[PATCH v2] rust: sync: add accessor for the lock behind a given guard

[Alice Ryhl <aliceryhl@google.com>]

Binder has some methods where the caller provides a lock guard, and
Binder needs to be able to assert that the guard is associated with the
right lock. To enable this, add an accessor to obtain a reference to the
underlying lock that you can pass to `ptr::eq`.

Signed-off-by: Alice Ryhl <aliceryhl@google.com>
---
Changes in v2:
- Rename to lock_ref() to avoid confusion with lock().
- Rebase on v6.14-rc1.
- Link to v1: https://lore.kernel.org/r/20250130-guard-get-lock-v1-1-8ed87899920a@google.com
---
 rust/kernel/sync/lock.rs | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
index eb80048e0110..8e7e6d5f61e4 100644
--- a/rust/kernel/sync/lock.rs
+++ b/rust/kernel/sync/lock.rs
@@ -199,7 +199,12 @@ pub struct Guard<'a, T: ?Sized, B: Backend> {
 // SAFETY: `Guard` is sync when the data protected by the lock is also sync.
 unsafe impl<T: Sync + ?Sized, B: Backend> Sync for Guard<'_, T, B> {}
 
-impl<T: ?Sized, B: Backend> Guard<'_, T, B> {
+impl<'a, T: ?Sized, B: Backend> Guard<'a, T, B> {
+    /// Returns the lock that this guard originates from.
+    pub fn lock_ref(&self) -> &'a Lock<T, B> {
+        self.lock
+    }
+
     pub(crate) fn do_unlocked<U>(&mut self, cb: impl FnOnce() -> U) -> U {
         // SAFETY: The caller owns the lock, so it is safe to unlock it.
         unsafe { B::unlock(self.lock.state.get(), &self.state) };

---
base-commit: 2014c95afecee3e76ca4a56956a936e23283f05b
change-id: 20250130-guard-get-lock-dd5452793d9a

Best regards,
-- 
Alice Ryhl <aliceryhl@google.com>