[v8,11/11] dm: add power-of-2 zoned target for non-power-of-2 zoned devices

Commit Message

Pankaj Raghav July 27, 2022, 4:22 p.m. UTC

Only power-of-2(po2) zoned devices were supported in linux but now non
power-of-2(npo2) zoned device support has been added to the block layer.

Filesystems such as F2FS and btrfs have support for zoned devices with
po2 zone size assumption. Before adding native support for npo2 zoned
devices, it was suggested to create a dm target for npo2 zoned device to
appear as a po2 target so that file systems can initially work without any
explicit changes by using this target.

The design of this target is very simple: introduce gaps between the
underlying device's zone size and the nearest po2 device zone size.
Device's actual zone size becomes the zone capacity of the target and
device's nearest po2 zone size becomes the target's zone size.

For e.g., a device with a zone size/capacity of 3M will have an equivalent
target layout as follows:

Device layout :-
zone capacity = 3M
zone size = 3M

|--------------|-------------|
0             3M            6M

Target layout :-
zone capacity=3M
zone size = 4M

|--------------|---|--------------|---|
0             3M  4M             7M  8M

All IOs will be remapped from target to the actual device location.

The area between target's zone capacity and zone size will be emulated
in the target.
The read IOs that fall in the emulated gap area will return 0 filled
bio and all the other IOs in that area will result in an error.
If a read IO span across the emulated area boundary, then the IOs are
split across them. All other IO operations that span across the emulated
area boundary will result in an error.

The target can be easily created as follows:
dmsetup create <label> --table '0 <size_sects> po2z /dev/nvme<id>'

Signed-off-by: Pankaj Raghav <[e-mail]>
Suggested-by: Johannes Thumshirn <[e-mail]>
Suggested-by: Damien Le Moal <[e-mail]>
Suggested-by: Hannes Reinecke <[e-mail]>
---
 drivers/md/Kconfig            |   9 ++
 drivers/md/Makefile           |   2 +
 drivers/md/dm-po2z-target.c   | 261 ++++++++++++++++++++++++++++++++++
 drivers/md/dm-table.c         |  13 +-
 drivers/md/dm-zone.c          |   1 +
 include/linux/device-mapper.h |   9 ++
 6 files changed, 292 insertions(+), 3 deletions(-)
 create mode 100644 drivers/md/dm-po2z-target.c

Comments

Damien Le Moal July 28, 2022, 4:33 a.m. UTC | #1

On 7/28/22 01:22, Pankaj Raghav wrote:
> Only power-of-2(po2) zoned devices were supported in linux but now non
> power-of-2(npo2) zoned device support has been added to the block layer.

Please rephrase this spelling out "zone size" in the text. As mentioned
before, "power-of-2(po2) zoned devices" is very unclear to people not
familiar with zoned block devices.

> 
> Filesystems such as F2FS and btrfs have support for zoned devices with
> po2 zone size assumption. Before adding native support for npo2 zoned
> devices, it was suggested to create a dm target for npo2 zoned device to
> appear as a po2 target so that file systems can initially work without any
> explicit changes by using this target.
> 
> The design of this target is very simple: introduce gaps between the
> underlying device's zone size and the nearest po2 device zone size.
> Device's actual zone size becomes the zone capacity of the target and
> device's nearest po2 zone size becomes the target's zone size.

The design of this target is very simple: remap the device zone size to
the zone capacity and change the zone size to be the nearest power of 2
numner of sectors.

> 
> For e.g., a device with a zone size/capacity of 3M will have an equivalent
> target layout as follows:
> 
> Device layout :-
> zone capacity = 3M
> zone size = 3M
> 
> |--------------|-------------|
> 0             3M            6M
> 
> Target layout :-
> zone capacity=3M
> zone size = 4M
> 
> |--------------|---|--------------|---|
> 0             3M  4M             7M  8M
> 
> All IOs will be remapped from target to the actual device location.

That is what DM does... Instead of this obvious statement, explain how the
remapping is done.

> 
> The area between target's zone capacity and zone size will be emulated
> in the target.
> The read IOs that fall in the emulated gap area will return 0 filled
> bio and all the other IOs in that area will result in an error.
> If a read IO span across the emulated area boundary, then the IOs are
> split across them. All other IO operations that span across the emulated
> area boundary will result in an error.
> 
> The target can be easily created as follows:
> dmsetup create <label> --table '0 <size_sects> po2z /dev/nvme<id>'

0 -> <start offset> ? Or are you allowing only entire devices ?

> 
> Signed-off-by: Pankaj Raghav <[e-mail]>
> Suggested-by: Johannes Thumshirn <[e-mail]>
> Suggested-by: Damien Le Moal <[e-mail]>
> Suggested-by: Hannes Reinecke <[e-mail]>
> ---
>  drivers/md/Kconfig            |   9 ++
>  drivers/md/Makefile           |   2 +
>  drivers/md/dm-po2z-target.c   | 261 ++++++++++++++++++++++++++++++++++
>  drivers/md/dm-table.c         |  13 +-
>  drivers/md/dm-zone.c          |   1 +
>  include/linux/device-mapper.h |   9 ++
>  6 files changed, 292 insertions(+), 3 deletions(-)
>  create mode 100644 drivers/md/dm-po2z-target.c
> 
> diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
> index 998a5cfdbc4e..d58ccfee765b 100644
> --- a/drivers/md/Kconfig
> +++ b/drivers/md/Kconfig
> @@ -518,6 +518,15 @@ config DM_FLAKEY
>  	help
>  	 A target that intermittently fails I/O for debugging purposes.
>  
> +config DM_PO2Z

Maybe DM_PO2_ZONE ?

or DM_ZONE_PO2SIZE ?

To be clearer...

> +	tristate "Power-of-2 target for non power-of-2 zoned devices"

...for zoned block devices with a zone size that is not a power of 2
number of sectors.

> +	depends on BLK_DEV_DM
> +	depends on BLK_DEV_ZONED
> +	help
> +	  A target that converts a zoned device with non power-of-2 zone size to
> +	  be power of 2. This is done by introducing gaps in between the zone

...to have zones with size equal to a power of 2 n umber of sectors. And
drop the "This done...".
How the target works and how to use it should be documented under
Documentation/admin-guide/device-mapper/

> +	  capacity and the power of 2 zone size.
> +
>  config DM_VERITY
>  	tristate "Verity target support"
>  	depends on BLK_DEV_DM
> diff --git a/drivers/md/Makefile b/drivers/md/Makefile
> index 270f694850ec..98af4ed98f73 100644
> --- a/drivers/md/Makefile
> +++ b/drivers/md/Makefile
> @@ -26,6 +26,7 @@ dm-era-y	+= dm-era-target.o
>  dm-clone-y	+= dm-clone-target.o dm-clone-metadata.o
>  dm-verity-y	+= dm-verity-target.o
>  dm-zoned-y	+= dm-zoned-target.o dm-zoned-metadata.o dm-zoned-reclaim.o
> +dm-po2z-y       += dm-po2z-target.o

dm-po2zone ?

