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

[Benno Lossin]

On Tue Oct 7, 2025 at 12:58 PM CEST, Alice Ryhl wrote:
> On Mon, Oct 06, 2025 at 09:31:43PM +0200, Benno Lossin wrote:
>> 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@xxxxxxxxxxxxx>
>> > ---
>> >  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.
>
> What? People need to know what the assigned index is.

The documentation says "allocated id", so I assumed that it was some
internal, implementation-dependent thing, not an index. In that case we
should change the docs instead.

---
Cheers,
Benno