pfcwd cmd check (sonic-net#342)

* require root privilege for all pfcwd configuration commands (sonic-net#330)

Signed-off-by: Guohan Lu <gulv@microsoft.com>

* pfcwd start: 1) default restoration time to 2 times detection time if
not defined; 2) check if options are prefixed with "--";

Signed-off-by: Wenda <wenni@microsoft.com>

* Check if ports list has invalid string element;

Correct typo restoration-time

Signed-off-by: Wenda <wenni@microsoft.com>

pfcwd/main.py

@@ -2,6 +2,7 @@
 
 import click
 import swsssdk
+import os
 from tabulate import tabulate
 from natsort import natsorted
 
@@ -124,18 +125,30 @@ def config(ports):
 @cli.command()
 @click.option('--action', '-a', type=click.Choice(['drop', 'forward', 'alert']))
 @click.option('--restoration-time', '-r', type=click.IntRange(100, 60000))
-@click.argument('ports', nargs = -1)
+@click.argument('ports', nargs=-1)
 @click.argument('detection-time', type=click.IntRange(100, 5000))
 def start(action, restoration_time, ports, detection_time):
-    """ Start PFC watchdog on port(s). To config all ports, use all as input. """
+    """
+    Start PFC watchdog on port(s). To config all ports, use all as input.
+
+    Example:
+
+    sudo pfcwd start --action drop ports all detection-time 400 --restoration-time 400
+
+    """
     if os.geteuid() != 0:
         exit("Root privileges are required for this operation")
+    allowed_strs = ['ports', 'all', 'detection-time']
     configdb = swsssdk.ConfigDBConnector()
     configdb.connect()
     countersdb = swsssdk.SonicV2Connector(host='127.0.0.1')
     countersdb.connect(countersdb.COUNTERS_DB)
 
     all_ports = get_all_ports(countersdb)
+    allowed_strs = allowed_strs + all_ports
+    for p in ports:
+        if p not in allowed_strs:
+            raise click.BadOptionUsage("Bad command line format. Try 'pfcwd start --help' for usage")
 
     if len(ports) == 0:
         ports = all_ports
@@ -147,6 +160,9 @@ def start(action, restoration_time, ports, detection_time):
         pfcwd_info['action'] = action
     if restoration_time is not None:
         pfcwd_info['restoration_time'] = restoration_time
+    else:
+        pfcwd_info['restoration_time'] = 2 * detection_time
+        print "restoration time not defined; default to 2 times detection time: %d ms" % (2 * detection_time)
 
     for port in ports:
         if port == "all":