can't compile simple netfilter hook

can't compile simple netfilter hook

[Bogdan DUMITRIU]

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I have tried to compile the following netfilter hook (found in one of the documents listed in the documentation area at www.netfilter.org) and I just can't make it.

Here's how I tried to compile it:

gcc -c -I/lib/modules/`uname -r`/build/include ./netmod.c -Wall

Here's the error I got:

In file included from ./netfmod.c:4:
/lib/modules/2.4.18-4GB/build/include/linux/netfilter_ipv4.h:53: `INT_MIN' undeclared here (not in a function)
/lib/modules/2.4.18-4GB/build/include/linux/netfilter_ipv4.h:53: enumerator value for `NF_IP_PRI_FIRST' not integer constant
/lib/modules/2.4.18-4GB/build/include/linux/netfilter_ipv4.h:59: `INT_MAX' undeclared here (not in a function)
/lib/modules/2.4.18-4GB/build/include/linux/netfilter_ipv4.h:59: enumerator value for `NF_IP_PRI_LAST' not integer constant
./netfmod.c:12: warning: `struct net_device' declared inside parameter list
./netfmod.c:12: warning: its scope is only this definition or declaration, which is probably not what you want.
./netfmod.c:12: warning: `struct sk_buff' declared inside parameter list
./netfmod.c: In function `stupid_hook':
./netfmod.c:14: dereferencing pointer to incomplete type
./netfmod.c: At top level:
./netfmod.c:21: variable `stupid_ops' has initializer but incomplete type
./netfmod.c:21: extra brace group at end of initializer
./netfmod.c:21: (near initialization for `stupid_ops')
./netfmod.c:21: `NULL' undeclared here (not in a function)
./netfmod.c:21: `NULL' undeclared here (not in a function)
./netfmod.c:21: warning: excess elements in struct initializer
./netfmod.c:21: warning: (near initialization for `stupid_ops')
./netfmod.c:21: warning: excess elements in struct initializer
./netfmod.c:21: warning: (near initialization for `stupid_ops')
./netfmod.c:21: `PF_INET' undeclared here (not in a function)
./netfmod.c:21: warning: excess elements in struct initializer
./netfmod.c:21: warning: (near initialization for `stupid_ops')
./netfmod.c:21: warning: excess elements in struct initializer
./netfmod.c:21: warning: (near initialization for `stupid_ops')
./netfmod.c:21: warning: excess elements in struct initializer
./netfmod.c:21: warning: (near initialization for `stupid_ops')
./netfmod.c:23: parse error before `init'
./netfmod.c:24: warning: return-type defaults to `int'
./netfmod.c: In function `init':
./netfmod.c:25: warning: implicit declaration of function `nf_register_hook'
./netfmod.c: At top level:
./netfmod.c:28: parse error before `fini'
./netfmod.c:29: warning: return-type defaults to `int'
./netfmod.c: In function `fini':
./netfmod.c:30: warning: implicit declaration of function `nf_unregister_hook'
./netfmod.c:30: `linuxmag_ops' undeclared (first use in this function)
./netfmod.c:30: (Each undeclared identifier is reported only once
./netfmod.c:30: for each function it appears in.)
./netfmod.c:31: warning: control reaches end of non-void function
./netfmod.c: At top level:
./netfmod.c:33: warning: type defaults to `int' in declaration of `module_init'
./netfmod.c:33: warning: parameter names (without types) in function declaration
./netfmod.c:33: warning: data definition has no type or storage class
./netfmod.c:34: warning: type defaults to `int' in declaration of `module_exit'
./netfmod.c:34: warning: parameter names (without types) in function declaration
./netfmod.c:34: warning: data definition has no type or storage class 

Here is the code in netmod.c:

/* Rusty's Dumb netfilter hook example */
#include <linux/config.h>
#include <linux/module.h>
#include <linux/netfilter_ipv4.h>
#include <linux/ip.h>

/* The work comes in here from netfilter.c. */
static unsigned int
stupid_hook(unsigned int hook,
           struct sk_buff **pskb,
           const struct net_device *indev,
           const struct net_device *outdev,
           int (*okfn)(struct sk_buff *))
{
       if ((*pskb)->len == 200)
               return NF_DROP;

       return NF_ACCEPT;
}

static struct nf_hook_ops stupid_ops
= { { NULL, NULL }, stupid_hook, PF_INET, NF_IP_POST_ROUTING, 0 };

static int __init init(void)
{
        return nf_register_hook(&stupid_ops);
}

static void __exit fini(void)
{
        nf_unregister_hook(&linuxmag_ops);
}

module_init(init);
module_exit(fini);

I run a SuSE 8.0 Linux, kernel version 2.4.18, gcc version 2.95.3.

Please help with this as I need it for a school project and I can't get to actually doing what I have to do because I just can't make this work.

Thanks.
Bogdan.

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