[PATCH 0/4] scsi: Bind sd to LUs in the ALUA unavailable state

[Brian Bunker <brian@purestorage.com>]

A LU that is in the ALUA unavailable state on a target port reports
peripheral qualifier 001b in its INQUIRY data. scsi_bus_match() only
matches devices with peripheral qualifier 000b, so if a host scans such
a path, no upper-level driver is ever bound to it. When the target port
later becomes available, 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.

This series fixes that at scan time. The SCSI core reads the ALUA access
state of a device with REPORT TARGET PORT GROUPS before the device is
registered, and matches sd to PQ 001b devices whose access state is
unavailable. This is the same situation as a path in the standby state,
to which sd already binds. The path then stays in the multipath map as a
failed path, and the existing UNIT ATTENTION handling brings it back
when the target port becomes available.

PQ 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. An unmapped
LUN fails REPORT TARGET PORT GROUPS, so the access state is what tells
the two cases apart.

  1/4 moves submit_rtpg() out of scsi_dh_alua into the SCSI core as
      scsi_report_tpgs(), so the core can read the ALUA state of a
      device itself. No functional change.
  2/4 sends REPORT TARGET PORT GROUPS from scsi_add_lun() for a device
      that reports TPGS support and sets sdev->access_state from the
      descriptor of the target port group of this path.
  3/4 starts a new port group in scsi_dh_alua in the access state the
      core read, rather than active/optimized, so that no I/O is let
      through to an unavailable path before the handler's first RTPG
      completes.
  4/4 matches PQ 001b devices whose access state is unavailable.

This is an alternative to the series that refreshes the INQUIRY data
and reprobes the device on rescan ("scsi: Refresh INQUIRY data and
reprobe on rescan", v8 last posted). That series needs a way to update
the INQUIRY data of a live device and to reprobe it. This one does not
change the INQUIRY data after the device is discovered, and has no
reprobe, so none of the locking and ordering issues that came with
refreshing it.

The INQUIRY data in sysfs is unchanged by this series. It is read and
created once, when the device is discovered, and keeps the peripheral
qualifier reported at that time like the rest of the INQUIRY data. At
any given time that cached peripheral qualifier can be out of sync with
the device, for example after the target port moves between available
and unavailable. An INQUIRY sent to the device returns the current
value, and the access_state attribute shows the current ALUA state.

Brian Bunker (4):
  scsi: core: Move REPORT TARGET PORT GROUPS into the SCSI core
  scsi: core: Read the ALUA access state when a device is scanned
  scsi: scsi_dh_alua: Start a port group in the scanned access state
  scsi: core: Match ULDs to logical units in the ALUA unavailable state

 drivers/scsi/device_handler/scsi_dh_alua.c | 72 ++++++-----------
 drivers/scsi/scsi_lib.c                    | 52 ++++++++++++
 drivers/scsi/scsi_scan.c                   | 94 ++++++++++++++++++++++
 drivers/scsi/scsi_sysfs.c                  | 14 +++-
 include/scsi/scsi_device.h                 |  3 +
 include/scsi/scsi_proto.h                  |  3 +
 6 files changed, 188 insertions(+), 50 deletions(-)

-- 
2.56.0