[PATCH v8 00/14] hrtimer Rust API

[PATCH v8 00/14] hrtimer Rust API

[Andreas Hindborg]

This series adds support for using the `hrtimer` subsystem from Rust code.

The series adds support for timer mode and clock source configuration during
timer initialization. Examples and functionality to execute closures at timer
expiration has been removed, as these depend on either atomics [3] or
`SpinLockIrq` [4], which are still being worked on.

This series is a dependency for unmerged features of the Rust null block driver
[1], and for rkvms [2].

Link: https://git.kernel.org/pub/scm/linux/kernel/git/a.hindborg/linux.git/log/?h=rnull-v6.11-rc2 [1]
Link: https://gitlab.freedesktop.org/lyudess/linux/-/tree/rvkms-wip [2]
Link: https://lore.kernel.org/rust-for-linux/20240612223025.1158537-1-boqun.feng@gmail.com/ [3]
Link: https://lore.kernel.org/rust-for-linux/20240916213025.477225-1-lyude@redhat.com/ [4]
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
Changes in v8:
- Publicly expose timer handles.
- Link to v7: https://lore.kernel.org/r/20250203-hrtimer-v3-v6-12-rc2-v7-0-189144725399@kernel.org

Changes in v7:
- fix a typo in commit message for "rust: time: Add Ktime::from_ns()"
- fix a typo in safety comment in `HrTimer::new`
- fix a typo in `HrTimer::raw_cancel`
- fix a typo in the vocabulary
- fix a typo in `HrTimerCallback` docs
- refactor module documentation
- add an ascii state diagram to module documentation
- specify reason for adding `Arc::as_ptr`'
- change `boxed` to `this` in `Box::into_pin`
- change `from_ns` to `from_nanos` to align with std
- imporove safety comment for `impl Send for HrTimer`
- remove useless paragraph in docs for `HrTimerPointer`
- rephrase docs for `HrTimerPointer::TimerHandle`
- update docs for `HrTimerCallback::CallbackTarget`
- explain how users should use safe functions for cancelling a timer
- rename generics for consistency
- remove a note about storing mode in `HrTimer` - this is still required
- rebase on v6.14-rc1
- Link to v6: https://lore.kernel.org/r/20250110-hrtimer-v3-v6-12-rc2-v6-0-f71d50f16482@kernel.org

Changes in v6:
- prefix all hrtimer related type names with `Hr`
- add a few links for type names in the documentation
- Link to v5: https://lore.kernel.org/r/20241217-hrtimer-v3-v6-12-rc2-v5-0-b34c20ac2cb7@kernel.org

Changes in v5:
- Fix a typo in `impl_has_timer`
- Implement `Box::into_pin` in terms of `impl From<Box> for Pin<Box>`
- Link to v4: https://lore.kernel.org/r/20241206-hrtimer-v3-v6-12-rc2-v4-0-6cb8c3673682@kernel.org

Changes in v4:
- rebase on v6.13-rc1 and adapt to kernel `Box`
- add a missing safety comment to `hrtimer::start`
- use `hrtimer_setup`
- fix a build issue when `bindings::hrtimer_restart` is signed
- fix a memory leak where box was not destroyed
- fix a documentation typo
- remove `as` coercion at multiple locations
- use fully qualified syntax when invoking `deref`
- move `hrtimer` into `time` module
- Link to v3: https://lore.kernel.org/r/20241017-hrtimer-v3-v6-12-rc2-v3-0-59a75cbb44da@kernel.org

Changes in v3:
- support timer mode selection
- support clock source selection
- eliminate `Arc::clone_from_raw` in favor of using `ArcBorrow`
- make `Arc::as_ptr` an associated method
- update safety requirement for `ArcBorrow::from_raw`
- remove examples (pending `SpinLockIrq` and `CondVar` patches)
- remove `start_function` (v2 `schedule_function`, pending `SpinLockIrq` and `CondVar` patches)
- change function naming from schedule/armed to start/running
- add vocabulary to documentation
- update safety comment in `Arc::as_ptr`
- Link to v2: https://lore.kernel.org/r/20240917222739.1298275-1-a.hindborg@kernel.org

Changes in v2:
- use a handle to own the timer callback target
- add ability to for callback to reschedule timer
- improve `impl_has_timer` to allow generics
- add support for stack allocated timers
- add support for scheduling closures
- use `Ktime` for setting expiration
- use `CondVar` instead of `AtomicBool` in examples
- rebase on 6.11
- improve documentation
- Link to v1: https://lore.kernel.org/r/20240425094634.262674-1-nmi@metaspace.dk

---
Andreas Hindborg (13):
      rust: hrtimer: introduce hrtimer support
      rust: sync: add `Arc::as_ptr`
      rust: hrtimer: implement `HrTimerPointer` for `Arc`
      rust: hrtimer: allow timer restart from timer handler
      rust: hrtimer: add `UnsafeHrTimerPointer`
      rust: hrtimer: add `hrtimer::ScopedHrTimerPointer`
      rust: hrtimer: implement `UnsafeHrTimerPointer` for `Pin<&T>`
      rust: hrtimer: implement `UnsafeHrTimerPointer` for `Pin<&mut T>`
      rust: alloc: add `Box::into_pin`
      rust: hrtimer: implement `HrTimerPointer` for `Pin<Box<T>>`
      rust: hrtimer: add `HrTimerMode`
      rust: hrtimer: add clocksource selection through `ClockSource`
      rust: hrtimer: add maintainer entry

Lyude Paul (1):
      rust: time: Add Ktime::from_ns()

 MAINTAINERS                         |  10 +
 rust/kernel/alloc/kbox.rs           |   6 +
 rust/kernel/sync/arc.rs             |  13 +-
 rust/kernel/time.rs                 |  10 +
 rust/kernel/time/hrtimer.rs         | 539 ++++++++++++++++++++++++++++++++++++
 rust/kernel/time/hrtimer/arc.rs     |  87 ++++++
 rust/kernel/time/hrtimer/pin.rs     |  95 +++++++
 rust/kernel/time/hrtimer/pin_mut.rs |  97 +++++++
 rust/kernel/time/hrtimer/tbox.rs    | 102 +++++++
 9 files changed, 957 insertions(+), 2 deletions(-)
---
base-commit: 2014c95afecee3e76ca4a56956a936e23283f05b
change-id: 20241017-hrtimer-v3-v6-12-rc2-215dc6b169bf

Best regards,
-- 
Andreas Hindborg <a.hindborg@kernel.org>

[PATCH v8 01/14] rust: time: Add Ktime::from_ns()

[Andreas Hindborg]

From: Lyude Paul <lyude@redhat.com>

A simple function to turn the provided value in nanoseconds into a Ktime
value. We allow any type which implements Into<bindings::ktime_t>, which
resolves to Into<i64>.

This is useful for some of the older DRM APIs that never got moved to
Ktime.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 rust/kernel/time.rs | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/rust/kernel/time.rs b/rust/kernel/time.rs
index 379c0f5772e57..87e47f2f5618d 100644
--- a/rust/kernel/time.rs
+++ b/rust/kernel/time.rs
@@ -8,6 +8,8 @@
 //! C header: [`include/linux/jiffies.h`](srctree/include/linux/jiffies.h).
 //! C header: [`include/linux/ktime.h`](srctree/include/linux/ktime.h).
 
+use core::convert::Into;
+
 /// The number of nanoseconds per millisecond.
 pub const NSEC_PER_MSEC: i64 = bindings::NSEC_PER_MSEC as i64;
 
@@ -63,6 +65,12 @@ pub fn to_ns(self) -> i64 {
     pub fn to_ms(self) -> i64 {
         self.divns_constant::<NSEC_PER_MSEC>()
     }
+
+    /// Creates a new Ktime from the given duration in nanoseconds.
+    #[inline]
+    pub fn from_nanos(ns: impl Into<bindings::ktime_t>) -> Self {
+        Self { inner: ns.into() }
+    }
 }
 
 /// Returns the number of milliseconds between two ktimes.

-- 
2.47.0

[PATCH v8 02/14] rust: hrtimer: introduce hrtimer support

[Andreas Hindborg]

This patch adds support for intrusive use of the hrtimer system. For now,
only one timer can be embedded in a Rust struct.

The hrtimer Rust API is based on the intrusive style pattern introduced by
the Rust workqueue API.

Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 rust/kernel/time.rs         |   2 +
 rust/kernel/time/hrtimer.rs | 312 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 314 insertions(+)

diff --git a/rust/kernel/time.rs b/rust/kernel/time.rs
index 87e47f2f5618d..2cf365cfb412e 100644
--- a/rust/kernel/time.rs
+++ b/rust/kernel/time.rs
@@ -10,6 +10,8 @@
 
 use core::convert::Into;
 
+pub mod hrtimer;
+
 /// The number of nanoseconds per millisecond.
 pub const NSEC_PER_MSEC: i64 = bindings::NSEC_PER_MSEC as i64;
 
