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

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Message-Id: <20250614.105841.879936495340347805.fujita.tomonori@gmail.com>
Date: Sat, 14 Jun 2025 10:58:41 +0900 (JST)
From: FUJITA Tomonori <fujita.tomonori@...il.com>
To: lyude@...hat.com
Cc: rust-for-linux@...r.kernel.org, a.hindborg@...nel.org,
 linux-kernel@...r.kernel.org, boqun.feng@...il.com,
 fujita.tomonori@...il.com, frederic@...nel.org, tglx@...utronix.de,
 anna-maria@...utronix.de, jstultz@...gle.com, sboyd@...nel.org,
 ojeda@...nel.org, alex.gaynor@...il.com, gary@...yguo.net,
 bjorn3_gh@...tonmail.com, lossin@...nel.org, aliceryhl@...gle.com,
 tmgross@...ch.edu, dakr@...nel.org
Subject: Re: [PATCH v5 7/7] rust: hrtimer: Add forward_now() to HrTimer and
 HrTimerCallbackContext

On Fri, 13 Jun 2025 19:22:28 -0400
Lyude Paul <lyude@...hat.com> wrote:

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

To the current time of the clock for the hrtimer, would it be possible
to write it like the following instead?

let now: Instant<<T::TimerMode as HrTimerMode>::Clock> = Instant::now();

Then we can drop #5 and #6 patches and remove some unsafe code.


By the way, where can I find the latest rvkms code that uses this
patchset?