Since using scsi_req() is only allowed against request queues for
which struct scsi_request is the first member of their private
request data, refuse to submit SCSI commands against a queue for
which this is not the case.
References: commit 
82ed4db499b8 ("block: split scsi_request out of struct request")
Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: J. Bruce Fields <bfields@redhat.com>
Cc: Jeff Layton <jlayton@poochiereds.net>
Cc: Omar Sandoval <osandov@fb.com>
Cc: linux-nfs@vger.kernel.org
Signed-off-by: Jens Axboe <axboe@fb.com>
        u8 *buf, *d, type, assoc;
        int error;
 
+       if (WARN_ON_ONCE(!blk_queue_scsi_passthrough(q)))
+               return -EINVAL;
+
        buf = kzalloc(bufflen, GFP_KERNEL);
        if (!buf)
                return -ENOMEM;