Spelling out "zone" makes things clearer I think.

>  
>  md-mod-y	+= md.o md-bitmap.o
>  raid456-y	+= raid5.o raid5-cache.o raid5-ppl.o
> @@ -60,6 +61,7 @@ obj-$(CONFIG_DM_CRYPT)		+= dm-crypt.o
>  obj-$(CONFIG_DM_DELAY)		+= dm-delay.o
>  obj-$(CONFIG_DM_DUST)		+= dm-dust.o
>  obj-$(CONFIG_DM_FLAKEY)		+= dm-flakey.o
> +obj-$(CONFIG_DM_PO2Z)		+= dm-po2z.o
>  obj-$(CONFIG_DM_MULTIPATH)	+= dm-multipath.o dm-round-robin.o
>  obj-$(CONFIG_DM_MULTIPATH_QL)	+= dm-queue-length.o
>  obj-$(CONFIG_DM_MULTIPATH_ST)	+= dm-service-time.o
> diff --git a/drivers/md/dm-po2z-target.c b/drivers/md/dm-po2z-target.c
> new file mode 100644
> index 000000000000..e9c5b7d00eda
> --- /dev/null
> +++ b/drivers/md/dm-po2z-target.c
> @@ -0,0 +1,261 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2022 Samsung Electronics Co., Ltd.
> + */
> +
> +#include <linux/device-mapper.h>
> +
> +#define DM_MSG_PREFIX "po2z"

s/po2z/po2zone ?

> +
> +struct dm_po2z_target {
> +	struct dm_dev *dev;
> +	sector_t zone_size; /* Actual zone size of the underlying dev*/
> +	sector_t zone_size_po2; /* zone_size rounded to the nearest po2 value */
> +	sector_t zone_size_diff; /* diff between zone_size_po2 and zone_size */
> +	u32 nr_zones;

s/u32/unsigned int. This is not a hw driver.

> +};
> +
> +static inline u32 npo2_zone_no(struct dm_po2z_target *dmh, sector_t sect)
> +{
> +	return div64_u64(sect, dmh->zone_size);
> +}
> +
> +static inline u32 po2_zone_no(struct dm_po2z_target *dmh, sector_t sect)
> +{
> +	return sect >> ilog2(dmh->zone_size_po2);

You could saves the shift as "zone_size_po2_shift" in struct dm_po2z_target.

> +}
> +
> +static inline sector_t target_to_device_sect(struct dm_po2z_target *dmh,
> +					     sector_t sect)
> +{
> +	u32 zone_idx = po2_zone_no(dmh, sect);
> +
> +	return sect - (zone_idx * dmh->zone_size_diff);

The idx variable seems unnecessary. And use unsgined int, not u32.

> +}
> +
> +static inline sector_t device_to_target_sect(struct dm_po2z_target *dmh,
> +					     sector_t sect)
> +{
> +	u32 zone_idx = npo2_zone_no(dmh, sect);
> +
> +	return sect + (zone_idx * dmh->zone_size_diff);

same.

> +}
> +
> +/*
> + * This target works on the complete zoned device. Partial mapping is not
> + * supported.
> + * Construct a zoned po2 logical device: <dev-path>
> + */
> +static int dm_po2z_ctr(struct dm_target *ti, unsigned int argc, char **argv)
> +{
> +	struct dm_po2z_target *dmh = NULL;
> +	int ret;
> +	sector_t zone_size;
> +	sector_t dev_capacity;
> +
> +	if (argc < 1)

	if (argc != 1) ?

> +		return -EINVAL;
> +
> +	dmh = kmalloc(sizeof(*dmh), GFP_KERNEL);
> +	if (!dmh)
> +		return -ENOMEM;
> +
> +	ret = dm_get_device(ti, argv[0], dm_table_get_mode(ti->table),
> +			    &dmh->dev);
> +
> +	if (ret) {
> +		ti->error = "Device lookup failed";
> +		return ret;

You are leaking dmh.

> +	}
> +
> +	zone_size = bdev_zone_sectors(dmh->dev->bdev);
> +	dev_capacity = get_capacity(dmh->dev->bdev->bd_disk);
> +	if (ti->len != dev_capacity || ti->begin) {
> +		DMERR("%pg Partial mapping of the target not supported",
> +		      dmh->dev->bdev);

dmh is leaked.

> +		return -EINVAL;
> +	}
> +
> +	if (is_power_of_2(zone_size)) {
> +		DMERR("%pg: this target is not useful for power-of-2 zoned devices",
> +		      dmh->dev->bdev);
> +		return -EINVAL;

Same here.

And as suggested before, we could simply warn here but let the target be
created. If used with a power of 2 zone size device, it should still work.

> +	}
> +
> +	dmh->zone_size = zone_size;
> +	dmh->zone_size_po2 = 1 << get_count_order_long(zone_size);
> +	dmh->zone_size_diff = dmh->zone_size_po2 - dmh->zone_size;
> +	ti->private = dmh;
> +	dmh->nr_zones = npo2_zone_no(dmh, ti->len);
> +	ti->len = dmh->zone_size_po2 * dmh->nr_zones;
> +
> +	return 0;
> +}
> +
> +static int dm_po2z_report_zones_cb(struct blk_zone *zone, unsigned int idx,
> +				   void *data)
> +{
> +	struct dm_report_zones_args *args = data;
> +	struct dm_po2z_target *dmh = args->tgt->private;
> +
> +	zone->start = device_to_target_sect(dmh, zone->start);
> +	zone->wp = device_to_target_sect(dmh, zone->wp);

You could simplify this to a single call to device_to_target_sect() by
saving the diff between device zone start and remapped zone start and add
that diff to the wp field.

