add cbench application

This simple application does _only_ what cbench expects. As usual, you
can use this application in the following way:

$ ryu-manager --app_lists ryu.app.cbench.Cbench

Currently, this supports only the latency mode.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>

ryu/app/cbench.py

@@ -0,0 +1,26 @@
+# Copyright (C) 2012 Nippon Telegraph and Telephone Corporation.
+# Copyright (C) 2012 Isaku Yamahata <yamahata at valinux co jp>
+
+from ryu.controller import ofp_event
+from ryu.controller.handler import MAIN_DISPATCHER
+from ryu.controller.handler import set_ev_cls
+
+
+class Cbench(object):
+    def __init__(self, *_args, **kwargs):
+        pass
+
+    @set_ev_cls(ofp_event.EventOFPPacketIn, MAIN_DISPATCHER)
+    def packet_in_handler(self, ev):
+        msg = ev.msg
+        datapath = msg.datapath
+        ofproto = datapath.ofproto
+
+        match = datapath.ofproto_parser.OFPMatch(ofproto.OFPFW_ALL,
+                                                 0, 0, 0, 0, 0,
+                                                 0, 0, 0, 0, 0, 0, 0)
+
+        datapath.send_flow_mod(
+            match=match, cookie=0, command=ofproto.OFPFC_ADD,
+            idle_timeout=0, hard_timeout=0, priority=32768,
+            flags=0, actions=None)