From mboxrd@z Thu Jan  1 00:00:00 1970
From: rohan.puri15@gmail.com (rohan puri)
Date: Tue, 8 May 2012 19:31:11 +0530
Subject: Why I can't compile a simple netfilter hook module?
In-Reply-To: <CAC_t5gCuNMTT_t3T7Qbsk=WLKUQLU26ZMJRD6PM6PnFMbQEakw@mail.gmail.com>
References: <CAC_t5gCuNMTT_t3T7Qbsk=WLKUQLU26ZMJRD6PM6PnFMbQEakw@mail.gmail.com>
Message-ID: <CALJfu6PHr94jWAr4poduxOkECJodVdhbutJuEvAFjkWE234GKg@mail.gmail.com>
To: kernelnewbies@lists.kernelnewbies.org
List-Id: kernelnewbies.lists.kernelnewbies.org

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]
> *

you may have declared the header, thn check whether the path is correct or
the symbol name spelling.

> * /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*
>
> _______________________________________________
> Kernelnewbies mailing list
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>
> Also dont delete previous mail thread contents.

- Rohan
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