> +	zone->len = dmh->zone_size_po2;
> +	args->next_sector = zone->start + zone->len;
> +
> +	return args->orig_cb(zone, args->zone_idx++, args->orig_data);
> +}
> +
> +static int dm_po2z_report_zones(struct dm_target *ti,
> +				struct dm_report_zones_args *args,
> +				unsigned int nr_zones)
> +{
> +	struct dm_po2z_target *dmh = ti->private;
> +	sector_t sect = po2_zone_no(dmh, args->next_sector) * dmh->zone_size;
> +
> +	return blkdev_report_zones(dmh->dev->bdev, sect, nr_zones,
> +				   dm_po2z_report_zones_cb, args);
> +}
> +
> +static int dm_po2z_end_io(struct dm_target *ti, struct bio *bio,
> +			  blk_status_t *error)
> +{
> +	struct dm_po2z_target *dmh = ti->private;
> +
> +	if (bio->bi_status == BLK_STS_OK && bio_op(bio) == REQ_OP_ZONE_APPEND)
> +		bio->bi_iter.bi_sector =
> +			device_to_target_sect(dmh, bio->bi_iter.bi_sector);
> +
> +	return DM_ENDIO_DONE;
> +}
> +
> +static void dm_po2z_io_hints(struct dm_target *ti, struct queue_limits *limits)
> +{
> +	struct dm_po2z_target *dmh = ti->private;
> +
> +	limits->chunk_sectors = dmh->zone_size_po2;
> +}
> +
> +static bool bio_across_emulated_zone_area(struct dm_po2z_target *dmh,
> +					  struct bio *bio)
> +{
> +	u32 zone_idx = po2_zone_no(dmh, bio->bi_iter.bi_sector);
> +	sector_t size = bio->bi_iter.bi_size >> SECTOR_SHIFT;

Rename that to nr_sectors to be clear about the unit.

> +
> +	return (bio->bi_iter.bi_sector - (zone_idx * dmh->zone_size_po2) +
> +		size) > dmh->zone_size;

This is hard to read and actually seems very wrong. Shouldn't this be simply:

	return bio->bi_iter.bi_sector + nr_sectors >
		zone_idx * dmh->zone_size_po2 + dmh->zone_size;

Thatis, check that the BIO goes beyond the zone capacity of the target.
?

> +}
> +
> +static int dm_po2z_map_read(struct dm_po2z_target *dmh, struct bio *bio)
> +{
> +	sector_t start_sect, size, relative_sect_in_zone, split_io_pos;
> +	u32 zone_idx;
> +
> +	/*
> +	 * Read does not extend into the emulated zone area (area between
> +	 * zone capacity and zone size)
> +	 */
> +	if (!bio_across_emulated_zone_area(dmh, bio)) {

hu... why not use dm_accept_partial_bio() in dm_po2z_map() to never have
to deal with this here ? That is, dm_po2z_map_read() is called for any
read BIO fully within the zone capacity. And create a
dm_po2z_map_read_zero() helper for any read BIO that is after the zone
capacity. Way simpler I think.

> +		bio->bi_iter.bi_sector =
> +			target_to_device_sect(dmh, bio->bi_iter.bi_sector);
> +		return DM_MAPIO_REMAPPED;
> +	}
> +
> +	start_sect = bio->bi_iter.bi_sector;
> +	size = bio->bi_iter.bi_size >> SECTOR_SHIFT;
> +	zone_idx = po2_zone_no(dmh, start_sect);
> +	relative_sect_in_zone = start_sect - (zone_idx * dmh->zone_size_po2);
> +
> +	/*
> +	 * If the starting sector is in the emulated area then fill
> +	 * all the bio with zeros. If bio is across emulated zone boundary,
> +	 * split the bio across boundaries and fill zeros only for the
> +	 * bio that is between the zone capacity and the zone size.
> +	 */
> +	if (relative_sect_in_zone < dmh->zone_size &&
> +	    ((relative_sect_in_zone + size) > dmh->zone_size)) {
> +		split_io_pos = (zone_idx * dmh->zone_size_po2) + dmh->zone_size;
> +		dm_accept_partial_bio(bio, split_io_pos - start_sect);

See above. Do that in dm_po2z_map(). This will simplify this function.

> +		bio->bi_iter.bi_sector = target_to_device_sect(dmh, start_sect);
> +
> +		return DM_MAPIO_REMAPPED;
> +	} else if (relative_sect_in_zone >= dmh->zone_size &&
> +		   ((relative_sect_in_zone + size) > dmh->zone_size_po2)) {

No need for the else after return. And this can NEVER happen since BIOs
can never cross zone boundaries.

> +		split_io_pos = (zone_idx + 1) * dmh->zone_size_po2;
> +		dm_accept_partial_bio(bio, split_io_pos - start_sect);
> +	}
> +
> +	zero_fill_bio(bio);
> +	bio_endio(bio);
> +	return DM_MAPIO_SUBMITTED;
> +}
> +
> +static int dm_po2z_map(struct dm_target *ti, struct bio *bio)
> +{
> +	struct dm_po2z_target *dmh = ti->private;
> +
> +	bio_set_dev(bio, dmh->dev->bdev);
> +	if (bio_sectors(bio) || op_is_zone_mgmt(bio_op(bio))) {
> +		/*
> +		 * Read operation on the emulated zone area (between zone capacity
> +		 * and zone size) will fill the bio with zeroes. Any other operation
> +		 * in the emulated area should return an error.
> +		 */
> +		if (bio_op(bio) == REQ_OP_READ)
> +			return dm_po2z_map_read(dmh, bio);
> +
> +		if (!bio_across_emulated_zone_area(dmh, bio)) {
> +			bio->bi_iter.bi_sector = target_to_device_sect(dmh,
> +								       bio->bi_iter.bi_sector);
> +			return DM_MAPIO_REMAPPED;
> +		}
> +		return DM_MAPIO_KILL;
> +	}
> +	return DM_MAPIO_REMAPPED;
> +}
> +
> +static int dm_po2z_iterate_devices(struct dm_target *ti,
> +				   iterate_devices_callout_fn fn, void *data)
> +{
> +	struct dm_po2z_target *dmh = ti->private;
> +	sector_t len = dmh->nr_zones * dmh->zone_size;
> +
> +	return fn(ti, dmh->dev, 0, len, data);
> +}
> +
> +static struct target_type dm_po2z_target = {
> +	.name = "po2z",
> +	.version = { 1, 0, 0 },
> +	.features = DM_TARGET_ZONED_HM | DM_TARGET_EMULATED_ZONES,
> +	.map = dm_po2z_map,
> +	.end_io = dm_po2z_end_io,
> +	.report_zones = dm_po2z_report_zones,
> +	.iterate_devices = dm_po2z_iterate_devices,
> +	.module = THIS_MODULE,
> +	.io_hints = dm_po2z_io_hints,
> +	.ctr = dm_po2z_ctr,
> +};
> +
> +static int __init dm_po2z_init(void)
> +{
> +	int r = dm_register_target(&dm_po2z_target);
> +
> +	if (r < 0)
> +		DMERR("register failed %d", r);
> +
> +	return r;

Simplify:

	return dm_register_target(&dm_po2z_target);

> +}
> +
> +static void __exit dm_po2z_exit(void)
> +{
> +	dm_unregister_target(&dm_po2z_target);
> +}
> +
> +/* Module hooks */
> +module_init(dm_po2z_init);
> +module_exit(dm_po2z_exit);
> +
> +MODULE_DESCRIPTION(DM_NAME "power-of-2 zoned target");
> +MODULE_AUTHOR("Pankaj Raghav <[e-mail]>");
> +MODULE_LICENSE("GPL");
> +

the changes below should be a different prep patch.

> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> index 534fddfc2b42..d77feff124af 100644
> --- a/drivers/md/dm-table.c
> +++ b/drivers/md/dm-table.c
> @@ -1614,13 +1614,20 @@ static bool dm_table_supports_zoned_model(struct dm_table *t,
>  	return true;
>  }
>  
> -static int device_not_matches_zone_sectors(struct dm_target *ti, struct dm_dev *dev,
> +/*
> + * Callback function to check for device zone sector across devices. If the
> + * DM_TARGET_EMULATED_ZONES target feature flag is not set, then the target
> + * should have the same zone sector as the underlying devices.
> + */
> +static int check_valid_device_zone_sectors(struct dm_target *ti, struct dm_dev *dev,
>  					   sector_t start, sector_t len, void *data)
>  {
>  	unsigned int *zone_sectors = data;
>  
> -	if (!bdev_is_zoned(dev->bdev))
> +	if (!bdev_is_zoned(dev->bdev) ||
> +	    dm_target_supports_emulated_zones(ti->type))
>  		return 0;
> +
>  	return bdev_zone_sectors(dev->bdev) != *zone_sectors;
>  }
>  
> @@ -1646,7 +1653,7 @@ static int validate_hardware_zoned_model(struct dm_table *t,
>  	if (!zone_sectors)
>  		return -EINVAL;
>  
> -	if (dm_table_any_dev_attr(t, device_not_matches_zone_sectors, &zone_sectors)) {
> +	if (dm_table_any_dev_attr(t, check_valid_device_zone_sectors, &zone_sectors)) {
>  		DMERR("%s: zone sectors is not consistent across all zoned devices",
>  		      dm_device_name(t->md));
>  		return -EINVAL;
> diff --git a/drivers/md/dm-zone.c b/drivers/md/dm-zone.c
> index 31c16aafdbfc..2b6b3883471f 100644
> --- a/drivers/md/dm-zone.c
> +++ b/drivers/md/dm-zone.c
> @@ -302,6 +302,7 @@ int dm_set_zones_restrictions(struct dm_table *t, struct request_queue *q)
>  	if (dm_table_supports_zone_append(t)) {
>  		clear_bit(DMF_EMULATE_ZONE_APPEND, &md->flags);
>  		dm_cleanup_zoned_dev(md);
> +
>  		return 0;
>  	}
>  
> diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
> index 920085dd7f3b..7dbd28b8de01 100644
> --- a/include/linux/device-mapper.h
> +++ b/include/linux/device-mapper.h
> @@ -294,6 +294,15 @@ struct target_type {
>  #define dm_target_supports_mixed_zoned_model(type) (false)
>  #endif
>  
> +#ifdef CONFIG_BLK_DEV_ZONED
> +#define DM_TARGET_EMULATED_ZONES	0x00000400
> +#define dm_target_supports_emulated_zones(type) \
> +	((type)->features & DM_TARGET_EMULATED_ZONES)
> +#else
> +#define DM_TARGET_EMULATED_ZONES	0x00000000
> +#define dm_target_supports_emulated_zones(type) (false)
> +#endif
> +
>  struct dm_target {
>  	struct dm_table *table;
>  	struct target_type *type;

Pankaj Raghav Aug. 1, 2022, 8:35 a.m. UTC | #2

On 2022-07-28 06:33, Damien Le Moal wrote:
>>
>> The area between target's zone capacity and zone size will be emulated
>> in the target.
>> The read IOs that fall in the emulated gap area will return 0 filled
>> bio and all the other IOs in that area will result in an error.
>> If a read IO span across the emulated area boundary, then the IOs are
>> split across them. All other IO operations that span across the emulated
>> area boundary will result in an error.
>>
>> The target can be easily created as follows:
>> dmsetup create <label> --table '0 <size_sects> po2z /dev/nvme<id>'
> 
> 0 -> <start offset> ? Or are you allowing only entire devices ?
> 
Yeah, partially mapping is not allowed.
>>
>> Signed-off-by: Pankaj Raghav <[e-mail]>
>> Suggested-by: Johannes Thumshirn <[e-mail]>
>> Suggested-by: Damien Le Moal <[e-mail]>
>> Suggested-by: Hannes Reinecke <[e-mail]>
>> ---
>>  drivers/md/Kconfig            |   9 ++
>>  drivers/md/Makefile           |   2 +
>>  drivers/md/dm-po2z-target.c   | 261 ++++++++++++++++++++++++++++++++++
>>  drivers/md/dm-table.c         |  13 +-
>>  drivers/md/dm-zone.c          |   1 +
>>  include/linux/device-mapper.h |   9 ++
>>  6 files changed, 292 insertions(+), 3 deletions(-)
>>  create mode 100644 drivers/md/dm-po2z-target.c
>>
>> diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
>> index 998a5cfdbc4e..d58ccfee765b 100644
>> --- a/drivers/md/Kconfig
>> +++ b/drivers/md/Kconfig
>> @@ -518,6 +518,15 @@ config DM_FLAKEY
>>  	help
>>  	 A target that intermittently fails I/O for debugging purposes.
>>  
>> +config DM_PO2Z
> 
> Maybe DM_PO2_ZONE ?
> 
I prefer this.

