def test_get_root_bdm(self):
     root_bdm = {'device_name': 'vda', 'boot_index': 0}
     bdms = [root_bdm,
             {'device_name': 'vdb', 'boot_index': 1},
             {'device_name': 'vdc', 'boot_index': -1},
             {'device_name': 'vdd'}]
     self.assertEqual(root_bdm, block_device.get_root_bdm(bdms))
     self.assertEqual(root_bdm, block_device.get_root_bdm([bdms[0]]))
     self.assertIsNone(block_device.get_root_bdm(bdms[1:]))
     self.assertIsNone(block_device.get_root_bdm(bdms[2:]))
     self.assertIsNone(block_device.get_root_bdm(bdms[3:]))
     self.assertIsNone(block_device.get_root_bdm([]))

 def test_get_root_bdm(self):
     root_bdm = {"device_name": "vda", "boot_index": 0}
     bdms = [
         root_bdm,
         {"device_name": "vdb", "boot_index": 1},
         {"device_name": "vdc", "boot_index": -1},
         {"device_name": "vdd"},
     ]
     self.assertEqual(root_bdm, block_device.get_root_bdm(bdms))
     self.assertEqual(root_bdm, block_device.get_root_bdm([bdms[0]]))
     self.assertIsNone(block_device.get_root_bdm(bdms[1:]))
     self.assertIsNone(block_device.get_root_bdm(bdms[2:]))
     self.assertIsNone(block_device.get_root_bdm(bdms[3:]))
     self.assertIsNone(block_device.get_root_bdm([]))

def get_disk_mapping(virt_type, instance,
                     disk_bus, cdrom_bus,
                     block_device_info=None,
                     image_meta=None, rescue=False):
    """Determine how to map default disks to the virtual machine.

       This is about figuring out whether the default 'disk',
       'disk.local', 'disk.swap' and 'disk.config' images have
       been overridden by the block device mapping.

       Returns the guest disk mapping for the devices.
    """

    inst_type = flavors.extract_flavor(instance)

    mapping = {}

    pre_assigned_device_names = \
    [block_device.strip_dev(get_device_name(bdm)) for bdm in itertools.chain(
        driver.block_device_info_get_ephemerals(block_device_info),
        [driver.block_device_info_get_swap(block_device_info)],
        driver.block_device_info_get_mapping(block_device_info))
     if get_device_name(bdm)]

    if rescue:
        rescue_info = get_next_disk_info(mapping,
                                         disk_bus, boot_index=1)
        mapping['disk.rescue'] = rescue_info
        mapping['root'] = rescue_info

        os_info = get_next_disk_info(mapping,
                                     disk_bus)
        mapping['disk'] = os_info

        return mapping

    # NOTE (ndipanov): root_bdm can be None when we boot from image
    # as there is no driver represenation of local targeted images
    # and they will not be in block_device_info list.
    root_bdm = block_device.get_root_bdm(
        driver.block_device_info_get_mapping(block_device_info))

    root_device_name = block_device.strip_dev(
        driver.block_device_info_get_root(block_device_info))
    root_info = get_root_info(virt_type, image_meta, root_bdm,
                              disk_bus, cdrom_bus, root_device_name)

    mapping['root'] = root_info
    # NOTE (ndipanov): This implicitly relies on image->local BDMs not
    #                  being considered in the driver layer - so missing
    #                  bdm with boot_index 0 means - use image, unless it was
    #                  overridden. This can happen when using legacy syntax and
    #                  no root_device_name is set on the instance.
    if not root_bdm and not block_device.volume_in_mapping(root_info['dev'],
                                                           block_device_info):
        mapping['disk'] = root_info

    default_eph = has_default_ephemeral(instance, disk_bus, block_device_info,
                                        mapping)
    if default_eph:
        mapping['disk.local'] = default_eph

    for idx, eph in enumerate(driver.block_device_info_get_ephemerals(
            block_device_info)):
        eph_info = get_info_from_bdm(
            virt_type, eph, mapping, disk_bus,
            assigned_devices=pre_assigned_device_names)
        mapping[get_eph_disk(idx)] = eph_info
        update_bdm(eph, eph_info)

    swap = driver.block_device_info_get_swap(block_device_info)
    if swap and swap.get('swap_size', 0) > 0:
        swap_info = get_info_from_bdm(virt_type, swap, mapping, disk_bus)
        mapping['disk.swap'] = swap_info
        update_bdm(swap, swap_info)
    elif inst_type['swap'] > 0:
        swap_info = get_next_disk_info(mapping,
                                       disk_bus)
        if not block_device.volume_in_mapping(swap_info['dev'],
                                              block_device_info):
            mapping['disk.swap'] = swap_info

    block_device_mapping = driver.block_device_info_get_mapping(
        block_device_info)

    for vol in block_device_mapping:
        vol_info = get_info_from_bdm(
            virt_type, vol, mapping,
            assigned_devices=pre_assigned_device_names)
        mapping[block_device.prepend_dev(vol_info['dev'])] = vol_info
        update_bdm(vol, vol_info)

    if configdrive.required_by(instance):
        device_type = get_config_drive_type()
        disk_bus = get_disk_bus_for_device_type(virt_type,
                                                image_meta,
                                                device_type)
        config_info = get_next_disk_info(mapping,
                                         disk_bus,
                                         device_type,
#.........这里部分代码省略.........