Updating check_switch_started in p4runtime_switch.py (#85)

The previous implementation had a race conditiona between the
socket check and the BMv2 startup. Sometimes, if the check happen
just before (or as) BMv2 was trying to bind the port, it would
not be able to bind it. This solution uses psutil's equivalent
to 'netstat' to determine whether is BMv2 has bound the port yet.

Also, some minor README and comment improvements.

P4D2_2017_Fall/exercises/p4runtime/README.md

@@ -5,7 +5,7 @@
 In this exercise, we will be using P4 Runtime to send flow entries to the 
 switch instead of using the switch's CLI. We will be building on the same P4
 program that you used in the [basic_tunnel](../basic_tunnel) exercise. The
-P4 program has be renamed to `advanced_tunnel.py` and has been augmented
+P4 program has been renamed to `advanced_tunnel.py` and has been augmented
 with two counters (`ingressTunnelCounter`, `egressTunnelCounter`) and
 two new actions (`myTunnel_ingress`, `myTunnel_egress`).
  
@@ -20,7 +20,7 @@ necessary to tunnel traffic between host 1 and 2.
 ## Step 1: Run the (incomplete) starter code
 
 The starter code for this assignment is in a file called `mycontroller.py`,
-and it will install only some of the rules that you need tunnel traffic between
+and it will install only some of the rules that you need to tunnel traffic between
 two hosts.
 
 Let's first compile the new P4 program, start the network, use `mycontroller.py`

P4D2_2017_Fall/exercises/p4runtime/mycontroller.py

@@ -43,13 +43,19 @@ def writeTunnelRules(p4info_helper, ingress_sw, egress_sw, tunnel_id,
 
     # 2) Tunnel Transit Rule
     # The rule will need to be added to the myTunnel_exact table and match on
-    # the tunnel ID (hdr.myTunnel.dst_id). For our simple topology, transit
+    # the tunnel ID (hdr.myTunnel.dst_id). Traffic will need to be forwarded
-    # traffic will need to be forwarded on the using the myTunnel_forward action
+    # using the myTunnel_forward action on the port connected to the next switch.
-    # on the SWITCH_TO_SWITCH_PORT (port 2).
     #
-    # We will only need on transit rule on the ingress switch because we are
+    # For our simple topology, switch 1 and switch 2 are connected using a
+    # link attached to port 2 on both switches. We have defined a variable at
+    # the top of the file, SWITCH_TO_SWITCH_PORT, that you can use as the output
+    # port for this action.
+    #
+    # We will only need a transit rule on the ingress switch because we are
     # using a simple topology. In general, you'll need on transit rule for
-    # each switch in the path (except the last one).
+    # each switch in the path (except the last switch, which has the egress rule),
+    # and you will need to select the port dynamically for each switch based on
+    # your topology.
 
     # TODO build the transit rule
     # TODO install the transit rule on the ingress switch

P4D2_2017_Fall/exercises/p4runtime/solution/mycontroller.py

@@ -48,13 +48,20 @@ def writeTunnelRules(p4info_helper, ingress_sw, egress_sw, tunnel_id,
 
     # 2) Tunnel Transit Rule
     # The rule will need to be added to the myTunnel_exact table and match on
-    # the tunnel ID (hdr.myTunnel.dst_id). For our simple topology, transit
+    # the tunnel ID (hdr.myTunnel.dst_id). Traffic will need to be forwarded
-    # traffic will need to be forwarded on the using the myTunnel_forward action
+    # using the myTunnel_forward action on the port connected to the next switch.
-    # on the SWITCH_TO_SWITCH_PORT (port 2).
     #
-    # We will only need on transit rule on the ingress switch because we are
+    # For our simple topology, switch 1 and switch 2 are connected using a
+    # link attached to port 2 on both switches. We have defined a variable at
+    # the top of the file, SWITCH_TO_SWITCH_PORT, that you can use as the output
+    # port for this action.
+    #
+    # We will only need a transit rule on the ingress switch because we are
     # using a simple topology. In general, you'll need on transit rule for
-    # each switch in the path (except the last one).
+    # each switch in the path (except the last switch, which has the egress rule),
+    # and you will need to select the port dynamically for each switch based on
+    # your topology.
+
     table_entry = p4info_helper.buildTableEntry(
         table_name="myTunnel_exact",
         match_fields={

P4D2_2017_Fall/utils/p4runtime_switch.py

@@ -25,6 +25,14 @@ from mininet.log import info, error, debug
 sys.path.append('/home/vagrant/behavioral-model/mininet')
 from p4_mininet import P4Switch
 
+SWITCH_START_TIMEOUT = 10 # seconds
+
+import psutil
+def check_listening_on_port(port):
+    for c in psutil.net_connections(kind='inet'):
+        if c.status == 'LISTEN' and c.laddr[1] == port:
+            return True
+    return False
 
 class P4RuntimeSwitch(P4Switch):
     "BMv2 switch with gRPC support"
@@ -59,6 +67,10 @@ class P4RuntimeSwitch(P4Switch):
             self.grpc_port = P4RuntimeSwitch.next_grpc_port
             P4RuntimeSwitch.next_grpc_port += 1
 
+        if check_listening_on_port(self.grpc_port):
+            error('%s cannot bind port %d because it is bound by another process\n' % (self.name, self.grpc_port))
+            exit(1)
+
         self.verbose = verbose
         logfile = "/tmp/p4s.{}.log".format(self.name)
         self.output = open(logfile, 'w')
@@ -75,17 +87,12 @@ class P4RuntimeSwitch(P4Switch):
 
 
     def check_switch_started(self, pid):
-        while True:
+        for _ in range(SWITCH_START_TIMEOUT * 2):
             if not os.path.exists(os.path.join("/proc", str(pid))):
                 return False
-            sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+            if check_listening_on_port(self.grpc_port):
-            sock.settimeout(0.5)
-            result = sock.connect_ex(("localhost", self.grpc_port))
-            if result == 0:
-                # TODO It seems like sometimes BMv2 can hang if multiple instances start up too quickly;
-                #      this sleep might also do nothing...
-                sleep(0.5)
                 return True
+            sleep(0.5)
 
     def start(self, controllers):
         info("Starting P4 switch {}.\n".format(self.name))