请高手答疑（看linux设备驱动第一版pipe.c有疑问）

yifenqian

read_write_t scull_p_read (struct inode *inode, struct file *filp,
                char *buf, count_t count)
{
    Scull_Pipe *dev = filp->private_data;

    while (dev->rp == dev->wp) { /* nothing to read */
        if (filp->f_flags & O_NONBLOCK)
            return -EAGAIN;
        PDEBUG("\"%s\" reading: going to sleep\n",current->comm);
        interruptible_sleep_on(&dev->inq);
        if (current->signal & ~current->blocked) /* a signal arrived */
          return -ERESTARTSYS; /* tell the fs layer to handle it */
        /* otherwise loop */
    }
    /* ok, data is there, return something */
    if (dev->wp > dev->rp)
        count = min(count, dev->wp - dev->rp);
    else /* the write pointer has wrapped, return data up to dev->end */
        count = min(count, dev->end - dev->rp);
    memcpy_tofs(buf, dev->rp, count);
    dev->rp += count;
    if (dev->rp == dev->end)
        dev->rp = dev->buffer; /* wrapped */

    /* finally, awake any writers and return */
    wake_up_interruptible(&dev->outq);
    PDEBUG("\"%s\" did read %li bytes\n",current->comm, (long)count);
    return count;
}
疑问一：第五行为什么是while不是if，个人觉得用if 才对
疑问二：２４行怎么用了wake_up_interruptble函数，如果前面的while循环没有执行，也就是讲没有前面的interruptable_sleep_on函数，这也要wake up 进程吗？
thanks!

xinlinux

你怎么不看第二版