Iput设备使用分析--2(应用层面)



5.input设备使用分析--2(应用层面)

应用程序打开一个设备(需要包含内核一些头文件.h)---

/*struct   input_event
{
 struct timeval time;
 __u16 type;
 __u16 code;
 __s32 value;
};
*/
void main()
{
 struct input_event key_event;
 
 int fd = open("/dev/event0", O_RDWR); /*最后执行-->evdev_open；*/
 int cnt = 0;
 
 while( (cnt = read(fd, &key_event, sizeof(struct input_event)) > 0)  /*最后执行evdev_read*/
 {
  printf("%d,%d,%d,%d\n", key_event.type, key_event.code, key_event.value); 
  
 }
 
 
}

/************************接着分析evdev_open******************/
static int evdev_open(struct inode *inode, struct file *file)
{
 struct evdev *evdev;
 
 struct evdev_client *client;
 
 int i = iminor(inode) - EVDEV_MINOR_BASE;
 
 unsigned int bufsize;
 
 evdev = evdev_table[i];    /*根据号码取得evdev设备*/
 if (evdev)
  get_device(&evdev->dev);

 bufsize = evdev_compute_buffer_size(evdev->handle.dev);  /*构造bufsize和client*/

 client = kzalloc(sizeof(struct evdev_client) +    
    bufsize * sizeof(struct input_event),
    GFP_KERNEL); 

 client->bufsize = bufsize;

 client->evdev = evdev;  
   
 evdev_attach_client(evdev, client);   /*将evdev添加到evdev->client_list链表中-->list_add_tail_rcu(&client->node, &evdev->client_list);*/

 
 if (error)
  goto err_free_client;

 file->private_data = client;    /*将client作为file的私有数据*/
 return 0;
}

/********************接着分析evdev_read()***********************************/
static ssize_t evdev_read(struct file *file, char __user *buffer,
     size_t count, loff_t *ppos)
{
 struct evdev_client *client = file->private_data; /*取得相应的evdev_client*/
 struct evdev *evdev = client->evdev;
 struct input_event event;
 int retval;

 while (retval + input_event_size() <= count &&
      
        evdev_fetch_next_event(client, &event)) {  /*将client->buffer中的数据放到event中*/

  if (input_event_to_user(buffer + retval, &event)) /*将event中的数据拷贝到应用层buffer中*/
   return -EFAULT;

  retval += input_event_size();
 }

 return retval;
}