Re: [PATCH 4/9] block: Remove partition support for zoned block devices

[Hannes Reinecke <hare@suse.de>]

On 11/8/19 2:56 AM, Damien Le Moal wrote:
> No known partitioning tool supports zoned block devices, especially the
> host managed flavor with strong sequential write constraints.
> Furthermore, there are also no known user nor use cases for partitioned
> zoned block devices.
> 
> This patch removes partition device creation for zoned block devices,
> which allows simplifying the processing of zone commands for zoned
> block devices. A warning is added if a partition table is found on the
> device.
> 
> For report zones operations no zone sector information remapping is
> necessary anymore, simplifying the code. Of note is that remapping of
> zone reports for DM targets is still necessary as done by
> dm_remap_zone_report().
> 
> Similarly, remaping of a zone reset bio is not necessary anymore.
> Testing for the applicability of the zone reset all request also becomes
> simpler and only needs to check that the number of sectors of the
> requested zone range is equal to the disk capacity.
> 
> Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
> ---
>  block/blk-core.c          |  6 +---
>  block/blk-zoned.c         | 62 ++++++--------------------------
>  block/partition-generic.c | 74 +++++----------------------------------
>  drivers/md/dm.c           |  3 --
>  4 files changed, 21 insertions(+), 124 deletions(-)
> 
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 3306a3c5bed6..df6b70476187 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -851,11 +851,7 @@ static inline int blk_partition_remap(struct bio *bio)
>  	if (unlikely(bio_check_ro(bio, p)))
>  		goto out;
>  
> -	/*
> -	 * Zone management bios do not have a sector count but they do have
> -	 * a start sector filled out and need to be remapped.
> -	 */
> -	if (bio_sectors(bio) || op_is_zone_mgmt(bio_op(bio))) {
> +	if (bio_sectors(bio)) {
>  		if (bio_check_eod(bio, part_nr_sects_read(p)))
>  			goto out;
>  		bio->bi_iter.bi_sector += p->start_sect;
> diff --git a/block/blk-zoned.c b/block/blk-zoned.c
> index ea4e086ba00e..ae665e490858 100644
> --- a/block/blk-zoned.c
> +++ b/block/blk-zoned.c
> @@ -93,32 +93,10 @@ unsigned int blkdev_nr_zones(struct block_device *bdev)
>  	if (!blk_queue_is_zoned(q))
>  		return 0;
>  
> -	return __blkdev_nr_zones(q, bdev->bd_part->nr_sects);
> +	return __blkdev_nr_zones(q, get_capacity(bdev->bd_disk));
>  }
>  EXPORT_SYMBOL_GPL(blkdev_nr_zones);
>  
> -/*
> - * Check that a zone report belongs to this partition, and if yes, fix its start
> - * sector and write pointer and return true. Return false otherwise.
> - */
> -static bool blkdev_report_zone(struct block_device *bdev, struct blk_zone *rep)
> -{
> -	sector_t offset = get_start_sect(bdev);
> -
> -	if (rep->start < offset)
> -		return false;
> -
> -	rep->start -= offset;
> -	if (rep->start + rep->len > bdev->bd_part->nr_sects)
> -		return false;
> -
> -	if (rep->type == BLK_ZONE_TYPE_CONVENTIONAL)
> -		rep->wp = rep->start + rep->len;
> -	else
> -		rep->wp -= offset;
> -	return true;
> -}
> -
>  /**
>   * blkdev_report_zones - Get zones information
>   * @bdev:	Target block device
> @@ -140,8 +118,7 @@ int blkdev_report_zones(struct block_device *bdev, sector_t sector,
>  {
>  	struct request_queue *q = bdev_get_queue(bdev);
>  	struct gendisk *disk = bdev->bd_disk;
> -	unsigned int i, nrz;
> -	int ret;
> +	sector_t capacity = get_capacity(disk);
>  
>  	if (!blk_queue_is_zoned(q))
>  		return -EOPNOTSUPP;
> @@ -154,27 +131,14 @@ int blkdev_report_zones(struct block_device *bdev, sector_t sector,
>  	if (WARN_ON_ONCE(!disk->fops->report_zones))
>  		return -EOPNOTSUPP;
>  
> -	if (!*nr_zones || sector >= bdev->bd_part->nr_sects) {
> +	if (!*nr_zones || sector >= capacity) {
>  		*nr_zones = 0;
>  		return 0;
>  	}
>  
> -	nrz = min(*nr_zones,
> -		  __blkdev_nr_zones(q, bdev->bd_part->nr_sects - sector));
> -	ret = disk->fops->report_zones(disk, get_start_sect(bdev) + sector,
> -				       zones, &nrz);
> -	if (ret)
> -		return ret;
> +	*nr_zones = min(*nr_zones, __blkdev_nr_zones(q, capacity - sector));
>  
> -	for (i = 0; i < nrz; i++) {
> -		if (!blkdev_report_zone(bdev, zones))
> -			break;
> -		zones++;
> -	}
> -
> -	*nr_zones = i;
> -
> -	return 0;
> +	return disk->fops->report_zones(disk, sector, zones, nr_zones);
>  }
>  EXPORT_SYMBOL_GPL(blkdev_report_zones);
>  
> @@ -185,15 +149,11 @@ static inline bool blkdev_allow_reset_all_zones(struct block_device *bdev,
>  	if (!blk_queue_zone_resetall(bdev_get_queue(bdev)))
