c - Linux 内核 write() 和 read() 函数

Question

您好，我的学校代码需要一些帮助。

读取函数不应该返回0，所以老师告诉我们使用wait_event_interruptible。

我的问题是当我想在控制台中使用(例如)命令来尝试它时:

echo 1234 > ringdev # my character device
echo 5 > ringdev 
cat ringdev

我只得到一个结果:5。

我想得到一个结果:

1234
5.。

全局变量:

 static char ringdev_buf[4096];
 static size_t ringdev_len;

读取功能:

static ssize_t ringdev_read(struct file *filp, char __user *buf, size_t count,
        loff_t *off)
{      
    ssize_t ret = 0;
    while(1) {
        wait_event_interruptible(head,ringdev_len!=0);
        mutex_lock(&ringdev_lock);
        if(ringdev_len!=0) {
            ret = -EFAULT;
            if (copy_to_user(buf, ringdev_buf,ringdev_len)) { // I was trying everything in the ringdev_len position. 
                ret = ringdev_len;
                goto out_unlock;
            }
        }
        mutex_unlock(&ringdev_lock);
    }
    out_unlock:
    mutex_unlock(&ringdev_lock);
    return ret;
}

我试图在函数 copy_to_user(buf,ringdev_buf,count) 中将任何值放入 count 中，但结果始终相同。

static ssize_t ringdev_write(struct file *filp, const char __user *buf,
        size_t count, loff_t *off)
{
    ssize_t ret=0;
    mutex_lock(&ringdev_lock);
    ret=-EFAULT;
    if(ringdev_len + count < sizeof(ringdev_buf)) {
        if (copy_from_user(ringdev_buf+ringdev_len, buf, count)==0) {
            ringdev_len=ringdev_len+count;
            ret=count;
            wake_up_interruptible(&head);
            goto out_unlock;
        }
    } else {
       ret=-ENOSPC;
    }
    out_unlock:
    mutex_unlock(&ringdev_lock);
    return ret;
}

Answer 1

调用copy_to_user(buf,ringdev_buf,1)会导致从ringdev_buf到buf的1字节复制，所以它是正确的，如果你想将整个缓冲区复制到用户空间，你必须将其更改为copy_to_user(buf,ringdev_buf,ringdev_len)