linux-kernel - [tip: locking/core] rust: sync: atomic: Add atomic bool support via i8 representation

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Message-ID: <176830139219.510.11680138596134249383.tip-bot2@tip-bot2>
Date: Tue, 13 Jan 2026 10:49:52 -0000
From: "tip-bot2 for FUJITA Tomonori" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: FUJITA Tomonori <fujita.tomonori@...il.com>, Gary Guo <gary@...yguo.net>,
 Boqun Feng <boqun.feng@...il.com>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: locking/core] rust: sync: atomic: Add atomic bool support via
 i8 representation

The following commit has been merged into the locking/core branch of tip:

Commit-ID:     06bd0e52bfd78eae1c7dd5db163ce64161b495e7
Gitweb:        https://git.kernel.org/tip/06bd0e52bfd78eae1c7dd5db163ce64161b495e7
Author:        FUJITA Tomonori <fujita.tomonori@...il.com>
AuthorDate:    Thu, 01 Jan 2026 12:49:21 +09:00
Committer:     Boqun Feng <boqun.feng@...il.com>
CommitterDate: Fri, 09 Jan 2026 19:01:41 +08:00

rust: sync: atomic: Add atomic bool support via i8 representation

Add `bool` support, `Atomic<bool>` by using `i8` as its underlying
representation.

Rust specifies that `bool` has size 1 and alignment 1 [1], so it
matches `i8` on layout; keep `static_assert!()` checks to enforce this
assumption at build time.

[boqun: Remove the unnecessary impl AtomicImpl for bool]

Link: https://doc.rust-lang.org/reference/types/boolean.html [1]
Signed-off-by: FUJITA Tomonori <fujita.tomonori@...il.com>
Reviewed-by: Gary Guo <gary@...yguo.net>
Signed-off-by: Boqun Feng <boqun.feng@...il.com>
Link: https://patch.msgid.link/20260101034922.2020334-2-fujita.tomonori@gmail.com
---
 rust/kernel/sync/atomic/predefine.rs | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/rust/kernel/sync/atomic/predefine.rs b/rust/kernel/sync/atomic/predefine.rs
index 248d265..3fc9917 100644
--- a/rust/kernel/sync/atomic/predefine.rs
+++ b/rust/kernel/sync/atomic/predefine.rs
@@ -5,6 +5,17 @@
 use crate::static_assert;
 use core::mem::{align_of, size_of};
 
+// Ensure size and alignment requirements are checked.
+static_assert!(size_of::<bool>() == size_of::<i8>());
+static_assert!(align_of::<bool>() == align_of::<i8>());
+
+// SAFETY: `bool` has the same size and alignment as `i8`, and Rust guarantees that `bool` has
+// only two valid bit patterns: 0 (false) and 1 (true). Those are valid `i8` values, so `bool` is
+// round-trip transmutable to `i8`.
+unsafe impl super::AtomicType for bool {
+    type Repr = i8;
+}
+
 // SAFETY: `i8` has the same size and alignment with itself, and is round-trip transmutable to
 // itself.
 unsafe impl super::AtomicType for i8 {