From: Alasdair G Kergon <[email-masked]>

Further experimental cleanup of clone_bio code.
Add core num_write_bios support.

 - split this into 3: renames, code moves, num_write_bios

---
 drivers/md/dm.c               |  236 ++++++++++++++++++++++++------------------
 include/linux/device-mapper.h |   15 ++
 2 files changed, 153 insertions(+), 98 deletions(-)

Index: linux/drivers/md/dm.c
===================================================================
--- linux.orig/drivers/md/dm.c
+++ linux/drivers/md/dm.c
@@ -1063,9 +1063,9 @@ static void clone_bio_integrity(struct b
 /*
  * Creates a little bio that just does part of a bvec.
  */
-static void split_bvec(struct dm_target_io *tio, struct bio *bio,
-		       sector_t sector, unsigned short idx, unsigned int offset,
-		       unsigned int len)
+static void clone_split_bio(struct dm_target_io *tio, struct bio *bio,
+			    sector_t sector, unsigned short idx,
+			    unsigned offset, unsigned len)
 {
 	struct bio *clone = &tio->clone;
 	struct bio_vec *bv = bio->bi_io_vec + idx;
@@ -1121,10 +1121,40 @@ static struct dm_target_io *alloc_tio(st
 	return tio;
 }
 
-static void __issue_target_request(struct clone_info *ci, struct dm_target *ti,
-				   unsigned target_bio_nr, sector_t len)
+static void __clone_and_map_data_bio(struct clone_info *ci,
+				     struct dm_target *ti,
+				     sector_t sector, int nr_iovecs,
+				     unsigned short idx, unsigned bv_count,
+				     unsigned len,
+				     unsigned split_bvec)
 {
-	struct dm_target_io *tio = alloc_tio(ci, ti, ci->bio->bi_max_vecs, target_bio_nr);
+	struct bio *bio = ci->bio;
+	struct dm_target_io *tio;
+	unsigned target_bio_nr;
+	unsigned num_target_bios = 1;
+
+	/*
+	 * 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);
+
+	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, bv_count, len);
+		else
+			clone_bio(tio, bio, sector, idx, bv_count, len);
+		__map_bio(tio);
+	}
+}
+
+static void __clone_and_map_simple_bio(struct clone_info *ci,
+				       struct dm_target *ti,
+				       unsigned target_bio_nr, sector_t len)
+{
+	struct dm_target_io *tio = alloc_tio(ci, ti, ci->bio->bi_max_vecs,
+					     target_bio_nr);
 	struct bio *clone = &tio->clone;
 
 	/*
@@ -1139,42 +1169,27 @@ static void __issue_target_request(struc
 	__map_bio(tio);
 }
 
-static void __issue_target_bios(struct clone_info *ci, struct dm_target *ti,
-				unsigned num_bios, sector_t len)
+static void __send_duplicate_bios(struct clone_info *ci, struct dm_target *ti,
+				  unsigned num_bios, sector_t len)
 {
 	unsigned target_bio_nr;
 
 	for (target_bio_nr = 0; target_bio_nr < num_bios; target_bio_nr++)
-		__issue_target_request(ci, ti, target_bio_nr, len);
+		__clone_and_map_simple_bio(ci, ti, target_bio_nr, len);
 }
 
-static int __clone_and_map_empty_flush(struct clone_info *ci)
+static int __send_empty_flush(struct clone_info *ci)
 {
 	unsigned target_nr = 0;
 	struct dm_target *ti;
 
 	BUG_ON(bio_has_data(ci->bio));
 	while ((ti = dm_table_get_target(ci->map, target_nr++)))
-		__issue_target_bios(ci, ti, ti->num_flush_bios, 0);
+		__send_duplicate_bios(ci, ti, ti->num_flush_bios, 0);
 
 	return 0;
 }
 
-/*
- * Perform all io with a single clone.
- */
-static void __clone_and_map_simple(struct clone_info *ci, struct dm_target *ti)
-{
-	struct bio *bio = ci->bio;
-	struct dm_target_io *tio;
-
-	tio = alloc_tio(ci, ti, bio->bi_max_vecs, 0);
-	clone_bio(tio, bio, ci->sector, ci->idx, bio->bi_vcnt - ci->idx,
-		  ci->sector_count);
-	__map_bio(tio);
-	ci->sector_count = 0;
-}
-
 typedef unsigned (*get_num_bios_fn)(struct dm_target *ti);
 
 static unsigned get_num_discard_bios(struct dm_target *ti)
@@ -1194,9 +1209,9 @@ static bool is_split_required_for_discar
 	return ti->split_discard_bios;
 }
 
