[PATCH v12 05/13] rust: hrtimer: add `UnsafeHrTimerPointer`

From: Andreas Hindborg
Date: Sun Mar 09 2025 - 11:23:45 EST


Add a trait to allow unsafely queuing stack allocated timers.

Acked-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
Reviewed-by: Benno Lossin <benno.lossin@xxxxxxxxx>
Reviewed-by: Lyude Paul <lyude@xxxxxxxxxx>
Signed-off-by: Andreas Hindborg <a.hindborg@xxxxxxxxxx>
---
rust/kernel/time/hrtimer.rs | 31 +++++++++++++++++++++++++++++++
1 file changed, 31 insertions(+)

diff --git a/rust/kernel/time/hrtimer.rs b/rust/kernel/time/hrtimer.rs
index 78afb093aee8..0a9ca18df665 100644
--- a/rust/kernel/time/hrtimer.rs
+++ b/rust/kernel/time/hrtimer.rs
@@ -188,6 +188,37 @@ pub trait HrTimerPointer: Sync + Sized {
fn start(self, expires: Ktime) -> Self::TimerHandle;
}

+/// Unsafe version of [`HrTimerPointer`] for situations where leaking the
+/// [`HrTimerHandle`] returned by `start` would be unsound. This is the case for
+/// stack allocated timers.
+///
+/// Typical implementers are pinned references such as [`Pin<&T>`].
+///
+/// # Safety
+///
+/// Implementers of this trait must ensure that instances of types implementing
+/// [`UnsafeHrTimerPointer`] outlives any associated [`HrTimerPointer::TimerHandle`]
+/// instances.
+pub unsafe trait UnsafeHrTimerPointer: Sync + Sized {
+ /// A handle representing a running timer.
+ ///
+ /// # Safety
+ ///
+ /// If the timer is running, or if the timer callback is executing when the
+ /// handle is dropped, the drop method of [`Self::TimerHandle`] must not return
+ /// until the timer is stopped and the callback has completed.
+ type TimerHandle: HrTimerHandle;
+
+ /// Start the timer after `expires` time units. If the timer was already
+ /// running, it is restarted at the new expiry time.
+ ///
+ /// # Safety
+ ///
+ /// Caller promises keep the timer structure alive until the timer is dead.
+ /// Caller can ensure this by not leaking the returned [`Self::TimerHandle`].
+ unsafe fn start(self, expires: Ktime) -> Self::TimerHandle;
+}
+
/// Implemented by [`HrTimerPointer`] implementers to give the C timer callback a
/// function to call.
// This is split from `HrTimerPointer` to make it easier to specify trait bounds.

--
2.47.0