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

[Alvin Sun <alvin.sun@linux.dev>]

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
>>