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

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Date:	Wed, 22 Oct 2014 16:00:12 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Wang Nan <wangnan0@...wei.com>
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 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?

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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