linux-kernel - [PATCH v2 03/13] rust: pin-init: add `zeroed()` & `Zeroable::zeroed()` functions

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Message-ID: <20250523145125.523275-4-lossin@kernel.org>
Date: Fri, 23 May 2025 16:50:59 +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 03/13] rust: pin-init: add `zeroed()` & `Zeroable::zeroed()` functions

`zeroed()` returns a zeroed out value of a sized type implementing
`Zeroable`.

The function is added as a free standing function, in addition to an
associated function on `Zeroable`, because then it can be marked `const`
(functions in traits can't be const at the moment).

Link: https://github.com/Rust-for-Linux/pin-init/pull/56/commits/809e4ec160579c1601dce5d78b432a5b6c8e4e40
Signed-off-by: Benno Lossin <lossin@...nel.org>
---
 rust/pin-init/src/lib.rs | 52 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)

diff --git a/rust/pin-init/src/lib.rs b/rust/pin-init/src/lib.rs
index 436fa3bc0339..7535c3fcc961 100644
--- a/rust/pin-init/src/lib.rs
+++ b/rust/pin-init/src/lib.rs
@@ -1482,6 +1482,33 @@ fn init_zeroed() -> impl Init<Self>
     {
         init_zeroed()
     }
+
+    /// Create a `Self` consisting of all zeroes.
+    ///
+    /// Whenever a type implements [`Zeroable`], this function should be preferred over
+    /// [`core::mem::zeroed()`] or using `MaybeUninit<T>::zeroed().assume_init()`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use pin_init::{Zeroable, zeroed};
+    ///
+    /// #[derive(Zeroable)]
+    /// struct Point {
+    ///     x: u32,
+    ///     y: u32,
+    /// }
+    ///
+    /// let point: Point = zeroed();
+    /// assert_eq!(point.x, 0);
+    /// assert_eq!(point.y, 0);
+    /// ```
+    fn zeroed() -> Self
+    where
+        Self: Sized,
+    {
+        zeroed()
+    }
 }
 
 /// Marker trait for types that allow `Option<Self>` to be set to all zeroes in order to write
@@ -1510,6 +1537,31 @@ pub fn init_zeroed<T: Zeroable>() -> impl Init<T> {
     }
 }
 
+/// Create a `T` consisting of all zeroes.
+///
+/// Whenever a type implements [`Zeroable`], this function should be preferred over
+/// [`core::mem::zeroed()`] or using `MaybeUninit<T>::zeroed().assume_init()`.
+///
+/// # Examples
+///
+/// ```
+/// use pin_init::{Zeroable, zeroed};
+///
+/// #[derive(Zeroable)]
+/// struct Point {
+///     x: u32,
+///     y: u32,
+/// }
+///
+/// let point: Point = zeroed();
+/// assert_eq!(point.x, 0);
+/// assert_eq!(point.y, 0);
+/// ```
+pub const fn zeroed<T: Zeroable>() -> T {
+    // SAFETY:By the type invariants of `Zeroable`, all zeroes is a valid bit pattern for `T`.
+    unsafe { core::mem::zeroed() }
+}
+
 macro_rules! impl_zeroable {
     ($($({$($generics:tt)*})? $t:ty, )*) => {
         // SAFETY: Safety comments written in the macro invocation.

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