内核阻塞式IO

static ssize_t fifo_read (struct file *f, char __user *p, size_t n, loff_t *off){int size;if(FIFO.cursize == 0)//let this procss go to sleepwait_event_interruptible(FIFO.readqueue, FIFO.cursize != 0);size = n>FIFO.cursize?FIFO.cursize:n;//return 0;int len1, len2;if(FIFO.start <= FIFO.end)// copy once{if(copy_to_user(p, FIFO.qbuf, size)){printk("copy to user fail1\n");return -EINVAL;}}else{len1 = FIFO.maxsize-FIFO.start;if(copy_to_user(p, &FIFO.qbuf[FIFO.start], len1)){printk("copy to user fail2\n");return -EINVAL;}len2 = size-len1;if(copy_to_user(p+len1, FIFO.qbuf, len2)){printk("copy to user fail3\n");return -EINVAL;}}FIFO.start = (FIFO.start+size)%FIFO.maxsize;FIFO.cursize -= size;return size;}static ssize_t fifo_write (struct file *f, const char __user *p, size_t n, loff_t *off){int space = FIFO.maxsize - FIFO.cursize;int size = n>space?space:n;int len1 = (FIFO.maxsize-1 - FIFO.end);int len2;if(!space)return 0;//copy_from_user(&FIFO.qbuf[end+1], p, size);if(len1 >= size)//copy once{if(copy_from_user(&FIFO.qbuf[FIFO.end+1], p, size)){printk("copy from user fail1\n");return -EINVAL;}}else{if(copy_from_user(&FIFO.qbuf[FIFO.end+1], p, len1)){printk("copy from user fail2\n");return -EINVAL;}len2 = size-len1;if(copy_from_user(FIFO.qbuf, p+len1,  len2)){printk("copy from user fail3\n");return -EINVAL;}}FIFO.end = (FIFO.end+size)%FIFO.maxsize;FIFO.cursize += size;//woke up processeswake_up_interruptible(&FIFO.readqueue);//wake_up(&FIFO.readqueue);return size;}

总结：利用等待队列机制构建内核阻塞IO模型