From 8abea79da85def035ac69f5665683323cfad7289 Mon Sep 17 00:00:00 2001
From: Alasdair G Kergon <agk@redhat.com>
Date: Fri, 1 Mar 2013 22:45:49 +0000
Subject: [PATCH] --- yaml --- r: 360327 b: refs/heads/master c:
 b0d8ed4d96a26ef3ac54a4aa8911c9413070662e h: refs/heads/master i:   360325:
 3b83f2c7ed4061c03a808f1e19b8bb221bc776d7   360323:
 eaceeba1b13a33e7ab68e3e535df38269aa91b95   360319:
 0e137718f537d00c505f76efa40afc3471dfd8ff v: v3

---
 [refs]                              |  2 +-
 trunk/drivers/md/dm.c               | 22 +++++++++++++++-------
 trunk/include/linux/device-mapper.h | 15 +++++++++++++++
 3 files changed, 31 insertions(+), 8 deletions(-)

diff --git a/[refs] b/[refs]
index db732c9477de..0e45a970d7d1 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: df5d2e9089c7d5b8c46f767e4278610ea3e815b9
+refs/heads/master: b0d8ed4d96a26ef3ac54a4aa8911c9413070662e
diff --git a/trunk/drivers/md/dm.c b/trunk/drivers/md/dm.c
index e417cf0a69ef..7e469260fe5e 100644
--- a/trunk/drivers/md/dm.c
+++ b/trunk/drivers/md/dm.c
@@ -1152,15 +1152,23 @@ static void __clone_and_map_data_bio(struct clone_info *ci, struct dm_target *ti
 {
 	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);
-
-	if (split_bvec)
-		clone_split_bio(tio, bio, sector, idx, offset, len);
-	else
-		clone_bio(tio, bio, sector, idx, bv_count, len);
+	/*
+	 * 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);
 
-	__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/trunk/include/linux/device-mapper.h b/trunk/include/linux/device-mapper.h
index d5f984b07466..1e483fa7afb4 100644
--- a/trunk/include/linux/device-mapper.h
+++ b/trunk/include/linux/device-mapper.h
@@ -175,6 +175,14 @@ struct target_type {
 #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 @@ struct dm_target {
 	 */
 	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;