block: Introduce queue flag QUEUE_FLAG_SCSI_PASSTHROUGH

From the context where a SCSI command is submitted it is not always
possible to figure out whether or not the queue the command is
submitted to has struct scsi_request as the first member of its
private data. Hence introduce the flag QUEUE_FLAG_SCSI_PASSTHROUGH.

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Cc: Omar Sandoval <osandov@fb.com>
Cc: Don Brace <don.brace@microsemi.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

drivers/ide/ide-probe.c

@@ -773,6 +773,7 @@ static int ide_init_queue(ide_drive_t *drive)
 	q->request_fn = do_ide_request;
 	q->init_rq_fn = ide_init_rq;
 	q->cmd_size = sizeof(struct ide_request);
+	queue_flag_set_unlocked(QUEUE_FLAG_SCSI_PASSTHROUGH, q);
 	if (blk_init_allocated_queue(q) < 0) {
 		blk_cleanup_queue(q);
 		return 1;