6083f24135
The interaction steps should be presented as a numbered list and not as a literal block, which makes it look like bash comments. Change-Id: Id00ae50255a3487830d1d77b6cb5862e186283ee
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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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http://www.apache.org/licenses/LICENSE-2.0
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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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Convention for heading levels in Neutron devref:
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======= Heading 0 (reserved for the title in a document)
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------- Heading 1
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~~~~~~~ Heading 2
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+++++++ Heading 3
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''''''' Heading 4
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(Avoid deeper levels because they do not render well.)
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L2 agent extensions
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===================
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All reference agents support common extension mechanism that allows to easily
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reuse code between agents and to avoid the need to patch an agent for each new
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core resource extension. Those extensions can be especially interesting to
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third parties that don't want to maintain their code in Neutron tree.
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Extensions are referenced through stevedore entry points defined under
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neutron.agent.l2.extensions namespace. On each port event, handle_port is
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triggered by the agent.
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* neutron.agent.l2.agent_extension:
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This module defines an abstract extension interface.
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* neutron.agent.l2.extensions.manager:
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This module contains a manager that allows to register multiple extensions,
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and passes handle_port events down to all enabled extensions.
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Agent API object
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----------------
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Every agent can pass a so-called agent API object into extensions to expose
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some of its internals to them in controlled way.
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If an extension is interested in using the object, it should define
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consume_api() method that will receive the object before extension's
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initialize() method is called by the extension manager.
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This agent API object is part of public Neutron interface for third parties.
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All changes to the interface will be managed in backwards compatible way.
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At the moment, only Open vSwitch agent provides an agent API object to
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extensions.
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Open vSwitch agent API
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~~~~~~~~~~~~~~~~~~~~~~
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* neutron.plugins.ml2.drivers.openvswitch.agent.ovs_agent_extension_api
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Open vSwitch agent API object includes two methods that return wrapped and
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hardened bridge objects with cookie values allocated for calling extensions.
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#. request_int_br
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#. request_tun_br
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Bridge objects returned by those methods already have new default cookie values
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allocated for extension flows. All flow management methods (add_flow, mod_flow,
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...) enforce those allocated cookies.
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Extensions are able to use those wrapped bridge objects to set their own flows,
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while the agent relies on the collection of those allocated values when
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cleaning up stale flows from the previous agent session::
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+-----------+
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| Agent API +--------------------------------------------------+
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+-----+-----+ |
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| +-----------+ |
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|1 +--+ Extension +--+ |
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| | +-----------+ | |
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+---+-+-+---+ 2 +--------------+ 3 | | 4 |
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| Agent +-----+ Ext. manager +-----+--+ .... +--+-----+
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+-----------+ +--------------+ | |
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| +-----------+ |
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+--+ Extension +--+
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+-----------+
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Interactions with the agent API object are in the following order:
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#. The agent initializes the agent API object (bridges, other internal state).
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#. The agent passes the agent API object into the extension manager.
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#. The manager passes the agent API object into each extension.
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#. An extension calls the new agent API object method to receive bridge wrappers with cookies allocated.
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Call #4 also registers allocated cookies with the agent bridge objects.
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