kconfig: refactor option parse code

The current option parse code is clumsy.

The 's' option is separately handled in an if-conditional due to the
following code:

    input_mode = (enum input_mode)opt;

If 's' is moved to the switch statement, the invalid value 's' would
be assigned to the input_mode.

Another potential problem is that we are mixing 'enum input_mode' and
ASCII characters. They could overwrap if we add more input modes.

To separate them out, set the flag field of long options to a pointer
of input_mode_opt. For mode select options, getopt_long() returns 0,
which never causes overwrap with ASCII characters that represent short
options.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

scripts/kconfig/conf.c

@@ -37,7 +37,7 @@ enum input_mode {
 	mod2yesconfig,
 };
 static enum input_mode input_mode = oldaskconfig;
-
+static int input_mode_opt;
 static int indent = 1;
 static int tty_stdio;
 static int sync_kconfig;
@@ -474,21 +474,21 @@ static void check_conf(struct menu *menu)
 }
 
 static struct option long_opts[] = {
-	{"oldaskconfig",    no_argument,       NULL, oldaskconfig},
-	{"oldconfig",       no_argument,       NULL, oldconfig},
-	{"syncconfig",      no_argument,       NULL, syncconfig},
-	{"defconfig",       required_argument, NULL, defconfig},
-	{"savedefconfig",   required_argument, NULL, savedefconfig},
-	{"allnoconfig",     no_argument,       NULL, allnoconfig},
-	{"allyesconfig",    no_argument,       NULL, allyesconfig},
-	{"allmodconfig",    no_argument,       NULL, allmodconfig},
-	{"alldefconfig",    no_argument,       NULL, alldefconfig},
-	{"randconfig",      no_argument,       NULL, randconfig},
-	{"listnewconfig",   no_argument,       NULL, listnewconfig},
-	{"helpnewconfig",   no_argument,       NULL, helpnewconfig},
-	{"olddefconfig",    no_argument,       NULL, olddefconfig},
-	{"yes2modconfig",   no_argument,       NULL, yes2modconfig},
-	{"mod2yesconfig",   no_argument,       NULL, mod2yesconfig},
+	{"oldaskconfig",  no_argument,       &input_mode_opt, oldaskconfig},
+	{"oldconfig",     no_argument,       &input_mode_opt, oldconfig},
+	{"syncconfig",    no_argument,       &input_mode_opt, syncconfig},
+	{"defconfig",     required_argument, &input_mode_opt, defconfig},
+	{"savedefconfig", required_argument, &input_mode_opt, savedefconfig},
+	{"allnoconfig",   no_argument,       &input_mode_opt, allnoconfig},
+	{"allyesconfig",  no_argument,       &input_mode_opt, allyesconfig},
+	{"allmodconfig",  no_argument,       &input_mode_opt, allmodconfig},
+	{"alldefconfig",  no_argument,       &input_mode_opt, alldefconfig},
+	{"randconfig",    no_argument,       &input_mode_opt, randconfig},
+	{"listnewconfig", no_argument,       &input_mode_opt, listnewconfig},
+	{"helpnewconfig", no_argument,       &input_mode_opt, helpnewconfig},
+	{"olddefconfig",  no_argument,       &input_mode_opt, olddefconfig},
+	{"yes2modconfig", no_argument,       &input_mode_opt, yes2modconfig},
+	{"mod2yesconfig", no_argument,       &input_mode_opt, mod2yesconfig},
 	{NULL, 0, NULL, 0}
 };
 
@@ -526,43 +526,38 @@ int main(int ac, char **av)
 	tty_stdio = isatty(0) && isatty(1);
 
 	while ((opt = getopt_long(ac, av, "hs", long_opts, NULL)) != -1) {
-		if (opt == 's') {
-			conf_set_message_callback(NULL);
-			continue;
-		}
-		input_mode = (enum input_mode)opt;
 		switch (opt) {
-		case syncconfig:
-			/*
-			 * syncconfig is invoked during the build stage.
-			 * Suppress distracting "configuration written to ..."
-			 */
-			conf_set_message_callback(NULL);
-			sync_kconfig = 1;
-			break;
-		case defconfig:
-		case savedefconfig:
-			defconfig_file = optarg;
-			break;
-		case randconfig:
-			set_randconfig_seed();
-			break;
-		case oldaskconfig:
-		case oldconfig:
-		case allnoconfig:
-		case allyesconfig:
-		case allmodconfig:
-		case alldefconfig:
-		case listnewconfig:
-		case helpnewconfig:
-		case olddefconfig:
-		case yes2modconfig:
-		case mod2yesconfig:
-			break;
 		case 'h':
 			conf_usage(progname);
 			exit(1);
 			break;
+		case 's':
+			conf_set_message_callback(NULL);
+			break;
+		case 0:
+			input_mode = input_mode_opt;
+			switch (input_mode) {
+			case syncconfig:
+				/*
+				 * syncconfig is invoked during the build stage.
+				 * Suppress distracting
+				 *   "configuration written to ..."
+				 */
+				conf_set_message_callback(NULL);
+				sync_kconfig = 1;
+				break;
+			case defconfig:
+			case savedefconfig:
+				defconfig_file = optarg;
+				break;
+			case randconfig:
+				set_randconfig_seed();
+				break;
+			default:
+				break;
+			}
+		default:
+			break;
 		}
 	}
 	if (ac == optind) {