bpftool: Add current libbpf_strict mode to version output

+ bpftool --legacy --version
bpftool v5.15.0
features: libbfd, skeletons
+ bpftool --version
bpftool v5.15.0
features: libbfd, libbpf_strict, skeletons

+ bpftool --legacy --help
Usage: bpftool [OPTIONS] OBJECT { COMMAND | help }
       bpftool batch file FILE
       bpftool version

       OBJECT := { prog | map | link | cgroup | perf | net | feature | btf | gen | struct_ops | iter }
       OPTIONS := { {-j|--json} [{-p|--pretty}] | {-d|--debug} | {-l|--legacy} |
                    {-V|--version} }
+ bpftool --help
Usage: bpftool [OPTIONS] OBJECT { COMMAND | help }
       bpftool batch file FILE
       bpftool version

       OBJECT := { prog | map | link | cgroup | perf | net | feature | btf | gen | struct_ops | iter }
       OPTIONS := { {-j|--json} [{-p|--pretty}] | {-d|--debug} | {-l|--legacy} |
                    {-V|--version} }

+ bpftool --legacy
Usage: bpftool [OPTIONS] OBJECT { COMMAND | help }
       bpftool batch file FILE
       bpftool version

       OBJECT := { prog | map | link | cgroup | perf | net | feature | btf | gen | struct_ops | iter }
       OPTIONS := { {-j|--json} [{-p|--pretty}] | {-d|--debug} | {-l|--legacy} |
                    {-V|--version} }
+ bpftool
Usage: bpftool [OPTIONS] OBJECT { COMMAND | help }
       bpftool batch file FILE
       bpftool version

       OBJECT := { prog | map | link | cgroup | perf | net | feature | btf | gen | struct_ops | iter }
       OPTIONS := { {-j|--json} [{-p|--pretty}] | {-d|--debug} | {-l|--legacy} |
                    {-V|--version} }

+ bpftool --legacy version
bpftool v5.15.0
features: libbfd, skeletons
+ bpftool version
bpftool v5.15.0
features: libbfd, libbpf_strict, skeletons

+ bpftool --json --legacy version
{"version":"5.15.0","features":{"libbfd":true,"libbpf_strict":false,"skeletons":true}}
+ bpftool --json version
{"version":"5.15.0","features":{"libbfd":true,"libbpf_strict":true,"skeletons":true}}
Suggested-by: Quentin Monnet <quentin@isovalent.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Quentin Monnet <quentin@isovalent.com>
Link: https://lore.kernel.org/bpf/20211116000448.2918854-1-sdf@google.com

tools/bpf/bpftool/main.c

@@ -93,6 +93,7 @@ static int do_version(int argc, char **argv)
 		jsonw_name(json_wtr, "features");
 		jsonw_start_object(json_wtr);	/* features */
 		jsonw_bool_field(json_wtr, "libbfd", has_libbfd);
+		jsonw_bool_field(json_wtr, "libbpf_strict", !legacy_libbpf);
 		jsonw_bool_field(json_wtr, "skeletons", has_skeletons);
 		jsonw_end_object(json_wtr);	/* features */
 
@@ -106,6 +107,10 @@ static int do_version(int argc, char **argv)
 			printf(" libbfd");
 			nb_features++;
 		}
+		if (!legacy_libbpf) {
+			printf("%s libbpf_strict", nb_features++ ? "," : "");
+			nb_features++;
+		}
 		if (has_skeletons)
 			printf("%s skeletons", nb_features++ ? "," : "");
 		printf("\n");
@@ -400,6 +405,7 @@ int main(int argc, char **argv)
 		{ "legacy",	no_argument,	NULL,	'l' },
 		{ 0 }
 	};
+	bool version_requested = false;
 	int opt, ret;
 
 	last_do_help = do_help;
@@ -414,7 +420,8 @@ int main(int argc, char **argv)
 				  options, NULL)) >= 0) {
 		switch (opt) {
 		case 'V':
-			return do_version(argc, argv);
+			version_requested = true;
+			break;
 		case 'h':
 			return do_help(argc, argv);
 		case 'p':
@@ -479,6 +486,9 @@ int main(int argc, char **argv)
 	if (argc < 0)
 		usage();
 
+	if (version_requested)
+		return do_version(argc, argv);
+
 	ret = cmd_select(cmds, argc, argv, do_help);
 
 	if (json_output)