# Copyright 2010 United States Government as represented by the
# Administrator of the National Aeronautics and Space Administration.
# All Rights Reserved.
# Copyright (c) 2010 Citrix Systems, Inc.
# Copyright (c) 2011 Piston Cloud Computing, Inc
# Copyright (c) 2012 University Of Minho
# (c) Copyright 2013 Hewlett-Packard Development Company, L.P.
#
#    Licensed under the Apache License, Version 2.0 (the "License"); you may
#    not use this file except in compliance with the License. You may obtain
#    a copy of the License at
#
#         http://www.apache.org/licenses/LICENSE-2.0
#
#    Unless required by applicable law or agreed to in writing, software
#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
#    License for the specific language governing permissions and limitations
#    under the License.

"""
Manages information about the host OS and hypervisor.

This class encapsulates a connection to the libvirt
daemon and provides certain higher level APIs around
the raw libvirt API. These APIs are then used by all
the other libvirt related classes
"""

from collections import defaultdict
import fnmatch
import glob
import inspect
import operator
import os
import queue
import socket
import threading
import typing as ty

from eventlet import greenio
from eventlet import greenthread
from eventlet import patcher
from eventlet import tpool
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

from nova.compute import utils as compute_utils
import nova.conf
from nova import context as nova_context
from nova import exception
from nova.i18n import _
from nova.objects import fields
from nova.pci import utils as pci_utils
from nova import rpc
from nova import utils
from nova.virt import event as virtevent
from nova.virt.libvirt import config as vconfig
from nova.virt.libvirt import event as libvirtevent
from nova.virt.libvirt import guest as libvirt_guest
from nova.virt.libvirt import migration as libvirt_migrate
from nova.virt.libvirt import utils as libvirt_utils

if ty.TYPE_CHECKING:
    import libvirt
else:
    libvirt = None

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"

SEV_KERNEL_PARAM_FILE = '/sys/module/kvm_amd/parameters/sev'

# These are taken from the spec
# https://github.com/qemu/qemu/blob/v5.2.0/docs/interop/firmware.json
QEMU_FIRMWARE_DESCRIPTOR_PATHS = [
    '/usr/share/qemu/firmware',
    '/etc/qemu/firmware',
    # we intentionally ignore '$XDG_CONFIG_HOME/qemu/firmware'
]


def _get_loaders():
    if not any(
        os.path.exists(path) for path in QEMU_FIRMWARE_DESCRIPTOR_PATHS
    ):
        msg = _("Failed to locate firmware descriptor files")
        raise exception.InternalError(msg)

    _loaders = []

    for path in QEMU_FIRMWARE_DESCRIPTOR_PATHS:
        if not os.path.exists(path):
            continue

        for spec_path in sorted(glob.glob(f'{path}/*.json')):
            with open(spec_path, 'rb') as fh:
                spec = jsonutils.load(fh)

            _loaders.append(spec)

    return _loaders


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
        self._conn_event_handler = conn_event_handler
        self._conn_event_handler_queue: queue.Queue[ty.Callable] = (
          queue.Queue())
        self._lifecycle_event_handler = lifecycle_event_handler
        self._caps = None
        self._domain_caps = None
        self._hostname = None

        self._wrapped_conn = None
        self._wrapped_conn_lock = threading.Lock()
        self._event_queue: ty.Optional[queue.Queue[ty.Callable]] = None

        self._events_delayed = {}
        # Note(toabctl): During a reboot of a domain, STOPPED and
        #                STARTED events are sent. To prevent shutting
        #                down the domain during a reboot, delay the
        #                STOPPED lifecycle event some seconds.
        self._lifecycle_delay = 15

        self._initialized = False
        self._libvirt_proxy_classes = self._get_libvirt_proxy_classes(libvirt)
        self._libvirt_proxy = self._wrap_libvirt_proxy(libvirt)

        self._loaders: ty.Optional[ty.List[dict]] = None

        # A number of features are conditional on support in the hardware,
        # kernel, QEMU, and/or libvirt. These are determined on demand and
        # memoized by various properties below
        self._supports_amd_sev: ty.Optional[bool] = None
        self._supports_uefi: ty.Optional[bool] = None
        self._supports_secure_boot: ty.Optional[bool] = None

        self._has_hyperthreading: ty.Optional[bool] = None

    @staticmethod
    def _get_libvirt_proxy_classes(libvirt_module):
        """Return a tuple for tpool.Proxy's autowrap argument containing all
        public vir* classes defined by the libvirt module.
        """

        # Get a list of (name, class) tuples of libvirt classes
        classes = inspect.getmembers(libvirt_module, inspect.isclass)

        # Return a list of just the vir* classes, filtering out libvirtError
        # and any private globals pointing at private internal classes.
        return tuple([cls[1] for cls in classes if cls[0].startswith("vir")])

    def _wrap_libvirt_proxy(self, obj):
        """Return an object wrapped in a tpool.Proxy using autowrap appropriate
        for the libvirt module.
        """

        # libvirt is not pure python, so eventlet monkey patching doesn't work
        # on it. Consequently long-running libvirt calls will not yield to
        # eventlet's event loop, starving all other greenthreads until
        # completion. eventlet's tpool.Proxy handles this situation for us by
        # executing proxied calls in a native thread.
        return tpool.Proxy(obj, autowrap=self._libvirt_proxy_classes)

    def _native_thread(self):
        """Receives async events coming in from libvirtd.

        This is a native thread which runs the default
        libvirt event loop implementation. This processes
        any incoming async events from libvirtd and queues
        them for later dispatch. This thread is only
        permitted to use libvirt python APIs, and the
        driver.queue_event method. In particular any use
        of logging is forbidden, since it will confuse
        eventlet's greenthread integration
        """

        while True:
            libvirt.virEventRunDefaultImpl()

    def _dispatch_thread(self):
        """Dispatches async events coming in from libvirtd.

        This is a green thread which waits for events to
        arrive from the libvirt event loop thread. This
        then dispatches the events to the compute manager.
        """

        while True:
            self._dispatch_events()

    def _conn_event_thread(self):
        """Dispatches async connection events"""
        # NOTE(mdbooth): This thread doesn't need to jump through the same
        # hoops as _dispatch_thread because it doesn't interact directly
        # with the libvirt native thread.
        while True:
            self._dispatch_conn_event()

    def _dispatch_conn_event(self):
        # NOTE(mdbooth): Splitting out this loop looks redundant, but it
        # means we can easily dispatch events synchronously from tests and
        # it isn't completely awful.
        handler = self._conn_event_handler_queue.get()
        try:
            handler()
        except Exception:
            LOG.exception('Exception handling connection event')
        finally:
            self._conn_event_handler_queue.task_done()

    @staticmethod
    def _event_device_removed_callback(conn, dom, dev, opaque):
        """Receives device removed events from libvirt.

        NB: this method is executing in a native thread, not
        an eventlet coroutine. It can only invoke other libvirt
        APIs, or use self._queue_event(). Any use of logging APIs
        in particular is forbidden.
        """
        self = opaque
        uuid = dom.UUIDString()
        self._queue_event(libvirtevent.DeviceRemovedEvent(uuid, dev))

    @staticmethod
    def _event_device_removal_failed_callback(conn, dom, dev, opaque):
        """Receives device removed events from libvirt.

