mirror of
https://github.com/torvalds/linux.git
synced 2024-12-04 01:51:34 +00:00
17ed5c1a9e
Document the spec format used by netlink-raw families like rt and tc. Reviewed-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Donald Hunter <donald.hunter@gmail.com> Link: https://lore.kernel.org/r/20231215093720.18774-4-donald.hunter@gmail.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>
153 lines
4.2 KiB
ReStructuredText
153 lines
4.2 KiB
ReStructuredText
.. SPDX-License-Identifier: BSD-3-Clause
|
|
|
|
======================================================
|
|
Netlink specification support for raw Netlink families
|
|
======================================================
|
|
|
|
This document describes the additional properties required by raw Netlink
|
|
families such as ``NETLINK_ROUTE`` which use the ``netlink-raw`` protocol
|
|
specification.
|
|
|
|
Specification
|
|
=============
|
|
|
|
The netlink-raw schema extends the :doc:`genetlink-legacy <genetlink-legacy>`
|
|
schema with properties that are needed to specify the protocol numbers and
|
|
multicast IDs used by raw netlink families. See :ref:`classic_netlink` for more
|
|
information. The raw netlink families also make use of type-specific
|
|
sub-messages.
|
|
|
|
Globals
|
|
-------
|
|
|
|
protonum
|
|
~~~~~~~~
|
|
|
|
The ``protonum`` property is used to specify the protocol number to use when
|
|
opening a netlink socket.
|
|
|
|
.. code-block:: yaml
|
|
|
|
# SPDX-License-Identifier: ((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause)
|
|
|
|
name: rt-addr
|
|
protocol: netlink-raw
|
|
protonum: 0 # part of the NETLINK_ROUTE protocol
|
|
|
|
|
|
Multicast group properties
|
|
--------------------------
|
|
|
|
value
|
|
~~~~~
|
|
|
|
The ``value`` property is used to specify the group ID to use for multicast
|
|
group registration.
|
|
|
|
.. code-block:: yaml
|
|
|
|
mcast-groups:
|
|
list:
|
|
-
|
|
name: rtnlgrp-ipv4-ifaddr
|
|
value: 5
|
|
-
|
|
name: rtnlgrp-ipv6-ifaddr
|
|
value: 9
|
|
-
|
|
name: rtnlgrp-mctp-ifaddr
|
|
value: 34
|
|
|
|
Sub-messages
|
|
------------
|
|
|
|
Several raw netlink families such as
|
|
:doc:`rt_link<../../networking/netlink_spec/rt_link>` and
|
|
:doc:`tc<../../networking/netlink_spec/tc>` use attribute nesting as an
|
|
abstraction to carry module specific information.
|
|
|
|
Conceptually it looks as follows::
|
|
|
|
[OUTER NEST OR MESSAGE LEVEL]
|
|
[GENERIC ATTR 1]
|
|
[GENERIC ATTR 2]
|
|
[GENERIC ATTR 3]
|
|
[GENERIC ATTR - wrapper]
|
|
[MODULE SPECIFIC ATTR 1]
|
|
[MODULE SPECIFIC ATTR 2]
|
|
|
|
The ``GENERIC ATTRs`` at the outer level are defined in the core (or rt_link or
|
|
core TC), while specific drivers, TC classifiers, qdiscs etc. can carry their
|
|
own information wrapped in the ``GENERIC ATTR - wrapper``. Even though the
|
|
example above shows attributes nesting inside the wrapper, the modules generally
|
|
have full freedom to define the format of the nest. In practice the payload of
|
|
the wrapper attr has very similar characteristics to a netlink message. It may
|
|
contain a fixed header / structure, netlink attributes, or both. Because of
|
|
those shared characteristics we refer to the payload of the wrapper attribute as
|
|
a sub-message.
|
|
|
|
A sub-message attribute uses the value of another attribute as a selector key to
|
|
choose the right sub-message format. For example if the following attribute has
|
|
already been decoded:
|
|
|
|
.. code-block:: json
|
|
|
|
{ "kind": "gre" }
|
|
|
|
and we encounter the following attribute spec:
|
|
|
|
.. code-block:: yaml
|
|
|
|
-
|
|
name: data
|
|
type: sub-message
|
|
sub-message: linkinfo-data-msg
|
|
selector: kind
|
|
|
|
Then we look for a sub-message definition called ``linkinfo-data-msg`` and use
|
|
the value of the ``kind`` attribute i.e. ``gre`` as the key to choose the
|
|
correct format for the sub-message:
|
|
|
|
.. code-block:: yaml
|
|
|
|
sub-messages:
|
|
name: linkinfo-data-msg
|
|
formats:
|
|
-
|
|
value: bridge
|
|
attribute-set: linkinfo-bridge-attrs
|
|
-
|
|
value: gre
|
|
attribute-set: linkinfo-gre-attrs
|
|
-
|
|
value: geneve
|
|
attribute-set: linkinfo-geneve-attrs
|
|
|
|
This would decode the attribute value as a sub-message with the attribute-set
|
|
called ``linkinfo-gre-attrs`` as the attribute space.
|
|
|
|
A sub-message can have an optional ``fixed-header`` followed by zero or more
|
|
attributes from an ``attribute-set``. For example the following
|
|
``tc-options-msg`` sub-message defines message formats that use a mixture of
|
|
``fixed-header``, ``attribute-set`` or both together:
|
|
|
|
.. code-block:: yaml
|
|
|
|
sub-messages:
|
|
-
|
|
name: tc-options-msg
|
|
formats:
|
|
-
|
|
value: bfifo
|
|
fixed-header: tc-fifo-qopt
|
|
-
|
|
value: cake
|
|
attribute-set: tc-cake-attrs
|
|
-
|
|
value: netem
|
|
fixed-header: tc-netem-qopt
|
|
attribute-set: tc-netem-attrs
|
|
|
|
Note that a selector attribute must appear in a netlink message before any
|
|
sub-message attributes that depend on it.
|