From: Li Zefan <lizf@cn.fujitsu.com>
To: Johannes Berg <johannes@sipsolutions.net>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@elte.hu>,
Frederic Weisbecker <fweisbec@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>
Subject: Re: event tracing, ringbuffer and RB_MAX_SMALL_DATA
Date: Wed, 15 Jul 2009 09:08:06 +0800 [thread overview]
Message-ID: <4A5D2BF6.6010802@cn.fujitsu.com> (raw)
In-Reply-To: <1247591891.7178.20.camel@johannes.local>
Johannes Berg wrote:
> Hi,
>
> By code inspection, I think there's a bug if your event contains only
>
> __dynamic_array(u8, buf, buflen)
>
> and your buflen is only, say, 3. Then the event size will be the common
> event size (12 bytes) plus this, so 15, which is well below
> RB_MAX_SMALL_DATA (4*28 = 112), so it'll be divided by four to be stored
> into type_len. At this point, however, you've lost the information that
> your dynamic array was only three bytes, and it'll be considered _four_
> bytes long by parsers as far as I can tell?
>
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.
next prev parent reply other threads:[~2009-07-15 1:09 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-07-14 17:18 event tracing, ringbuffer and RB_MAX_SMALL_DATA Johannes Berg
2009-07-15 1:08 ` Li Zefan [this message]
2009-07-15 9:48 ` Johannes Berg
2009-07-16 0:48 ` Li Zefan
2009-07-21 1:25 ` Steven Rostedt
2009-07-21 1:30 ` Li Zefan
2009-07-21 1:42 ` Steven Rostedt
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