        NB: this method is executing in a native thread, not
        an eventlet coroutine. It can only invoke other libvirt
        APIs, or use self._queue_event(). Any use of logging APIs
        in particular is forbidden.
        """
        self = opaque
        uuid = dom.UUIDString()
        self._queue_event(libvirtevent.DeviceRemovalFailedEvent(uuid, dev))

    @staticmethod
    def _event_lifecycle_callback(conn, dom, event, detail, opaque):
        """Receives lifecycle events from libvirt.

        NB: this method is executing in a native thread, not
        an eventlet coroutine. It can only invoke other libvirt
        APIs, or use self._queue_event(). Any use of logging APIs
        in particular is forbidden.
        """

        self = opaque

        uuid = dom.UUIDString()
        transition = None
        if event == libvirt.VIR_DOMAIN_EVENT_STOPPED:
            transition = virtevent.EVENT_LIFECYCLE_STOPPED
        elif event == libvirt.VIR_DOMAIN_EVENT_STARTED:
            transition = virtevent.EVENT_LIFECYCLE_STARTED
        elif event == libvirt.VIR_DOMAIN_EVENT_SUSPENDED:
            if detail == libvirt.VIR_DOMAIN_EVENT_SUSPENDED_POSTCOPY:
                transition = virtevent.EVENT_LIFECYCLE_POSTCOPY_STARTED
            elif detail == libvirt.VIR_DOMAIN_EVENT_SUSPENDED_MIGRATED:
                # VIR_DOMAIN_EVENT_SUSPENDED_MIGRATED is also sent when live
                # migration of the guest fails, so we cannot simply rely
                # on the event itself but need to check if the job itself was
                # successful.
                # NOTE(mriedem): The job check logic here is copied from
                # LibvirtDriver._live_migration_monitor.
                guest = libvirt_guest.Guest(dom)
                info = guest.get_job_info()
                if info.type == libvirt.VIR_DOMAIN_JOB_NONE:
                    # Either still running, or failed or completed,
                    # lets untangle the mess.
                    info.type = libvirt_migrate.find_job_type(
                        guest, instance=None, logging_ok=False)

                if info.type == libvirt.VIR_DOMAIN_JOB_COMPLETED:
                    transition = virtevent.EVENT_LIFECYCLE_MIGRATION_COMPLETED
                else:
                    # Failed or some other status we don't know about, so just
                    # opt to report the guest is paused.
                    transition = virtevent.EVENT_LIFECYCLE_PAUSED
            else:
                transition = virtevent.EVENT_LIFECYCLE_PAUSED
        elif event == libvirt.VIR_DOMAIN_EVENT_RESUMED:
            transition = virtevent.EVENT_LIFECYCLE_RESUMED

        if transition is not None:
            self._queue_event(virtevent.LifecycleEvent(uuid, transition))

    def _close_callback(self, conn, reason, opaque):
        close_info = {'conn': conn, 'reason': reason}
        self._queue_event(close_info)

    @staticmethod
    def _test_connection(conn):
        try:
            conn.getLibVersion()
            return True
        except libvirt.libvirtError as e:
            if (e.get_error_code() in (libvirt.VIR_ERR_SYSTEM_ERROR,
                                       libvirt.VIR_ERR_INTERNAL_ERROR) and
                e.get_error_domain() in (libvirt.VIR_FROM_REMOTE,
                                         libvirt.VIR_FROM_RPC)):
                LOG.debug('Connection to libvirt broke')
                return False
            raise

    @staticmethod
    def _connect_auth_cb(creds, opaque):
        if len(creds) == 0:
            return 0
        raise exception.InternalError(
            _("Can not handle authentication request for %d credentials")
            % len(creds))

    def _connect(self, uri, read_only):
        auth = [[libvirt.VIR_CRED_AUTHNAME,
                 libvirt.VIR_CRED_ECHOPROMPT,
                 libvirt.VIR_CRED_REALM,
                 libvirt.VIR_CRED_PASSPHRASE,
                 libvirt.VIR_CRED_NOECHOPROMPT,
                 libvirt.VIR_CRED_EXTERNAL],
                Host._connect_auth_cb,
                None]

        flags = 0
        if read_only:
            flags = libvirt.VIR_CONNECT_RO
        return self._libvirt_proxy.openAuth(uri, auth, flags)

    def _queue_event(self, event):
        """Puts an event on the queue for dispatch.

        This method is called by the native event thread to
        put events on the queue for later dispatch by the
        green thread. Any use of logging APIs is forbidden.
        """

        if self._event_queue is None:
            return

        # Queue the event...
        self._event_queue.put(event)

        # ...then wakeup the green thread to dispatch it
        c = ' '.encode()
        self._event_notify_send.write(c)
        self._event_notify_send.flush()

    def _dispatch_events(self):
        """Wait for & dispatch events from native thread

        Blocks until native thread indicates some events
        are ready. Then dispatches all queued events.
        """

        # Wait to be notified that there are some
        # events pending
        try:
            _c = self._event_notify_recv.read(1)
            assert _c
        except ValueError:
            return  # will be raised when pipe is closed

        # Process as many events as possible without
        # blocking
        last_close_event = None
        # required for mypy
        if self._event_queue is None:
            return
        while not self._event_queue.empty():
            try:
                event_type = ty.Union[
                    virtevent.InstanceEvent, ty.Mapping[str, ty.Any]]
                event: event_type = self._event_queue.get(block=False)
                if issubclass(type(event), virtevent.InstanceEvent):
                    # call possibly with delay
                    self._event_emit_delayed(event)

                elif 'conn' in event and 'reason' in event:
                    last_close_event = event
            except native_Queue.Empty:
                pass
        if last_close_event is None:
            return
        conn = last_close_event['conn']
        # get_new_connection may already have disabled the host,
        # in which case _wrapped_conn is None.
        with self._wrapped_conn_lock:
            if conn == self._wrapped_conn:
                reason = str(last_close_event['reason'])
                msg = _("Connection to libvirt lost: %s") % reason
                self._wrapped_conn = None
                self._queue_conn_event_handler(False, msg)

    def _event_emit_delayed(self, event):
        """Emit events - possibly delayed."""
        def event_cleanup(gt, *args, **kwargs):
            """Callback function for greenthread. Called
            to cleanup the _events_delayed dictionary when an event
            was called.
            """
            event = args[0]
            self._events_delayed.pop(event.uuid, None)

        # Cleanup possible delayed stop events.
        if event.uuid in self._events_delayed.keys():
            self._events_delayed[event.uuid].cancel()
            self._events_delayed.pop(event.uuid, None)
            LOG.debug("Removed pending event for %s due to event", event.uuid)

        if (isinstance(event, virtevent.LifecycleEvent) and
            event.transition == virtevent.EVENT_LIFECYCLE_STOPPED):
            # Delay STOPPED event, as they may be followed by a STARTED
            # event in case the instance is rebooting
            id_ = greenthread.spawn_after(self._lifecycle_delay,
                                          self._event_emit, event)
            self._events_delayed[event.uuid] = id_
            # add callback to cleanup self._events_delayed dict after
            # event was called
            id_.link(event_cleanup, event)
        else:
            self._event_emit(event)

    def _event_emit(self, event):
        if self._lifecycle_event_handler is not None:
            self._lifecycle_event_handler(event)

    def _init_events_pipe(self):
        """Create a self-pipe for the native thread to synchronize on.

