> T { // INVARIANT: This is the exception case in the invariant; it is not visible to callers // because this function consumes `self`. self.0.take().unwrap().0 } } impl ScopeGuard<(), fn(())> { /// Creates a new guarded object with the given cleanup function. pub fn new(cleanup: impl FnOnce()) -> ScopeGuard<(), impl FnOnce(())> { ScopeGuard::new_with_data((), move |()| cleanup()) } } impl<T, F: FnOnce(T)> Deref for ScopeGuard<T, F> { type Target = T; fn deref(&self) -> &T { // The type invariants guarantee that `unwrap` will succeed. &self.0.as_ref().unwrap().0 } } impl<T, F: FnOnce(T)> DerefMut for ScopeGuard<T, F> { fn deref_mut(&mut self) -> &mut T { // The type invariants guarantee that `unwrap` will succeed. &mut self.0.as_mut().unwrap().0 } } impl<T, F: FnOnce(T)> Drop for ScopeGuard<T, F> { fn drop(&mut self) { // Run the cleanup function if one is still present. if let Some((data, cleanup)) = self.0.take() { cleanup(data) } } } /// Stores an opaque value. /// /// [`Opaque<T>`] is meant to be used with FFI objects that are never interpreted by Rust code. /// /// It is used to wrap structs from the C side, like for example `Opaque<bindings::mutex>`. /// It gets rid of all the usual assumptions that Rust has for a value: /// /// * The value is allowed to be uninitialized (for example have invalid bit patterns: `3` for a /// [`bool`]). /// * The value is allowed to be mutated, when a `&Opaque<T>` exists on the Rust side. /// * No uniqueness for mutable references: it is fine to have multiple `&mut Opaque<T>` point to /// the same value. /// * The value is not allowed to be shared with other threads (i.e. it is `!Sync`). /// /// This has to be used for all values that the C side has access to, because it can't be ensured /// that the C side is adhering to the usual constraints that Rust needs. /// /// Using [`Opaque<T>`] allows to continue to use references on the Rust side even for values shared /// with C. /// /// # Examples /// /// ``` /// # #![expect(unreachable_pub, clippy::disallowed_names)] /// use kernel::types::Opaque; /// # // Emulate a C struct binding which is from C, maybe uninitialized or not, only the C side /// # // knows. /// # mod bindings { /// # pub struct Foo { /// # pub val: u8, /// # } /// # } /// /// // `foo.val` is assumed to be handled on the C side, so we use `Opaque` to wrap it. /// pub struct Foo { /// foo: Opaque<bindings::Foo>, /// } /// /// impl Foo { /// pub fn get_val(&self) -> u8 { /// let ptr = Opaque::get(&self.foo); /// /// // SAFETY: `Self` is valid from C side. /// unsafe { (*ptr).val } /// } /// } /// /// // Create an instance of `Foo` with the `Opaque` wrapper. /// let foo = Foo { /// foo: Opaque::new(bindings::Foo { val: 0xdb }), /// }; /// /// assert_eq!(foo.get_val(), 0xdb); /// ``` #[repr(transparent)] pub struct Opaque<T> { value: UnsafeCell<MaybeUninit<T>>, _pin: PhantomPinned, } // SAFETY: `Opaque<T>` allows the inner value to be any bit pattern, including all zeros. unsafe impl<T> Zeroable for Opaque<T> {} impl<T> Opaque<T> { /// Creates a new opaque value. pub const fn new(value: T) -> Self { Self { value: UnsafeCell::new(MaybeUninit::new(value)), _pin: PhantomPinned, } } /// Creates an uninitialised value. pub const fn uninit() -> Self { Self { value: UnsafeCell::new(MaybeUninit::uninit()), _pin: PhantomPinned, } } /// Create an opaque pin-initializer from the given pin-initializer. pub fn pin_init(slot: impl PinInit<T>) -> impl PinInit<Self> { Self::ffi_init(|ptr: *mut T| { // SAFETY: // - `ptr` is a valid pointer to uninitialized memory, // - `slot` is not accessed on error; the call is infallible, // - `slot` is pinned in memory. let _ = unsafe { PinInit::<T>::__pinned_init(slot, ptr) }; }) } /// Creates a pin-initializer from the given initializer closure. /// /// The returned initializer calls the given closure with the pointer to the inner `T` of this /// `Opaque`. Since this memory is uninitialized, the closure is not allowed to read from it. /// /// This function is safe, because the `T` inside of an `Opaque` is allowed to be /// uninitialized. Additionally, access to the inner `T` requires `unsafe`, so the caller needs /// to verify at that point that the inner value is valid. pub fn ffi_init(init_func: impl FnOnce(*mut T)) -> impl PinInit<Self> { // SAFETY: We contain a `MaybeUninit`, so it is OK for the `init_func` to not fully // initialize the `T`. unsafe { pin_init::pin_init_from_closure::<_, ::core::convert::Infallible>(move |slot| { init_func(Self::raw_get(slot)); Ok(()) }) } } /// Creates a fallible pin-initializer from the given initializer closure. /// /// The returned initializer calls the given closure with the pointer to the inner `T` of this /// `Opaque`. Since this memory is uninitialized, the closure is not allowed to read from it. /// /// This function is safe, because the `T` inside of an `Opaque` is allowed to be /// uninitialized. Additionally, access to the inner `T` requires `unsafe`, so the caller needs /// to verify at that point that the inner value is valid. pub fn try_ffi_init<E>( init_func: