Maintain: Added detailed notes for preorder traversal.

src/rbtree.c

@@ -847,12 +847,20 @@ struct rb_node *rb_pre_next(const struct rb_node *node)
     if (!node)
         return NULL;
 
+    /**
+     * If there are left and right child nodes,
+     * then we iterate directly.
+     */
     if (node->left)
         return node->left;
 
     if (node->right)
         return node->right;
 
+    /**
+     * if we have no children, Go up till we find an ancestor
+     * which have a another right-hand child.
+     */
     while ((parent = node->parent) && (!parent->right || node == parent->right))
         node = parent;
 
@@ -870,8 +878,7 @@ struct rb_node *rb_post_first(const struct rb_root *root)
     if (!root || !node)
         return NULL;
 
-    node = rb_left_deep(node);
-    return node;
+    return rb_left_deep(node);
 }
 
 struct rb_node *rb_post_next(const struct rb_node *node)

src/rbtree.h

@@ -657,7 +657,7 @@ static inline void rb_delete_augmented(struct rb_root *root, struct rb_node *nod
          pos; pos = rb_next_entry(pos, member))
 
 /**
- * rb_for_each_entry_reverse - iterate backwards over cached rbtree of given type.
+ * rb_cached_for_each_entry_reverse - iterate backwards over cached rbtree of given type.
  * @pos: the type * to use as a loop cursor.
  * @cached: the cached root for your rbtree.
  * @member: the name of the rb_node within the struct.