- /* device offset where the dentry_set locates, or
- * the empty slot locates or EOF if not found.
+ /*
+ * If the dentry_set found:
+ * - device offset where the dentry_set locates.
+ * If the dentry_set not found:
+ * - device offset where the first empty dentry_set locates
+ * if in.dentry_count > 0 and there are enough empty dentry.
+ * - device offset where the last empty dentry_set locates
+ * if in.dentry_count = 0 or no enough empty dentry.
+ * - EOF if no empty dentry_set.