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;
}
最佳答案
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)
关于c - Linux 内核 write() 和 read() 函数,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/41359672/