From mboxrd@z Thu Jan  1 00:00:00 1970
From: qber66 <tim.vandermeersch@pandora.be>
Subject: Problems determining the correct tcp header size
Date: Wed, 19 Mar 2003 20:04:47 +0000 (UTC)
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Date: Tue, 25 Mar 2003 18:26:11 +0100
List-Id: netfilter-devel.vger.kernel.org

Hi,

I'm making a new target for iptables, but I'n having a problems with 
determining the correct tcp header lenght in the following function:

static unsigned int ipt_mytarget_target(struct sk_buff **pskb, unsigned 
int hooknum,
        const struct net_device *in, const struct net_device *out,
        const void *targetinfo, void *userinfo)
{
    struct tcphdr *tcph = (struct tcphdr *) (*pskb)->h.th;
    struct iphdr *iph = (struct iphdr *) (*pskb)->nh.iph;

    printk(KERN_WARNING "iphdr lenght: %d, tcphdr lenght: %d\n", 
iph->ihl*4, tcph->doff*4);
}


When I use this rule:

iptables -t mangle -A POSTROUTING -p TCP -j MYTARGET

I get the following output:

iphdr lenght: 20, tcphdr lenght: 0
iphdr lenght: 20, tcphdr lenght: 0
iphdr lenght: 20, tcphdr lenght: 16
iphdr lenght: 20, tcphdr lenght: 0
iphdr lenght: 20, tcphdr lenght: 4
iphdr lenght: 20, tcphdr lenght: 16
iphdr lenght: 20, tcphdr lenght: 16
iphdr lenght: 20, tcphdr lenght: 0
iphdr lenght: 20, tcphdr lenght: 0
iphdr lenght: 20, tcphdr lenght: 4
iphdr lenght: 20, tcphdr lenght: 0
iphdr lenght: 20, tcphdr lenght: 16
iphdr lenght: 20, tcphdr lenght: 4
iphdr lenght: 20, tcphdr lenght: 0
.....

Can any one tell me what I'm doing wrong?

Thanks in advance,
Tim Vandermeersch.