        This code is taken from the eventlet tpool module, under terms
        of the Apache License v2.0.
        """

        self._event_queue = native_Queue.Queue()
        try:
            rpipe, wpipe = os.pipe()
            self._event_notify_send = greenio.GreenPipe(wpipe, 'wb', 0)
            self._event_notify_recv = greenio.GreenPipe(rpipe, 'rb', 0)
        except (ImportError, NotImplementedError):
            # This is Windows compatibility -- use a socket instead
            #  of a pipe because pipes don't really exist on Windows.
            sock = native_socket.socket(socket.AF_INET, socket.SOCK_STREAM)
            sock.bind(('localhost', 0))
            sock.listen(50)
            csock = native_socket.socket(socket.AF_INET, socket.SOCK_STREAM)
            csock.connect(('localhost', sock.getsockname()[1]))
            nsock, addr = sock.accept()
            self._event_notify_send = nsock.makefile('wb', 0)
            gsock = greenio.GreenSocket(csock)
            self._event_notify_recv = gsock.makefile('rb', 0)

    def _init_events(self):
        """Initializes the libvirt events subsystem.

        This requires running a native thread to provide the
        libvirt event loop integration. This forwards events
        to a green thread which does the actual dispatching.
        """

        self._init_events_pipe()

        LOG.debug("Starting native event thread")
        self._event_thread = native_threading.Thread(
            target=self._native_thread)
        self._event_thread.setDaemon(True)
        self._event_thread.start()

        LOG.debug("Starting green dispatch thread")
        utils.spawn(self._dispatch_thread)

    def _get_new_connection(self):
        # call with _wrapped_conn_lock held
        LOG.debug('Connecting to libvirt: %s', self._uri)

        # This will raise an exception on failure
        wrapped_conn = self._connect(self._uri, self._read_only)

        try:
            LOG.debug("Registering for lifecycle events %s", self)
            wrapped_conn.domainEventRegisterAny(
                None,
                libvirt.VIR_DOMAIN_EVENT_ID_LIFECYCLE,
                self._event_lifecycle_callback,
                self)
            wrapped_conn.domainEventRegisterAny(
                None,
                libvirt.VIR_DOMAIN_EVENT_ID_DEVICE_REMOVED,
                self._event_device_removed_callback,
                self)
            wrapped_conn.domainEventRegisterAny(
                None,
                libvirt.VIR_DOMAIN_EVENT_ID_DEVICE_REMOVAL_FAILED,
                self._event_device_removal_failed_callback,
                self)
        except Exception as e:
            LOG.warning("URI %(uri)s does not support events: %(error)s",
                        {'uri': self._uri, 'error': e})

        try:
            LOG.debug("Registering for connection events: %s", str(self))
            wrapped_conn.registerCloseCallback(self._close_callback, None)
        except libvirt.libvirtError as e:
            LOG.warning("URI %(uri)s does not support connection"
                        " events: %(error)s",
                        {'uri': self._uri, 'error': e})

        return wrapped_conn

    def _queue_conn_event_handler(self, *args, **kwargs):
        if self._conn_event_handler is None:
            return

        def handler():
            return self._conn_event_handler(*args, **kwargs)

        self._conn_event_handler_queue.put(handler)

    def _get_connection(self):
        # multiple concurrent connections are protected by _wrapped_conn_lock
        with self._wrapped_conn_lock:
            # Drop the existing connection if it is not usable
            if (self._wrapped_conn is not None and
                    not self._test_connection(self._wrapped_conn)):
                self._wrapped_conn = None
                # Connection was previously up, and went down
                self._queue_conn_event_handler(
                    False, _('Connection to libvirt lost'))

            if self._wrapped_conn is None:
                try:
                    # This will raise if it fails to get a connection
                    self._wrapped_conn = self._get_new_connection()
                except Exception as ex:
                    with excutils.save_and_reraise_exception():
                        # If we previously had a connection and it went down,
                        # we generated a down event for that above.
                        # We also want to generate a down event for an initial
                        # failure, which won't be handled above.
                        if self._initial_connection:
                            self._queue_conn_event_handler(
                                False,
                                _('Failed to connect to libvirt: %(msg)s') %
                                {'msg': ex})
                finally:
                    self._initial_connection = False

                self._queue_conn_event_handler(True, None)

        return self._wrapped_conn

    def get_connection(self):
        """Returns a connection to the hypervisor

        This method should be used to create and return a well
        configured connection to the hypervisor.

        :returns: a libvirt.virConnect object
        """
        try:
            conn = self._get_connection()
        except libvirt.libvirtError as ex:
            LOG.exception("Connection to libvirt failed: %s", ex)
            payload = {'ip': CONF.my_ip, 'method': '_connect', 'reason': ex}
            ctxt = nova_context.get_admin_context()
            rpc.get_notifier('compute').error(ctxt,
                                              'compute.libvirt.error',
                                              payload)
            compute_utils.notify_about_libvirt_connect_error(
                ctxt, ip=CONF.my_ip, exception=ex)
            raise exception.HypervisorUnavailable()

        return conn

    @staticmethod
    def _libvirt_error_handler(context, err):
        # Just ignore instead of default outputting to stderr.
        pass

    def initialize(self):
        if self._initialized:
            return

        # NOTE(dkliban): Error handler needs to be registered before libvirt
        #                connection is used for the first time.  Otherwise, the
        #                handler does not get registered.
        libvirt.registerErrorHandler(self._libvirt_error_handler, None)
        libvirt.virEventRegisterDefaultImpl()
        self._init_events()

        LOG.debug("Starting connection event dispatch thread")
        utils.spawn(self._conn_event_thread)

        self._initialized = True

    def _version_check(self, lv_ver=None, hv_ver=None, hv_type=None,
                       op=operator.lt):
        """Check libvirt version, hypervisor version, and hypervisor type

        :param hv_type: hypervisor driver from the top of this file.
        """
        conn = self.get_connection()
        try:
            if lv_ver is not None:
                libvirt_version = conn.getLibVersion()
                if op(libvirt_version,
                      versionutils.convert_version_to_int(lv_ver)):
                    return False

            if hv_ver is not None:
                hypervisor_version = conn.getVersion()
                if op(hypervisor_version,
                      versionutils.convert_version_to_int(hv_ver)):
                    return False

            if hv_type is not None:
                hypervisor_type = conn.getType()
                if hypervisor_type != hv_type:
                    return False

            return True
        except Exception:
            return False

    def has_min_version(self, lv_ver=None, hv_ver=None, hv_type=None):
        return self._version_check(
            lv_ver=lv_ver, hv_ver=hv_ver, hv_type=hv_type, op=operator.lt)

    def has_version(self, lv_ver=None, hv_ver=None, hv_type=None):
        return self._version_check(
            lv_ver=lv_ver, hv_ver=hv_ver, hv_type=hv_type, op=operator.ne)

    def get_guest(self, instance):
        """Retrieve libvirt guest object for an instance.

        All libvirt error handling should be handled in this method and
        relevant nova exceptions should be raised in response.

        :param instance: a nova.objects.Instance object

        :returns: a nova.virt.libvirt.Guest object
        :raises exception.InstanceNotFound: The domain was not found
        :raises exception.InternalError: A libvirt error occurred
        """
        return libvirt_guest.Guest(self._get_domain(instance))

    def _get_domain(self, instance):
        """Retrieve libvirt domain object for an instance.