>  		return false;
>  
> -	if (sector || nr_sectors != part_nr_sects_read(bdev->bd_part))
> -		return false;
>  	/*
> -	 * REQ_OP_ZONE_RESET_ALL can be executed only if the block device is
> -	 * the entire disk, that is, if the blocks device start offset is 0 and
> -	 * its capacity is the same as the entire disk.
> +	 * REQ_OP_ZONE_RESET_ALL can be executed only if the number of sectors
> +	 * of the applicable zone range is the entire disk.
>  	 */
> -	return get_start_sect(bdev) == 0 &&
> -	       part_nr_sects_read(bdev->bd_part) == get_capacity(bdev->bd_disk);
> +	return !sector && nr_sectors == get_capacity(bdev->bd_disk);
>  }
>  
>  /**
> @@ -218,6 +178,7 @@ int blkdev_zone_mgmt(struct block_device *bdev, enum req_opf op,
>  {
>  	struct request_queue *q = bdev_get_queue(bdev);
>  	sector_t zone_sectors = blk_queue_zone_sectors(q);
> +	sector_t capacity = get_capacity(bdev->bd_disk);
>  	sector_t end_sector = sector + nr_sectors;
>  	struct bio *bio = NULL;
>  	int ret;
> @@ -231,7 +192,7 @@ int blkdev_zone_mgmt(struct block_device *bdev, enum req_opf op,
>  	if (!op_is_zone_mgmt(op))
>  		return -EOPNOTSUPP;
>  
> -	if (!nr_sectors || end_sector > bdev->bd_part->nr_sects)
> +	if (!nr_sectors || end_sector > capacity)
>  		/* Out of range */
>  		return -EINVAL;
>  
> @@ -239,8 +200,7 @@ int blkdev_zone_mgmt(struct block_device *bdev, enum req_opf op,
>  	if (sector & (zone_sectors - 1))
>  		return -EINVAL;
>  
> -	if ((nr_sectors & (zone_sectors - 1)) &&
> -	    end_sector != bdev->bd_part->nr_sects)
> +	if ((nr_sectors & (zone_sectors - 1)) && end_sector != capacity)
>  		return -EINVAL;
>  
>  	while (sector < end_sector) {
> diff --git a/block/partition-generic.c b/block/partition-generic.c
> index aee643ce13d1..31bff3fb28af 100644
> --- a/block/partition-generic.c
> +++ b/block/partition-generic.c
> @@ -459,56 +459,6 @@ static int drop_partitions(struct gendisk *disk, struct block_device *bdev)
>  	return 0;
>  }
>  
> -static bool part_zone_aligned(struct gendisk *disk,
> -			      struct block_device *bdev,
> -			      sector_t from, sector_t size)
> -{
> -	unsigned int zone_sectors = bdev_zone_sectors(bdev);
> -
> -	/*
> -	 * If this function is called, then the disk is a zoned block device
> -	 * (host-aware or host-managed). This can be detected even if the
> -	 * zoned block device support is disabled (CONFIG_BLK_DEV_ZONED not
> -	 * set). In this case, however, only host-aware devices will be seen
> -	 * as a block device is not created for host-managed devices. Without
> -	 * zoned block device support, host-aware drives can still be used as
> -	 * regular block devices (no zone operation) and their zone size will
> -	 * be reported as 0. Allow this case.
> -	 */
> -	if (!zone_sectors)
> -		return true;
> -
> -	/*
> -	 * Check partition start and size alignement. If the drive has a
> -	 * smaller last runt zone, ignore it and allow the partition to
> -	 * use it. Check the zone size too: it should be a power of 2 number
> -	 * of sectors.
> -	 */
> -	if (WARN_ON_ONCE(!is_power_of_2(zone_sectors))) {
> -		u32 rem;
> -
> -		div_u64_rem(from, zone_sectors, &rem);
> -		if (rem)
> -			return false;
> -		if ((from + size) < get_capacity(disk)) {
> -			div_u64_rem(size, zone_sectors, &rem);
> -			if (rem)
> -				return false;
> -		}
> -
> -	} else {
> -
> -		if (from & (zone_sectors - 1))
> -			return false;
> -		if ((from + size) < get_capacity(disk) &&
> -		    (size & (zone_sectors - 1)))
> -			return false;
> -
> -	}
> -
> -	return true;
> -}
> -
>  int rescan_partitions(struct gendisk *disk, struct block_device *bdev)
>  {
>  	struct parsed_partitions *state = NULL;
> @@ -544,6 +494,14 @@ int rescan_partitions(struct gendisk *disk, struct block_device *bdev)
>  		}
>  		return -EIO;
>  	}
> +
> +	/* Partitions are not supported on zoned block devices */
> +	if (bdev_is_zoned(bdev)) {
> +		pr_warn("%s: ignoring partition table on zoned block device\n",
> +			disk->disk_name);
> +		goto out;
> +	}
> +
>  	/*
>  	 * If any partition code tried to read beyond EOD, try
>  	 * unlocking native capacity even if partition table is

While I do applaud removing special cases for zoned devices, we do have
the GENHD_FL_NO_PART_SCAN for precisely this use case.
Any particular reason why this isn't being used, nor even set?

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      Teamlead Storage & Networking
hare@suse.de			                  +49 911 74053 688
SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 247165 (AG München), GF: Felix Imendörffer