From: Boqun Feng <boqun.feng@gmail.com>
To: Benno Lossin <lossin@kernel.org>
Cc: linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org,
lkmm@lists.linux.dev, linux-arch@vger.kernel.org,
"Miguel Ojeda" <ojeda@kernel.org>,
"Alex Gaynor" <alex.gaynor@gmail.com>,
"Gary Guo" <gary@garyguo.net>,
"Björn Roy Baron" <bjorn3_gh@protonmail.com>,
"Andreas Hindborg" <a.hindborg@kernel.org>,
"Alice Ryhl" <aliceryhl@google.com>,
"Trevor Gross" <tmgross@umich.edu>,
"Danilo Krummrich" <dakr@kernel.org>,
"Will Deacon" <will@kernel.org>,
"Peter Zijlstra" <peterz@infradead.org>,
"Mark Rutland" <mark.rutland@arm.com>,
"Wedson Almeida Filho" <wedsonaf@gmail.com>,
"Viresh Kumar" <viresh.kumar@linaro.org>,
"Lyude Paul" <lyude@redhat.com>, "Ingo Molnar" <mingo@kernel.org>,
"Mitchell Levy" <levymitchell0@gmail.com>,
"Paul E. McKenney" <paulmck@kernel.org>,
"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
"Linus Torvalds" <torvalds@linux-foundation.org>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Alan Stern" <stern@rowland.harvard.edu>
Subject: Re: [PATCH v6 4/9] rust: sync: atomic: Add generic atomics
Date: Sun, 13 Jul 2025 12:51:24 -0700 [thread overview]
Message-ID: <aHQOPPhTRI2mcEKq@tardis-2.local> (raw)
In-Reply-To: <DB92I10114UN.33MAFJVWIX4AB@kernel.org>
On Fri, Jul 11, 2025 at 10:03:07AM +0200, Benno Lossin wrote:
[...]
> > +/// # Round-trip transmutability
[...]
> > +///
> > +/// This essentially means a valid bit pattern of `T: AllowAtomic` has to be a valid bit pattern
> > +/// of `T::Repr`. This is needed because [`Atomic<T: AllowAtomic>`] operates on `T::Repr` to
> > +/// implement atomic operations on `T`.
> > +///
> > +/// Note that this is more relaxed than bidirectional transmutability (i.e. [`transmute()`] is
> > +/// always sound between `T` and `T::Repr`) because of the support for atomic variables over
>
> s/between `T` and `T::Repr`/from `T` to `T::Repr` and back/
>
Hmm.. I'm going to keep the "between" form, because here we are talking
about bi-directional transmutability, "from .. to .. and back" sounds
like describing round-trip transmutability.
I also re-aranged the doc comment a bit:
/// Types that support basic atomic operations.
///
/// # Round-trip transmutability
///
/// `T` is round-trip transmutable to `U` if and only if both of these properties hold:
///
/// - Any valid bit pattern for `T` is also a valid bit pattern for `U`.
/// - Transmuting (e.g. using [`transmute()`]) a value of type `T` to `U` and then to `T` again
/// yields a value that is in all aspects equivalent to the original value.
///
/// # Safety
///
/// - [`Self`] must have the same size and alignment as [`Self::Repr`].
/// - [`Self`] must be [round-trip transmutable] to [`Self::Repr`].
///
/// Note that this is more relaxed than requiring the bi-directional transmutability (i.e.
/// [`transmute()`] is always sound between `U` to `T`) because of the support for atomic variables
/// over unit-only enums, see [Examples].
///
/// # Limitations
///
/// ...
///
/// # Examples
///
/// A unit-only enum that implements [`AllowAtomic`]:
///
/// ```
/// use kernel::sync::atomic::{generic::AllowAtomic, Atomic, Relaxed};
///
/// #[derive(Clone, Copy, PartialEq, Eq)]
/// #[repr(i32)]
/// enum State {
/// Uninit = 0,
/// Working = 1,
/// Done = 2,
/// };
///
/// ...
/// ```
/// [`transmute()`]: core::mem::transmute
/// [round-trip transmutable]: AllowAtomic#round-trip-transmutability
/// [Examples]: AllowAtomic#examples
Thanks!
Regards,
Boqun
> > +/// unit-only enums:
>
> What are "unit-only" enums? Do you mean enums that don't have associated
> data?
>
> > +///
> > +/// ```
> > +/// #[repr(i32)]
> > +/// enum State { Init = 0, Working = 1, Done = 2, }
> > +/// ```
[...]
