block: add a queue_has_disk helper

Add a helper to check if a gendisk is associated with a request_queue.

Signed-off-by: Christoph Hellwig <[e-mail]>
Reviewed-by: Jan Kara <[e-mail]>
Reviewed-by: Johannes Thumshirn <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jens Axboe <[e-mail]>

include/linux/blkdev.h

···
 	dma_map_page_attrs(dev, (bv)->bv_page, (bv)->bv_offset, (bv)->bv_len, \
 	(dir), (attrs))
 
+#define queue_has_disk(q)	((q)->kobj.parent != NULL)
 #define queue_to_disk(q)	(dev_to_disk(kobj_to_dev((q)->kobj.parent)))
 
 static inline bool queue_is_mq(struct request_queue *q)