Re: [tipc-discussion] [PATCH 5/5] tipc: add ip/udp media type

[Erik H. <eri...@er...>]

On Mon, Jan 19, 2015 at 06:38:56PM +0800, Ying Xue wrote:
> > I'm wondering if this would be feasible:
> > 1. export the udp_send_skb() function
> > 2. skb_push(sizeof udphdr) on the TIPC SKB.
> > 3. Do a routing lookup for the destination ip and pass that, together with the
> >    TIPC SKB to udp_send_skb()
> >
> 
> It sounds like this is a hack method. Instead, we can understand how
> these tunnels deal with our encountered issue as long as we look through
> the tunnel interfaces implemented in networking with UDP socket. For
> example, if we take a closer look at VXLAN code, we will find a better
> approach to solve our issue. Actually VXLAN uses udp_tunnel to overcome
> the difficulty:
> 
> 1. Create UDP socket:
> 
> vxlan_create_sock()
>   udp_sock_create()
> 
> 2. Deliver SKB:
> 
> vxlan_xmit_one()
>   vxlan_xmit_skb()
>     udp_tunnel_xmit_skb()
> 
> In the entire sending path, no SKB copy happens. Moreover, when we use
> the interfaces provided by udp_tunnel, both IPV4 and IPv6 are supported :)
> 
> It seems that this is a perfect solution for us :)
> 
> Maybe my analysis is not completely right as I just look through the
> code of VXLAN. If I am wrong, please correct me :)

Thanks for the tip!
I replaced all deferred sending with something like this:
	clone = skb_clone(skb, GFP_ATOMIC);
	/*Routing lookup*/
	memset(&fl, 0, sizeof(fl));
	fl.daddr = dst->sin_addr.s_addr;
	fl.saddr = src->sin_addr.s_addr;
	fl.flowi4_mark = clone->mark;
	fl.flowi4_proto = IPPROTO_UDP;

	rt = ip_route_output_key(net, &fl);
	if (IS_ERR(rt)) {
		err = PTR_ERR(rt);
		pr_err("routing lookup failed\n");
	}

	df = htons(IP_DF);
	clone->ignore_df = 0;
	skb_set_inner_protocol(clone, htons(ETH_P_TIPC));

	sent = udp_tunnel_xmit_skb(ub->transmit, rt, clone, src->sin_addr.s_addr,
				   dst->sin_addr.s_addr, 0, 255, df, src->sin_port,
				   dst->sin_port, false);

Works perfectly :)
(i had to expand the BUF_HEADROM for tipc messages to have enough headroom for
an IP+UDP header)

//E