Re: [PATCH 1/3] rust: xarray: abstract `xa_alloc`

["Benno Lossin" <lossin@kernel.org>]

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@onurozkan.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"
> +        );