linux-kernel - Re: [PATCH v5 3/7] rust: hrtimer: Add HrTimer::raw

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Message-ID: <875xgubpat.fsf@kernel.org>
Date: Tue, 17 Jun 2025 13:06:18 +0200
From: Andreas Hindborg <a.hindborg@...nel.org>
To: "Lyude Paul" <lyude@...hat.com>
Cc: <rust-for-linux@...r.kernel.org>,  <linux-kernel@...r.kernel.org>,
  "Boqun Feng" <boqun.feng@...il.com>,  "FUJITA Tomonori"
 <fujita.tomonori@...il.com>,  "Frederic Weisbecker" <frederic@...nel.org>,
  "Thomas Gleixner" <tglx@...utronix.de>,  "Anna-Maria Behnsen"
 <anna-maria@...utronix.de>,  "John Stultz" <jstultz@...gle.com>,  "Stephen
 Boyd" <sboyd@...nel.org>,  "Miguel Ojeda" <ojeda@...nel.org>,  "Alex
 Gaynor" <alex.gaynor@...il.com>,  "Gary Guo" <gary@...yguo.net>,
  Björn
 Roy Baron <bjorn3_gh@...tonmail.com>,  "Benno Lossin" <lossin@...nel.org>,
  "Alice Ryhl" <aliceryhl@...gle.com>,  "Trevor Gross" <tmgross@...ch.edu>,
  "Danilo Krummrich" <dakr@...nel.org>
Subject: Re: [PATCH v5 3/7] rust: hrtimer: Add HrTimer::raw_forward() and
 forward()

"Lyude Paul" <lyude@...hat.com> writes:

> Within the hrtimer API there are quite a number of functions that can only
> be safely called from one of two contexts:
>
> * When we have exclusive access to the hrtimer and the timer is not active.
> * When we're within the hrtimer's callback context as it is being executed.
>
> This commit adds bindings for hrtimer_forward() for the first such context,
> along with HrTimer::raw_forward() for later use in implementing the
> hrtimer_forward() in the latter context.
>
> Signed-off-by: Lyude Paul <lyude@...hat.com>
>
> ---
> V4:
> * Fix the safety contract for raw_forward()
> * Require Pin<&mut Self>, not &mut self
> * Drop incorrect UniquePin example
> * Rewrite documentation a bit (re: Andreas)
>
> Signed-off-by: Lyude Paul <lyude@...hat.com>
> ---
>  rust/kernel/time/hrtimer.rs | 48 +++++++++++++++++++++++++++++++++++++
>  1 file changed, 48 insertions(+)
>
> diff --git a/rust/kernel/time/hrtimer.rs b/rust/kernel/time/hrtimer.rs
> index c775d7abdf5ce..6fdd54e3328c5 100644
> --- a/rust/kernel/time/hrtimer.rs
> +++ b/rust/kernel/time/hrtimer.rs
> @@ -168,6 +168,54 @@ pub(crate) unsafe fn raw_cancel(this: *const Self) -> bool {
>          // handled on the C side.
>          unsafe { bindings::hrtimer_cancel(c_timer_ptr) != 0 }
>      }
> +
> +    /// Forward the timer expiry for a given timer pointer.
> +    ///
> +    /// # Safety
> +    ///
> +    /// - `self_ptr` must point to a valid `Self`.
> +    /// - The caller must either have exclusive access to the data pointed at by `self_ptr`, or be
> +    ///   within the context of the timer callback.
> +    #[inline]
> +    unsafe fn raw_forward(self_ptr: *mut Self, now: HrTimerInstant<T>, interval: Delta) -> u64
> +    where
> +        T: HasHrTimer<T>,
> +    {
> +        // SAFETY:
> +        // * The C API requirements for this function are fulfilled by our safety contract.
> +        // * `self_ptr` is guaranteed to point to a valid `Self` via our safety contract
> +        unsafe {
> +            bindings::hrtimer_forward(
> +                Self::raw_get(self_ptr),
> +                now.into_nanos(),
> +                interval.into_nanos(),
> +            )
> +        }
> +    }
> +
> +    /// Conditionally forward the timer.
> +    ///
> +    /// If the timer expires after `now`, this function does nothing and returns 0. If the timer
> +    /// expired at or before `now`, this function forwards the timer by `interval` until the timer
> +    /// expires after `now` and then returns the number of times the timer was forwarded by
> +    /// `interval`.
> +    ///
> +    /// This function is mainly useful for timer types which can provide exclusive access to the
> +    /// timer when the timer is not running. For forwarding the timer from within the timer callback
> +    /// context, see [`HrTimerCallbackContext::forward()`].

I think rustdoc is going to complain about this link being broken. Can
you add the last sentence when add the target of the link?


Best regards,
Andreas Hindborg