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Date:   Tue, 27 Sep 2022 18:07:56 +0200
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Subject: Re: [PATCH v15 13/13] dm: add power-of-2 target for zoned devices
 with non power-of-2 zone sizes
Content-Language: en-US
To:     <snitzer@kernel.org>
CC:     <jaegeuk@kernel.org>, <agk@redhat.com>, <axboe@kernel.dk>,
        <damien.lemoal@opensource.wdc.com>, <hch@lst.de>,
        <gost.dev@samsung.com>, <bvanassche@acm.org>,
        <linux-kernel@vger.kernel.org>, <hare@suse.de>,
        <matias.bjorling@wdc.com>, <Johannes.Thumshirn@wdc.com>,
        <linux-block@vger.kernel.org>, <linux-nvme@lists.infradead.org>,
        <pankydev8@gmail.com>, <dm-devel@redhat.com>,
        Damien Le Moal <damien.lemoal@wdc.com>
From:   Pankaj Raghav <p.raghav@samsung.com>
In-Reply-To: <20220923173618.6899-14-p.raghav@samsung.com>
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References: <20220923173618.6899-1-p.raghav@samsung.com>
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Gentle ping Mike.

On 2022-09-23 19:36, Pankaj Raghav wrote:
> Only zoned devices with power-of-2(po2) number of sectors per zone(zone
> size) were supported in linux but now non power-of-2(npo2) zone sizes
> 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 zone
> sizes, it was suggested to create a dm target for npo2 zone size device to
> appear as a po2 zone size target so that file systems can initially
> work without any explicit changes.
> 
> 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
> value.
> 
> 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
> 
> 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> po2zoned /dev/nvme<id>'
> 
> The target does not support partial mapping of the underlying
> device as there is no use-case for it.
> 
> Note:
> This target is not related to dm-zoned target, which exposes a zoned block
> device as a regular block device without any write constraint.
> 
> This target only exposes a different zone size than the underlying device.
> The underlying device's other constraints will be directly exposed to the
> target.
> 
> Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
> Suggested-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
> Suggested-by: Damien Le Moal <damien.lemoal@wdc.com>
> Suggested-by: Hannes Reinecke <hare@suse.de>
> ---
>  .../admin-guide/device-mapper/dm-po2zoned.rst |  79 +++++
>  .../admin-guide/device-mapper/index.rst       |   1 +
>  drivers/md/Kconfig                            |  10 +
>  drivers/md/Makefile                           |   2 +
>  drivers/md/dm-po2zoned-target.c               | 293 ++++++++++++++++++
>  5 files changed, 385 insertions(+)
>  create mode 100644 Documentation/admin-guide/device-mapper/dm-po2zoned.rst
>  create mode 100644 drivers/md/dm-po2zoned-target.c
> 
> diff --git a/Documentation/admin-guide/device-mapper/dm-po2zoned.rst b/Documentation/admin-guide/device-mapper/dm-po2zoned.rst
> new file mode 100644
> index 000000000000..8a35eab0b714
> --- /dev/null
> +++ b/Documentation/admin-guide/device-mapper/dm-po2zoned.rst
> @@ -0,0 +1,79 @@
> +===========
> +dm-po2zoned
> +===========
> +The dm-po2zoned device mapper target exposes a zoned block device with a
> +non-power-of-2(npo2) number of sectors per zone as a power-of-2(po2)
> +number of sectors per zone(zone size).
> +The filesystems that support zoned block devices such as F2FS and BTRFS
> +assume po2 zone size as the kernel has traditionally only supported
> +those devices. However, as the kernel now supports zoned block devices with
> +npo2 zone sizes, the filesystems can run on top of the dm-po2zoned target before
> +adding native support.
> +
> +Partial mapping of the underlying device is not supported by this target as
> +there is no use-case for it.
> +
> +.. note::
> +   This target is **not related** to **dm-zoned target**, which exposes a
> +   zoned block device as a regular block device without any write constraint.
