1 files changed, 89 insertions, 8 deletions

diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
index 8484c814609a..63a66761d0c7 100644
--- a/rust/kernel/sync/arc.rs
+++ b/rust/kernel/sync/arc.rs
@@ -19,12 +19,14 @@
 use crate::{
     alloc::{AllocError, Flags, KBox},
     bindings,
+    ffi::c_void,
     init::InPlaceInit,
     try_init,
     types::{ForeignOwnable, Opaque},
 };
 use core::{
     alloc::Layout,
+    borrow::{Borrow, BorrowMut},
     fmt,
     marker::PhantomData,
     mem::{ManuallyDrop, MaybeUninit},
@@ -135,7 +137,7 @@ pub struct Arc<T: ?Sized> {
     // meaningful with respect to dropck - but this may change in the future so this is left here
     // out of an abundance of caution.
     //
-    // See https://doc.rust-lang.org/nomicon/phantom-data.html#generic-parameters-and-drop-checking
+    // See <https://doc.rust-lang.org/nomicon/phantom-data.html#generic-parameters-and-drop-checking>
     // for more detail on the semantics of dropck in the presence of `PhantomData`.
     _p: PhantomData<ArcInner<T>>,
 }
@@ -371,15 +373,19 @@ impl<T: ?Sized> Arc<T> {
     }
 }
 
-impl<T: 'static> ForeignOwnable for Arc<T> {
+// SAFETY: The pointer returned by `into_foreign` comes from a well aligned
+// pointer to `ArcInner<T>`.
+unsafe impl<T: 'static> ForeignOwnable for Arc<T> {
+    const FOREIGN_ALIGN: usize = core::mem::align_of::<ArcInner<T>>();
+
     type Borrowed<'a> = ArcBorrow<'a, T>;
     type BorrowedMut<'a> = Self::Borrowed<'a>;
 
-    fn into_foreign(self) -> *mut crate::ffi::c_void {
+    fn into_foreign(self) -> *mut c_void {
         ManuallyDrop::new(self).ptr.as_ptr().cast()
     }
 
-    unsafe fn from_foreign(ptr: *mut crate::ffi::c_void) -> Self {
+    unsafe fn from_foreign(ptr: *mut 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>>()) };
@@ -390,7 +396,7 @@ impl<T: 'static> ForeignOwnable for Arc<T> {
         unsafe { Self::from_inner(inner) }
     }
 
-    unsafe fn borrow<'a>(ptr: *mut crate::ffi::c_void) -> ArcBorrow<'a, T> {
+    unsafe fn borrow<'a>(ptr: *mut 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>>()) };
@@ -400,10 +406,10 @@ impl<T: 'static> ForeignOwnable for Arc<T> {
         unsafe { ArcBorrow::new(inner) }
     }
 
-    unsafe fn borrow_mut<'a>(ptr: *mut crate::ffi::c_void) -> ArcBorrow<'a, T> {
+    unsafe fn borrow_mut<'a>(ptr: *mut c_void) -> ArcBorrow<'a, T> {
         // SAFETY: The safety requirements for `borrow_mut` are a superset of the safety
         // requirements for `borrow`.
-        unsafe { Self::borrow(ptr) }
+        unsafe { <Self as ForeignOwnable>::borrow(ptr) }
     }
 }
 
@@ -423,6 +429,31 @@ impl<T: ?Sized> AsRef<T> for Arc<T> {
     }
 }
 
+/// # Examples
+///
+/// ```
+/// # use core::borrow::Borrow;
+/// # use kernel::sync::Arc;
+/// struct Foo<B: Borrow<u32>>(B);
+///
+/// // Owned instance.
+/// let owned = Foo(1);
+///
+/// // Shared instance.
+/// let arc = Arc::new(1, GFP_KERNEL)?;
+/// let shared = Foo(arc.clone());
+///
+/// let i = 1;
+/// // Borrowed from `i`.
+/// let borrowed = Foo(&i);
+/// # Ok::<(), Error>(())
+/// ```
+impl<T: ?Sized> Borrow<T> for Arc<T> {
+    fn borrow(&self) -> &T {
+        self.deref()
+    }
+}
+
 impl<T: ?Sized> Clone for Arc<T> {
     fn clone(&self) -> Self {
         // SAFETY: By the type invariant, there is necessarily a reference to the object, so it is
@@ -489,7 +520,7 @@ impl<T: ?Sized> From<Pin<UniqueArc<T>>> for Arc<T> {
 /// There are no mutable references to the underlying [`Arc`], and it remains valid for the
 /// lifetime of the [`ArcBorrow`] instance.
 ///
-/// # Example
+/// # Examples
 ///
 /// ```
 /// use kernel::sync::{Arc, ArcBorrow};
@@ -831,6 +862,56 @@ impl<T: ?Sized> DerefMut for UniqueArc<T> {
     }
 }
 
+/// # Examples
+///
+/// ```
+/// # use core::borrow::Borrow;
+/// # use kernel::sync::UniqueArc;
+/// struct Foo<B: Borrow<u32>>(B);
+///
+/// // Owned instance.
+/// let owned = Foo(1);
+///
+/// // Owned instance using `UniqueArc`.
+/// let arc = UniqueArc::new(1, GFP_KERNEL)?;
+/// let shared = Foo(arc);
+///
+/// let i = 1;
+/// // Borrowed from `i`.
+/// let borrowed = Foo(&i);
+/// # Ok::<(), Error>(())
+/// ```
+impl<T: ?Sized> Borrow<T> for UniqueArc<T> {
+    fn borrow(&self) -> &T {
+        self.deref()
+    }
+}
+
+/// # Examples
+///
+/// ```
+/// # use core::borrow::BorrowMut;
+/// # use kernel::sync::UniqueArc;
+/// struct Foo<B: BorrowMut<u32>>(B);
+///
+/// // Owned instance.
+/// let owned = Foo(1);
+///
+/// // Owned instance using `UniqueArc`.
+/// let arc = UniqueArc::new(1, GFP_KERNEL)?;
+/// let shared = Foo(arc);
+///
+/// let mut i = 1;
+/// // Borrowed from `i`.
+/// let borrowed = Foo(&mut i);
+/// # Ok::<(), Error>(())
+/// ```
+impl<T: ?Sized> BorrowMut<T> for UniqueArc<T> {
+    fn borrow_mut(&mut self) -> &mut T {
+        self.deref_mut()
+    }
+}
+
 impl<T: fmt::Display + ?Sized> fmt::Display for UniqueArc<T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         fmt::Display::fmt(self.deref(), f)