// SPDX-License-Identifier: GPL-2.0 //! A kernel mutex.//!//! This module allows Rust code to use the kernel's `struct mutex`. /// Creates a [`Mutex`] initialiser with the given name and a newly-created lock class.////// It uses the name if one is given, otherwise it generates one based on the file name and line/// number.#[macro_export]macro_rules! new_mutex {    ($inner:expr $(, $name:literal)? $(,)?) => {        $crate::sync::Mutex::new(            $inner, $crate::optional_name!($($name)?), $crate::static_lock_class!())    };}pub use new_mutex; /// A mutual exclusion primitive.////// Exposes the kernel's [`struct mutex`]. When multiple threads attempt to lock the same mutex,/// only one at a time is allowed to progress, the others will block (sleep) until the mutex is/// unlocked, at which point another thread will be allowed to wake up and make progress.////// Since it may block, [`Mutex`] needs to be used with care in atomic contexts.////// Instances of [`Mutex`] need a lock class and to be pinned. The recommended way to create such/// instances is with the [`pin_init`](crate::pin_init) and [`new_mutex`] macros.////// # Examples////// The following example shows how to declare, allocate and initialise a struct (`Example`) that/// contains an inner struct (`Inner`) that is protected by a mutex.////// ```/// use kernel::sync::{new_mutex, Mutex};////// struct Inner {///     a: u32,///     b: u32,/// }////// #[pin_data]/// struct Example {///     c: u32,///     #[pin]///     d: Mutex<Inner>,/// }////// impl Example {///     fn new() -> impl PinInit<Self> {///         pin_init!(Self {///             c: 10,///             d <- new_mutex!(Inner { a: 20, b: 30 }),///         })///     }/// }////// // Allocate a boxed `Example`./// let e = Box::pin_init(Example::new(), GFP_KERNEL)?;/// assert_eq!(e.c, 10);/// assert_eq!(e.d.lock().a, 20);/// assert_eq!(e.d.lock().b, 30);/// # Ok::<(), Error>(())/// ```////// The following example shows how to use interior mutability to modify the contents of a struct/// protected by a mutex despite only having a shared reference:////// ```/// use kernel::sync::Mutex;////// struct Example {///     a: u32,///     b: u32,/// }////// fn example(m: &Mutex<Example>) {///     let mut guard = m.lock();///     guard.a += 10;///     guard.b += 20;/// }/// ```////// [`struct mutex`]: srctree/include/linux/mutex.hpub type Mutex<T> = super::Lock<T, MutexBackend>; /// A kernel `struct mutex` lock backend.pub struct MutexBackend; // SAFETY: The underlying kernel `struct mutex` object ensures mutual exclusion.unsafe impl super::Backend for MutexBackend {    type State = bindings::mutex;    type GuardState = ();     unsafe fn init(        ptr: *mut Self::State,        name: *const core::ffi::c_char,        key: *mut bindings::lock_class_key,    ) {        // SAFETY: The safety requirements ensure that `ptr` is valid for writes, and `name` and        // `key` are valid for read indefinitely.        unsafe { bindings::__mutex_init(ptr, name, key) }    }     unsafe fn lock(ptr: *mut Self::State) -> Self::GuardState {        // SAFETY: The safety requirements of this function ensure that `ptr` points to valid        // memory, and that it has been initialised before.        unsafe { bindings::mutex_lock(ptr) };    }     unsafe fn unlock(ptr: *mut Self::State, _guard_state: &Self::GuardState) {        // SAFETY: The safety requirements of this function ensure that `ptr` is valid and that the        // caller is the owner of the mutex.        unsafe { bindings::mutex_unlock(ptr) };    }}