Added example of adding hw interface to mininet.

examples/hwintf.py

+#!/usr/bin/python
+
+"""
+This example shows how to add an interface (for example a real
+hardware interface) to a network after the network is created.
+"""
+
+import re
+
+from mininet.cli import CLI
+from mininet.log import setLogLevel, info, error
+from mininet.net import Mininet
+from mininet.topolib import TreeTopo
+from mininet.util import quietRun
+
+def checkIntf( intf ):
+    "Make sure intf exists and is not configured."
+    if ( ' %s:' % intf ) not in quietRun( 'ip link show' ):
+        error( 'Error:', intf, 'does not exist!\n' )
+        exit( 1 )
+    ips = re.findall( r'\d+\.\d+\.\d+\.\d+', quietRun( 'ifconfig ' + intf ) )
+    if ips:
+        error( 'Error:', intf, 'has an IP address,'
+            'and is probably in use!\n' )
+        exit( 1 )
+
+if __name__ == '__main__':
+    setLogLevel( 'info' )
+
+    newIntf = 'veth1'
+    info( '*** Checking', newIntf, '\n' )
+    checkIntf( newIntf )
+
+    info( '*** Creating network\n' )
+    net = Mininet( topo=TreeTopo( depth=1, fanout=2 ) )
+
+    switch = net.switches[ 0 ]
+    info( '*** Adding', newIntf, 'to switch', switch.name, '\n' )
+    switch.addIntf( newIntf )
+
+    net.start()
+    CLI( net )
+    net.stop()