> or DM_ZONE_PO2SIZE ?
> 
> To be clearer...
> 
>> +
>> +struct dm_po2z_target {
>> +	struct dm_dev *dev;
>> +	sector_t zone_size; /* Actual zone size of the underlying dev*/
>> +	sector_t zone_size_po2; /* zone_size rounded to the nearest po2 value */
>> +	sector_t zone_size_diff; /* diff between zone_size_po2 and zone_size */
>> +	u32 nr_zones;
> 
> s/u32/unsigned int. This is not a hw driver.
> 
Ok.
>> +}
>> +
>> +/*
>> + * This target works on the complete zoned device. Partial mapping is not
>> + * supported.
>> + * Construct a zoned po2 logical device: <dev-path>
>> + */
>> +static int dm_po2z_ctr(struct dm_target *ti, unsigned int argc, char **argv)
>> +{
>> +	struct dm_po2z_target *dmh = NULL;
>> +	int ret;
>> +	sector_t zone_size;
>> +		return -EINVAL;
>> +	}
>> +
>> +	if (is_power_of_2(zone_size)) {
>> +		DMERR("%pg: this target is not useful for power-of-2 zoned devices",
>> +		      dmh->dev->bdev);
>> +		return -EINVAL;
> 
> Same here.
> 
> And as suggested before, we could simply warn here but let the target be
> created. If used with a power of 2 zone size device, it should still work.
> 
I will do this in the next revision. I will change DMERR to DMWARN with
no return err.
>> +	}
>> +
>> +	dmh->zone_size = zone_size;
>> +	dmh->zone_size_po2 = 1 << get_count_order_long(zone_size);
>> +	dmh->zone_size_diff = dmh->zone_size_po2 - dmh->zone_size;
>> +	ti->private = dmh;
>> +	dmh->nr_zones = npo2_zone_no(dmh, ti->len);
>> +	ti->len = dmh->zone_size_po2 * dmh->nr_zones;
>> +
>> +	return 0;
>> +}
>> +
>> +
>> +static int dm_po2z_end_io(struct dm_target *ti, struct bio *bio,
>> +			  blk_status_t *error)
>> +{
>> +	struct dm_po2z_target *dmh = ti->private;
>> +
>> +	if (bio->bi_status == BLK_STS_OK && bio_op(bio) == REQ_OP_ZONE_APPEND)
>> +		bio->bi_iter.bi_sector =
>> +			device_to_target_sect(dmh, bio->bi_iter.bi_sector);
>> +
>> +	return DM_ENDIO_DONE;
>> +}
>> +
>> +static void dm_po2z_io_hints(struct dm_target *ti, struct queue_limits *limits)
>> +{
>> +	struct dm_po2z_target *dmh = ti->private;
>> +
>> +	limits->chunk_sectors = dmh->zone_size_po2;
>> +}
>> +
>> +static bool bio_across_emulated_zone_area(struct dm_po2z_target *dmh,
>> +					  struct bio *bio)
>> +{
>> +	u32 zone_idx = po2_zone_no(dmh, bio->bi_iter.bi_sector);
>> +	sector_t size = bio->bi_iter.bi_size >> SECTOR_SHIFT;
> 
> Rename that to nr_sectors to be clear about the unit.
> 
>> +
>> +	return (bio->bi_iter.bi_sector - (zone_idx * dmh->zone_size_po2) +
>> +		size) > dmh->zone_size;
> 
> This is hard to read and actually seems very wrong. Shouldn't this be simply:
> 
> 	return bio->bi_iter.bi_sector + nr_sectors >
> 		zone_idx * dmh->zone_size_po2 + dmh->zone_size;
> 
> Thatis, check that the BIO goes beyond the zone capacity of the target.
> ?
> 
Yeah, this reads better. I will change it.
>> +}
>> +
>> +static int dm_po2z_map_read(struct dm_po2z_target *dmh, struct bio *bio)
>> +{
>> +	sector_t start_sect, size, relative_sect_in_zone, split_io_pos;
>> +	u32 zone_idx;
>> +
>> +	/*
>> +	 * Read does not extend into the emulated zone area (area between
>> +	 * zone capacity and zone size)
>> +	 */
>> +	if (!bio_across_emulated_zone_area(dmh, bio)) {
> 
> hu... why not use dm_accept_partial_bio() in dm_po2z_map() to never have
> to deal with this here ? That is, dm_po2z_map_read() is called for any
> read BIO fully within the zone capacity. And create a
> dm_po2z_map_read_zero() helper for any read BIO that is after the zone
> capacity. Way simpler I think.
> 
>> +		bio->bi_iter.bi_sector =
>> +			target_to_device_sect(dmh, bio->bi_iter.bi_sector);
>> +		return DM_MAPIO_REMAPPED;
>> +	}
>> +
>> +	start_sect = bio->bi_iter.bi_sector;
>> +	size = bio->bi_iter.bi_size >> SECTOR_SHIFT;
>> +	zone_idx = po2_zone_no(dmh, start_sect);
>> +	relative_sect_in_zone = start_sect - (zone_idx * dmh->zone_size_po2);
>> +
>> +	/*
>> +	 * If the starting sector is in the emulated area then fill
>> +	 * all the bio with zeros. If bio is across emulated zone boundary,
>> +	 * split the bio across boundaries and fill zeros only for the
>> +	 * bio that is between the zone capacity and the zone size.
>> +	 */
>> +	if (relative_sect_in_zone < dmh->zone_size &&
>> +	    ((relative_sect_in_zone + size) > dmh->zone_size)) {
>> +		split_io_pos = (zone_idx * dmh->zone_size_po2) + dmh->zone_size;
>> +		dm_accept_partial_bio(bio, split_io_pos - start_sect);
> 
> See above. Do that in dm_po2z_map(). This will simplify this function.
> 
>> +		bio->bi_iter.bi_sector = target_to_device_sect(dmh, start_sect);
>> +
>> +		return DM_MAPIO_REMAPPED;
>> +	} else if (relative_sect_in_zone >= dmh->zone_size &&
>> +		   ((relative_sect_in_zone + size) > dmh->zone_size_po2)) {
> 
> No need for the else after return. And this can NEVER happen since BIOs
> can never cross zone boundaries.
> 
This did not happen and that is why this else if condition was
introduced. But I had missed assigning the t->max_io_len in the ctr
which led to bio crossing the zone boundary.

With t->max_io_len set to zone_nr_sectors, we don't need the else if
condition and we can simplify the map_read.
Thanks for pointing it out.
>> +		split_io_pos = (zone_idx + 1) * dmh->zone_size_po2;
>> +		dm_accept_partial_bio(bio, split_io_pos - start_sect);
>> +	}
>> +
>> +	zero_fill_bio(bio);
>> +	bio_endio(bio);
>> +	return DM_MAPIO_SUBMITTED;
>> +}
>> +
>> +static int dm_po2z_map(struct dm_target *ti, struct bio *bio)
>> +{
>> +	struct dm_po2z_target *dmh = ti->private;
>> +
>> +	bio_set_dev(bio, dmh->dev->bdev);
>> +	if (bio_sectors(bio) || op_is_zone_mgmt(bio_op(bio))) {
>> +		/*
>> +		 * Read operation on the emulated zone area (between zone capacity
>> +		 * and zone size) will fill the bio with zeroes. Any other operation
>> +		 * in the emulated area should return an error.
>> +		 */
>> +		if (bio_op(bio) == REQ_OP_READ)
>> +			return dm_po2z_map_read(dmh, bio);
>> +
>> +		if (!bio_across_emulated_zone_area(dmh, bio)) {
>> +			bio->bi_iter.bi_sector = target_to_device_sect(dmh,
>> +								       bio->bi_iter.bi_sector);
>> +			return DM_MAPIO_REMAPPED;
>> +		}
>> +		return DM_MAPIO_KILL;
>> +	}
>> +	return DM_MAPIO_REMAPPED;
>> +}
>> +
>> +static int dm_po2z_iterate_devices(struct dm_target *ti,
>> +				   iterate_devices_callout_fn fn, void *data)
>> +{
>> +	struct dm_po2z_target *dmh = ti->private;
>> +	sector_t len = dmh->nr_zones * dmh->zone_size;
>> +
>> +	return fn(ti, dmh->dev, 0, len, data);
>> +}
>> +
>> +static struct target_type dm_po2z_target = {
>> +	.name = "po2z",
>> +	.version = { 1, 0, 0 },
>> +	.features = DM_TARGET_ZONED_HM | DM_TARGET_EMULATED_ZONES,
>> +	.map = dm_po2z_map,
>> +	.end_io = dm_po2z_end_io,
>> +	.report_zones = dm_po2z_report_zones,
>> +	.iterate_devices = dm_po2z_iterate_devices,
>> +	.module = THIS_MODULE,
>> +	.io_hints = dm_po2z_io_hints,
>> +	.ctr = dm_po2z_ctr,
>> +};
>> +
>> +static int __init dm_po2z_init(void)
>> +{
>> +	int r = dm_register_target(&dm_po2z_target);
>> +
>> +	if (r < 0)
>> +		DMERR("register failed %d", r);
>> +
>> +	return r;
> 
> Simplify:
> 
> 	return dm_register_target(&dm_po2z_target);
> 
>> +}
>> +
>> +static void __exit dm_po2z_exit(void)
>> +{
>> +	dm_unregister_target(&dm_po2z_target);
>> +}
>> +
>> +/* Module hooks */
>> +module_init(dm_po2z_init);
>> +module_exit(dm_po2z_exit);
>> +
>> +MODULE_DESCRIPTION(DM_NAME "power-of-2 zoned target");
>> +MODULE_AUTHOR("Pankaj Raghav <[e-mail]>");
>> +MODULE_LICENSE("GPL");
>> +
> 
> the changes below should be a different prep patch.
> 
Ok. `dm:introduce DM_EMULATED_ZONE target type` before introducing this
new target.

>> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
>> index 534fddfc2b42..d77feff124af 100644
>> --- a/drivers/md/dm-table.c
>> +++ b/drivers/md/dm-table.c
>> @@ -1614,13 +1614,20 @@ static bool dm_table_supports_zoned_model(struct dm_table *t,
>>  	return true;
>>  }
>>  
>> -static int device_not_matches_zone_sectors(struct dm_target *ti, struct dm_dev *dev,
>> +/*
>> + * Callback function to check for device zone sector across devices. If the
>> + * DM_TARGET_EMULATED_ZONES target feature flag is not set, then the target
>> + * should have the same zone sector as the underlying devices.
>> + */
>> +static int check_valid_device_zone_sectors(struct dm_target *ti, struct dm_dev *dev,
>>  					   sector_t start, sector_t len, void *data)
>>  {
>>  	unsigned int *zone_sectors = data;
>>  
>> -	if (!bdev_is_zoned(dev->bdev))
>> +	if (!bdev_is_zoned(dev->bdev) ||
>> +	    dm_target_supports_emulated_zones(ti->type))
>>  		return 0;
>> +
>>  	return bdev_zone_sectors(dev->bdev) != *zone_sectors;
>>  }
>>  
>> @@ -1646,7 +1653,7 @@ static int validate_hardware_zoned_model(struct dm_table *t,
>>  	if (!zone_sectors)
>>  		return -EINVAL;
>>  
>> -	if (dm_table_any_dev_attr(t, device_not_matches_zone_sectors, &zone_sectors)) {
>> +	if (dm_table_any_dev_attr(t, check_valid_device_zone_sectors, &zone_sectors)) {
>>  		DMERR("%s: zone sectors is not consistent across all zoned devices",
>>  		      dm_device_name(t->md));
>>  		return -EINVAL;
>> diff --git a/drivers/md/dm-zone.c b/drivers/md/dm-zone.c
>> index 31c16aafdbfc..2b6b3883471f 100644
>> --- a/drivers/md/dm-zone.c
>> +++ b/drivers/md/dm-zone.c
>> @@ -302,6 +302,7 @@ int dm_set_zones_restrictions(struct dm_table *t, struct request_queue *q)
>>  	if (dm_table_supports_zone_append(t)) {
>>  		clear_bit(DMF_EMULATE_ZONE_APPEND, &md->flags);
>>  		dm_cleanup_zoned_dev(md);
>> +
>>  		return 0;
>>  	}
>>  
>> diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
>> index 920085dd7f3b..7dbd28b8de01 100644
>> --- a/include/linux/device-mapper.h
>> +++ b/include/linux/device-mapper.h
>> @@ -294,6 +294,15 @@ struct target_type {
>>  #define dm_target_supports_mixed_zoned_model(type) (false)
>>  #endif
>>  
>> +#ifdef CONFIG_BLK_DEV_ZONED
>> +#define DM_TARGET_EMULATED_ZONES	0x00000400
>> +#define dm_target_supports_emulated_zones(type) \
>> +	((type)->features & DM_TARGET_EMULATED_ZONES)
>> +#else
>> +#define DM_TARGET_EMULATED_ZONES	0x00000000
>> +#define dm_target_supports_emulated_zones(type) (false)
>> +#endif
>> +
>>  struct dm_target {
>>  	struct dm_table *table;
>>  	struct target_type *type;
> 
> 

--
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Patch

diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
index 998a5cfdbc4e..d58ccfee765b 100644
--- a/drivers/md/Kconfig
+++ b/drivers/md/Kconfig
@@ -518,6 +518,15 @@  config DM_FLAKEY
 	help
 	 A target that intermittently fails I/O for debugging purposes.
 
+config DM_PO2Z
+	tristate "Power-of-2 target for non power-of-2 zoned devices"
+	depends on BLK_DEV_DM
+	depends on BLK_DEV_ZONED
+	help
+	  A target that converts a zoned device with non power-of-2 zone size to
+	  be power of 2. This is done by introducing gaps in between the zone
+	  capacity and the power of 2 zone size.
+
 config DM_VERITY
 	tristate "Verity target support"
 	depends on BLK_DEV_DM
diff --git a/drivers/md/Makefile b/drivers/md/Makefile
index 270f694850ec..98af4ed98f73 100644
--- a/drivers/md/Makefile
+++ b/drivers/md/Makefile
@@ -26,6 +26,7 @@  dm-era-y	+= dm-era-target.o
 dm-clone-y	+= dm-clone-target.o dm-clone-metadata.o
 dm-verity-y	+= dm-verity-target.o
 dm-zoned-y	+= dm-zoned-target.o dm-zoned-metadata.o dm-zoned-reclaim.o
+dm-po2z-y       += dm-po2z-target.o
 
