Message-ID: <49DC6F01.6030203@cn.fujitsu.com>
Date: Wed, 08 Apr 2009 17:31:45 +0800
From: Lai Jiangshan <laijs@cn.fujitsu.com>
User-Agent: Thunderbird 2.0.0.6 (Windows/20070728)
MIME-Version: 1.0
To: Ingo Molnar <mingo@elte.hu>
CC: Steven Rostedt <srostedt@redhat.com>,
       Frederic Weisbecker <fweisbec@gmail.com>,
       LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 4/4] tracing: fix splice return too large
References: <49D46674.9030804@cn.fujitsu.com> <20090403131629.GA8875@elte.hu>
In-Reply-To: <20090403131629.GA8875@elte.hu>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1209
Lines: 38

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.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/