[RFC PATCH] dm-zoned: extend the way of exposing zoned block device

[Nobody <Nobody@nobody.com>]

From: Bob Liu <bob.liu@oracle.com>

Motivation:
Now the dm-zoned device mapper target exposes a zoned block device(ZBC) as a
regular block device by storing metadata and buffering random writes in
conventional zones.
This way is not very flexible, there must be enough conventional zones and the
performance may be constrained.
By putting metadata(also buffering random writes) in separated device we can get
more flexibility and potential performance improvement e.g by storing metadata
in faster device like persistent memory.

This patch try to split the metadata of dm-zoned to an extra block
device instead of zoned block device itself.
(Buffering random writes also in the todo list.)

Patch is at the very early stage, just want to receive some feedback about
this extension.
Another option is to create an new md-zoned device with separated metadata
device based on md framework.

Signed-off-by: Bob Liu <bob.liu@oracle.com>
---
 drivers/md/dm-zoned-metadata.c |  6 +++---
 drivers/md/dm-zoned-target.c   | 15 +++++++++++++--
 drivers/md/dm-zoned.h          |  1 +
 3 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/drivers/md/dm-zoned-metadata.c b/drivers/md/dm-zoned-metadata.c
index 22b3cb0..89cd554 100644
--- a/drivers/md/dm-zoned-metadata.c
+++ b/drivers/md/dm-zoned-metadata.c
@@ -439,7 +439,7 @@ static struct dmz_mblock *dmz_get_mblock_slow(struct dmz_metadata *zmd,
 
 	/* Submit read BIO */
 	bio->bi_iter.bi_sector = dmz_blk2sect(block);
-	bio_set_dev(bio, zmd->dev->bdev);
+	bio_set_dev(bio, zmd->dev->meta_bdev);
 	bio->bi_private = mblk;
 	bio->bi_end_io = dmz_mblock_bio_end_io;
 	bio_set_op_attrs(bio, REQ_OP_READ, REQ_META | REQ_PRIO);
@@ -593,7 +593,7 @@ static int dmz_write_mblock(struct dmz_metadata *zmd, struct dmz_mblock *mblk,
 	set_bit(DMZ_META_WRITING, &mblk->state);
 
 	bio->bi_iter.bi_sector = dmz_blk2sect(block);
-	bio_set_dev(bio, zmd->dev->bdev);
+	bio_set_dev(bio, zmd->dev->meta_bdev);
 	bio->bi_private = mblk;
 	bio->bi_end_io = dmz_mblock_bio_end_io;
 	bio_set_op_attrs(bio, REQ_OP_WRITE, REQ_META | REQ_PRIO);
@@ -620,7 +620,7 @@ static int dmz_rdwr_block(struct dmz_metadata *zmd, int op, sector_t block,
 		return -ENOMEM;
 
 	bio->bi_iter.bi_sector = dmz_blk2sect(block);
-	bio_set_dev(bio, zmd->dev->bdev);
+	bio_set_dev(bio, zmd->dev->meta_bdev);
 	bio_set_op_attrs(bio, op, REQ_SYNC | REQ_META | REQ_PRIO);
 	bio_add_page(bio, page, DMZ_BLOCK_SIZE, 0);
 	ret = submit_bio_wait(bio);
diff --git a/drivers/md/dm-zoned-target.c b/drivers/md/dm-zoned-target.c
index 70a1063..55c64fe 100644
--- a/drivers/md/dm-zoned-target.c
+++ b/drivers/md/dm-zoned-target.c
@@ -39,6 +39,7 @@ struct dm_chunk_work {
  */
 struct dmz_target {
 	struct dm_dev		*ddev;
+	struct dm_dev           *metadata_dev;
 
 	unsigned long		flags;
 
@@ -701,6 +702,7 @@ static int dmz_get_zoned_device(struct dm_target *ti, char *path)
 		goto err;
 	}
 
+	dev->meta_bdev = dmz->metadata_dev->bdev;
 	dev->bdev = dmz->ddev->bdev;
 	(void)bdevname(dev->bdev, dev->name);
 
@@ -761,7 +763,7 @@ static int dmz_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 	int ret;
 
 	/* Check arguments */
-	if (argc != 1) {
+	if (argc != 2) {
 		ti->error = "Invalid argument count";
 		return -EINVAL;
 	}
@@ -774,8 +776,16 @@ static int dmz_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 	}
 	ti->private = dmz;
 
+	/* Get the metadata block device */
+	ret = dm_get_device(ti, argv[0], dm_table_get_mode(ti->table),
+			&dmz->metadata_dev);
+	if (ret) {
+		dmz->metadata_dev = NULL;
+		goto err;
+	}
+
 	/* Get the target zoned block device */
-	ret = dmz_get_zoned_device(ti, argv[0]);
+	ret = dmz_get_zoned_device(ti, argv[1]);
 	if (ret) {
 		dmz->ddev = NULL;
 		goto err;
@@ -856,6 +866,7 @@ static int dmz_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 err_dev:
 	dmz_put_zoned_device(ti);
 err:
+	dm_put_device(ti, dmz->metadata_dev);
 	kfree(dmz);
 
 	return ret;
diff --git a/drivers/md/dm-zoned.h b/drivers/md/dm-zoned.h
index 5b5e493..e789ff5 100644
--- a/drivers/md/dm-zoned.h
+++ b/drivers/md/dm-zoned.h
@@ -50,6 +50,7 @@
  */
 struct dmz_dev {
 	struct block_device	*bdev;
+	struct block_device     *meta_bdev;
 
 	char			name[BDEVNAME_SIZE];
 
-- 
2.9.5