diff --git a/rust/kernel/time/hrtimer.rs b/rust/kernel/time/hrtimer.rs
new file mode 100644
index 0000000000000..a6332924efabd
--- /dev/null
+++ b/rust/kernel/time/hrtimer.rs
@@ -0,0 +1,312 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Intrusive high resolution timers.
+//!
+//! Allows running timer callbacks without doing allocations at the time of
+//! starting the timer. For now, only one timer per type is allowed.
+//!
+//! # Vocabulary
+//!
+//! States:
+//!
+//! * Stopped
+//! * Running
+//!
+//! Operations:
+//!
+//! * Start
+//! * Cancel
+//! * Stop
+//! * Restart
+//!
+//! Events:
+//!
+//! * Expire
+//!
+//! ## State Diagram
+//!
+//! ```text
+//!                  <-- Stop ----
+//!                  <-- Cancel --
+//!                  --- Start -->
+//!        +---------+        +---------+
+//!   O--->| Stopped |        | Running |---o
+//!        +---------+        +---------+   |
+//!                                  ^      |
+//!                  <- Expire --    |      |
+//!                                  o------o
+//!                                   Restart
+//! ```
+//!
+//! A timer is initialized in the **stopped** state. A stopped timer can be
+//! **started** with an **expiry** time. After the timer is started, it is
+//! **running**. When the timer **expires**, the timer handler is executed.
+//! After the handler has executed, the timer may be **restarted** or
+//! **stopped**. A running timer can be **canceled** before it's handler is
+//! executed. A timer that is cancelled enters the **stopped** state.
+//!
+
+use crate::{init::PinInit, prelude::*, time::Ktime, types::Opaque};
+use core::marker::PhantomData;
+
+/// A timer backed by a C `struct hrtimer`.
+///
+/// # Invariants
+///
+/// * `self.timer` is initialized by `bindings::hrtimer_setup`.
+#[pin_data]
+#[repr(C)]
+pub struct HrTimer<T> {
+    #[pin]
+    timer: Opaque<bindings::hrtimer>,
+    _t: PhantomData<T>,
+}
+
+// SAFETY: Ownership of an `HrTimer` can be moved to other threads and
+// used/dropped from there.
+unsafe impl<T> Send for HrTimer<T> {}
+
+// SAFETY: Timer operations are locked on C side, so it is safe to operate on a
+// timer from multiple threads
+unsafe impl<T> Sync for HrTimer<T> {}
+
+impl<T> HrTimer<T> {
+    /// Return an initializer for a new timer instance.
+    pub fn new() -> impl PinInit<Self>
+    where
+        T: HrTimerCallback,
+    {
+        pin_init!(Self {
+            // INVARIANTS: We initialize `timer` with `hrtimer_setup` below.
+            timer <- Opaque::ffi_init(move |place: *mut bindings::hrtimer| {
+                // SAFETY: By design of `pin_init!`, `place` is a pointer to a
+                // live allocation. hrtimer_setup will initialize `place` and
+                // does not require `place` to be initialized prior to the call.
+                unsafe {
+                    bindings::hrtimer_setup(
+                        place,
+                        Some(T::CallbackTarget::run),
+                        bindings::CLOCK_MONOTONIC as i32,
+                        bindings::hrtimer_mode_HRTIMER_MODE_REL,
+                    );
+                }
+            }),
+            _t: PhantomData,
+        })
+    }
+
+    /// Get a pointer to the contained `bindings::hrtimer`.
+    ///
+    /// # Safety
+    ///
+    /// `ptr` must point to a live allocation of at least the size of `Self`.
+    unsafe fn raw_get(ptr: *const Self) -> *mut bindings::hrtimer {
+        // SAFETY: The field projection to `timer` does not go out of bounds,
+        // because the caller of this function promises that `ptr` points to an
+        // allocation of at least the size of `Self`.
+        unsafe { Opaque::raw_get(core::ptr::addr_of!((*ptr).timer)) }
+    }
+
+    /// Cancel an initialized and potentially running timer.
+    ///
+    /// If the timer handler is running, this will block until the handler is
+    /// finished.
+    ///
+    /// Users of the `HrTimer` API would not usually call this method directly.
+    /// Instead they would use the safe `cancel` method on the [`HrTimerHandle`]
+    /// returned when the timer was started.
+    ///
+    /// # Safety
+    ///
+    /// `self_ptr` must point to a valid `Self`.
+    #[allow(dead_code)]
+    pub(crate) unsafe fn raw_cancel(self_ptr: *const Self) -> bool {
+        // SAFETY: timer_ptr points to an allocation of at least `HrTimer` size.
+        let c_timer_ptr = unsafe { HrTimer::raw_get(self_ptr) };
+
+        // If the handler is running, this will wait for the handler to finish
+        // before returning.
+        // SAFETY: `c_timer_ptr` is initialized and valid. Synchronization is
+        // handled on C side.
+        unsafe { bindings::hrtimer_cancel(c_timer_ptr) != 0 }
+    }
+}
+
+/// Implemented by pointer types that point to structs that embed a [`HrTimer`].
+///
+/// Target (pointee) must be [`Sync`] because timer callbacks happen in another
+/// thread of execution (hard or soft interrupt context).
+///
+/// Starting a timer returns a [`HrTimerHandle`] that can be used to manipulate
+/// the timer. Note that it is OK to call the start function repeatedly, and
+/// that more than one [`HrTimerHandle`] associated with a [`HrTimerPointer`] may
+/// exist. A timer can be manipulated through any of the handles, and a handle
+/// may represent a cancelled timer.
+pub trait HrTimerPointer: Sync + Sized {
+    /// A handle representing a started or restarted timer.
+    ///
+    /// If the timer is running or if the timer callback is executing when the
+    /// handle is dropped, the drop method of [`HrTimerHandle`] should not return
+    /// until the timer is stopped and the callback has completed.
+    ///
+    /// Note: When implementing this trait, consider that it is not unsafe to
+    /// leak the handle.
+    type TimerHandle: HrTimerHandle;
+
+    /// Start the timer with expiry after `expires` time units. If the timer was
+    /// already running, it is restarted with the new expiry time.
+    fn start(self, expires: Ktime) -> Self::TimerHandle;
+}
+
+/// 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.
+pub trait RawHrTimerCallback {
+    /// Callback to be called from C when timer fires.
+    ///
+    /// # Safety
+    ///
+    /// Only to be called by C code in `hrtimer` subsystem. `ptr` must point to
+    /// the `bindings::hrtimer` structure that was used to start the timer.
+    unsafe extern "C" fn run(ptr: *mut bindings::hrtimer) -> bindings::hrtimer_restart;
+}
+
+/// Implemented by structs that can be the target of a timer callback.
+pub trait HrTimerCallback {
+    /// The type whose [`RawHrTimerCallback::run`] method will be invoked when
+    /// the timer expires.
+    type CallbackTarget<'a>: RawHrTimerCallback;
+
+    /// This type is passed to the timer callback function. It may be a borrow
+    /// of [`Self::CallbackTarget`], or it may be `Self::CallbackTarget` if the
+    /// implementation can guarantee exclusive access to the target during timer
+    /// handler execution.
+    type CallbackTargetParameter<'a>;
+
+    /// Called by the timer logic when the timer fires.
+    fn run(this: Self::CallbackTargetParameter<'_>)
+    where
+        Self: Sized;
+}
+
+/// A handle representing a potentially running timer.
+///
+/// More than one handle representing the same timer might exist.
+///
+/// # Safety
+///
+/// When dropped, the timer represented by this handle must be cancelled, if it
+/// is running. If the timer handler is running when the handle is dropped, the
+/// drop method must wait for the handler to finish before returning.
+pub unsafe trait HrTimerHandle {
+    /// Cancel the timer, if it is running. If the timer handler is running, block
+    /// till the handler has finished.
+    fn cancel(&mut self) -> bool;
+}
+
+/// Implemented by structs that contain timer nodes.
+///
+/// Clients of the timer API would usually safely implement this trait by using
+/// the [`crate::impl_has_hr_timer`] macro.
+///
+/// # Safety
+///
+/// Implementers of this trait must ensure that the implementer has a [`HrTimer`]
+/// field at the offset specified by `OFFSET` and that all trait methods are
+/// implemented according to their documentation.
+///
+/// [`impl_has_timer`]: crate::impl_has_timer
+pub unsafe trait HasHrTimer<T> {
+    /// Offset of the [`HrTimer`] field within `Self`
+    const OFFSET: usize;
+
+    /// Return a pointer to the [`HrTimer`] within `Self`.
+    ///
+    /// # Safety
+    ///
+    /// `ptr` must point to a valid struct of type `Self`.
+    unsafe fn raw_get_timer(ptr: *const Self) -> *const HrTimer<T> {
+        // SAFETY: By the safety requirement of this trait, the trait
+        // implementor will have a `HrTimer` field at the specified offset.
+        unsafe { ptr.cast::<u8>().add(Self::OFFSET).cast::<HrTimer<T>>() }
+    }
+
+    /// Return a pointer to the struct that is embedding the [`HrTimer`] pointed
+    /// to by `ptr`.
+    ///
+    /// # Safety
+    ///
+    /// `ptr` must point to a [`HrTimer<T>`] field in a struct of type `Self`.
+    unsafe fn timer_container_of(ptr: *mut HrTimer<T>) -> *mut Self
+    where
+        Self: Sized,
+    {
+        // SAFETY: By the safety requirement of this function and the `HasHrTimer`
+        // trait, the following expression will yield a pointer to the `Self`
+        // containing the timer addressed by `ptr`.
+        unsafe { ptr.cast::<u8>().sub(Self::OFFSET).cast::<Self>() }
+    }
+
+    /// Get pointer to embedded `bindings::hrtimer` struct.
+    ///
+    /// # Safety
+    ///
+    /// `self_ptr` must point to a valid `Self`.
+    unsafe fn c_timer_ptr(self_ptr: *const Self) -> *const bindings::hrtimer {
+        // SAFETY: `self_ptr` is a valid pointer to a `Self`.
+        let timer_ptr = unsafe { Self::raw_get_timer(self_ptr) };
+
+        // SAFETY: timer_ptr points to an allocation of at least `HrTimer` size.
+        unsafe { HrTimer::raw_get(timer_ptr) }
+    }
+
+    /// Start the timer contained in the `Self` pointed to by `self_ptr`. If
+    /// it is already running it is removed and inserted.
+    ///
+    /// # Safety
+    ///
+    /// `self_ptr` must point to a valid `Self`.
+    unsafe fn start(self_ptr: *const Self, expires: Ktime) {
+        // SAFETY: By function safety requirement, `self_ptr`is a valid `Self`.
+        unsafe {
+            bindings::hrtimer_start_range_ns(
+                Self::c_timer_ptr(self_ptr).cast_mut(),
+                expires.to_ns(),
+                0,
+                bindings::hrtimer_mode_HRTIMER_MODE_REL,
+            );
+        }
+    }
+}
+
+/// Use to implement the [`HasHrTimer<T>`] trait.
+///
+/// See [`module`] documentation for an example.
+///
+/// [`module`]: crate::time::hrtimer
+#[macro_export]
+macro_rules! impl_has_hr_timer {
+    (
+        impl$({$($generics:tt)*})?
+            HasHrTimer<$timer_type:ty>
+            for $self:ty
+        { self.$field:ident }
+        $($rest:tt)*
+    ) => {
+        // SAFETY: This implementation of `raw_get_timer` only compiles if the
+        // field has the right type.
+        unsafe impl$(<$($generics)*>)? $crate::time::hrtimer::HasHrTimer<$timer_type> for $self {
+            const OFFSET: usize = ::core::mem::offset_of!(Self, $field) as usize;
+
+            #[inline]
+            unsafe fn raw_get_timer(ptr: *const Self) ->
+                *const $crate::time::hrtimer::HrTimer<$timer_type>
+            {
+                // SAFETY: The caller promises that the pointer is not dangling.
+                unsafe {
+                    ::core::ptr::addr_of!((*ptr).$field)
+                }
+            }
+        }
+    }
+}

-- 
2.47.0

[PATCH v8 03/14] rust: sync: add `Arc::as_ptr`

[Andreas Hindborg]

Add a method to get a pointer to the data contained in an `Arc`.

Reviewed-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---

This is a dependency for:

rust: hrtimer: implement `HrTimerPointer` for `Arc`
---
 rust/kernel/sync/arc.rs | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
index 3cefda7a43725..1dfa75714f9d6 100644
--- a/rust/kernel/sync/arc.rs
+++ b/rust/kernel/sync/arc.rs
@@ -246,6 +246,15 @@ pub fn into_raw(self) -> *const T {
         unsafe { core::ptr::addr_of!((*ptr).data) }
     }
 
+    /// Return a raw pointer to the data in this arc.
+    pub fn as_ptr(this: &Self) -> *const T {
+        let ptr = this.ptr.as_ptr();
+
+        // SAFETY: As `ptr` points to a valid allocation of type `ArcInner`,
+        // field projection to `data`is within bounds of the allocation.
+        unsafe { core::ptr::addr_of!((*ptr).data) }
+    }
+
     /// Recreates an [`Arc`] instance previously deconstructed via [`Arc::into_raw`].
     ///
     /// # Safety
@@ -539,11 +548,11 @@ unsafe fn new(inner: NonNull<ArcInner<T>>) -> Self {
     }
 
     /// Creates an [`ArcBorrow`] to an [`Arc`] that has previously been deconstructed with
-    /// [`Arc::into_raw`].
+    /// [`Arc::into_raw`] or [`Arc::as_ptr`].
     ///
     /// # Safety
     ///
-    /// * The provided pointer must originate from a call to [`Arc::into_raw`].
+    /// * The provided pointer must originate from a call to [`Arc::into_raw`] or [`Arc::as_ptr`].
     /// * For the duration of the lifetime annotated on this `ArcBorrow`, the reference count must
     ///   not hit zero.
     /// * For the duration of the lifetime annotated on this `ArcBorrow`, there must not be a

-- 
2.47.0

[PATCH v8 04/14] rust: hrtimer: implement `HrTimerPointer` for `Arc`

[Andreas Hindborg]

This patch allows the use of intrusive `hrtimer` fields in structs that are
managed by an `Arc`.

Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 rust/kernel/time/hrtimer.rs     |  4 +-
 rust/kernel/time/hrtimer/arc.rs | 89 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 92 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/time/hrtimer.rs b/rust/kernel/time/hrtimer.rs
index a6332924efabd..b2a3130bc21d7 100644
--- a/rust/kernel/time/hrtimer.rs
+++ b/rust/kernel/time/hrtimer.rs
@@ -119,7 +119,6 @@ unsafe fn raw_get(ptr: *const Self) -> *mut bindings::hrtimer {
     /// # Safety
     ///
     /// `self_ptr` must point to a valid `Self`.
-    #[allow(dead_code)]
     pub(crate) unsafe fn raw_cancel(self_ptr: *const Self) -> bool {
         // SAFETY: timer_ptr points to an allocation of at least `HrTimer` size.
         let c_timer_ptr = unsafe { HrTimer::raw_get(self_ptr) };
@@ -310,3 +309,6 @@ unsafe fn raw_get_timer(ptr: *const Self) ->
         }
     }
 }
+
+mod arc;
+pub use arc::ArcHrTimerHandle;
diff --git a/rust/kernel/time/hrtimer/arc.rs b/rust/kernel/time/hrtimer/arc.rs
new file mode 100644
index 0000000000000..d1c90631d0036
--- /dev/null
+++ b/rust/kernel/time/hrtimer/arc.rs
@@ -0,0 +1,89 @@
+// SPDX-License-Identifier: GPL-2.0
+
+use super::HasHrTimer;
+use super::HrTimer;
+use super::HrTimerCallback;
+use super::HrTimerHandle;
+use super::HrTimerPointer;
+use super::RawHrTimerCallback;
+use crate::sync::Arc;
+use crate::sync::ArcBorrow;
+use crate::time::Ktime;
+
+/// A handle for an `Arc<HasHrTimer<T>>` returned by a call to
+/// [`HrTimerPointer::start`].
+pub struct ArcHrTimerHandle<T>
+where
+    T: HasHrTimer<T>,
+{
+    pub(crate) inner: Arc<T>,
+}
+
+// SAFETY: We implement drop below, and we cancel the timer in the drop
+// implementation.
+unsafe impl<T> HrTimerHandle for ArcHrTimerHandle<T>
+where
+    T: HasHrTimer<T>,
+{
+    fn cancel(&mut self) -> bool {
+        let self_ptr = Arc::as_ptr(&self.inner);
+
+        // SAFETY: As we obtained `self_ptr` from a valid reference above, it
+        // must point to a valid `T`.
+        let timer_ptr = unsafe { <T as HasHrTimer<T>>::raw_get_timer(self_ptr) };
+
+        // SAFETY: As `timer_ptr` points into `T` and `T` is valid, `timer_ptr`
+        // must point to a valid `HrTimer` instance.
+        unsafe { HrTimer::<T>::raw_cancel(timer_ptr) }
+    }
+}
+
+impl<T> Drop for ArcHrTimerHandle<T>
+where
+    T: HasHrTimer<T>,
+{
+    fn drop(&mut self) {
+        self.cancel();
+    }
+}
+
+impl<T> HrTimerPointer for Arc<T>
+where
+    T: Send + Sync,
+    T: HasHrTimer<T>,
+    T: for<'a> HrTimerCallback<CallbackTarget<'a> = Self>,
+{
+    type TimerHandle = ArcHrTimerHandle<T>;
+
+    fn start(self, expires: Ktime) -> ArcHrTimerHandle<T> {
+        // SAFETY: Since we generate the pointer passed to `start` from a
+        // valid reference, it is a valid pointer.
+        unsafe { T::start(Arc::as_ptr(&self), expires) };
+
+        ArcHrTimerHandle { inner: self }
+    }
+}
+
+impl<T> RawHrTimerCallback for Arc<T>
+where
+    T: HasHrTimer<T>,
+    T: for<'a> HrTimerCallback<CallbackTarget<'a> = Self>,
+    T: for<'a> HrTimerCallback<CallbackTargetParameter<'a> = ArcBorrow<'a, T>>,
+{
+    unsafe extern "C" fn run(ptr: *mut bindings::hrtimer) -> bindings::hrtimer_restart {
+        // `HrTimer` is `repr(C)`
+        let timer_ptr = ptr.cast::<super::HrTimer<T>>();
+
+        // SAFETY: By C API contract `ptr` is the pointer we passed when
+        // queuing the timer, so it is a `HrTimer<T>` embedded in a `T`.
+        let data_ptr = unsafe { T::timer_container_of(timer_ptr) };
+
+        // SAFETY: `data_ptr` points to the `T` that was used to queue the
+        // timer. This `T` is contained in an `Arc`.
+        let receiver = unsafe { ArcBorrow::from_raw(data_ptr) };
+
+        T::run(receiver);
+
+        bindings::hrtimer_restart_HRTIMER_NORESTART
+    }
+}

-- 
2.47.0

[PATCH v8 05/14] rust: hrtimer: allow timer restart from timer handler

[Andreas Hindborg]

This patch allows timer handlers to report that they want a timer to be
restarted after the timer handler has finished executing.

Also update the `hrtimer` documentation to showcase the new feature.

Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 rust/kernel/time/hrtimer.rs     | 28 +++++++++++++++++++++++++++-
 rust/kernel/time/hrtimer/arc.rs |  4 +---
 2 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/rust/kernel/time/hrtimer.rs b/rust/kernel/time/hrtimer.rs
index b2a3130bc21d7..e342193f985eb 100644
--- a/rust/kernel/time/hrtimer.rs
+++ b/rust/kernel/time/hrtimer.rs
@@ -183,7 +183,7 @@ pub trait HrTimerCallback {
     type CallbackTargetParameter<'a>;
 
     /// Called by the timer logic when the timer fires.
-    fn run(this: Self::CallbackTargetParameter<'_>)
+    fn run(this: Self::CallbackTargetParameter<'_>) -> HrTimerRestart
     where
         Self: Sized;
 }
@@ -278,6 +278,32 @@ unsafe fn start(self_ptr: *const Self, expires: Ktime) {
     }
 }
 
+/// Restart policy for timers.
+pub enum HrTimerRestart {
+    /// Timer should not be restarted.
+    NoRestart,
+    /// Timer should be restarted.
+    Restart,
+}
+
+impl From<bindings::hrtimer_restart> for HrTimerRestart {
+    fn from(value: u32) -> Self {
+        match value {
+            bindings::hrtimer_restart_HRTIMER_NORESTART => Self::NoRestart,
+            _ => Self::Restart,
+        }
+    }
+}
+
+impl From<HrTimerRestart> for bindings::hrtimer_restart {
+    fn from(value: HrTimerRestart) -> Self {
+        match value {
+            HrTimerRestart::NoRestart => bindings::hrtimer_restart_HRTIMER_NORESTART,
+            HrTimerRestart::Restart => bindings::hrtimer_restart_HRTIMER_RESTART,
+        }
+    }
+}
+
 /// Use to implement the [`HasHrTimer<T>`] trait.
 ///
 /// See [`module`] documentation for an example.
diff --git a/rust/kernel/time/hrtimer/arc.rs b/rust/kernel/time/hrtimer/arc.rs
index d1c90631d0036..109eded0e73be 100644
--- a/rust/kernel/time/hrtimer/arc.rs
+++ b/rust/kernel/time/hrtimer/arc.rs
@@ -82,8 +82,6 @@ impl<T> RawHrTimerCallback for Arc<T>
         // timer. This `T` is contained in an `Arc`.
         let receiver = unsafe { ArcBorrow::from_raw(data_ptr) };
 
-        T::run(receiver);
-
-        bindings::hrtimer_restart_HRTIMER_NORESTART
+        T::run(receiver).into()
     }
 }

-- 
2.47.0

[PATCH v8 06/14] rust: hrtimer: add `UnsafeHrTimerPointer`

[Andreas Hindborg]

Add a trait to allow unsafely queuing stack allocated timers.

Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 rust/kernel/time/hrtimer.rs | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/rust/kernel/time/hrtimer.rs b/rust/kernel/time/hrtimer.rs
index e342193f985eb..196794089f033 100644
--- a/rust/kernel/time/hrtimer.rs
+++ b/rust/kernel/time/hrtimer.rs
@@ -157,6 +157,37 @@ pub trait HrTimerPointer: Sync + Sized {
     fn start(self, expires: Ktime) -> Self::TimerHandle;
 }
 
+/// Unsafe version of [`HrTimerPointer`] for situations where leaking the
+/// [`HrTimerHandle`] returned by `start` would be unsound. This is the case for
+/// stack allocated timers.
+///
+/// Typical implementers are pinned references such as [`Pin<&T>`].
+///
+/// # Safety
+///
+/// Implementers of this trait must ensure that instances of types implementing
+/// [`UnsafeHrTimerPointer`] outlives any associated [`HrTimerPointer::TimerHandle`]
+/// instances.
+pub unsafe trait UnsafeHrTimerPointer: Sync + Sized {
+    /// A handle representing a running timer.
+    ///
+    /// # Safety
+    ///
+    /// If the timer is running, or if the timer callback is executing when the
+    /// handle is dropped, the drop method of [`Self::TimerHandle`] must not return
+    /// until the timer is stopped and the callback has completed.
+    type TimerHandle: HrTimerHandle;
+
+    /// Start the timer after `expires` time units. If the timer was already
+    /// running, it is restarted at the new expiry time.
+    ///
+    /// # Safety
+    ///
+    /// Caller promises keep the timer structure alive until the timer is dead.
+    /// Caller can ensure this by not leaking the returned [`Self::TimerHandle`].
+    unsafe fn start(self, expires: Ktime) -> Self::TimerHandle;
+}
+
 /// 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.

-- 
2.47.0

[PATCH v8 07/14] rust: hrtimer: add `hrtimer::ScopedHrTimerPointer`

[Andreas Hindborg]

Add the trait `ScopedHrTimerPointer` 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 `UnsafeHrTimerPointer`.

Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 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 196794089f033..666bcd6e46a11 100644
--- a/rust/kernel/time/hrtimer.rs
+++ b/rust/kernel/time/hrtimer.rs
@@ -188,6 +188,39 @@ pub unsafe trait UnsafeHrTimerPointer: 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 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.

-- 
2.47.0

[PATCH v8 08/14] rust: hrtimer: implement `UnsafeHrTimerPointer` for `Pin<&T>`

[Andreas Hindborg]

Allow pinned references to structs that contain a `HrTimer` node to be
scheduled with the `hrtimer` subsystem.

Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 rust/kernel/time/hrtimer.rs     |  2 +
 rust/kernel/time/hrtimer/pin.rs | 95 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 97 insertions(+)

diff --git a/rust/kernel/time/hrtimer.rs b/rust/kernel/time/hrtimer.rs
index 666bcd6e46a11..3228ed916b4fe 100644
--- a/rust/kernel/time/hrtimer.rs
+++ b/rust/kernel/time/hrtimer.rs
@@ -402,3 +402,5 @@ unsafe fn raw_get_timer(ptr: *const Self) ->
 
