Add set_immediate to ringloop and use it for bs/osd ops to prevent reenterability issues

src/ringloop.h

@@ -119,6 +119,7 @@ struct ring_consumer_t
 
 class ring_loop_t
 {
+    std::vector<std::function<void()>> immediate_queue, immediate_queue2;
     std::vector<ring_consumer_t*> consumers;
     struct ring_data_t *ring_datas;
     int *free_ring_data;
@@ -143,6 +144,10 @@ public:
         }
         return sqe;
     }
+    inline void set_immediate(const std::function<void()> cb)
+    {
+        immediate_queue.push_back(cb);
+    }
     inline int submit()
     {
         return io_uring_submit(&ring);