Add root access check to cns server.

media/tools/constrained_network_server/traffic_control.py

Index: media/tools/constrained_network_server/traffic_control.py
diff --git a/media/tools/constrained_network_server/traffic_control.py b/media/tools/constrained_network_server/traffic_control.py
index c27a255365b766cdd68ade24204916fc9d02285d..38756776ca98f9818c9c566937eca11ec7af1251 100755
--- a/media/tools/constrained_network_server/traffic_control.py
+++ b/media/tools/constrained_network_server/traffic_control.py
@@ -9,6 +9,7 @@ Traffic to the constrained port is forwarded to a specified server port.
 """
 
 import logging
+import os
 import re
 import subprocess
 
@@ -37,6 +38,22 @@ class TrafficControlError(BaseException):
     self.error = error
 
 
+def CheckRequirements():
+  """Checks if permissions are available to run traffic control commands.
+
+  Raises:
+    TrafficControlError: If permissions to run traffic control commands are not
+    available.
+  """
+  if os.geteuid() != 0:
+    _Exec(['sudo', '-n', 'tc', '-help'],

[Ami GONE FROM CHROMIUM, 2012/01/10 22:30:56]

Note that this isn't fool-proof; sudo uses an expiring (per-tty?) cookie to
prevent asking for a PW too frequently, so a sudo -n might succeed at the
beginning of a CNS run but later fail.

Still, probably good enough for this use.

+          msg=('Cannot run \'tc\' command. Traffic Control must be run as root '
+               'or have password-less sudo access to this command.'))
+    _Exec(['sudo', '-n', 'iptables', '-help'],
+          msg=('Cannot run \'iptables\' command. Traffic Control must be run '
+               'as root or have password-less sudo access to this command.'))
+
+
 def CreateConstrainedPort(config):
   """Creates a new constrained port.