 mod arc;
 pub use arc::ArcHrTimerHandle;
+mod pin;
+pub use pin::PinHrTimerHandle;
diff --git a/rust/kernel/time/hrtimer/pin.rs b/rust/kernel/time/hrtimer/pin.rs
new file mode 100644
index 0000000000000..ecab39118662e
--- /dev/null
+++ b/rust/kernel/time/hrtimer/pin.rs
@@ -0,0 +1,95 @@
+// SPDX-License-Identifier: GPL-2.0
+
+use super::HasHrTimer;
+use super::HrTimer;
+use super::HrTimerCallback;
+use super::HrTimerHandle;
+use super::RawHrTimerCallback;
+use super::UnsafeHrTimerPointer;
+use crate::time::Ktime;
+use core::pin::Pin;
+
+/// A handle for a `Pin<&HasHrTimer>`. When the handle exists, the timer might be
+/// running.
+pub struct PinHrTimerHandle<'a, T>
+where
+    T: HasHrTimer<T>,
+{
+    pub(crate) inner: Pin<&'a T>,
+}
+
+// SAFETY: We cancel the timer when the handle is dropped. The implementation of
+// the `cancel` method will block if the timer handler is running.
+unsafe impl<'a, T> HrTimerHandle for PinHrTimerHandle<'a, T>
+where
+    T: HasHrTimer<T>,
+{
+    fn cancel(&mut self) -> bool {
+        let self_ptr: *const T = self.inner.get_ref();
+
+        // SAFETY: As we got `self_ptr` from a reference above, it must point to
+        // a valid `T`.
+        let timer_ptr = unsafe { <T as HasHrTimer<T>>::raw_get_timer(self_ptr) };
+
+        // SAFETY: As `timer_ptr` is derived from a reference, it must point to
+        // a valid and initialized `HrTimer`.
+        unsafe { HrTimer::<T>::raw_cancel(timer_ptr) }
+    }
+}
+
+impl<'a, T> Drop for PinHrTimerHandle<'a, T>
+where
+    T: HasHrTimer<T>,
+{
+    fn drop(&mut self) {
+        self.cancel();
+    }
+}
+
+// SAFETY: We capture the lifetime of `Self` when we create a `PinHrTimerHandle`,
+// so `Self` will outlive the handle.
+unsafe impl<'a, T> UnsafeHrTimerPointer for Pin<&'a T>
+where
+    T: Send + Sync,
+    T: HasHrTimer<T>,
+    T: HrTimerCallback<CallbackTarget<'a> = Self>,
+{
+    type TimerHandle = PinHrTimerHandle<'a, T>;
+
+    unsafe fn start(self, expires: Ktime) -> Self::TimerHandle {
+        // Cast to pointer
+        let self_ptr: *const T = <Self as core::ops::Deref>::deref(&self);
+
+        // SAFETY: As we derive `self_ptr` from a reference above, it must point
+        // to a valid `T`.
+        unsafe { T::start(self_ptr, expires) };
+
+        PinHrTimerHandle { inner: self }
+    }
+}
+
+impl<'a, T> RawHrTimerCallback for Pin<&'a T>
+where
+    T: HasHrTimer<T>,
+    T: HrTimerCallback<CallbackTarget<'a> = Self>,
+    T: HrTimerCallback<CallbackTargetParameter<'a> = Self>,
+{
+    unsafe extern "C" fn run(ptr: *mut bindings::hrtimer) -> bindings::hrtimer_restart {
+        // `HrTimer` is `repr(C)`
+        let timer_ptr = ptr as *mut HrTimer<T>;
+
+        // SAFETY: By the safety requirement of this function, `timer_ptr`
+        // points to a `HrTimer<T>` contained in an `T`.
+        let receiver_ptr = unsafe { T::timer_container_of(timer_ptr) };
+
+        // SAFETY: By the safety requirement of this function, `timer_ptr`
+        // points to a `HrTimer<T>` contained in an `T`.
+        let receiver_ref = unsafe { &*receiver_ptr };
+
+        // SAFETY: `receiver_ref` only exists as pinned, so it is safe to pin it
+        // here.
+        let receiver_pin = unsafe { Pin::new_unchecked(receiver_ref) };
+
+        T::run(receiver_pin).into()
+    }
+}

-- 
2.47.0

[PATCH v8 09/14] rust: hrtimer: implement `UnsafeHrTimerPointer` for `Pin<&mut T>`

[Andreas Hindborg]

Allow pinned mutable references to structs that contain a `HrTimer` node to
be scheduled with the `hrtimer` subsystem.

Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 rust/kernel/time/hrtimer.rs         |  2 +
 rust/kernel/time/hrtimer/pin_mut.rs | 97 +++++++++++++++++++++++++++++++++++++
 2 files changed, 99 insertions(+)

diff --git a/rust/kernel/time/hrtimer.rs b/rust/kernel/time/hrtimer.rs
index 3228ed916b4fe..f36513cba4351 100644
--- a/rust/kernel/time/hrtimer.rs
+++ b/rust/kernel/time/hrtimer.rs
@@ -404,3 +404,5 @@ unsafe fn raw_get_timer(ptr: *const Self) ->
 pub use arc::ArcHrTimerHandle;
 mod pin;
 pub use pin::PinHrTimerHandle;
+mod pin_mut;
+pub use pin_mut::PinMutHrTimerHandle;
diff --git a/rust/kernel/time/hrtimer/pin_mut.rs b/rust/kernel/time/hrtimer/pin_mut.rs
new file mode 100644
index 0000000000000..153e89b86caf2
--- /dev/null
+++ b/rust/kernel/time/hrtimer/pin_mut.rs
@@ -0,0 +1,97 @@
+// SPDX-License-Identifier: GPL-2.0
+
+use super::HasHrTimer;
+use super::HrTimer;
+use super::HrTimerCallback;
+use super::HrTimerHandle;
+use super::RawHrTimerCallback;
+use super::UnsafeHrTimerPointer;
+use crate::time::Ktime;
+use core::pin::Pin;
+
+/// A handle for a `Pin<&mut HasHrTimer>`. When the handle exists, the timer might
+/// be running.
+pub struct PinMutHrTimerHandle<'a, T>
+where
+    T: HasHrTimer<T>,
+{
+    pub(crate) inner: Pin<&'a mut T>,
+}
+
+// SAFETY: We cancel the timer when the handle is dropped. The implementation of
+// the `cancel` method will block if the timer handler is running.
+unsafe impl<'a, T> HrTimerHandle for PinMutHrTimerHandle<'a, T>
+where
+    T: HasHrTimer<T>,
+{
+    fn cancel(&mut self) -> bool {
+        // SAFETY: We are not moving out of `self` or handing out mutable
+        // references to `self`.
+        let self_ptr = unsafe { self.inner.as_mut().get_unchecked_mut() as *mut T };
+
+        // SAFETY: As we got `self_ptr` from a reference above, it must point to
+        // a valid `T`.
+        let timer_ptr = unsafe { <T as HasHrTimer<T>>::raw_get_timer(self_ptr) };
+
+        // SAFETY: As `timer_ptr` is derived from a reference, it must point to
+        // a valid and initialized `HrTimer`.
+        unsafe { HrTimer::<T>::raw_cancel(timer_ptr) }
+    }
+}
+
+impl<'a, T> Drop for PinMutHrTimerHandle<'a, T>
+where
+    T: HasHrTimer<T>,
+{
+    fn drop(&mut self) {
+        self.cancel();
+    }
+}
+
+// SAFETY: We capture the lifetime of `Self` when we create a
+// `PinMutHrTimerHandle`, so `Self` will outlive the handle.
+unsafe impl<'a, T> UnsafeHrTimerPointer for Pin<&'a mut T>
+where
+    T: Send + Sync,
+    T: HasHrTimer<T>,
+    T: HrTimerCallback<CallbackTarget<'a> = Self>,
+{
+    type TimerHandle = PinMutHrTimerHandle<'a, T>;
+
+    unsafe fn start(self, expires: Ktime) -> Self::TimerHandle {
+        // Cast to pointer
+        let self_ptr: *const T = <Self as core::ops::Deref>::deref(&self);
+
+        // SAFETY: As we derive `self_ptr` from a reference above, it must point
+        // to a valid `T`.
+        unsafe { T::start(self_ptr, expires) };
+
+        PinMutHrTimerHandle { inner: self }
+    }
+}
+
+impl<'a, T> RawHrTimerCallback for Pin<&'a mut T>
+where
+    T: HasHrTimer<T>,
+    T: HrTimerCallback<CallbackTarget<'a> = Self>,
+    T: HrTimerCallback<CallbackTargetParameter<'a> = Self>,
+{
+    unsafe extern "C" fn run(ptr: *mut bindings::hrtimer) -> bindings::hrtimer_restart {
+        // `HrTimer` is `repr(C)`
+        let timer_ptr = ptr as *mut HrTimer<T>;
+
+        // SAFETY: By the safety requirement of this function, `timer_ptr`
+        // points to a `HrTimer<T>` contained in an `T`.
+        let receiver_ptr = unsafe { T::timer_container_of(timer_ptr) };
+
+        // SAFETY: By the safety requirement of this function, `timer_ptr`
+        // points to a `HrTimer<T>` contained in an `T`.
+        let receiver_ref = unsafe { &mut *receiver_ptr };
+
+        // SAFETY: `receiver_ref` only exists as pinned, so it is safe to pin it
+        // here.
+        let receiver_pin = unsafe { Pin::new_unchecked(receiver_ref) };
+
+        T::run(receiver_pin).into()
+    }
+}

-- 
2.47.0

[PATCH v8 10/14] rust: alloc: add `Box::into_pin`

[Andreas Hindborg]

Add an associated function to convert a `Box<T>` into a `Pin<Box<T>>`.

Acked-by: Danilo Krummrich <dakr@kernel.org>
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 rust/kernel/alloc/kbox.rs | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/rust/kernel/alloc/kbox.rs b/rust/kernel/alloc/kbox.rs
index cb4ebea3b0742..9da4a32e60bc3 100644
--- a/rust/kernel/alloc/kbox.rs
+++ b/rust/kernel/alloc/kbox.rs
@@ -245,6 +245,12 @@ pub fn pin(x: T, flags: Flags) -> Result<Pin<Box<T, A>>, AllocError>
         Ok(Self::new(x, flags)?.into())
     }
 
+    /// Convert a [`Box<T,A>`] to a [`Pin<Box<T,A>>`]. If `T` does not implement
+    /// [`Unpin`], then `x` will be pinned in memory and can't be moved.
+    pub fn into_pin(this: Self) -> Pin<Self> {
+        this.into()
+    }
+
     /// Forgets the contents (does not run the destructor), but keeps the allocation.
     fn forget_contents(this: Self) -> Box<MaybeUninit<T>, A> {
         let ptr = Self::into_raw(this);

-- 
2.47.0

[PATCH v8 11/14] rust: hrtimer: implement `HrTimerPointer` for `Pin<Box<T>>`

[Andreas Hindborg]

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

Signed-off-by: Andreas Hindborg <a.hindborg@kernel.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 f36513cba4351..de9edf52ebb07 100644
--- a/rust/kernel/time/hrtimer.rs
+++ b/rust/kernel/time/hrtimer.rs
@@ -406,3 +406,6 @@ unsafe fn raw_get_timer(ptr: *const Self) ->
 pub use pin::PinHrTimerHandle;
 mod pin_mut;
 pub use pin_mut::PinMutHrTimerHandle;
+// `box` is a reserved keyword, so prefix with `t` for timer
+mod tbox;
+pub use tbox::BoxHrTimerHandle;
diff --git a/rust/kernel/time/hrtimer/tbox.rs b/rust/kernel/time/hrtimer/tbox.rs
new file mode 100644
index 0000000000000..39db96de023a8
--- /dev/null
+++ b/rust/kernel/time/hrtimer/tbox.rs
@@ -0,0 +1,102 @@
+// SPDX-License-Identifier: GPL-2.0
+
+use super::HasHrTimer;
+use super::HrTimer;
+use super::HrTimerCallback;
+use super::HrTimerHandle;
+use super::HrTimerPointer;
+use super::RawHrTimerCallback;
+use crate::prelude::*;
+use crate::time::Ktime;
+use core::mem::ManuallyDrop;
+
+/// A handle for a [`Box<HasHrTimer<T>>`] returned by a call to
+/// [`HrTimerPointer::start`].
+pub struct BoxHrTimerHandle<T, A>
+where
+    T: HasHrTimer<T>,
+    A: crate::alloc::Allocator,
+{
+    pub(crate) inner: *mut T,
+    _p: core::marker::PhantomData<A>,
+}
+
+// SAFETY: We implement drop below, and we cancel the timer in the drop
+// implementation.
+unsafe impl<T, A> HrTimerHandle for BoxHrTimerHandle<T, A>
+where
+    T: HasHrTimer<T>,
+    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 `T`.
+        let timer_ptr = unsafe { <T as HasHrTimer<T>>::raw_get_timer(self.inner) };
+
+        // SAFETY: As `timer_ptr` points into `T` and `T` is valid, `timer_ptr`
+        // must point to a valid `HrTimer` instance.
+        unsafe { HrTimer::<T>::raw_cancel(timer_ptr) }
+    }
+}
+
+impl<T, A> Drop for BoxHrTimerHandle<T, A>
+where
+    T: HasHrTimer<T>,
+    A: crate::alloc::Allocator,
+{
+    fn drop(&mut self) {
+        self.cancel();
+        // SAFETY: `self.inner` came from a `Box::into_raw` call
+        drop(unsafe { Box::<T, A>::from_raw(self.inner) })
+    }
+}
+
+impl<T, A> HrTimerPointer for Pin<Box<T, A>>
+where
+    T: Send + Sync,
+    T: HasHrTimer<T>,
+    T: for<'a> HrTimerCallback<CallbackTarget<'a> = Pin<Box<T, A>>>,
+    T: for<'a> HrTimerCallback<CallbackTargetParameter<'a> = Pin<&'a T>>,
+    A: crate::alloc::Allocator,
+{
+    type TimerHandle = BoxHrTimerHandle<T, A>;
+
+    fn start(self, expires: Ktime) -> Self::TimerHandle {
+        let self_ptr: *const T = <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 { T::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) };
+
+        BoxHrTimerHandle {
+            inner: Box::into_raw(inner),
+            _p: core::marker::PhantomData,
+        }
+    }
+}
+
+impl<T, A> RawHrTimerCallback for Pin<Box<T, A>>
+where
+    T: HasHrTimer<T>,
+    T: for<'a> HrTimerCallback<CallbackTarget<'a> = Pin<Box<T, A>>>,
+    T: for<'a> HrTimerCallback<CallbackTargetParameter<'a> = Pin<&'a T>>,
+    A: crate::alloc::Allocator,
+{
+    unsafe extern "C" fn run(ptr: *mut bindings::hrtimer) -> bindings::hrtimer_restart {
+        // `HrTimer` is `repr(C)`
+        let timer_ptr = ptr.cast::<super::HrTimer<T>>();
+
+        // SAFETY: By C API contract `ptr` is the pointer we passed when
+        // queuing the timer, so it is a `HrTimer<T>` embedded in a `T`.
+        let data_ptr = unsafe { T::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::<T, A>::from_raw(data_ptr) }));
+
+        T::run(tbox.as_ref()).into()
+    }
+}

