linux-kernel - Re: [PATCH] perf tools: ensure return negitive value when write header error

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Date:	Wed, 22 Oct 2014 15:52:11 +0800
From:	Wang Nan <wangnan0@...wei.com>
To:	Namhyung Kim <namhyung@...nel.org>
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Namhyung Kim <namhyung.kim@....com>,
	Waiman Long <Waiman.Long@...com>,
	<linux-kernel@...r.kernel.org>, Li Zefan <lizefan@...wei.com>
Subject: Re: [PATCH] perf tools: ensure return negitive value when write header
 error

On 2014/10/22 15:00, Namhyung Kim wrote:
> On Thu, 16 Oct 2014 11:08:29 +0800, Wang Nan wrote:
>> When 'perf record' write headers, it calls write_xxx in
>> tools/perf/util/header.c, and check return value. It rolls back all
>> working only when return value is negative.
>>
>> This patch ensures write_cpudesc() and write_total_mem() return negative number
>> when error. Without this patch, headers reported by 'perf report' header is
>> error in some platform. Following output is caputured on ARM, which doesn't
>> contain "Processor" field in /proc/cpuinfo. See "cpudesc", "total memory" and
>> "cmdline" field.
>>
>>    bash-4.2# perf record ls
>>    ...
>>    [ perf record: Woken up 1 times to write data ]
>>    [ perf record: Captured and wrote 0.001 MB perf.data (~36 samples) ]
>>    bash-4.2# perf report --stdio --header
>>    Error:
>>    The perf.data file has no samples!
>>    # ========
>>    # captured on: Fri Sep 12 10:09:10 2014
>>    # hostname : arma15el
>>    # os release : 3.17.0+
>>    # perf version : 3.10.53
>>    # arch : armv7l
>>    # nrcpus online : 4
>>    # nrcpus avail : 1
>>    # cpudesc : (null)
>>    # total memory : 0 kB
>>    # cmdline :
>>    # event : name = cycles, type = 0, config = 0x0, config1 = 0x0, config2 = 0x0, excl_usr = 0, excl_kern = 0, excl_host = 0, excl_guest = 1, precise_ip = 0
>>    # pmu mappings: not available
>>    # ========
>>    #
>>
>> Signed-off-by: Wang Nan <wangnan0@...wei.com>
> 
> I guess the total_memory, cmdline and pmu mappings are somehow affected
> by the broken cpudesc.  Do they have their own problem on ARM?
> 

The buggy output is caused by cpudesc's problem. I didn't trigger their own problem on ARM because
'total memory' and cmdline are always success. I find the error in write_total_mem() by checking
code by hand.

Thanks.

> Anyway I think it's good to check the result properly, so
> 
> Acked-by: Namhyung Kim <namhyung@...nel.org>
> 
> Thanks,
> Namhyung
> 
> 
>> ---
>>  tools/perf/util/header.c | 7 +++++--
>>  1 file changed, 5 insertions(+), 2 deletions(-)
>>
>> diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
>> index ce0de00..39b80ac 100644
>> --- a/tools/perf/util/header.c
>> +++ b/tools/perf/util/header.c
>> @@ -605,8 +605,10 @@ static int write_cpudesc(int fd, struct perf_header *h __maybe_unused,
>>  			break;
>>  	}
>>  
>> -	if (ret)
>> +	if (ret) {
>> +		ret = -1;
>>  		goto done;
>> +	}
>>  
>>  	s = buf;
>>  
>> @@ -950,7 +952,8 @@ static int write_total_mem(int fd, struct perf_header *h __maybe_unused,
>>  		n = sscanf(buf, "%*s %"PRIu64, &mem);
>>  		if (n == 1)
>>  			ret = do_write(fd, &mem, sizeof(mem));
>> -	}
>> +	} else
>> +		ret = -1;
>>  	free(buf);
>>  	fclose(fp);
>>  	return ret;


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