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

[Alvin Sun]

Hi Onur,

On 4/17/26 16:28, Onur Özkan wrote:
> 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`;

Yeah, you're right - we can let the compiler infer the type automatically.
I haven't gotten used to that convenience yet :P

> > +        // 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.

I'm still not very used to the chained syntax style. For me, the if/else
approach is quite intuitive.

Best regards,
Alvin

> -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