-- 
2.47.0

[PATCH v8 12/14] rust: hrtimer: add `HrTimerMode`

[Andreas Hindborg]

Allow selection of timer mode by passing a `HrTimerMode` variant to
`HrTimer::new`.

Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 rust/kernel/time/hrtimer.rs | 86 +++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 83 insertions(+), 3 deletions(-)

diff --git a/rust/kernel/time/hrtimer.rs b/rust/kernel/time/hrtimer.rs
index de9edf52ebb07..db49061f830c3 100644
--- a/rust/kernel/time/hrtimer.rs
+++ b/rust/kernel/time/hrtimer.rs
@@ -59,6 +59,7 @@
 pub struct HrTimer<T> {
     #[pin]
     timer: Opaque<bindings::hrtimer>,
+    mode: HrTimerMode,
     _t: PhantomData<T>,
 }
 
@@ -72,7 +73,7 @@ unsafe impl<T> Sync for HrTimer<T> {}
 
 impl<T> HrTimer<T> {
     /// Return an initializer for a new timer instance.
-    pub fn new() -> impl PinInit<Self>
+    pub fn new(mode: HrTimerMode) -> impl PinInit<Self>
     where
         T: HrTimerCallback,
     {
@@ -87,10 +88,11 @@ pub fn new() -> impl PinInit<Self>
                         place,
                         Some(T::CallbackTarget::run),
                         bindings::CLOCK_MONOTONIC as i32,
-                        bindings::hrtimer_mode_HRTIMER_MODE_REL,
+                        mode.into(),
                     );
                 }
             }),
+            mode: mode,
             _t: PhantomData,
         })
     }
@@ -336,7 +338,7 @@ unsafe fn start(self_ptr: *const Self, expires: Ktime) {
                 Self::c_timer_ptr(self_ptr).cast_mut(),
                 expires.to_ns(),
                 0,
-                bindings::hrtimer_mode_HRTIMER_MODE_REL,
+                (*Self::raw_get_timer(self_ptr)).mode.into(),
             );
         }
     }
@@ -368,6 +370,84 @@ fn from(value: HrTimerRestart) -> Self {
     }
 }
 
+/// Operational mode of [`HrTimer`].
+#[derive(Clone, Copy)]
+pub enum HrTimerMode {
+    /// Timer expires at the given expiration time.
+    Absolute,
+    /// Timer expires after the given expiration time interpreted as a duration from now.
+    Relative,
+    /// Timer does not move between CPU cores.
+    Pinned,
+    /// Timer handler is executed in soft irq context.
+    Soft,
+    /// Timer handler is executed in hard irq context.
+    Hard,
+    /// Timer expires at the given expiration time.
+    /// Timer does not move between CPU cores.
+    AbsolutePinned,
+    /// Timer expires after the given expiration time interpreted as a duration from now.
+    /// Timer does not move between CPU cores.
+    RelativePinned,
+    /// Timer expires at the given expiration time.
+    /// Timer handler is executed in soft irq context.
+    AbsoluteSoft,
+    /// Timer expires after the given expiration time interpreted as a duration from now.
+    /// Timer handler is executed in soft irq context.
+    RelativeSoft,
+    /// Timer expires at the given expiration time.
+    /// Timer does not move between CPU cores.
+    /// Timer handler is executed in soft irq context.
+    AbsolutePinnedSoft,
+    /// Timer expires after the given expiration time interpreted as a duration from now.
+    /// Timer does not move between CPU cores.
+    /// Timer handler is executed in soft irq context.
+    RelativePinnedSoft,
+    /// Timer expires at the given expiration time.
+    /// Timer handler is executed in hard irq context.
+    AbsoluteHard,
+    /// Timer expires after the given expiration time interpreted as a duration from now.
+    /// Timer handler is executed in hard irq context.
+    RelativeHard,
+    /// Timer expires at the given expiration time.
+    /// Timer does not move between CPU cores.
+    /// Timer handler is executed in hard irq context.
+    AbsolutePinnedHard,
+    /// Timer expires after the given expiration time interpreted as a duration from now.
+    /// Timer does not move between CPU cores.
+    /// Timer handler is executed in hard irq context.
+    RelativePinnedHard,
+}
+
+impl From<HrTimerMode> for bindings::hrtimer_mode {
+    fn from(value: HrTimerMode) -> Self {
+        use bindings::*;
+        match value {
+            HrTimerMode::Absolute => hrtimer_mode_HRTIMER_MODE_ABS,
+            HrTimerMode::Relative => hrtimer_mode_HRTIMER_MODE_REL,
+            HrTimerMode::Pinned => hrtimer_mode_HRTIMER_MODE_PINNED,
+            HrTimerMode::Soft => hrtimer_mode_HRTIMER_MODE_SOFT,
+            HrTimerMode::Hard => hrtimer_mode_HRTIMER_MODE_HARD,
+            HrTimerMode::AbsolutePinned => hrtimer_mode_HRTIMER_MODE_ABS_PINNED,
+            HrTimerMode::RelativePinned => hrtimer_mode_HRTIMER_MODE_REL_PINNED,
+            HrTimerMode::AbsoluteSoft => hrtimer_mode_HRTIMER_MODE_ABS_SOFT,
+            HrTimerMode::RelativeSoft => hrtimer_mode_HRTIMER_MODE_REL_SOFT,
+            HrTimerMode::AbsolutePinnedSoft => hrtimer_mode_HRTIMER_MODE_ABS_PINNED_SOFT,
+            HrTimerMode::RelativePinnedSoft => hrtimer_mode_HRTIMER_MODE_REL_PINNED_SOFT,
+            HrTimerMode::AbsoluteHard => hrtimer_mode_HRTIMER_MODE_ABS_HARD,
+            HrTimerMode::RelativeHard => hrtimer_mode_HRTIMER_MODE_REL_HARD,
+            HrTimerMode::AbsolutePinnedHard => hrtimer_mode_HRTIMER_MODE_ABS_PINNED_HARD,
+            HrTimerMode::RelativePinnedHard => hrtimer_mode_HRTIMER_MODE_REL_PINNED_HARD,
+        }
+    }
+}
+
+impl From<HrTimerMode> for u64 {
+    fn from(value: HrTimerMode) -> Self {
+        Into::<bindings::hrtimer_mode>::into(value) as u64
+    }
+}
+
 /// Use to implement the [`HasHrTimer<T>`] trait.
 ///
 /// See [`module`] documentation for an example.

-- 
2.47.0

[PATCH v8 13/14] rust: hrtimer: add clocksource selection through `ClockSource`

[Andreas Hindborg]

Allow selecting a clock source for timers by passing a `ClockSource`
variant to `HrTimer::new`.

Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 rust/kernel/time/hrtimer.rs | 52 +++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 50 insertions(+), 2 deletions(-)

diff --git a/rust/kernel/time/hrtimer.rs b/rust/kernel/time/hrtimer.rs
index db49061f830c3..2b46d66eaa313 100644
--- a/rust/kernel/time/hrtimer.rs
+++ b/rust/kernel/time/hrtimer.rs
@@ -73,7 +73,7 @@ unsafe impl<T> Sync for HrTimer<T> {}
 
 impl<T> HrTimer<T> {
     /// Return an initializer for a new timer instance.
-    pub fn new(mode: HrTimerMode) -> impl PinInit<Self>
+    pub fn new(mode: HrTimerMode, clock: ClockSource) -> impl PinInit<Self>
     where
         T: HrTimerCallback,
     {
@@ -87,7 +87,7 @@ pub fn new(mode: HrTimerMode) -> impl PinInit<Self>
                     bindings::hrtimer_setup(
                         place,
                         Some(T::CallbackTarget::run),
-                        bindings::CLOCK_MONOTONIC as i32,
+                        clock.into(),
                         mode.into(),
                     );
                 }
@@ -448,6 +448,54 @@ fn from(value: HrTimerMode) -> Self {
     }
 }
 
+/// The clock source to use for a [`HrTimer`].
+pub enum ClockSource {
+    /// A settable system-wide clock that measures real (i.e., wall-clock) time.
+    /// Setting this clock requires appropriate privileges. This clock is
+    /// affected by discontinuous jumps in the system time (e.g., if the system
+    /// administrator manually changes the clock), and by frequency adjustments
+    /// performed by NTP and similar applications via adjtime(3), adjtimex(2),
+    /// clock_adjtime(2), and ntp_adjtime(3). This clock normally counts the
+    /// number of seconds since 1970-01-01 00:00:00 Coordinated Universal Time
+    /// (UTC) except that it ignores leap seconds; near a leap second it is
+    /// typically adjusted by NTP to stay roughly in sync with UTC.
+    RealTime,
+    /// A nonsettable system-wide clock that represents monotonic time since—as
+    /// described by POSIX—"some unspecified point in the past". On Linux, that
+    /// point corresponds to the number of seconds that the system has been
+    /// running since it was booted.
+    ///
+    /// The CLOCK_MONOTONIC clock is not affected by discontinuous jumps in the
+    /// system time (e.g., if the system administrator manually changes the
+    /// clock), but is affected by frequency adjustments. This clock does not
+    /// count time that the system is suspended.
+    Monotonic,
+    /// A nonsettable system-wide clock that is identical to CLOCK_MONOTONIC,
+    /// except that it also includes any time that the system is suspended. This
+    /// allows applications to get a suspend-aware monotonic clock without
+    /// having to deal with the complications of CLOCK_REALTIME, which may have
+    /// discontinuities if the time is changed using settimeofday(2) or similar.
+    BootTime,
+    /// A nonsettable system-wide clock derived from wall-clock time but
+    /// counting leap seconds. This clock does not experience discontinuities or
+    /// frequency adjustments caused by inserting leap seconds as CLOCK_REALTIME
+    /// does.
+    ///
+    /// The acronym TAI refers to International Atomic Time.
+    TAI,
+}
+
+impl From<ClockSource> for bindings::clockid_t {
+    fn from(value: ClockSource) -> Self {
+        match value {
+            ClockSource::RealTime => bindings::CLOCK_REALTIME as i32,
+            ClockSource::Monotonic => bindings::CLOCK_MONOTONIC as i32,
+            ClockSource::BootTime => bindings::CLOCK_BOOTTIME as i32,
+            ClockSource::TAI => bindings::CLOCK_TAI as i32,
+        }
+    }
+}
+
 /// Use to implement the [`HasHrTimer<T>`] trait.
 ///
 /// See [`module`] documentation for an example.

