Re: [PATCH 1/3] rust: revocable: implement Revocable::access()

Christian Schrefl
2025-04-26T16:44:06Z

On 26.04.25 3:30 PM, Danilo Krummrich wrote:
> Implement an unsafe direct accessor for the data stored within the
> Revocable.
>
> This is useful for cases where we can proof that the data stored within
> the Revocable is not and cannot be revoked for the duration of the
> lifetime of the returned reference.
>
> Signed-off-by: Danilo Krummrich <dakr@kernel.org>
> ---
> The explicit lifetimes in access() probably don't serve a practical
> purpose, but I found them to be useful for documentation purposes.
> ---> rust/kernel/revocable.rs | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
> diff --git a/rust/kernel/revocable.rs b/rust/kernel/revocable.rs
> index 971d0dc38d83..33535de141ce 100644
> --- a/rust/kernel/revocable.rs
> +++ b/rust/kernel/revocable.rs
> @@ -139,6 +139,18 @@ pub fn try_access_with<R, F: FnOnce(&T) -> R>(&self, f: F) -> Option<R> {
> self.try_access().map(|t| f(&*t))
> }
>
> + /// Directly access the revocable wrapped object.
> + ///
> + /// # Safety
> + ///
> + /// The caller must ensure this [`Revocable`] instance hasn't been revoked and won't be revoked
> + /// for the duration of `'a`.
> + pub unsafe fn access<'a, 's: 'a>(&'s self) -> &'a T {
I'm not sure if the `'s` lifetime really carries much meaning here.
I find just (explicit) `'a` on both parameter and return value is clearer to me,
but I'm not sure what others (particularly those not very familiar with rust)
think of this.

Either way:

Reviewed-by: Christian Schrefl <chrisi.schrefl@gmail.com>

> + // SAFETY: By the safety requirement of this function it is guaranteed that
> + // `self.data.get()` is a valid pointer to an instance of `T`.
> + unsafe { &*self.data.get() }
> + }
> +
> /// # Safety
> ///
> /// Callers must ensure that there are no more concurrent users of the revocable object.