Added sshd example, which starts up sshd on each host, allowing host access via ssh.

(It also adds a route from the root namespace to the data network via
the first OpenFlow switch, so when you ssh in you go through OpenFlow!)

Modified Network() to optionally decouple starting the network, running
tests, and stopping the network. This allows multiple tests to be run
(or additional modifications to be made to the network before actually
starting the switches and controller.)

Still tweaking xterms - it sort of works but the screen sessions are not
cleaned up, which leads to nasty garbage.

mininet.py

@@ -445,15 +445,12 @@ class Network( object ):
          print "*** Error: ofdatapath not loaded:",
          print " kernel datapath not supported"
          exit( 1 )
-   # In progress: we probably want to decouple creating/starting/stopping
-   # the network and running tests, since we might wish to run
-   # multiple tests on the same network. It's not clear if the network
-   # should always be started/stopped for each test or not. Probably
-   # not...
-   def run( self, test ):
+      # Create network, but don't start things up yet!
+      self.prepareNet()
+   def prepareNet( self ):
       """Create a network by calling makeNet as follows: 
          (switches, hosts ) = makeNet()
-         and then run test( controller, switches, hosts ) on it."""
+         Create a controller here as well."""
       kernel = self.kernel
       if kernel: print "*** Using kernel datapath"
       else: print "*** Using user datapath"
@@ -467,21 +464,39 @@ class Network( object ):
          configRoutedControlNetwork( controller, switches )
       print "*** Configuring hosts"
       configHosts( hosts, self.startAddr )
+      self.controllers = [ controller ]
+      self.switches = switches
+      self.hosts = hosts
+   def start( self ):
+      "Start controller and switches"
       print "*** Starting reference controller"
-      controller.start()
-      print "*** Starting", len( switches ), "switches"
-      for switch in switches:
-         switch.start( controller )
-      print "*** Running test"
-      result = test( [ controller ], switches, hosts )
+      for controller in self.controllers:
+         controller.start()
+      print "*** Starting", len( self.switches ), "switches"
+      for switch in self.switches:
+         switch.start( self.controllers[ 0 ] )
+   def stop( self ):
+      "Stop the controller(s), switches and hosts"
       print "*** Stopping controller"
-      controller.stop(); controller.terminate()
+      for controller in self.controllers:
+         controller.stop(); controller.terminate()
       print "*** Stopping switches"
-      for switch in switches:
+      for switch in self.switches:
          switch.stop() ; switch.terminate()
       print "*** Stopping hosts"
-      for host in hosts: host.terminate()
+      for host in self.hosts: 
+         host.terminate()
       print "*** Test complete"
+   def runTest( self, test ):
+      "Run a given test, called as test( controllers, switches, hosts)"
+      return test( self.controllers, self.switches, self.hosts )
+   def run( self, test ):
+      """Perform a complete start/test/stop cycle; test is of the form
+         test( controllers, switches, hosts )"""
+      self.start()
+      print "*** Running test"
+      result = self.runTest( test )
+      self.stop()
       return result
    def interact( self ):
       "Create a network and run our simple CLI."