block: Expose queue nr_zones in sysfs

block: Expose queue nr_zones in sysfs

Expose through sysfs the nr_zones field of struct request_queue.
Exposing this value helps in debugging disk issues as well as
facilitating scripts based use of the disk (e.g. blktests).

For zoned block devices, the nr_zones field indicates the total number
of zones of the device calculated using the known disk capacity and
zone size. This number of zones is always 0 for regular block devices.

Since nr_zones is defined conditionally with CONFIG_BLK_DEV_ZONED,
introduce the blk_queue_nr_zones() function to return the correct value
for any device, regardless if CONFIG_BLK_DEV_ZONED is set.

Reviewed-by: Christoph Hellwig <[email protected]>
Reviewed-by: Hannes Reinecke <[email protected]>
Signed-off-by: Damien Le Moal <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>