v4.19.13 snapshot.
diff --git a/lib/interval_tree.c b/lib/interval_tree.c
new file mode 100644
index 0000000..c85f660
--- /dev/null
+++ b/lib/interval_tree.c
@@ -0,0 +1,16 @@
+#include <linux/interval_tree.h>
+#include <linux/interval_tree_generic.h>
+#include <linux/compiler.h>
+#include <linux/export.h>
+
+#define START(node) ((node)->start)
+#define LAST(node) ((node)->last)
+
+INTERVAL_TREE_DEFINE(struct interval_tree_node, rb,
+ unsigned long, __subtree_last,
+ START, LAST,, interval_tree)
+
+EXPORT_SYMBOL_GPL(interval_tree_insert);
+EXPORT_SYMBOL_GPL(interval_tree_remove);
+EXPORT_SYMBOL_GPL(interval_tree_iter_first);
+EXPORT_SYMBOL_GPL(interval_tree_iter_next);