Re: [PATCH v2 3/4] rust: completion: add complete()

["Onur Özkan" <work@onurozkan.dev>]

On Sat, 20 Jun 2026 10:45:47 +0200
Maurice Hieronymus <mhi@mailbox.org> wrote:

> The initial completion abstraction only added complete_all() and
> wait_for_completion(). complete_all() marks the completion permanently
> done, which makes a single Completion unsuitable for signalling the same
> event repeatedly: once complete_all() has run, every subsequent
> wait_for_completion() returns immediately without waiting.
> 
> Add complete(), which wakes a single waiter and increments the internal
> counter by one. Paired one-to-one with wait_for_completion(), it allows
> the same completion to be reused across multiple cycles, e.g. to wait for
> consecutive DMA transfers to finish.
> 
> Signed-off-by: Maurice Hieronymus <mhi@mailbox.org>
> ---
>  rust/kernel/sync/completion.rs | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/rust/kernel/sync/completion.rs b/rust/kernel/sync/completion.rs
> index 35ff049ff078..a54361b53644 100644
> --- a/rust/kernel/sync/completion.rs
> +++ b/rust/kernel/sync/completion.rs
> @@ -90,6 +90,17 @@ fn as_raw(&self) -> *mut bindings::completion {
>          self.inner.get()
>      }
>  
> +    /// Signal a single task waiting on this completion.
> +    ///
> +    /// This method wakes up a single task waiting on this completion.
> +    /// If no task is currently waiting, the next
> +    /// [`Completion::wait_for_completion`] returns immediately.
> +    #[inline]
> +    pub fn complete(&self) {
> +        // SAFETY: `self.as_raw()` is a pointer to a valid `struct completion`.

I think the safety comment is a bit weak here. It would be nice to add why
self.as_raw() is guaranteed to be a valid pointer.

- Onur

> +        unsafe { bindings::complete(self.as_raw()) };
> +    }
> +
>      /// Signal all tasks waiting on this completion.
>      ///
>      /// This method wakes up all tasks waiting on this completion; after this operation the
> 
> -- 
> 2.51.2
>