linux-kernel - Re: [PATCH RFC v2 2/3] rust: kernel: add bounded integer types

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Message-ID: <aOoySkWjPcJLVDrG@google.com>
Date: Sat, 11 Oct 2025 10:33:10 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Alexandre Courbot <acourbot@...dia.com>
Cc: Danilo Krummrich <dakr@...nel.org>, Joel Fernandes <joelagnelf@...dia.com>, 
	Yury Norov <yury.norov@...il.com>, Jesung Yang <y.j3ms.n@...il.com>, 
	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>, Trevor Gross <tmgross@...ch.edu>, nouveau@...ts.freedesktop.org, 
	linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org
Subject: Re: [PATCH RFC v2 2/3] rust: kernel: add bounded integer types

On Thu, Oct 09, 2025 at 09:37:09PM +0900, Alexandre Courbot wrote:
> Add the BoundedInt type, which restricts the number of bits allowed to
> be used in a given integer value. This is useful to carry guarantees
> when setting bitfields.
> 
> Alongside this type, many `From` and `TryFrom` implementations are
> provided to reduce friction when using with regular integer types. Proxy
> implementations of common integer traits are also provided.
> 
> Signed-off-by: Alexandre Courbot <acourbot@...dia.com>

> +    pub const fn enlarge<const NEW_NUM_BITS: u32>(self) -> BoundedInt<T, NEW_NUM_BITS>
> +    where
> +        T: Boundable<NEW_NUM_BITS>,
> +        T: Copy,
> +    {
> +        build_assert!(NEW_NUM_BITS >= NUM_BITS);

This assertion can be evaluated in const context.

const {
    assert!(NEW_NUM_BITS >= NUM_BITS);
}

Alice