linux-kernel - Re: [PATCH v3] rust: cpufreq: Ensure C ABI compatibility in all unsafe

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Message-ID: <20250619065713.hm5ye2uhikaei2xo@vireshk-i7>
Date: Thu, 19 Jun 2025 12:27:13 +0530
From: Viresh Kumar <viresh.kumar@...aro.org>
To: Abhinav Ananthu <abhinav.ogl@...il.com>
Cc: "Rafael J . Wysocki" <rafael@...nel.org>,
	Miguel Ojeda <ojeda@...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>,
	Benno Lossin <lossin@...nel.org>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>,
	Danilo Krummrich <dakr@...nel.org>, linux-pm@...r.kernel.org,
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] rust: cpufreq: Ensure C ABI compatibility in all
 unsafe

On 13-06-25, 15:48, Abhinav Ananthu wrote:
> Update all `unsafe extern "C"` callback functions in the cpufreq module to
> use `kernel::ffi` types (`c_int`, `c_uint`, etc.) instead of Rust-native
> types like `i32`, `u32`, or `usize`.
> 
> This change ensures that all Rust callbacks have signatures that are
> ABI-compatible with their corresponding C counterparts, which is critical
> for FFI correctness and safety.
> 
> Suggested-by: Miguel Ojeda <ojeda@...nel.org>
> Link: https://github.com/Rust-for-Linux/linux/issues/1170
> Signed-off-by: Abhinav Ananthu <abhinav.ogl@...il.com>
> ---
>  rust/kernel/cpufreq.rs | 26 +++++++++++++-------------
>  1 file changed, 13 insertions(+), 13 deletions(-)
> 
> diff --git a/rust/kernel/cpufreq.rs b/rust/kernel/cpufreq.rs
> index 11b03e9d7e89..481a6d2dc362 100644
> --- a/rust/kernel/cpufreq.rs
> +++ b/rust/kernel/cpufreq.rs
> @@ -1207,8 +1207,8 @@ impl<T: Driver> Registration<T> {
>      /// - The pointer arguments must be valid pointers.
>      unsafe extern "C" fn target_callback(
>          ptr: *mut bindings::cpufreq_policy,
> -        target_freq: u32,
> -        relation: u32,
> +        target_freq: c_uint,
> +        relation: c_uint,

I think the one in prelude points to core::ffi::* instead, while we
want to use kernel::ffi::* ?

Miguel ?

Also why does prelude use ::ffi::* instead of kernel::ffi::* ? I was always a
bit confused about it.

-- 
viresh