> +
> +   This target only exposes a different **zone size** than the underlying device.
> +   The underlying device's other **constraints** will be exposed to the target.
> +
> +Algorithm
> +=========
> +The device mapper target maps the underlying device's zone size to the
> +zone capacity and changes the zone size to the nearest po2 zone size.
> +The gap between the zone capacity and the zone size is emulated in the target.
> +E.g., a zoned block device with a zone size (and capacity) of 3M will have an
> +equivalent target layout with mapping as follows:
> +
> +::
> +
> +  0M           3M  4M        6M 8M
> +  |             |  |          |  |
> +  +x------------+--+x---------+--+x-------  Target
> +  |x            |  |x         |  |x
> +   x               x             x
> +   x               x             x
> +   x              x             x
> +   x             x             x
> +  |x            |x            |x
> +  +x------------+x------------+x----------  Device
> +  |             |             |
> +  0M           3M            6M
> +
> +A simple remap is performed for all the BIOs that do not cross the
> +emulation gap area, i.e., the area between the zone capacity and size.
> +
> +If a BIO lies in the emulation gap area, the following operations are performed:
> +
> +	Read:
> +		- If the BIO lies entirely in the emulation gap area, then zero out the BIO and complete it.
> +		- If the BIO spans the emulation gap area, split the BIO across the zone capacity boundary
> +                  and remap only the BIO within the zone capacity boundary. The other part of the split BIO
> +                  will be zeroed out.
> +
> +	Other operations:
> +                - Return an error
> +
> +Table parameters
> +================
> +
> +::
> +
> +  <dev path>
> +
> +Mandatory parameters:
> +
> +    <dev path>:
> +        Full pathname to the underlying block-device, or a
> +        "major:minor" device-number.
> +
> +Examples
> +========
> +
> +::
> +
> +  #!/bin/sh
> +  echo "0 `blockdev --getsz $1` po2zoned $1" | dmsetup create po2z
> diff --git a/Documentation/admin-guide/device-mapper/index.rst b/Documentation/admin-guide/device-mapper/index.rst
> index cde52cc09645..5df93711cef5 100644
> --- a/Documentation/admin-guide/device-mapper/index.rst
> +++ b/Documentation/admin-guide/device-mapper/index.rst
> @@ -23,6 +23,7 @@ Device Mapper
>      dm-service-time
>      dm-uevent
>      dm-zoned
> +    dm-po2zoned
>      era
>      kcopyd
>      linear
> diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
> index 998a5cfdbc4e..74fdfd02ab5f 100644
> --- a/drivers/md/Kconfig
> +++ b/drivers/md/Kconfig
> @@ -518,6 +518,16 @@ config DM_FLAKEY
>  	help
>  	 A target that intermittently fails I/O for debugging purposes.
>  
> +config DM_PO2ZONED
> +	tristate "Zoned block devices target emulating a power-of-2 number of sectors per zone"
> +	depends on BLK_DEV_DM
> +	depends on BLK_DEV_ZONED
> +	help
> +	  A target that converts a zoned block device with non-power-of-2(npo2)
> +	  number of sectors per zone to be power-of-2(po2). Use this target for
> +	  zoned block devices with npo2 number of sectors per zone until native
> +	  support is added to the filesystems and applications.
