common/io_lock: add helper to query if lock is taken.

Not just for debugging; we actually need to know if a write is active for
the coming hack.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

common/io_lock.c

@@ -80,3 +80,8 @@ void io_lock_release(struct io_lock *lock)
 	lock->locked = false;
 	io_wake(lock);
 }
+
+bool io_lock_taken(const struct io_lock *lock)
+{
+	return lock->locked;
+}

common/io_lock.h

@@ -47,4 +47,9 @@ struct io_plan *io_lock_acquire_in_(struct io_conn *conn, struct io_lock *lock,
  */
 void io_lock_release(struct io_lock *lock);
 
+/**
+ * Is this lock acquired?
+ */
+bool io_lock_taken(const struct io_lock *lock);
+
 #endif /* LIGHTNING_COMMON_IO_LOCK_H */