linux-kernel - [PATCH] rust: dma: require mutable reference for as_slice

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Message-ID: <20250628165120.90149-1-dakr@kernel.org>
Date: Sat, 28 Jun 2025 18:49:54 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: abdiel.janulgue@...il.com,
	daniel.almeida@...labora.com,
	robin.murphy@....com,
	a.hindborg@...nel.org,
	ojeda@...nel.org,
	alex.gaynor@...il.com,
	boqun.feng@...il.com,
	gary@...yguo.net,
	bjorn3_gh@...tonmail.com,
	lossin@...nel.org,
	aliceryhl@...gle.com,
	tmgross@...ch.edu,
	acourbot@...dia.com
Cc: rust-for-linux@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Danilo Krummrich <dakr@...nel.org>
Subject: [PATCH] rust: dma: require mutable reference for as_slice_mut() and write()

Given the safety requirements of as_slice_mut() and write() taking an
immutable reference is technically not incorrect.

However, let's leverage the compiler's capabilities and require a
mutable reference to ensure exclusive access.

This also fixes a clippy warning introduced with 1.88:

  warning: mutable borrow from immutable input(s)
     --> rust/kernel/dma.rs:297:78
      |
  297 |     pub unsafe fn as_slice_mut(&self, offset: usize, count: usize) -> Result<&mut [T]> {
      |                                                                              ^^^^^^^^

Fixes: d37a39f607c4 ("rust: dma: add as_slice/write functions for CoherentAllocation")
Signed-off-by: Danilo Krummrich <dakr@...nel.org>
---
 rust/kernel/dma.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/rust/kernel/dma.rs b/rust/kernel/dma.rs
index 25dfa0e6cc3c..2ac4c47aeed3 100644
--- a/rust/kernel/dma.rs
+++ b/rust/kernel/dma.rs
@@ -294,7 +294,7 @@ pub unsafe fn as_slice(&self, offset: usize, count: usize) -> Result<&[T]> {
     ///   slice is live.
     /// * Callers must ensure that this call does not race with a read or write to the same region
     ///   while the returned slice is live.
-    pub unsafe fn as_slice_mut(&self, offset: usize, count: usize) -> Result<&mut [T]> {
+    pub unsafe fn as_slice_mut(&mut self, offset: usize, count: usize) -> Result<&mut [T]> {
         self.validate_range(offset, count)?;
         // SAFETY:
         // - The pointer is valid due to type invariant on `CoherentAllocation`,
@@ -326,7 +326,7 @@ pub unsafe fn as_slice_mut(&self, offset: usize, count: usize) -> Result<&mut [T
     /// unsafe { alloc.write(buf, 0)?; }
     /// # Ok::<(), Error>(()) }
     /// ```
-    pub unsafe fn write(&self, src: &[T], offset: usize) -> Result {
+    pub unsafe fn write(&mut self, src: &[T], offset: usize) -> Result {
         self.validate_range(offset, src.len())?;
         // SAFETY:
         // - The pointer is valid due to type invariant on `CoherentAllocation`

base-commit: c7e03c5cf06a90ff234ae3c628c6b74e5cba7426
-- 
2.50.0