block: introduce blkdev_get_zone_info()

Introduce the function blkdev_get_zone_info() to obtain a single zone
information from cached zone data, that is, either from the zone write
plug for the target zone if it exists and from the disk zones_cond
array otherwise.

Since sequential zones that do not have a zone write plug are either
full, empty or in a bad state (read-only or offline), the zone write
pointer can be inferred from the zone condition cached in the disk
zones_cond array. For sequential zones that have a zone write plug, the
zone condition and zone write pointer are obtained from the condition
and write pointer offset managed with the zone write plug. This allows
obtaining the information for a zone much more quickly than having to
execute a report zones command on the device.

blkdev_get_zone_info() falls back to using a regular zone report if the
target zone is flagged as needing an update with the
BLK_ZONE_WPLUG_NEED_WP_UPDATE flag, or if the target device does not
use zone write plugs (i.e. a device mapper device). In this case, the
new function blkdev_report_zone_fallback() is used and the zone
condition is reported consistantly with the cahced report, that is, the
BLK_ZONE_COND_ACTIVE condition is used in place of the implicit open,
explicit open and closed conditions. This is achieved by adding the
.report_active field to struct blk_report_zones_args and by having
disk_report_zone() sets the correct zone condition if .report_active is
true.

In preparation for using blkdev_get_zone_info() in upcoming file systems
changes, also export this function as a GPL symbol.

Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 53bcfbc2f68f..03a594b4dfbc 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -436,6 +436,9 @@ typedef int (*report_zones_cb)(struct blk_zone *zone, unsigned int idx,
 int disk_report_zone(struct gendisk *disk, struct blk_zone *zone,
 		     unsigned int idx, struct blk_report_zones_args *args);
 
+int blkdev_get_zone_info(struct block_device *bdev, sector_t sector,
+			 struct blk_zone *zone);
+
 #define BLK_ALL_ZONES  ((unsigned int)-1)
 int blkdev_report_zones(struct block_device *bdev, sector_t sector,
 		unsigned int nr_zones, report_zones_cb cb, void *data);