> +
>  config DM_VERITY
>  	tristate "Verity target support"
>  	depends on BLK_DEV_DM
> diff --git a/drivers/md/Makefile b/drivers/md/Makefile
> index 84291e38dca8..ee05722bc637 100644
> --- a/drivers/md/Makefile
> +++ b/drivers/md/Makefile
> @@ -26,6 +26,7 @@ dm-era-y	+= dm-era-target.o
>  dm-clone-y	+= dm-clone-target.o dm-clone-metadata.o
>  dm-verity-y	+= dm-verity-target.o
>  dm-zoned-y	+= dm-zoned-target.o dm-zoned-metadata.o dm-zoned-reclaim.o
> +dm-po2zoned-y	+= dm-po2zoned-target.o
>  
>  md-mod-y	+= md.o md-bitmap.o
>  raid456-y	+= raid5.o raid5-cache.o raid5-ppl.o
> @@ -60,6 +61,7 @@ obj-$(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_PO2ZONED)	+= dm-po2zoned.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-po2zoned-target.c b/drivers/md/dm-po2zoned-target.c
> new file mode 100644
> index 000000000000..0f8f768a94cf
> --- /dev/null
> +++ b/drivers/md/dm-po2zoned-target.c
> @@ -0,0 +1,293 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2022 Samsung Electronics Co., Ltd.
> + */
> +
> +#include <linux/device-mapper.h>
> +
> +#define DM_MSG_PREFIX "po2zoned"
> +
> +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 */
> +	unsigned int zone_size_po2_shift;
> +	sector_t zone_size_diff; /* diff between zone_size_po2 and zone_size */
> +	unsigned int nr_zones;
> +};
> +
> +static inline unsigned int npo2_zone_no(struct dm_po2z_target *dmh,
> +					sector_t sect)
> +{
> +	return div64_u64(sect, dmh->zone_size);
> +}
> +
> +static inline unsigned int po2_zone_no(struct dm_po2z_target *dmh,
> +				       sector_t sect)
> +{
> +	return sect >> dmh->zone_size_po2_shift;
> +}
> +
> +static inline sector_t device_to_target_sect(struct dm_target *ti,
> +					     sector_t sect)
> +{
> +	struct dm_po2z_target *dmh = ti->private;
> +
> +	return sect + (npo2_zone_no(dmh, sect) * dmh->zone_size_diff) +
> +	       ti->begin;
> +}
> +
> +/*
> + * 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";
> +		goto free;
> +	}
> +
> +	if (!bdev_is_zoned(dmh->dev->bdev)) {
> +		DMERR("%pg is not a zoned device", dmh->dev->bdev);
> +		ret = -EINVAL;
> +		goto bad;
> +	}
> +
> +	zone_size = bdev_zone_sectors(dmh->dev->bdev);
> +	dev_capacity = get_capacity(dmh->dev->bdev->bd_disk);
> +	if (ti->len != dev_capacity) {
> +		DMERR("%pg Partial mapping of the target is not supported",
> +		      dmh->dev->bdev);
> +		ret = -EINVAL;
> +		goto bad;
> +	}
> +
> +	if (is_power_of_2(zone_size))
> +		DMWARN("%pg: underlying device has a power-of-2 number of sectors per zone",
> +		       dmh->dev->bdev);
> +
> +	dmh->zone_size = zone_size;
> +	dmh->zone_size_po2 = 1 << get_count_order_long(zone_size);
> +	dmh->zone_size_po2_shift = ilog2(dmh->zone_size_po2);
> +	dmh->zone_size_diff = dmh->zone_size_po2 - dmh->zone_size;
> +	ti->private = dmh;
> +	ti->max_io_len = dmh->zone_size_po2;
> +	dmh->nr_zones = npo2_zone_no(dmh, ti->len);
> +	ti->len = dmh->zone_size_po2 * dmh->nr_zones;
> +	return 0;
> +
> +bad:
> +	dm_put_device(ti, dmh->dev);
> +free:
> +	kfree(dmh);
> +	return ret;
> +}
> +
> +static void dm_po2z_dtr(struct dm_target *ti)
> +{
> +	struct dm_po2z_target *dmh = ti->private;
> +
> +	dm_put_device(ti, dmh->dev);
> +	kfree(dmh);
> +}
> +
> +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_target *ti = args->tgt;
> +	struct dm_po2z_target *dmh = ti->private;
> +
> +	zone->start = device_to_target_sect(ti, zone->start);
> +	zone->wp = device_to_target_sect(ti, 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, dm_target_offset(ti, 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)
> +{
> +	if (bio->bi_status == BLK_STS_OK && bio_op(bio) == REQ_OP_ZONE_APPEND)
> +		bio->bi_iter.bi_sector =
