scsi: Use blk_mq_rq_to_pdu() to convert a request to a SCSI command pointer

Since commit e9c787e65c0c ("scsi: allocate scsi_cmnd structures as
part of struct request") struct request and struct scsi_cmnd are
adjacent. This means that there is now an alternative to reading
req->special to convert a pointer to a prepared request into a
SCSI command pointer, namely by using blk_mq_rq_to_pdu(). Make
this change where appropriate. Although this patch does not
change any functionality, it slightly improves performance and
slightly improves readability.

Signed-off-by: Bart Van Assche <[e-mail]>
Reviewed-by: Hannes Reinecke <[e-mail]>
Reviewed-by: Johannes Thumshirn <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/scsi/scsi_error.c

···
  */
 enum blk_eh_timer_return scsi_times_out(struct request *req)
 {
-	struct scsi_cmnd *scmd = req->special;
+	struct scsi_cmnd *scmd = blk_mq_rq_to_pdu(req);
 	enum blk_eh_timer_return rtn = BLK_EH_NOT_HANDLED;
 	struct Scsi_Host *host = scmd->device->host;
 

drivers/scsi/scsi_lib.c

···
 static bool scsi_end_request(struct request *req, blk_status_t error,
 		unsigned int bytes, unsigned int bidi_bytes)
 {
-	struct scsi_cmnd *cmd = req->special;
+	struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(req);
 	struct scsi_device *sdev = cmd->device;
 	struct request_queue *q = sdev->request_queue;
 
···
 
 static int scsi_setup_scsi_cmnd(struct scsi_device *sdev, struct request *req)
 {
-	struct scsi_cmnd *cmd = req->special;
+	struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(req);
 
 	/*
 	 * Passthrough requests may transfer data, in which case they must
···
  */
 static int scsi_setup_fs_cmnd(struct scsi_device *sdev, struct request *req)
 {
-	struct scsi_cmnd *cmd = req->special;
+	struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(req);
 
 	if (unlikely(sdev->handler && sdev->handler->prep_fn)) {
 		int ret = sdev->handler->prep_fn(sdev, req);
···
 
 static int scsi_setup_cmnd(struct scsi_device *sdev, struct request *req)
 {
-	struct scsi_cmnd *cmd = req->special;
+	struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(req);
 
 	if (!blk_rq_bytes(req))
 		cmd->sc_data_direction = DMA_NONE;
···
 
 static void scsi_unprep_fn(struct request_queue *q, struct request *req)
 {
-	scsi_uninit_cmd(req->special);
+	scsi_uninit_cmd(blk_mq_rq_to_pdu(req));
 }
 
 /*
···
  */
 static void scsi_kill_request(struct request *req, struct request_queue *q)
 {
-	struct scsi_cmnd *cmd = req->special;
+	struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(req);
 	struct scsi_device *sdev;
 	struct scsi_target *starget;
 	struct Scsi_Host *shost;
···
 
 static void scsi_softirq_done(struct request *rq)
 {
-	struct scsi_cmnd *cmd = rq->special;
+	struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(rq);
 	unsigned long wait_for = (cmd->allowed + 1) * rq->timeout;
 	int disposition;
 
···
 			blk_start_request(req);
 
 		spin_unlock_irq(q->queue_lock);
-		cmd = req->special;
-		if (unlikely(cmd == NULL)) {
+		cmd = blk_mq_rq_to_pdu(req);
+		if (cmd != req->special) {
 			printk(KERN_CRIT "impossible request in %s.\n"
 					 "please mail a stack trace to "
 					 "[e-mail]\n",

include/scsi/scsi_tcq.h

···
 
 	if (!req)
 		return NULL;
-	return req->special;
+	return blk_mq_rq_to_pdu(req);
 }
 
 #endif /* CONFIG_BLOCK */