Re: [PATCH 4/4] tracing: fix splice return too large

[Lai Jiangshan <laijs@cn.fujitsu.com>]

Ingo Molnar wrote:
> * Lai Jiangshan <laijs@cn.fujitsu.com> wrote:
> 
>> -	for (i = 0; i < PIPE_BUFFERS && len; i++, len -= size) {
>> +	if (*ppos & (PAGE_SIZE - 1)) {
>> +		WARN_ONCE(1, "Ftrace: previous read must page-align\n");
>> +		return -EINVAL;
>> +	}
>> +
>> +	if (len & (PAGE_SIZE - 1)) {
>> +		WARN_ONCE(1, "Ftrace: splice_read should page-align\n");
>> +		if (len < PAGE_SIZE)
>> +			return -EINVAL;
>> +		len &= PAGE_MASK;
>> +	}
> 
> Hm, the fix looks good, but is it a good idea to allow the 
> triggering of this message from user-space?
> 

But it is only triggered once.

If user get content from trace_pipe_raw with non-page-align,
the content is garbage. It's wasting, the kernel disallows it.
This message tell user why he read failed.

These 4 patches make trace_pipe_raw more robustious and consistent
(read by read(2) and splice). I focus on handling raw ftrace data
in userspace, these raw ftrace data should be trustiness.

Thanks.
Lai.