Why I can't compile a simple netfilter hook module?

[io.chir0n@gmail.com (Dexter)]

On Tue, 2012-05-08 at 09:49 +0530, rohan puri wrote:
> 
> 
> On Tue, May 8, 2012 at 9:37 AM, Chir0n <io.chir0n@gmail.com> wrote:
>         I'm using this Makefile:
>         
>         obj-m += hello.o
>         
>         all:
>                make -C /lib/modules/$(shell uname -r)/build M=$(PWD)
>         modules
>         
>         clean:
>                make -C /lib/modules/$(shell uname -r)/build M=$(PWD)
>         clean
>         
>         
>         The hello.c is this:
>         
>         #include <linux/kernel.h>
>         #include <linux/module.h>
>         #include <linux/netfilter.h>
>         #include <linux/netfilter_ipv4.h>
>         
>         static struct nf_hook_ops nfho;         //struct holding set
>         of hook function options
>         
>         //function to be called by hook
>         unsigned int hook_func(unsigned int hooknum, struct sk_buff
>         **skb, const struct net_device *in, const struct net_device
>         *out, int (*okfn)(struct sk_buff *))
>         {
>          printk(KERN_INFO "packet dropped\n");
>                               //log to var/log/messages
>          return NF_DROP;
>                               //drops the packet
>         }
>         
>         //Called when module loaded using 'insmod'
>         int init_module()
>         {
>          nfho.hook = hook_func;                       //function to
>         call when conditions below met
>          nfho.hooknum = NF_IP_PRE_ROUTING;            //called right
>         after packet recieved, first hook in Netfilter
>          nfho.pf = PF_INET;                           //IPV4 packets
>          nfho.priority = NF_IP_PRI_FIRST;             //set to highest
>         priority over all other hook functions
>          nf_register_hook(&nfho);                     //register hook
>         
>          return 0;                                    //return 0 for
>         success
>         }
>         
>         //Called when module unloaded using 'rmmod'
>         void cleanup_module()
>         {
>          nf_unregister_hook(&nfho);                     //cleanup ?
>         unregister hook
>         }
>         
>         
>         Here are the error message:
>         
>         $ make
>         make -C /lib/modules/3.3.2-6.fc16.x86_64/build
>         M=/home/fabio/Desktop/modules modules
>         make[1]: Entering directory
>         `/usr/src/kernels/3.3.2-6.fc16.x86_64'
>          CC [M]  /home/fabio/Desktop/modules/hello.o
>         /home/fabio/Desktop/modules/hello.c: In function
>         ?init_module?:
>         /home/fabio/Desktop/modules/hello.c:18:13: warning: assignment
>         from incompatible pointer type [enabled by default]
>         /home/fabio/Desktop/modules/hello.c:19:18: error:
>         ?NF_IP_PRE_ROUTING? undeclared (first use in this function)
>         /home/fabio/Desktop/modules/hello.c:19:18: note: each
>         undeclared identifier is reported only once for each function
>         it appears in
>         make[2]: *** [/home/fabio/Desktop/modules/hello.o] Error 1
>         make[1]: *** [_module_/home/fabio/Desktop/modules] Error 2
>         make[1]: Leaving directory
>         `/usr/src/kernels/3.3.2-6.fc16.x86_64'
>         make: *** [all] Error 2
>         
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>         
> Hi,
> 
> 
> You need to include header which defines "NF_IP_PRE_ROUTING"
> 
> 
> - Rohan


Hi,

But I have declared this header:

#include <linux/netfilter_ipv4.h>