diff --git a/kernel-shared/volumes.c b/kernel-shared/volumes.c
index d924035b..a55bc8d3 100644
--- a/kernel-shared/volumes.c
+++ b/kernel-shared/volumes.c
@@ -238,6 +238,13 @@ int btrfs_bg_type_to_nparity(u64 flags)
 	return btrfs_raid_array[index].nparity;
 }
 
+int btrfs_bg_type_to_sub_stripes(u64 flags)
+{
+	const int index = btrfs_bg_flags_to_raid_index(flags);
+
+	return btrfs_raid_array[index].sub_stripes;
+}
+
 static inline int nr_data_stripes(struct map_lookup *map)
 {
 	return map->num_stripes - btrfs_bg_type_to_nparity(map->type);
diff --git a/kernel-shared/volumes.h b/kernel-shared/volumes.h
index a2e44bfa..58d882c1 100644
--- a/kernel-shared/volumes.h
+++ b/kernel-shared/volumes.h
@@ -311,5 +311,6 @@ int btrfs_bg_type_to_tolerated_failures(u64 flags);
 int btrfs_bg_type_to_devs_min(u64 flags);
 int btrfs_bg_type_to_ncopies(u64 flags);
 int btrfs_bg_type_to_nparity(u64 flags);
+int btrfs_bg_type_to_sub_stripes(u64 flags);
 
 #endif