[SCSI] Don't add scsi_device for devices that return PQ=1, PDT=0x1f

Some targets may return slight variations of PQ and PDT to indicate
no LUN mapped.  USB UFI setting PDT=0x1f but having reserved bits for
PQ is one example, and NetApp targets returning PQ=1 and PDT=0x1f is
another.  Both instances seem like reasonable responses according to
SPC-3 and UFI specs.

The current scsi_probe_and_add_lun() code adds a scsi_device
for targets that return PQ=1 and PDT=0x1f.  This causes LUNs of type
"UNKNOWN" to show up in /proc/scsi/scsi when no LUNs are mapped.
In addition, subsequent rescans fail to recognize LUNs that may be
added on the target, unless preceded by a write to the delete attribute
of the "UNKNOWN" LUN.

This patch addresses this problem by skipping over the scsi_add_lun()
when PQ=1,PDT=0x1f is encountered, and just returns
SCSI_SCAN_TARGET_PRESENT.

Signed-off-by: Dave Wysochanski <davidw@netapp.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>

1 files changed, 19 insertions, 4 deletions

diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
index 114e2067dce5..a24d3461fc78 100644
--- a/drivers/scsi/scsi_scan.c
+++ b/drivers/scsi/scsi_scan.c
@@ -893,11 +893,26 @@ static int scsi_probe_and_add_lun(struct scsi_target *starget,
         }
 
         /*
-         * Non-standard SCSI targets may set the PDT to 0x1f (unknown or
-         * no device type) instead of using the Peripheral Qualifier to
-         * indicate that no LUN is present.  For example, USB UFI does this.
+         * Some targets may set slight variations of PQ and PDT to signal
+         * that no LUN is present, so don't add sdev in these cases.
+         * Two specific examples are:
+         * 1) NetApp targets: return PQ=1, PDT=0x1f
+         * 2) USB UFI: returns PDT=0x1f, with the PQ bits being "reserved"
+         *    in the UFI 1.0 spec (we cannot rely on reserved bits).
+         *
+         * References:
+         * 1) SCSI SPC-3, pp. 145-146
+         * PQ=1: "A peripheral device having the specified peripheral
+         * device type is not connected to this logical unit. However, the
+         * device server is capable of supporting the specified peripheral
+         * device type on this logical unit."
+         * PDT=0x1f: "Unknown or no device type"
+         * 2) USB UFI 1.0, p. 20
+         * PDT=00h Direct-access device (floppy)
+         * PDT=1Fh none (no FDD connected to the requested logical unit)
          */
-        if (starget->pdt_1f_for_no_lun && (result[0] & 0x1f) == 0x1f) {
+        if (((result[0] >> 5) == 1 || starget->pdt_1f_for_no_lun) &&
+             (result[0] & 0x1f) == 0x1f) {
                 SCSI_LOG_SCAN_BUS(3, printk(KERN_INFO
                                         "scsi scan: peripheral device type"
                                         " of 31, no device added\n"));