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

[Andreas Hindborg <a.hindborg@kernel.org>]

Add a trait to allow unsafely queuing stack allocated timers.

Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 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