rust: kernel: reorder ForeignOwnable items

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

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

Reviewed-by: Alice Ryhl <[email protected]>
Reviewed-by: Andreas Hindborg <[email protected]>
Signed-off-by: Tamir Duberstein <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
[ Reworded title slightly. - Miguel ]
Signed-off-by: Miguel Ojeda <[email protected]>

Author: tamird

rust/kernel/sync/arc.rs

@@ -349,25 +349,25 @@ impl<T: 'static> ForeignOwnable for Arc<T> {
         ManuallyDrop::new(self).ptr.as_ptr().cast()
     }
 
-    unsafe fn borrow<'a>(ptr: *mut crate::ffi::c_void) -> ArcBorrow<'a, T> {
+    unsafe fn from_foreign(ptr: *mut crate::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 crate::ffi::c_void) -> Self {
+    unsafe fn borrow<'a>(ptr: *mut crate::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) }
     }
 }
 

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 crate::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 crate::ffi::c_void) -> Self::Borrowed<'a>;
-
     /// Converts a foreign-owned object back to a Rust-owned one.
     ///
     /// # Safety
@@ -67,6 +59,14 @@ pub trait ForeignOwnable: Sized {
             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 crate::ffi::c_void) -> Self::Borrowed<'a>;
 }
 
 impl ForeignOwnable for () {
@@ -76,9 +76,9 @@ impl ForeignOwnable for () {
         core::ptr::NonNull::dangling().as_ptr()
     }
 
-    unsafe fn borrow<'a>(_: *mut crate::ffi::c_void) -> Self::Borrowed<'a> {}
-
     unsafe fn from_foreign(_: *mut crate::ffi::c_void) -> Self {}
+
+    unsafe fn borrow<'a>(_: *mut crate::ffi::c_void) -> Self::Borrowed<'a> {}
 }
 
 /// Runs a cleanup function/closure when dropped.