linux-kernel - Re: [PATCH 2/4] rust: devres: replace Devres::new_foreign

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Message-Id: <DASIPSH2IFKL.O55ZBVZFPVWB@kernel.org>
Date: Sat, 21 Jun 2025 23:10:14 +0200
From: "Benno Lossin" <lossin@...nel.org>
To: "Danilo Krummrich" <dakr@...nel.org>, <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>
Cc: <rust-for-linux@...r.kernel.org>, <linux-kernel@...r.kernel.org>, "Dave
 Airlie" <airlied@...hat.com>, "Simona Vetter" <simona.vetter@...ll.ch>,
 "Viresh Kumar" <viresh.kumar@...aro.org>
Subject: Re: [PATCH 2/4] rust: devres: replace Devres::new_foreign_owned()

On Thu Jun 12, 2025 at 4:51 PM CEST, Danilo Krummrich wrote:
> diff --git a/rust/kernel/cpufreq.rs b/rust/kernel/cpufreq.rs
> index b0a9c6182aec..f20636079f7a 100644
> --- a/rust/kernel/cpufreq.rs
> +++ b/rust/kernel/cpufreq.rs
> @@ -12,7 +12,7 @@
>      clk::Hertz,
>      cpumask,
>      device::{Bound, Device},
> -    devres::Devres,
> +    devres,
>      error::{code::*, from_err_ptr, from_result, to_result, Result, VTABLE_DEFAULT_ERROR},
>      ffi::{c_char, c_ulong},
>      prelude::*,
> @@ -910,7 +910,7 @@ unsafe impl<T: Driver> Sync for Registration<T> {}
>  /// thread.
>  unsafe impl<T: Driver> Send for Registration<T> {}
>  
> -impl<T: Driver> Registration<T> {
> +impl<T: Driver + 'static> Registration<T> {

This change should probably be its own patch? If not, then it should be
mentioned in the commit message.

>      const VTABLE: bindings::cpufreq_driver = bindings::cpufreq_driver {
>          name: Self::copy_name(T::NAME),
>          boost_enabled: T::BOOST_ENABLED,
> @@ -1044,10 +1044,10 @@ pub fn new() -> Result<Self> {
>  
>      /// Same as [`Registration::new`], but does not return a [`Registration`] instance.
>      ///
> -    /// Instead the [`Registration`] is owned by [`Devres`] and will be revoked / dropped, once the
> +    /// Instead the [`Registration`] is owned by [`kernel::devres`] and will be dropped, once the
>      /// device is detached.
>      pub fn new_foreign_owned(dev: &Device<Bound>) -> Result {

I think we can improve the names here. How about `new_attached`? See
more below.

> -        Devres::new_foreign_owned(dev, Self::new()?, GFP_KERNEL)
> +        devres::register_foreign_boxed(dev, Self::new()?, GFP_KERNEL)
>      }
>  }

> +/// Encapsulate `data` in a [`KBox`] and [`Drop::drop`] `data` once `dev` is unbound.
> +///
> +/// # Examples
> +///
> +/// ```no_run
> +/// use kernel::{device::{Bound, Device}, devres};
> +///
> +/// struct Registration;
> +///
> +/// impl Registration {
> +///     fn new() -> Self {
> +///         // register (e.g. class device, IRQ, etc.)
> +///
> +///         Self
> +///     }
> +/// }
> +///
> +/// impl Drop for Registration {
> +///     fn drop(&mut self) {
> +///        // unregister
> +///     }
> +/// }
> +///
> +/// fn from_bound_context(dev: &Device<Bound>) -> Result {
> +///     devres::register_foreign_boxed(dev, Registration::new(), GFP_KERNEL)
> +/// }
> +/// ```
> +pub fn register_foreign_boxed<T, E>(

I don't really get the name of this function. The data isn't really
foreign and that the user also shouldn't really care about the fact that
you use `KBox` under the hood.

How about we call this something like `attach_data`? 

---
Cheers,
Benno

> +    dev: &Device<Bound>,
> +    data: impl PinInit<T, E>,
> +    flags: Flags,
> +) -> Result
> +where
> +    T: 'static,
> +    Error: From<E>,
> +{
> +    let data = KBox::pin_init(data, flags)?;
> +
> +    register_foreign(dev, data)
> +}