Re: [PATCH] rust: alloc: add missing trait item MIN_ALIGN to Cmalloc

[Alice Ryhl <aliceryhl@google.com>]

On Sun, Aug 24, 2025 at 2:07 PM Danilo Krummrich <dakr@kernel.org> wrote:
>
> Cmalloc is missing the trait item MIN_ALIGN introduced by commit
> 1b1a946dc2b5 ("rust: alloc: specify the minimum alignment of each
> allocator"), causing the following error on the `rusttest` make target.
>
>         error[E0046]: not all trait items implemented, missing: `MIN_ALIGN`
>            --> rust/kernel/alloc/allocator_test.rs:37:1
>             |
>         37  | unsafe impl Allocator for Cmalloc {
>             | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ missing `MIN_ALIGN` in implementation
>             |
>            ::: rust/kernel/alloc.rs:146:5
>             |
>         146 |     const MIN_ALIGN: usize;
>             |     ---------------------- `MIN_ALIGN` from trait
>
> Implement MIN_ALIGN for Cmalloc to fix this.
>
> Reported-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
> Closes: https://lore.kernel.org/all/CANiq72k0FSBTB2yOjiAy9PnAuyM=-PHxL3uQQ_Cv+zwswnr_bA@mail.gmail.com/
> Fixes: 1b1a946dc2b5 ("rust: alloc: specify the minimum alignment of each allocator")
> Signed-off-by: Danilo Krummrich <dakr@kernel.org>

Thanks for taking of it. Assuming a satisfactory answer to the quesiton below:

Reviewed-by: Alice Ryhl <aliceryhl@google.com>

> ---
>  rust/kernel/alloc/allocator_test.rs | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/rust/kernel/alloc/allocator_test.rs b/rust/kernel/alloc/allocator_test.rs
> index a3074480bd8d..0d3c78ddcd69 100644
> --- a/rust/kernel/alloc/allocator_test.rs
> +++ b/rust/kernel/alloc/allocator_test.rs
> @@ -35,6 +35,8 @@
>  // - passing a pointer to a valid memory allocation created by this `Allocator` is always OK,
>  // - `realloc` provides the guarantees as provided in the `# Guarantees` section.
>  unsafe impl Allocator for Cmalloc {
> +    const MIN_ALIGN: usize = bindings::ARCH_KMALLOC_MINALIGN;

Is this the right value for normal malloc?

Alice