linux-kernel - Re: [PATCH v6 9/9] rust: sync: atomic: Add Atomic<{usize,isize}>

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Message-ID: <CANiq72kvZ7-fMoE9g7SBUrBZy4QMbSL1p8KgBqGhOkenrsr=3w@mail.gmail.com>
Date: Fri, 11 Jul 2025 16:40:15 +0200
From: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To: Boqun Feng <boqun.feng@...il.com>
Cc: Benno Lossin <lossin@...nel.org>, 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>, 
	Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v6 9/9] rust: sync: atomic: Add Atomic<{usize,isize}>

On Fri, Jul 11, 2025 at 4:07 PM Boqun Feng <boqun.feng@...il.com> wrote:
>
> Thanks Miguel.
>
> Maybe we can do even better: having a type alias mapping to the exact
> i{32,64,128} based on kernel configs? Like
>
> (in kernel/lib.rs or ffi.rs)
>
> // Want to buy a better name ;-)
> #[cfg(CONFIG_128BIT)]
> type isize_mapping = i128;
> #[cfg(CONFIG_64BIT)]
> type isize_mapping = i64;
> #[cfg(not(any(CONFIG_128BIT, CONFIG_64BIT)))]
> type isize_mapping = i32;
>
> similar for usize.
>
> Thoughts?

Yeah, I wondered about that too, but I don't know how common it will
be (so you may want to keep it local anyway), and I wasn't sure what
to call it either, because e.g. something like `isize_mapping` sounds
like we are talking about `c_long`.

What we want is a Rust fixed-width integer of the same size of `isize`
-- so I think you should try to pick a word that evokes a bit that
part. Something like `fixed_isize` or words like `underlying` or
`repr` perhaps?

Cheers,
Miguel