scsi: core: Show nr_hw_queues in sysfs

So that we don't use a value of 0 for when Scsi_Host.nr_hw_queues is unset,
use the tag_set->nr_hw_queues (which holds 1 for this case).
Signed-off-by: John Garry <john.garry@huawei.com>
Tested-by: Douglas Gilbert <dgilbert@interlog.com>
Acked-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/scsi/scsi_sysfs.c

@@ -393,6 +393,16 @@ show_use_blk_mq(struct device *dev, struct device_attribute *attr, char *buf)
 }
 static DEVICE_ATTR(use_blk_mq, S_IRUGO, show_use_blk_mq, NULL);
 
+static ssize_t
+show_nr_hw_queues(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	struct Scsi_Host *shost = class_to_shost(dev);
+	struct blk_mq_tag_set *tag_set = &shost->tag_set;
+
+	return snprintf(buf, 20, "%d\n", tag_set->nr_hw_queues);
+}
+static DEVICE_ATTR(nr_hw_queues, S_IRUGO, show_nr_hw_queues, NULL);
+
 static struct attribute *scsi_sysfs_shost_attrs[] = {
 	&dev_attr_use_blk_mq.attr,
 	&dev_attr_unique_id.attr,
@@ -411,6 +421,7 @@ static struct attribute *scsi_sysfs_shost_attrs[] = {
 	&dev_attr_prot_guard_type.attr,
 	&dev_attr_host_reset.attr,
 	&dev_attr_eh_deadline.attr,
+	&dev_attr_nr_hw_queues.attr,
 	NULL
 };