linux-kernel - Re: [PATCH 1/4] tools lib traceevent: Add state member to struct trace

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Date:	Mon, 06 Jan 2014 16:44:18 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...nel.org>,
	Namhyung Kim <namhyung.kim@....com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] tools lib traceevent: Add state member to struct trace_seq

Hi Jiri,

On Fri, 3 Jan 2014 14:24:25 +0100, Jiri Olsa wrote:
> On Thu, Dec 19, 2013 at 06:34:23PM +0900, Namhyung Kim wrote:
>> From: Namhyung Kim <namhyung.kim@....com>
>> 
>> The trace_seq->state is for tracking errors during the use of
>> trace_seq APIs and getting rid of die() in it.
>> 
>> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
>> ---
>>  tools/lib/traceevent/event-parse.h |  7 +++++++
>>  tools/lib/traceevent/trace-seq.c   | 41 ++++++++++++++++++++++++++++++++++----
>>  2 files changed, 44 insertions(+), 4 deletions(-)
>> 
>> diff --git a/tools/lib/traceevent/event-parse.h b/tools/lib/traceevent/event-parse.h
>> index cf5db9013f2c..3c890cb28db7 100644
>> --- a/tools/lib/traceevent/event-parse.h
>> +++ b/tools/lib/traceevent/event-parse.h
>> @@ -58,6 +58,12 @@ struct pevent_record {
>>  #endif
>>  };
>>  
>> +enum trace_seq_fail {
>> +	TRACE_SEQ__GOOD,
>> +	TRACE_SEQ__BUFFER_POISONED,
>> +	TRACE_SEQ__MEM_ALLOC_FAILED,
>> +};
>> +
>>  /*
>>   * Trace sequences are used to allow a function to call several other functions
>>   * to create a string of data to use (up to a max of PAGE_SIZE).
>> @@ -68,6 +74,7 @@ struct trace_seq {
>>  	unsigned int		buffer_size;
>>  	unsigned int		len;
>>  	unsigned int		readpos;
>> +	enum trace_seq_fail	state;
>>  };
>>  
>>  void trace_seq_init(struct trace_seq *s);
>> diff --git a/tools/lib/traceevent/trace-seq.c b/tools/lib/traceevent/trace-seq.c
>> index d7f2e68bc5b9..976ad2a146b3 100644
>> --- a/tools/lib/traceevent/trace-seq.c
>> +++ b/tools/lib/traceevent/trace-seq.c
>> @@ -32,8 +32,8 @@
>>  #define TRACE_SEQ_POISON	((void *)0xdeadbeef)
>>  #define TRACE_SEQ_CHECK(s)						\
>>  do {									\
>> -	if ((s)->buffer == TRACE_SEQ_POISON)			\
>> -		die("Usage of trace_seq after it was destroyed");	\
>> +	if ((s)->buffer == TRACE_SEQ_POISON)				\
>> +		(s)->state = TRACE_SEQ__BUFFER_POISONED;		\
>
> So unless we use trace_seq_do_printf we dont have any
> notification that this went wrong..?

Right.

>
> How about use some sort of WARN_ONCE any time the state
> is set != GOOD ?

I'm not sure what's the right thing to do for that case.  Printing a
warning message might disturb user's output since it can be in a middle
of some (other) processing and she doesn't want to print anything during
the processing for some reason.

I just thought that it's not so important to print message so keeps the
error internally until it gets printed.  But I can be wrong as usual...

Thanks,
Namhyung
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