Re: Help in tcp/ip source hacking

["Juan M . de la Torre" <jmtorre@gmx.net>]

On Tue, Dec 18, 2001 at 02:38:03AM -0800, vamshi varma wrote:
> Can anybody exlain what is the code flow between skb->dst->output and
> dev_queue_xmit. And where this dst->output is being initialised. 
>

 Check net/ipv4/ip_output.c. dst->output is setted by ip_route_output for
outgoing packets or ip_route_input for incoming packets.

 i.e, local packets are sent by ip_queue_xmit, that calls ip_queue_xmit2 throught
NF_IP_LOCAL_OUT; in ip_queue_xmit2 the skb is sent by calling skb->dst->output (skb),
that points to ip_output. ip_output calls ip_finish_output, that calls ip_finish_output2
through NF_IP_POST_ROUTING. In ip_finish_output2 the ethernet header is added and 
the packet is sent:

static inline int ip_finish_output2(struct sk_buff *skb)
{
        struct dst_entry *dst = skb->dst;
        struct hh_cache *hh = dst->hh;

#ifdef CONFIG_NETFILTER_DEBUG
        nf_debug_ip_finish_output2(skb);
#endif /*CONFIG_NETFILTER_DEBUG*/

        if (hh) {
                read_lock_bh(&hh->hh_lock);
                memcpy(skb->data - 16, hh->hh_data, 16);
                read_unlock_bh(&hh->hh_lock);
                skb_push(skb, hh->hh_len);
                return hh->hh_output(skb);
        } else if (dst->neighbour)
                return dst->neighbour->output(skb);

        if (net_ratelimit())
                printk(KERN_DEBUG "ip_finish_output2: No header cache and no neighbour!\n");
        kfree_skb(skb);
        return -EINVAL;
}

 Cheers,
      
            Juanma

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