        All libvirt error handling should be handled in this method and
        relevant nova exceptions should be raised in response.

        :param instance: a nova.objects.Instance object

        :returns: a libvirt.Domain object
        :raises exception.InstanceNotFound: The domain was not found
        :raises exception.InternalError: A libvirt error occurred
        """
        try:
            conn = self.get_connection()
            return conn.lookupByUUIDString(instance.uuid)
        except libvirt.libvirtError as ex:
            error_code = ex.get_error_code()
            if error_code == libvirt.VIR_ERR_NO_DOMAIN:
                raise exception.InstanceNotFound(instance_id=instance.uuid)

            msg = (_('Error from libvirt while looking up %(instance_name)s: '
                     '[Error Code %(error_code)s] %(ex)s') %
                   {'instance_name': instance.name,
                    'error_code': error_code,
                    'ex': ex})
            raise exception.InternalError(msg)

    def list_guests(self, only_running=True):
        """Get a list of Guest objects for nova instances

        :param only_running: True to only return running instances

        See method "list_instance_domains" for more information.

        :returns: list of Guest objects
        """
        domains = self.list_instance_domains(only_running=only_running)
        return [libvirt_guest.Guest(dom) for dom in domains]

    def list_instance_domains(self, only_running=True):
        """Get a list of libvirt.Domain objects for nova instances

        :param only_running: True to only return running instances

        Query libvirt to a get a list of all libvirt.Domain objects
        that correspond to nova instances. If the only_running parameter
        is true this list will only include active domains, otherwise
        inactive domains will be included too.

        :returns: list of libvirt.Domain objects
        """
        flags = libvirt.VIR_CONNECT_LIST_DOMAINS_ACTIVE
        if not only_running:
            flags = flags | libvirt.VIR_CONNECT_LIST_DOMAINS_INACTIVE

        # listAllDomains() returns <list of virDomain>, not <virDomain>, so
        # tpool.Proxy's autowrap won't catch it. We need to wrap the
        # contents of the list we return.
        alldoms = (self._wrap_libvirt_proxy(dom)
                   for dom in self.get_connection().listAllDomains(flags))

        doms = []
        for dom in alldoms:
            doms.append(dom)

        return doms

    def get_online_cpus(self):
        """Get the set of CPUs that are online on the host

        :returns: set of online CPUs, raises libvirtError on error
        """
        cpus, cpu_map, online = self.get_connection().getCPUMap()

        online_cpus = set()
        for cpu in range(cpus):
            if cpu_map[cpu]:
                online_cpus.add(cpu)

        return online_cpus

    def get_cpu_model_names(self):
        """Get the cpu models based on host CPU arch

        :returns: a list of cpu models which supported by the given CPU arch
        """
        arch = self.get_capabilities().host.cpu.arch
        return self.get_connection().getCPUModelNames(arch)

    @staticmethod
    def _log_host_capabilities(xmlstr):
        # NOTE(mriedem): This looks a bit weird but we do this so we can stub
        # out this method in unit/functional test runs since the xml string is
        # big and it can cause subunit parsing to fail (see bug 1813147).
        LOG.info("Libvirt host capabilities %s", xmlstr)

    def get_capabilities(self):
        """Returns the host capabilities information

        Returns an instance of config.LibvirtConfigCaps representing
        the capabilities of the host.

        Note: The result is cached in the member attribute _caps.

        :returns: a config.LibvirtConfigCaps object
        """
        if self._caps:
            return self._caps

        xmlstr = self.get_connection().getCapabilities()
        self._log_host_capabilities(xmlstr)
        self._caps = vconfig.LibvirtConfigCaps()
        self._caps.parse_str(xmlstr)

        # NOTE(mriedem): Don't attempt to get baseline CPU features
        # if libvirt can't determine the host cpu model.
        if (
            hasattr(libvirt, 'VIR_CONNECT_BASELINE_CPU_EXPAND_FEATURES') and
            self._caps.host.cpu.model is not None
        ):
            try:
                xml_str = self._caps.host.cpu.to_xml()
                if isinstance(xml_str, bytes):
                    xml_str = xml_str.decode('utf-8')
                # NOTE(kevinz): The baseline CPU info on Aarch64 will not
                # include any features. So on Aarch64, we use the original
                # features from LibvirtConfigCaps.
                if self._caps.host.cpu.arch != fields.Architecture.AARCH64:
                    features = self.get_connection().baselineCPU(
                        [xml_str],
                        libvirt.VIR_CONNECT_BASELINE_CPU_EXPAND_FEATURES)
                    if features:
                        cpu = vconfig.LibvirtConfigCPU()
                        cpu.parse_str(features)
                        self._caps.host.cpu.features = cpu.features
            except libvirt.libvirtError as ex:
                error_code = ex.get_error_code()
                if error_code == libvirt.VIR_ERR_NO_SUPPORT:
                    LOG.warning(
                        "URI %(uri)s does not support full set of host "
                        "capabilities: %(error)s",
                        {'uri': self._uri, 'error': ex})
                else:
                    raise

        return self._caps

    def get_domain_capabilities(self):
        """Returns the capabilities you can request when creating a
        domain (VM) with that hypervisor, for various combinations of
        architecture and machine type.

        In this context the fuzzy word "hypervisor" implies QEMU
        binary, libvirt itself and the host config.  libvirt provides
        this in order that callers can determine what the underlying
        emulator and/or libvirt is capable of, prior to creating a domain
        (for instance via virDomainCreateXML or virDomainDefineXML).
        However nova needs to know the capabilities much earlier, when
        the host's compute service is first initialised, in order that
        placement decisions can be made across many compute hosts.
        Therefore this is expected to be called during the init_host()
        phase of the driver lifecycle rather than just before booting
        an instance.

        This causes an additional complication since the Python
        binding for this libvirt API call requires the architecture
        and machine type to be provided.  So in order to gain a full
        picture of the hypervisor's capabilities, technically we need
        to call it with the right parameters, once for each
        (architecture, machine_type) combination which we care about.
        However the libvirt experts have advised us that in practice
        the domain capabilities do not (yet, at least) vary enough
        across machine types to justify the cost of calling
        getDomainCapabilities() once for every single (architecture,
        machine_type) combination.  In particular, SEV support isn't
        reported per-machine type, and since there are usually many
        machine types, we heed the advice of the experts that it's
        typically sufficient to call it once per host architecture:

            https://bugzilla.redhat.com/show_bug.cgi?id=1683471#c7

        However, that's not quite sufficient in the context of nova,
        because SEV guests typically require a q35 machine type, as do
        KVM/QEMU guests that want Secure Boot, whereas the current
        default machine type for x86_64 is 'pc'.  So we need results
        from the getDomainCapabilities API for at least those two.
        Fortunately we can take advantage of the results from the
        getCapabilities API which marks selected machine types as
        canonical, e.g.:

            <machine canonical='pc-i440fx-2.11' maxCpus='255'>pc</machine>
            <machine canonical='pc-q35-2.11' maxCpus='288'>q35</machine>

        So for now, we call getDomainCapabilities for these canonical
        machine types of each architecture, plus for the
        architecture's default machine type, if that is not one of the
        canonical types.

        Future domain capabilities might report SEV in a more
        fine-grained manner, and we also expect to use this method to
        detect other features, such as for gracefully handling machine
        types and potentially for detecting OVMF binaries.  Therefore
        we memoize the results of the API calls in a nested dict where
        the top-level keys are architectures, and second-level keys
        are machine types, in order to allow easy expansion later.

