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

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Message-Id: <DBCIZY29JWTD.1G6AKZ08ZWBQG@kernel.org>
Date: Tue, 15 Jul 2025 11:36:49 +0200
From: "Benno Lossin" <lossin@...nel.org>
To: "Boqun Feng" <boqun.feng@...il.com>
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 5:32 PM CEST, Boqun Feng wrote:
> 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.

The same would apply if you had to import `AllowAtomic` from atomic
directly? I don't really see the value in this.

---
Cheers,
Benno