I would like to revert commit 948e922fc446 ("scsi: core: map PQ=1,
PDT=other values to SCSI_SCAN_TARGET_PRESENT").
I have been spending quite a bit of time digging through old SCSI and
controller specs. As far as I can tell the original Linux behavior was
correct. Recent SPC specs are very abstract in this department resulting
in unfortunate ambiguity. But originally PQ=1 meant "LUN supports this
peripheral device type but no physical device is currently connected".
Based on this original definition, PQ=1 has been widely used throughout
the industry as a means to avoid associating an ULD driver with a
device. The LUN is accessible (primary commands, etc.) but no media is
present (no physical device connected).
Our original algorithm, which I would like to reinstate, is essentially
the following (in slightly unrolled form):
if (PQ == 3)
/* Don't expose device */
else if ((PQ == 1 || sdev->pdt_1f_for_no_lun) && PDT == 0x1f)
/* Don't expose device */
else if (PQ == 1) {
/* Expose device, don't bind ULD */
} else /* PQ == 0 */
/* Expose device, bind ULD if PDT is supported */
I would like to understand why -- in the case of the IBM 2145 --
exposing the sg device caused problems. Li: Can you shed some light on
the problems caused by 2145 LUNs reporting PQ=1?
Thanks!
--
Martin K. Petersen Oracle Linux Engineering
