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60405863b5
Create a document to describe the how it works and known limitations and update the NEWS accordingly. Signed-off-by: Flavio Leitner <fbl@sysclose.org> Signed-off-by: Ben Pfaff <blp@ovn.org>
69 lines
2.7 KiB
ReStructuredText
69 lines
2.7 KiB
ReStructuredText
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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 Open vSwitch documentation:
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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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===========================================
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Open vSwitch Networking Namespaces on Linux
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===========================================
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The Open vSwitch has networking namespaces basic support on Linux. That allows
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ovs-vswitchd daemon to continue tracking status and statistics after moving a
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port to another networking namespace.
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How It Works
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------------
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The daemon ovs-vswitchd runs on what is called parent network namespace. It
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listens to netlink event messages from all networking namespaces (netns)
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with an identifier on the parent. Each netlink message contains the network
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namespace identifier (netnsid) as ancillary data which is used to match the
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event to the corresponding port.
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The ovs-vswitchd uses an extended openvswitch kernel API [1]_ to get the
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current netnsid (stored in struct netdev_linux) and statistics from a specific
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port. The netnsid remains cached in userspace until a changing event is
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received, for example, when the port is moved to another network namespace.
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Using another extended kernel API [2]_, the daemon gets port's information
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such as flags, MTU, MAC address and ifindex from a port already in another
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namespace.
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The upstream kernel 4.15 includes the necessary changes for the basic support.
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In case of the running kernel doesn't provide the APIs, the daemon falls back
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to the previous behavior.
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.. [1] Request cmd: OVS_VPORT_CMD_GET, attribute: OVS_VPORT_ATTR_NETNSID
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.. [2] Request cmd: RTM_GETLINK passing IFLA_IF_NETNSID attribute.
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Limitations
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-----------
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Currently it is only possible to retrieve the information listed in the
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above section. Most of other operations, for example querying MII or
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setting MTU, lacks the proper API in the kernel, so they remain unsupported.
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In most use cases that needs to move ports to another networking namespaces
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should use veth pairs instead because it offers a cleaner and more robust
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solution with no noticeable performance penalty.
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