linux-kernel - Re: [PATCH v5 7/7] rust: hrtimer: Add forward_now() to HrTimer and HrTimerCallbackContext

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Message-ID: <87jz5aa9fm.fsf@kernel.org>
Date: Tue, 17 Jun 2025 13:34:21 +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 7/7] rust: hrtimer: Add forward_now() to HrTimer and
 HrTimerCallbackContext

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

> Using the HrTimer::raw_time_cb() function, we can now add an equivalent to

You called it `raw_cb_time`.

> hrtimer_forward_now() to both HrTimer and HrTimerCallbackContext.
>
> Signed-off-by: Lyude Paul <lyude@...hat.com>
>
> ---
> V2:
> * Change from Ktime to Delta
> * Make sure that forward_now() takes a mutable reference to the timer
>   struct
> * Reword this to point out that we're adding forward_now() to both callback
>   context and mutable timer reference
> * Rename interval to duration
>
> V4:
> * Fix rust documentation for HrTimerCallbackContext (forgot to update both
>   forward_now() declarations)
> * Use Pin<&mut Self> for context-less forward.
>
> Signed-off-by: Lyude Paul <lyude@...hat.com>
> ---
>  rust/kernel/time/hrtimer.rs | 58 ++++++++++++++++++++++++++++++++++++-
>  1 file changed, 57 insertions(+), 1 deletion(-)
>
> diff --git a/rust/kernel/time/hrtimer.rs b/rust/kernel/time/hrtimer.rs
> index 79d86e1099a1e..0908359b0550a 100644
> --- a/rust/kernel/time/hrtimer.rs
> +++ b/rust/kernel/time/hrtimer.rs
> @@ -201,7 +201,6 @@ unsafe fn raw_forward(self_ptr: *mut Self, now: HrTimerInstant<T>, interval: Del
>      /// - The caller must ensure that the `hrtimer_clock_base` cannot possibly change in the context
>      ///   this function is being called in. This means either exclusive access to `self_ptr` is
>      ///   required, or we must be from within the timer callback context of `self_ptr`.
> -    #[expect(unused)]
>      unsafe fn raw_cb_time(self_ptr: *const Self) -> HrTimerInstant<T>
>      where
>          T: HasHrTimer<T>,
> @@ -243,6 +242,44 @@ pub fn forward(self: Pin<&mut Self>, now: HrTimerInstant<T>, interval: Delta) ->
>          //   exclusive access to it - fulfilling the requirements of the C API.
>          unsafe { Self::raw_forward(self.get_unchecked_mut(), now, interval) }
>      }
> +
> +    /// Conditionally forward the timer.
> +    ///
> +    /// This is a variant of [`forward()`](Self::forward) that uses an interval after the current
> +    /// time of the base clock for the [`HrTimer`].
> +    pub fn forward_now(self: Pin<&mut Self>, interval: Delta) -> u64
> +    where
> +        T: HasHrTimer<T>,
> +    {
> +        // SAFETY: `self` is a mutable reference, guaranteeing it is both a valid pointer to Self
> +        // and that we also have exclusive access to `self`.
> +        let now = unsafe { Self::raw_cb_time(&*self.as_ref()) };
> +
> +        self.forward(now, interval)
> +    }
> +
> +    /// Return the time expiry for this [`HrTimer`].
> +    ///
> +    /// This value should only be used as a snapshot, as the actual expiry time could change after
> +    /// this function is called.
> +    pub fn expires(&self) -> HrTimerInstant<T>

Commit message does not mention this method.


Best regards,
Andreas Hindborg