> +			device_to_target_sect(ti, 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 void dm_po2z_status(struct dm_target *ti, status_type_t type,
> +			   unsigned int status_flags, char *result,
> +			   unsigned int maxlen)
> +{
> +	struct dm_po2z_target *dmh = ti->private;
> +	size_t sz = 0;
> +
> +	switch (type) {
> +	case STATUSTYPE_INFO:
> +		DMEMIT("%s %lld", dmh->dev->name,
> +		       (unsigned long long)dmh->zone_size);
> +		break;
> +
> +	case STATUSTYPE_TABLE:
> +		DMEMIT("%s", dmh->dev->name);
> +		break;
> +
> +	case STATUSTYPE_IMA:
> +		result[0] = '\0';
> +		break;
> +	}
> +}
> +
> +/**
> + * dm_po2z_bio_in_emulated_zone_area - check if bio is in the emulated zone area
> + * @dmh:	target data
> + * @bio:	bio
> + * @offset:	bio offset to emulated zone boundary
> + *
> + * Check if a @bio is partly or completely in the emulated zone area. If the
> + * @bio is partly in the emulated zone area, @offset can be used to split
> + * the @bio across the emulated zone boundary. @offset
> + * will be negative if the @bio completely lies in the emulated area.
> + *
> + */
> +static bool dm_po2z_bio_in_emulated_zone_area(struct dm_po2z_target *dmh,
> +					      struct bio *bio, int *offset)
> +{
> +	unsigned int zone_idx = po2_zone_no(dmh, bio->bi_iter.bi_sector);
> +	sector_t nr_sectors = bio->bi_iter.bi_size >> SECTOR_SHIFT;
> +	sector_t sector_offset =
> +		bio->bi_iter.bi_sector - (zone_idx << dmh->zone_size_po2_shift);
> +
> +	*offset = dmh->zone_size - sector_offset;
> +
> +	return sector_offset + nr_sectors > dmh->zone_size;
> +}
> +
> +static inline void dm_po2z_read_zeroes(struct bio *bio)
> +{
> +	zero_fill_bio(bio);
> +	bio_endio(bio);
> +}
> +
> +static int dm_po2z_map(struct dm_target *ti, struct bio *bio)
> +{
> +	struct dm_po2z_target *dmh = ti->private;
> +	int split_io_pos;
> +
> +	bio_set_dev(bio, dmh->dev->bdev);
> +	bio->bi_iter.bi_sector = dm_target_offset(ti, bio->bi_iter.bi_sector);
> +
> +	if (op_is_zone_mgmt(bio_op(bio)) || !bio_sectors(bio))
> +		goto remap_sector;
> +
> +	if (!dm_po2z_bio_in_emulated_zone_area(dmh, bio, &split_io_pos))
> +		goto remap_sector;
> +
> +	/*
> +	 * 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) {
> +		/*
> +		 * If the bio is across emulated zone boundary, split the bio at
> +		 * the boundary.
> +		 */
> +		if (split_io_pos > 0) {
> +			dm_accept_partial_bio(bio, split_io_pos);
> +			goto remap_sector;
> +		}
> +
> +		dm_po2z_read_zeroes(bio);
> +		return DM_MAPIO_SUBMITTED;
> +	}
> +	/* Other IOs in emulated zone area should result in an error */
> +	return DM_MAPIO_KILL;
> +
> +remap_sector:
> +	/* convert from target sector to device sector */
> +	bio->bi_iter.bi_sector -= (po2_zone_no(dmh, bio->bi_iter.bi_sector) *
> +				   dmh->zone_size_diff);
> +	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 = "po2zoned",
> +	.version = { 1, 0, 0 },
> +	.features = DM_TARGET_ZONED_HM | DM_TARGET_EMULATED_ZONES |
> +		    DM_TARGET_NOWAIT,
> +	.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,
> +	.status = dm_po2z_status,
> +	.ctr = dm_po2z_ctr,
> +	.dtr = dm_po2z_dtr,
> +};
> +
> +static int __init dm_po2z_init(void)
> +{
> +	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 <p.raghav@samsung.com>");
> +MODULE_LICENSE("GPL");
> +

From mboxrd@z Thu Jan  1 00:00:00 1970
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X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8
Subject: Re: [dm-devel] [PATCH v15 13/13] dm: add power-of-2 target for
 zoned devices with non power-of-2 zone sizes
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Cc: axboe@kernel.dk, Damien Le Moal <damien.lemoal@wdc.com>, bvanassche@acm.org,
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Gentle ping Mike.

