“曾经有一份真诚的爱情摆在面前，我却不理解爱惜;曾经有一个许诺，我却倍感爱惜，今日一定要好好讲讲..”
讲讲啥，讲讲上节说的那个异步告诉的比如呗，我们喜爱看代码，咋们就先上代码:
struct globalfifo_dev
{
struct cdev cdev; /*cdev结构体*/
unsigned int current_len; /*fifo有用数据长度*/
unsigned char mem[GLOBALFIFO_SIZE]; /*大局内存*/
struct semaphore sem; /*并发操控用的信号量*/
wait_queue_head_t r_wait; /*堵塞读用的等候行列头*/
wait_queue_head_t w_wait; /*堵塞写用的等候行列头*/
struct fasync_struct *async_queue; /* 异步结构体指针，用于读 */
};
/*文件开释函数*/
int globalfifo_release(struct inode *inode, struct file *filp)
{
/* 将文件从异步告诉列表中删去 */
globalmem_fasync( – 1, filp, 0);
return 0;
}
static int globalfifo_fasync(int fd, struct file *filp, int mode)
{
struct globalfifo_dev *dev = filp->private_data;
return fasync_helper(fd, filp, mode, &dev->async_queue);
}
/*globalfifo写操作*/
static ssize_t globalfifo_write(struct file *filp, const char __user *buf,
size_t count, loff_t *ppos)
{
struct globalfifo_dev *dev = filp->private_data; //取得设备结构体指针
int ret;
DECLARE_WAITQUEUE(wait, current); //界说等候行列
down(&dev->sem); //获取信号量
add_wait_queue(&dev->w_wait, &wait); //进入写等候行列头
/* 等候FIFO非满 */
if (dev->current_len == GLOBALFIFO_SIZE)
{
if (filp->f_flags &O_NONBLOCK)
//假如对错堵塞拜访
{
ret = – EAGAIN;
goto out;
}
__set_current_state(TASK_INTERRUPTIBLE); //改动进程状况为睡觉
up(&dev->sem);
schedule(); //调度其他进程履行
if (signal_pending(current))
//假如是因为信号唤醒
{
ret = – ERESTARTSYS;
goto out2;
}
down(&dev->sem); //取得信号量
}
/*从用户空间拷贝到内核空间*/
if (count > GLOBALFIFO_SIZE – dev->current_len)
count = GLOBALFIFO_SIZE – dev->current_len;
if (copy_from_user(dev->mem + dev->current_len, buf, count))
{
ret = – EFAULT;
goto out;
}
else
{
dev->current_len += count;
printk(KERN_INFO "written %d bytes(s),current_len:%d\n", count, dev
->current_len);
wake_up_interruptible(&dev->r_wait); //唤醒读等候行列
/* 发生异步读信号 */
if (dev->async_queue)
kill_fasync(&dev->async_queue, SIGIO, POLL_IN);
ret = count;
}
out: up(&dev->sem); //开释信号量
out2:remove_wait_queue(&dev->w_wait, &wait); //从隶属的等候行列头移除
set_current_state(TASK_RUNNING);
return ret;
}
下面再给出测验程序：
#include …
//接收到异步读信号的动作
void input_handler(int signum)
{
printf("Receive a signal from globalfifo,signalnum:%d\n",signum);
}
int main()
{
int fd, oflags;
fd = open("/dev/globalfifo", O_RDWR, S_IRUSR | S_IWUSR);
if (fd != – 1)
{
//发动信号驱动机制
signal(SIGIO, input_handler); //让input_handler()处理SIGIO信号
fcntl(fd, F_SETOWN, getpid());
oflags = fcntl(fd, F_GETFL);
fcntl(fd, F_SETFL, oflags | FASYNC);
while(1)
{
sleep(100);
}
}
else
{
printf("device open failure\n");
}
}
当我们加载完驱动并创立完设备节点后，运转上述程序，每逢经过echo向/dev/globalfilfo写入新的数据后，input_handler将会被调用。如下所示：
echo 0>/dev/globalfifo
receive a signal from globalfifo ,signalnum:29
echo 0>/dev/globalfifo
receive a signal from globalfifo ,signalnum:29
echo 0>/dev/globalfifo
receive a signal from globalfifo ,signalnum:29
经过上边实践的比如，小王，理解了吧，我的许诺也实现了，下次我们可要开端更高档的东西了..
