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

[Ying X. <yin...@wi...>]

On 02/06/2015 07:50 PM, Erik Hugne wrote:
> 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)
> 

Good news! :)

Regards,
Ying

> //E
> 
>