On 2022-09-23 19:36, Pankaj Raghav wrote:
> Only zoned devices with power-of-2(po2) number of sectors per zone(zone
> size) were supported in linux but now non power-of-2(npo2) zone sizes
> 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 zone
> sizes, it was suggested to create a dm target for npo2 zone size device to
> appear as a po2 zone size target so that file systems can initially
> work without any explicit changes.
> 
> 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
> value.
> 
> 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
> 
> 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> po2zoned /dev/nvme<id>'
> 
> The target does not support partial mapping of the underlying
> device as there is no use-case for it.
> 
> Note:
> This target is not related to dm-zoned target, which exposes a zoned block
> device as a regular block device without any write constraint.
> 
> This target only exposes a different zone size than the underlying device.
> The underlying device's other constraints will be directly exposed to the
> target.
> 
> Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
> Suggested-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
> Suggested-by: Damien Le Moal <damien.lemoal@wdc.com>
> Suggested-by: Hannes Reinecke <hare@suse.de>
> ---
>  .../admin-guide/device-mapper/dm-po2zoned.rst |  79 +++++
>  .../admin-guide/device-mapper/index.rst       |   1 +
>  drivers/md/Kconfig                            |  10 +
>  drivers/md/Makefile                           |   2 +
>  drivers/md/dm-po2zoned-target.c               | 293 ++++++++++++++++++
>  5 files changed, 385 insertions(+)
>  create mode 100644 Documentation/admin-guide/device-mapper/dm-po2zoned.rst
>  create mode 100644 drivers/md/dm-po2zoned-target.c
> 
> diff --git a/Documentation/admin-guide/device-mapper/dm-po2zoned.rst b/Documentation/admin-guide/device-mapper/dm-po2zoned.rst
> new file mode 100644
> index 000000000000..8a35eab0b714
> --- /dev/null
> +++ b/Documentation/admin-guide/device-mapper/dm-po2zoned.rst
> @@ -0,0 +1,79 @@
> +===========
> +dm-po2zoned
> +===========
> +The dm-po2zoned device mapper target exposes a zoned block device with a
> +non-power-of-2(npo2) number of sectors per zone as a power-of-2(po2)
> +number of sectors per zone(zone size).
> +The filesystems that support zoned block devices such as F2FS and BTRFS
> +assume po2 zone size as the kernel has traditionally only supported
> +those devices. However, as the kernel now supports zoned block devices with
> +npo2 zone sizes, the filesystems can run on top of the dm-po2zoned target before
> +adding native support.
> +
> +Partial mapping of the underlying device is not supported by this target as
> +there is no use-case for it.
> +
> +.. note::
> +   This target is **not related** to **dm-zoned target**, which exposes a
> +   zoned block device as a regular block device without any write constraint.
> +
> +   This target only exposes a different **zone size** than the underlying device.
> +   The underlying device's other **constraints** will be exposed to the target.
> +
> +Algorithm
> +=========
> +The device mapper target maps the underlying device's zone size to the
> +zone capacity and changes the zone size to the nearest po2 zone size.
> +The gap between the zone capacity and the zone size is emulated in the target.
