为驱动程序添加代码，实现自动生成/dev/下节点

下面代码模板是使用的宋宝华老师的代码，希望他不要生气，本为只是为了共享一些学习经验！！

/*======================================================================

    A "seond" device driver as an example of kernel timer
    
    The initial developer of the original code is Baohua Song
    <author@linuxdriver.cn>. All Rights Reserved.
======================================================================*/
#include <linux/module.h>
#include <linux/types.h>
#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/cdev.h>
#include <asm/io.h>
#include <asm/system.h>
#include <asm/uaccess.h>
#include <linux/timer.h> /*包括timer.h头文件*/

#include <asm/atomic.h>

#include <linux/slab.h> //by jeffreyst

#include <linux/device.h> //by jeffreyst

#define SECOND_MAJOR 212    /*预设的second的主设备号*/

static int second_major = SECOND_MAJOR;

/*second设备结构体*/
struct second_dev
{
  struct cdev cdev; /*cdev结构体*/
  atomic_t counter;/* 一共经历了多少秒？*/
  struct timer_list s_timer; /*设备要使用的定时器*/
};

struct second_dev *second_devp; /*设备结构体指针*/

/*定时器处理函数*/
static void second_timer_handle(unsigned long arg)
{
  mod_timer(&second_devp->s_timer,jiffies + HZ);//重新启动定时器，expery time为1HZ
  atomic_inc(&second_devp->counter);//调用原子操作，给counter加1；
 
  printk(KERN_NOTICE "current jiffies is %ld\n", jiffies);
}

/*文件打开函数*/
int second_open(struct inode *inode, struct file *filp)
{
  /*初始化定时器*/
  init_timer(&second_devp->s_timer);
  second_devp->s_timer.function = &second_timer_handle;
  second_devp->s_timer.expires = jiffies + HZ;
 
  add_timer(&second_devp->s_timer); /*添加（注册）定时器*/
 
  atomic_set(&second_devp->counter,0); //计数清0

  return 0;
}
/*文件释放函数*/
int second_release(struct inode *inode, struct file *filp)
{
  del_timer(&second_devp->s_timer);
 
  return 0;
}

/*globalfifo读函数*/
static ssize_t second_read(struct file *filp, char __user *buf, size_t count,
  loff_t *ppos)
{  
  int counter;
 
  counter = atomic_read(&second_devp->counter);
  if(put_user(counter, (int*)buf))
      return - EFAULT;
  else
      return sizeof(unsigned int);  
}

/*文件操作结构体*/
static const struct file_operations second_fops =
{
  .owner = THIS_MODULE,
  .open = second_open,
  .release = second_release,
  .read = second_read,
};

/*初始化并注册cdev*/
static void second_setup_cdev(struct second_dev *dev, int index)
{
  int err, devno = MKDEV(second_major, index);

  cdev_init(&dev->cdev, &second_fops);
  dev->cdev.owner = THIS_MODULE;
  dev->cdev.ops = &second_fops;
  err = cdev_add(&dev->cdev, devno, 1);
  if (err)
    printk(KERN_NOTICE "Error %d adding LED%d", err, index);
}

//add by jeffreyst, class & device struct definiton

static struct class *time_class;
struct device * temp_dev ;

/*设备驱动模块加载函数*/
int second_init(void)
{
  int ret;
  dev_t devno = MKDEV(second_major, 0);

  /* 申请设备号*/
  if (second_major)
    ret = register_chrdev_region(devno, 1, "second");
  else  /* 动态申请设备号 */
  {
    ret = alloc_chrdev_region(&devno, 0, 1, "second");
    second_major = MAJOR(devno);
  }
  if (ret < 0)
    return ret;
  /* 动态申请设备结构体的内存*/
  second_devp = kmalloc(sizeof(struct second_dev), GFP_KERNEL);
  if (!second_devp)    /*申请失败*/
  {
    ret =  - ENOMEM;
    goto fail_malloc;
  }

  memset(second_devp, 0, sizeof(struct second_dev));

  second_setup_cdev(second_devp, 0);

//add by jeffreyst, create class & devive object
  time_class = class_create(THIS_MODULE, "time_class");
  if(IS_ERR(time_class))
  {
      printk("error creat class.\n");
      return -1;
  }
  temp_dev = device_create(time_class, NULL, MKDEV(second_major, 0),0,"second" );
  if(temp_dev = NULL)
  {
      printk("error creat device.\n");
      return -1;

  }
//

  return 0;

  fail_malloc: unregister_chrdev_region(devno, 1);
}

/*模块卸载函数*/
void second_exit(void)

{

 dev_t devno = MKDEV(second_major, 0);//by jeffreyst

  dev_t devno = MKDEV(second_major, 0);

  cdev_del(&second_devp->cdev);   /*注销cdev*/

  kfree(second_devp);     /*释放设备结构体内存*/

  //add by jeffreyst, destroy class & device

  device_destroy(time_class, MKDEV(second_major, 0));//
  class_destroy(time_class);//

  unregister_chrdev_region(MKDEV(second_major, 0), 1); /*释放设备号*/
}

MODULE_AUTHOR("Song Baohua");
MODULE_LICENSE("Dual BSD/GPL");

module_param(second_major, int, S_IRUGO);

module_init(second_init);

module_exit(second_exit);

/*

编辑好源码和makefile后，sudo make 后生成XXX.ko，

使用sudo insmod XXX.ko安装驱动

使用lsmod和cat /proc/devices查看安装结果

/dev/下如果有自己创建的设备，则证明carete_class和create_device运行成功

*/

/*************************************************************************************************************/

虚拟机环境是Ubuntu+Linux ubuntu 2.6.38-15-generic

makefile：

obj-m :=test_timer.o
KDIR :=/usr/src/linux-headers-2.6.38-15-generic
all :  
    make -C $(KDIR) M=$(shell pwd) modules  
clean:  
    make -C $(KDIR) M=$(shell pwd) clean

/*************************************************************************************************************/

用户态应用程序：

#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/time.h>

main()
{
  int fd;
  int counter = 0;
  int old_counter = 0;
 
  /*打开/dev/second设备文件*/
  fd = open("/dev/second", O_RDONLY);
  if (fd !=  - 1)
  {
    while (1)
    {
      read(fd,&counter, sizeof(unsigned int));//读目前经历的秒数
      if(counter!=old_counter)
      {    
          printf("seconds after open /dev/second :%d\n",counter);
          old_counter = counter;
      }    
    }    
  }
  else
  {
    printf("Device open failure\n");
  }
}