OpenStack How to debug neutron contrail plugin

1)
Add log
#sudo vim /usr/lib/python2.7/dist-packages/neutron_plugin_contrail/plugins/opencontrail/contrail_plugin.py
LOG.warn(_('your debug message here'))

2)
Restart server
#sudo service neutron-server restart

3)
Run the CLI command
#neutron net-list --debug

4)
Check the logs
#sudo tail -f /var/log/neutron/server.log