这个代码是 Character Device Drivers的一个实例代码。参考地址：http://www.tldp.org/LDP/lkmpg/2.6/html/x569.html

basic.c

#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/moduleparam.h>	/* Param header */

#include <linux/fs.h>
/*
 * register_chrdev_region(){}
 * alloc_chrdev_region(){}
 * unsregister_chrdev_region(){}
 * */

#include <linux/types.h>
/* 
 *  dev_t
 *  MKDEV
 *  MAJOR, MINOR
 * */

#include <linux/cdev.h>
#include <linux/slab.h>
/* kfree(){} */


#define DRIVER_AUTHOR "icecream <creamidea@gmail.com>"
#define DRIVER_DESC "A sample driver"

#define MAJOR_NUM 200		/* 主设备号 */
#define MINOR_NUM 0		/* 次设备号 */
#define DEV_NAME "chardev"	/* 设备名称 */

typedef struct {
  struct cdev cdev;
} global_dev;
global_dev* global_devp = NULL;	/* 全局的指针 */

/* 实现file_operations结构体 */
static struct file_operations fops = {
  .owner = THIS_MODULE		/* 指向当前指针模块 */
};

static int major_num = 0;

/* 将设备添加到系统中去实现函数 */
static void setup(global_dev* devp) 
{
  /* 把当前添加到内核中正在使用的列表中 */
  cdev_init(&devp->cdev, &fops);
  /*  */
  cdev_add(&devp->cdev, MKDEV(major_num, 0), 1);
}

static int __init basic_init(void) 
{
  int ret;
  /* Makesure number of device */
  dev_t devno;			/* 设备编号 */
  devno = MKDEV(MAJOR_NUM, MINOR_NUM);
  /* register the devno to kernel */
  ret = register_chrdev_region(devno, 1, DEV_NAME);
  if (ret < 0) {		/* 主动注册失败 */
    /* 让系统帮忙注册 */
    alloc_chrdev_region(&devno, 0, 1, DEV_NAME);
  }

  major_num = MAJOR(devno);	/* 提取主设备号 */
  printk("major_num = %d\n", major_num);

  /* 申请内存空间 */
  /* GFP_KERNEL will block(sleep) */
  global_devp = (global_dev*)kmalloc(sizeof(global_dev), GFP_KERNEL);
  if (global_devp == NULL) {
    goto err;
  }

  /* global_devp 是全局，不传也可以 */
  setup(global_devp);
  
  return 0;

 err:
  return -1;			/* 告诉上层失败原因 */
}

static void __exit basic_exit(void)
{
  /* 删除设备，空间，释放空间 */
  cdev_del(&global_devp->cdev);
  kfree(global_devp);

  /* 注销设备 */
  /* 利用主次编号获取设备编号 */
  unregister_chrdev_region(MKDEV(major_num, 0), 1);
  printk("unregister devno finished!\n");

  printk("Exit the driver module!\n");
}

module_init(basic_init); 	/* enter */
module_exit(basic_exit);	/* out */

MODULE_LICENSE("Dual BSD/GPL");
MODULE_AUTHOR(DRIVER_AUTHOR);
MODULE_DESCRIPTION(DRIVER_DESC);
MODULE_ALIAS("Module Exercise");