[PATCH 4/4] scsi: core: Match ULDs to logical units in the ALUA unavailable state

[Brian Bunker <brian@purestorage.com>]

scsi_bus_match() only matches devices with peripheral qualifier 000b,
so a LU that is in the ALUA unavailable state on a target port when
the host scans it never gets an upper-level driver on that path. When
the target port becomes available again, nothing binds sd and the path
stays unusable until the device is deleted and rescanned. A host that
was already running when the path became unavailable keeps sd bound,
so the result depends on when the host scanned.

Peripheral qualifier 001b cannot be matched on its own: an unmapped
LUN reports it as well, and some targets report every possible LUN in
REPORT LUNS. Binding sd to all of those would create disks with no
backing LU.

The SCSI core now reads the access state of a device that supports
target port groups with REPORT TARGET PORT GROUPS before the device is
registered, and an unmapped LUN fails that command. Also match PQ 001b
devices whose access state is unavailable. sd then binds to the
unavailable path like it does to a standby path, the path stays in the
multipath map as a failed path, and the existing UNIT ATTENTION
handling brings it back when the target port becomes available.

This is the same situation as a path in the standby state, to which sd
already binds: SPC-4 requires READ CAPACITY in neither state. The
cached INQUIRY data in sysfs keeps the peripheral qualifier reported at
scan time, like the rest of the INQUIRY data; access_state shows the
current ALUA state.

Co-developed-by: Krishna Kant <krishna.kant@purestorage.com>
Signed-off-by: Krishna Kant <krishna.kant@purestorage.com>
Signed-off-by: Brian Bunker <brian@purestorage.com>
---
 drivers/scsi/scsi_sysfs.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
index fe54792ed69e..8d90f0c715ce 100644
--- a/drivers/scsi/scsi_sysfs.c
+++ b/drivers/scsi/scsi_sysfs.c
@@ -539,7 +539,19 @@ static int scsi_bus_match(struct device *dev, const struct device_driver *gendrv
 	sdp = to_scsi_device(dev);
 	if (sdp->no_uld_attach)
 		return 0;
-	return (sdp->inq_periph_qual == SCSI_INQ_PQ_CON)? 1: 0;
+	if (sdp->inq_periph_qual == SCSI_INQ_PQ_CON)
+		return 1;
+	/*
+	 * Peripheral qualifier 001b is also what a LU reports while it is in
+	 * the ALUA unavailable state on this target port (SPC-4 5.15.2.4.5).
+	 * scsi_add_lun() reads that state with REPORT TARGET PORT GROUPS
+	 * before the device is registered. A LUN that is not mapped reports
+	 * 001b too, but fails REPORT TARGET PORT GROUPS and so is not
+	 * matched.
+	 */
+	return sdp->inq_periph_qual == SCSI_INQ_PQ_NOT_CON &&
+	       (sdp->access_state & SCSI_ACCESS_STATE_MASK) ==
+			SCSI_ACCESS_STATE_UNAVAILABLE;
 }
 
 static int scsi_bus_uevent(const struct device *dev, struct kobj_uevent_env *env)
-- 
2.56.0