MDEV-13825 mariabackup --lock-ddl-per-table does not properly lock

FULLTEXT auxiliary tables

Change the logic to take mdl lock on all tables before tablespaces are
copied, rather than  lock every single tablespace just before it is
copied.

extra/mariabackup/xtrabackup.cc

@@ -433,6 +433,22 @@ datafiles_iter_free(datafiles_iter_t *it)
 	free(it);
 }
 
+void mdl_lock_all()
+{
+	mdl_lock_init();
+	datafiles_iter_t *it = datafiles_iter_new(fil_system);
+	if (!it)
+		return;
+
+	while (fil_node_t *node = datafiles_iter_next(it)){
+		if (fil_is_user_tablespace_id(node->space->id)
+			&& check_if_skip_table(node->space->name))
+			continue;
+
+		mdl_lock_table(node->space->id);
+	}
+	datafiles_iter_free(it);
+}
 /* ======== Date copying thread context ======== */
 
 typedef struct {
@@ -2199,10 +2215,6 @@ xtrabackup_copy_datafile(fil_node_t* node, uint thread_n)
 		return(FALSE);
 	}
 
-	if (opt_lock_ddl_per_table) {
-		mdl_lock_table(node->space->id);
-	}
-
 	if (!changed_page_bitmap) {
 		read_filter = &rf_pass_through;
 	}
@@ -3562,9 +3574,7 @@ xtrabackup_backup_func()
 		    "or RENAME TABLE during the backup, inconsistent backup will be "
 		    "produced.\n");
 
-	if (opt_lock_ddl_per_table) {
-		mdl_lock_init();
-	}
+
 
 	/* initialize components */
         if(innodb_init_param()) {
@@ -3879,6 +3889,10 @@ xtrabackup_backup_func()
 		    "files transfer\n", xtrabackup_parallel);
 	}
 
+	if (opt_lock_ddl_per_table) {
+		mdl_lock_all();
+	}
+
 	it = datafiles_iter_new(fil_system);
 	if (it == NULL) {
 		msg("mariabackup: Error: datafiles_iter_new() failed.\n");