From f31c21e4365c02ccf7226c33ea978cd5dbfc351e Mon Sep 17 00:00:00 2001
From: NeilBrown <neilb@suse.com>
Date: Wed, 22 Nov 2017 14:25:18 +1100
Subject: [PATCH] dm: remove unused 'num_write_bios' target interface
Git-commit: f31c21e4365c02ccf7226c33ea978cd5dbfc351e
Patch-mainline: v4.16-rc1
References: bsc#1093023

No DM target provides num_write_bios and none has since dm-cache's
brief use in 2013.

Having the possibility of num_write_bios > 1 complicates bio
allocation.  So remove the interface and assume there is only one bio
needed.

If a target ever needs more, it must provide a suitable bioset and
allocate itself based on its particular needs.

(Coly Li: remove change of struct dm_target to keep kABI consistency)

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Coly Li <colyli@suse.de>

---
 drivers/md/dm.c               | 30 ++++++++++--------------------
 include/linux/device-mapper.h | 15 ---------------
 2 files changed, 10 insertions(+), 35 deletions(-)

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 07dec8ece083..2480c6abe8f1 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1319,32 +1319,22 @@ static int __send_empty_flush(struct clone_info *ci)
 }
 
 static int __clone_and_map_data_bio(struct clone_info *ci, struct dm_target *ti,
-				     sector_t sector, unsigned *len)
+				    sector_t sector, unsigned *len)
 {
 	struct bio *bio = ci->bio;
 	struct dm_target_io *tio;
-	unsigned target_bio_nr;
-	unsigned num_target_bios = 1;
-	int r = 0;
+	int r;
 
-	/*
-	 * 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, target_bio_nr);
-		tio->len_ptr = len;
-		r = clone_bio(tio, bio, sector, *len);
-		if (r < 0) {
-			free_tio(tio);
-			break;
-		}
-		__map_bio(tio);
+	tio = alloc_tio(ci, ti, 0);
+	tio->len_ptr = len;
+	r = clone_bio(tio, bio, sector, *len);
+	if (r < 0) {
+		free_tio(tio);
+		return r;
 	}
+	__map_bio(tio);
 
-	return r;
+	return 0;
 }
 
 typedef unsigned (*get_num_bios_fn)(struct dm_target *ti);
-- 
2.16.3