It seems, upon reading the 2.2.16 and 2.4.0-test1 source, that the
peripheral qualifier field of a SCSI inquiry isn't really used (except to
skip LUNs where a physical device is
not supported). To refresh, the peripheral qualifier field is the top 3
bits of byte 0 of the inquiry data, particularly the two values:
000b - physical device is connected to this LUN
001b - physical device *can* be connected to this LUN, but is not
presently
We have a device, part of a storage area network (SAN), that returns 000b in
this field if there is a disk attached that can be directly accessed by this
system, or 001b if the LUN would be supported, but is actually being handled
by a different controller. This would seem to be the proper use of this
field.
Since the scsi layer does not currently use these bits, when the LUN shows
up as TYPE_DISK, a READ_CAPACITY command is issued to the disk. In the 000b
case, this is proper. In the 001b, this is not, as the device isn't really
there, it's merely a placeholder, and the command returns with a check
condition, and no further I/Os are performed. The outcome is proper, but
there's an error printed that could be avoided by making use of the
peripheral qualifier bits, which could lead to a customer satisfaction
issue, tech support calls about SCSI errors, and the like.
I'd like sd.c to be able to ignore 001b devices, so it looks like the right
thing to do is to set SDp->online = FALSE in scan_scsis_single() in this
case. Patches to 2.2.16 and 2.4.0-test1 below.
Thoughts? Linus, if there are no objections, please apply.
Thanks,
Matt Domsch
Dell Enterprise Systems Group
Linux Development Team
--- linux-2.4.0-test1/drivers/scsi/scsi_scan.c.orig Tue Jul 11 11:41:56
2000
+++ linux/drivers/scsi/scsi_scan.c Tue Jul 11 11:44:33 2000
@@ -552,7 +552,9 @@
memcpy(SDpnt->rev, scsi_result + 32, 4);
SDpnt->removable = (0x80 & scsi_result[1]) >> 7;
- SDpnt->online = TRUE;
+ /* Use the peripheral qualifier field to determine online/offline
*/
+ if (((scsi_result[0] >> 5) & 7) == 1) SDpnt->online = FALSE;
+ else SDpnt->online = TRUE;
SDpnt->lockable = SDpnt->removable;
SDpnt->changed = 0;
SDpnt->access_count = 0;
--- linux-2.2.16/drivers/scsi/scsi.c.orig Tue Jul 4 04:20:59 2000
+++ linux/drivers/scsi/scsi.c scsi.c Tue Jul 11 06:45:46 2000
@@ -796,7 +796,9 @@
memcpy (SDpnt->rev, scsi_result + 32, 4);
SDpnt->removable = (0x80 & scsi_result[1]) >> 7;
- SDpnt->online = TRUE;
+ /* Use the peripheral qualifier field to determine online/offline */
+ if (((scsi_result[0] >> 5) & 7) == 1) SDpnt->online = FALSE;
+ else SDpnt->online = TRUE;
SDpnt->lockable = SDpnt->removable;
SDpnt->changed = 0;
SDpnt->access_count = 0;
-
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