-- 
2.47.0

[PATCH v8 14/14] rust: hrtimer: add maintainer entry

[Andreas Hindborg]

Add Andreas Hindborg as maintainer for Rust `hrtimer` abstractions. Also
add Boqun Feng as reviewer.

Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
Acked-by: Boqun Feng <boqun.feng@gmail.com>
---
 MAINTAINERS | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 896a307fa0654..60fa77c41b3fb 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -10355,6 +10355,16 @@ F:	kernel/time/timer_list.c
 F:	kernel/time/timer_migration.*
 F:	tools/testing/selftests/timers/
 
+HIGH-RESOLUTION TIMERS [RUST]
+M:	Andreas Hindborg <a.hindborg@kernel.org>
+R:	Boqun Feng <boqun.feng@gmail.com>
+L:	rust-for-linux@vger.kernel.org
+S:	Supported
+W:	https://rust-for-linux.com
+B:	https://github.com/Rust-for-Linux/linux/issues
+F:	rust/kernel/time/hrtimer.rs
+F:	rust/kernel/time/hrtimer/
+
 HIGH-SPEED SCC DRIVER FOR AX.25
 L:	linux-hams@vger.kernel.org
 S:	Orphan

-- 
2.47.0

Re: [PATCH v8 00/14] hrtimer Rust API

[Andreas Hindborg]

"Andreas Hindborg" <a.hindborg@kernel.org> writes:

> This series adds support for using the `hrtimer` subsystem from Rust code.
>
> The series adds support for timer mode and clock source configuration during
> timer initialization. Examples and functionality to execute closures at timer
> expiration has been removed, as these depend on either atomics [3] or
> `SpinLockIrq` [4], which are still being worked on.
>
> This series is a dependency for unmerged features of the Rust null block driver
> [1], and for rkvms [2].
>

@ timer subsystem maintainers: did you discuss how you want to set up
maintenance for this yet? As mentioned, I'm happy stepping up to
maintain this, but if you want to handle it with existing resources that
is perfectly fine as well.

I was hoping we could merge the patches in the near future. The patches
have been on list for quite a while now, and I am happy with the shape
of them. They are in my critical path for merging dependent code in the
rust null block driver.

Let me know if there is anything I can do to help move the process
forward.


Best regards,
Andreas Hindborg

Re: [PATCH v8 01/14] rust: time: Add Ktime::from_ns()

[Benno Lossin]

On 18.02.25 14:27, Andreas Hindborg wrote:
> From: Lyude Paul <lyude@redhat.com>
> 
> A simple function to turn the provided value in nanoseconds into a Ktime
> value. We allow any type which implements Into<bindings::ktime_t>, which
> resolves to Into<i64>.
> 
> This is useful for some of the older DRM APIs that never got moved to
> Ktime.

Are these older DRM APIs on the C side, or on the Rust side? If they are
on the Rust side, we should just move them to Ktime, no?

> Signed-off-by: Lyude Paul <lyude@redhat.com>
> Reviewed-by: Lyude Paul <lyude@redhat.com>

This seems wrong considering the `From Lyude Paul` line above :) (or is
it possible to review your own patch?)

The patch itself looks good, so iff the above question is answered with
"the older DRM APIs are on the C side" then:

Reviewed-by: Benno Lossin <benno.lossin@proton.me>

---
Cheers,
Benno

> Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
> ---
>  rust/kernel/time.rs | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/rust/kernel/time.rs b/rust/kernel/time.rs
> index 379c0f5772e57..87e47f2f5618d 100644
> --- a/rust/kernel/time.rs
> +++ b/rust/kernel/time.rs
> @@ -8,6 +8,8 @@
>  //! C header: [`include/linux/jiffies.h`](srctree/include/linux/jiffies.h).
>  //! C header: [`include/linux/ktime.h`](srctree/include/linux/ktime.h).
> 
> +use core::convert::Into;
> +
>  /// The number of nanoseconds per millisecond.
>  pub const NSEC_PER_MSEC: i64 = bindings::NSEC_PER_MSEC as i64;
> 
> @@ -63,6 +65,12 @@ pub fn to_ns(self) -> i64 {
>      pub fn to_ms(self) -> i64 {
>          self.divns_constant::<NSEC_PER_MSEC>()
>      }
> +
> +    /// Creates a new Ktime from the given duration in nanoseconds.
> +    #[inline]
> +    pub fn from_nanos(ns: impl Into<bindings::ktime_t>) -> Self {
> +        Self { inner: ns.into() }
> +    }
>  }
> 
>  /// Returns the number of milliseconds between two ktimes.
> 
> --
> 2.47.0
> 
> 

Re: [PATCH v8 01/14] rust: time: Add Ktime::from_ns()

[Andreas Hindborg]

"Benno Lossin" <benno.lossin@proton.me> writes:

> On 18.02.25 14:27, Andreas Hindborg wrote:
>> From: Lyude Paul <lyude@redhat.com>
>>
>> A simple function to turn the provided value in nanoseconds into a Ktime
>> value. We allow any type which implements Into<bindings::ktime_t>, which
>> resolves to Into<i64>.
>>
>> This is useful for some of the older DRM APIs that never got moved to
>> Ktime.
>
> Are these older DRM APIs on the C side, or on the Rust side? If they are
> on the Rust side, we should just move them to Ktime, no?
>
>> Signed-off-by: Lyude Paul <lyude@redhat.com>
>> Reviewed-by: Lyude Paul <lyude@redhat.com>
>
> This seems wrong considering the `From Lyude Paul` line above :) (or is
> it possible to review your own patch?)
>
> The patch itself looks good, so iff the above question is answered with
> "the older DRM APIs are on the C side" then:
>
> Reviewed-by: Benno Lossin <benno.lossin@proton.me>

It occurs to me that I am actually not relying on this patch for this
series any longer, so I will just drop it.


Best regards,
Andreas Hindborg

Re: [PATCH v8 02/14] rust: hrtimer: introduce hrtimer support

[Tamir Duberstein]

On Tue, Feb 18, 2025 at 8:29 AM Andreas Hindborg <a.hindborg@kernel.org> wrote:
>
> This patch adds support for intrusive use of the hrtimer system. For now,
> only one timer can be embedded in a Rust struct.
>
> The hrtimer Rust API is based on the intrusive style pattern introduced by
> the Rust workqueue API.
>
> Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
> ---
>  rust/kernel/time.rs         |   2 +
>  rust/kernel/time/hrtimer.rs | 312 ++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 314 insertions(+)
>
> diff --git a/rust/kernel/time.rs b/rust/kernel/time.rs
> index 87e47f2f5618d..2cf365cfb412e 100644
> --- a/rust/kernel/time.rs
> +++ b/rust/kernel/time.rs
> @@ -10,6 +10,8 @@
>
>  use core::convert::Into;
>
> +pub mod hrtimer;
> +
>  /// The number of nanoseconds per millisecond.
>  pub const NSEC_PER_MSEC: i64 = bindings::NSEC_PER_MSEC as i64;
>
> diff --git a/rust/kernel/time/hrtimer.rs b/rust/kernel/time/hrtimer.rs
> new file mode 100644
> index 0000000000000..a6332924efabd
> --- /dev/null
> +++ b/rust/kernel/time/hrtimer.rs
> @@ -0,0 +1,312 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +//! Intrusive high resolution timers.
> +//!
> +//! Allows running timer callbacks without doing allocations at the time of
> +//! starting the timer. For now, only one timer per type is allowed.
> +//!
> +//! # Vocabulary
> +//!
> +//! States:
> +//!
> +//! * Stopped
> +//! * Running
> +//!
> +//! Operations:
> +//!
> +//! * Start
> +//! * Cancel
> +//! * Stop
> +//! * Restart
> +//!
> +//! Events:
> +//!
> +//! * Expire
> +//!
> +//! ## State Diagram
> +//!
> +//! ```text
> +//!                  <-- Stop ----
> +//!                  <-- Cancel --
> +//!                  --- Start -->
> +//!        +---------+        +---------+
> +//!   O--->| Stopped |        | Running |---o
> +//!        +---------+        +---------+   |
> +//!                                  ^      |
> +//!                  <- Expire --    |      |
> +//!                                  o------o
> +//!                                   Restart
> +//! ```
> +//!
> +//! A timer is initialized in the **stopped** state. A stopped timer can be
> +//! **started** with an **expiry** time. After the timer is started, it is
> +//! **running**. When the timer **expires**, the timer handler is executed.
> +//! After the handler has executed, the timer may be **restarted** or
> +//! **stopped**. A running timer can be **canceled** before it's handler is

"it's" = it is. This should be "its" (possessive).

Just to be clear, after the handler has executed and before the timer
has been **restarted** or **stopped** the timer is still in the
**running** state?


> +//! executed. A timer that is cancelled enters the **stopped** state.
> +//!
> +
> +use crate::{init::PinInit, prelude::*, time::Ktime, types::Opaque};
> +use core::marker::PhantomData;
> +
> +/// A timer backed by a C `struct hrtimer`.
> +///
> +/// # Invariants
> +///
> +/// * `self.timer` is initialized by `bindings::hrtimer_setup`.
> +#[pin_data]
> +#[repr(C)]
> +pub struct HrTimer<T> {
> +    #[pin]
> +    timer: Opaque<bindings::hrtimer>,
> +    _t: PhantomData<T>,
> +}
> +
> +// SAFETY: Ownership of an `HrTimer` can be moved to other threads and
> +// used/dropped from there.
> +unsafe impl<T> Send for HrTimer<T> {}
> +
> +// SAFETY: Timer operations are locked on C side, so it is safe to operate on a
> +// timer from multiple threads
> +unsafe impl<T> Sync for HrTimer<T> {}
> +
> +impl<T> HrTimer<T> {
> +    /// Return an initializer for a new timer instance.
> +    pub fn new() -> impl PinInit<Self>
> +    where
> +        T: HrTimerCallback,
> +    {
> +        pin_init!(Self {
> +            // INVARIANTS: We initialize `timer` with `hrtimer_setup` below.
> +            timer <- Opaque::ffi_init(move |place: *mut bindings::hrtimer| {
> +                // SAFETY: By design of `pin_init!`, `place` is a pointer to a
> +                // live allocation. hrtimer_setup will initialize `place` and
> +                // does not require `place` to be initialized prior to the call.
> +                unsafe {
> +                    bindings::hrtimer_setup(
> +                        place,
> +                        Some(T::CallbackTarget::run),
> +                        bindings::CLOCK_MONOTONIC as i32,
> +                        bindings::hrtimer_mode_HRTIMER_MODE_REL,
> +                    );
> +                }
> +            }),
> +            _t: PhantomData,
> +        })
> +    }
> +
> +    /// Get a pointer to the contained `bindings::hrtimer`.
> +    ///
> +    /// # Safety
> +    ///
> +    /// `ptr` must point to a live allocation of at least the size of `Self`.
> +    unsafe fn raw_get(ptr: *const Self) -> *mut bindings::hrtimer {
> +        // SAFETY: The field projection to `timer` does not go out of bounds,
> +        // because the caller of this function promises that `ptr` points to an
> +        // allocation of at least the size of `Self`.
> +        unsafe { Opaque::raw_get(core::ptr::addr_of!((*ptr).timer)) }
> +    }

Can you help me understand why the various functions here operate on
*const Self? I understand the need to obtain a C pointer to interact
with bindings, but I don't understand why we're dealing in raw
pointers to the abstraction rather than references. This extends to
HrTimerPointer, which is intended to be implemented by *pointers to*
structs that embed `HrTimer`; why isn't it implemented on by the
embedder itself?

I realize we discussed this on v6, sorry for not keeping up there.

