Add a method to get a pointer to the data contained in an `Arc`.

Reviewed-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Benno Lossin <benno.lossin@proton.me>
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---

This is a dependency for:

rust: hrtimer: implement `HrTimerPointer` for `Arc`
---
 rust/kernel/sync/arc.rs | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
index 3cefda7a4372..1dfa75714f9d 100644
--- a/rust/kernel/sync/arc.rs
+++ b/rust/kernel/sync/arc.rs
@@ -246,6 +246,15 @@ pub fn into_raw(self) -> *const T {
         unsafe { core::ptr::addr_of!((*ptr).data) }
     }
 
+    /// Return a raw pointer to the data in this arc.
+    pub fn as_ptr(this: &Self) -> *const T {
+        let ptr = this.ptr.as_ptr();
+
+        // SAFETY: As `ptr` points to a valid allocation of type `ArcInner`,
+        // field projection to `data`is within bounds of the allocation.
+        unsafe { core::ptr::addr_of!((*ptr).data) }
+    }
+
     /// Recreates an [`Arc`] instance previously deconstructed via [`Arc::into_raw`].
     ///
     /// # Safety
@@ -539,11 +548,11 @@ unsafe fn new(inner: NonNull<ArcInner<T>>) -> Self {
     }
 
     /// Creates an [`ArcBorrow`] to an [`Arc`] that has previously been deconstructed with
-    /// [`Arc::into_raw`].
+    /// [`Arc::into_raw`] or [`Arc::as_ptr`].
     ///
     /// # Safety
     ///
-    /// * The provided pointer must originate from a call to [`Arc::into_raw`].
+    /// * The provided pointer must originate from a call to [`Arc::into_raw`] or [`Arc::as_ptr`].
     /// * For the duration of the lifetime annotated on this `ArcBorrow`, the reference count must
     ///   not hit zero.
     /// * For the duration of the lifetime annotated on this `ArcBorrow`, there must not be a

-- 
2.47.0