Re: [PATCH v8 4/9] rust: sync: atomic: Add generic atomics

On Tue, Aug 12, 2025 at 09:59:39AM +0200, Benno Lossin wrote:
> On Sat Jul 19, 2025 at 5:08 AM CEST, Boqun Feng wrote:
> > To provide using LKMM atomics for Rust code, a generic `Atomic<T>` is
> > added, currently `T` needs to be Send + Copy because these are the
> > straightforward usages and all basic types support this.
> >
> > Implement `AtomicType` for `i32` and `i64`, and so far only basic
> > operations load() and store() are introduced.
> >
> > Reviewed-by: Alice Ryhl <[email protected]>
> > Signed-off-by: Boqun Feng <[email protected]>
> 
> Reviewed-by: Benno Lossin <[email protected]>
> 

Thanks!

> > ---
> >  rust/kernel/sync/atomic.rs           | 274 +++++++++++++++++++++++++++
> >  rust/kernel/sync/atomic/predefine.rs |  15 ++
> >  2 files changed, 289 insertions(+)
> >  create mode 100644 rust/kernel/sync/atomic/predefine.rs
> 
> > +/// # Limitations
> > +///
> > +/// Because C primitives are used to implement the atomic operations, and a C function requires a
> > +/// valid object of a type to operate on (i.e. no `MaybeUninit<_>`), hence at the Rust <-> C
> > +/// surface, only types with all the bits initialized can be passed. As a result, types like `(u8,
> > +/// u16)` (padding bytes are uninitialized) are currently not supported. Note that technically
> > +/// these types can be supported if some APIs are removed for them and the inner implementation is
> > +/// tweaked, but the justification of support such a type is not strong enough at the moment. This
> > +/// should be resolved if there is an implementation for `MaybeUninit<i32>` as `AtomicImpl`.
> 
> I'd remove the last sentence, as it makes it sound like one only would
> have to add that impl and be finished.
> 

Yeah, sounds good to me, will remove the last sentence starting with
"Note that technically .."

Regards,
Boqun

> ---
> Cheers,
> Benno
>