diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 83fa09a..6237732 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -225,15 +225,29 @@ static int virtblk_ioctl(struct block_device *bdev, fmode_t mode,
 	struct gendisk *disk = bdev->bd_disk;
 	struct virtio_blk *vblk = disk->private_data;
 
+	/* user passes the address of a char[] for return of the id string
+	 * and has set char[0] to the array size.  copy id string to this
+	 * char[] and return the number of non-nul characters in the internal
+	 * id string.  The caller can then determine if all were received.
+	 */
 	if (cmd == 0x56424944) { /* 'VBID' */
 		void __user *usr_data = (void __user *)data;
 		char id_str[VIRTIO_BLK_ID_BYTES];
-		int err;
-
-		err = virtblk_get_id(disk, id_str);
-		if (!err && copy_to_user(usr_data, id_str, VIRTIO_BLK_ID_BYTES))
-			err = -EFAULT;
-		return err;
+		unsigned char idlen;
+		int rv;
+
+		if (copy_from_user(&idlen, usr_data, sizeof (idlen)))
+			return -EFAULT;
+		if (VIRTIO_BLK_ID_BYTES < idlen)
+			idlen = VIRTIO_BLK_ID_BYTES;
+		if ((rv = virtblk_get_id(disk, id_str)))
+			return rv;
+		if (copy_to_user(usr_data, id_str, idlen))
+			return -EFAULT;
+		for (rv = 0; rv < VIRTIO_BLK_ID_BYTES; ++rv)
+			if (!id_str[rv])
+				break;
+		return rv;
 	}
 	/*
 	 * Only allow the generic SCSI ioctls if the host can support it.