[PATCH v4 09/14] rust: hrtimer: add `hrtimer::ScopedTimerPointer`

From: Andreas Hindborg
Date: Fri Dec 06 2024 - 14:38:59 EST


Add the trait `ScopedTimerPointer` to allow safe use of stack allocated
timers. Safety is achieved by pinning the stack in place while timers are
running.

Implement the trait for all types that implement `UnsafeTimerPointer`.

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

diff --git a/rust/kernel/time/hrtimer.rs b/rust/kernel/time/hrtimer.rs
index efcb5e44a0dc3660a09f230c01cca998b763e8d9..7835a33677ec32999c495d5b874ded2ff0786c9e 100644
--- a/rust/kernel/time/hrtimer.rs
+++ b/rust/kernel/time/hrtimer.rs
@@ -175,6 +175,39 @@ pub unsafe trait UnsafeTimerPointer: Sync + Sized {
unsafe fn start(self, expires: Ktime) -> Self::TimerHandle;
}

+/// A trait for stack allocated timers.
+///
+/// # Safety
+///
+/// Implementers must ensure that `start_scoped` does not return until the
+/// timer is dead and the timer handler is not running.
+pub unsafe trait ScopedTimerPointer {
+ /// Start the timer to run after `expires` time units and immediately
+ /// after call `f`. When `f` returns, the timer is cancelled.
+ fn start_scoped<T, F>(self, expires: Ktime, f: F) -> T
+ where
+ F: FnOnce() -> T;
+}
+
+// SAFETY: By the safety requirement of `UnsafeTimerPointer`, dropping the
+// handle returned by [`UnsafeTimerPointer::start`] ensures that the timer is
+// killed.
+unsafe impl<U> ScopedTimerPointer for U
+where
+ U: UnsafeTimerPointer,
+{
+ fn start_scoped<T, F>(self, expires: Ktime, f: F) -> T
+ where
+ F: FnOnce() -> T,
+ {
+ // SAFETY: We drop the timer handle below before returning.
+ let handle = unsafe { UnsafeTimerPointer::start(self, expires) };
+ let t = f();
+ drop(handle);
+ t
+ }
+}
+
/// 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