diff --git a/drivers/md/dm-thin-metadata.h b/drivers/md/dm-thin-metadata.h
index fac01a9..f11f140 100644
--- a/drivers/md/dm-thin-metadata.h
+++ b/drivers/md/dm-thin-metadata.h
@@ -147,6 +147,15 @@
 		       int can_issue_io, struct dm_thin_lookup_result *result);
 
 /*
+ * Retrieve the next run of contiguously mapped blocks.  Useful for working
+ * out where to break up IO.  Returns 0 on success, < 0 on error.
+ */
+int dm_thin_find_mapped_range(struct dm_thin_device *td,
+			      dm_block_t begin, dm_block_t end,
+			      dm_block_t *thin_begin, dm_block_t *thin_end,
+			      dm_block_t *pool_begin, bool *maybe_shared);
+
+/*
  * Obtain an unused block.
  */
 int dm_pool_alloc_data_block(struct dm_pool_metadata *pmd, dm_block_t *result);