OpenStack Study: configuration.py

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# Copyright (c) 2012 Rackspace Hosting

# 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.

"""

Configuration support for all drivers.

This module allows support for setting configurations either from default

or from a particular FLAGS group, to be able to set multiple configurations

for a given set of values.

For instance, two lvm configurations can be set by naming them in groups as

[lvm1]

volume_group=lvm-group-1

...

[lvm2]

volume_group=lvm-group-2

...

And the configuration group name will be passed in so that all calls to

configuration.volume_group within that instance will be mapped to the proper

named group.

This class also ensures the implementation's configuration is grafted into the

option group. This is due to the way cfg works. All cfg options must be defined

and registered in the group in which they are used.

"""

from oslo.config import cfg

from cinder.openstack.common import log as logging

CONF = cfg.CONF

LOG = logging.getLogger(__name__)

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class Configuration(object):

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    def __init__(self, volume_opts, config_group=None):

        """This takes care of grafting the implementation's config

           values into the config group

        """

        self.config_group = config_group

        # set the local conf so that __call__'s know what to use

        if self.config_group:

            self._ensure_config_values(volume_opts)

            self.local_conf = CONF._get(self.config_group)

        else:

            self.local_conf = CONF

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    def _ensure_config_values(self, volume_opts):

        CONF.register_opts(volume_opts, group=self.config_group)

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    def append_config_values(self, volume_opts):

        self._ensure_config_values(volume_opts)

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    def safe_get(self, value):

        try:

            return self.__getattr__(value)

        except cfg.NoSuchOptError:

            return None

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    def __getattr__(self, value):

        return getattr(self.local_conf, value)