Implements resume_state_on_host_boot for libvirt.

Adds a new virt driver function to help resume guest states
on host boot. This fixes a couple issue with using a reboot
(like we did previously):

 * Using reboot would clear some task states (VERIFY_RESIZE for example)
 * Provides a mechanism for hypervisor specific guest restarts.
   Reboot would not have worked for XenServer for example...
 * Updates libvirt to use a hard reboot (instead of soft)

Fixes LP Bug #985162.

Change-Id: Iaf5aad75ec9b91f44710a18ddaf3a93378573a62
(cherry picked from commit 6548c50)

nova/compute/manager.py

@@ -246,15 +246,21 @@ def init_host(self):
             LOG.debug(_('Current state is %(drv_state)s, state in DB is '
                         '%(db_state)s.'), locals(), instance=instance)
 
+            net_info = self._get_instance_nw_info(context, instance)
             if ((expect_running and FLAGS.resume_guests_state_on_host_boot) or
                 FLAGS.start_guests_on_host_boot):
                 LOG.info(_('Rebooting instance after nova-compute restart.'),
                          locals(), instance=instance)
-                self.reboot_instance(context, instance['uuid'])
+                try:
+                    self.driver.resume_state_on_host_boot(context, instance,
+                                self._legacy_nw_info(net_info))
+                except NotImplementedError:
+                    LOG.warning(_('Hypervisor driver does not support '
+                                  'resume guests'), instance=instance)
+
             elif drv_state == power_state.RUNNING:
                 # Hyper-V and VMWareAPI drivers will raise an exception
                 try:
-                    net_info = self._get_instance_nw_info(context, instance)
                     self.driver.ensure_filtering_rules_for_instance(instance,
                                                 self._legacy_nw_info(net_info))
                 except NotImplementedError:

nova/tests/test_virt_drivers.py

@@ -142,6 +142,12 @@ def test_agent_update(self):
         self.connection.agent_update(instance_ref, 'http://www.openstack.org/',
                                      'd41d8cd98f00b204e9800998ecf8427e')
 
+    @catch_notimplementederror
+    def test_resume_state_on_host_boot(self):
+        instance_ref, network_info = self._get_running_instance()
+        self.connection.resume_state_on_host_boot(self.ctxt, instance_ref,
+                                                  network_info)
+
     @catch_notimplementederror
     def test_rescue(self):
         instance_ref, network_info = self._get_running_instance()

nova/virt/driver.py

@@ -335,6 +335,10 @@ def resume(self, instance):
         # TODO(Vek): Need to pass context in for access to auth_token
         raise NotImplementedError()
 
+    def resume_state_on_host_boot(self, context, instance, network_info):
+        """resume guest state when a host is booted"""
+        raise NotImplementedError()
+
     def rescue(self, context, instance, network_info, image_meta):
         """Rescue the specified instance"""
         raise NotImplementedError()

nova/virt/fake.py

@@ -131,6 +131,9 @@ def inject_file(self, instance, b64_path, b64_contents):
     def agent_update(self, instance, url, md5hash):
         pass
 
+    def resume_state_on_host_boot(self, context, instance, network_info):
+        pass
+
     def rescue(self, context, instance, network_info, image_meta):
         pass
 

nova/virt/libvirt/connection.py

@@ -824,6 +824,13 @@ def resume(self, instance):
         dom = self._lookup_by_name(instance.name)
         dom.create()
 
+    @exception.wrap_exception()
+    def resume_state_on_host_boot(self, context, instance, network_info):
+        """resume guest state when a host is booted"""
+        # NOTE(dprince): use hard reboot to ensure network and firewall
+        # rules are configured
+        self._hard_reboot(instance, network_info)
+
     @exception.wrap_exception()
     def rescue(self, context, instance, network_info, image_meta):
         """Loads a VM using rescue images.