linux-kernel - Re: [PATCH 1/3] rust: xarray: abstract `xa

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Message-Id: <DDBHMNEIU9HJ.68MGF28IF58I@kernel.org>
Date: Mon, 06 Oct 2025 21:31:43 +0200
From: "Benno Lossin" <lossin@...nel.org>
To: Onur Özkan <work@...rozkan.dev>,
 <rust-for-linux@...r.kernel.org>
Cc: <ojeda@...nel.org>, <alex.gaynor@...il.com>, <boqun.feng@...il.com>,
 <gary@...yguo.net>, <bjorn3_gh@...tonmail.com>, <aliceryhl@...gle.com>,
 <tmgross@...ch.edu>, <dakr@...nel.org>, <linux-kernel@...r.kernel.org>,
 <acourbot@...dia.com>, <airlied@...il.com>, <simona@...ll.ch>,
 <maarten.lankhorst@...ux.intel.com>, <mripard@...nel.org>,
 <tzimmermann@...e.de>, <corbet@....net>, <lyude@...hat.com>,
 <linux-doc@...r.kernel.org>
Subject: Re: [PATCH 1/3] rust: xarray: abstract `xa_alloc`

On Mon Oct 6, 2025 at 6:30 PM CEST, Onur Özkan wrote:
> Implements `alloc` function to `XArray<T>` that wraps
> `xa_alloc` safely.
>
> Resolves a task from the nova/core task list under the "XArray
> bindings [XARR]" section in "Documentation/gpu/nova/core/todo.rst"
> file.
>
> Signed-off-by: Onur Özkan <work@...rozkan.dev>
> ---
>  rust/kernel/xarray.rs | 39 +++++++++++++++++++++++++++++++++++++++
>  1 file changed, 39 insertions(+)
>
> diff --git a/rust/kernel/xarray.rs b/rust/kernel/xarray.rs
> index a49d6db28845..1b882cd2f58b 100644
> --- a/rust/kernel/xarray.rs
> +++ b/rust/kernel/xarray.rs
> @@ -266,6 +266,45 @@ pub fn store(
>              Ok(unsafe { T::try_from_foreign(old) })
>          }
>      }
> +
> +    /// Allocates an empty slot within the given limit range and stores `value` there.
> +    ///
> +    /// May drop the lock if needed to allocate memory, and then reacquire it afterwards.
> +    ///
> +    /// On success, returns the allocated id.
> +    ///
> +    /// On failure, returns the element which was attempted to be stored.
> +    pub fn alloc(
> +        &mut self,
> +        limit: bindings::xa_limit,
> +        value: T,
> +        gfp: alloc::Flags,
> +    ) -> Result<u32, StoreError<T>> {

I think it would be a good idea to make the id a newtype wrapper around
u32. Maybe not even allow users to manually construct it or even inspect
it if possible.

---
Cheers,
Benno

> +        build_assert!(
> +            T::FOREIGN_ALIGN >= 4,
> +            "pointers stored in XArray must be 4-byte aligned"
> +        );