[PATCH 1/4] md/raid10: prepare per-r10bio dev slot tracking

["Chen Cheng" <chencheng@fnnas.com>]

From: Chen Cheng <chencheng@fnnas.com>

raid10 reuses r10bio objects from both r10bio_pool and r10buf_pool. Track
the number of devs[] slots used by each request in the r10bio itself and
initialize it whenever one of these objects is reused.

No functional change yet. A later patch will use this width when reshape
changes conf->geo.raid_disks.
---
 drivers/md/raid10.c | 4 ++++
 drivers/md/raid10.h | 1 +
 2 files changed, 5 insertions(+)

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 0653b5d8545a..e93933632893 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -1540,6 +1540,7 @@ static void __make_request(struct mddev *mddev, struct bio *bio, int sectors)
 	r10_bio->sector = bio->bi_iter.bi_sector;
 	r10_bio->state = 0;
 	r10_bio->read_slot = -1;
+	r10_bio->used_nr_devs = conf->geo.raid_disks;
 	memset(r10_bio->devs, 0, sizeof(r10_bio->devs[0]) *
 			conf->geo.raid_disks);
 
@@ -1727,6 +1728,7 @@ static int raid10_handle_discard(struct mddev *mddev, struct bio *bio)
 	r10_bio->mddev = mddev;
 	r10_bio->state = 0;
 	r10_bio->sectors = 0;
+	r10_bio->used_nr_devs = geo->raid_disks;
 	memset(r10_bio->devs, 0, sizeof(r10_bio->devs[0]) * geo->raid_disks);
 	wait_blocked_dev(mddev, r10_bio);
 
@@ -3061,6 +3063,8 @@ static struct r10bio *raid10_alloc_init_r10buf(struct r10conf *conf)
 	else
 		nalloc = 2; /* recovery */
 
+	r10bio->used_nr_devs = nalloc;
+
 	for (i = 0; i < nalloc; i++) {
 		bio = r10bio->devs[i].bio;
 		rp = bio->bi_private;
diff --git a/drivers/md/raid10.h b/drivers/md/raid10.h
index ec79d87fb92f..92e8743023e6 100644
--- a/drivers/md/raid10.h
+++ b/drivers/md/raid10.h
@@ -127,6 +127,7 @@ struct r10bio {
 	 * if the IO is in READ direction, then this is where we read
 	 */
 	int			read_slot;
+	unsigned int		used_nr_devs;
 
 	struct list_head	retry_list;
 	/*
-- 
2.53.0