linux-kernel - Re: [PATCH 7/9] perf util: Get rid of read_or

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Date:	Wed, 20 Mar 2013 10:24:32 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...nel.org>,
	Namhyung Kim <namhyung.kim@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 7/9] perf util: Get rid of read_or_die() in trace-event-read.c

On Tue, 19 Mar 2013 10:54:27 -0400, Steven Rostedt wrote:
> On Tue, 2013-03-19 at 17:53 +0900, Namhyung Kim wrote:
>> From: Namhyung Kim <namhyung.kim@....com>
>> 
>> Rename it to do_read and original do_read to __do_read, and check
>> their return value.
>> 
>> Cc: Steven Rostedt <rostedt@...dmis.org>
>> Cc: Frederic Weisbecker <fweisbec@...il.com>
>> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
>> ---
>>  tools/perf/util/trace-event-read.c | 80 +++++++++++++++++++++++++++-----------
>>  1 file changed, 57 insertions(+), 23 deletions(-)
>> 
>> diff --git a/tools/perf/util/trace-event-read.c b/tools/perf/util/trace-event-read.c
>> index 62dd2168f4f5..87f0ccd54cdc 100644
>> --- a/tools/perf/util/trace-event-read.c
>> +++ b/tools/perf/util/trace-event-read.c
>> @@ -48,7 +48,7 @@ static int long_size;
>>  static ssize_t calc_data_size;
>>  static bool repipe;
>>  
>> -static int do_read(int fd, void *buf, int size)
>> +static int __do_read(int fd, void *buf, int size)
>>  {
>>  	int rsize = size;
>>  
>> @@ -61,8 +61,10 @@ static int do_read(int fd, void *buf, int size)
>>  		if (repipe) {
>>  			int retw = write(STDOUT_FILENO, buf, ret);
>>  
>> -			if (retw <= 0 || retw != ret)
>> -				die("repiping input file");
>> +			if (retw <= 0 || retw != ret) {
>> +				pr_debug("repiping input file");
>
> Again, why debug and not err?

Well, there's a pr_err() at the caller of top-level trace_report() in
case of error.  So if we use pr_err() there'll be multiple error message
for one failure and I don't think it's so helpful to normal users.  If
one really wants to know what happens inside, she will set -v to see
this low-level debug message.

Does that make sense?

>
>> +				return -1;
>> +			}
>>  		}
>>  
>>  		size -= ret;
>> @@ -72,14 +74,16 @@ static int do_read(int fd, void *buf, int size)
>>  	return rsize;
>>  }
>>  
>> -static int read_or_die(void *data, int size)
>> +static int do_read(void *data, int size)
>>  {
>>  	int r;
>>  
>> -	r = do_read(input_fd, data, size);
>> -	if (r <= 0)
>> -		die("reading input file (size expected=%d received=%d)",
>> -		    size, r);
>> +	r = __do_read(input_fd, data, size);
>> +	if (r <= 0) {
>> +		pr_debug("reading input file (size expected=%d received=%d)",
>> +			 size, r);
>> +		return -1;
>> +	}
>>  
>>  	if (calc_data_size)
>>  		calc_data_size += r;
>> @@ -95,7 +99,7 @@ static void skip(int size)
>>  
>>  	while (size) {
>>  		r = size > BUFSIZ ? BUFSIZ : size;
>> -		read_or_die(buf, r);
>> +		do_read(buf, r);
>
> Shouldn't this check the result of do_read()?

I was not so sure about this, but I skipped the check since all it does
is to "skip" and comment said "If it fails, the next read will report
it". :-)

Thanks,
Namhyung

>
>>  		size -= r;
>>  	};
>>  }
>
> -- Steve
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