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

Alvin Sun
2026-04-17T12:44:14Z

Hi Onur,

On 4/17/26 16:28, Onur Özkan wrote:
> On Fri, 17 Apr 2026 09:05:54 +0800
> Alvin Sun <alvin.sun@linux.dev> 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@linux.dev>
>> ---
>> 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
>>