Message-Id: <20241206-hrtimer-v3-v6-12-rc2-v4-11-6cb8c3673682@kernel.org>
Date: Fri, 06 Dec 2024 20:33:03 +0100
From: Andreas Hindborg <a.hindborg@...nel.org>
To: Miguel Ojeda <ojeda@...nel.org>, 
 Anna-Maria Behnsen <anna-maria@...utronix.de>, 
 Frederic Weisbecker <frederic@...nel.org>, 
 Thomas Gleixner <tglx@...utronix.de>, Danilo Krummrich <dakr@...nel.org>
Cc: Alex Gaynor <alex.gaynor@...il.com>, Boqun Feng <boqun.feng@...il.com>, 
 Gary Guo <gary@...yguo.net>, 
 Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
 Benno Lossin <benno.lossin@...ton.me>, Alice Ryhl <aliceryhl@...gle.com>, 
 Trevor Gross <tmgross@...ch.edu>, Lyude Paul <lyude@...hat.com>, 
 rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Andreas Hindborg <a.hindborg@...nel.org>
Subject: [PATCH v4 11/14] rust: hrtimer: implement `TimerPointer` for
 `Pin<Box<T>>`

Allow `Pin<Box<T>>` to be the target of a timer callback.

Signed-off-by: Andreas Hindborg <a.hindborg@...nel.org>
---
 rust/kernel/time/hrtimer.rs      |   3 ++
 rust/kernel/time/hrtimer/tbox.rs | 102 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 105 insertions(+)

diff --git a/rust/kernel/time/hrtimer.rs b/rust/kernel/time/hrtimer.rs
index 7835a33677ec32999c495d5b874ded2ff0786c9e..976a7350d6bee0cebe3dcca04ccbe48fef31e430 100644
--- a/rust/kernel/time/hrtimer.rs
+++ b/rust/kernel/time/hrtimer.rs
@@ -395,6 +395,9 @@ unsafe fn raw_get_timer(ptr: *const Self) ->
     }
 }
 
+// `box` is a reserved keyword, so prefix with `t` for timer
+mod tbox;
+
 mod arc;
 mod pin;
 mod pin_mut;
diff --git a/rust/kernel/time/hrtimer/tbox.rs b/rust/kernel/time/hrtimer/tbox.rs
new file mode 100644
index 0000000000000000000000000000000000000000..4b932a20cf6fcacdff7c40fc280f8d73a45addc0
--- /dev/null
+++ b/rust/kernel/time/hrtimer/tbox.rs
@@ -0,0 +1,102 @@
+// SPDX-License-Identifier: GPL-2.0
+
+use super::HasTimer;
+use super::RawTimerCallback;
+use super::Timer;
+use super::TimerCallback;
+use super::TimerHandle;
+use super::TimerPointer;
+use crate::prelude::*;
+use crate::time::Ktime;
+use core::mem::ManuallyDrop;
+
+/// A handle for a `Box<HasTimer<U>>` returned by a call to
+/// [`TimerPointer::start`].
+pub struct BoxTimerHandle<U, A>
+where
+    U: HasTimer<U>,
+    A: crate::alloc::Allocator,
+{
+    pub(crate) inner: *mut U,
+    _p: core::marker::PhantomData<A>,
+}
+
+// SAFETY: We implement drop below, and we cancel the timer in the drop
+// implementation.
+unsafe impl<U, A> TimerHandle for BoxTimerHandle<U, A>
+where
+    U: HasTimer<U>,
+    A: crate::alloc::Allocator,
+{
+    fn cancel(&mut self) -> bool {
+        // SAFETY: As we obtained `self.inner` from a valid reference when we
+        // created `self`, it must point to a valid `U`.
+        let timer_ptr = unsafe { <U as HasTimer<U>>::raw_get_timer(self.inner) };
+
+        // SAFETY: As `timer_ptr` points into `U` and `U` is valid, `timer_ptr`
+        // must point to a valid `Timer` instance.
+        unsafe { Timer::<U>::raw_cancel(timer_ptr) }
+    }
+}
+
+impl<U, A> Drop for BoxTimerHandle<U, A>
+where
+    U: HasTimer<U>,
+    A: crate::alloc::Allocator,
+{
+    fn drop(&mut self) {
+        self.cancel();
+        // SAFETY: `self.inner` came from a `Box::into_raw` call
+        drop(unsafe { Box::<U, A>::from_raw(self.inner) })
+    }
+}
+
+impl<U, A> TimerPointer for Pin<Box<U, A>>
+where
+    U: Send + Sync,
+    U: HasTimer<U>,
+    U: for<'a> TimerCallback<CallbackTarget<'a> = Pin<Box<U, A>>>,
+    U: for<'a> TimerCallback<CallbackTargetParameter<'a> = Pin<&'a U>>,
+    A: crate::alloc::Allocator,
+{
+    type TimerHandle = BoxTimerHandle<U, A>;
+
+    fn start(self, expires: Ktime) -> Self::TimerHandle {
+        let self_ptr: *const U = <Self as core::ops::Deref>::deref(&self);
+
+        // SAFETY: Since we generate the pointer passed to `start` from a valid
+        // reference, it is a valid pointer.
+        unsafe { U::start(self_ptr, expires) };
+
+        // SAFETY: We will not move out of this box during timer callback (we
+        // pass an immutable reference to the callback).
+        let inner = unsafe { Pin::into_inner_unchecked(self) };
+
+        BoxTimerHandle {
+            inner: Box::into_raw(inner),
+            _p: core::marker::PhantomData,
+        }
+    }
+}
+
+impl<U, A> RawTimerCallback for Pin<Box<U, A>>
+where
+    U: HasTimer<U>,
+    U: for<'a> TimerCallback<CallbackTarget<'a> = Pin<Box<U, A>>>,
+    U: for<'a> TimerCallback<CallbackTargetParameter<'a> = Pin<&'a U>>,
+    A: crate::alloc::Allocator,
+{
+    unsafe extern "C" fn run(ptr: *mut bindings::hrtimer) -> bindings::hrtimer_restart {
+        // `Timer` is `repr(C)`
+        let timer_ptr = ptr.cast::<super::Timer<U>>();
+
+        // SAFETY: By C API contract `ptr` is the pointer we passed when
+        // queuing the timer, so it is a `Timer<T>` embedded in a `T`.
+        let data_ptr = unsafe { U::timer_container_of(timer_ptr) };
+
+        // SAFETY: We called `Box::into_raw` when we queued the timer.
+        let tbox = ManuallyDrop::new(Box::into_pin(unsafe { Box::<U, A>::from_raw(data_ptr) }));
+
+        U::run(tbox.as_ref()).into()
+    }
+}

-- 
2.46.0

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