scsi: disable automatic target scan

On larger installations it is useful to disable automatic LUN scanning,
and only add the required LUNs via udev rules.  This can speed up bootup
dramatically.

This patch introduces a new scan module parameter value 'manual', which
works like 'none', but can be overridden by setting the 'rescan' value
from scsi_scan_target to 'SCSI_SCAN_MANUAL'.  And it updates all
relevant callers to set the 'rescan' value to 'SCSI_SCAN_MANUAL' if
invoked via the 'scan' option in sysfs.

Signed-off-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Ewan D. Milne <emilne@redhat.com>
Tested-by: Laurence Oberman <loberman@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/scsi_transport_sas.c

@@ -1614,7 +1614,8 @@ int sas_rphy_add(struct sas_rphy *rphy)
 		else
 			lun = 0;
 
-		scsi_scan_target(&rphy->dev, 0, rphy->scsi_target_id, lun, 0);
+		scsi_scan_target(&rphy->dev, 0, rphy->scsi_target_id, lun,
+				 SCSI_SCAN_INITIAL);
 	}
 
 	return 0;
@@ -1739,8 +1740,8 @@ static int sas_user_scan(struct Scsi_Host *shost, uint channel,
 
 		if ((channel == SCAN_WILD_CARD || channel == 0) &&
 		    (id == SCAN_WILD_CARD || id == rphy->scsi_target_id)) {
-			scsi_scan_target(&rphy->dev, 0,
-					 rphy->scsi_target_id, lun, 1);
+			scsi_scan_target(&rphy->dev, 0, rphy->scsi_target_id,
+					 lun, SCSI_SCAN_MANUAL);
 		}
 	}
 	mutex_unlock(&sas_host->lock);