Add a "help" command

So that we can spawn the correct -t <type> backend
and have it print the usage information, including
type specific arguments.

Signed-off-by: Ronnie Sahlberg <[email protected]>

ublk.cpp

@@ -23,21 +23,6 @@ static const struct ublksrv_tgt_type *ublksrv_find_tgt_type(const char *name)
 	return NULL;
 }
 
-static void ublksrv_for_each_tgt_type(void (*handle_tgt_type)(unsigned idx,
-			const struct ublksrv_tgt_type *type, void *data),
-		void *data)
-{
-	int i;
-
-	for (i = 0; i < UBLKSRV_TGT_TYPE_MAX; i++) {
-                const struct ublksrv_tgt_type  *type = tgt_list[i];
-
-		if (!type)
-			continue;
-		handle_tgt_type(i, type, data);
-	}
-}
-
 int ublksrv_register_tgt_type(struct ublksrv_tgt_type *type)
 {
 	if (type->type < UBLKSRV_TGT_TYPE_MAX && !tgt_list[type->type]) {
@@ -178,8 +163,8 @@ static void cmd_dev_add_usage(const char *cmd)
 {
 	printf("%s add -t <type>\n", cmd);
 	ublksrv_print_std_opts();
-	printf("\ttarget specific command line:\n");
-	ublksrv_for_each_tgt_type(show_tgt_add_usage, NULL);
+	printf("\tFor type specific options, run:\n");
+	printf("\t\tublk help -t <type>\n");
 }
 
 static int __cmd_dev_del(int number, bool log, bool async)
@@ -553,10 +538,31 @@ static void cmd_usage(const char *cmd)
 	cmd_dev_recover_usage(cmd);
 	cmd_dev_get_features_help(cmd);
 
+	printf("%s help -t <target>\n", cmd);
 	printf("%s -v [--version]\n", cmd);
 	printf("%s -h [--help]\n", cmd);
 }
 
+static int cmd_dev_help(int argc, char *argv[])
+{
+	struct ublksrv_dev_data data = {0};
+	struct ublksrv_ctrl_dev *dev;
+	const struct ublksrv_tgt_type *tgt_type;
+	int ret;
+	const char *dump_buf;
+
+	ublksrv_parse_std_opts(&data, argc, argv);
+
+	if (data.tgt_type == NULL) {
+		cmd_usage("ublk");
+		return EXIT_SUCCESS;
+	}
+
+	ublksrv_execve_helper("help", data.tgt_type, argc, argv);
+	fprintf(stderr, "failed to spawn target\n");
+	return EXIT_FAILURE;
+}
+
 int main(int argc, char *argv[])
 {
 	const char *prog_name = "ublk";
@@ -579,6 +585,8 @@ int main(int argc, char *argv[])
 		ret = cmd_dev_add(argc, argv);
 	else if (!strcmp(cmd, "del"))
 		ret = cmd_dev_del(argc, argv);
+	else if (!strcmp(cmd, "help"))
+		ret = cmd_dev_help(argc, argv);
 	else if (!strcmp(cmd, "list"))
 		ret = cmd_list_dev_info(argc, argv);
 	else if (!strcmp(cmd, "recover"))