Re: [PATCH v7 6/9] rust: sync: atomic: Add the framework of arithmetic operations

On Wed Jul 16, 2025 at 5:48 PM CEST, Boqun Feng wrote:
> On Wed, Jul 16, 2025 at 05:36:05PM +0200, Benno Lossin wrote:
> [..]
>> >
>> > I have a better solution:
>> >
>> > in ops.rs
>> >
>> >     pub struct AtomicRepr<T: AtomicImpl>(UnsafeCell<T>)
>> >
>> >     impl AtomicArithmeticOps for i32 {
>> >         // a *safe* function
>> >         fn atomic_add(a: &AtomicRepr, v: i32) {
>> > 	    ...
>> > 	}
>> >     }
>> >
>> > in generic.rs
>> >
>> >     pub struct Atomic<T>(AtoimcRepr<T::Repr>);
>> >
>> >     impl<T: AtomicAdd> Atomic<T> {
>> >         fn add(&self, v: .., ...) {
>> > 	    T::Repr::atomic_add(&self.0, ...);
>> > 	}
>> >     }
>> >
>> > see:
>> >
>> > 	https://git.kernel.org/pub/scm/linux/kernel/git/boqun/linux.git/log/?h=rust-atomic-impl
>> 
>> Hmm what does the additional indirection give you?
>> 
>
> What additional indirection you mean? You cannot make atomic_add() safe
> with only `UnsafeCell<T::Repr>`.

What is the advantage of making it safe? It just moves the safety
comments into `ops.rs` which makes it harder to read due to the macros.

---
Cheers,
Benno