// SPDX-License-Identifier: GPL-2.0 //! Generic kernel lock and guard.//!//! It contains a generic Rust lock and guard that allow for different backends (e.g., mutexes,//! spinlocks, raw spinlocks) to be provided with minimal effort. use super::LockClassKey;use crate::{bindings, init::PinInit, pin_init, str::CStr, types::Opaque, types::ScopeGuard};use core::{cell::UnsafeCell, marker::PhantomData, marker::PhantomPinned};use macros::pin_data; pub mod mutex;pub mod spinlock; /// The "backend" of a lock.////// It is the actual implementation of the lock, without the need to repeat patterns used in all/// locks.////// # Safety////// - Implementers must ensure that only one thread/CPU may access the protected data once the lock/// is owned, that is, between calls to `lock` and `unlock`./// - Implementers must also ensure that `relock` uses the same locking method as the original/// lock operation.pub unsafe trait Backend {    /// The state required by the lock.    type State;     /// The state required to be kept between lock and unlock.    type GuardState;     /// Initialises the lock.    ///    /// # Safety    ///    /// `ptr` must be valid for write for the duration of the call, while `name` and `key` must    /// remain valid for read indefinitely.    unsafe fn init(        ptr: *mut Self::State,        name: *const core::ffi::c_char,        key: *mut bindings::lock_class_key,    );     /// Acquires the lock, making the caller its owner.    ///    /// # Safety    ///    /// Callers must ensure that [`Backend::init`] has been previously called.    #[must_use]    unsafe fn lock(ptr: *mut Self::State) -> Self::GuardState;     /// Releases the lock, giving up its ownership.    ///    /// # Safety    ///    /// It must only be called by the current owner of the lock.    unsafe fn unlock(ptr: *mut Self::State, guard_state: &Self::GuardState);     /// Reacquires the lock, making the caller its owner.    ///    /// # Safety    ///    /// Callers must ensure that `guard_state` comes from a previous call to [`Backend::lock`] (or    /// variant) that has been unlocked with [`Backend::unlock`] and will be relocked now.    unsafe fn relock(ptr: *mut Self::State, guard_state: &mut Self::GuardState) {        // SAFETY: The safety requirements ensure that the lock is initialised.        *guard_state = unsafe { Self::lock(ptr) };    }} /// A mutual exclusion primitive.////// Exposes one of the kernel locking primitives. Which one is exposed depends on the lock/// [`Backend`] specified as the generic parameter `B`.#[pin_data]pub struct Lock<T: ?Sized, B: Backend> {    /// The kernel lock object.    #[pin]    state: Opaque<B::State>,     /// Some locks are known to be self-referential (e.g., mutexes), while others are architecture    /// or config defined (e.g., spinlocks). So we conservatively require them to be pinned in case    /// some architecture uses self-references now or in the future.    #[pin]    _pin: PhantomPinned,     /// The data protected by the lock.    pub(crate) data: UnsafeCell<T>,} // SAFETY: `Lock` can be transferred across thread boundaries iff the data it protects can.unsafe impl<T: ?Sized + Send, B: Backend> Send for Lock<T, B> {} // SAFETY: `Lock` serialises the interior mutability it provides, so it is `Sync` as long as the// data it protects is `Send`.unsafe impl<T: ?Sized + Send, B: Backend> Sync for Lock<T, B> {} impl<T, B: Backend> Lock<T, B> {    /// Constructs a new lock initialiser.    pub fn new(t: T, name: &'static CStr, key: &'static LockClassKey) -> impl PinInit<Self> {        pin_init!(Self {            data: UnsafeCell::new(t),            _pin: PhantomPinned,            // SAFETY: `slot` is valid while the closure is called and both `name` and `key` have            // static lifetimes so they live indefinitely.            state <- Opaque::ffi_init(|slot| unsafe {                B::init(slot, name.as_char_ptr(), key.as_ptr())            }),        })    }} impl<T: ?Sized, B: Backend> Lock<T, B> {    /// Acquires the lock and gives the caller access to the data protected by it.    pub fn lock(&self) -> Guard<'_, T, B> {        // SAFETY: The constructor of the type calls `init`, so the existence of the object proves        // that `init` was called.        let state = unsafe { B::lock(self.state.get()) };        // SAFETY: The lock was just acquired.        unsafe { Guard::new(self, state) }    }} /// A lock guard.////// Allows mutual exclusion primitives that implement the [`Backend`] trait to automatically unlock/// when a guard goes out of scope. It also provides a safe and convenient way to access the data/// protected by the lock.#[must_use = "the lock unlocks immediately when the guard is unused"]pub struct Guard<'a, T: ?Sized, B: Backend> {    pub(crate) lock: &'a Lock<T, B>,    pub(crate) state: B::GuardState,    _not_send: PhantomData<*mut ()>,} // SAFETY: `Guard` is sync when the data protected by the lock is also sync.unsafe impl<T: Sync + ?Sized, B: Backend> Sync for Guard<'_, T, B> {} impl<T: ?Sized, B: Backend> Guard<'_, T, B> {    pub(crate) fn do_unlocked(&mut self, cb: impl FnOnce()) {        // SAFETY: The caller owns the lock, so it is safe to unlock it.        unsafe { B::unlock(self.lock.state.get(), &self.state) };         // SAFETY: The lock was just unlocked above and is being relocked now.        let _relock =            ScopeGuard::new(|| unsafe { B::relock(self.lock.state.get(), &mut self.state) });         cb();    }} impl<T: ?Sized, B: Backend> core::ops::Deref for Guard<'_, T, B> {    type Target = T;     fn deref(&self) -> &Self::Target {        // SAFETY: The caller owns the lock, so it is safe to deref the protected data.        unsafe { &*self.lock.data.get() }    }} impl<T: ?Sized, B: Backend> core::ops::DerefMut for Guard<'_, T, B> {    fn deref_mut(&mut self) -> &mut Self::Target {        // SAFETY: The caller owns the lock, so it is safe to deref the protected data.        unsafe { &mut *self.lock.data.get() }    }} impl<T: ?Sized, B: Backend> Drop for Guard<'_, T, B> {    fn drop(&mut self) {        // SAFETY: The caller owns the lock, so it is safe to unlock it.        unsafe { B::unlock(self.lock.state.get(), &self.state) };    }} impl<'a, T: ?Sized, B: Backend> Guard<'a, T, B> {    /// Constructs a new immutable lock guard.    ///    /// # Safety    ///    /// The caller must ensure that it owns the lock.    pub(crate) unsafe fn new(lock: &'a Lock<T, B>, state: B::GuardState) -> Self {        Self {            lock,            state,            _not_send: PhantomData,        }    }}