linux-kernel - Re: event tracing, ringbuffer and RB_MAX_SMALL

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Message-ID: <4A651A2D.1020804@cn.fujitsu.com>
Date:	Tue, 21 Jul 2009 09:30:21 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	Johannes Berg <johannes@...solutions.net>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: event tracing, ringbuffer and RB_MAX_SMALL_DATA

Steven Rostedt wrote:
> On Thu, 16 Jul 2009, Li Zefan wrote:
> 
>> Johannes Berg wrote:
>>> On Wed, 2009-07-15 at 09:08 +0800, Li Zefan wrote:
>>>
>>>> Right, the length of a dynamic array is not recorded, and this
>>>> causes 2 problems:
>>>>
>>>> - the event filter is not working properly for dynamic strings
>>>> - userspace parsers can't figure out the length of those arrays
>>>>
>>>> I had an idea some time ago, and hopefully will send out a
>>>> patch today or tomorrow. 
>>> Well except for the corner case I pointed out, you can determine the
>>> length of dynamic arrays by either
>>>  - the next dynamic array's offset or
>>>  - the length of the item.
>>>
>>> So, afaict, the simplest solution would be to not embed the length of
>>> the item in type_len if it's not divisible by four and contains dynamic
>>> members, though the latter condition might be hard to check.
>>>
>> Actually I'm going to encode the size of a dynamic array
>> in it's @offset, so the lower 16bits is offset and the
>> higher 16bits is size.
> 
> Was there a patch sent out to do this yet, or is this still something 
> being worked on?
> 

Haven't you pulled it as you said. ;)

http://lkml.org/lkml/2009/7/20/155

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