Re: [PATCH v8 06/10] rust: io: use generic read/write accessors for primitive accesses

[Alexandre Courbot]

On Tue Mar 10, 2026 at 12:29 AM JST, Gary Guo wrote:
> On Mon Mar 9, 2026 at 3:14 PM GMT, Alexandre Courbot wrote:
>> By providing the required `IoLoc` implementations on `usize`, we can
>> leverage the generic accessors and reduce the number of unsafe blocks in
>> the module.
>>
>> This also allows us to directly call the generic `read/write/update`
>> methods with primitive types, so add examples illustrating this.
>>
>> Signed-off-by: Alexandre Courbot <acourbot@xxxxxxxxxx>
>> ---
>>  rust/kernel/io.rs | 199 +++++++++++++++++++++++++++++++++++-------------------
>>  1 file changed, 131 insertions(+), 68 deletions(-)
>>
>> diff --git a/rust/kernel/io.rs b/rust/kernel/io.rs
>> index 1db6572f4a42..ed6fab001a39 100644
>> --- a/rust/kernel/io.rs
>> +++ b/rust/kernel/io.rs
>> @@ -197,6 +197,25 @@ pub trait IoLoc<T> {
>>      fn offset(&self) -> usize;
>>  }
>>  
>> +/// Implements [`IoLoc<$ty>`] for [`usize`], allowing to use `usize` as a parameter of
>> +/// [`Io::read`] and [`Io::write`].
>> +macro_rules! impl_usize_ioloc {
>> +    ($($ty:ty),*) => {
>> +        $(
>> +            impl IoLoc<$ty> for usize {
>> +                type IoType = $ty;
>> +
>
> #[inline(always)]
>
> the fact that this is a pointer is somewhat uneasy to me. I wonder if Clippy
> with its inlining tweak would cause optimisation failure here.
>
> Could this be just `fn offset(self)`?

Yes, this was a remnant from a previous design where I needed to either
make `IoLoc` require `Copy` or use a reference here, so I opted for the
latter.

With the current code though we are using `IoLoc`s exactly one time, so
we can consume `self` without requiring `Copy`.