Buffered output. Added net.monitor() and node.readline()

Moved monitor() and readline() into net.py and node.py respectively,
which will hopefully be useful for monitoring large sets of hosts,
as is done in udpbwtest.py.

Changed iperf to use interactive command infrastructure (such as it
is), which may make it more reliable. Hopefully it's a bit clearer
as well, although it is slightly more complicated.

mininet/net.py

@@ -85,6 +85,7 @@ method may be called to shut down the network.
 
 import os
 import re
+import select
 import signal
 from time import sleep
 
@@ -382,6 +383,25 @@ class Mininet( object ):
         self.stop()
         return result
 
+    def monitor( self, hosts=None ):
+        """Monitor a set of hosts (or all hosts by default),
+           and return their output, a line at a time.
+           returns: host, line"""
+        if hosts is None:
+            hosts = self.hosts
+        poller = select.poll()
+        Node = hosts[ 0 ] # so we can call class method fdToNode
+        for host in hosts:
+            poller.register( host.stdout )
+        while True:
+            ready = poller.poll()
+            for fd, event in ready:
+                host = Node.fdToNode( fd )
+                if event & select.POLLIN:
+                    line = host.readline()
+                    if line:
+                        yield host, line
+
     @staticmethod
     def _parsePing( pingOutput ):
         "Parse ping output and return packets sent, received."
@@ -460,10 +480,10 @@ class Mininet( object ):
             hosts = [ self.hosts[ 0 ], self.hosts[ -1 ] ]
         else:
             assert len( hosts ) == 2
-        host0, host1 = hosts
+        client, server = hosts
         output( '*** Iperf: testing ' + l4Type + ' bandwidth between ' )
-        output( "%s and %s\n" % ( host0.name, host1.name ) )
-        host0.cmd( 'killall -9 iperf' )
+        output( "%s and %s\n" % ( client.name, server.name ) )
+        server.cmd( 'killall -9 iperf' )
         iperfArgs = 'iperf '
         bwArgs = ''
         if l4Type == 'UDP':
@@ -471,14 +491,17 @@ class Mininet( object ):
             bwArgs = '-b ' + udpBw + ' '
         elif l4Type != 'TCP':
             raise Exception( 'Unexpected l4 type: %s' % l4Type )
-        server = host0.cmd( iperfArgs + '-s &' )
-        debug( '%s\n' % server )
-        client = host1.cmd( iperfArgs + '-t 5 -c ' + host0.IP() + ' ' +
+        server.sendCmd( iperfArgs + '-s', printPid=True )
+        servout = ''
+        while server.lastPid is None:
+            servout += server.monitor()
+        cliout = client.cmd( iperfArgs + '-t 5 -c ' + server.IP() + ' ' +
                            bwArgs )
-        debug( '%s\n' % client )
-        server = host0.cmd( 'killall -9 iperf' )
-        debug( '%s\n' % server )
-        result = [ self._parseIperf( server ), self._parseIperf( client ) ]
+        debug( 'Client output: %s\n' % cliout )
+        server.sendInt()
+        servout += server.waitOutput()
+        debug( 'Server output: %s\n' % servout )
+        result = [ self._parseIperf( servout ), self._parseIperf( cliout ) ]
         if l4Type == 'UDP':
             result.insert( 0, udpBw )
         output( '*** Results: %s\n' % result )