-static int __clone_and_map_changing_extent_only(struct clone_info *ci,
-						get_num_bios_fn get_num_bios,
-						is_split_required_fn is_split_required)
+static int __send_changing_extent_only(struct clone_info *ci,
+				       get_num_bios_fn get_num_bios,
+				       is_split_required_fn is_split_required)
 {
 	struct dm_target *ti;
 	sector_t len;
@@ -1222,7 +1237,7 @@ static int __clone_and_map_changing_exte
 		else
 			len = min(ci->sector_count, max_io_len(ci->sector, ti));
 
-		__issue_target_bios(ci, ti, num_bios, len);
+		__send_duplicate_bios(ci, ti, num_bios, len);
 
 		ci->sector += len;
 	} while (ci->sector_count -= len);
@@ -1230,28 +1245,86 @@ static int __clone_and_map_changing_exte
 	return 0;
 }
 
-static int __clone_and_map_discard(struct clone_info *ci)
+static int __send_discard(struct clone_info *ci)
 {
-	return __clone_and_map_changing_extent_only(ci, get_num_discard_bios,
-						    is_split_required_for_discard);
+	return __send_changing_extent_only(ci, get_num_discard_bios,
+					   is_split_required_for_discard);
 }
 
-static int __clone_and_map_write_same(struct clone_info *ci)
+static int __send_write_same(struct clone_info *ci)
+{
+	return __send_changing_extent_only(ci, get_num_write_same_bios, NULL);
+}
+
+/*
+ * Find maximum number of sectors / bvecs we can process with a single bio.
+ */
+static sector_t __len_within_target(struct clone_info *ci, sector_t max,
+				    int *idx)
 {
-	return __clone_and_map_changing_extent_only(ci, get_num_write_same_bios, NULL);
+	struct bio *bio = ci->bio;
+	sector_t bv_len, total_len = 0;
+
+	for (*idx = ci->idx; max && (*idx < bio->bi_vcnt); (*idx)++) {
+		bv_len = to_sector(bio->bi_io_vec[*idx].bv_len);
+
+		if (bv_len > max)
+			break;
+
+		max -= bv_len;
+		total_len += bv_len;
+	}
+
+	return total_len;
 }
 
+static int __split_bvec_across_targets(struct clone_info *ci,
+				       struct dm_target *ti, sector_t max)
+{
+	struct bio *bio = ci->bio;
+	struct bio_vec *bv = bio->bi_io_vec + ci->idx;
+	sector_t remaining = to_sector(bv->bv_len);
+	unsigned offset = 0;
+	sector_t len;
+
+	do {
+		if (offset) {
+			ti = dm_table_find_target(ci->map, ci->sector);
+			if (!dm_target_is_valid(ti))
+				return -EIO;
+
+			max = max_io_len(ci->sector, ti);
+		}
+
+		len = min(remaining, max);
+
+		__clone_and_map_data_bio(ci, ti, ci->sector, 1, ci->idx,
+					 bv->bv_offset + offset, len, 1);
+
+		ci->sector += len;
+		ci->sector_count -= len;
+		offset += to_bytes(len);
+	} while (remaining -= len);
+
+	ci->idx++;
+
+	return 0;
+}
+
+/*
+ * Select the correct strategy to for processing a bio.
+ */
 static int __clone_and_map(struct clone_info *ci)
 {
 	struct bio *bio = ci->bio;
 	struct dm_target *ti;
-	sector_t len = 0, max;
-	struct dm_target_io *tio;
+	sector_t len, max;
+	int idx;
 
 	if (unlikely(bio->bi_rw & REQ_DISCARD))
-		return __clone_and_map_discard(ci);
+		return __send_discard(ci);
 	else if (unlikely(bio->bi_rw & REQ_WRITE_SAME))
-		return __clone_and_map_write_same(ci);
+		return __send_write_same(ci);
 
 	ti = dm_table_find_target(ci->map, ci->sector);
 	if (!dm_target_is_valid(ti))
@@ -1259,78 +1332,45 @@ static int __clone_and_map(struct clone_
 
 	max = max_io_len(ci->sector, ti);
 
