+ * Exchanging steps of RDMA ioengine control messages:
+ * 1. client side sends test mode (RDMA_WRITE/RDMA_READ/SEND)
+ * to server side.
+ * 2. server side parses test mode, and sends back confirmation
+ * to client side. In RDMA WRITE/READ test, this confirmation
+ * includes memory information, such as rkey, address.
+ * 3. client side initiates test loop.
+ * 4. In RDMA WRITE/READ test, client side sends a completion
+ * notification to server side. Server side updates its
+ * td->done as true.
+ *