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

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Message-ID: <aHZUO4NwMlw-FsnZ@Mac.home>
Date: Tue, 15 Jul 2025 06:14:35 -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 Tue, Jul 15, 2025 at 11:36:49AM +0200, Benno Lossin wrote:
> 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.
> 

Because generic::AllowAtomic is more clear that the user is using the
generic part of the API, or the user is extending the Atomic type with
the generic ability. Grouping functionality with a namespace is
basically what I want to achieve here. It's similar to why do we put
`atomic` (and `lock`) under `sync`.

Regards,
Boqun

> ---
> Cheers,
> Benno