linux-kernel - Re: [PATCH 3/4] rust: devres: get rid of Devres' inner Arc

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Message-Id: <DATC6682WCNQ.3JVMT7MRUA4BF@kernel.org>
Date: Sun, 22 Jun 2025 22:15:10 +0200
From: "Benno Lossin" <lossin@...nel.org>
To: "Danilo Krummrich" <dakr@...nel.org>
Cc: <gregkh@...uxfoundation.org>, <rafael@...nel.org>, <ojeda@...nel.org>,
 <alex.gaynor@...il.com>, <boqun.feng@...il.com>, <gary@...yguo.net>,
 <bjorn3_gh@...tonmail.com>, <benno.lossin@...ton.me>,
 <a.hindborg@...nel.org>, <aliceryhl@...gle.com>, <tmgross@...ch.edu>,
 <rust-for-linux@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/4] rust: devres: get rid of Devres' inner Arc

On Sun Jun 22, 2025 at 5:45 PM CEST, Danilo Krummrich wrote:
> On Sun, Jun 22, 2025 at 09:05:51AM +0200, Benno Lossin wrote:
>> On Thu Jun 12, 2025 at 4:51 PM CEST, Danilo Krummrich wrote:
>> > +    fn remove_action(&self) -> bool {
>> > +        // SAFETY:
>> > +        // - `self.dev` is a valid `Device`,
>> > +        // - the `action` and `data` pointers are the exact same ones as given to devm_add_action()
>> > +        //   previously,
>> > +        // - `self` is always valid, even if the action has been released already.
>> > +        (unsafe {
>> > +            bindings::devm_remove_action_nowarn(
>> > +                self.dev.as_raw(),
>> > +                Some(self.callback),
>> > +                self.as_ptr().cast_mut().cast(),
>> > +            )
>> > +        } == 0)
>> 
>> I don't think the parenthesis are required?
>
> At least the compiler doesn't seem to be happy about removing them:
>
> error: expected expression, found `==`
>    --> rust/kernel/devres.rs:199:11
>     |
> 199 |         } == 0
>     |           ^^ expected expression
>
> error[E0308]: mismatched types
>    --> rust/kernel/devres.rs:194:13
>     |
> 194 | /             bindings::devm_remove_action_nowarn(
> 195 | |                 self.dev.as_raw(),
> 196 | |                 Some(self.callback),
> 197 | |                 self.inner().as_ptr().cast_mut().cast(),
> 198 | |             )
>     | |             ^- help: consider using a semicolon here: `;`
>     | |_____________|
>     |               expected `()`, found `i32`
>
> error: aborting due to 2 previous errors

Huh... Do you like this better?:

    let res = unsafe {
        bindings::devm_remove_action_nowarn(
            /*
             * ...
             */
        )
    };
    res == 0

Maybe it's more readable, but I'm not sure what is more idiomatic in
this case.

---
Cheers,
Benno