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

Boqun Feng
2025-02-23T07:21:25Z

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.

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
This depends on Alice's patch:

https://lore.kernel.org/all/20250130-guard-get-lock-v1-1-8ed87899920a@google.com/

I'm also OK to fold this in if Alice thinks it's fine.

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 3701fac6ebf6..6d868e35b0a3 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 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
}
--
2.39.5 (Apple Git-154)