Reload Xend session params when we got an XenAPI.Failure exception

Because we're caching e.g. uuid and metrics objects for the Xend session, we can get an exception
when the VM changed the power state between since we cached the object. We now catch this exception
and reload uuid and metrics object in the handler.

dom0/qvm-core/qubes.py

@@ -106,7 +106,8 @@ class XendSession(object):
             print "get_xend_session_new_api(): cannot open session!"
 
 
-xend_session = XendSession()
+if not dry_run:
+    xend_session = XendSession()
  
 class QubesException (Exception) : pass
 
@@ -178,12 +179,7 @@ class QubesVm(object):
         self.icon_path = self.dir_path + "/icon.png"
 
         if not dry_run and xend_session.session is not None:
-            uuids = xend_session.session.xenapi.VM.get_by_name_label (self.name)
+            self.refresh_xend_session()
-            self.session_uuid = uuids[0] if len (uuids) > 0 else None
-            if self.session_uuid is not None:
-                self.session_metrics = xend_session.session.xenapi.VM.get_metrics(self.session_uuid)
-            else:
-                self.session_metrics = None
 
     @property
     def qid(self):
@@ -273,11 +269,7 @@ class QubesVm(object):
 
         self.in_xen_storage = False
 
-    def update_xen_storage(self):
+    def refresh_xend_session(self):
-        self.remove_from_xen_storage()
-        self.add_to_xen_storage()
-
-        if not dry_run and xend_session.session is not None:
         uuids = xend_session.session.xenapi.VM.get_by_name_label (self.name)
         self.session_uuid = uuids[0] if len (uuids) > 0 else None
         if self.session_uuid is not None:
@@ -285,27 +277,46 @@ class QubesVm(object):
         else:
             self.session_metrics = None
 
-
+    def update_xen_storage(self):
+        self.remove_from_xen_storage()
+        self.add_to_xen_storage()
+        if not dry_run and xend_session.session is not None:
+            self.refresh_xend_session()
 
     def get_xid(self):
         if dry_run:
             return 666
 
+        try:
             xid = int (xend_session.session.xenapi.VM.get_domid (self.session_uuid))
+        except XenAPI.Failure:
+            self.refresh_xend_session()
+            xid = int (xend_session.session.xenapi.VM.get_domid (self.session_uuid))
+
         return xid
 
     def get_mem(self):
         if dry_run:
             return 666
 
+        try:
             mem = int (xend_session.session.xenapi.VM_metrics.get_memory_actual (self.session_metrics))
+        except XenAPI.Failure:
+            self.refresh_xend_session()
+            mem = int (xend_session.session.xenapi.VM_metrics.get_memory_actual (self.session_metrics))
+
         return mem
 
     def get_mem_static_max(self):
         if dry_run:
             return 666
 
+        try:
             mem = int(xend_session.session.xenapi.VM.get_memory_static_max(self.session_uuid))
+        except XenAPI.Failure:
+            self.refresh_xend_session()
+            mem = int(xend_session.session.xenapi.VM.get_memory_static_max(self.session_uuid))
+
         return mem
 
 
@@ -314,7 +325,12 @@ class QubesVm(object):
             import random
             return random.random() * 100
 
+        try:
             cpus_util = xend_session.session.xenapi.VM_metrics.get_VCPUs_utilisation (self.session_metrics)
+        except XenAPI.Failure:
+            self.refresh_xend_session()
+            cpus_util = xend_session.session.xenapi.VM_metrics.get_VCPUs_utilisation (self.session_metrics)
+
         if len (cpus_util) == 0:
             return 0
 
@@ -331,10 +347,14 @@ class QubesVm(object):
         if dry_run:
             return "NA"
 
+        try:
+            power_state = xend_session.session.xenapi.VM.get_power_state (self.session_uuid)
+        except XenAPI.Failure:
+            self.refresh_xend_session()
             if self.session_uuid is None:
                 return "NA"
-
             power_state = xend_session.session.xenapi.VM.get_power_state (self.session_uuid)
+
         return power_state
 
     def is_running(self):
@@ -343,7 +363,6 @@ class QubesVm(object):
         else:
             return False
 
-
     def get_disk_usage(self, file_or_dir):
         if not os.path.exists(file_or_dir):
             return 0
@@ -442,7 +461,12 @@ class QubesVm(object):
         if dom0_mem_new < dom0_min_memory:
             raise MemoryError ("ERROR: starting this VM would cause Dom0 memory to go below {0}B".format(dom0_min_memory))
 
+        try:
             xend_session.session.xenapi.VM.start (self.session_uuid, True) # Starting a VM paused
+        except XenAPI.Failure:
+            self.refresh_xend_session()
+            xend_session.session.xenapi.VM.start (self.session_uuid, True) # Starting a VM paused
+
         xid = int (xend_session.session.xenapi.VM.get_domid (self.session_uuid))
 
         if verbose:
@@ -487,6 +511,10 @@ class QubesVm(object):
         if dry_run:
             return
 
+        try:
+            xend_session.session.xenapi.VM.hard_shutdown (self.session_uuid)
+        except XenAPI.Failure:
+            self.refresh_xend_session()
             xend_session.session.xenapi.VM.hard_shutdown (self.session_uuid)
 
     def remove_from_disk(self):