[SCSI] Shorten the path length of scsi_cmd_to_driver()

This patch tries to shorten the path length of scsi_cmd_to_driver(). As only
REQ_TYPE_BLOCK_PC commands can be submitted without a driver, so we could
avoid the related NULL checking, as long as we make sure we don't use it for
REQ_TYPE_BLOCK_PC type commands. Plus, this fixes a bug where you get
different behaviors from REQ_TYPE_BLOCK_PC commands when a driver is and isn't
attached.
Signed-off-by: NLi Zhong <zhong@linux.vnet.ibm.com>
Reviewed-by: NMartin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: NJames Bottomley <JBottomley@Parallels.com>

drivers/scsi/scsi_error.c

@@ -789,7 +789,6 @@ static int scsi_send_eh_cmnd(struct scsi_cmnd *scmd, unsigned char *cmnd,
 			     int cmnd_size, int timeout, unsigned sense_bytes)
 {
 	struct scsi_device *sdev = scmd->device;
-	struct scsi_driver *sdrv = scsi_cmd_to_driver(scmd);
 	struct Scsi_Host *shost = sdev->host;
 	DECLARE_COMPLETION_ONSTACK(done);
 	unsigned long timeleft;
@@ -845,8 +844,11 @@ static int scsi_send_eh_cmnd(struct scsi_cmnd *scmd, unsigned char *cmnd,
 
 	scsi_eh_restore_cmnd(scmd, &ses);
 
-	if (sdrv && sdrv->eh_action)
-		rtn = sdrv->eh_action(scmd, cmnd, cmnd_size, rtn);
+	if (scmd->request->cmd_type != REQ_TYPE_BLOCK_PC) {
+		struct scsi_driver *sdrv = scsi_cmd_to_driver(scmd);
+		if (sdrv->eh_action)
+			rtn = sdrv->eh_action(scmd, cmnd, cmnd_size, rtn);
+	}
 
 	return rtn;
 }

include/scsi/scsi_cmnd.h

@@ -132,18 +132,10 @@ struct scsi_cmnd {
 	unsigned char tag;	/* SCSI-II queued command tag */
 };
 
+/* make sure not to use it with REQ_TYPE_BLOCK_PC commands */
 static inline struct scsi_driver *scsi_cmd_to_driver(struct scsi_cmnd *cmd)
 {
-	struct scsi_driver **sdp;
-
-	if (!cmd->request->rq_disk)
-		return NULL;
-
-	sdp = (struct scsi_driver **)cmd->request->rq_disk->private_data;
-	if (!sdp)
-		return NULL;
-
-	return *sdp;
+	return *(struct scsi_driver **)cmd->request->rq_disk->private_data;
 }
 
 extern struct scsi_cmnd *scsi_get_command(struct scsi_device *, gfp_t);