linux-kernel - Re: [PATCH v2] rust: transmute: add `as

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Message-ID: <a05133e0-0331-46ce-ab50-c423e40a3879@kernel.org>
Date: Fri, 25 Jul 2025 17:07:21 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: Alexandre Courbot <acourbot@...dia.com>
Cc: Abdiel Janulgue <abdiel.janulgue@...il.com>,
 Daniel Almeida <daniel.almeida@...labora.com>,
 Robin Murphy <robin.murphy@....com>, Andreas Hindborg
 <a.hindborg@...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>,
 Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>,
 "Christian S. Lima" <christiansantoslima21@...il.com>,
 rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] rust: transmute: add `as_bytes` method for `AsBytes`
 trait

On 7/25/25 3:08 PM, Alexandre Courbot wrote:
> diff --git a/rust/kernel/transmute.rs b/rust/kernel/transmute.rs
> index 1c7d43771a37b90150de86699f114a2ffb84db91..d4036986a3d7fb97e5da3e121e9590ad23b784e9 100644
> --- a/rust/kernel/transmute.rs
> +++ b/rust/kernel/transmute.rs
> @@ -47,7 +47,16 @@ macro_rules! impl_frombytes {
>   ///
>   /// Values of this type may not contain any uninitialized bytes. This type must not have interior
>   /// mutability.
> -pub unsafe trait AsBytes {}
> +pub unsafe trait AsBytes {
> +    /// Returns `self` as a slice of bytes.
> +    fn as_bytes(&self) -> &[u8] {
> +        let data = (self as *const Self).cast::<u8>();

I'd probably use from_ref() instead. With that,

	Reviewed-by: Danilo Krummrich <dakr@...nel.org>

> +        let len = size_of_val(self);
> +
> +        // SAFETY: `data` is non-null and valid for `len * sizeof::<u8>()` bytes.
> +        unsafe { core::slice::from_raw_parts(data, len) }
> +    }
> +}