[ovs-discuss] OVS custom action

[William Tu]

On Fri, Apr 24, 2020 at 9:50 AM Ben Pfaff <blp at ovn.org> wrote:
>
> 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.)

Hi Luca,

Here is an example of adding a new action Yi-Hung recently is working on.
https://mail.openvswitch.org/pipermail/ovs-dev/2020-April/369556.html

William