linux-kernel - Re: [PATCH v7 9/9] rust: sync: atomic: Add Atomic<{usize,isize}>

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Message-ID: <aHUKayPmRrAOd9JM@Mac.home>
Date: Mon, 14 Jul 2025 06:47:23 -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 9/9] rust: sync: atomic: Add Atomic<{usize,isize}>

On Mon, Jul 14, 2025 at 01:06:08PM +0200, Benno Lossin wrote:
> On Mon Jul 14, 2025 at 7:36 AM CEST, Boqun Feng wrote:
> > +// Defines an internal type that always maps to the integer type which has the same size alignment
> > +// as `isize` and `usize`, and `isize` and `usize` are always bi-directional transmutable to
> > +// `isize_atomic_repr`, which also always implements `AtomicImpl`.
> > +#[allow(non_camel_case_types)]
> > +#[cfg(not(CONFIG_64BIT))]
> > +type isize_atomic_repr = i32;
> > +#[allow(non_camel_case_types)]
> > +#[cfg(CONFIG_64BIT)]
> > +type isize_atomic_repr = i64;
> > +
> > +// Ensure size and alignment requirements are checked.
> > +crate::static_assert!(core::mem::size_of::<isize>() == core::mem::size_of::<isize_atomic_repr>());
> > +crate::static_assert!(core::mem::align_of::<isize>() == core::mem::align_of::<isize_atomic_repr>());
> > +crate::static_assert!(core::mem::size_of::<usize>() == core::mem::size_of::<isize_atomic_repr>());
> > +crate::static_assert!(core::mem::align_of::<usize>() == core::mem::align_of::<isize_atomic_repr>());
> 
> This is fine for now, but I would prefer for this to go into an
> `assumptions` module like Miguel proposed some time ago.
> 

Well, sure. Also if `assumptions` or other core kernel mod can provide
a definition similar to `isize_atomic_repr`, I'm happy to use it.

Regards,
Boqun

> ---
> Cheers,
> Benno