+/*
+ * 2.6.27 API change,
+ * The blk_queue_stackable() queue flag was added in 2.6.27 to handle dm
+ * stacking drivers. Prior to this request stacking drivers were detected
+ * by checking (q->request_fn == NULL), for earlier kernels we revert to
+ * this legacy behavior.
+ */
+#ifndef blk_queue_stackable
+#define blk_queue_stackable(q) ((q)->request_fn == NULL)
+#endif
+