block: Introduce blkdev_nr_zones() helper

Introduce the blkdev_nr_zones() helper function to get the total
number of zones of a zoned block device. This number is always 0 for a
regular block device (q->limits.zoned == BLK_ZONED_NONE case).

Replace hard-coded number of zones calculation in dmz_get_zoned_device()
with a call to this helper.
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>

block/blk-zoned.c

@@ -63,6 +63,33 @@ void __blk_req_zone_write_unlock(struct request *rq)
 }
 EXPORT_SYMBOL_GPL(__blk_req_zone_write_unlock);
 
+static inline unsigned int __blkdev_nr_zones(struct request_queue *q,
+					     sector_t nr_sectors)
+{
+	unsigned long zone_sectors = blk_queue_zone_sectors(q);
+
+	return (nr_sectors + zone_sectors - 1) >> ilog2(zone_sectors);
+}
+
+/**
+ * blkdev_nr_zones - Get number of zones
+ * @bdev:	Target block device
+ *
+ * Description:
+ *    Return the total number of zones of a zoned block device.
+ *    For a regular block device, the number of zones is always 0.
+ */
+unsigned int blkdev_nr_zones(struct block_device *bdev)
+{
+	struct request_queue *q = bdev_get_queue(bdev);
+
+	if (!blk_queue_is_zoned(q))
+		return 0;
+
+	return __blkdev_nr_zones(q, bdev->bd_part->nr_sects);
+}
+EXPORT_SYMBOL_GPL(blkdev_nr_zones);
+
 /*
  * Check that a zone report belongs to the partition.
  * If yes, fix its start sector and write pointer, copy it in the

drivers/md/dm-zoned-target.c

@@ -702,8 +702,7 @@ static int dmz_get_zoned_device(struct dm_target *ti, char *path)
 	dev->zone_nr_blocks = dmz_sect2blk(dev->zone_nr_sectors);
 	dev->zone_nr_blocks_shift = ilog2(dev->zone_nr_blocks);
 
-	dev->nr_zones = (dev->capacity + dev->zone_nr_sectors - 1)
-		>> dev->zone_nr_sectors_shift;
+	dev->nr_zones = blkdev_nr_zones(dev->bdev);
 
 	dmz->dev = dev;
 

include/linux/blkdev.h

@@ -401,6 +401,7 @@ struct blk_zone_report_hdr {
 	u8		padding[60];
 };
 
+extern unsigned int blkdev_nr_zones(struct block_device *bdev);
 extern int blkdev_report_zones(struct block_device *bdev,
 			       sector_t sector, struct blk_zone *zones,
 			       unsigned int *nr_zones, gfp_t gfp_mask);
@@ -414,6 +415,10 @@ extern int blkdev_reset_zones_ioctl(struct block_device *bdev, fmode_t mode,
 
 #else /* CONFIG_BLK_DEV_ZONED */
 
+static inline unsigned int blkdev_nr_zones(struct block_device *bdev)
+{
+	return 0;
+}
 static inline int blkdev_report_zones_ioctl(struct block_device *bdev,
 					    fmode_t mode, unsigned int cmd,
 					    unsigned long arg)