xen/blkfront: reorder tests in xlblk_init()

In case we don't want pv block devices we should not test parameters
for sanity and eventually print out error messages. So test precluding
conditions before checking parameters.
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

drivers/block/xen-blkfront.c

@@ -2708,6 +2708,15 @@ static int __init xlblk_init(void)
 	if (!xen_domain())
 		return -ENODEV;
 
+	if (!xen_has_pv_disk_devices())
+		return -ENODEV;
+
+	if (register_blkdev(XENVBD_MAJOR, DEV_NAME)) {
+		pr_warn("xen_blk: can't get major %d with name %s\n",
+			XENVBD_MAJOR, DEV_NAME);
+		return -ENODEV;
+	}
+
 	if (xen_blkif_max_segments < BLKIF_MAX_SEGMENTS_PER_REQUEST)
 		xen_blkif_max_segments = BLKIF_MAX_SEGMENTS_PER_REQUEST;
 
@@ -2723,15 +2732,6 @@ static int __init xlblk_init(void)
 		xen_blkif_max_queues = nr_cpus;
 	}
 
-	if (!xen_has_pv_disk_devices())
-		return -ENODEV;
-
-	if (register_blkdev(XENVBD_MAJOR, DEV_NAME)) {
-		printk(KERN_WARNING "xen_blk: can't get major %d with name %s\n",
-		       XENVBD_MAJOR, DEV_NAME);
-		return -ENODEV;
-	}
-
 	INIT_DELAYED_WORK(&blkfront_work, blkfront_delay_work);
 
 	ret = xenbus_register_frontend(&blkfront_driver);