From: Danilo Krummrich dakr@kernel.org
Implement ForeignOwnable for ARef<T>, making it possible for C code to own an ARef<T>.
Since ARef represents shared ownership, BorrowedMut is &T rather than &mut T, matching the semantics of the underlying reference-counted type.
Signed-off-by: Danilo Krummrich dakr@kernel.org Reviewed-by: Alice Ryhl aliceryhl@google.com --- rust/kernel/sync/aref.rs | 40 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 40 insertions(+)
diff --git a/rust/kernel/sync/aref.rs b/rust/kernel/sync/aref.rs index b721b2e00b98..540766613659 100644 --- a/rust/kernel/sync/aref.rs +++ b/rust/kernel/sync/aref.rs @@ -24,6 +24,11 @@ ptr::NonNull, // };
+use crate::{ + prelude::*, + types::ForeignOwnable, // +}; + /// Types that are _always_ reference counted. /// /// It allows such types to define their own custom ref increment and decrement functions. @@ -188,6 +193,41 @@ fn eq(&self, other: &ARef<U>) -> bool { } impl<T: AlwaysRefCounted + Eq> Eq for ARef<T> {}
+// SAFETY: `into_foreign` returns a pointer from `NonNull::as_ptr`, so it's non-null. The +// `ARef` invariant guarantees that `ptr` points to a valid `T`, so it's aligned to `T`. +unsafe impl<T: AlwaysRefCounted + 'static> ForeignOwnable for ARef<T> { + const FOREIGN_ALIGN: usize = core::mem::align_of::<T>(); + + type Borrowed<'a> = &'a T; + type BorrowedMut<'a> = &'a T; + + fn into_foreign(self) -> *mut c_void { + ARef::into_raw(self).as_ptr().cast() + } + + 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 ptr = unsafe { NonNull::new_unchecked(ptr.cast()) }; + + // SAFETY: `ptr` came from `into_foreign`, which consumed an `ARef` without decrementing + // the refcount, so we can transfer the ownership to the new `ARef`. + unsafe { ARef::from_raw(ptr) } + } + + unsafe fn borrow<'a>(ptr: *mut c_void) -> &'a T { + // SAFETY: The safety requirements of this method ensure that the object remains alive and + // immutable for the duration of 'a. + unsafe { &*ptr.cast() } + } + + unsafe fn borrow_mut<'a>(ptr: *mut c_void) -> &'a T { + // SAFETY: The safety requirements for `borrow_mut` are a superset of the safety + // requirements for `borrow`. + unsafe { <Self as ForeignOwnable>::borrow(ptr) } + } +} + impl<T, U> PartialEq<&'_ U> for ARef<T> where T: AlwaysRefCounted + PartialEq<U>,