On Fri, Apr 24, 2020 at 02:50:43PM +0000, Luca Mancini wrote:
> I am trying to implement a new openflow action on an openvswitch, that upon
> request by the controller buffers a given packet.
>
> So assume a topology like H1—s1--s2—H2 where h1 sends packets to h2, the
> controller would specify a BUFFER action to all packets going from h1 to h2
> Making the s1 switch create a buffer where all these packets are stored until
> the buffer is full and then send the buffer (as a new packet) down the path
> to H2.
> I have found very little material regarding the implementation of a new
> openflow action to ovs:
>
> I followed this guide a little bit but I’m finding some things a bit
> confusing https://mcfelix.me/blog/modifying-ovs/
> Some questions I have are:
> -is this type of action possible?
> -where exactly do I need to code the actual action function?
> -how and where are packets defined in OVS? I’m having trouble understading if
> the packet I need to be storing is the sk_buff that is passed as a parameter
> or if it’s something else
This should be possible. You'll need to make the action send packets
that need to be buffered to userspace, with a "userspace" kernel
action. Then you can accumulate the packets in userspace until they
should be released.
Since you'll only be dealing with userspace packets, struct dp_packet is
primarily what you need to care about.
The FAQ says this:
Q: How do I add support for a new OpenFlow action?
A: Add your new action to ``enum ofp_raw_action_type`` in
``lib/ofp-actions.c``, following the existing pattern. Then recompile and
fix all of the new warnings, implementing new functionality for the new
action as needed. (If you configure with ``--enable-Werror``, as described
in the :doc:`/intro/install/general`, then it is impossible to miss any
warnings.)
If you need to add an OpenFlow vendor extension action for a vendor that
doesn't yet have any extension actions, then you will also need to add the
vendor to ``vendor_map`` in ``build-aux/extract-ofp-actions``. Also, you
will need to add support for the vendor to ``ofpact_decode_raw()`` and
``ofpact_put_raw()`` in ``lib/ofp-actions.c``. (If you have a choice of
how to design your vendor extension actions, it will be easier if you make
them resemble the ONF and OVS extension actions.)
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