scsi_scan: Restrict sequential scan to 256 LUNs

Sequential scan for more than 256 LUNs is very fragile as
LUNs might not be numbered sequentially after that point.

SAM revisions later than SCSI-3 impose a structure on
LUNs larger than 256, making LUN numbers between 256
and 16384 illegal.
SCSI-3, however allows for plain 64-bit numbers with
no internal structure.

So restrict sequential LUN scan to 256 LUNs and add a
new blacklist flag 'BLIST_SCSI3LUN' to scan up to
max_lun devices.
Signed-off-by: NHannes Reinecke <hare@suse.de>
Reviewed-by: NEwan Milne <emilne@redhat.com>
Signed-off-by: NChristoph Hellwig <hch@lst.de>

drivers/scsi/scsi_scan.c

@@ -1234,6 +1234,12 @@ static void scsi_sequential_lun_scan(struct scsi_target *starget,
 	if (scsi_level < SCSI_3 && !(bflags & BLIST_LARGELUN))
 		max_dev_lun = min(8U, max_dev_lun);
 
+	/*
+	 * Stop scanning at 255 unless BLIST_SCSI3LUN
+	 */
+	if (!(bflags & BLIST_SCSI3LUN))
+		max_dev_lun = min(256U, max_dev_lun);
+
 	/*
 	 * We have already scanned LUN 0, so start at LUN 1. Keep scanning
 	 * until we reach the max, or no LUN is found and we are not

include/scsi/scsi_devinfo.h

@@ -32,4 +32,6 @@
 #define BLIST_ATTACH_PQ3	0x1000000 /* Scan: Attach to PQ3 devices */
 #define BLIST_NO_DIF		0x2000000 /* Disable T10 PI (DIF) */
 #define BLIST_SKIP_VPD_PAGES	0x4000000 /* Ignore SBC-3 VPD pages */
+#define BLIST_SCSI3LUN		0x8000000 /* Scan more than 256 LUNs
+					     for sequential scan */
 #endif