linux-kernel - Re: [PATCH v4 1/2] rust: add `Alignment` type

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Message-ID: <c3e8e0fc-5582-49ce-99fe-6dea37c39ddb@kernel.org>
Date: Mon, 8 Sep 2025 14:02:38 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: Alexandre Courbot <acourbot@...dia.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 <lossin@...nel.org>, Andreas Hindborg <a.hindborg@...nel.org>,
 Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>,
 linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
 nouveau@...ts.freedesktop.org
Subject: Re: [PATCH v4 1/2] rust: add `Alignment` type

On 8/21/25 2:42 PM, Alexandre Courbot wrote:
> +    /// Validates that `align` is a power of two at build-time, and returns an [`Alignment`] of the
> +    /// same value.
> +    ///
> +    /// A build error is triggered if `align` cannot be asserted to be a power of two.
> +    ///
> +    /// # Examples
> +    ///
> +    /// ```
> +    /// use kernel::ptr::Alignment;
> +    ///
> +    /// let v = Alignment::new(16);
> +    /// assert_eq!(v.as_usize(), 16);
> +    /// ```
> +    #[inline(always)]
> +    pub const fn new(align: usize) -> Self {
> +        build_assert!(align.is_power_of_two());
> +
> +        // INVARIANT: `align` is a power of two.
> +        // SAFETY: `align` is a power of two, and thus non-zero.
> +        Self(unsafe { NonZero::new_unchecked(align) })
> +    }

For DmaMask::new() we used a const generic instead, which makes it more obvious
to the caller that the argument must be known at compile time. So, I'd prefer
this here as well.

Either way,

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