        Whenever libvirt/QEMU are updated, cached domCapabilities
        would get outdated (because QEMU will contain new features and
        the capabilities will vary).  However, this should not be a
        problem here, because when libvirt/QEMU gets updated, the
        nova-compute agent also needs restarting, at which point the
        memoization will vanish because it's not persisted to disk.

        Note: The result is cached in the member attribute
        _domain_caps.

        :returns: a nested dict of dicts which maps architectures to
            machine types to instances of config.LibvirtConfigDomainCaps
            representing the domain capabilities of the host for that arch and
            machine type: ``{arch:  machine_type: LibvirtConfigDomainCaps}{``
        """
        if self._domain_caps:
            return self._domain_caps

        domain_caps: ty.Dict = defaultdict(dict)
        caps = self.get_capabilities()
        virt_type = CONF.libvirt.virt_type

        for guest in caps.guests:
            arch = guest.arch
            domain = guest.domains.get(virt_type, guest.default_domain)

            for machine_type in self._get_machine_types(arch, domain):
                # It is expected that if there are multiple <guest>
                # elements, each will have a different architecture;
                # for example, on x86 hosts one <guest> will contain
                # <arch name='i686'> and one will contain <arch
                # name='x86_64'>. But it doesn't hurt to add a safety
                # net to avoid needlessly calling libvirt's API more
                # times than we need.
                if machine_type and machine_type in domain_caps[arch]:
                    continue
                self._add_to_domain_capabilities(domain.emulator, arch,
                                                 domain_caps, machine_type,
                                                 virt_type)

        # NOTE(aspiers): Use a temporary variable to update the
        # instance variable atomically, otherwise if some API
        # calls succeeded and then one failed, we might
        # accidentally memoize a partial result.
        self._domain_caps = domain_caps

        return self._domain_caps

    def _get_machine_types(self, arch, domain):
        """Get the machine types for this architecture for which we need to
        call getDomainCapabilities, i.e. the canonical machine types,
        and the default machine type (if it's not one of the canonical
        machine types).

        See the docstring for get_domain_capabilities() for an explanation
        of why we choose this set of machine types.
        """
        # NOTE(aspiers): machine_type could be None here if nova
        # doesn't have a default machine type for this architecture.
        # See _add_to_domain_capabilities() below for how this is handled.
        mtypes = set([libvirt_utils.get_default_machine_type(arch)])
        mtypes.update(domain.aliases.keys())
        LOG.debug("Getting domain capabilities for %(arch)s via "
                  "machine types: %(mtypes)s",
                  {'arch': arch, 'mtypes': mtypes})
        return mtypes

    def _add_to_domain_capabilities(self, emulator_bin, arch, domain_caps,
                                    machine_type, virt_type):
        # NOTE(aspiers): machine_type could be None here if nova
        # doesn't have a default machine type for this architecture.
        # In that case we pass a machine_type of None to the libvirt
        # API and rely on it choosing a sensible default which will be
        # returned in the <machine> element.  It could also be an
        # alias like 'pc' rather than a full machine type.
        #
        # NOTE(kchamart): Prior to libvirt v4.7.0 libvirt picked its
        # default machine type for x86, 'pc', as reported by QEMU's
        # default.  From libvirt v4.7.0 onwards, libvirt _explicitly_
        # declared the "preferred" default for x86 as 'pc' (and
        # appropriate values for other architectures), and only uses
        # QEMU's reported default (whatever that may be) if 'pc' does
        # not exist.  This was done "to isolate applications from
        # hypervisor changes that may cause incompatibilities" --
        # i.e. if, or when, QEMU changes its default machine type to
        # something else.  Refer to this libvirt commit:
        #
        #   https://libvirt.org/git/?p=libvirt.git;a=commit;h=26cfb1a3
        try:
            cap_obj = self._get_domain_capabilities(
                emulator_bin=emulator_bin, arch=arch,
                machine_type=machine_type, virt_type=virt_type)
        except libvirt.libvirtError as ex:
            # NOTE(sean-k-mooney): This can happen for several
            # reasons, but one common example is if you have
            # multiple QEMU emulators installed and you set
            # virt-type=kvm. In this case any non-native emulator,
            # e.g. AArch64 on an x86 host, will (correctly) raise
            # an exception as KVM cannot be used to accelerate CPU
            # instructions for non-native architectures.
            error_code = ex.get_error_code()
            LOG.debug(
                "Error from libvirt when retrieving domain capabilities "
                "for arch %(arch)s / virt_type %(virt_type)s / "
                "machine_type %(mach_type)s: "
                "[Error Code %(error_code)s]: %(exception)s",
                {'arch': arch, 'virt_type': virt_type,
                 'mach_type': machine_type, 'error_code': error_code,
                 'exception': ex})
            # Remove archs added by default dict lookup when checking
            # if the machine type has already been recoded.
            if arch in domain_caps:
                domain_caps.pop(arch)
            return

        # Register the domain caps using the expanded form of
        # machine type returned by libvirt in the <machine>
        # element (e.g. pc-i440fx-2.11)
        if cap_obj.machine_type:
            domain_caps[arch][cap_obj.machine_type] = cap_obj
        else:
            # NOTE(aspiers): In theory this should never happen,
            # but better safe than sorry.
            LOG.warning(
                "libvirt getDomainCapabilities("
                "emulator_bin=%(emulator_bin)s, arch=%(arch)s, "
                "machine_type=%(machine_type)s, virt_type=%(virt_type)s) "
                "returned null <machine> type",
                {'emulator_bin': emulator_bin, 'arch': arch,
                 'machine_type': machine_type, 'virt_type': virt_type}
            )

        # And if we passed an alias, register the domain caps
        # under that too.
        if machine_type and machine_type != cap_obj.machine_type:
            domain_caps[arch][machine_type] = cap_obj
            cap_obj.machine_type_alias = machine_type

    def _get_domain_capabilities(self, emulator_bin=None, arch=None,
                                 machine_type=None, virt_type=None, flags=0):
        xmlstr = self.get_connection().getDomainCapabilities(
            emulator_bin,
            arch,
            machine_type,
            virt_type,
            flags
        )
        LOG.debug("Libvirt host hypervisor capabilities for arch=%s and "
                  "machine_type=%s:\n%s", arch, machine_type, xmlstr)
        caps = vconfig.LibvirtConfigDomainCaps()
        caps.parse_str(xmlstr)
        return caps

    def get_driver_type(self):
        """Get hypervisor type.

        :returns: hypervisor type (ex. qemu)

        """

        return self.get_connection().getType()

    def get_version(self):
        """Get hypervisor version.