> +E.g., a zoned block device with a zone size (and capacity) of 3M will have an
> +equivalent target layout with mapping as follows:
> +
> +::
> +
> +  0M           3M  4M        6M 8M
> +  |             |  |          |  |
> +  +x------------+--+x---------+--+x-------  Target
> +  |x            |  |x         |  |x
> +   x               x             x
> +   x               x             x
> +   x              x             x
> +   x             x             x
> +  |x            |x            |x
> +  +x------------+x------------+x----------  Device
> +  |             |             |
> +  0M           3M            6M
> +
> +A simple remap is performed for all the BIOs that do not cross the
> +emulation gap area, i.e., the area between the zone capacity and size.
> +
> +If a BIO lies in the emulation gap area, the following operations are performed:
> +
> +	Read:
> +		- If the BIO lies entirely in the emulation gap area, then zero out the BIO and complete it.
> +		- If the BIO spans the emulation gap area, split the BIO across the zone capacity boundary
> +                  and remap only the BIO within the zone capacity boundary. The other part of the split BIO
> +                  will be zeroed out.
> +
> +	Other operations:
> +                - Return an error
> +
> +Table parameters
> +================
> +
> +::
> +
> +  <dev path>
> +
> +Mandatory parameters:
> +
> +    <dev path>:
> +        Full pathname to the underlying block-device, or a
> +        "major:minor" device-number.
> +
> +Examples
> +========
> +
> +::
> +
> +  #!/bin/sh
> +  echo "0 `blockdev --getsz $1` po2zoned $1" | dmsetup create po2z
> diff --git a/Documentation/admin-guide/device-mapper/index.rst b/Documentation/admin-guide/device-mapper/index.rst
> index cde52cc09645..5df93711cef5 100644
> --- a/Documentation/admin-guide/device-mapper/index.rst
> +++ b/Documentation/admin-guide/device-mapper/index.rst
> @@ -23,6 +23,7 @@ Device Mapper
>      dm-service-time
>      dm-uevent
>      dm-zoned
> +    dm-po2zoned
>      era
>      kcopyd
>      linear
> diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
> index 998a5cfdbc4e..74fdfd02ab5f 100644
> --- a/drivers/md/Kconfig
> +++ b/drivers/md/Kconfig
> @@ -518,6 +518,16 @@ config DM_FLAKEY
>  	help
>  	 A target that intermittently fails I/O for debugging purposes.
>  
> +config DM_PO2ZONED
> +	tristate "Zoned block devices target emulating a power-of-2 number of sectors per zone"
> +	depends on BLK_DEV_DM
> +	depends on BLK_DEV_ZONED
> +	help
> +	  A target that converts a zoned block device with non-power-of-2(npo2)
> +	  number of sectors per zone to be power-of-2(po2). Use this target for
> +	  zoned block devices with npo2 number of sectors per zone until native
> +	  support is added to the filesystems and applications.
> +
>  config DM_VERITY
>  	tristate "Verity target support"
>  	depends on BLK_DEV_DM
> diff --git a/drivers/md/Makefile b/drivers/md/Makefile
> index 84291e38dca8..ee05722bc637 100644
> --- a/drivers/md/Makefile
> +++ b/drivers/md/Makefile
> @@ -26,6 +26,7 @@ dm-era-y	+= dm-era-target.o
>  dm-clone-y	+= dm-clone-target.o dm-clone-metadata.o
>  dm-verity-y	+= dm-verity-target.o
>  dm-zoned-y	+= dm-zoned-target.o dm-zoned-metadata.o dm-zoned-reclaim.o
> +dm-po2zoned-y	+= dm-po2zoned-target.o
>  
>  md-mod-y	+= md.o md-bitmap.o
>  raid456-y	+= raid5.o raid5-cache.o raid5-ppl.o
> @@ -60,6 +61,7 @@ obj-$(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_PO2ZONED)	+= dm-po2zoned.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-po2zoned-target.c b/drivers/md/dm-po2zoned-target.c
> new file mode 100644
> index 000000000000..0f8f768a94cf
> --- /dev/null
> +++ b/drivers/md/dm-po2zoned-target.c
> @@ -0,0 +1,293 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2022 Samsung Electronics Co., Ltd.
