linux-kernel - Re: [PATCH v8 02/14] rust: hrtimer: introduce hrtimer support

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Message-ID: <841150db-2f92-4cfe-bb1f-29b34b4662c1@proton.me>
Date: Fri, 21 Feb 2025 11:05:49 +0000
From: Benno Lossin <benno.lossin@...ton.me>
To: Andreas Hindborg <a.hindborg@...nel.org>
Cc: Miguel Ojeda <ojeda@...nel.org>, Anna-Maria Behnsen <anna-maria@...utronix.de>, Frederic Weisbecker <frederic@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, Danilo Krummrich <dakr@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>, Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, Björn Roy Baron <bjorn3_gh@...tonmail.com>, Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>, Lyude Paul <lyude@...hat.com>, Guangbo Cui <2407018371@...com>, Dirk Behme <dirk.behme@...il.com>, Daniel Almeida <daniel.almeida@...labora.com>, Tamir Duberstein <tamird@...il.com>, rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 02/14] rust: hrtimer: introduce hrtimer support

On 21.02.25 11:15, Andreas Hindborg wrote:
> Andreas Hindborg <a.hindborg@...nel.org> writes:
> 
>> "Benno Lossin" <benno.lossin@...ton.me> writes:
>>
>>> On 18.02.25 14:27, Andreas Hindborg wrote:
>>>> +pub trait HrTimerCallback {
>>>> +    /// The type whose [`RawHrTimerCallback::run`] method will be invoked when
>>>> +    /// the timer expires.
>>>> +    type CallbackTarget<'a>: RawHrTimerCallback;
>>>> +
>>>> +    /// This type is passed to the timer callback function. It may be a borrow
>>>> +    /// of [`Self::CallbackTarget`], or it may be `Self::CallbackTarget` if the
>>>> +    /// implementation can guarantee exclusive access to the target during timer
>>>
>>> Technically "exclusive" access is correct if the `CallbackTarget` is
>>> `Pin<&Self>`, since you will get exclusive access to a `Pin<&Self>`, but
>>> it might confuse people, because there can be multiple `Pin<&Self>`. So
>>> I would just drop the word "exclusive" here.
>>
>> Yes, maybe it should be "shared or exclusive access, depending on the type"?
>>
>>>
>>>> +    /// handler execution.
>>>> +    type CallbackTargetParameter<'a>;
>>>
>>> Also why can't this type be an associated type of `HrTimerPointer`?
>>> Since this seems to always be constrained in the impls of
>>> `RawHrTimerCallback`.
>>
>> That might be a nice improvement, I'll try that out.
> 
> Looking closer at this, I don't see how to achieve this. We need access
> to the type here, because it is used in the signature of `run`.
> `HrTimerCallback` has no bounds on it, and that is nice. If we want to
> move these associated types, we have to introduce a bound here.
> 
> We need to be generic over the type of the parameter to `run`, and by
> the time the user implements this trait, the type must be known and so
> the user has to specify somehow.

I think if you put the associated type on the `RawHrTimerCallback`
trait, it should work.

---
Cheers,
Benno