linux-kernel - Re: [PATCH 1/1] perf:Adding --list-opts to usage string

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Message-ID: <561F51AB.4040302@huawei.com>
Date:	Thu, 15 Oct 2015 15:11:39 +0800
From:	Yunlong Song <yunlong.song@...wei.com>
To:	Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
CC:	Sriram Raghunathan <sriram.r@...ia.com>,
	Wang Nan <wangnan0@...wei.com>,
	Ramkumar Ramachandra <artagnon@...il.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Jiri Olsa <jolsa@...nel.org>, Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	"Arnaldo Carvalho de Melo" <acme@...nel.org>
Subject: Re: [PATCH 1/1] perf:Adding --list-opts to usage string

On 2015/10/14 21:40, Arnaldo Carvalho de Melo wrote:
> 
> Le 14 oct. 2015 10:33 AM, "Yunlong Song" <yunlong.song@...wei.com <mailto:yunlong.song@...wei.com>> a écrit :
>>
>> On 2015/10/14 11:10, Arnaldo Carvalho de Melo wrote:
>>
>> > One doesn't show what options can be used, the other does, so there is
>> > an inconsistency, this and the fact that 'perf -h' outputs to stdout,
>> > 'perf stat -h' and the other builtins output to stderr. I think all
>> > should output to stdout, just like 'ls --help', what do you think?
>> >
>> > - Arnaldo
>> >
>>
>> I think the reason that options do not show in 'perf -h' but show in
>> other builtins is not the different use of stdout or stderr. I will
>> send a patch to fix this instead.
> 
> Sure, I mentioned two problems. The invonsistency in stdout/stderr usage has nothing to do with options being not showed in 'perf -h'. :-)
>>


Sorry, I understand now. I think it makes sense that the builtins use stderr everywhere
to show its usage info when the opts or cmds are incorrectly used. Usually, there is an
error description followed with the usage info, for example:
 # ./perf stat -f
  Error: unknown switch `f'

 Usage: perf stat [<options>] [<command>]

    -T, --transaction     hardware transaction statistics
    -e, --event <event>   event selector. use 'perf list' to list available events
        --filter <filter>
                          event filter
    -i, --no-inherit      child tasks do not inherit counters
<SNIP>
    -I, --interval-print <n>
                          print counts at regular interval in ms (>= 10)
        --per-socket      aggregate counts per processor socket
        --per-core        aggregate counts per physical processor core
        --per-thread      aggregate counts per thread
    -D, --delay <n>       ms to wait before starting measurement after program start

As shown above, I think the error description and the usage info should output to the same
stderr area as it is now to be clear.

Thus I think it is better to make perf output its usage info to stderr instead of stdout for
consistency. I will resend patches to fix this.

-- 
Thanks,
Yunlong Song

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