tools: bpftool: add option parsing to bpftool, --help and --version

Add an option parsing facility to bpftool, in prevision of future
options for demanding JSON output. Currently, two options are added:
--help and --version, that act the same as the respective commands
`help` and `version`.

Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/bpf/bpftool/Documentation/bpftool-map.rst

@@ -68,6 +68,14 @@ DESCRIPTION
 	**bpftool map help**
 		  Print short help message.
 
+OPTIONS
+=======
+	-h, --help
+		  Print short generic help message (similar to **bpftool help**).
+
+	-v, --version
+		  Print version number (similar to **bpftool version**).
+
 EXAMPLES
 ========
 **# bpftool map show**

tools/bpf/bpftool/Documentation/bpftool-prog.rst

@@ -50,6 +50,14 @@ DESCRIPTION
 	**bpftool prog help**
 		  Print short help message.
 
+OPTIONS
+=======
+	-h, --help
+		  Print short generic help message (similar to **bpftool help**).
+
+	-v, --version
+		  Print version number (similar to **bpftool version**).
+
 EXAMPLES
 ========
 **# bpftool prog show**

tools/bpf/bpftool/Documentation/bpftool.rst

@@ -31,6 +31,14 @@ DESCRIPTION
 	Note that format of the output of all tools is not guaranteed to be
 	stable and should not be depended upon.
 
+OPTIONS
+=======
+	-h, --help
+		  Print short help message (similar to **bpftool help**).
+
+	-v, --version
+		  Print version number (similar to **bpftool version**).
+
 SEE ALSO
 ========
 	**bpftool-map**\ (8), **bpftool-prog**\ (8)

tools/bpf/bpftool/main.c

@@ -36,6 +36,7 @@
 #include <bfd.h>
 #include <ctype.h>
 #include <errno.h>
+#include <getopt.h>
 #include <linux/bpf.h>
 #include <linux/version.h>
 #include <stdio.h>
@@ -215,8 +216,32 @@ err_close:
 
 int main(int argc, char **argv)
 {
+	static const struct option options[] = {
+		{ "help",	no_argument,	NULL,	'h' },
+		{ "version",	no_argument,	NULL,	'V' },
+		{ 0 }
+	};
+	int opt;
+
+	last_do_help = do_help;
 	bin_name = argv[0];
-	NEXT_ARG();
+
+	while ((opt = getopt_long(argc, argv, "Vh",
+				  options, NULL)) >= 0) {
+		switch (opt) {
+		case 'V':
+			return do_version(argc, argv);
+		case 'h':
+			return do_help(argc, argv);
+		default:
+			usage();
+		}
+	}
+
+	argc -= optind;
+	argv += optind;
+	if (argc < 0)
+		usage();
 
 	bfd_init();