How to use the nova.context.get_admin_context function in nova

def get_user_roles(self, uid, project_id=None):
        """Retrieve list of roles for user (or user and project)"""
        if project_id is None:
            roles = db.user_get_roles(context.get_admin_context(), uid)
            return roles
        else:
            roles = db.user_get_roles_for_project(context.get_admin_context(),
                                                  uid, project_id)
            return roles

keyfile = os.path.abspath(os.path.join(tmpdir, 'temp.key'))
        csrfile = os.path.abspath(os.path.join(tmpdir, 'temp.csr'))
        utils.execute('openssl', 'genrsa', '-out', keyfile, str(bits))
        utils.execute('openssl', 'req', '-new', '-key', keyfile, '-out',
                      csrfile, '-batch', '-subj', subject)
        with open(keyfile) as f:
            private_key = f.read()
        with open(csrfile) as f:
            csr = f.read()

    (serial, signed_csr) = sign_csr(csr, project_id)
    fname = os.path.join(ca_folder(project_id), 'newcerts/%s.pem' % serial)
    cert = {'user_id': user_id,
            'project_id': project_id,
            'file_name': fname}
    db.certificate_create(context.get_admin_context(), cert)
    return (private_key, signed_csr)

guest.name = instance['name']
        guest.uuid = instance['uuid']
        guest.memory = inst_type['memory_mb'] * 1024
        guest.vcpus = inst_type['vcpus']

        guest.cpu = self.get_guest_cpu_config()

        root_device_name = driver.block_device_info_get_root(block_device_info)
        if root_device_name:
            root_device = block_device.strip_dev(root_device_name)
        else:
            # NOTE(yamahata):
            # for nova.api.ec2.cloud.CloudController.get_metadata()
            root_device = self.default_root_device
            self.virtapi.instance_update(
                nova_context.get_admin_context(), instance['uuid'],
                {'root_device_name': '/dev/' + self.default_root_device})

        guest.os_type = vm_mode.get_from_instance(instance)

        if guest.os_type is None:
            if CONF.libvirt_type == "lxc":
                guest.os_type = vm_mode.EXE
            elif CONF.libvirt_type == "uml":
                guest.os_type = vm_mode.UML
            elif CONF.libvirt_type == "xen":
                guest.os_type = vm_mode.XEN
            else:
                guest.os_type = vm_mode.HVM

        if CONF.libvirt_type == "xen" and guest.os_type == vm_mode.HVM:
            guest.os_loader = CONF.xen_hvmloader_path

def _set_service_state(self, host, binary, is_disabled):
        "Enables/Disables service on host"

        ctxt = context.get_admin_context(read_deleted='no')
        service = objects.Service.get_by_args(ctxt, host, binary)
        service.disabled = is_disabled
        service.save()

except exception.DBNotAllowed:
                # This most likely means we are in a nova-compute service
                # configured with [upgrade_levels]/compute=auto and a
                # connection to the API database. We should not be attempting
                # to "get out" of our cell to look at the minimum versions of
                # nova-compute services in other cells, so DBNotAllowed was
                # raised. Log a user-friendly message and re-raise the error.
                with excutils.save_and_reraise_exception():
                    LOG.error('This service is configured for access to the '
                              'API database but is not allowed to directly '
                              'access the database. You should run this '
                              'service without the [api_database]/connection '
                              'config option.')
        else:
            service_version = objects.Service.get_minimum_version(
                context.get_admin_context(), 'nova-compute')

        history = service_obj.SERVICE_VERSION_HISTORY

        # NOTE(johngarbutt) when there are no nova-compute services running we
        # get service_version == 0. In that case we do not want to cache
        # this result, because we will get a better answer next time.
        # As a sane default, return the current version.
        if service_version == 0:
            if not NO_COMPUTES_WARNING:
                # NOTE(danms): Only show this warning once
                LOG.debug("Not caching compute RPC version_cap, because min "
                          "service_version is 0. Please ensure a nova-compute "
                          "service has been started. Defaulting to current "
                          "version.")
                NO_COMPUTES_WARNING = True
            return history[service_obj.SERVICE_VERSION]['compute_rpc']

def _persist(self):
        LOG.debug(_('Entering _persist for host uuid '
                  + self.compute_id))
        api.vm_host_save(get_admin_context(), self.vmHost)
        LOG.debug(_('Exiting _persist for host uuid '
                  + self.compute_id))

def get_host_stats(self, refresh=False):
        caps = []
        context = nova_context.get_admin_context()
        nodes = db.bm_node_get_all(context,
                                     service_host=CONF.host)
        for node in nodes:
            res = self._node_resource(node)
            nodename = str(node['uuid'])
            data = {}
            data['vcpus'] = res['vcpus']
            data['vcpus_used'] = res['vcpus_used']
            data['cpu_info'] = res['cpu_info']
            data['disk_total'] = res['local_gb']
            data['disk_used'] = res['local_gb_used']
            data['disk_available'] = res['local_gb'] - res['local_gb_used']
            data['host_memory_total'] = res['memory_mb']
            data['host_memory_free'] = res['memory_mb'] - res['memory_mb_used']
            data['hypervisor_type'] = res['hypervisor_type']
            data['hypervisor_version'] = res['hypervisor_version']

"""Queries the API database for cell mappings.

        .. note:: This method is unique in that it queries the database using
                  CellMappingList.get_all() rather than a direct query using
                  the sqlalchemy models. This is because
                  CellMapping.database_connection can be a template and the
                  object takes care of formatting the URL. We cannot use
                  RowProxy objects from sqlalchemy because we cannot set the
                  formatted 'database_connection' value back on those objects
                  (they are read-only).

        :param include_cell0: True if cell0 should be returned, False if cell0
            should be excluded from the results.
        :returns: list of nova.objects.CellMapping objects
        """
        ctxt = nova_context.get_admin_context()
        cell_mappings = cell_mapping_obj.CellMappingList.get_all(ctxt)
        if not include_cell0:
            # Since CellMappingList does not implement remove() we have to
            # create a new list and exclude cell0.
            mappings = [mapping for mapping in cell_mappings
                        if not mapping.is_cell0()]
            cell_mappings = cell_mapping_obj.CellMappingList(objects=mappings)
        return cell_mappings

try:
            node_id = q['i']
            deploy_key = q['k']
            address = q['a']
            port = q.get('p', '3260')
            iqn = q['n']
            lun = q.get('l', '1')
            err_msg = q.get('e')
        except KeyError as e:
            start_response('400 Bad Request', [('Content-type', 'text/plain')])
            return "parameter '%s' is not defined" % e

        if err_msg:
            LOG.error(_('Deploy agent error message: %s'), err_msg)

        context = nova_context.get_admin_context()
        d = db.bm_node_get(context, node_id)

        if d['deploy_key'] != deploy_key:
            start_response('400 Bad Request', [('Content-type', 'text/plain')])
            return 'key is not match'

        params = {'address': address,
                  'port': port,
                  'iqn': iqn,
                  'lun': lun,
                  'image_path': d['image_path'],
                  'pxe_config_path': d['pxe_config_path'],
                  'root_mb': int(d['root_mb']),
                  'swap_mb': int(d['swap_mb']),
                  'ephemeral_mb': int(d['ephemeral_mb']),
                  'preserve_ephemeral': d['preserve_ephemeral'],

def get_user_data(self, address):
        ctxt = context.get_admin_context()
        try:
            instance_ref = db.instance_get_by_fixed_ip(ctxt, address)
        except exception.NotFound:
            instance_ref = None
        if not instance_ref:
            return None

        data = {'user-data': self._format_user_data(instance_ref)}
        return data