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

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Message-ID: <87wmdf22ae.fsf@kernel.org>
Date: Mon, 24 Feb 2025 09:08:09 +0100
From: Andreas Hindborg <a.hindborg@...nel.org>
To: Boqun Feng <boqun.feng@...il.com>
Cc: linux-kernel@...r.kernel.org,  rust-for-linux@...r.kernel.org,  Peter
 Zijlstra <peterz@...radead.org>,  Ingo Molnar <mingo@...hat.com>,  Will
 Deacon <will@...nel.org>,  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>,  Alice Ryhl <aliceryhl@...gle.com>,
  Trevor Gross <tmgross@...ch.edu>
Subject: Re: [PATCH] rust: sync: lock: Add an example for Guard::lock_ref()

Boqun Feng <boqun.feng@...il.com> writes:

> 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));
> +    /// }

This seems super useful. Perhaps add this method as part of the lock api
instead of just having it in the example?


Best regards,
Andreas Hindborg