pin_mut.rs

  1// SPDX-License-Identifier: GPL-2.0
  2
  3use super::{
  4    HasHrTimer, HrTimer, HrTimerCallback, HrTimerCallbackContext, HrTimerHandle, HrTimerMode,
  5    RawHrTimerCallback, UnsafeHrTimerPointer,
  6};
  7use core::{marker::PhantomData, pin::Pin, ptr::NonNull};
  8
  9/// A handle for a `Pin<&mut HasHrTimer>`. When the handle exists, the timer might
 10/// be running.
 11pub struct PinMutHrTimerHandle<'a, T>
 12where
 13    T: HasHrTimer<T>,
 14{
 15    pub(crate) inner: NonNull<T>,
 16    _p: PhantomData<&'a mut T>,
 17}
 18
 19// SAFETY: We cancel the timer when the handle is dropped. The implementation of
 20// the `cancel` method will block if the timer handler is running.
 21unsafe impl<'a, T> HrTimerHandle for PinMutHrTimerHandle<'a, T>
 22where
 23    T: HasHrTimer<T>,
 24{
 25    fn cancel(&mut self) -> bool {
 26        let self_ptr = self.inner.as_ptr();
 27
 28        // SAFETY: As we got `self_ptr` from a reference above, it must point to
 29        // a valid `T`.
 30        let timer_ptr = unsafe { <T as HasHrTimer<T>>::raw_get_timer(self_ptr) };
 31
 32        // SAFETY: As `timer_ptr` is derived from a reference, it must point to
 33        // a valid and initialized `HrTimer`.
 34        unsafe { HrTimer::<T>::raw_cancel(timer_ptr) }
 35    }
 36}
 37
 38impl<'a, T> Drop for PinMutHrTimerHandle<'a, T>
 39where
 40    T: HasHrTimer<T>,
 41{
 42    fn drop(&mut self) {
 43        self.cancel();
 44    }
 45}
 46
 47// SAFETY: We capture the lifetime of `Self` when we create a
 48// `PinMutHrTimerHandle`, so `Self` will outlive the handle.
 49unsafe impl<'a, T> UnsafeHrTimerPointer for Pin<&'a mut T>
 50where
 51    T: Send + Sync,
 52    T: HasHrTimer<T>,
 53    T: HrTimerCallback<Pointer<'a> = Self>,
 54{
 55    type TimerMode = <T as HasHrTimer<T>>::TimerMode;
 56    type TimerHandle = PinMutHrTimerHandle<'a, T>;
 57
 58    unsafe fn start(
 59        mut self,
 60        expires: <<T as HasHrTimer<T>>::TimerMode as HrTimerMode>::Expires,
 61    ) -> Self::TimerHandle {
 62        // SAFETY:
 63        // - We promise not to move out of `self`. We only pass `self`
 64        //   back to the caller as a `Pin<&mut self>`.
 65        // - The return value of `get_unchecked_mut` is guaranteed not to be null.
 66        let self_ptr = unsafe { NonNull::new_unchecked(self.as_mut().get_unchecked_mut()) };
 67
 68        // SAFETY:
 69        //  - As we derive `self_ptr` from a reference above, it must point to a
 70        //    valid `T`.
 71        //  - We keep `self` alive by wrapping it in a handle below.
 72        unsafe { T::start(self_ptr.as_ptr(), expires) };
 73
 74        PinMutHrTimerHandle {
 75            inner: self_ptr,
 76            _p: PhantomData,
 77        }
 78    }
 79}
 80
 81impl<'a, T> RawHrTimerCallback for Pin<&'a mut T>
 82where
 83    T: HasHrTimer<T>,
 84    T: HrTimerCallback<Pointer<'a> = Self>,
 85{
 86    type CallbackTarget<'b> = Self;
 87
 88    unsafe extern "C" fn run(ptr: *mut bindings::hrtimer) -> bindings::hrtimer_restart {
 89        // `HrTimer` is `repr(C)`
 90        let timer_ptr = ptr.cast::<HrTimer<T>>();
 91
 92        // SAFETY: By the safety requirement of this function, `timer_ptr`
 93        // points to a `HrTimer<T>` contained in an `T`.
 94        let receiver_ptr = unsafe { T::timer_container_of(timer_ptr) };
 95
 96        // SAFETY:
 97        //  - By the safety requirement of this function, `timer_ptr`
 98        //    points to a `HrTimer<T>` contained in an `T`.
 99        //  - As per the safety requirements of the trait `HrTimerHandle`, the
100        //    `PinMutHrTimerHandle` associated with this timer is guaranteed to
101        //    be alive until this method returns. That handle borrows the `T`
102        //    behind `receiver_ptr` mutably thus guaranteeing the validity of
103        //    the reference created below.
104        let receiver_ref = unsafe { &mut *receiver_ptr };
105
106        // SAFETY: `receiver_ref` only exists as pinned, so it is safe to pin it
107        // here.
108        let receiver_pin = unsafe { Pin::new_unchecked(receiver_ref) };
109
110        // SAFETY:
111        // - By C API contract `timer_ptr` is the pointer that we passed when queuing the timer, so
112        //   it is a valid pointer to a `HrTimer<T>` embedded in a `T`.
113        // - We are within `RawHrTimerCallback::run`
114        let context = unsafe { HrTimerCallbackContext::from_raw(timer_ptr) };
115
116        T::run(receiver_pin, context).into_c()
117    }
118}