[tip: locking/core] rust: sync: lock: Add an example for Guard::lock_ref()

tip-bot2 for Boqun Feng
2025-03-03T18:52:03Z

The following commit has been merged into the locking/core branch of tip:

Commit-ID: 33530ab4613d7544ff43df2d690c54d8ff9288c6
Gitweb: https://git.kernel.org/tip/33530ab4613d7544ff43df2d690c54d8ff9288c6
Author: Boqun Feng <boqun.feng@gmail.com>
AuthorDate: Sat, 22 Feb 2025 23:09:24 -08:00
Committer: Boqun Feng <boqun.feng@gmail.com>
CommitterDate: Tue, 25 Feb 2025 08:52:48 -08:00

rust: sync: lock: Add an example for Guard::lock_ref()

To provide examples on usage of `Guard::lock_ref()` along with the unit
test, an "assert a lock is held by a guard" example is added.

[boqun: Apply feedback from Benno]

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Reviewed-by: Benno Lossin <benno.lossin@proton.me>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20250223072114.3715-1-boqun.feng@gmail.com
---
rust/kernel/sync/lock.rs | 24 ++++++++++++++++++++++++
1 file changed, 24 insertions(+)

diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
index 8e7e6d5..f53e87d 100644
--- a/rust/kernel/sync/lock.rs
+++ b/rust/kernel/sync/lock.rs
@@ -201,6 +201,30 @@ unsafe impl<T: Sync + ?Sized, B: Backend> Sync for Guard<'_, T, B> {}

impl<'a, T: ?Sized, B: Backend> Guard<'a, T, B> {
/// Returns the lock that this guard originates from.
+ ///
+ /// # Examples
+ ///
+ /// The following example shows how to use [`Guard::lock_ref()`] to assert the corresponding
+ /// lock is held.
+ ///
+ /// ```
+ /// # use kernel::{new_spinlock, stack_pin_init, sync::lock::{Backend, Guard, Lock}};
+ ///
+ /// fn assert_held<T, B: Backend>(guard: &Guard<'_, T, B>, lock: &Lock<T, B>) {
+ /// // Address-equal means the same lock.
+ /// assert!(core::ptr::eq(guard.lock_ref(), lock));
+ /// }
+ ///
+ /// // Creates a new lock on the stack.
+ /// stack_pin_init!{
+ /// let l = new_spinlock!(42)
+ /// }
+ ///
+ /// let g = l.lock();
+ ///
+ /// // `g` originates from `l`.
+ /// assert_held(&g, &l);
+ /// ```
pub fn lock_ref(&self) -> &'a Lock<T, B> {
self.lock
}