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

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Message-ID: <aHUjIQlqphtgVP2g@Mac.home>
Date: Mon, 14 Jul 2025 08:32:49 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Benno Lossin <lossin@...nel.org>
Cc: linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
	lkmm@...ts.linux.dev, linux-arch@...r.kernel.org,
	Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>, Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>,
	Danilo Krummrich <dakr@...nel.org>, Will Deacon <will@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Mark Rutland <mark.rutland@....com>,
	Wedson Almeida Filho <wedsonaf@...il.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Lyude Paul <lyude@...hat.com>, Ingo Molnar <mingo@...nel.org>,
	Mitchell Levy <levymitchell0@...il.com>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alan Stern <stern@...land.harvard.edu>
Subject: Re: [PATCH v7 4/9] rust: sync: atomic: Add generic atomics

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.
> 
[...]