/*imp1_k.c*/#ifndef __KERNEL__#define __KERNEL__#endif#ifndef MODULE#define MODULE#endif#include <linux/module.h>#include <linux/kernel.h>#include <linux/types.h>#include <linux/string.h>#include <linux/netfilter_ipv4.h>#include <linux/init.h>#include <asm/uaccess.h>#include "imp1.h"#define KMSG      "a message from kernel\n"#define KMSG_LEN  sizeof("a message from kernel\n")static int data_to_kernel(struct sock *sk, int cmd, void *user,			  unsigned int len){  switch(cmd)    {    case IMP1_SET:      {        char umsg[64];	memset(umsg, 0, sizeof(char)*64);        copy_from_user(umsg, user, sizeof(char)*64);        printk("umsg: %s", umsg);      }      break;    }  return 0;}static int data_from_kernel(struct sock *sk, int cmd, void *user, int *len){  switch(cmd)    {    case IMP1_GET:      {        copy_to_user(user, KMSG, KMSG_LEN);      }      break;    }  return 0;}static struct nf_sockopt_ops imp1_sockops ={  .pf = PF_INET,  .set_optmin = IMP1_SET,  .set_optmax = IMP1_MAX,  .set = data_to_kernel,  .get_optmin = IMP1_GET,  .get_optmax = IMP1_MAX,  .get = data_from_kernel,};static int __init init(void){  return nf_register_sockopt(&imp1_sockops);}static void __exit fini(void){  nf_unregister_sockopt(&imp1_sockops);}module_init(init);module_exit(fini);