xenapi: Make agent optional

Related to blueprint xenapi-config-drive

As config drive and agent are doing similar operations, this change
makes it possible to disable agent, thus config drive could perform
these operations.

Change-Id: I3fa536cb0fb3b60ff5bc035be9d86afe35905240

2 files changed, 74 insertions, 49 deletions

diff --git a/nova/virt/xenapi/agent.py b/nova/virt/xenapi/agent.py
index 0c17dccff..605c95cfd 100644
--- a/nova/virt/xenapi/agent.py
+++ b/nova/virt/xenapi/agent.py
@@ -49,6 +49,11 @@ xenapi_agent_opts = [
                     'configuration is not injected into the image. '
                     'Used if compute_driver=xenapi.XenAPIDriver and '
                     ' flat_injected=True'),
+    cfg.StrOpt('xenapi_disable_agent',
+               default=False,
+               help='Disable XenAPI agent. Reduces the amount of time '
+                    'it takes nova to detect that a VM has started, when '
+                    'that VM does not have the agent installed'),
 ]
 
 FLAGS = flags.FLAGS
@@ -244,6 +249,9 @@ def find_guest_agent(base_dir):
     tries to locate a guest agent at the path
     specificed by agent_rel_path
     """
+    if FLAGS.xenapi_disable_agent:
+        return False
+
     agent_rel_path = FLAGS.xenapi_agent_path
     agent_path = os.path.join(base_dir, agent_rel_path)
     if os.path.isfile(agent_path):
diff --git a/nova/virt/xenapi/vmops.py b/nova/virt/xenapi/vmops.py
index 1f8cafa3b..be143ed9b 100644
--- a/nova/virt/xenapi/vmops.py
+++ b/nova/virt/xenapi/vmops.py
@@ -156,8 +156,14 @@ class VMOps(object):
         self.vif_driver = vif_impl(xenapi_session=self._session)
         self.default_root_dev = '/dev/sda'
 
+    @property
+    def agent_enabled(self):
+        return not FLAGS.xenapi_disable_agent
+
     def _get_agent(self, instance, vm_ref):
-        return xapi_agent.XenAPIBasedAgent(self._session, instance, vm_ref)
+        if self.agent_enabled:
+            return xapi_agent.XenAPIBasedAgent(self._session, instance, vm_ref)
+        raise exception.NovaException(_("Error: Agent is disabled"))
 
     def list_instances(self):
         """List VM instances."""
@@ -514,17 +520,6 @@ class VMOps(object):
         self._start(instance, vm_ref)
 
         ctx = nova_context.get_admin_context()
-        agent_build = db.agent_build_get_by_triple(ctx, 'xen',
-                              instance['os_type'], instance['architecture'])
-        if agent_build:
-            LOG.info(_('Latest agent build for %(hypervisor)s/%(os)s'
-                       '/%(architecture)s is %(version)s') % agent_build)
-        else:
-            LOG.info(_('No agent build found for %(hypervisor)s/%(os)s'
-                       '/%(architecture)s') % {
-                        'hypervisor': 'xen',
-                        'os': instance['os_type'],
-                        'architecture': instance['architecture']})
 
         # Wait for boot to finish
         LOG.debug(_('Waiting for instance state to become running'),
@@ -537,34 +532,47 @@ class VMOps(object):
 
             greenthread.sleep(0.5)
 
-        # Update agent, if necessary
-        # This also waits until the agent starts
-        agent = self._get_agent(instance, vm_ref)
-        version = agent.get_agent_version()
-        if version:
-            LOG.info(_('Instance agent version: %s'), version,
-                     instance=instance)
-
-        if (version and agent_build and
-            cmp_version(version, agent_build['version']) < 0):
-            agent.agent_update(agent_build)
-
-        # if the guest agent is not available, configure the
-        # instance, but skip the admin password configuration
-        no_agent = version is None
-
-        # Inject files, if necessary
-        if injected_files:
-            # Inject any files, if specified
-            for path, contents in injected_files:
-                agent.inject_file(path, contents)
-
-        # Set admin password, if necessary
-        if admin_password and not no_agent:
-            agent.set_admin_password(admin_password)
-
-        # Reset network config
-        agent.resetnetwork()
+        if self.agent_enabled:
+            agent_build = db.agent_build_get_by_triple(
+                ctx, 'xen', instance['os_type'], instance['architecture'])
+            if agent_build:
+                LOG.info(_('Latest agent build for %(hypervisor)s/%(os)s'
+                           '/%(architecture)s is %(version)s') % agent_build)
+            else:
+                LOG.info(_('No agent build found for %(hypervisor)s/%(os)s'
+                           '/%(architecture)s') % {
+                            'hypervisor': 'xen',
+                            'os': instance['os_type'],
+                            'architecture': instance['architecture']})
+
+            # Update agent, if necessary
+            # This also waits until the agent starts
+            agent = self._get_agent(instance, vm_ref)
+            version = agent.get_agent_version()
+            if version:
+                LOG.info(_('Instance agent version: %s'), version,
+                         instance=instance)
+
+            if (version and agent_build and
+                cmp_version(version, agent_build['version']) < 0):
+                agent.agent_update(agent_build)
+
+            # if the guest agent is not available, configure the
+            # instance, but skip the admin password configuration
+            no_agent = version is None
+
+            # Inject files, if necessary
+            if injected_files:
+                # Inject any files, if specified
+                for path, contents in injected_files:
+                    agent.inject_file(path, contents)
+
+            # Set admin password, if necessary
+            if admin_password and not no_agent:
+                agent.set_admin_password(admin_password)
+
+            # Reset network config
+            agent.resetnetwork()
 
         # Set VCPU weight
         inst_type = db.instance_type_get(ctx, instance['instance_type_id'])
@@ -857,15 +865,21 @@ class VMOps(object):
 
     def set_admin_password(self, instance, new_pass):
         """Set the root/admin password on the VM instance."""
-        vm_ref = self._get_vm_opaque_ref(instance)
-        agent = self._get_agent(instance, vm_ref)
-        agent.set_admin_password(new_pass)
+        if self.agent_enabled:
+            vm_ref = self._get_vm_opaque_ref(instance)
+            agent = self._get_agent(instance, vm_ref)
+            agent.set_admin_password(new_pass)
+        else:
+            raise NotImplementedError()
 
     def inject_file(self, instance, path, contents):
         """Write a file to the VM instance."""
-        vm_ref = self._get_vm_opaque_ref(instance)
-        agent = self._get_agent(instance, vm_ref)
-        agent.inject_file(path, contents)
+        if self.agent_enabled:
+            vm_ref = self._get_vm_opaque_ref(instance)
+            agent = self._get_agent(instance, vm_ref)
+            agent.inject_file(path, contents)
+        else:
+            raise NotImplementedError()
 
     @staticmethod
     def _sanitize_xenstore_key(key):
@@ -1407,9 +1421,12 @@ class VMOps(object):
 
     def reset_network(self, instance):
         """Calls resetnetwork method in agent."""
-        vm_ref = self._get_vm_opaque_ref(instance)
-        agent = self._get_agent(instance, vm_ref)
-        agent.resetnetwork()
+        if self.agent_enabled:
+            vm_ref = self._get_vm_opaque_ref(instance)
+            agent = self._get_agent(instance, vm_ref)
+            agent.resetnetwork()
+        else:
+            raise NotImplementedError()
 
     def inject_hostname(self, instance, vm_ref, hostname):
         """Inject the hostname of the instance into the xenstore."""