----- Original Message -----
From: cranium2003 <cranium2003@xxxxxxxxx>
To: kernel newbies <kernelnewbies@xxxxxxxxxxxx>
Sent: Monday, May 02, 2005 10:58 AM
Subject: Problem with kernel modules
> Hello,
> I have written a kernel module that accesses skbuff
> and depending on whether packet is icmp or not it
> prints IP checksum and ICMP checksum. But I am getting
>
> sum.c: In function `hook_func1':
> sum.c:24: dereferencing pointer to incomplete type
> sum.c: In function `hook_func2':
> sum.c:40: dereferencing pointer to incomplete type
Hey just check out whether u r typecasting it properly when dereferencing in
case ur using Void Pointers.
sandeep
> Whats wrong?
> regards,
> cranium.
>
> *************************************************
>
> #define __KERNEL__
> #define MODULE
>
> #include <linux/module.h>
> #include <linux/kernel.h>
> #include <linux/skbuff.h>
> #include <linux/ip.h>
> #include <linux/netfilter.h>
> #include <linux/netfilter_ipv4.h>
>
> static struct nf_hook_ops nfho1,nfho2;
>
> unsigned int hook_func1(unsigned int hooknum,struct
> sk_buff **skb,
> const struct net_device *in,
> const struct net_device *out,
> int (*okfn)(struct sk_buff *))
> {
> struct sk_buff *sb = *skb;
>
> if(sb->nh.iph->protocol==1)
> {
> printk(KERN_DEBUG"ICMP packet\n");
> printk(KERN_DEBUG "ICMP cksum=%d,& IP
> cksum=%d\n",sb->h.icmph->checksum,sb->nh.iph->check);
> }
>
> return NF_ACCEPT;
> }
>
>
> unsigned int hook_func2(unsigned int hooknum,struct
> sk_buff **skb,
> const struct net_device *in,
> const struct net_device *out,
> int (*okfn)(struct sk_buff *))
> {
> struct sk_buff *sb = *skb;
> if(sb->nh.iph->protocol==1)
> {
> printk(KERN_DEBUG"ICMP packet\n");
> printk(KERN_DEBUG "ICMP cksum=%d,& IP
> cksum=%d\n",sb->h.icmph->checksum,sb->nh.iph->check);
> }
> return NF_ACCEPT;
> }
>
> static int __init init(void)
> {
> nfho1.hook = hook_func1;
> nfho1.hooknum = NF_IP_POST_ROUTING;
> nfho1.pf = PF_INET;
> nfho1.priority = NF_IP_PRI_FIRST;
> nf_register_hook(&nfho1);
>
> nfho2.hook = hook_func2;
> nfho2.hooknum = NF_IP_PRE_ROUTING;
> nfho2.pf = PF_INET;
> nfho2.priority = NF_IP_PRI_FIRST;
> nf_register_hook(&nfho2);
> return 0;
> }
>
> static void __exit fini(void)
> {
> nf_unregister_hook(&nfho1);
> nf_unregister_hook(&nfho2);
> }
> module_init(init);
> module_exit(fini);
> MODULE_LICENSE("GPL");
>
> *************************************************************
>
>
>
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