> + */
> +
> +#include <linux/device-mapper.h>
> +
> +#define DM_MSG_PREFIX "po2zoned"
> +
> +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 */
> +	unsigned int zone_size_po2_shift;
> +	sector_t zone_size_diff; /* diff between zone_size_po2 and zone_size */
> +	unsigned int nr_zones;
> +};
> +
> +static inline unsigned int npo2_zone_no(struct dm_po2z_target *dmh,
> +					sector_t sect)
> +{
> +	return div64_u64(sect, dmh->zone_size);
> +}
> +
> +static inline unsigned int po2_zone_no(struct dm_po2z_target *dmh,
> +				       sector_t sect)
> +{
> +	return sect >> dmh->zone_size_po2_shift;
> +}
> +
> +static inline sector_t device_to_target_sect(struct dm_target *ti,
> +					     sector_t sect)
> +{
> +	struct dm_po2z_target *dmh = ti->private;
> +
> +	return sect + (npo2_zone_no(dmh, sect) * dmh->zone_size_diff) +
> +	       ti->begin;
> +}
> +
> +/*
> + * 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";
> +		goto free;
> +	}
> +
> +	if (!bdev_is_zoned(dmh->dev->bdev)) {
> +		DMERR("%pg is not a zoned device", dmh->dev->bdev);
> +		ret = -EINVAL;
> +		goto bad;
> +	}
> +
> +	zone_size = bdev_zone_sectors(dmh->dev->bdev);
> +	dev_capacity = get_capacity(dmh->dev->bdev->bd_disk);
> +	if (ti->len != dev_capacity) {
> +		DMERR("%pg Partial mapping of the target is not supported",
> +		      dmh->dev->bdev);
> +		ret = -EINVAL;
> +		goto bad;
> +	}
> +
> +	if (is_power_of_2(zone_size))
> +		DMWARN("%pg: underlying device has a power-of-2 number of sectors per zone",
> +		       dmh->dev->bdev);
> +
> +	dmh->zone_size = zone_size;
> +	dmh->zone_size_po2 = 1 << get_count_order_long(zone_size);
> +	dmh->zone_size_po2_shift = ilog2(dmh->zone_size_po2);
> +	dmh->zone_size_diff = dmh->zone_size_po2 - dmh->zone_size;
> +	ti->private = dmh;
> +	ti->max_io_len = dmh->zone_size_po2;
> +	dmh->nr_zones = npo2_zone_no(dmh, ti->len);
> +	ti->len = dmh->zone_size_po2 * dmh->nr_zones;
> +	return 0;
> +
> +bad:
> +	dm_put_device(ti, dmh->dev);
> +free:
> +	kfree(dmh);
> +	return ret;
> +}
> +
> +static void dm_po2z_dtr(struct dm_target *ti)
> +{
> +	struct dm_po2z_target *dmh = ti->private;
> +
> +	dm_put_device(ti, dmh->dev);
> +	kfree(dmh);
> +}
> +
> +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_target *ti = args->tgt;
> +	struct dm_po2z_target *dmh = ti->private;
> +
> +	zone->start = device_to_target_sect(ti, zone->start);
> +	zone->wp = device_to_target_sect(ti, 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, dm_target_offset(ti, 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)
> +{
> +	if (bio->bi_status == BLK_STS_OK && bio_op(bio) == REQ_OP_ZONE_APPEND)
> +		bio->bi_iter.bi_sector =
> +			device_to_target_sect(ti, 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 void dm_po2z_status(struct dm_target *ti, status_type_t type,
> +			   unsigned int status_flags, char *result,
> +			   unsigned int maxlen)
> +{
> +	struct dm_po2z_target *dmh = ti->private;
> +	size_t sz = 0;
> +
> +	switch (type) {
> +	case STATUSTYPE_INFO:
> +		DMEMIT("%s %lld", dmh->dev->name,
> +		       (unsigned long long)dmh->zone_size);
> +		break;
> +
> +	case STATUSTYPE_TABLE:
> +		DMEMIT("%s", dmh->dev->name);
> +		break;
> +
> +	case STATUSTYPE_IMA:
> +		result[0] = '\0';
> +		break;
> +	}
> +}
> +
> +/**
> + * dm_po2z_bio_in_emulated_zone_area - check if bio is in the emulated zone area
> + * @dmh:	target data
> + * @bio:	bio
> + * @offset:	bio offset to emulated zone boundary
> + *
> + * Check if a @bio is partly or completely in the emulated zone area. If the
> + * @bio is partly in the emulated zone area, @offset can be used to split
> + * the @bio across the emulated zone boundary. @offset
> + * will be negative if the @bio completely lies in the emulated area.
