block: add and use scsi_blk_cmd_ioctl

Introduce a wrapper around scsi_cmd_ioctl that takes a block device.

The function will then be enhanced to detect partition block devices
and, in that case, subject the ioctls to whitelisting.

Cc: linux-scsi@vger.kernel.org
Cc: Jens Axboe <axboe@kernel.dk>
Cc: James Bottomley <JBottomley@parallels.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/cdrom/cdrom.c b/drivers/cdrom/cdrom.c
index 1bbf764..55eaf47 100644
--- a/drivers/cdrom/cdrom.c
+++ b/drivers/cdrom/cdrom.c
@@ -2746,12 +2746,11 @@
 {
 	void __user *argp = (void __user *)arg;
 	int ret;
-	struct gendisk *disk = bdev->bd_disk;
 
 	/*
 	 * Try the generic SCSI command ioctl's first.
 	 */
-	ret = scsi_cmd_ioctl(disk->queue, disk, mode, cmd, argp);
+	ret = scsi_cmd_blk_ioctl(bdev, mode, cmd, argp);
 	if (ret != -ENOTTY)
 		return ret;