linux-kernel - Re: [PATCH] perf debug: List available options when no variable is specified

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Date:   Tue, 31 Oct 2023 12:42:12 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Yang Jihong <yangjihong1@...wei.com>
Cc:     peterz@...radead.org, mingo@...hat.com, mark.rutland@....com,
        alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
        namhyung@...nel.org, irogers@...gle.com, adrian.hunter@...el.com,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf debug: List available options when no variable is
 specified

Em Tue, Oct 31, 2023 at 08:08:23AM +0000, Yang Jihong escreveu:
> Before:
 
>   # perf --debug
>   No variable specified for --debug.
 
> After:
 
>   # perf --debug
>   No variable specified for --debug, available options: verbose,ordered-events,stderr,data-convert,perf-event-open.

Looks useful, but the implementation can be different to reduce
maintainership costs, see below:

> +++ b/tools/perf/perf.c
> @@ -279,7 +279,9 @@ static int handle_options(const char ***argv, int *argc, int *envchanged)
>  		} else if (!strcmp(cmd, "--debug")) {
>  			if (*argc < 2) {
> -				fprintf(stderr, "No variable specified for --debug.\n");
> +				fprintf(stderr,
> +					"No variable specified for --debug, available options: %s.\n",
> +					perf_debug_options_string);
>  				usage(perf_usage_string);

> +++ b/tools/perf/util/debug.c
> @@ -215,6 +215,9 @@ void trace_event(union perf_event *event)
>  		     trace_event_printer, event);
>  }
>  
> +const char perf_debug_options_string[] =
> +	"verbose,ordered-events,stderr,data-convert,perf-event-open";

Instead of adding a new variable that has to be kept in sync with
debug_opts[], you could provide a function that iterates debug_opts,
printing its options names, then use that function on perf.c handle_options.

- Arnaldo

>  static struct sublevel_option debug_opts[] = {
>  	{ .name = "verbose",		.value_ptr = &verbose },
>  	{ .name = "ordered-events",	.value_ptr = &debug_ordered_events},