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

Benno Lossin
2025-02-24T10:06:46Z

On 24.02.25 09:08, Andreas Hindborg wrote:
> Boqun Feng <boqun.feng@gmail.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@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));
>> + /// }
>
> This seems super useful. Perhaps add this method as part of the lock api
> instead of just having it in the example?

I don't think it should be an assert. Instead make it return a
`Result<(), ()>`. (or create better named unit error types)

---
Cheers,
Benno