tools lib subcmd: Show parent options in help

I've just realized that help message in a subcommand didn't show one
in the parent command.  Since the option parser understands the parent,
display code should do the same.  For example, `perf ftrace latency -h`
should show options in the `perf ftrace` command too.

Before:

  $ perf ftrace latency -h

   Usage: perf ftrace [<options>] [<command>]
      or: perf ftrace [<options>] -- [<command>] [<options>]
      or: perf ftrace {trace|latency} [<options>] [<command>]
      or: perf ftrace {trace|latency} [<options>] -- [<command>] [<options>]

      -b, --use-bpf         Use BPF to measure function latency
      -n, --use-nsec        Use nano-second histogram
      -T, --trace-funcs <func>
                            Show latency of given function

After:

  $ perf ftrace latency -h

   Usage: perf ftrace [<options>] [<command>]
      or: perf ftrace [<options>] -- [<command>] [<options>]
      or: perf ftrace {trace|latency} [<options>] [<command>]
      or: perf ftrace {trace|latency} [<options>] -- [<command>] [<options>]

      -a, --all-cpus        System-wide collection from all CPUs
      -b, --use-bpf         Use BPF to measure function latency
      -C, --cpu <cpu>       List of cpus to monitor
      -n, --use-nsec        Use nano-second histogram
      -p, --pid <pid>       Trace on existing process id
      -T, --trace-funcs <func>
                            Show latency of given function
      -v, --verbose         Be more verbose
          --tid <tid>       Trace on existing thread id (exclusive to --pid)

Reviewed-by: Ian Rogers <irogers@google.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20240429233707.1511175-1-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

Author: namhyung

tools/lib/subcmd/parse-options.c

@@ -808,18 +808,30 @@ static int option__cmp(const void *va, const void *vb)
 
 static struct option *options__order(const struct option *opts)
 {
-	int nr_opts = 0, nr_group = 0, len;
-	const struct option *o = opts;
-	struct option *opt, *ordered, *group;
-
-	for (o = opts; o->type != OPTION_END; o++)
-		++nr_opts;
-
-	len = sizeof(*o) * (nr_opts + 1);
-	ordered = malloc(len);
-	if (!ordered)
-		goto out;
-	memcpy(ordered, opts, len);
+	int nr_opts = 0, nr_group = 0, nr_parent = 0, len;
+	const struct option *o, *p = opts;
+	struct option *opt, *ordered = NULL, *group;
+
+	/* flatten the options that have parents */
+	for (p = opts; p != NULL; p = o->parent) {
+		for (o = p; o->type != OPTION_END; o++)
+			++nr_opts;
+
+		/*
+		 * the length is given by the number of options plus a null
+		 * terminator for the last loop iteration.
+		 */
+		len = sizeof(*o) * (nr_opts + !o->parent);
+		group = realloc(ordered, len);
+		if (!group)
+			goto out;
+		ordered = group;
+		memcpy(&ordered[nr_parent], p, sizeof(*o) * (nr_opts - nr_parent));
+
+		nr_parent = nr_opts;
+	}
+	/* copy the last OPTION_END */
+	memcpy(&ordered[nr_opts], o, sizeof(*o));
 
 	/* sort each option group individually */
 	for (opt = group = ordered; opt->type != OPTION_END; opt++) {