[PATCH 1/2] rust: sync: add Arc::DATA_OFFSET

[Alice Ryhl <aliceryhl@google.com>]

This constant will be used to expose some offset constants from the Rust
Binder driver to tracepoints which are implemented in C. The constant is
usually equal to sizeof(refcount_t), but may be larger if T has a large
alignment.

Signed-off-by: Alice Ryhl <aliceryhl@google.com>
---
 rust/kernel/sync/arc.rs | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
index 289f77abf415a2a52e039a2c0291413eda01217c..921e19333b895f0d971591c4753047d0248a3029 100644
--- a/rust/kernel/sync/arc.rs
+++ b/rust/kernel/sync/arc.rs
@@ -240,6 +240,9 @@ pub fn new(contents: T, flags: Flags) -> Result<Self, AllocError> {
         // `Arc` object.
         Ok(unsafe { Self::from_inner(inner) })
     }
+
+    /// The offset that the value is stored at.
+    pub const DATA_OFFSET: usize = core::mem::offset_of!(ArcInner<T>, data);
 }
 
 impl<T: ?Sized> Arc<T> {

-- 
2.52.0.158.g65b55ccf14-goog