linux-kernel - Re: [PATCH 2/6] rust: hrtimer: Add HrTimerCallbackContext and ::forward()

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Message-ID: <87lds993l9.fsf@kernel.org>
Date: Wed, 09 Apr 2025 09:49:38 +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>,  "Frederic Weisbecker"
 <frederic@...nel.org>,  "Thomas Gleixner" <tglx@...utronix.de>,
  "Anna-Maria Behnsen" <anna-maria@...utronix.de>,  "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" <benno.lossin@...ton.me>,  "Alice Ryhl" <aliceryhl@...gle.com>,
  "Trevor Gross" <tmgross@...ch.edu>
Subject: Re: [PATCH 2/6] rust: hrtimer: Add HrTimerCallbackContext and
 ::forward()

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

> On Tue, 2025-04-08 at 13:47 +0200, Andreas Hindborg wrote:
>> "Lyude Paul" <lyude@...hat.com> writes:
>>
>> > With Linux's hrtimer API, certain functions require we either acquire
>> > proper locking to call specific methods - or that we call said methods from
>> > the context of the timer callback. hrtimer_forward() is one of these
>> > functions, so we start by adding a new HrTimerCallbackContext type which
>> > provides a way of calling these methods that is inaccessible outside of
>> > hrtimer callbacks.
>>
>> Based on tglx comment, we should be able to call this function if the
>> timer is stopped and we have a unique ownership of the timer. Do you
>> want to add that? If not, could you add a note about this somewhere?
>
>
> Happy to! So, I think if we were to add a function for this I assume we would
> want something like this?
>
> fn forward(&mut self, now: Instant, interval: Duration) -> u64 {
>     self.cancel();
>     /* Do actual forward stuff here */
> }
>
> Of course with some documentation pointing out that this function will stop
> the timer if required.

Yes, something like that. My first thought was to check if the timer was
running and return `Err` if that is the case. But it might be more
simple to just call `cancel`. What do you think?


Best regards,
Andreas Hindborg