linux-kernel - [PATCH] rust: sync: lock: Add an example for Guard::lock

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Message-Id: <20250223072114.3715-1-boqun.feng@gmail.com>
Date: Sat, 22 Feb 2025 23:21:14 -0800
From: Boqun Feng <boqun.feng@...il.com>
To: linux-kernel@...r.kernel.org,
	rust-for-linux@...r.kernel.org
Cc: Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Will Deacon <will@...nel.org>,
	Boqun Feng <boqun.feng@...il.com>,
	Waiman Long <longman@...hat.com>,
	Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>,
	Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <benno.lossin@...ton.me>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>,
	Trevor Gross <tmgross@...ch.edu>
Subject: [PATCH] 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.

Signed-off-by: Boqun Feng <boqun.feng@...il.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)