+	/*
+	 * Optimise for the simple case where we can do all of
+	 * the remaining io with a single clone.
+	 */
 	if (ci->sector_count <= max) {
-		/*
-		 * Optimise for the simple case where we can do all of
-		 * the remaining io with a single clone.
-		 */
-		__clone_and_map_simple(ci, ti);
-
-	} else if (to_sector(bio->bi_io_vec[ci->idx].bv_len) <= max) {
-		/*
-		 * There are some bvecs that don't span targets.
-		 * Do as many of these as possible.
-		 */
-		int i;
-		sector_t remaining = max;
-		sector_t bv_len;
+		__clone_and_map_data_bio(ci, ti, ci->sector, bio->bi_max_vecs,
+					 ci->idx, bio->bi_vcnt - ci->idx,
+					 ci->sector_count, 0);
 
-		for (i = ci->idx; remaining && (i < bio->bi_vcnt); i++) {
-			bv_len = to_sector(bio->bi_io_vec[i].bv_len);
+		ci->sector_count = 0;
 
-			if (bv_len > remaining)
-				break;
+		return 0;
+	}
 
-			remaining -= bv_len;
-			len += bv_len;
-		}
+	/*
+	 * There are some bvecs that don't span targets.
+	 * Do as many of these as possible.
+	 */
+	if (to_sector(bio->bi_io_vec[ci->idx].bv_len) <= max) {
+		len = __len_within_target(ci, max, &idx);
 
-		tio = alloc_tio(ci, ti, bio->bi_max_vecs, 0);
-		clone_bio(tio, bio, ci->sector, ci->idx, i - ci->idx, len);
-		__map_bio(tio);
+		__clone_and_map_data_bio(ci, ti, ci->sector, bio->bi_max_vecs,
+					 ci->idx, idx - ci->idx, len, 0);
 
 		ci->sector += len;
 		ci->sector_count -= len;
-		ci->idx = i;
-
-	} else {
-		/*
-		 * Handle a bvec that must be split between two or more targets.
-		 */
-		struct bio_vec *bv = bio->bi_io_vec + ci->idx;
-		sector_t remaining = to_sector(bv->bv_len);
-		unsigned int offset = 0;
+		ci->idx = idx;
 
-		do {
-			if (offset) {
-				ti = dm_table_find_target(ci->map, ci->sector);
-				if (!dm_target_is_valid(ti))
-					return -EIO;
-
-				max = max_io_len(ci->sector, ti);
-			}
-
-			len = min(remaining, max);
-
-			tio = alloc_tio(ci, ti, 1, 0);
-			split_bvec(tio, bio, ci->sector, ci->idx,
-				   bv->bv_offset + offset, len);
-
-			__map_bio(tio);
-
-			ci->sector += len;
-			ci->sector_count -= len;
-			offset += to_bytes(len);
-		} while (remaining -= len);
-
-		ci->idx++;
+		return 0;
 	}
 
-	return 0;
+	/*
+	 * Handle a bvec that must be split between two or more targets.
+	 */
+	return __split_bvec_across_targets(ci, ti, max);
 }
 
 /*
- * Split the bio into several clones and submit it to targets.
+ * Entry point to split the bio into several clones and submit it to targets.
  */
 static void __split_and_process_bio(struct mapped_device *md, struct bio *bio)
 {
@@ -1358,7 +1398,7 @@ static void __split_and_process_bio(stru
 	if (bio->bi_rw & REQ_FLUSH) {
 		ci.bio = &ci.md->flush_bio;
 		ci.sector_count = 0;
-		error = __clone_and_map_empty_flush(&ci);
+		error = __send_empty_flush(&ci);
 		/* dec_pending submits any data associated with flush */
 	} else {
 		ci.bio = bio;
Index: linux/include/linux/device-mapper.h
===================================================================
--- linux.orig/include/linux/device-mapper.h
+++ linux/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;