> + *
> + */
> +static bool dm_po2z_bio_in_emulated_zone_area(struct dm_po2z_target *dmh,
> +					      struct bio *bio, int *offset)
> +{
> +	unsigned int zone_idx = po2_zone_no(dmh, bio->bi_iter.bi_sector);
> +	sector_t nr_sectors = bio->bi_iter.bi_size >> SECTOR_SHIFT;
> +	sector_t sector_offset =
> +		bio->bi_iter.bi_sector - (zone_idx << dmh->zone_size_po2_shift);
> +
> +	*offset = dmh->zone_size - sector_offset;
> +
> +	return sector_offset + nr_sectors > dmh->zone_size;
> +}
> +
> +static inline void dm_po2z_read_zeroes(struct bio *bio)
> +{
> +	zero_fill_bio(bio);
> +	bio_endio(bio);
> +}
> +
> +static int dm_po2z_map(struct dm_target *ti, struct bio *bio)
> +{
> +	struct dm_po2z_target *dmh = ti->private;
> +	int split_io_pos;
> +
> +	bio_set_dev(bio, dmh->dev->bdev);
> +	bio->bi_iter.bi_sector = dm_target_offset(ti, bio->bi_iter.bi_sector);
> +
> +	if (op_is_zone_mgmt(bio_op(bio)) || !bio_sectors(bio))
> +		goto remap_sector;
> +
> +	if (!dm_po2z_bio_in_emulated_zone_area(dmh, bio, &split_io_pos))
> +		goto remap_sector;
> +
> +	/*
> +	 * 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) {
> +		/*
> +		 * If the bio is across emulated zone boundary, split the bio at
> +		 * the boundary.
> +		 */
> +		if (split_io_pos > 0) {
> +			dm_accept_partial_bio(bio, split_io_pos);
> +			goto remap_sector;
> +		}
> +
> +		dm_po2z_read_zeroes(bio);
> +		return DM_MAPIO_SUBMITTED;
> +	}
> +	/* Other IOs in emulated zone area should result in an error */
> +	return DM_MAPIO_KILL;
> +
> +remap_sector:
> +	/* convert from target sector to device sector */
> +	bio->bi_iter.bi_sector -= (po2_zone_no(dmh, bio->bi_iter.bi_sector) *
> +				   dmh->zone_size_diff);
> +	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 = "po2zoned",
> +	.version = { 1, 0, 0 },
> +	.features = DM_TARGET_ZONED_HM | DM_TARGET_EMULATED_ZONES |
> +		    DM_TARGET_NOWAIT,
> +	.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,
> +	.status = dm_po2z_status,
> +	.ctr = dm_po2z_ctr,
> +	.dtr = dm_po2z_dtr,
> +};
> +
> +static int __init dm_po2z_init(void)
> +{
> +	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 <p.raghav@samsung.com>");
> +MODULE_LICENSE("GPL");
> +

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