linux-kernel - [PATCH 1/2] rust: file: mark `LocalFile` as `repr(transparent)`

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Message-ID: <20250527204636.12573-1-pekkarr@protonmail.com>
Date: Tue, 27 May 2025 20:48:55 +0000
From: Pekka Ristola <pekkarr@...tonmail.com>
To: Alexander Viro <viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>, Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>
Cc: Jan Kara <jack@...e.cz>, Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, Björn Roy Baron <bjorn3_gh@...tonmail.com>, Benno Lossin <lossin@...nel.org>, Andreas Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>, Danilo Krummrich <dakr@...nel.org>, linux-fsdevel@...r.kernel.org, rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org, Pekka Ristola <pekkarr@...tonmail.com>
Subject: [PATCH 1/2] rust: file: mark `LocalFile` as `repr(transparent)`

Unsafe code in `LocalFile`'s methods assumes that the type has the same
layout as the inner `bindings::file`. This is not guaranteed by the default
struct representation in Rust, but requires specifying the `transparent`
representation.

The `File` struct (which also wraps `bindings::file`) is already marked as
`repr(transparent)`, so this change makes their layouts equivalent.

Fixes: 851849824bb5 ("rust: file: add Rust abstraction for `struct file`")
Closes: https://github.com/Rust-for-Linux/linux/issues/1165
Signed-off-by: Pekka Ristola <pekkarr@...tonmail.com>
---
 rust/kernel/fs/file.rs | 1 +
 1 file changed, 1 insertion(+)

diff --git a/rust/kernel/fs/file.rs b/rust/kernel/fs/file.rs
index 13a0e44cd1aa..138693bdeb3f 100644
--- a/rust/kernel/fs/file.rs
+++ b/rust/kernel/fs/file.rs
@@ -219,6 +219,7 @@ unsafe fn dec_ref(obj: ptr::NonNull<File>) {
 ///   must be on the same thread as this file.
 ///
 /// [`assume_no_fdget_pos`]: LocalFile::assume_no_fdget_pos
+#[repr(transparent)]
 pub struct LocalFile {
     inner: Opaque<bindings::file>,
 }
-- 
2.49.0