1 files changed, 159 insertions, 0 deletions
diff --git a/lib/interval_tree.c b/lib/interval_tree.c
new file mode 100644
index 00000000000..6fd540b1e49
--- /dev/null
+++ b/lib/interval_tree.c
@@ -0,0 +1,159 @@
+#include <linux/init.h>
+#include <linux/interval_tree.h>
+
+/* Callbacks for augmented rbtree insert and remove */
+
+static inline unsigned long
+compute_subtree_last(struct interval_tree_node *node)
+{
+	unsigned long max = node->last, subtree_last;
+	if (node->rb.rb_left) {
+		subtree_last = rb_entry(node->rb.rb_left,
+			struct interval_tree_node, rb)->__subtree_last;
+		if (max < subtree_last)
+			max = subtree_last;
+	}
+	if (node->rb.rb_right) {
+		subtree_last = rb_entry(node->rb.rb_right,
+			struct interval_tree_node, rb)->__subtree_last;
+		if (max < subtree_last)
+			max = subtree_last;
+	}
+	return max;
+}
+
+RB_DECLARE_CALLBACKS(static, augment_callbacks, struct interval_tree_node, rb,
+		     unsigned long, __subtree_last, compute_subtree_last)
+
+/* Insert / remove interval nodes from the tree */
+
+void interval_tree_insert(struct interval_tree_node *node,
+			  struct rb_root *root)
+{
+	struct rb_node **link = &root->rb_node, *rb_parent = NULL;
+	unsigned long start = node->start, last = node->last;
+	struct interval_tree_node *parent;
+
+	while (*link) {
+		rb_parent = *link;
+		parent = rb_entry(rb_parent, struct interval_tree_node, rb);
+		if (parent->__subtree_last < last)
+			parent->__subtree_last = last;
+		if (start < parent->start)
+			link = &parent->rb.rb_left;
+		else
+			link = &parent->rb.rb_right;
+	}
+
+	node->__subtree_last = last;
+	rb_link_node(&node->rb, rb_parent, link);
+	rb_insert_augmented(&node->rb, root, &augment_callbacks);
+}
+
+void interval_tree_remove(struct interval_tree_node *node,
+			  struct rb_root *root)
+{
+	rb_erase_augmented(&node->rb, root, &augment_callbacks);
+}
+
+/*
+ * Iterate over intervals intersecting [start;last]
+ *
+ * Note that a node's interval intersects [start;last] iff:
+ *   Cond1: node->start <= last
+ * and
+ *   Cond2: start <= node->last
+ */
+
+static struct interval_tree_node *
+subtree_search(struct interval_tree_node *node,
+	       unsigned long start, unsigned long last)
+{
+	while (true) {
+		/*
+		 * Loop invariant: start <= node->__subtree_last
+		 * (Cond2 is satisfied by one of the subtree nodes)
+		 */
+		if (node->rb.rb_left) {
+			struct interval_tree_node *left =
+				rb_entry(node->rb.rb_left,
+					 struct interval_tree_node, rb);
+			if (start <= left->__subtree_last) {
+				/*
+				 * Some nodes in left subtree satisfy Cond2.
+				 * Iterate to find the leftmost such node N.
+				 * If it also satisfies Cond1, that's the match
+				 * we are looking for. Otherwise, there is no
+				 * matching interval as nodes to the right of N
+				 * can't satisfy Cond1 either.
+				 */
+				node = left;
+				continue;
+			}
+		}
+		if (node->start <= last) {		/* Cond1 */
+			if (start <= node->last)	/* Cond2 */
+				return node;	/* node is leftmost match */
+			if (node->rb.rb_right) {
+				node = rb_entry(node->rb.rb_right,
+					struct interval_tree_node, rb);
+				if (start <= node->__subtree_last)
+					continue;
+			}
+		}
+		return NULL;	/* No match */
+	}
+}
+
+struct interval_tree_node *
+interval_tree_iter_first(struct rb_root *root,
+			 unsigned long start, unsigned long last)
+{
+	struct interval_tree_node *node;
+
+	if (!root->rb_node)
+		return NULL;
+	node = rb_entry(root->rb_node, struct interval_tree_node, rb);
+	if (node->__subtree_last < start)
+		return NULL;
+	return subtree_search(node, start, last);
+}
+
+struct interval_tree_node *
+interval_tree_iter_next(struct interval_tree_node *node,
+			unsigned long start, unsigned long last)
+{
+	struct rb_node *rb = node->rb.rb_right, *prev;
+
+	while (true) {
+		/*
+		 * Loop invariants:
+		 *   Cond1: node->start <= last
+		 *   rb == node->rb.rb_right
+		 *
+		 * First, search right subtree if suitable
+		 */
+		if (rb) {
+			struct interval_tree_node *right =
+				rb_entry(rb, struct interval_tree_node, rb);
+			if (start <= right->__subtree_last)
+				return subtree_search(right, start, last);
+		}
+
+		/* Move up the tree until we come from a node's left child */
+		do {
+			rb = rb_parent(&node->rb);
+			if (!rb)
+				return NULL;
+			prev = &node->rb;
+			node = rb_entry(rb, struct interval_tree_node, rb);
+			rb = node->rb.rb_right;
+		} while (prev == rb);
+
+		/* Check if the node intersects [start;last] */
+		if (last < node->start)		/* !Cond1 */
+			return NULL;
+		else if (start <= node->last)	/* Cond2 */
+			return node;
+	}
+}