Re: [PATCH 4/4] rust: xarray: Add Guard::find() helper

[Onur Özkan]

On Fri, 17 Apr 2026 09:05:54 +0800
Alvin Sun <alvin.sun@xxxxxxxxx> wrote:

> Add a helper to find the first present entry in the XArray.
> 
> Returns the index of the first present entry, or None if the array
> is empty.
> 
> Signed-off-by: Alvin Sun <alvin.sun@xxxxxxxxx>
> ---
>  rust/kernel/xarray.rs | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/rust/kernel/xarray.rs b/rust/kernel/xarray.rs
> index 235fda0e394ba..e43129d032d9d 100644
> --- a/rust/kernel/xarray.rs
> +++ b/rust/kernel/xarray.rs
> @@ -217,6 +217,28 @@ pub fn remove(&mut self, index: usize) -> Option<T> {
>          unsafe { T::try_from_foreign(ptr) }
>      }
>  
> +    /// Finds the first present entry.
> +    ///
> +    /// Returns the index of the first present entry, or `None` if the array is empty.
> +    pub fn find(&mut self) -> Option<usize> {
> +        let mut index = 0usize;

Nit: I don't know if this verbosity can ever be useful, it can simply be `= 0`;

> +        // SAFETY: `self.xa.xa` is always valid by the type invariant, and we hold the lock.
> +        let ptr = unsafe {
> +            bindings::xa_find(
> +                self.xa.xa.get(),
> +                &mut index,
> +                usize::MAX,
> +                bindings::XA_PRESENT,
> +            )
> +        };
> +
> +        if ptr.is_null() {
> +            None
> +        } else {
> +            Some(index)
> +        }

This can be written with the `then_some` chain e.g., !ptr.is_null().then_some(..
.) but I don't know if it ever makes it more readable or simpler. I guess it's
up to preference.

-Onur

> +    }
> +
>      /// Stores an element at the given index.
>      ///
>      /// May drop the lock if needed to allocate memory, and then reacquire it afterwards.
> 
> -- 
> 2.43.0
>