Something

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/fs.h>
#include "hhv.h"

int                             init_module(void);
void                            cleanup_module(void);
static int                      device_open(struct inode *, struct file *);
static int                      device_release(struct inode *, struct file *);

static int      dev_open = 0;
static int      last_ret = 2323;

static int 
device_open(struct inode *inode, struct file *file)
{
  printk(KERN_ALERT "device_open(%p)\n", file);
  if (dev_open)
    {
      printk(KERN_ALERT "Device is busy\n");
      return -EBUSY;
    }
  dev_open++;
  printk(KERN_ALERT "Opened char device ...\n");
  try_module_get(THIS_MODULE);
  return 0;
}

static int
device_release(struct inode *inode, struct file *file)
{
  dev_open--;
  last_ret = 0;
  printk(KERN_ALERT "Closed char device ...\n");
  module_put(THIS_MODULE);
  return 0;
}

int device_ioctl(struct inode *inode, struct file *file,
                 unsigned int ioctl_num,
                 unsigned long ioctl_param)
{
  unsigned long num;

  printk(KERN_ALERT "ioctl num=%d ioctl_param%d\n", ioctl_num,
         ioctl_param);

  switch (ioctl_num)
    {
    case IOCTL_SET_NUMCALL:
      num = ioctl_param;
      __asm__ volatile("mr %%r11,%0;\n" \
                       "sc 1;\n" \
                       "mr %1,%%r3;\n"
                       : "=r" (last_ret)
                       : "r" (num));
      break;

    case IOCTL_GET_RETVAL:
      return last_ret;
      break;
    }
  return 0;
}


static struct file_operations fops =
  {
    ioctl : device_ioctl,
    open : device_open,
    release : device_release
  };


int     init_module(void)
{
  int ret;

  if ((ret = register_chrdev(MAJOR_NUM, DEVNAME, &fops)) < 0)
    {
      printk(KERN_ALERT "Can't register character device\n");
      return ret;
    }
  printk("Run : \"mknod /dev/%s c %d 0\"\n", DEVNAME, MAJOR_NUM);
  return 0;
}

void    cleanup_module(void)
{
  int ret;

  if ((ret = unregister_chrdev(MAJOR_NUM, DEVNAME)) < 0)
    printk(KERN_ALERT "Can't unregister char device\n");
  printk(KERN_ALERT "Removin module\n");
}