Linux內核開發之異步通知與異步I/O(二)
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“曾經有一份真摯的愛情擺在面前，我卻不懂珍惜;曾經有一個承諾，我卻倍感珍惜，今天一定要好好講講..”
本文引用地址：http://www.104case.com/article/201612/341380.htm講講啥，講講上節說的那個異步通知的例子唄，大家喜歡看代碼，咋們就先上代碼:
struct globalfifo_dev
{
struct cdev cdev; /*cdev結構體*/
unsigned int current_len; /*fifo有效數據長度*/
unsigned char mem[GLOBALFIFO_SIZE]; /*全局內存*/
struct semaphore sem; /*并發控制用的信號量*/
wait_queue_head_t r_wait; /*阻塞讀用的等待隊列頭*/
wait_queue_head_t w_wait; /*阻塞寫用的等待隊列頭*/
struct fasync_struct *async_queue; /* 異步結構體指針，用于讀 */
};
/*文件釋放函數*/
int globalfifo_release(struct inode *inode, struct file *filp)
{
/* 將文件從異步通知列表中刪除 */
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寫操作*/
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; //獲得設備結構體指針
int ret;
DECLARE_WAITQUEUE(wait, current); //定義等待隊列
down(&dev->sem); //獲取信號量
add_wait_queue(&dev->w_wait, &wait); //進入寫等待隊列頭
/* 等待FIFO非滿 */
if (dev->current_len == GLOBALFIFO_SIZE)
{
if (filp->f_flags &O_NONBLOCK)
//如果是非阻塞訪問
{
ret = - EAGAIN;
goto out;
}
__set_current_state(TASK_INTERRUPTIBLE); //改變進程狀態為睡眠
up(&dev->sem);
schedule(); //調度其他進程執行
if (signal_pending(current))
//如果是因為信號喚醒
{
ret = - ERESTARTSYS;
goto out2;
}
down(&dev->sem); //獲得信號量
}
/*從用戶空間拷貝到內核空間*/
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:%dn", count, dev
->current_len);
wake_up_interruptible(&dev->r_wait); //喚醒讀等待隊列
/* 產生異步讀信號 */
if (dev->async_queue)
kill_fasync(&dev->async_queue, SIGIO, POLL_IN);
ret = count;
}
out: up(&dev->sem); //釋放信號量
out2:remove_wait_queue(&dev->w_wait, &wait); //從附屬的等待隊列頭移除
set_current_state(TASK_RUNNING);
return ret;
}
下面再給出測試程序：
#include ...
//接收到異步讀信號的動作
void input_handler(int signum)
{
printf("Receive a signal from globalfifo,signalnum:%dn",signum);
}
int main()
{
int fd, oflags;
fd = open("/dev/globalfifo", O_RDWR, S_IRUSR | S_IWUSR);
if (fd != - 1)
{
//啟動信號驅動機制
signal(SIGIO, input_handler); //讓input_handler()處理SIGIO信號
fcntl(fd, F_SETOWN, getpid());
oflags = fcntl(fd, F_GETFL);
fcntl(fd, F_SETFL, oflags | FASYNC);
while(1)
{
sleep(100);
}
}
else
{
printf("device open failuren");
}
}
當我們加載完驅動并創建完設備節點后，運行上述程序，每當通過echo向/dev/globalfilfo寫入新的數據后，input_handler將會被調用。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
通過上邊實際的例子，小王，明白了吧，我的承諾也兌現了，下次咱們可要開始更高級的東西了..
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