[PATCH 1/6] rbtree: add rb_find_add_cached() to rbtree.h

[Roger L. Beckermeyer III]

Adds rb_find_add_cached() as a helper function for use with
red-black trees. Used in btrfs to reduce boilerplate code.

Suggested-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
Signed-off-by: Roger L. Beckermeyer III <beckerlee3@xxxxxxxxx>
---
 include/linux/rbtree.h | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/include/linux/rbtree.h b/include/linux/rbtree.h
index 7c173aa64e1e..0d4444c0cfb3 100644
--- a/include/linux/rbtree.h
+++ b/include/linux/rbtree.h
@@ -210,6 +210,43 @@ rb_add(struct rb_node *node, struct rb_root *tree,
 	rb_insert_color(node, tree);
 }
 
+/**
+ * rb_find_add_cached() - find equivalent @node in @tree, or add @node
+ * @node: node to look-for / insert
+ * @tree: tree to search / modify
+ * @cmp: operator defining the node order
+ *
+ * Returns the rb_node matching @node, or NULL when no match is found and @node
+ * is inserted.
+ */
+static __always_inline struct rb_node *
+rb_find_add_cached(struct rb_node *node, struct rb_root_cached *tree,
+	    int (*cmp)(struct rb_node *, const struct rb_node *))
+{
+	bool leftmost = true;
+	struct rb_node **link = &tree->rb_root.rb_node;
+	struct rb_node *parent = NULL;
+	int c;
+
+	while (*link) {
+		parent = *link;
+		c = cmp(node, parent);
+
+		if (c < 0) {
+			link = &parent->rb_left;
+		} else if (c > 0) {
+			link = &parent->rb_right;
+			leftmost = false;
+		} else {
+			return parent;
+		}
+	}
+
+	rb_link_node(node, parent, link);
+	rb_insert_color_cached(node, tree, leftmost);
+	return NULL;
+}
+
 /**
  * rb_find_add() - find equivalent @node in @tree, or add @node
  * @node: node to look-for / insert
-- 
2.45.2