        :returns: hypervisor version (ex. 12003)

        """

        return self.get_connection().getVersion()

    def get_hostname(self):
        """Returns the hostname of the hypervisor."""
        hostname = self.get_connection().getHostname()
        if self._hostname is None:
            self._hostname = hostname
        elif hostname != self._hostname:
            LOG.error('Hostname has changed from %(old)s '
                      'to %(new)s. A restart is required to take effect.',
                      {'old': self._hostname, 'new': hostname})
        return self._hostname

    def find_secret(self, usage_type, usage_id):
        """Find a secret.

        usage_type: one of 'iscsi', 'ceph', 'rbd' or 'volume'
        usage_id: name of resource in secret
        """
        if usage_type == 'iscsi':
            usage_type_const = libvirt.VIR_SECRET_USAGE_TYPE_ISCSI
        elif usage_type in ('rbd', 'ceph'):
            usage_type_const = libvirt.VIR_SECRET_USAGE_TYPE_CEPH
        elif usage_type == 'volume':
            usage_type_const = libvirt.VIR_SECRET_USAGE_TYPE_VOLUME
        else:
            msg = _("Invalid usage_type: %s")
            raise exception.InternalError(msg % usage_type)

        try:
            conn = self.get_connection()
            return conn.secretLookupByUsage(usage_type_const, usage_id)
        except libvirt.libvirtError as e:
            if e.get_error_code() == libvirt.VIR_ERR_NO_SECRET:
                return None

    def create_secret(self, usage_type, usage_id, password=None, uuid=None):
        """Create a secret.

        :param usage_type: one of 'iscsi', 'ceph', 'rbd', 'volume', 'vtpm'.
                           'rbd' will be converted to 'ceph'. 'vtpm' secrets
                           are private and ephemeral; others are not.
        :param usage_id: name of resource in secret
        :param password: optional secret value to set
        :param uuid: optional UUID of the secret; else one is generated by
            libvirt
        """
        secret_conf = vconfig.LibvirtConfigSecret()
        secret_conf.ephemeral = usage_type == 'vtpm'
        secret_conf.private = usage_type == 'vtpm'
        secret_conf.usage_id = usage_id
        secret_conf.uuid = uuid
        if usage_type in ('rbd', 'ceph'):
            secret_conf.usage_type = 'ceph'
        elif usage_type == 'iscsi':
            secret_conf.usage_type = 'iscsi'
        elif usage_type == 'volume':
            secret_conf.usage_type = 'volume'
        elif usage_type == 'vtpm':
            secret_conf.usage_type = 'vtpm'
        else:
            msg = _("Invalid usage_type: %s")
            raise exception.InternalError(msg % usage_type)

        xml = secret_conf.to_xml()
        try:
            LOG.debug('Secret XML: %s', xml)
            conn = self.get_connection()
            secret = conn.secretDefineXML(xml)
            if password is not None:
                secret.setValue(password)
            return secret
        except libvirt.libvirtError:
            with excutils.save_and_reraise_exception():
                LOG.error('Error defining a secret with XML: %s', xml)

    def delete_secret(self, usage_type, usage_id):
        """Delete a secret.

        :param usage_type: one of 'iscsi', 'ceph', 'rbd', 'volume' or 'vtpm'
        :param usage_id: name of resource in secret
        """
        secret = self.find_secret(usage_type, usage_id)
        if secret is not None:
            secret.undefine()

    def _get_hardware_info(self):
        """Returns hardware information about the Node.

        Note that the memory size is reported in MiB instead of KiB.
        """
        return self.get_connection().getInfo()

    def get_memory_mb_total(self):
        """Get the total memory size(MB) of physical computer.

        :returns: the total amount of memory(MB).
        """
        if CONF.libvirt.file_backed_memory > 0:
            return CONF.libvirt.file_backed_memory
        else:
            return self._get_hardware_info()[1]

    def _sum_domain_memory_mb(self):
        """Get the total memory consumed by guest domains."""
        used = 0
        for guest in self.list_guests():
            try:
                # TODO(sahid): Use get_info...
                dom_mem = int(guest._get_domain_info()[2])
            except libvirt.libvirtError as e:
                LOG.warning("couldn't obtain the memory from domain:"
                            " %(uuid)s, exception: %(ex)s",
                            {"uuid": guest.uuid, "ex": e})
                continue
            used += dom_mem
        # Convert it to MB
        return used // units.Ki

    @staticmethod
    def _get_avail_memory_kb():
        with open('/proc/meminfo') as fp:
            m = fp.read().split()
        idx1 = m.index('MemFree:')
        idx2 = m.index('Buffers:')
        idx3 = m.index('Cached:')

        avail = int(m[idx1 + 1]) + int(m[idx2 + 1]) + int(m[idx3 + 1])

        return avail

    def get_memory_mb_used(self):
        """Get the used memory size(MB) of physical computer.

        :returns: the total usage of memory(MB).
        """
        if CONF.libvirt.file_backed_memory > 0:
            # For file_backed_memory, report the total usage of guests,
            # ignoring host memory
            return self._sum_domain_memory_mb()
        else:
            return (self.get_memory_mb_total() -
                   (self._get_avail_memory_kb() // units.Ki))

    def get_cpu_stats(self):
        """Returns the current CPU state of the host with frequency."""
        stats = self.get_connection().getCPUStats(
            libvirt.VIR_NODE_CPU_STATS_ALL_CPUS, 0)
        # getInfo() returns various information about the host node
        # No. 3 is the expected CPU frequency.
        stats["frequency"] = self._get_hardware_info()[3]
        return stats

    def write_instance_config(self, xml):
        """Defines a domain, but does not start it.

        :param xml: XML domain definition of the guest.

        :returns: an instance of Guest
        """
        domain = self.get_connection().defineXML(xml)
        return libvirt_guest.Guest(domain)

    def device_lookup_by_name(self, name):
        """Lookup a node device by its name.


        :returns: a virNodeDevice instance
        """
        return self.get_connection().nodeDeviceLookupByName(name)

    def _get_pcinet_info(
        self,
        dev: 'libvirt.virNodeDevice',
        net_devs: ty.List['libvirt.virNodeDevice']
    ) -> ty.Optional[ty.List[str]]:
        """Returns a dict of NET device."""
        net_dev = {dev.parent(): dev for dev in net_devs}.get(dev.name(), None)
        if net_dev is None:
            return None
        xmlstr = net_dev.XMLDesc(0)
        cfgdev = vconfig.LibvirtConfigNodeDevice()
        cfgdev.parse_str(xmlstr)
        return cfgdev.pci_capability.features

    def _get_pf_details(self, device: dict, pci_address: str) -> dict:
        if device.get('dev_type') != fields.PciDeviceType.SRIOV_PF:
            return {}

        try:
            return {
                'mac_address': pci_utils.get_mac_by_pci_address(pci_address)
            }
        except exception.PciDeviceNotFoundById:
            LOG.debug(
                'Cannot get MAC address of the PF %s. It is probably attached '
                'to a guest already', pci_address)
            return {}

    def _get_pcidev_info(
        self,
        devname: str,
        dev: 'libvirt.virNodeDevice',
        net_devs: ty.List['libvirt.virNodeDevice'],
        vdpa_devs: ty.List['libvirt.virNodeDevice'],
    ) -> ty.Dict[str, ty.Union[str, dict]]:
        """Returns a dict of PCI device."""

        def _get_device_type(
            cfgdev: vconfig.LibvirtConfigNodeDevice,
            pci_address: str,
            device: 'libvirt.virNodeDevice',
            net_devs: ty.List['libvirt.virNodeDevice'],
            vdpa_devs: ty.List['libvirt.virNodeDevice'],
        ) -> ty.Dict[str, str]:
            """Get a PCI device's device type.

