linux-kernel - Re: [PATCH 2/2] perf record: Add --dry-run option to check cmdline options

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Date:	Thu, 16 Jun 2016 13:48:15 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Wang Nan <wangnan0@...wei.com>
Cc:	linux-kernel@...r.kernel.org, pi3orama@....com,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Jiri Olsa <jolsa@...nel.org>
Subject: Re: [PATCH 2/2] perf record: Add --dry-run option to check cmdline
 options

Em Thu, Jun 16, 2016 at 08:02:41AM +0000, Wang Nan escreveu:
> With '--dry-run', 'perf record' doesn't do reall recording. Combine with
> llvm.dump-obj option, --dry-run can be used to help compile BPF objects for
> embedded platform.

So these are nice and have value, but can we have a subcommand to do all
this with an expressive name, Something like:

  perf bpfcc foo.c -o foo

or shorter:

  perf bcc foo.c -o foo

Just like one would use gcc or some other compiler to generate something
for later use?

That if called as:

  perf bcc foo.c

Would default to generating a foo.o file.

  Then, later, one could use this as a event name, i.e.

  trace --event foo

Would, knowing that there is no event named "foo", look at the current
directory (and in some other places perhaps) for a file named "foo" that
was a bpf object file to use as it would a foo.c, shortcircuiting the
bpf compilation code.

If this was done instead:

  trace --event foo.c

And foo.c wasn't present, it would fallback to the behaviour described
in the previous paragraph: look for a foo.o or foo bpf object file, etc.

What do you think?

- Arnaldo
 
> Signed-off-by: Wang Nan <wangnan0@...wei.com>
> Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
> Cc: Alexei Starovoitov <ast@...nel.org>
> Cc: Jiri Olsa <jolsa@...nel.org>
> ---
>  tools/perf/Documentation/perf-record.txt | 7 +++++++
>  tools/perf/builtin-record.c              | 7 +++++++
>  2 files changed, 14 insertions(+)
> 
> diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
> index 8dbee83..5b46b1d 100644
> --- a/tools/perf/Documentation/perf-record.txt
> +++ b/tools/perf/Documentation/perf-record.txt
> @@ -360,6 +360,13 @@ particular perf.data snapshot should be kept or not.
>  
>  Implies --timestamp-filename, --no-buildid and --no-buildid-cache.
>  
> +--dry-run::
> +Parse options then exit. --dry-run can be used to detect errors in cmdline
> +options.
> +
> +'perf record --dry-run -e' can act as a BPF script compiler if llvm.dump-obj
> +in config file is set to true.
> +
>  SEE ALSO
>  --------
>  linkperf:perf-stat[1], linkperf:perf-list[1]
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index d4cf1b0..b1304eb 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -1274,6 +1274,8 @@ static struct record record = {
>  const char record_callchain_help[] = CALLCHAIN_RECORD_HELP
>  	"\n\t\t\t\tDefault: fp";
>  
> +static bool dry_run;
> +
>  /*
>   * XXX Will stay a global variable till we fix builtin-script.c to stop messing
>   * with it and switch to use the library functions in perf_evlist that came
> @@ -1393,6 +1395,8 @@ struct option __record_options[] = {
>  		    "append timestamp to output filename"),
>  	OPT_BOOLEAN(0, "switch-output", &record.switch_output,
>  		    "Switch output when receive SIGUSR2"),
> +	OPT_BOOLEAN(0, "dry-run", &dry_run,
> +		    "Parse options then exit"),
>  	OPT_END()
>  };
>  
> @@ -1462,6 +1466,9 @@ int cmd_record(int argc, const char **argv, const char *prefix __maybe_unused)
>  	if (err)
>  		return err;
>  
> +	if (dry_run)
> +		return 0;
> +
>  	err = bpf__setup_stdout(rec->evlist);
>  	if (err) {
>  		bpf__strerror_setup_stdout(rec->evlist, err, errbuf, sizeof(errbuf));
> -- 
> 1.8.3.4