addon: handle unsupported modules

Example: If /sbin/ethtool is not installed dont run the
ethtool addon module.

Signed-off-by: Roopa Prabhu <roopa@cumulusnetworks.com>

addons/ethtool.py

@@ -7,12 +7,14 @@ import json
 import ifupdown.policymanager as policymanager
 
 try:
+    import os
     from ipaddr import IPNetwork
     from sets import Set
     from ifupdown.iface import *
+    from ifupdown.exceptions import moduleNotSupported
     from ifupdown.utils import utils
     from ifupdownaddons.utilsbase import *
-    from ifupdownaddons.modulebase import moduleBase
+    from ifupdownaddons.modulebase import moduleBase, NotSupported
     from ifupdownaddons.iproute2 import iproute2
     import ifupdown.ifupdownflags as ifupdownflags
 except ImportError, e:
@@ -41,6 +43,8 @@ class ethtool(moduleBase,utilsBase):
 
     def __init__(self, *args, **kargs):
         moduleBase.__init__(self, *args, **kargs)
+        if not os.path.exists('/sbin/ethtool'):
+            raise moduleNotSupported('module init failed: no /sbin/ethtool found')
         self.ipcmd = None
         # keep a list of iface objects who have modified link attributes
         self.ifaceobjs_modified_configs = []

ifupdown/exceptions.py

@@ -21,3 +21,6 @@ class invalidValueError(Error):
 
 class errorReadingStateError(Error):
     pass
+
+class moduleNotSupported(Error):
+    pass

ifupdown/ifupdownmain.py

@@ -24,6 +24,7 @@ from scheduler import *
 from collections import deque
 from collections import OrderedDict
 from graph import *
+from exceptions import *
 from sets import Set
 
 """
@@ -829,7 +830,15 @@ class ifupdownMain(ifupdownBase):
                             mclass = getattr(m, mname)
                         except:
                             raise
+                        try:
                             minstance = mclass()
+                        except moduleNotSupported, e:
+                            self.logger.info('module %s not loaded (%s)\n'
+                                             %(mname, str(e)))
+                            pass
+                            continue
+                        except:
+                            raise
                         self.modules[mname] = minstance
                         try:
                             self.module_attrs[mname] = minstance.get_modinfo()

ifupdownaddons/modulebase.py

@@ -15,6 +15,9 @@ from ifupdown.iface import *
 import ifupdown.policymanager as policymanager
 import ifupdown.ifupdownflags as ifupdownflags
 
+class NotSupported(Exception):
+    pass
+
 class moduleBase(object):
     """ Base class for ifupdown addon modules