Show help when no or an invalid device is given

Signed-off-by: Jon Derrick <jonathan.derrick@intel.com>

argconfig.c

@@ -119,7 +119,7 @@ static void show_option(const struct argconfig_commandline_options *option)
 	fprintf(stderr, "\n");
 }
 
-static void argconfig_print_help(const char *program_desc,
+void argconfig_print_help(const char *program_desc,
 			  const struct argconfig_commandline_options *options)
 {
 	const struct argconfig_commandline_options *s;

argconfig.h

@@ -78,6 +78,8 @@ extern "C" {
 
 typedef void argconfig_help_func();
 void argconfig_append_usage(const char *str);
+void argconfig_print_help(const char *program_desc,
+			  const struct argconfig_commandline_options *options);
 int argconfig_parse(int argc, char *argv[], const char *program_desc,
 		    const struct argconfig_commandline_options *options,
 		    void *config_out, size_t config_size);

nvme.c

@@ -135,10 +135,8 @@ static int get_dev(int argc, char **argv)
 	int ret;
 
 	ret = check_arg_dev(argc, argv);
-	if (ret) {
-		fprintf(stderr, "expected nvme device (ex: /dev/nvme0), none provided\n");
+	if (ret)
 		return ret;
-	}
 
 	return open_dev((const char *)argv[optind]);
 }
@@ -152,7 +150,11 @@ int parse_and_open(int argc, char **argv, const char *desc,
 	if (ret)
 		return ret;
 
-	return get_dev(argc, argv);
+	ret = get_dev(argc, argv);
+	if (ret < 0)
+		argconfig_print_help(desc, clo);
+
+	return ret;
 }
 
 static const char *output_format = "Output format: normal|json|binary";