linux-kernel - Re: [PATCH v10] rust: transmute: Add methods for FromBytes trait

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Message-ID: <aKw52m-lh62DXwz7@google.com>
Date: Mon, 25 Aug 2025 10:24:26 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: "Christian S. Lima" <christiansantoslima21@...il.com>
Cc: 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 <benno.lossin@...ton.me>, 
	Andreas Hindborg <a.hindborg@...nel.org>, Trevor Gross <tmgross@...ch.edu>, 
	Danilo Krummrich <dakr@...nel.org>, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org, ~lkcamp/patches@...ts.sr.ht, 
	richard120310@...il.com
Subject: Re: [PATCH v10] rust: transmute: Add methods for FromBytes trait

On Sun, Aug 24, 2025 at 06:31:33PM -0300, Christian S. Lima wrote:
> The two methods added take a slice of bytes and return those bytes in
> a specific type. These methods are useful when we need to transform
> the stream of bytes into specific type.
> 
> Since the `is_aligned` method for pointer types has been stabilized in
> `1.79` version and is being used in this patch. I'm enabling the
> feature. In this case, using this method is useful to check the
> alignment and avoid a giant boilerplate, such as `(foo.as_ptr() as
> usize) % core::mem::align_of::<T>() == 0`.
> 
> Even enabling in `rust/kernel/lib.rs` when compiling with `make LLVM=1
> CLIPPY=1` a warning is issued, so in order to compile, it was used
> locally the `#[allow(clippy::incompatible_msrv)]`.
> 
> Link: https://github.com/Rust-for-Linux/linux/issues/1119
> Suggested-by: Alexandre Courbot <acourbot@...dia.com>
> Signed-off-by: Christian S. Lima <christiansantoslima21@...il.com>

With my comments addressed:
Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>

> -pub unsafe trait FromBytes {}
> +pub unsafe trait FromBytes {
> +    /// Converts a slice of bytes to a reference to `Self`.
> +    ///
> +    /// When the reference is properly aligned and the size of slice is equal to that of `T`
> +    /// and is different from zero.
> +    ///
> +    /// In another case, it will return `None`.
> +    #[allow(clippy::incompatible_msrv)]

Does the warning appear on all configurations? If so, this #[allow]
should be an #[expect].

>  macro_rules! impl_frombytes {
>      ($($({$($generics:tt)*})? $t:ty, )*) => {
> @@ -28,7 +94,6 @@ macro_rules! impl_frombytes {
>  
>      // SAFETY: If all bit patterns are acceptable for individual values in an array, then all bit
>      // patterns are also acceptable for arrays of that type.
> -    {<T: FromBytes>} [T],

Why is this impl removed? I would think that with the Self: Sized
bounds, you don't need to remove it anymore.

Alice