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Date: Sun, 22 Jun 2025 22:15:10 +0200
Message-Id: <DATC6682WCNQ.3JVMT7MRUA4BF@kernel.org>
Cc: <gregkh@linuxfoundation.org>, <rafael@kernel.org>, <ojeda@kernel.org>,
 <alex.gaynor@gmail.com>, <boqun.feng@gmail.com>, <gary@garyguo.net>,
 <bjorn3_gh@protonmail.com>, <benno.lossin@proton.me>,
 <a.hindborg@kernel.org>, <aliceryhl@google.com>, <tmgross@umich.edu>,
 <rust-for-linux@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 3/4] rust: devres: get rid of Devres' inner Arc
From: "Benno Lossin" <lossin@kernel.org>
To: "Danilo Krummrich" <dakr@kernel.org>
X-Mailer: aerc 0.20.1
References: <20250612145145.12143-1-dakr@kernel.org>
 <20250612145145.12143-4-dakr@kernel.org>
 <DASVDU1WY5RH.1VLCIQ4TIS0FP@kernel.org> <aFglHG6lK0a94SIu@pollux>
In-Reply-To: <aFglHG6lK0a94SIu@pollux>

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 rele=
ased already.
>> > +        (unsafe {
>> > +            bindings::devm_remove_action_nowarn(
>> > +                self.dev.as_raw(),
>> > +                Some(self.callback),
>> > +                self.as_ptr().cast_mut().cast(),
>> > +            )
>> > +        } =3D=3D 0)
>>=20
>> 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 `=3D=3D`
>    --> rust/kernel/devres.rs:199:11
>     |
> 199 |         } =3D=3D 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 =3D unsafe {
        bindings::devm_remove_action_nowarn(
            /*
             * ...
             */
        )
    };
    res =3D=3D 0

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

---
Cheers,
Benno