6817d66bd2
The Stevedore library is used for loading backend drivers rather than using importutils. This provides a level of indirection for deployers/packagers. The importutils method of loading drivers is still supported, but it's deprecated. bp stevedore Change-Id: Id77ebf7056987ff1d3b9f62fab411845e63c86c3
104 lines
3.8 KiB
Python
104 lines
3.8 KiB
Python
# Copyright 2012 OpenStack Foundation
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#
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# Licensed under the Apache License, Version 2.0 (the "License"); you may
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# not use this file except in compliance with the License. You may obtain
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# a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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# License for the specific language governing permissions and limitations
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# under the License.
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import functools
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from oslo_utils import importutils
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import stevedore
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from keystone.openstack.common import versionutils
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def response_truncated(f):
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"""Truncate the list returned by the wrapped function.
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This is designed to wrap Manager list_{entity} methods to ensure that
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any list limits that are defined are passed to the driver layer. If a
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hints list is provided, the wrapper will insert the relevant limit into
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the hints so that the underlying driver call can try and honor it. If the
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driver does truncate the response, it will update the 'truncated' attribute
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in the 'limit' entry in the hints list, which enables the caller of this
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function to know if truncation has taken place. If, however, the driver
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layer is unable to perform truncation, the 'limit' entry is simply left in
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the hints list for the caller to handle.
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A _get_list_limit() method is required to be present in the object class
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hierarchy, which returns the limit for this backend to which we will
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truncate.
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If a hints list is not provided in the arguments of the wrapped call then
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any limits set in the config file are ignored. This allows internal use
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of such wrapped methods where the entire data set is needed as input for
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the calculations of some other API (e.g. get role assignments for a given
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project).
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"""
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@functools.wraps(f)
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def wrapper(self, *args, **kwargs):
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if kwargs.get('hints') is None:
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return f(self, *args, **kwargs)
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list_limit = self.driver._get_list_limit()
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if list_limit:
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kwargs['hints'].set_limit(list_limit)
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return f(self, *args, **kwargs)
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return wrapper
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def load_driver(namespace, driver_name, *args):
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try:
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driver_manager = stevedore.DriverManager(namespace,
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driver_name,
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invoke_on_load=True,
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invoke_args=args)
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return driver_manager.driver
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except RuntimeError:
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# Ignore failure to load driver using stevedore and continue on.
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pass
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@versionutils.deprecated(as_of=versionutils.deprecated.LIBERTY,
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in_favor_of='entrypoints',
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what='direct import of driver')
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def _load_using_import(driver_name, *args):
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return importutils.import_object(driver_name, *args)
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# For backwards-compatibility, an unregistered class reference can
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# still be used.
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return _load_using_import(driver_name, *args)
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class Manager(object):
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"""Base class for intermediary request layer.
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The Manager layer exists to support additional logic that applies to all
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or some of the methods exposed by a service that are not specific to the
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HTTP interface.
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It also provides a stable entry point to dynamic backends.
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An example of a probable use case is logging all the calls.
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"""
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driver_namespace = None
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def __init__(self, driver_name):
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self.driver = load_driver(self.driver_namespace, driver_name)
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def __getattr__(self, name):
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"""Forward calls to the underlying driver."""
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f = getattr(self.driver, name)
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setattr(self, name, f)
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return f
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