linux-kernel - [PATCH v2 04/13] rust: pin-init: implement `ZeroableOption` for `&T` and `&mut T`

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Message-ID: <20250523145125.523275-5-lossin@kernel.org>
Date: Fri, 23 May 2025 16:51:00 +0200
From: Benno Lossin <lossin@...nel.org>
To: Benno Lossin <lossin@...nel.org>,
	Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>,
	Boqun Feng <boqun.feng@...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>,
	Fiona Behrens <me@...enk.dev>,
	Christian Schrefl <chrisi.schrefl@...il.com>
Cc: Lyude Paul <lyude@...hat.com>,
	rust-for-linux@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2 04/13] rust: pin-init: implement `ZeroableOption` for `&T` and `&mut T`

`Option<&T>` and `Option<&mut T>` are documented [1] to have the `None`
variant be all zeroes.

Link: https://doc.rust-lang.org/stable/std/option/index.html#representation [1]
Link: https://github.com/Rust-for-Linux/pin-init/pull/56/commits/5ef1638c79e019d3dc0c62db5905601644c2e60a
Signed-off-by: Benno Lossin <lossin@...nel.org>
---
 rust/pin-init/src/lib.rs | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/rust/pin-init/src/lib.rs b/rust/pin-init/src/lib.rs
index 7535c3fcc961..bdd2a050f7c8 100644
--- a/rust/pin-init/src/lib.rs
+++ b/rust/pin-init/src/lib.rs
@@ -1522,6 +1522,13 @@ pub unsafe trait ZeroableOption {}
 // SAFETY: by the safety requirement of `ZeroableOption`, this is valid.
 unsafe impl<T: ZeroableOption> Zeroable for Option<T> {}
 
+// SAFETY: `Option<&T>` is part of the option layout optimization guarantee:
+// <https://doc.rust-lang.org/stable/std/option/index.html#representation>.
+unsafe impl<T> ZeroableOption for &T {}
+// SAFETY: `Option<&mut T>` is part of the option layout optimization guarantee:
+// <https://doc.rust-lang.org/stable/std/option/index.html#representation>.
+unsafe impl<T> ZeroableOption for &mut T {}
+
 /// Create an initializer for a zeroed `T`.
 ///
 /// The returned initializer will write `0x00` to every byte of the given `slot`.

base-commit: ae8b3a83fb9de394f609035041cd7a668fda2ab3
prerequisite-patch-id: https://lore.kernel.org/all/20250523125424.192843-2-lossin@kernel.org
prerequisite-patch-id: https://lore.kernel.org/all/20250523125424.192843-3-lossin@kernel.org
prerequisite-patch-id: https://lore.kernel.org/all/20250523125424.192843-4-lossin@kernel.org
-- 
2.49.0