Source code for cinderlib.persistence

# Copyright (c) 2018, Red Hat, Inc.
# 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 inspect

import six
from stevedore import driver

from cinderlib import exception
from cinderlib.persistence import base


DEFAULT_STORAGE = 'memory'


def setup(config):
    """Setup persistence to be used in cinderlib.

    By default memory persistance will be used, but there are other mechanisms
    available and other ways to use custom mechanisms:

    - Persistence plugins: Plugin mechanism uses Python entrypoints under
      namespace cinderlib.persistence.storage, and cinderlib comes with 3
      different mechanisms, "memory", "dbms", and "memory_dbms".  To use any of
      these one must pass the string name in the storage parameter and any
      other configuration as keyword arguments.
    - Passing a class that inherits from PersistenceDriverBase as storage
      parameter and initialization parameters as keyword arguments.
    - Passing an instance that inherits from PersistenceDriverBase as storage
      parameter.
    """
    if config is None:
        config = {}
    else:
        config = config.copy()

    # Default configuration is using memory storage
    storage = config.pop('storage', None) or DEFAULT_STORAGE
    if isinstance(storage, base.PersistenceDriverBase):
        return storage

    if inspect.isclass(storage) and issubclass(storage,
                                               base.PersistenceDriverBase):
        return storage(**config)

    if not isinstance(storage, six.string_types):
        raise exception.InvalidPersistence(storage)

    persistence_driver = driver.DriverManager(
        namespace='cinderlib.persistence.storage',
        name=storage,
        invoke_on_load=True,
        invoke_kwds=config,
    )
    return persistence_driver.driver