scsi: provide mq_ops->busy() hook

Only the SCSI legacy path provides a way to check if target is
currently busy, provide the same for the MQ path.

Cc: linux-scsi@vger.kernel.org
Reviewed-by: Hannes Reinecke <hare@suse.com>
Tested-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Omar Sandoval <osandov@fb.com>
Acked-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/scsi/scsi_lib.c

@@ -1675,6 +1675,11 @@ static int scsi_lld_busy(struct request_queue *q)
 	return 0;
 }
 
+static bool scsi_mq_lld_busy(struct request_queue *q)
+{
+	return scsi_lld_busy(q);
+}
+
 /*
  * Kill a request for a dead device
  */
@@ -2326,6 +2331,7 @@ static const struct blk_mq_ops scsi_mq_ops = {
 	.init_request	= scsi_mq_init_request,
 	.exit_request	= scsi_mq_exit_request,
 	.initialize_rq_fn = scsi_initialize_rq,
+	.busy		= scsi_mq_lld_busy,
 	.map_queues	= scsi_map_queues,
 };