Fix a stack on pushdisks in the container.kvm driver

Happens when the container configuration file is not present.

This patch makes sure we return an empty devices mapping in this case.
And switches a free-style cache implementation to a lazy property.

lib/resContainerKvm.py

@@ -4,7 +4,7 @@
 import os
 import rcExceptions as ex
 from rcGlobalEnv import rcEnv
-from rcUtilities import justcall, cache, clear_cache
+from rcUtilities import justcall, cache, clear_cache, lazy
 from rcUtilitiesLinux import check_ping
 import resContainer
 
@@ -156,15 +156,13 @@ def install_drp_flag(self):
         tree = ElementTree()
         tree.parse(self.cf)
 
-        """ create the vdisk if it does not exist yet
-        """
+        # create the vdisk if it does not exist yet
         if not os.path.exists(flag_disk_path):
             with open(flag_disk_path, 'w') as f:
                 f.write('')
                 f.close()
 
-        """ check if drp flag is already set up
-        """
+        # check if drp flag is already set up
         for disk in tree.getiterator("disk"):
             e = disk.find('source')
             if e is None:
@@ -174,8 +172,7 @@ def install_drp_flag(self):
                 self.log.info("flag virtual disk already exists")
                 return
 
-        """ add vdisk to the vm xml config
-        """
+        # add vdisk to the vm xml config
         self.log.info("install drp flag virtual disk")
         devices = tree.find("devices")
         e = SubElement(devices, "disk", {'device': 'disk', 'type': 'file'})
@@ -185,17 +182,19 @@ def install_drp_flag(self):
         tree.write(self.cf)
 
     def sub_devs(self):
-        devmapping = self.devmap()
-        devs = set(map(lambda x: x[0], devmapping))
+        devs = set(map(lambda x: x[0], self.devmapping))
         return devs
 
-    def devmap(self):
-        try:
-            return getattr(self, "devmapping")
-        except AttributeError:
-            pass
-
-        self.devmapping = []
+    @lazy
+    def devmapping(self):
+        """
+        Return a list of (src, dst) devices tuples fount in the container
+        conifguration file.
+        """
+        if not os.path.exists(self.cf):
+            # not yet received from peer node ?
+            return []
+        data = []
 
         from xml.etree.ElementTree import ElementTree, SubElement
         tree = ElementTree()
@@ -213,8 +212,8 @@ def devmap(self):
             if 'dev' not in s.attrib:
                  continue
             dst = s.attrib['dev']
-            self.devmapping.append((src, dst))
-        return self.devmapping
+            data.append((src, dst))
+        return data
 
     def _status(self, verbose=False):
         return resContainer.Container._status(self, verbose=verbose)