/dev/null 的原理是什么？大量写入会影响系统性能吗？

找到一个解释：https://bbs.archlinux.org/viewtopic.php?id=137861

It's all implemented via file_operations (drivers/char/mem.c if you're curious to look yourself):

```
static const struct file_operations null_fops = {
.llseek = null_lseek,
.read = read_null,
.write = write_null,
.splice_write = splice_write_null,
};
```

write_null is what's called when you write to /dev/null. It always returns the same number of bytes
that you write to it:

```
static ssize_t write_null(struct file *file, const char __user *buf,
size_t count, loff_t *ppos)
{
return count;
}
```

That's it. The buffer is just ignored.


写时竟然还 return 一个 size !