linux-kernel - [PATCH v4 2/5] rust: make `Arc::into_unique_or

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Message-ID: <20250622125802.3224264-3-gary@kernel.org>
Date: Sun, 22 Jun 2025 13:57:28 +0100
From: Gary Guo <gary@...nel.org>
To: 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>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>,
	Trevor Gross <tmgross@...ch.edu>,
	Danilo Krummrich <dakr@...nel.org>,
	Tamir Duberstein <tamird@...il.com>,
	Xiangfei Ding <dingxiangfei2009@...il.com>,
	Alex Mantel <alexmantel93@...lbox.org>
Cc: Will Deacon <will@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Mark Rutland <mark.rutland@....com>,
	rust-for-linux@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v4 2/5] rust: make `Arc::into_unique_or_drop` associated function

From: Gary Guo <gary@...yguo.net>

Make `Arc::into_unique_or_drop` to become a mere associated function
instead of a method (i.e. removing the `self` receiver).

It's a general convention for Rust smart pointers to avoid having
methods defined on them, because if the pointee type has a method of the
same name, then it is shadowed. This is normally for avoiding semver
breakage, which isn't an issue for kernel codebase, but it's still
generally a good practice to follow this rule, so that `ptr.foo()` would
always be calling a method on the pointee type.

Signed-off-by: Gary Guo <gary@...yguo.net>
---
 rust/kernel/sync/arc.rs | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
index c7af0aa48a0a..09a471fea4da 100644
--- a/rust/kernel/sync/arc.rs
+++ b/rust/kernel/sync/arc.rs
@@ -320,7 +320,7 @@ pub fn ptr_eq(this: &Self, other: &Self) -> bool {
     /// use kernel::sync::{Arc, UniqueArc};
     ///
     /// let arc = Arc::new(42, GFP_KERNEL)?;
-    /// let unique_arc = arc.into_unique_or_drop();
+    /// let unique_arc = Arc::into_unique_or_drop(arc);
     ///
     /// // The above conversion should succeed since refcount of `arc` is 1.
     /// assert!(unique_arc.is_some());
@@ -336,18 +336,18 @@ pub fn ptr_eq(this: &Self, other: &Self) -> bool {
     /// let arc = Arc::new(42, GFP_KERNEL)?;
     /// let another = arc.clone();
     ///
-    /// let unique_arc = arc.into_unique_or_drop();
+    /// let unique_arc = Arc::into_unique_or_drop(arc);
     ///
     /// // The above conversion should fail since refcount of `arc` is >1.
     /// assert!(unique_arc.is_none());
     ///
     /// # Ok::<(), Error>(())
     /// ```
-    pub fn into_unique_or_drop(self) -> Option<Pin<UniqueArc<T>>> {
+    pub fn into_unique_or_drop(this: Self) -> Option<Pin<UniqueArc<T>>> {
         // We will manually manage the refcount in this method, so we disable the destructor.
-        let me = ManuallyDrop::new(self);
+        let this = ManuallyDrop::new(this);
         // SAFETY: We own a refcount, so the pointer is still valid.
-        let refcount = unsafe { me.ptr.as_ref() }.refcount.get();
+        let refcount = unsafe { this.ptr.as_ref() }.refcount.get();
 
         // If the refcount reaches a non-zero value, then we have destroyed this `Arc` and will
         // return without further touching the `Arc`. If the refcount reaches zero, then there are
@@ -364,7 +364,7 @@ pub fn into_unique_or_drop(self) -> Option<Pin<UniqueArc<T>>> {
             // must pin the `UniqueArc` because the values was previously in an `Arc`, and they pin
             // their values.
             Some(Pin::from(UniqueArc {
-                inner: ManuallyDrop::into_inner(me),
+                inner: ManuallyDrop::into_inner(this),
             }))
         } else {
             None
-- 
2.49.0