tbox.rs

  1// SPDX-License-Identifier: GPL-2.0
  2
  3use super::HasHrTimer;
  4use super::HrTimer;
  5use super::HrTimerCallback;
  6use super::HrTimerCallbackContext;
  7use super::HrTimerHandle;
  8use super::HrTimerMode;
  9use super::HrTimerPointer;
 10use super::RawHrTimerCallback;
 11use crate::prelude::*;
 12use core::ptr::NonNull;
 13
 14/// A handle for a [`Box<HasHrTimer<T>>`] returned by a call to
 15/// [`HrTimerPointer::start`].
 16///
 17/// # Invariants
 18///
 19/// - `self.inner` comes from a `Box::into_raw` call.
 20pub struct BoxHrTimerHandle<T, A>
 21where
 22    T: HasHrTimer<T>,
 23    A: crate::alloc::Allocator,
 24{
 25    pub(crate) inner: NonNull<T>,
 26    _p: core::marker::PhantomData<A>,
 27}
 28
 29// SAFETY: We implement drop below, and we cancel the timer in the drop
 30// implementation.
 31unsafe impl<T, A> HrTimerHandle for BoxHrTimerHandle<T, A>
 32where
 33    T: HasHrTimer<T>,
 34    A: crate::alloc::Allocator,
 35{
 36    fn cancel(&mut self) -> bool {
 37        // SAFETY: As we obtained `self.inner` from a valid reference when we
 38        // created `self`, it must point to a valid `T`.
 39        let timer_ptr = unsafe { <T as HasHrTimer<T>>::raw_get_timer(self.inner.as_ptr()) };
 40
 41        // SAFETY: As `timer_ptr` points into `T` and `T` is valid, `timer_ptr`
 42        // must point to a valid `HrTimer` instance.
 43        unsafe { HrTimer::<T>::raw_cancel(timer_ptr) }
 44    }
 45}
 46
 47impl<T, A> Drop for BoxHrTimerHandle<T, A>
 48where
 49    T: HasHrTimer<T>,
 50    A: crate::alloc::Allocator,
 51{
 52    fn drop(&mut self) {
 53        self.cancel();
 54        // SAFETY: By type invariant, `self.inner` came from a `Box::into_raw`
 55        // call.
 56        drop(unsafe { Box::<T, A>::from_raw(self.inner.as_ptr()) })
 57    }
 58}
 59
 60impl<T, A> HrTimerPointer for Pin<Box<T, A>>
 61where
 62    T: 'static,
 63    T: Send + Sync,
 64    T: HasHrTimer<T>,
 65    T: for<'a> HrTimerCallback<Pointer<'a> = Pin<Box<T, A>>>,
 66    A: crate::alloc::Allocator,
 67{
 68    type TimerMode = <T as HasHrTimer<T>>::TimerMode;
 69    type TimerHandle = BoxHrTimerHandle<T, A>;
 70
 71    fn start(
 72        self,
 73        expires: <<T as HasHrTimer<T>>::TimerMode as HrTimerMode>::Expires,
 74    ) -> Self::TimerHandle {
 75        // SAFETY:
 76        //  - We will not move out of this box during timer callback (we pass an
 77        //    immutable reference to the callback).
 78        //  - `Box::into_raw` is guaranteed to return a valid pointer.
 79        let inner =
 80            unsafe { NonNull::new_unchecked(Box::into_raw(Pin::into_inner_unchecked(self))) };
 81
 82        // SAFETY:
 83        //  - We keep `self` alive by wrapping it in a handle below.
 84        //  - Since we generate the pointer passed to `start` from a valid
 85        //    reference, it is a valid pointer.
 86        unsafe { T::start(inner.as_ptr(), expires) };
 87
 88        // INVARIANT: `inner` came from `Box::into_raw` above.
 89        BoxHrTimerHandle {
 90            inner,
 91            _p: core::marker::PhantomData,
 92        }
 93    }
 94}
 95
 96impl<T, A> RawHrTimerCallback for Pin<Box<T, A>>
 97where
 98    T: 'static,
 99    T: HasHrTimer<T>,
100    T: for<'a> HrTimerCallback<Pointer<'a> = Pin<Box<T, A>>>,
101    A: crate::alloc::Allocator,
102{
103    type CallbackTarget<'a> = Pin<&'a mut T>;
104
105    unsafe extern "C" fn run(ptr: *mut bindings::hrtimer) -> bindings::hrtimer_restart {
106        // `HrTimer` is `repr(C)`
107        let timer_ptr = ptr.cast::<super::HrTimer<T>>();
108
109        // SAFETY: By C API contract `ptr` is the pointer we passed when
110        // queuing the timer, so it is a `HrTimer<T>` embedded in a `T`.
111        let data_ptr = unsafe { T::timer_container_of(timer_ptr) };
112
113        // SAFETY:
114        //  - As per the safety requirements of the trait `HrTimerHandle`, the
115        //   `BoxHrTimerHandle` associated with this timer is guaranteed to
116        //   be alive until this method returns. That handle owns the `T`
117        //   behind `data_ptr` thus guaranteeing the validity of
118        //   the reference created below.
119        // - As `data_ptr` comes from a `Pin<Box<T>>`, only pinned references to
120        //   `data_ptr` exist.
121        let data_mut_ref = unsafe { Pin::new_unchecked(&mut *data_ptr) };
122
123        // SAFETY:
124        // - By C API contract `timer_ptr` is the pointer that we passed when queuing the timer, so
125        //   it is a valid pointer to a `HrTimer<T>` embedded in a `T`.
126        // - We are within `RawHrTimerCallback::run`
127        let context = unsafe { HrTimerCallbackContext::from_raw(timer_ptr) };
128
129        T::run(data_mut_ref, context).into_c()
130    }
131}