linux-kernel - Re: [PATCH v2 4/8] rust: hrtimer: Add HrTimerClockBase

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Message-ID: <87y0vrkqrc.fsf@kernel.org>
Date: Wed, 23 Apr 2025 14:27:57 +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>,  =?utf-8?Q?Bj=C3=B6rn?= Roy Baron
 <bjorn3_gh@...tonmail.com>,
  Benno Lossin <benno.lossin@...ton.me>,  Alice Ryhl
 <aliceryhl@...gle.com>,  Trevor Gross <tmgross@...ch.edu>,  Danilo
 Krummrich <dakr@...nel.org>
Subject: Re: [PATCH v2 4/8] rust: hrtimer: Add HrTimerClockBase

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

> This adds a simple wrapper for the hrtimer_clock_base struct, which can be
> obtained from a HrTimerCallbackContext. We'll use this in the next commit to
> add a function to acquire the current time for the base clock driving a
> hrtimer.
>
> Signed-off-by: Lyude Paul <lyude@...hat.com>
>
> ---
> V2:
> * Convert safety comment to invariant comment in from_raw()
> - Add raw_clock_base() and implement clock_base() on HrTimer<T> as well
>
> Signed-off-by: Lyude Paul <lyude@...hat.com>
> ---
>  rust/kernel/time/hrtimer.rs | 50 +++++++++++++++++++++++++++++++++++++
>  1 file changed, 50 insertions(+)
>
> diff --git a/rust/kernel/time/hrtimer.rs b/rust/kernel/time/hrtimer.rs
> index 507fff67f8ab2..a56c66104f692 100644
> --- a/rust/kernel/time/hrtimer.rs
> +++ b/rust/kernel/time/hrtimer.rs
> @@ -183,6 +183,25 @@ unsafe fn raw_forward(self_ptr: *mut Self, now: Instant, interval: Delta) -> u64
>          }
>      }
>  
> +    /// Retrieve the [`HrTimerClockBase`] for a given timer pointer.
> +    ///
> +    /// # Safety
> +    ///
> +    /// `self_ptr` must point to a valid `Self`.
> +    unsafe fn raw_clock_base<'a>(self_ptr: *const Self) -> &'a HrTimerClockBase {
> +        // SAFETY:
> +        // - By our safety contract, `self_ptr` always points to a valid `HrTimer<T>`.
> +        // - `base` is initialized and points to a valid `hrtimer_clock_base` for as long as
> +        //   `HrTimer<T>` is exposed to users.
> +        unsafe { HrTimerClockBase::from_raw((*Self::raw_get(self_ptr)).base) }
> +    }
> +
> +    /// Retrieve the [`HrTimerClockBase`] for this [`HrTimer`].
> +    pub fn clock_base(&self) -> &HrTimerClockBase {
> +        // SAFETY: `self` is an immutable reference and thus always points to a valid `HrTimer`
> +        unsafe { Self::raw_clock_base(self) }
> +    }
> +
>      /// Forward the timer expiry so it expires at `duration` after `now`.
>      ///
>      /// This is mainly useful for timer types that can start off providing a mutable reference (e.g.
> @@ -200,6 +219,30 @@ pub fn forward(&mut self, now: Instant, duration: Delta) -> u64 {
>      }
>  }
>  
> +/// The timer base for a specific clock.
> +///

Please elaborate what a clock base is and what the use of this structure
is.

Is it the timer base for a specific clock, or the clock base for a
specific timer?


Best regards,
Andreas Hindborg