 md-mod-y	+= md.o md-bitmap.o
 raid456-y	+= raid5.o raid5-cache.o raid5-ppl.o
@@ -60,6 +61,7 @@  obj-$(CONFIG_DM_CRYPT)		+= dm-crypt.o
 obj-$(CONFIG_DM_DELAY)		+= dm-delay.o
 obj-$(CONFIG_DM_DUST)		+= dm-dust.o
 obj-$(CONFIG_DM_FLAKEY)		+= dm-flakey.o
+obj-$(CONFIG_DM_PO2Z)		+= dm-po2z.o
 obj-$(CONFIG_DM_MULTIPATH)	+= dm-multipath.o dm-round-robin.o
 obj-$(CONFIG_DM_MULTIPATH_QL)	+= dm-queue-length.o
 obj-$(CONFIG_DM_MULTIPATH_ST)	+= dm-service-time.o
diff --git a/drivers/md/dm-po2z-target.c b/drivers/md/dm-po2z-target.c
new file mode 100644
index 000000000000..e9c5b7d00eda
--- /dev/null
+++ b/drivers/md/dm-po2z-target.c
@@ -0,0 +1,261 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2022 Samsung Electronics Co., Ltd.
+ */
+
+#include <linux/device-mapper.h>
+
+#define DM_MSG_PREFIX "po2z"
+
+struct dm_po2z_target {
+	struct dm_dev *dev;
+	sector_t zone_size; /* Actual zone size of the underlying dev*/
+	sector_t zone_size_po2; /* zone_size rounded to the nearest po2 value */
+	sector_t zone_size_diff; /* diff between zone_size_po2 and zone_size */
+	u32 nr_zones;
+};
+
+static inline u32 npo2_zone_no(struct dm_po2z_target *dmh, sector_t sect)
+{
+	return div64_u64(sect, dmh->zone_size);
+}
+
+static inline u32 po2_zone_no(struct dm_po2z_target *dmh, sector_t sect)
+{
+	return sect >> ilog2(dmh->zone_size_po2);
+}
+
+static inline sector_t target_to_device_sect(struct dm_po2z_target *dmh,
+					     sector_t sect)
+{
+	u32 zone_idx = po2_zone_no(dmh, sect);
+
+	return sect - (zone_idx * dmh->zone_size_diff);
+}
+
+static inline sector_t device_to_target_sect(struct dm_po2z_target *dmh,
+					     sector_t sect)
+{
+	u32 zone_idx = npo2_zone_no(dmh, sect);
+
+	return sect + (zone_idx * dmh->zone_size_diff);
+}
+
+/*
+ * This target works on the complete zoned device. Partial mapping is not
+ * supported.
+ * Construct a zoned po2 logical device: <dev-path>
+ */
+static int dm_po2z_ctr(struct dm_target *ti, unsigned int argc, char **argv)
+{
+	struct dm_po2z_target *dmh = NULL;
+	int ret;
+	sector_t zone_size;
+	sector_t dev_capacity;
+
+	if (argc < 1)
+		return -EINVAL;
+
+	dmh = kmalloc(sizeof(*dmh), GFP_KERNEL);
+	if (!dmh)
+		return -ENOMEM;
+
+	ret = dm_get_device(ti, argv[0], dm_table_get_mode(ti->table),
+			    &dmh->dev);
+
+	if (ret) {
+		ti->error = "Device lookup failed";
+		return ret;
+	}
+
+	zone_size = bdev_zone_sectors(dmh->dev->bdev);
+	dev_capacity = get_capacity(dmh->dev->bdev->bd_disk);
+	if (ti->len != dev_capacity || ti->begin) {
+		DMERR("%pg Partial mapping of the target not supported",
+		      dmh->dev->bdev);
+		return -EINVAL;
+	}
+
+	if (is_power_of_2(zone_size)) {
+		DMERR("%pg: this target is not useful for power-of-2 zoned devices",
+		      dmh->dev->bdev);
+		return -EINVAL;
+	}
+
+	dmh->zone_size = zone_size;
+	dmh->zone_size_po2 = 1 << get_count_order_long(zone_size);
+	dmh->zone_size_diff = dmh->zone_size_po2 - dmh->zone_size;
+	ti->private = dmh;
+	dmh->nr_zones = npo2_zone_no(dmh, ti->len);
+	ti->len = dmh->zone_size_po2 * dmh->nr_zones;
+
+	return 0;
+}
+
+static int dm_po2z_report_zones_cb(struct blk_zone *zone, unsigned int idx,
+				   void *data)
+{
+	struct dm_report_zones_args *args = data;
+	struct dm_po2z_target *dmh = args->tgt->private;
+
+	zone->start = device_to_target_sect(dmh, zone->start);
+	zone->wp = device_to_target_sect(dmh, zone->wp);
+	zone->len = dmh->zone_size_po2;
+	args->next_sector = zone->start + zone->len;
+
+	return args->orig_cb(zone, args->zone_idx++, args->orig_data);
+}
+
+static int dm_po2z_report_zones(struct dm_target *ti,
+				struct dm_report_zones_args *args,
+				unsigned int nr_zones)
+{
+	struct dm_po2z_target *dmh = ti->private;
+	sector_t sect = po2_zone_no(dmh, args->next_sector) * dmh->zone_size;
+
+	return blkdev_report_zones(dmh->dev->bdev, sect, nr_zones,
+				   dm_po2z_report_zones_cb, args);
+}
+
+static int dm_po2z_end_io(struct dm_target *ti, struct bio *bio,
+			  blk_status_t *error)
+{
+	struct dm_po2z_target *dmh = ti->private;
+
+	if (bio->bi_status == BLK_STS_OK && bio_op(bio) == REQ_OP_ZONE_APPEND)
+		bio->bi_iter.bi_sector =
+			device_to_target_sect(dmh, bio->bi_iter.bi_sector);
+
+	return DM_ENDIO_DONE;
+}
+
+static void dm_po2z_io_hints(struct dm_target *ti, struct queue_limits *limits)
+{
+	struct dm_po2z_target *dmh = ti->private;
+
+	limits->chunk_sectors = dmh->zone_size_po2;
+}
+
+static bool bio_across_emulated_zone_area(struct dm_po2z_target *dmh,
+					  struct bio *bio)
+{
+	u32 zone_idx = po2_zone_no(dmh, bio->bi_iter.bi_sector);
+	sector_t size = bio->bi_iter.bi_size >> SECTOR_SHIFT;
+
+	return (bio->bi_iter.bi_sector - (zone_idx * dmh->zone_size_po2) +
+		size) > dmh->zone_size;
+}
+
+static int dm_po2z_map_read(struct dm_po2z_target *dmh, struct bio *bio)
+{
+	sector_t start_sect, size, relative_sect_in_zone, split_io_pos;
+	u32 zone_idx;
+
+	/*
+	 * Read does not extend into the emulated zone area (area between
+	 * zone capacity and zone size)
+	 */
+	if (!bio_across_emulated_zone_area(dmh, bio)) {
+		bio->bi_iter.bi_sector =
+			target_to_device_sect(dmh, bio->bi_iter.bi_sector);
+		return DM_MAPIO_REMAPPED;
+	}
+
+	start_sect = bio->bi_iter.bi_sector;
+	size = bio->bi_iter.bi_size >> SECTOR_SHIFT;
+	zone_idx = po2_zone_no(dmh, start_sect);
+	relative_sect_in_zone = start_sect - (zone_idx * dmh->zone_size_po2);
+
+	/*
+	 * If the starting sector is in the emulated area then fill
+	 * all the bio with zeros. If bio is across emulated zone boundary,
+	 * split the bio across boundaries and fill zeros only for the
+	 * bio that is between the zone capacity and the zone size.
+	 */
+	if (relative_sect_in_zone < dmh->zone_size &&
+	    ((relative_sect_in_zone + size) > dmh->zone_size)) {
+		split_io_pos = (zone_idx * dmh->zone_size_po2) + dmh->zone_size;
+		dm_accept_partial_bio(bio, split_io_pos - start_sect);
+		bio->bi_iter.bi_sector = target_to_device_sect(dmh, start_sect);
+
+		return DM_MAPIO_REMAPPED;
+	} else if (relative_sect_in_zone >= dmh->zone_size &&
+		   ((relative_sect_in_zone + size) > dmh->zone_size_po2)) {
+		split_io_pos = (zone_idx + 1) * dmh->zone_size_po2;
+		dm_accept_partial_bio(bio, split_io_pos - start_sect);
+	}
+
+	zero_fill_bio(bio);
+	bio_endio(bio);
+	return DM_MAPIO_SUBMITTED;
+}
+
+static int dm_po2z_map(struct dm_target *ti, struct bio *bio)
+{
+	struct dm_po2z_target *dmh = ti->private;
+
+	bio_set_dev(bio, dmh->dev->bdev);
+	if (bio_sectors(bio) || op_is_zone_mgmt(bio_op(bio))) {
+		/*
+		 * Read operation on the emulated zone area (between zone capacity
+		 * and zone size) will fill the bio with zeroes. Any other operation
+		 * in the emulated area should return an error.
+		 */
+		if (bio_op(bio) == REQ_OP_READ)
+			return dm_po2z_map_read(dmh, bio);
+
+		if (!bio_across_emulated_zone_area(dmh, bio)) {
+			bio->bi_iter.bi_sector = target_to_device_sect(dmh,
+								       bio->bi_iter.bi_sector);
+			return DM_MAPIO_REMAPPED;
+		}
+		return DM_MAPIO_KILL;
+	}
+	return DM_MAPIO_REMAPPED;
+}
+
+static int dm_po2z_iterate_devices(struct dm_target *ti,
+				   iterate_devices_callout_fn fn, void *data)
+{
+	struct dm_po2z_target *dmh = ti->private;
+	sector_t len = dmh->nr_zones * dmh->zone_size;
+
+	return fn(ti, dmh->dev, 0, len, data);
+}
+
+static struct target_type dm_po2z_target = {
+	.name = "po2z",
+	.version = { 1, 0, 0 },
+	.features = DM_TARGET_ZONED_HM | DM_TARGET_EMULATED_ZONES,
+	.map = dm_po2z_map,
+	.end_io = dm_po2z_end_io,
+	.report_zones = dm_po2z_report_zones,
+	.iterate_devices = dm_po2z_iterate_devices,
+	.module = THIS_MODULE,
+	.io_hints = dm_po2z_io_hints,
+	.ctr = dm_po2z_ctr,
+};
+
+static int __init dm_po2z_init(void)
+{
+	int r = dm_register_target(&dm_po2z_target);
+
+	if (r < 0)
+		DMERR("register failed %d", r);
+
+	return r;
+}
+
+static void __exit dm_po2z_exit(void)
+{
+	dm_unregister_target(&dm_po2z_target);
+}
+
+/* Module hooks */
+module_init(dm_po2z_init);
+module_exit(dm_po2z_exit);
+
+MODULE_DESCRIPTION(DM_NAME "power-of-2 zoned target");
+MODULE_AUTHOR("Pankaj Raghav <[e-mail]>");
+MODULE_LICENSE("GPL");
+
diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 534fddfc2b42..d77feff124af 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -1614,13 +1614,20 @@  static bool dm_table_supports_zoned_model(struct dm_table *t,
 	return true;
 }
 