> +
> +    /// Cancel an initialized and potentially running timer.
> +    ///
> +    /// If the timer handler is running, this will block until the handler is
> +    /// finished.
> +    ///
> +    /// Users of the `HrTimer` API would not usually call this method directly.
> +    /// Instead they would use the safe `cancel` method on the [`HrTimerHandle`]
> +    /// returned when the timer was started.
> +    ///
> +    /// # Safety
> +    ///
> +    /// `self_ptr` must point to a valid `Self`.
> +    #[allow(dead_code)]
> +    pub(crate) unsafe fn raw_cancel(self_ptr: *const Self) -> bool {
> +        // SAFETY: timer_ptr points to an allocation of at least `HrTimer` size.
> +        let c_timer_ptr = unsafe { HrTimer::raw_get(self_ptr) };
> +
> +        // If the handler is running, this will wait for the handler to finish
> +        // before returning.
> +        // SAFETY: `c_timer_ptr` is initialized and valid. Synchronization is
> +        // handled on C side.
> +        unsafe { bindings::hrtimer_cancel(c_timer_ptr) != 0 }
> +    }
> +}
> +
> +/// Implemented by pointer types that point to structs that embed a [`HrTimer`].
> +///
> +/// Target (pointee) must be [`Sync`] because timer callbacks happen in another
> +/// thread of execution (hard or soft interrupt context).
> +///
> +/// Starting a timer returns a [`HrTimerHandle`] that can be used to manipulate
> +/// the timer. Note that it is OK to call the start function repeatedly, and
> +/// that more than one [`HrTimerHandle`] associated with a [`HrTimerPointer`] may
> +/// exist. A timer can be manipulated through any of the handles, and a handle
> +/// may represent a cancelled timer.
> +pub trait HrTimerPointer: Sync + Sized {
> +    /// A handle representing a started or restarted timer.
> +    ///
> +    /// If the timer is running or if the timer callback is executing when the
> +    /// handle is dropped, the drop method of [`HrTimerHandle`] should not return
> +    /// until the timer is stopped and the callback has completed.
> +    ///
> +    /// Note: When implementing this trait, consider that it is not unsafe to
> +    /// leak the handle.
> +    type TimerHandle: HrTimerHandle;
> +
> +    /// Start the timer with expiry after `expires` time units. If the timer was
> +    /// already running, it is restarted with the new expiry time.
> +    fn start(self, expires: Ktime) -> Self::TimerHandle;
> +}
> +
> +/// 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.
> +pub trait RawHrTimerCallback {
> +    /// Callback to be called from C when timer fires.
> +    ///
> +    /// # Safety
> +    ///
> +    /// Only to be called by C code in `hrtimer` subsystem. `ptr` must point to
> +    /// the `bindings::hrtimer` structure that was used to start the timer.
> +    unsafe extern "C" fn run(ptr: *mut bindings::hrtimer) -> bindings::hrtimer_restart;
> +}
> +
> +/// Implemented by structs that can be the target of a timer callback.
> +pub trait HrTimerCallback {
> +    /// The type whose [`RawHrTimerCallback::run`] method will be invoked when
> +    /// the timer expires.
> +    type CallbackTarget<'a>: RawHrTimerCallback;
> +
> +    /// This type is passed to the timer callback function. It may be a borrow
> +    /// of [`Self::CallbackTarget`], or it may be `Self::CallbackTarget` if the
> +    /// implementation can guarantee exclusive access to the target during timer
> +    /// handler execution.
> +    type CallbackTargetParameter<'a>;
> +
> +    /// Called by the timer logic when the timer fires.
> +    fn run(this: Self::CallbackTargetParameter<'_>)
> +    where
> +        Self: Sized;
> +}
> +
> +/// A handle representing a potentially running timer.
> +///
> +/// More than one handle representing the same timer might exist.
> +///
> +/// # Safety
> +///
> +/// When dropped, the timer represented by this handle must be cancelled, if it
> +/// is running. If the timer handler is running when the handle is dropped, the
> +/// drop method must wait for the handler to finish before returning.

Between this comment and the comment on cancel we say "if it is
running" 3 times. Can we say it just once, on the method, and here say
that cancel must be called in Drop?

> +pub unsafe trait HrTimerHandle {
> +    /// Cancel the timer, if it is running. If the timer handler is running, block
> +    /// till the handler has finished.
> +    fn cancel(&mut self) -> bool;
> +}
> +
> +/// Implemented by structs that contain timer nodes.
> +///
> +/// Clients of the timer API would usually safely implement this trait by using
> +/// the [`crate::impl_has_hr_timer`] macro.
> +///
> +/// # Safety
> +///
> +/// Implementers of this trait must ensure that the implementer has a [`HrTimer`]
> +/// field at the offset specified by `OFFSET` and that all trait methods are
> +/// implemented according to their documentation.
> +///
> +/// [`impl_has_timer`]: crate::impl_has_timer
> +pub unsafe trait HasHrTimer<T> {
> +    /// Offset of the [`HrTimer`] field within `Self`
> +    const OFFSET: usize;

Does this need to be part of the trait? As an alternative the provided
methods could be generated in the macro below and reduce the
opportunity to implement this trait incorrectly.

> +
> +    /// Return a pointer to the [`HrTimer`] within `Self`.
> +    ///
> +    /// # Safety
> +    ///
> +    /// `ptr` must point to a valid struct of type `Self`.
> +    unsafe fn raw_get_timer(ptr: *const Self) -> *const HrTimer<T> {
> +        // SAFETY: By the safety requirement of this trait, the trait
> +        // implementor will have a `HrTimer` field at the specified offset.
> +        unsafe { ptr.cast::<u8>().add(Self::OFFSET).cast::<HrTimer<T>>() }
> +    }
> +
> +    /// Return a pointer to the struct that is embedding the [`HrTimer`] pointed
> +    /// to by `ptr`.
> +    ///
> +    /// # Safety
> +    ///
> +    /// `ptr` must point to a [`HrTimer<T>`] field in a struct of type `Self`.
> +    unsafe fn timer_container_of(ptr: *mut HrTimer<T>) -> *mut Self
> +    where
> +        Self: Sized,
> +    {
> +        // SAFETY: By the safety requirement of this function and the `HasHrTimer`
> +        // trait, the following expression will yield a pointer to the `Self`
> +        // containing the timer addressed by `ptr`.
> +        unsafe { ptr.cast::<u8>().sub(Self::OFFSET).cast::<Self>() }
> +    }
> +
> +    /// Get pointer to embedded `bindings::hrtimer` struct.
> +    ///
> +    /// # Safety
> +    ///
> +    /// `self_ptr` must point to a valid `Self`.
> +    unsafe fn c_timer_ptr(self_ptr: *const Self) -> *const bindings::hrtimer {
> +        // SAFETY: `self_ptr` is a valid pointer to a `Self`.
> +        let timer_ptr = unsafe { Self::raw_get_timer(self_ptr) };
> +
> +        // SAFETY: timer_ptr points to an allocation of at least `HrTimer` size.
> +        unsafe { HrTimer::raw_get(timer_ptr) }
> +    }
> +
> +    /// Start the timer contained in the `Self` pointed to by `self_ptr`. If
> +    /// it is already running it is removed and inserted.
> +    ///
> +    /// # Safety
> +    ///
> +    /// `self_ptr` must point to a valid `Self`.
> +    unsafe fn start(self_ptr: *const Self, expires: Ktime) {
> +        // SAFETY: By function safety requirement, `self_ptr`is a valid `Self`.
> +        unsafe {
> +            bindings::hrtimer_start_range_ns(
> +                Self::c_timer_ptr(self_ptr).cast_mut(),
> +                expires.to_ns(),
> +                0,
> +                bindings::hrtimer_mode_HRTIMER_MODE_REL,
> +            );
> +        }
> +    }
> +}
> +
> +/// Use to implement the [`HasHrTimer<T>`] trait.
> +///
> +/// See [`module`] documentation for an example.
> +///
> +/// [`module`]: crate::time::hrtimer
> +#[macro_export]
> +macro_rules! impl_has_hr_timer {
> +    (
> +        impl$({$($generics:tt)*})?
> +            HasHrTimer<$timer_type:ty>
> +            for $self:ty
> +        { self.$field:ident }
> +        $($rest:tt)*
> +    ) => {
> +        // SAFETY: This implementation of `raw_get_timer` only compiles if the
> +        // field has the right type.
> +        unsafe impl$(<$($generics)*>)? $crate::time::hrtimer::HasHrTimer<$timer_type> for $self {
> +            const OFFSET: usize = ::core::mem::offset_of!(Self, $field) as usize;
> +
> +            #[inline]
> +            unsafe fn raw_get_timer(ptr: *const Self) ->
> +                *const $crate::time::hrtimer::HrTimer<$timer_type>
> +            {
> +                // SAFETY: The caller promises that the pointer is not dangling.
> +                unsafe {
> +                    ::core::ptr::addr_of!((*ptr).$field)
> +                }
> +            }
> +        }
> +    }
> +}
>
> --
> 2.47.0
>
>

Re: [PATCH v8 00/14] hrtimer Rust API

[Frederic Weisbecker]

Le Wed, Feb 19, 2025 at 12:02:50PM +0100, Andreas Hindborg a écrit :
> "Andreas Hindborg" <a.hindborg@kernel.org> writes:
> 
> > This series adds support for using the `hrtimer` subsystem from Rust code.
> >
> > The series adds support for timer mode and clock source configuration during
> > timer initialization. Examples and functionality to execute closures at timer
> > expiration has been removed, as these depend on either atomics [3] or
> > `SpinLockIrq` [4], which are still being worked on.
> >
> > This series is a dependency for unmerged features of the Rust null block driver
> > [1], and for rkvms [2].
> >
> 
> @ timer subsystem maintainers: did you discuss how you want to set up
> maintenance for this yet? As mentioned, I'm happy stepping up to
> maintain this, but if you want to handle it with existing resources that
> is perfectly fine as well.

You're the best candidate to maintain this code since you wrote it :-)

Also I personally have near zero skills in Rust as of today so all I can do
is to vaguely keep an eye on the binding's interface and keep in touch
with the changes.

So I suggest you to add a new entry with you as a maintainer (I suggested
something similar to Fujita for some other timer related things) but please
keep us Cc'ed for future changes.

> I was hoping we could merge the patches in the near future. The patches
> have been on list for quite a while now, and I am happy with the shape
> of them. They are in my critical path for merging dependent code in the
> rust null block driver.
> 
> Let me know if there is anything I can do to help move the process
> forward.

Let me have a last look...

Thanks.


> 
> 
> Best regards,
> Andreas Hindborg
> 
> 
> 
> 

Re: [PATCH v8 02/14] rust: hrtimer: introduce hrtimer support

[Andreas Hindborg]

"Tamir Duberstein" <tamird@gmail.com> writes:

> On Tue, Feb 18, 2025 at 8:29 AM Andreas Hindborg <a.hindborg@kernel.org> wrote:
>>

[...]

>> +//! ## State Diagram
>> +//!
>> +//! ```text
>> +//!                  <-- Stop ----
>> +//!                  <-- Cancel --
>> +//!                  --- Start -->
>> +//!        +---------+        +---------+
>> +//!   O--->| Stopped |        | Running |---o
>> +//!        +---------+        +---------+   |
>> +//!                                  ^      |
>> +//!                  <- Expire --    |      |
>> +//!                                  o------o
>> +//!                                   Restart
>> +//! ```
>> +//!
>> +//! A timer is initialized in the **stopped** state. A stopped timer can be
>> +//! **started** with an **expiry** time. After the timer is started, it is
>> +//! **running**. When the timer **expires**, the timer handler is executed.
>> +//! After the handler has executed, the timer may be **restarted** or
>> +//! **stopped**. A running timer can be **canceled** before it's handler is
>
> "it's" = it is. This should be "its" (possessive).

Thanks 👍

> Just to be clear, after the handler has executed and before the timer
> has been **restarted** or **stopped** the timer is still in the
> **running** state?

It depends on the return value of the handler. If the handler returns restart,
the timer the timer does not enter the stopped state. If the handler
returns stop, the timer enters the stopped state.

The timer is still considered to be in running state the handler is
running.

