perf tools: Add the bash completion for listing subsubcommands of perf help

The bash completion does not support listing subsubcommands for 'perf
help <TAB>', so fix it.

Example:

Before this patch:

 $ perf help <TAB>
 $

As shown above, the subsubcommands of perf help does not come out.

After this patch:

 $ perf help <TAB>
 annotate       buildid-cache  data           evlist         inject
 kvm            lock           probe          report         script
 test           top
 bench          buildid-list   diff           help           kmem
 list           mem            record         sched          stat
 timechart      trace

As shown above, the subsubcommands of perf help can come out now.

Signed-off-by: Yunlong Song <yunlong.song@huawei.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1426685758-25488-9-git-send-email-yunlong.song@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-help.c

@@ -437,7 +437,18 @@ int cmd_help(int argc, const char **argv, const char *prefix __maybe_unused)
 			HELP_FORMAT_INFO),
 	OPT_END(),
 	};
-	const char * const builtin_help_usage[] = {
+	const char * const builtin_help_subcommands[] = {
+		"buildid-cache", "buildid-list", "diff", "evlist", "help", "list",
+		"record", "report", "bench", "stat", "timechart", "top", "annotate",
+		"script", "sched", "kmem", "lock", "kvm", "test", "inject", "mem", "data",
+#ifdef HAVE_LIBELF_SUPPORT
+		"probe",
+#endif
+#ifdef HAVE_LIBAUDIT_SUPPORT
+		"trace",
+#endif
+	NULL };
+	const char *builtin_help_usage[] = {
 		"perf help [--all] [--man|--web|--info] [command]",
 		NULL
 	};
@@ -448,8 +459,8 @@ int cmd_help(int argc, const char **argv, const char *prefix __maybe_unused)
 
 	perf_config(perf_help_config, &help_format);
 
-	argc = parse_options(argc, argv, builtin_help_options,
-			builtin_help_usage, 0);
+	argc = parse_options_subcommand(argc, argv, builtin_help_options,
+			builtin_help_subcommands, builtin_help_usage, 0);
 
 	if (show_all) {
 		printf("\n usage: %s\n\n", perf_usage_string);

tools/perf/perf-completion.sh

@@ -143,7 +143,7 @@ __perf_main ()
 		__perfcomp_colon "$evts" "$cur"
 	else
 		# List subcommands for perf commands
-		if [[ $prev_skip_opts == @(kvm|kmem|mem|lock|sched|data) ]]; then
+		if [[ $prev_skip_opts == @(kvm|kmem|mem|lock|sched|data|help) ]]; then
 			subcmds=$($cmd $prev_skip_opts --list-cmds)
 			__perfcomp_colon "$subcmds" "$cur"
 		fi