linux-kernel - [PATCH v5 1/2] rust: transmute: add `as

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Message-Id: <20250801-as_bytes-v5-1-975f87d5dc85@nvidia.com>
Date: Fri, 01 Aug 2025 22:24:09 +0900
From: Alexandre Courbot <acourbot@...dia.com>
To: Abdiel Janulgue <abdiel.janulgue@...il.com>, 
 Danilo Krummrich <dakr@...nel.org>, 
 Daniel Almeida <daniel.almeida@...labora.com>, 
 Robin Murphy <robin.murphy@....com>, 
 Andreas Hindborg <a.hindborg@...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>, 
 Benno Lossin <lossin@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>, 
 Trevor Gross <tmgross@...ch.edu>
Cc: "Christian S. Lima" <christiansantoslima21@...il.com>, 
 rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Alexandre Courbot <acourbot@...dia.com>
Subject: [PATCH v5 1/2] rust: transmute: add `as_bytes` method for
 `AsBytes` trait

Every type that implements `AsBytes` should be able to provide its byte
representation. Introduce the `as_bytes` method that returns the
implementer as a stream of bytes, and provide a default implementation
that should be suitable for any type that satisfies `AsBytes`'s safety
requirements.

Reviewed-by: Danilo Krummrich <dakr@...nel.org>
Reviewed-by: Benno Lossin <lossin@...nel.org>
Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>
Reviewed-by: Gary Guo <gary@...yguo.net>
Signed-off-by: Alexandre Courbot <acourbot@...dia.com>
---
 rust/kernel/transmute.rs | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/transmute.rs b/rust/kernel/transmute.rs
index 1c7d43771a37b90150de86699f114a2ffb84db91..08e6f0ff92a563e90895efa31f31f887aa05a0ae 100644
--- a/rust/kernel/transmute.rs
+++ b/rust/kernel/transmute.rs
@@ -47,7 +47,17 @@ macro_rules! impl_frombytes {
 ///
 /// Values of this type may not contain any uninitialized bytes. This type must not have interior
 /// mutability.
-pub unsafe trait AsBytes {}
+pub unsafe trait AsBytes {
+    /// Returns `self` as a slice of bytes.
+    fn as_bytes(&self) -> &[u8] {
+        // CAST: `Self` implements `AsBytes` thus all bytes of `self` are initialized.
+        let data = core::ptr::from_ref(self).cast::<u8>();
+        let len = size_of_val(self);
+
+        // SAFETY: `data` is non-null and valid for reads of `len * sizeof::<u8>()` bytes.
+        unsafe { core::slice::from_raw_parts(data, len) }
+    }
+}

 macro_rules! impl_asbytes {
     ($($({$($generics:tt)*})? $t:ty, )*) => {

-- 
2.50.1