> > +pub unsafe trait AllowAtomic: Sized + Send + Copy {
[...]
next prev parent reply other threads:[~2025-07-13 19:51 UTC|newest]
Thread overview: 65+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-07-10 6:00 [PATCH v6 0/9] LKMM generic atomics in Rust Boqun Feng
2025-07-10 6:00 ` [PATCH v6 1/9] rust: Introduce atomic API helpers Boqun Feng
2025-07-10 6:00 ` [PATCH v6 2/9] rust: sync: Add basic atomic operation mapping framework Boqun Feng
2025-07-10 11:04 ` Benno Lossin
2025-07-10 15:12 ` Boqun Feng
2025-07-10 15:46 ` Benno Lossin
2025-07-10 16:16 ` Boqun Feng
2025-07-10 19:21 ` Benno Lossin
2025-07-10 20:29 ` Boqun Feng
2025-07-11 8:15 ` Benno Lossin
2025-07-10 6:00 ` [PATCH v6 3/9] rust: sync: atomic: Add ordering annotation types Boqun Feng
2025-07-10 11:08 ` Benno Lossin
2025-07-10 12:00 ` Andreas Hindborg
2025-07-10 14:42 ` Boqun Feng
2025-07-10 15:05 ` Benno Lossin
2025-07-10 15:57 ` Boqun Feng
2025-07-10 19:19 ` Benno Lossin
2025-07-10 18:32 ` Miguel Ojeda
2025-07-10 19:06 ` Miguel Ojeda
2025-07-10 6:00 ` [PATCH v6 4/9] rust: sync: atomic: Add generic atomics Boqun Feng
2025-07-11 8:03 ` Benno Lossin
2025-07-11 13:22 ` Boqun Feng
2025-07-11 13:34 ` Benno Lossin
2025-07-11 13:51 ` Boqun Feng
2025-07-11 18:34 ` Benno Lossin
2025-07-11 21:25 ` Boqun Feng
2025-07-11 13:58 ` Boqun Feng
2025-07-11 18:35 ` Benno Lossin
2025-07-14 7:08 ` Boqun Feng
2025-07-13 19:51 ` Boqun Feng [this message]
2025-07-10 6:00 ` [PATCH v6 5/9] rust: sync: atomic: Add atomic {cmp,}xchg operations Boqun Feng
2025-07-11 8:42 ` Benno Lossin
2025-07-10 6:00 ` [PATCH v6 6/9] rust: sync: atomic: Add the framework of arithmetic operations Boqun Feng
2025-07-11 8:53 ` Benno Lossin
2025-07-11 14:39 ` Boqun Feng
2025-07-11 17:41 ` Boqun Feng
2025-07-11 19:07 ` Benno Lossin
2025-07-11 18:55 ` Benno Lossin
2025-07-11 19:51 ` Boqun Feng
2025-07-11 21:03 ` Benno Lossin
2025-07-11 21:22 ` Boqun Feng
2025-07-14 4:20 ` Boqun Feng
2025-07-10 6:00 ` [PATCH v6 7/9] rust: sync: atomic: Add Atomic<u{32,64}> Boqun Feng
2025-07-11 8:54 ` Benno Lossin
2025-07-10 6:00 ` [PATCH v6 8/9] rust: sync: Add memory barriers Boqun Feng
2025-07-11 8:57 ` Benno Lossin
2025-07-11 13:32 ` Boqun Feng
2025-07-11 18:57 ` Benno Lossin
2025-07-11 19:26 ` Boqun Feng
2025-07-11 21:04 ` Benno Lossin
2025-07-11 21:34 ` Boqun Feng
2025-07-11 18:20 ` Boqun Feng
2025-07-14 15:42 ` Ralf Jung
2025-07-15 15:21 ` Boqun Feng
2025-07-15 15:35 ` Ralf Jung
2025-07-15 15:56 ` Boqun Feng
2025-07-16 19:42 ` Ralf Jung
2025-07-10 6:00 ` [PATCH v6 9/9] rust: sync: atomic: Add Atomic<{usize,isize}> Boqun Feng
2025-07-11 9:00 ` Benno Lossin
2025-07-11 13:45 ` Miguel Ojeda
2025-07-11 14:07 ` Boqun Feng
2025-07-11 14:40 ` Miguel Ojeda
2025-07-11 15:46 ` Boqun Feng
2025-07-11 18:35 ` Miguel Ojeda
2025-07-11 19:05 ` Benno Lossin
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