Re: [PATCH v7 4/9] rust: sync: atomic: Add generic atomics

[Boqun Feng <boqun.feng@gmail.com>]

On Mon, Jul 14, 2025 at 05:05:40PM +0200, Benno Lossin wrote:
[...]
> >> >  //!
> >> >  //! [`LKMM`]: srctree/tools/memory-model/
> >> >  
> >> > +pub mod generic;
> >> 
> >> Hmm, maybe just re-export the stuff? I don't think there's an advantage
> >> to having the generic module be public.
> >> 
> >
> > If `generic` is not public, then in the kernel::sync::atomic page, it
> > won't should up, and there is no mentioning of struct `Atomic` either.
> >
> > If I made it public and also re-export the `Atomic`, there would be a
> > "Re-export" section mentioning all the re-exports, so I will keep
> > `generic` unless you have some tricks that I don't know.
> 
> Just use `#[doc(inline)]` :)
> 
>     https://doc.rust-lang.org/rustdoc/write-documentation/the-doc-attribute.html#inline-and-no_inline
> 
> > Also I feel it's a bit naturally that `AllowAtomic` and `AllowAtomicAdd`
> > stay under `generic` (instead of re-export them at `atomic` mod level)
> > because they are about the generic part of `Atomic`, right?
> 
> Why is that more natural? It only adds an extra path layer in any import
> for atomics.
> 

Exactly, users need to go through extra steps if they want to use the
"generic" part of the atomic, and I think that makes user more aware of
what they are essentially doing:

- If you want to use the predefined types for atomic, just

  use kernel::sync::atomic::Atomic;

  and just operate on an `Atomic<_>`.

- If you want to bring your own type for atomic operations, you need to

  use kernel::sync::atomic::generic::AllowAtomic;

  (essentially you go into the "generic" part of the atomic)

  and provide your own implementation for `AllowAtomic` and then you
  could use it for your own type.

I feel it's natural because for extra features you fetch more modules
in.

Regards,
Boqun

> Unless you at some point want to add `concrete::Atomic<T>` etc, I would
> just re-export them.
> 
[...]