Source code for glance.common.location_strategy

# Copyright 2014 IBM Corp.
# All Rights Reserved.
#
#    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.

import copy

from oslo_config import cfg
from oslo_log import log as logging
import stevedore

from glance.i18n import _, _LE

location_strategy_opts = [
    cfg.StrOpt('location_strategy', default='location_order',
               choices=('location_order', 'store_type'),
               help=_("This value sets what strategy will be used to "
                      "determine the image location order. Currently "
                      "two strategies are packaged with Glance "
                      "'location_order' and 'store_type'."))
]

CONF = cfg.CONF
CONF.register_opts(location_strategy_opts)

LOG = logging.getLogger(__name__)


def _load_strategies():
    """Load all strategy modules."""
    modules = {}
    namespace = "glance.common.image_location_strategy.modules"
    ex = stevedore.extension.ExtensionManager(namespace)
    for module_name in ex.names():
        try:
            mgr = stevedore.driver.DriverManager(
                namespace=namespace,
                name=module_name,
                invoke_on_load=False)

            # Obtain module name
            strategy_name = str(mgr.driver.get_strategy_name())
            if strategy_name in modules:
                msg = (_('%(strategy)s is registered as a module twice. '
                         '%(module)s is not being used.') %
                       {'strategy': strategy_name, 'module': module_name})
                LOG.warn(msg)
            else:
                # Initialize strategy module
                mgr.driver.init()
                modules[strategy_name] = mgr.driver
        except Exception as e:
            LOG.error(_LE("Failed to load location strategy module "
                          "%(module)s: %(e)s") % {'module': module_name,
                                                  'e': e})
    return modules


_available_strategies = _load_strategies()


# TODO(kadachi): Not used but don't remove this until glance_store
#                development/migration stage.
def verify_location_strategy(conf=None, strategies=_available_strategies):
    """Validate user configured 'location_strategy' option value."""
    if not conf:
        conf = CONF.location_strategy
    if conf not in strategies:
        msg = (_('Invalid location_strategy option: %(name)s. '
                 'The valid strategy option(s) is(are): %(strategies)s') %
               {'name': conf, 'strategies': ", ".join(strategies.keys())})
        LOG.error(msg)
        raise RuntimeError(msg)


def get_ordered_locations(locations, **kwargs):
    """
    Order image location list by configured strategy.

    :param locations: The original image location list.
    :param kwargs: Strategy-specific arguments for under layer strategy module.
    :returns: The image location list with strategy-specific order.
    """
    if not locations:
        return []
    strategy_module = _available_strategies[CONF.location_strategy]
    return strategy_module.get_ordered_locations(copy.deepcopy(locations),
                                                 **kwargs)


def choose_best_location(locations, **kwargs):
    """
    Choose best location from image location list by configured strategy.

    :param locations: The original image location list.
    :param kwargs: Strategy-specific arguments for under layer strategy module.
    :returns: The best location from image location list.
    """
    locations = get_ordered_locations(locations, **kwargs)
    if locations:
        return locations[0]
    else:
        return None