linux-kernel - Re: [PATCH] tracing/events: make struct trace

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Message-ID: <49EEE104.9050709@cn.fujitsu.com>
Date:	Wed, 22 Apr 2009 17:19:00 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	Ingo Molnar <mingo@...e.hu>, Steven Rostedt <rostedt@...dmis.org>,
	Tom Zanussi <tzanussi@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tracing/events: make struct trace_entry->type to be	int
 type

Frederic Weisbecker wrote:
> On Wed, Apr 22, 2009 at 04:53:34PM +0800, Li Zefan wrote:
>> struct trace_entry->type is unsigned char, while trace event's id is
>> int type, thus for a event with id >= 256, it's entry->type is cast
>> to (id % 256), and then we can't see the trace output of this event.
>>
>>  # insmod trace-events-sample.ko
>>  # echo foo_bar > /mnt/tracing/set_event
>>  # cat /debug/tracing/events/trace-events-sample/foo_bar/id
>>  256
>>  # cat /mnt/tracing/trace_pipe
>>            <...>-3548  [001]   215.091142: Unknown type 0
>>            <...>-3548  [001]   216.089207: Unknown type 0
>>            <...>-3548  [001]   217.087271: Unknown type 0
>>            <...>-3548  [001]   218.085332: Unknown type 0
>>
>> [ Impact: fix output for trace events with id >= 256 ]
>>
>> Signed-off-by: Li Zefan <lizf@...fujitsu.com>
> 
> 
> Indeed, now with the trace_events, we are approaching this possible
> overflow and the type is indeed an int:
> 
> struct trace_event *ftrace_find_event(int type)
> 
> Curious: does it only happen with the trace-event-sample?
> I doubt we already reached this threshold of event number.
> But anyway, it's a good thing.
> 

I guess we haven't reached this limit, at least for mainline. :)

And the biggest id is 48 in my config.

> Acked-by: Frederic Weisbecker <fweisbec@...il.com>

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