libvirt: Remove import hacks

This has been on the TODO list for over 8 years. Time to resolve it.

Change-Id: Ic5367a1042ae5da974a25c135b58a1ebf22eb531
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>

nova/virt/libvirt/driver.py

@@ -134,12 +134,16 @@ from nova.virt.libvirt.volume import volume
 from nova.virt import netutils
 from nova.volume import cinder
 
-libvirt: ty.Any = None
+try:
+    # This is optional for unit testing but required at runtime. We check for
+    # it during driver init.
+    import libvirt
+except ImportError:
+    libvirt = None
 
 uefi_logged = False
 
 LOG = logging.getLogger(__name__)
-
 CONF = nova.conf.CONF
 
 MAX_CONSOLE_BYTES = 100 * units.Ki
@@ -396,6 +400,12 @@ class AsyncDeviceEventsHandler:
 
 class LibvirtDriver(driver.ComputeDriver):
     def __init__(self, virtapi, read_only=False):
+        if libvirt is None:
+            # the libvirt driver is "customer 0" of the libvirt API: if we
+            # haven't been able to import it, fail early by attempting to
+            # import again
+            __import__('libvirt')
+
         # NOTE(aspiers) Some of these are dynamic, so putting
         # capabilities on the instance rather than on the class.
         # This prevents the risk of one test setting a capability
@@ -443,17 +453,12 @@ class LibvirtDriver(driver.ComputeDriver):
             "supports_ephemeral_encryption_luks":
                 self.image_backend.backend().SUPPORTS_LUKS,
         }
-        super(LibvirtDriver, self).__init__(virtapi)
+        super().__init__(virtapi)
 
         if not sys.platform.startswith('linux'):
             raise exception.InternalError(
                 _('The libvirt driver only works on Linux'))
 
-        global libvirt
-        if libvirt is None:
-            libvirt = importutils.import_module('libvirt')
-            libvirt_migrate.libvirt = libvirt
-
         self._host = host.Host(self._uri(), read_only,
                                lifecycle_event_handler=self.emit_event,
                                conn_event_handler=self._handle_conn_event)

nova/virt/libvirt/guest.py

@@ -34,7 +34,6 @@ from lxml import etree
 from oslo_log import log as logging
 from oslo_utils import encodeutils
 from oslo_utils import excutils
-from oslo_utils import importutils
 
 from nova.compute import power_state
 from nova import exception
@@ -42,10 +41,11 @@ from nova.i18n import _
 from nova.virt import hardware
 from nova.virt.libvirt import config as vconfig
 
-
-if ty.TYPE_CHECKING:
+try:
+    # This is optional for unit testing but required at runtime. We check for
+    # it during driver init.
     import libvirt
-else:
+except ImportError:
     libvirt = None
 
 try:
@@ -103,14 +103,9 @@ LIBVIRT_BLOCK_JOB_TYPE = {
 }
 
 
-class Guest(object):
+class Guest:
 
     def __init__(self, domain):
-
-        global libvirt
-        if libvirt is None:
-            libvirt = importutils.import_module('libvirt')
-
         self._domain = domain
 
     def __repr__(self):

nova/virt/libvirt/host.py

@@ -31,7 +31,6 @@ from collections import defaultdict
 import fnmatch
 import glob
 import inspect
-from lxml import etree
 import operator
 import os
 import queue
@@ -41,10 +40,10 @@ import typing as ty
 from eventlet import greenio
 from eventlet import greenthread
 from eventlet import patcher
+from lxml import etree
 from oslo_log import log as logging
 from oslo_serialization import jsonutils
 from oslo_utils import excutils
-from oslo_utils import importutils
 from oslo_utils import strutils
 from oslo_utils import units
 from oslo_utils import versionutils
@@ -67,20 +66,20 @@ from nova.virt.libvirt import migration as libvirt_migrate
 from nova.virt.libvirt import utils as libvirt_utils
 import nova.virt.node  # noqa
 
-if ty.TYPE_CHECKING:
+try:
+    # This is optional for unit testing but required at runtime. We check for
+    # it during driver init.
     import libvirt
-else:
+except ImportError:
     libvirt = None
 
+CONF = nova.conf.CONF
 LOG = logging.getLogger(__name__)
 
 native_socket = patcher.original('socket')
 native_threading = patcher.original("threading")
 native_Queue = patcher.original("queue")
 
-CONF = nova.conf.CONF
-
-
 # This list is for libvirt hypervisor drivers that need special handling.
 # This is *not* the complete list of supported hypervisor drivers.
 HV_DRIVER_QEMU = "QEMU"
@@ -125,11 +124,6 @@ class Host(object):
     def __init__(self, uri, read_only=False,
                  conn_event_handler=None,
                  lifecycle_event_handler=None):
-
-        global libvirt
-        if libvirt is None:
-            libvirt = importutils.import_module('libvirt')
-
         self._uri = uri
         self._read_only = read_only
         self._initial_connection = True

nova/virt/libvirt/migration.py

@@ -12,10 +12,8 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+"""Utility methods to manage guests migration."""
 
-"""Utility methods to manage guests migration
-
-"""
 from collections import deque
 
 from lxml import etree
@@ -28,15 +26,16 @@ from nova import objects
 from nova.virt import hardware
 from nova.virt.libvirt import config as vconfig
 
+try:
+    # This is optional for unit testing but required at runtime. We check for
+    # it during driver init.
+    import libvirt
+except ImportError:
+    libvirt = None
+
 LOG = logging.getLogger(__name__)
-
 CONF = nova.conf.CONF
 
-# TODO(berrange): hack to avoid a "import libvirt" in this file.
-# Remove this and similar hacks in guest.py, driver.py, host.py
-# etc in Ocata.
-libvirt = None
-
 
 def graphics_listen_addrs(migrate_data):
     """Returns listen addresses of vnc/spice from a LibvirtLiveMigrateData"""