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

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Message-ID: <49DC6F01.6030203@cn.fujitsu.com>
Date:	Wed, 08 Apr 2009 17:31:45 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Steven Rostedt <srostedt@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/4] tracing: fix splice return too large

Ingo Molnar wrote:
> * Lai Jiangshan <laijs@...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.

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