[PATCH] perf debug: List available options when no variable is specified

[Yang Jihong]

Minor help message improvement for `perf --debug`

Before:

  # perf --debug
  No variable specified for --debug.

   Usage: perf [--version] [--help] [OPTIONS] COMMAND [ARGS]

After:

  # perf --debug
  No variable specified for --debug, available options: verbose,ordered-events,stderr,data-convert,perf-event-open.

Signed-off-by: Yang Jihong <yangjihong1@xxxxxxxxxx>
---
 tools/perf/perf.c       | 4 +++-
 tools/perf/util/debug.c | 3 +++
 tools/perf/util/debug.h | 1 +
 3 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/tools/perf/perf.c b/tools/perf/perf.c
index d3fc8090413c..0fc4719e6825 100644
--- a/tools/perf/perf.c
+++ b/tools/perf/perf.c
@@ -279,7 +279,9 @@ static int handle_options(const char ***argv, int *argc, int *envchanged)
 			exit(0);
 		} 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);
 			}
 			if (perf_debug_option((*argv)[1]))
diff --git a/tools/perf/util/debug.c b/tools/perf/util/debug.c
index 88378c4c5dd9..e02f6d97b826 100644
--- a/tools/perf/util/debug.c
+++ 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";
+
 static struct sublevel_option debug_opts[] = {
 	{ .name = "verbose",		.value_ptr = &verbose },
 	{ .name = "ordered-events",	.value_ptr = &debug_ordered_events},
diff --git a/tools/perf/util/debug.h b/tools/perf/util/debug.h
index f99468a7f681..b9b4d17a1845 100644
--- a/tools/perf/util/debug.h
+++ b/tools/perf/util/debug.h
@@ -13,6 +13,7 @@ extern int debug_peo_args;
 extern bool quiet, dump_trace;
 extern int debug_ordered_events;
 extern int debug_data_convert;
+extern const char perf_debug_options_string[];
 
 #ifndef pr_fmt
 #define pr_fmt(fmt) fmt
-- 
2.34.1