XenAPI: Add option for running nova independently from hypervisor

Add the independent compute option and ensure appropriate failure cases
for all incompatible options.

Change-Id: I76c1e3a80da8142639328b204aea5da59551eea3
Implements-blueprint: xenapi-independent-nova

nova/conf/xenserver.py

@@ -343,6 +343,20 @@ xenapi_opts = [
                default='sd',
                help='Specify prefix to remap VBD dev to '
                     '(ex. /dev/xvdb -> /dev/sdb)'),
+    cfg.BoolOpt('independent_compute',
+                default=False,
+                help="""
+                Used to prevent attempts to attach VBDs locally, so Nova can
+                be run in a VM on a different host.
+
+                This setting is incompatible with:
+                * ``CONF.flat_injected`` (Must be False)
+                * ``CONF.xenserver.check_host`` (Must be False)
+                * ``CONF.default_ephemeral_format`` (Must be unset or 'ext3')
+                * Joining host aggregates (will error if attempted)
+                * Swap disks for Windows VMs (will error if attempted)
+                * Nova-based auto_configure_disk (will error if attempted)
+                """),
 ]
 
 xenapi_vmops_opts = [

nova/exception.py

@@ -2090,3 +2090,9 @@ class ConcurrentUpdateDetected(NovaException):
 class UnsupportedPointerModelRequested(Invalid):
     msg_fmt = _("Pointer model '%(model)s' requested is not supported by "
                 "host.")
+
+
+class NotSupportedWithOption(Invalid):
+    msg_fmt = _("%(operation)s is not supported in conjunction with the "
+                "current %(option)s setting.  Please refer to the nova "
+                "config-reference.")

nova/virt/xenapi/driver.py

@@ -34,6 +34,7 @@ import six.moves.urllib.parse as urlparse
 
 import nova.conf
 from nova.i18n import _, _LE, _LW
+from nova import exception
 from nova.virt import driver
 from nova.virt.xenapi.client import session
 from nova.virt.xenapi import host
@@ -82,13 +83,35 @@ class XenAPIDriver(driver.ComputeDriver):
         return self._host_state
 
     def init_host(self, host):
+        if CONF.xenserver.independent_compute:
+            def invalid_option(option_name, recommended_value):
+                LOG.exception(_LE('Current value of '
+                       'CONF.xenserver.%(option)s option incompatible with '
+                       'CONF.xenserver.independent_compute=True.  '
+                       'Consider using "%(recommended)s"') % {
+                           'option': option_name,
+                           'recommended': recommended_value})
+                raise exception.NotSupportedWithOption(
+                    operation=option_name,
+                    option='CONF.xenserver.independent_compute')
+
+            # Check various options are in the correct state:
+            if CONF.xenserver.check_host:
+                invalid_option('CONF.xenserver.check_host', False)
+            if CONF.flat_injected:
+                invalid_option('CONF.flat_injected', False)
+            if CONF.default_ephemeral_format and \
+               CONF.default_ephemeral_format != 'ext3':
+                invalid_option('CONF.default_ephemeral_format', 'ext3')
+
         if CONF.xenserver.check_host:
             vm_utils.ensure_correct_host(self._session)
 
-        try:
-            vm_utils.cleanup_attached_vdis(self._session)
-        except Exception:
-            LOG.exception(_LE('Failure while cleaning up attached VDIs'))
+        if not CONF.xenserver.independent_compute:
+            try:
+                vm_utils.cleanup_attached_vdis(self._session)
+            except Exception:
+                LOG.exception(_LE('Failure while cleaning up attached VDIs'))
 
     def instance_exists(self, instance):
         """Checks existence of an instance on the host.

nova/virt/xenapi/pool.py

@@ -63,6 +63,11 @@ class ResourcePool(object):
         if not pool_states.is_hv_pool(aggregate.metadata):
             return
 
+        if CONF.xenserver.independent_compute:
+            raise exception.NotSupportedWithOption(
+                operation='adding to a XenServer pool',
+                option='CONF.xenserver.independent_compute')
+
         invalid = {pool_states.CHANGING: _('setup in progress'),
                    pool_states.DISMISSED: _('aggregate deleted'),
                    pool_states.ERROR: _('aggregate in error')}

nova/virt/xenapi/vm_utils.py

@@ -924,6 +924,10 @@ def _auto_configure_disk(session, vdi_ref, new_gb):
 
 
 def try_auto_configure_disk(session, vdi_ref, new_gb):
+    if CONF.xenserver.independent_compute:
+        raise exception.NotSupportedWithOption(
+            operation='auto_configure_disk',
+            option='CONF.xenserver.independent_compute')
     try:
         _auto_configure_disk(session, vdi_ref, new_gb)
     except exception.CannotResizeDisk as e:
@@ -1031,6 +1035,11 @@ def generate_swap(session, instance, vm_ref, userdevice, name_label, swap_mb):
     is_windows = instance['os_type'] == "windows"
     fs_type = "vfat" if is_windows else "swap"
 
+    if CONF.xenserver.independent_compute and fs_type != "swap":
+        raise exception.NotSupportedWithOption(
+            operation='swap drives for Windows',
+            option='CONF.xenserver.independent_compute')
+
     _generate_disk(session, instance, vm_ref, userdevice, name_label,
                    'swap', swap_mb, fs_type)
 
@@ -1139,6 +1148,11 @@ def _create_kernel_image(context, session, instance, name_label, image_id,
 
     Returns: A list of dictionaries that describe VDIs
     """
+    if CONF.xenserver.independent_compute:
+        raise exception.NotSupportedWithOption(
+            operation='Non-VHD images',
+            option='CONF.xenserver.independent_compute')
+
     filename = ""
     if CONF.xenserver.cache_images != 'none':
         args = {}
@@ -1308,6 +1322,10 @@ def _fetch_image(context, session, instance, name_label, image_id, image_type):
     if image_type == ImageType.DISK_VHD:
         vdis = _fetch_vhd_image(context, session, instance, image_id)
     else:
+        if CONF.xenserver.independent_compute:
+            raise exception.NotSupportedWithOption(
+                operation='Non-VHD images',
+                option='CONF.xenserver.independent_compute')
         vdis = _fetch_disk_image(context, session, instance, name_label,
                                  image_id, image_type)
 
@@ -2198,6 +2216,16 @@ def _get_dom0_ref(session):
 
 
 def get_this_vm_uuid(session):
+    if CONF.xenserver.independent_compute:
+        msg = _LE("This host has been configured with the independent "
+                  "compute flag.  An operation has been attempted which is "
+                  "incompatible with this flag, but should have been "
+                  "caught earlier.  Please raise a bug against the "
+                  "OpenStack Nova project")
+        LOG.error(msg)
+        raise exception.NotSupportedWithOption(
+            operation='uncaught operation',
+            option='CONF.xenserver.independent_compute')
     if session and session.is_local_connection:
         # UUID is the control domain running on this host
         vms = session.call_xenapi("VM.get_all_records_where",