linux底层驱动之poll的调用

poll//8 poll的使用
/定义
.poll = globalfifo_poll,

//结构体
/*globalfifo设备结构体*/
struct globalfifo_dev                                     
{                                                        
 struct cdev cdev; /*cdev结构体*/                       
 unsigned int current_len;    /*fifo有效数据长度*/
 unsigned char mem[GLOBALFIFO_SIZE]; /*全局内存*/        
 struct semaphore sem; /*并发控制用的信号量*/           
 wait_queue_head_t r_wait; /*阻塞读用的等待队列头*/     
 wait_queue_head_t w_wait; /*阻塞写用的等待队列头*/     
};

//函数调用
 static unsigned int globalfifo_poll(struct file *filp, poll_table *wait)
{
 unsigned int mask = 0;
 struct globalfifo_dev *dev = filp->private_data; /*获得设备结构体指针*/

 down(&dev->sem);

 poll_wait(filp, &dev->r_wait, wait);
 poll_wait(filp, &dev->w_wait, wait); 

 /*fifo非空*/
 if (dev->current_len != 0)
 {
  mask |= POLLIN | POLLRDNORM; /*标示数据可获得*/
 }
 /*fifo非满*/
 if (dev->current_len != GLOBALFIFO_SIZE)
 {
  mask |= POLLOUT | POLLWRNORM; /*标示数据可写入*/
 }

 up(&dev->sem);
 return mask;
}

poll应用程序编写
int main()
{
 int fd, num;
 char rd_ch[BUFFER_LEN];
 fd_set rfds,wfds;

 /*以非阻塞方式打开/dev/globalmem设备文件*/
 fd = open("/dev/globalfifo", O_RDONLY | O_NONBLOCK);
 if (fd !=  - 1)
 {
  /*FIFO清0*/
  if (ioctl(fd, FIFO_CLEAR, 0) < 0)
  {
   printf("ioctl command failed\n");
  }
  while (1)
  {
   FD_ZERO(&rfds);
   FD_ZERO(&wfds);
   FD_SET(fd, &rfds);
   FD_SET(fd, &wfds);

   select(fd + 1, &rfds, &wfds, NULL, NULL);
   /*数据可获得*/
   if (FD_ISSET(fd, &rfds))
   {
    printf("Poll monitor:can be read\n");
   }
   /*数据可写入*/
   if (FD_ISSET(fd, &wfds))
   {
    printf("Poll monitor:can be written\n");
   }     

   sleep(1);
  }
 }
 else
 {
  printf("Device open failure\n");
 }
}