ovs 3.6.3

Open vSwitch library

The openvswitch package provides the official Python language bindings for Open vSwitch. They are developed in-tree as part of the Open vSwitch Package.

Installation

You can install the package using pip:

$ pip install ovs

The package include an optional flow parsing library. To use this package, you must install its required dependencies. The flow extra is provided for this purpose:

$ pip install ovs[flow]

Examples

Inspecting the database schema

The OVSDB schema is described in a JSON file, typically called vswitch.ovsschema. It can be inspected via schema provided locally on the host or remotely via the JSON-RPC API. For example, to view it from the local file:

import json
import ovs.dirs

schema_path = f'{ovs.dirs.PKGDATADIR}/vswitch.ovsschema'

with open(schema_path) as fh:
    schema = json.load(fh)

print(schema)

To do the same via the JSON-RPC, using TCP:

import json
import sys
import ovs.jsonrpc

remote = 'tcp:127.0.0.1:6640'

error, stream = ovs.stream.Stream.open_block(ovs.stream.Stream.open(remote))
if error:
    print(error)
    sys.exit(1)

rpc = ovs.jsonrpc.Connection(stream)
request = ovs.jsonrpc.Message.create_request('get_schema', ['Open_vSwitch'])
error, reply = rpc.transact_block(request)
rpc.close()
if error:
    print(error)
    sys.exit(1)

schema = reply.result
print(schema)

Note

The above assumes the default port (6640) is used and Open vSwitch is running on the localhost (127.0.0.1).

Dumping tables, ports and interfaces

The Open vSwitch Database (OVSDB) Interface Definition Language (IDL) maintains an in-memory replica of a database. It issues RPC requests to an OVSDB database server and parses the responses, converting raw JSON into data structures that are easier for clients to digest. You can use the IDL for database transactions along with simpler operations such as dumping information about the schema. The Python implementation of the OVSDB IDL is provided in ovs.db.idl via the Idl class. To initialise this, you need a schema helper and a “remote” or interface through which to communicate with the OVSDB. We can re-use and build upon the schema example from above to create an instance of ovs.db.idl.SchemaHelper. Once done, you can create an instance of ovs.db.idl.IDL and use this to iterate over the bridges, ports and interfaces available:

import ovs.db.idl
import ovs.dirs

# Create the schema helper.
schema_path = f'{ovs.dirs.PKGDATADIR}/vswitch.ovsschema'
schema_helper = ovs.db.idl.SchemaHelper(schema_path)
schema_helper.register_all()  # Register all tables for monitoring.

# Connect over TCP.
remote = 'tcp:127.0.0.1:6640'

idl = ovs.db.idl.Idl(remote, schema_helper)

# Wait until we have all information retrieved from the database.
while not idl.has_ever_connected():
    poller = ovs.poller.Poller()
    idl.wait(poller)
    poller.block()
    idl.run()

# Print bridges, ports and interfaces, à la 'ovs-vsctl show'.
for bridge in idl.tables['Bridge'].rows.values():
    print(f'Bridge {bridge.name}')
    for port in bridge.ports:
        print(f'\tPort {port.name}')
        for interface in port.interfaces:
            print(f'\t\tInterface {interface.name}')
            print(f'\t\t\ttype: {interface.type}')

Note

The above connects to OVSDB via TCP. You could also connect via the unix socket by replacing the remote with e.g.

remote = f'unix:{ovs.dirs.RUNDIR}/db.sock'

Note

This is only an example. Production code should be prepared for failures while retrieving information and may wish to incorporate retry logic.

Documentation

Documentation is included in the Python source. To view this, you can install the package and use pydoc. For example:

$ python -m pydoc ovs

Alternatively, you can use the help function from the Python REPL:

>>> import ovs
>>> help(ovs)