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 <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 11 insertions, 0 deletions

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 3772671cf2bc..92be8092ca4f 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -300,6 +300,11 @@ static ssize_t queue_zoned_show(struct request_queue *q, char *page)
         }
 }
 
+static ssize_t queue_nr_zones_show(struct request_queue *q, char *page)
+{
+        return queue_var_show(blk_queue_nr_zones(q), page);
+}
+
 static ssize_t queue_nomerges_show(struct request_queue *q, char *page)
 {
         return queue_var_show((blk_queue_nomerges(q) << 1) |
@@ -637,6 +642,11 @@ static struct queue_sysfs_entry queue_zoned_entry = {
         .show = queue_zoned_show,
 };
 
+static struct queue_sysfs_entry queue_nr_zones_entry = {
+        .attr = {.name = "nr_zones", .mode = 0444 },
+        .show = queue_nr_zones_show,
+};
+
 static struct queue_sysfs_entry queue_nomerges_entry = {
         .attr = {.name = "nomerges", .mode = 0644 },
         .show = queue_nomerges_show,
@@ -727,6 +737,7 @@ static struct attribute *default_attrs[] = {
         &queue_write_zeroes_max_entry.attr,
         &queue_nonrot_entry.attr,
         &queue_zoned_entry.attr,
+        &queue_nr_zones_entry.attr,
         &queue_nomerges_entry.attr,
         &queue_rq_affinity_entry.attr,
         &queue_iostats_entry.attr,