Re: [Xenomai] Odp: Re: RTnet -- receive broadcast frame at the local machine

["Mariusz Janiak" <mariuszjaniak@wp.pl>]

Dnia Środa, 2 Marca 2016 14:07 Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org> napisał(a) 
> On Tue, Mar 01, 2016 at 11:24:55PM +0100, Mariusz Janiak wrote:
> > > From what I understand from this post, it is not easy to fix, as it
> > > requires duplicating packets. So, patch welcome.
> > 
> > Ok, we went back to the original question, could someone point the
> > place that has to be modified. I have played a little bit with the
> > RTnet stack recently, but this task require far better
> > understanding of the stack. Maybe someone more advanced can give
> > some guidelines.
> 
> It is not that complicated. The udp send function (rt_udp_sendmsg)
> is in udp.c, it calls rt_ip_route_output (found in route.c) to find
> the output route, than rt_ip_build_xmit (found in ip_output.c) to
> build the packet and send in on the device. rt_ip_build_xmit calls
> rt_eth_header to build the ethernet header (found in eth.c), then
> rtdev_xmit (found in dev.c) to send the packet.
> 
> So you can do this either at the IP level in rt_ip_build_xmit, or at
> the ethernet level in rtdev_xmit. What you need to do is that when
> the destination is broadcast (there should be a macro to test that
> an IP address is broadcast if you want to do it at IP level, and the
> mac address for broadcast is just ff:ff:ff:ff:ff:ff if you want to
> do it at ethernet level) you need to duplicate the packet, and
> either trigger a receive on the same device, or send the packet on
> the loopback device. If you go the ethernet route, you will have to
> use a per-device callback to test if the destination is broadcast,
> as rtdev_xmit is supposed to not be specific to ethernet, like is
> done with the hard_header and start_xmit callbacks.

Thank you Gilles, I see it more clearly now. I think I will go the ethernet route. I will back with patch soon. 

Regards,
Marisz 

> Hope this helps.
> Regards.
> 
> -- 
> 					    Gilles.
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