[PATCH v3 06/13] rust: hrtimer: add `UnsafeTimerPointer`

From: Andreas Hindborg
Date: Thu Oct 17 2024 - 09:12:03 EST


Add a trait to allow unsafely queuing stack allocated timers.

Signed-off-by: Andreas Hindborg <a.hindborg@xxxxxxxxxx>
---
rust/kernel/hrtimer.rs | 33 +++++++++++++++++++++++++++++++++
1 file changed, 33 insertions(+)

diff --git a/rust/kernel/hrtimer.rs b/rust/kernel/hrtimer.rs
index eeed2afd501b64b94d57cc658616659e28785078..e97d7b8ec63ce6c9ac3fe9522192a28fba78b8ba 100644
--- a/rust/kernel/hrtimer.rs
+++ b/rust/kernel/hrtimer.rs
@@ -151,6 +151,39 @@ pub trait TimerPointer: Sync + Sized {
fn start(self, expires: Ktime) -> Self::TimerHandle;
}

+/// Unsafe version of [`TimerPointer`] for situations where leaking the
+/// `TimerHandle` 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
+/// [`UnsafeTimerPointer`] outlives any associated [`TimerPointer::TimerHandle`]
+/// instances.
+///
+/// [`Pin<&T>`]: Box
+pub unsafe trait UnsafeTimerPointer: 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 `TimerHandle` must not return
+ /// until the timer is stopped and the callback has completed.
+ type TimerHandle: TimerHandle;
+
+ /// 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 [`TimerPointer`] implementers to give the C timer callback a
/// function to call.
// This is split from `TimerPointer` to make it easier to specify trait bounds.

--
2.46.0