linux-kernel - event tracing, ringbuffer and RB_MAX_SMALL

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Message-Id: <1247591891.7178.20.camel@johannes.local>
Date:	Tue, 14 Jul 2009 19:18:11 +0200
From:	Johannes Berg <johannes@...solutions.net>
To:	linux-kernel <linux-kernel@...r.kernel.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: event tracing, ringbuffer and RB_MAX_SMALL_DATA

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?

johannes

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