-static int device_not_matches_zone_sectors(struct dm_target *ti, struct dm_dev *dev,
+/*
+ * Callback function to check for device zone sector across devices. If the
+ * DM_TARGET_EMULATED_ZONES target feature flag is not set, then the target
+ * should have the same zone sector as the underlying devices.
+ */
+static int check_valid_device_zone_sectors(struct dm_target *ti, struct dm_dev *dev,
 					   sector_t start, sector_t len, void *data)
 {
 	unsigned int *zone_sectors = data;
 
-	if (!bdev_is_zoned(dev->bdev))
+	if (!bdev_is_zoned(dev->bdev) ||
+	    dm_target_supports_emulated_zones(ti->type))
 		return 0;
+
 	return bdev_zone_sectors(dev->bdev) != *zone_sectors;
 }
 
@@ -1646,7 +1653,7 @@  static int validate_hardware_zoned_model(struct dm_table *t,
 	if (!zone_sectors)
 		return -EINVAL;
 
-	if (dm_table_any_dev_attr(t, device_not_matches_zone_sectors, &zone_sectors)) {
+	if (dm_table_any_dev_attr(t, check_valid_device_zone_sectors, &zone_sectors)) {
 		DMERR("%s: zone sectors is not consistent across all zoned devices",
 		      dm_device_name(t->md));
 		return -EINVAL;
diff --git a/drivers/md/dm-zone.c b/drivers/md/dm-zone.c
index 31c16aafdbfc..2b6b3883471f 100644
--- a/drivers/md/dm-zone.c
+++ b/drivers/md/dm-zone.c
@@ -302,6 +302,7 @@  int dm_set_zones_restrictions(struct dm_table *t, struct request_queue *q)
 	if (dm_table_supports_zone_append(t)) {
 		clear_bit(DMF_EMULATE_ZONE_APPEND, &md->flags);
 		dm_cleanup_zoned_dev(md);
+
 		return 0;
 	}
 
diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index 920085dd7f3b..7dbd28b8de01 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -294,6 +294,15 @@  struct target_type {
 #define dm_target_supports_mixed_zoned_model(type) (false)
 #endif
 
+#ifdef CONFIG_BLK_DEV_ZONED
+#define DM_TARGET_EMULATED_ZONES	0x00000400
+#define dm_target_supports_emulated_zones(type) \
+	((type)->features & DM_TARGET_EMULATED_ZONES)
+#else
+#define DM_TARGET_EMULATED_ZONES	0x00000000
+#define dm_target_supports_emulated_zones(type) (false)
+#endif
+
 struct dm_target {
 	struct dm_table *table;
 	struct target_type *type;