diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index e417cf0..7e46926 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1152,15 +1152,23 @@
 {
 	struct bio *bio = ci->bio;
 	struct dm_target_io *tio;
+	unsigned target_bio_nr;
+	unsigned num_target_bios = 1;
 
-	tio = alloc_tio(ci, ti, nr_iovecs, 0);
+	/*
+	 * Does the target want to receive duplicate copies of the bio?
+	 */
+	if (bio_data_dir(bio) == WRITE && ti->num_write_bios)
+		num_target_bios = ti->num_write_bios(ti, bio);
 
-	if (split_bvec)
-		clone_split_bio(tio, bio, sector, idx, offset, len);
-	else
-		clone_bio(tio, bio, sector, idx, bv_count, len);
-
-	__map_bio(tio);
+	for (target_bio_nr = 0; target_bio_nr < num_target_bios; target_bio_nr++) {
+		tio = alloc_tio(ci, ti, nr_iovecs, target_bio_nr);
+		if (split_bvec)
+			clone_split_bio(tio, bio, sector, idx, offset, len);
+		else
+			clone_bio(tio, bio, sector, idx, bv_count, len);
+		__map_bio(tio);
+	}
 }
 
 typedef unsigned (*get_num_bios_fn)(struct dm_target *ti);
diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index d5f984b..1e483fa 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -175,6 +175,14 @@
 #define DM_TARGET_IMMUTABLE		0x00000004
 #define dm_target_is_immutable(type)	((type)->features & DM_TARGET_IMMUTABLE)
 
+/*
+ * Some targets need to be sent the same WRITE bio severals times so
+ * that they can send copies of it to different devices.  This function
+ * examines any supplied bio and returns the number of copies of it the
+ * target requires.
+ */
+typedef unsigned (*dm_num_write_bios_fn) (struct dm_target *ti, struct bio *bio);
+
 struct dm_target {
 	struct dm_table *table;
 	struct target_type *type;
@@ -214,6 +222,13 @@
 	 */
 	unsigned per_bio_data_size;
 
+	/*
+	 * If defined, this function is called to find out how many
+	 * duplicate bios should be sent to the target when writing
+	 * data.
+	 */
+	dm_num_write_bios_fn num_write_bios;
+
 	/* target specific data */
 	void *private;