[PATCH 2/2] md: modify dm_io() so it could return bios instead of submitting it

[Robin Dong <robin.k.dong@gmail.com>]

From: Robin Dong <sanbai@taobao.com>

When trying to modify flashcache to request based (current it's bio based), we need
to make request from bios by ourselves, but dm_io() will submit these bios directly,
so we propose to modify the dm_io() to return bios instead of submiting it.

This could also improve the flexibility of dm_io().

Signed-off-by: Robin Dong <sanbai@taobao.com>
---
 drivers/md/dm.c               |   11 +++++++++++
 include/linux/device-mapper.h |    3 +++
 2 files changed, 14 insertions(+), 0 deletions(-)

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 4e09b6f..bf6e3bb 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1459,11 +1459,22 @@ static int dm_request_based(struct mapped_device *md)
 static void dm_request(struct request_queue *q, struct bio *bio)
 {
 	struct mapped_device *md = q->queuedata;
+	struct dm_table *map = dm_get_live_table(md);
+	struct dm_target *ti = dm_table_find_target(map, bio->bi_sector);
+
+	if (ti->type->mk_rq) {
+		ti->type->mk_rq(ti, q, bio);
+		goto out;
+	}
 
 	if (dm_request_based(md))
 		blk_queue_bio(q, bio);
 	else
 		_dm_request(q, bio);
+
+out:
+	dm_table_put(map);
+	return;
 }
 
 void dm_dispatch_request(struct request *rq)
diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index 38d27a1..2386389 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -50,6 +50,8 @@ typedef int (*dm_map_fn) (struct dm_target *ti, struct bio *bio,
 			  union map_info *map_context);
 typedef int (*dm_map_request_fn) (struct dm_target *ti, struct request *clone,
 				  union map_info *map_context);
+typedef int (*dm_make_request_fn) (struct dm_target *ti,
+				struct request_queue *q, struct bio *bio);
 
 /*
  * Returns:
@@ -136,6 +138,7 @@ struct target_type {
 	dm_dtr_fn dtr;
 	dm_map_fn map;
 	dm_map_request_fn map_rq;
+	dm_make_request_fn mk_rq;
 	dm_endio_fn end_io;
 	dm_request_endio_fn rq_end_io;
 	dm_presuspend_fn presuspend;
-- 
1.7.1