block: track zone conditions

The function blk_revalidate_zone_cond() already caches the condition of
all zones of a zoned block device in the zones_cond array of a gendisk.
However, the zone conditions are updated only when the device is scanned
or revalidated.

Implement tracking of the runtime changes to zone conditions using
the new cond field in struct blk_zone_wplug. The size of this structure
remains 112 Bytes as the new field replaces the 4 Bytes padding at the
end of the structure.

Beause zones that do not have a zone write plug can be in the empty,
implicit open, explicit open or full condition, the zones_cond array of
a disk is used to track the conditions, of zones that do not have a zone
write plug. The condition of such zone is updated in the disk zones_cond
array when a zone reset, reset all or finish operation is executed, and
also when a zone write plug is removed from the disk hash table when the
zone becomes full.

Since a device may automatically close an implicitly open zone when
writing to an empty or closed zone, if the total number of open zones
has reached the device limit, the BLK_ZONE_COND_IMP_OPEN and
BLK_ZONE_COND_CLOSED zone conditions cannot be precisely tracked. To
overcome this, the zone condition BLK_ZONE_COND_ACTIVE is introduced to
represent a zone that has the condition BLK_ZONE_COND_IMP_OPEN,
BLK_ZONE_COND_EXP_OPEN or BLK_ZONE_COND_CLOSED.  This follows the
definition of an active zone as defined in the NVMe Zoned Namespace
specifications. As such, for a zoned device that has a limit on the
maximum number of open zones, we will never have more zones in the
BLK_ZONE_COND_ACTIVE condition than the device limit. This is compatible
with the SCSI ZBC and ATA ZAC specifications for SMR HDDs as these
devices do not have a limit on the number of active zones.

The function disk_zone_wplug_set_wp_offset() is modified to use the new
helper disk_zone_wplug_update_cond() to update a zone write plug
condition whenever a zone write plug write offset is updated on
submission or merging of write BIOs to a zone.

The functions blk_zone_reset_bio_endio(), blk_zone_reset_all_bio_endio()
and blk_zone_finish_bio_endio() are modified to update the condition of
the zones targeted by reset, reset_all and finish operations, either
using though disk_zone_wplug_set_wp_offset() for zones that have a
zone write plug, or using the disk_zone_set_cond() helper to update the
zones_cond array of the disk for zones that do not have a zone write
plug.

When a zone write plug is removed from the disk hash table (when the
zone becomes empty or full), the condition of struct blk_zone_wplug is
used to update the disk zones_cond array. Conversely, when a zone write
plug is added to the disk hash table, the zones_cond array is used to
initialize the zone write plug condition.

Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 11 insertions, 0 deletions

diff --git a/include/uapi/linux/blkzoned.h b/include/uapi/linux/blkzoned.h
index f85743ef6e7d..5c7662971414 100644
--- a/include/uapi/linux/blkzoned.h
+++ b/include/uapi/linux/blkzoned.h
@@ -48,6 +48,8 @@ enum blk_zone_type {
  *                      FINISH ZONE command.
  * @BLK_ZONE_COND_READONLY: The zone is read-only.
  * @BLK_ZONE_COND_OFFLINE: The zone is offline (sectors cannot be read/written).
+ * @BLK_ZONE_COND_ACTIVE: The zone is either implicitly open, explicitly open,
+ *			  or closed.
  *
  * The Zone Condition state machine in the ZBC/ZAC standards maps the above
  * deinitions as:
@@ -61,6 +63,13 @@ enum blk_zone_type {
  *
  * Conditions 0x5 to 0xC are reserved by the current ZBC/ZAC spec and should
  * be considered invalid.
+ *
+ * The condition BLK_ZONE_COND_ACTIVE is used only with cached zone reports.
+ * It is used to report any of the BLK_ZONE_COND_IMP_OPEN,
+ * BLK_ZONE_COND_EXP_OPEN and BLK_ZONE_COND_CLOSED conditions. Conversely, a
+ * regular zone report will never report a zone condition using
+ * BLK_ZONE_COND_ACTIVE and instead use the conditions BLK_ZONE_COND_IMP_OPEN,
+ * BLK_ZONE_COND_EXP_OPEN or BLK_ZONE_COND_CLOSED as reported by the device.
  */
 enum blk_zone_cond {
 	BLK_ZONE_COND_NOT_WP	= 0x0,
@@ -71,6 +80,8 @@ enum blk_zone_cond {
 	BLK_ZONE_COND_READONLY	= 0xD,
 	BLK_ZONE_COND_FULL	= 0xE,
 	BLK_ZONE_COND_OFFLINE	= 0xF,
+
+	BLK_ZONE_COND_ACTIVE	= 0xFF,
 };
 
 /**