            An assignable PCI device can be a normal PCI device,
            a SR-IOV Physical Function (PF), or a SR-IOV Virtual
            Function (VF).
            """
            net_dev_parents = {dev.parent() for dev in net_devs}
            vdpa_parents = {dev.parent() for dev in vdpa_devs}
            for fun_cap in cfgdev.pci_capability.fun_capability:
                if fun_cap.type == 'virt_functions':
                    return {
                        'dev_type': fields.PciDeviceType.SRIOV_PF,
                    }
                if (
                    fun_cap.type == 'phys_function' and
                    len(fun_cap.device_addrs) != 0
                ):
                    phys_address = "%04x:%02x:%02x.%01x" % (
                        fun_cap.device_addrs[0][0],
                        fun_cap.device_addrs[0][1],
                        fun_cap.device_addrs[0][2],
                        fun_cap.device_addrs[0][3])
                    result = {
                        'dev_type': fields.PciDeviceType.SRIOV_VF,
                        'parent_addr': phys_address,
                    }
                    parent_ifname = None
                    # NOTE(sean-k-mooney): if the VF is a parent of a netdev
                    # the PF should also have a netdev, however on some exotic
                    # hardware such as Cavium ThunderX this may not be the case
                    # see bug #1915255 for details. As such we wrap this in a
                    # try except block.
                    if device.name() in net_dev_parents:
                        try:
                            parent_ifname = (
                                pci_utils.get_ifname_by_pci_address(
                                    pci_address, pf_interface=True))
                            result['parent_ifname'] = parent_ifname
                        except exception.PciDeviceNotFoundById:
                            # NOTE(sean-k-mooney): we ignore this error as it
                            # is expected when the virtual function is not a
                            # NIC or the VF does not have a parent PF with a
                            # netdev. We do not log here as this is called
                            # in a periodic task and that would be noisy at
                            # debug level.
                            pass
                    if device.name() in vdpa_parents:
                        result['dev_type'] = fields.PciDeviceType.VDPA
                    return result

            return {'dev_type': fields.PciDeviceType.STANDARD}

        def _get_device_capabilities(
            device_dict: dict,
            device: 'libvirt.virNodeDevice',
            net_devs: ty.List['libvirt.virNodeDevice']
        ) -> ty.Dict[str, ty.Dict[str, ty.Any]]:
            """Get PCI VF device's additional capabilities.

            If a PCI device is a virtual function, this function reads the PCI
            parent's network capabilities (must be always a NIC device) and
            appends this information to the device's dictionary.
            """
            caps: ty.Dict[str, ty.Dict[str, ty.Any]] = {}

            if device_dict.get('dev_type') == fields.PciDeviceType.SRIOV_VF:
                pcinet_info = self._get_pcinet_info(device, net_devs)
                if pcinet_info:
                    return {'capabilities': {'network': pcinet_info}}
            return caps

        xmlstr = dev.XMLDesc(0)
        cfgdev = vconfig.LibvirtConfigNodeDevice()
        cfgdev.parse_str(xmlstr)

        address = "%04x:%02x:%02x.%1x" % (
            cfgdev.pci_capability.domain,
            cfgdev.pci_capability.bus,
            cfgdev.pci_capability.slot,
            cfgdev.pci_capability.function)

        device = {
            "dev_id": cfgdev.name,
            "address": address,
            "product_id": "%04x" % cfgdev.pci_capability.product_id,
            "vendor_id": "%04x" % cfgdev.pci_capability.vendor_id,
            }

        device["numa_node"] = cfgdev.pci_capability.numa_node

        # requirement by DataBase Model
        device['label'] = 'label_%(vendor_id)s_%(product_id)s' % device
        device.update(
            _get_device_type(cfgdev, address, dev, net_devs, vdpa_devs))
        device.update(_get_device_capabilities(device, dev, net_devs))
        device.update(self._get_pf_details(device, address))
        return device

    def get_vdpa_nodedev_by_address(
        self, pci_address: str,
    ) -> vconfig.LibvirtConfigNodeDevice:
        """Finds a vDPA device by the parent VF PCI device address.

        :param pci_address: Parent PCI device address
        :returns: A libvirt nodedev representing the vDPA device
        :raises: StopIteration if not found
        """
        dev_flags = (
            libvirt.VIR_CONNECT_LIST_NODE_DEVICES_CAP_VDPA |
            libvirt.VIR_CONNECT_LIST_NODE_DEVICES_CAP_PCI_DEV
        )
        devices = {
            dev.name(): dev for dev in
            self.list_all_devices(flags=dev_flags)}
        vdpa_devs = [
            dev for dev in devices.values() if "vdpa" in dev.listCaps()]
        pci_info = [
            self._get_pcidev_info(name, dev, [], vdpa_devs) for name, dev
            in devices.items() if "pci" in dev.listCaps()]
        parent_dev = next(
            dev for dev in pci_info if dev['address'] == pci_address)
        vdpa_dev = next(
            dev for dev in vdpa_devs if dev.parent() == parent_dev['dev_id'])
        xmlstr = vdpa_dev.XMLDesc(0)
        cfgdev = vconfig.LibvirtConfigNodeDevice()
        cfgdev.parse_str(xmlstr)
        return cfgdev

    def get_vdpa_device_path(
        self, pci_address: str,
    ) -> str:
        """Finds a vDPA device path by the parent VF PCI device address.

        :param pci_address: Parent PCI device address
        :returns: Device path as string
        :raises: StopIteration if not found
        """
        nodedev = self.get_vdpa_nodedev_by_address(pci_address)
        return nodedev.vdpa_capability.dev_path

    def list_pci_devices(self, flags=0):
        """Lookup pci devices.

        :returns: a list of virNodeDevice instance
        """
        return self._list_devices("pci", flags=flags)

    def list_mdev_capable_devices(self, flags=0):
        """Lookup devices supporting mdev capabilities.

        :returns: a list of virNodeDevice instance
        """
        return self._list_devices("mdev_types", flags=flags)

    def list_mediated_devices(self, flags=0):
        """Lookup mediated devices.

        :returns: a list of strings with the name of the instance
        """
        return self._list_devices("mdev", flags=flags)

    def _list_devices(self, cap, flags=0):
        """Lookup devices.

        :returns: a list of virNodeDevice instance
        """
        try:
            return self.get_connection().listDevices(cap, flags)
        except libvirt.libvirtError as ex:
            error_code = ex.get_error_code()
            if error_code == libvirt.VIR_ERR_NO_SUPPORT:
                LOG.warning("URI %(uri)s does not support "
                            "listDevices: %(error)s",
                            {'uri': self._uri, 'error': ex})
                return []
            else:
                raise

    def list_all_devices(
        self, flags: int = 0,
    ) -> ty.List['libvirt.virNodeDevice']:
        """Lookup devices.

        :param flags: a bitmask of flags to filter the returned devices.
        :returns: a list of virNodeDevice xml strings.
        """
        try:
            return self.get_connection().listAllDevices(flags) or []
        except libvirt.libvirtError as ex:
            LOG.warning(ex)
            return []

    def compare_cpu(self, xmlDesc, flags=0):
        """Compares the given CPU description with the host CPU."""
        return self.get_connection().compareCPU(xmlDesc, flags)

    def is_cpu_control_policy_capable(self):
        """Returns whether kernel configuration CGROUP_SCHED is enabled

        CONFIG_CGROUP_SCHED may be disabled in some kernel configs to
        improve scheduler latency.
        """
        try:
            with open("/proc/self/mounts", "r") as fd:
                for line in fd.readlines():
                    # mount options and split options
                    bits = line.split()[3].split(",")
                    if "cpu" in bits:
                        return True
                return False
        except IOError:
            return False

    def get_canonical_machine_type(self, arch, machine) -> str:
        """Resolve a machine type to its canonical representation.