impl FnOnce(*mut T) -> Result<(), E>, ) -> impl PinInit<Self, E> { // SAFETY: We contain a `MaybeUninit`, so it is OK for the `init_func` to not fully // initialize the `T`. unsafe { pin_init::pin_init_from_closure::<_, E>(move |slot| init_func(Self::raw_get(slot))) } } /// Returns a raw pointer to the opaque data. pub const fn get(&self) -> *mut T { UnsafeCell::get(&self.value).cast::<T>() } /// Gets the value behind `this`. /// /// This function is useful to get access to the value without creating intermediate /// references. pub const fn raw_get(this: *const Self) -> *mut T { UnsafeCell::raw_get(this.cast::<UnsafeCell<MaybeUninit<T>>>()).cast::<T>() } } /// Types that are _always_ reference counted. /// /// It allows such types to define their own custom ref increment and decrement functions. /// Additionally, it allows users to convert from a shared reference `&T` to an owned reference /// [`ARef<T>`]. /// /// This is usually implemented by wrappers to existing structures on the C side of the code. For /// Rust code, the recommendation is to use [`Arc`](crate::sync::Arc) to create reference-counted /// instances of a type. /// /// # Safety /// /// Implementers must ensure that increments to the reference count keep the object alive in memory /// at least until matching decrements are performed. /// /// Implementers must also ensure that all instances are reference-counted. (Otherwise they /// won't be able to honour the requirement that [`AlwaysRefCounted::inc_ref`] keep the object /// alive.) pub unsafe trait AlwaysRefCounted { /// Increments the reference count on the object. fn inc_ref(&self); /// Decrements the reference count on the object. /// /// Frees the object when the count reaches zero. /// /// # Safety /// /// Callers must ensure that there was a previous matching increment to the reference count, /// and that the object is no longer used after its reference count is decremented (as it may /// result in the object being freed), unless the caller owns another increment on the refcount /// (e.g., it calls [`AlwaysRefCounted::inc_ref`] twice, then calls /// [`AlwaysRefCounted::dec_ref`] once). unsafe fn dec_ref(obj: NonNull<Self>); } /// An owned reference to an always-reference-counted object. /// /// The object's reference count is automatically decremented when an instance of [`ARef`] is /// dropped. It is also automatically incremented when a new instance is created via /// [`ARef::clone`]. /// /// # Invariants /// /// The pointer stored in `ptr` is non-null and valid for the lifetime of the [`ARef`] instance. In /// particular, the [`ARef`] instance owns an increment on the underlying object's reference count. pub struct ARef<T: AlwaysRefCounted> { ptr: NonNull<T>, _p: PhantomData<T>, } // SAFETY: It is safe to send `ARef<T>` to another thread when the underlying `T` is `Sync` because // it effectively means sharing `&T` (which is safe because `T` is `Sync`); additionally, it needs // `T` to be `Send` because any thread that has an `ARef<T>` may ultimately access `T` using a // mutable reference, for example, when the reference count reaches zero and `T` is dropped. unsafe impl<T: AlwaysRefCounted + Sync + Send> Send for ARef<T> {} // SAFETY: It is safe to send `&ARef<T>` to another thread when the underlying `T` is `Sync` // because it effectively means sharing `&T` (which is safe because `T` is `Sync`); additionally, // it needs `T` to be `Send` because any thread that has a `&ARef<T>` may clone it and get an // `ARef<T>` on that thread, so the thread may ultimately access `T` using a mutable reference, for // example, when the reference count reaches zero and `T` is dropped. unsafe impl<T: AlwaysRefCounted + Sync + Send> Sync for ARef<T> {} impl<T: AlwaysRefCounted> ARef<T> { /// Creates a new instance of [`ARef`]. /// /// It takes over an increment of the reference count on the underlying object. /// /// # Safety /// /// Callers must ensure that the reference count was incremented at least once, and that they /// are properly relinquishing one increment. That is, if there is only one increment, callers /// must not use the underlying object anymore -- it is only safe to do so via the newly /// created [`ARef`]. pub unsafe fn from_raw(ptr: NonNull<T>) -> Self { // INVARIANT: The safety requirements guarantee that the new instance now owns the // increment on the refcount. Self { ptr, _p: PhantomData, } } /// Consumes the `ARef`, returning a raw pointer. /// /// This function does not change the refcount. After calling this function, the caller is /// responsible for the refcount previously managed by the `ARef`. /// /// # Examples /// /// ``` /// use core::ptr::NonNull; /// use kernel::types::{ARef, AlwaysRefCounted}; /// /// struct Empty {} /// /// # // SAFETY: TODO. /// unsafe impl AlwaysRefCounted for Empty { /// fn inc_ref(&self) {} /// unsafe fn dec_ref(_obj: NonNull<Self>) {} /// } /// /// let mut data = Empty {}; /// let ptr = NonNull::<Empty>::new(&mut data).unwrap(); /// # // SAFETY: TODO. /// let data_ref: ARef<Empty> = unsafe { ARef::from_raw(ptr) };