linux-kernel - [PATCH v2 5/6] rust: reorder `ForeignOwnable` items

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Message-Id: <20241104-borrow-mut-v2-5-de650678648d@gmail.com>
Date: Mon, 04 Nov 2024 17:20:31 -0400
From: Tamir Duberstein <tamird@...il.com>
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 <benno.lossin@...ton.me>, 
 Andreas Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>, 
 Trevor Gross <tmgross@...ch.edu>, Danilo Krummrich <dakr@...nel.org>
Cc: rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Tamir Duberstein <tamird@...il.com>
Subject: [PATCH v2 5/6] rust: reorder `ForeignOwnable` items

`{into,from}_foreign` before `borrow` is slightly more logical.

This removes an inconsistency with `kbox.rs` which already uses this
ordering.

Signed-off-by: Tamir Duberstein <tamird@...il.com>
---
 rust/kernel/sync/arc.rs | 18 +++++++++---------
 rust/kernel/types.rs    | 20 ++++++++++----------
 2 files changed, 19 insertions(+), 19 deletions(-)

diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
index 10819dc28b64038b9abc55b01c069826d1e5befa..3c779b343aa8c396d2d4b7efdbc0f1ef524a0f1c 100644
--- a/rust/kernel/sync/arc.rs
+++ b/rust/kernel/sync/arc.rs
@@ -337,25 +337,25 @@ fn into_foreign(self) -> *mut core::ffi::c_void {
         ManuallyDrop::new(self).ptr.as_ptr().cast()
     }
 
-    unsafe fn borrow<'a>(ptr: *mut core::ffi::c_void) -> ArcBorrow<'a, T> {
+    unsafe fn from_foreign(ptr: *mut core::ffi::c_void) -> Self {
         // SAFETY: The safety requirements of this function ensure that `ptr` comes from a previous
         // call to `Self::into_foreign`.
         let inner = unsafe { NonNull::new_unchecked(ptr.cast::<ArcInner<T>>()) };
 
-        // SAFETY: The safety requirements of `from_foreign` ensure that the object remains alive
-        // for the lifetime of the returned value.
-        unsafe { ArcBorrow::new(inner) }
+        // SAFETY: By the safety requirement of this function, we know that `ptr` came from
+        // a previous call to `Arc::into_foreign`, which guarantees that `ptr` is valid and
+        // holds a reference count increment that is transferrable to us.
+        unsafe { Self::from_inner(inner) }
     }
 
-    unsafe fn from_foreign(ptr: *mut core::ffi::c_void) -> Self {
+    unsafe fn borrow<'a>(ptr: *mut core::ffi::c_void) -> ArcBorrow<'a, T> {
         // SAFETY: The safety requirements of this function ensure that `ptr` comes from a previous
         // call to `Self::into_foreign`.
         let inner = unsafe { NonNull::new_unchecked(ptr.cast::<ArcInner<T>>()) };
 
-        // SAFETY: By the safety requirement of this function, we know that `ptr` came from
-        // a previous call to `Arc::into_foreign`, which guarantees that `ptr` is valid and
-        // holds a reference count increment that is transferrable to us.
-        unsafe { Self::from_inner(inner) }
+        // SAFETY: The safety requirements of `from_foreign` ensure that the object remains alive
+        // for the lifetime of the returned value.
+        unsafe { ArcBorrow::new(inner) }
     }
 }
 
diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
index 59e71bd158713bb8e12cac95e134f57a277c1b49..b8f3594737401a3df841f30a20c4bd85743853ef 100644
--- a/rust/kernel/types.rs
+++ b/rust/kernel/types.rs
@@ -31,14 +31,6 @@ pub trait ForeignOwnable: Sized {
     /// [`ForeignOwnable::try_from_foreign`] can result in undefined behavior.
     fn into_foreign(self) -> *mut core::ffi::c_void;
 
-    /// Borrows a foreign-owned object.
-    ///
-    /// # Safety
-    ///
-    /// `ptr` must have been returned by a previous call to [`ForeignOwnable::into_foreign`] for
-    /// which a previous matching [`ForeignOwnable::from_foreign`] hasn't been called yet.
-    unsafe fn borrow<'a>(ptr: *mut core::ffi::c_void) -> Self::Borrowed<'a>;
-
     /// Converts a foreign-owned object back to a Rust-owned one.
     ///
     /// # Safety
@@ -67,6 +59,14 @@ unsafe fn try_from_foreign(ptr: *mut core::ffi::c_void) -> Option<Self> {
             unsafe { Some(Self::from_foreign(ptr)) }
         }
     }
+
+    /// Borrows a foreign-owned object.
+    ///
+    /// # Safety
+    ///
+    /// `ptr` must have been returned by a previous call to [`ForeignOwnable::into_foreign`] for
+    /// which a previous matching [`ForeignOwnable::from_foreign`] hasn't been called yet.
+    unsafe fn borrow<'a>(ptr: *mut core::ffi::c_void) -> Self::Borrowed<'a>;
 }
 
 impl ForeignOwnable for () {
@@ -76,9 +76,9 @@ fn into_foreign(self) -> *mut core::ffi::c_void {
         core::ptr::NonNull::dangling().as_ptr()
     }
 
-    unsafe fn borrow<'a>(_: *mut core::ffi::c_void) -> Self::Borrowed<'a> {}
-
     unsafe fn from_foreign(_: *mut core::ffi::c_void) -> Self {}
+
+    unsafe fn borrow<'a>(_: *mut core::ffi::c_void) -> Self::Borrowed<'a> {}
 }
 
 /// Runs a cleanup function/closure when dropped.

-- 
2.47.0