        Libvirt supports machine type aliases. On an x86 host the 'pc' machine
        type is an alias for e.g. 'pc-1440fx-5.1'. Resolve the provided machine
        type to its canonical representation so that it can be used for other
        operations.

        :param arch: The guest arch.
        :param machine: The guest machine type.
        :returns: The canonical machine type.
        :raises: exception.InternalError if the machine type cannot be resolved
            to its canonical representation.
        """
        for guest in self.get_capabilities().guests:
            if guest.arch != arch:
                continue

            for domain in guest.domains:
                if machine in guest.domains[domain].machines:
                    return machine

                if machine in guest.domains[domain].aliases:
                    return guest.domains[domain].aliases[machine]['canonical']

        msg = _('Invalid machine type: %s')
        raise exception.InternalError(msg % machine)

    @property
    def has_hyperthreading(self) -> bool:
        """Determine if host CPU has SMT, a.k.a. HyperThreading.

        :return: True if the host has SMT enabled, else False.
        """
        if self._has_hyperthreading is not None:
            return self._has_hyperthreading

        self._has_hyperthreading = False

        # we don't use '/capabilities/host/cpu/topology' since libvirt doesn't
        # guarantee the accuracy of this information
        for cell in self.get_capabilities().host.topology.cells:
            if any(len(cpu.siblings) > 1 for cpu in cell.cpus if cpu.siblings):
                self._has_hyperthreading = True
                break

        return self._has_hyperthreading

    @property
    def supports_uefi(self) -> bool:
        """Determine if the host supports UEFI bootloaders for guests.

        This checks whether the feature is supported by *any* machine type.
        This is only used for trait-reporting purposes and a machine
        type-specific check should be used when creating guests.
        """

        if self._supports_uefi is not None:
            return self._supports_uefi

        # we only check the host architecture since nova doesn't support
        # non-host architectures currently
        arch = self.get_capabilities().host.cpu.arch
        domain_caps = self.get_domain_capabilities()
        for machine_type in domain_caps[arch]:
            LOG.debug("Checking UEFI support for host arch (%s)", arch)
            _domain_caps = domain_caps[arch][machine_type]
            if _domain_caps.os.uefi_supported:
                LOG.info('UEFI support detected')
                self._supports_uefi = True
                return True

        LOG.debug('No UEFI support detected')
        self._supports_uefi = False
        return False

    @property
    def supports_secure_boot(self) -> bool:
        """Determine if the host supports UEFI Secure Boot for guests.

        This checks whether the feature is supported by *any* machine type.
        This is only used for trait-reporting purposes and a machine
        type-specific check should be used when creating guests.
        """

        if self._supports_secure_boot is not None:
            return self._supports_secure_boot

        # we only check the host architecture since the libvirt driver doesn't
        # truely support non-host architectures currently
        arch = self.get_capabilities().host.cpu.arch
        domain_caps = self.get_domain_capabilities()
        for machine_type in domain_caps[arch]:
            LOG.debug(
                "Checking secure boot support for host arch (%s)",
                arch,
            )
            _domain_caps = domain_caps[arch][machine_type]
            if _domain_caps.os.secure_boot_supported:
                LOG.info('Secure Boot support detected')
                self._supports_secure_boot = True
                return True

        LOG.debug('No Secure Boot support detected')
        self._supports_secure_boot = False
        return False

    def _kernel_supports_amd_sev(self) -> bool:
        if not os.path.exists(SEV_KERNEL_PARAM_FILE):
            LOG.debug("%s does not exist", SEV_KERNEL_PARAM_FILE)
            return False

        with open(SEV_KERNEL_PARAM_FILE) as f:
            content = f.read()
            LOG.debug("%s contains [%s]", SEV_KERNEL_PARAM_FILE, content)
            return strutils.bool_from_string(content)

    @property
    def supports_amd_sev(self) -> bool:
        """Determine if the host supports AMD SEV for guests.

        Returns a boolean indicating whether AMD SEV (Secure Encrypted
        Virtualization) is supported.  This is conditional on support
        in the hardware, kernel, qemu, and libvirt.

        This checks whether the feature is supported by *any* machine type.
        This is only used for trait-reporting purposes and a machine
        type-specific check should be used when creating guests.
        """
        if self._supports_amd_sev is not None:
            return self._supports_amd_sev

        self._supports_amd_sev = False

        caps = self.get_capabilities()
        if caps.host.cpu.arch != fields.Architecture.X86_64:
            return self._supports_amd_sev

        if not self._kernel_supports_amd_sev():
            LOG.info("kernel doesn't support AMD SEV")
            return self._supports_amd_sev

        domain_caps = self.get_domain_capabilities()
        for arch in domain_caps:
            for machine_type in domain_caps[arch]:
                LOG.debug("Checking SEV support for arch %s "
                          "and machine type %s", arch, machine_type)
                for feature in domain_caps[arch][machine_type].features:
                    feature_is_sev = isinstance(
                        feature, vconfig.LibvirtConfigDomainCapsFeatureSev)
                    if feature_is_sev and feature.supported:
                        LOG.info("AMD SEV support detected")
                        self._supports_amd_sev = True
                        return self._supports_amd_sev

        LOG.debug("No AMD SEV support detected for any (arch, machine_type)")
        return self._supports_amd_sev

    @property
    def loaders(self) -> ty.List[dict]:
        """Retrieve details of loader configuration for the host.

        Inspect the firmware metadata files provided by QEMU [1] to retrieve
        information about the firmware supported by this host. Note that most
        distros only publish this information for UEFI loaders currently.

        This should be removed when libvirt correctly supports switching
        between loaders with or without secure boot enabled [2].

        [1] https://github.com/qemu/qemu/blob/v5.2.0/docs/interop/firmware.json
        [2] https://bugzilla.redhat.com/show_bug.cgi?id=1906500

        :returns: An ordered list of loader configuration dictionaries.
        """
        if self._loaders is not None:
            return self._loaders

        self._loaders = _get_loaders()
        return self._loaders

    def get_loader(
        self,
        arch: str,
        machine: str,
        has_secure_boot: bool,
    ) -> ty.Tuple[str, str, bool]:
        """Get loader for the specified architecture and machine type.

        :returns: A the bootloader executable path and the NVRAM
            template path and a bool indicating if we need to enable SMM.
        """

        machine = self.get_canonical_machine_type(arch, machine)

        for loader in self.loaders:
            for target in loader['targets']:
                if arch != target['architecture']:
                    continue

                for machine_glob in target['machines']:
                    # the 'machines' attribute supports glob patterns (e.g.
                    # 'pc-q35-*') so we need to resolve these
                    if fnmatch.fnmatch(machine, machine_glob):
                        break
                else:
                    continue

                # if we've got this far, we have a match on the target
                break
            else:
                continue

            # if we request secure boot then we should get it and vice versa
            if has_secure_boot != ('secure-boot' in loader['features']):
                continue

            return (
                loader['mapping']['executable']['filename'],
                loader['mapping']['nvram-template']['filename'],
                'requires-smm' in loader['features'],
            )

        raise exception.UEFINotSupported()
