rust: hrtimer: add `hrtimer::ScopedHrTimerPointer`

    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 ScopedHrTimerPointer {

    /// 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 [`UnsafeHrTimerPointer`], dropping the

// handle returned by [`UnsafeHrTimerPointer::start`] ensures that the timer is

// killed.

unsafe impl<T> ScopedHrTimerPointer for T

where

    T: UnsafeHrTimerPointer,

{

    fn start_scoped<U, F>(self, expires: Ktime, f: F) -> U

    where

        F: FnOnce() -> U,

    {

        // SAFETY: We drop the timer handle below before returning.

        let handle = unsafe { UnsafeHrTimerPointer::start(self, expires) };

        let t = f();

        drop(handle);

        t

    }

}

/// 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.