I can add this info to the section.

>
>
>> +//! executed. A timer that is cancelled enters the **stopped** state.
>> +//!
>> +
>> +use crate::{init::PinInit, prelude::*, time::Ktime, types::Opaque};
>> +use core::marker::PhantomData;
>> +
>> +/// A timer backed by a C `struct hrtimer`.
>> +///
>> +/// # Invariants
>> +///
>> +/// * `self.timer` is initialized by `bindings::hrtimer_setup`.
>> +#[pin_data]
>> +#[repr(C)]
>> +pub struct HrTimer<T> {
>> +    #[pin]
>> +    timer: Opaque<bindings::hrtimer>,
>> +    _t: PhantomData<T>,
>> +}
>> +
>> +// SAFETY: Ownership of an `HrTimer` can be moved to other threads and
>> +// used/dropped from there.
>> +unsafe impl<T> Send for HrTimer<T> {}
>> +
>> +// SAFETY: Timer operations are locked on C side, so it is safe to operate on a
>> +// timer from multiple threads
>> +unsafe impl<T> Sync for HrTimer<T> {}
>> +
>> +impl<T> HrTimer<T> {
>> +    /// Return an initializer for a new timer instance.
>> +    pub fn new() -> impl PinInit<Self>
>> +    where
>> +        T: HrTimerCallback,
>> +    {
>> +        pin_init!(Self {
>> +            // INVARIANTS: We initialize `timer` with `hrtimer_setup` below.
>> +            timer <- Opaque::ffi_init(move |place: *mut bindings::hrtimer| {
>> +                // SAFETY: By design of `pin_init!`, `place` is a pointer to a
>> +                // live allocation. hrtimer_setup will initialize `place` and
>> +                // does not require `place` to be initialized prior to the call.
>> +                unsafe {
>> +                    bindings::hrtimer_setup(
>> +                        place,
>> +                        Some(T::CallbackTarget::run),
>> +                        bindings::CLOCK_MONOTONIC as i32,
>> +                        bindings::hrtimer_mode_HRTIMER_MODE_REL,
>> +                    );
>> +                }
>> +            }),
>> +            _t: PhantomData,
>> +        })
>> +    }
>> +
>> +    /// Get a pointer to the contained `bindings::hrtimer`.
>> +    ///
>> +    /// # Safety
>> +    ///
>> +    /// `ptr` must point to a live allocation of at least the size of `Self`.
>> +    unsafe fn raw_get(ptr: *const Self) -> *mut bindings::hrtimer {
>> +        // SAFETY: The field projection to `timer` does not go out of bounds,
>> +        // because the caller of this function promises that `ptr` points to an
>> +        // allocation of at least the size of `Self`.
>> +        unsafe { Opaque::raw_get(core::ptr::addr_of!((*ptr).timer)) }
>> +    }
>
> Can you help me understand why the various functions here operate on
> *const Self? I understand the need to obtain a C pointer to interact
> with bindings, but I don't understand why we're dealing in raw
> pointers to the abstraction rather than references.

We cannot reference the `bindings::hrtimer` without wrapping it in
`Opaque`. This would be the primary reason. At other times, we cannot
produce references because we might not be able to prove that we satisfy
the safety requirements for turning a pointer into a reference. If we
are just doing offset arithmetic anyway, we don't need a reference.


> This extends to
> HrTimerPointer, which is intended to be implemented by *pointers to*
> structs that embed `HrTimer`; why isn't it implemented on by the
> embedder itself?

Not sure what you mean here. If you refer to for instance the
implementation of `HrTimerPointer for Arc<T>`, I get why you might
wonder, why does `HasHrTimer::start` not take a reference instead of a
pointer? We could do that, but we would just immediately break it down
again in the implementation of `HasHrTimer::start`. Might still be a
good idea though.

>
> I realize we discussed this on v6, sorry for not keeping up there.

No worries, it is good that we discuss this.

[...]

>> +
>> +/// A handle representing a potentially running timer.
>> +///
>> +/// More than one handle representing the same timer might exist.
>> +///
>> +/// # Safety
>> +///
>> +/// When dropped, the timer represented by this handle must be cancelled, if it
>> +/// is running. If the timer handler is running when the handle is dropped, the
>> +/// drop method must wait for the handler to finish before returning.
>
> Between this comment and the comment on cancel we say "if it is
> running" 3 times. Can we say it just once, on the method, and here say
> that cancel must be called in Drop?

Well, the comment on `cancel` is just a description of what the function
does. This piece of text is a safety requirement.

We could make the safety requirement for implementing the trait "Implement
the methods according to their documentation". But that would not help with
the drop requirement.

>
>> +pub unsafe trait HrTimerHandle {
>> +    /// Cancel the timer, if it is running. If the timer handler is running, block
>> +    /// till the handler has finished.
>> +    fn cancel(&mut self) -> bool;
>> +}
>> +
>> +/// Implemented by structs that contain timer nodes.
>> +///
>> +/// Clients of the timer API would usually safely implement this trait by using
>> +/// the [`crate::impl_has_hr_timer`] macro.
>> +///
>> +/// # Safety
>> +///
>> +/// Implementers of this trait must ensure that the implementer has a [`HrTimer`]
>> +/// field at the offset specified by `OFFSET` and that all trait methods are
>> +/// implemented according to their documentation.
>> +///
>> +/// [`impl_has_timer`]: crate::impl_has_timer
>> +pub unsafe trait HasHrTimer<T> {
>> +    /// Offset of the [`HrTimer`] field within `Self`
>> +    const OFFSET: usize;
>
> Does this need to be part of the trait? As an alternative the provided
> methods could be generated in the macro below and reduce the
> opportunity to implement this trait incorrectly.

There is no risk of implementing the trait wrong, because it is usually
derived by a macro.

We need at least one of the methods to be able to have the type system
verify that the type for which we implement `HasHrTImer` actually has a
field with the name we specify, and that this field has the right type.
And to have that, we need the OFFSET.



Best regards,
Andreas Hindborg

Re: [PATCH v8 02/14] rust: hrtimer: introduce hrtimer support

[Tamir Duberstein]

On Thu, Feb 20, 2025 at 4:19 PM Andreas Hindborg <a.hindborg@kernel.org> wrote:
>
> "Tamir Duberstein" <tamird@gmail.com> writes:
>
> > On Tue, Feb 18, 2025 at 8:29 AM Andreas Hindborg <a.hindborg@kernel.org> wrote:
> >>
>
> [...]
>
> >> +//! ## State Diagram
> >> +//!
> >> +//! ```text
> >> +//!                  <-- Stop ----
> >> +//!                  <-- Cancel --
> >> +//!                  --- Start -->
> >> +//!        +---------+        +---------+
> >> +//!   O--->| Stopped |        | Running |---o
> >> +//!        +---------+        +---------+   |
> >> +//!                                  ^      |
> >> +//!                  <- Expire --    |      |
> >> +//!                                  o------o
> >> +//!                                   Restart
> >> +//! ```
> >> +//!
> >> +//! A timer is initialized in the **stopped** state. A stopped timer can be
> >> +//! **started** with an **expiry** time. After the timer is started, it is
> >> +//! **running**. When the timer **expires**, the timer handler is executed.
> >> +//! After the handler has executed, the timer may be **restarted** or
> >> +//! **stopped**. A running timer can be **canceled** before it's handler is
> >
> > "it's" = it is. This should be "its" (possessive).
>
> Thanks 👍
>
> > Just to be clear, after the handler has executed and before the timer
> > has been **restarted** or **stopped** the timer is still in the
> > **running** state?
>
> It depends on the return value of the handler. If the handler returns restart,
> the timer the timer does not enter the stopped state. If the handler
> returns stop, the timer enters the stopped state.
>
> The timer is still considered to be in running state the handler is
> running.
>
> I can add this info to the section.

Yeah, some clarification here would be useful.

> >
> >
> >> +//! executed. A timer that is cancelled enters the **stopped** state.
> >> +//!
> >> +
> >> +use crate::{init::PinInit, prelude::*, time::Ktime, types::Opaque};
> >> +use core::marker::PhantomData;
> >> +
> >> +/// A timer backed by a C `struct hrtimer`.
> >> +///
> >> +/// # Invariants
> >> +///
> >> +/// * `self.timer` is initialized by `bindings::hrtimer_setup`.
> >> +#[pin_data]
> >> +#[repr(C)]
> >> +pub struct HrTimer<T> {
> >> +    #[pin]
> >> +    timer: Opaque<bindings::hrtimer>,
> >> +    _t: PhantomData<T>,
> >> +}
> >> +
> >> +// SAFETY: Ownership of an `HrTimer` can be moved to other threads and
> >> +// used/dropped from there.
> >> +unsafe impl<T> Send for HrTimer<T> {}
> >> +
> >> +// SAFETY: Timer operations are locked on C side, so it is safe to operate on a
> >> +// timer from multiple threads
> >> +unsafe impl<T> Sync for HrTimer<T> {}
> >> +
> >> +impl<T> HrTimer<T> {
> >> +    /// Return an initializer for a new timer instance.
> >> +    pub fn new() -> impl PinInit<Self>
> >> +    where
> >> +        T: HrTimerCallback,
> >> +    {
> >> +        pin_init!(Self {
> >> +            // INVARIANTS: We initialize `timer` with `hrtimer_setup` below.
> >> +            timer <- Opaque::ffi_init(move |place: *mut bindings::hrtimer| {
> >> +                // SAFETY: By design of `pin_init!`, `place` is a pointer to a
> >> +                // live allocation. hrtimer_setup will initialize `place` and
> >> +                // does not require `place` to be initialized prior to the call.
> >> +                unsafe {
> >> +                    bindings::hrtimer_setup(
> >> +                        place,
> >> +                        Some(T::CallbackTarget::run),
> >> +                        bindings::CLOCK_MONOTONIC as i32,
> >> +                        bindings::hrtimer_mode_HRTIMER_MODE_REL,
> >> +                    );
> >> +                }
> >> +            }),
> >> +            _t: PhantomData,
> >> +        })
> >> +    }
> >> +
> >> +    /// Get a pointer to the contained `bindings::hrtimer`.
> >> +    ///
> >> +    /// # Safety
> >> +    ///
> >> +    /// `ptr` must point to a live allocation of at least the size of `Self`.
> >> +    unsafe fn raw_get(ptr: *const Self) -> *mut bindings::hrtimer {
> >> +        // SAFETY: The field projection to `timer` does not go out of bounds,
> >> +        // because the caller of this function promises that `ptr` points to an
> >> +        // allocation of at least the size of `Self`.
> >> +        unsafe { Opaque::raw_get(core::ptr::addr_of!((*ptr).timer)) }
> >> +    }
> >
> > Can you help me understand why the various functions here operate on
> > *const Self? I understand the need to obtain a C pointer to interact
> > with bindings, but I don't understand why we're dealing in raw
> > pointers to the abstraction rather than references.
>
> We cannot reference the `bindings::hrtimer` without wrapping it in
> `Opaque`. This would be the primary reason. At other times, we cannot
> produce references because we might not be able to prove that we satisfy
> the safety requirements for turning a pointer into a reference. If we
> are just doing offset arithmetic anyway, we don't need a reference.

Why do we have a pointer, rather than a reference, to Self in the
first place? I think this is the key thing I don't understand.

>
>
> > This extends to
> > HrTimerPointer, which is intended to be implemented by *pointers to*
> > structs that embed `HrTimer`; why isn't it implemented on by the
> > embedder itself?
>
> Not sure what you mean here. If you refer to for instance the
> implementation of `HrTimerPointer for Arc<T>`, I get why you might
> wonder, why does `HasHrTimer::start` not take a reference instead of a
> pointer? We could do that, but we would just immediately break it down
> again in the implementation of `HasHrTimer::start`. Might still be a
> good idea though.

I was trying to say that my question (which I clarified above,
hopefully) extends to the description and name of this trait.
Specifically for this trait I don't understand why its semantics are
described in terms of pointers rather than references (and