Re: [PATCH 00/13] scsi: Core ALUA driver

[Benjamin Marzinski <bmarzins@redhat.com>]

On Tue, Mar 17, 2026 at 12:06:50PM +0000, John Garry wrote:
> Following on the back of the ALUA support for native SCSI multipath
> proposal at [0], this is an attempt to move to a SCSI core ALUA driver.
> 
> Essentially this series move the bulk of the ALUA handling from
> scsi_dh_alua.c to a core driver. We still need to support ALUA for DH, so
> the scsi_dh_alua.c is still responsible for driving ALUA support and the
> SCSI core ALUA driver just provides a set of library functions for that.
> 
> The SCSI core ALUA driver also provides implicit ALUA support for no DH,
> like when we would be native SCSI multipath.
> 
> This series is just really an RFC quality work and its purpose is
> to decide on the direction of ALUA support for native SCSI multipath.
> 
> I think that this work is a real regression possibility for
> dm-multipath, so we need to be careful.

At the risk of showing just how limited my SCSI knowledge is, I need to
ask, Is any of this actually necessary to get native scsi multipath
working with Implicit ALUA?

If the goal is to limit this to IMPLICT ALUA only, I was expecting that
you could just leave the scsi_dh_alua code completely alone. If native
scsi multipathing didn't disable the device handler, it seemed that this
would basically just work. With the device handler attached, when the
array updates the ALUA state, that should, at least I believe, trigger a
unit attention that will fire off a RTPG command. That should update the
sdev->access_state, which the multipath code could use to pick the
correct path. Right? What am I missing here? Is this just a parallel
exercise to overhaul the ALUA code?

-Ben

> 
> [0] https://lore.kernel.org/linux-scsi/20260310114925.1222263-1-john.g.garry@oracle.com/T/#m9c054433076812dff464d0e3b50a00620cfe0af1
> 
> John Garry (13):
>   scsi: scsi_dh_alua: Delete alua_port_group
>   scsi: alua: Create a core ALUA driver
>   scsi: alua: Add scsi_alua_rtpg()
>   scsi: alua: Add scsi_alua_stpg()
>   scsi: alua: Add scsi_alua_tur()
>   scsi: alua: Add scsi_alua_rtpg_run()
>   scsi: alua: Add scsi_alua_stpg_run()
>   scsi: alua: Add scsi_alua_check_tpgs()
>   scsi: alua: Add scsi_alua_handle_state_transition()
>   scsi: alua: Add scsi_alua_prep_fn()
>   scsi: alua: Add scsi_device_alua_implicit()
>   scsi: scsi_dh_alua: Switch to use core support
>   scsi: core: Add implicit ALUA support
> 
>  drivers/scsi/Kconfig                       |   10 +-
>  drivers/scsi/Makefile                      |    1 +
>  drivers/scsi/device_handler/Kconfig        |    1 +
>  drivers/scsi/device_handler/scsi_dh_alua.c | 1003 ++------------------
>  drivers/scsi/scsi.c                        |    7 +
>  drivers/scsi/scsi_alua.c                   |  748 +++++++++++++++
>  drivers/scsi/scsi_error.c                  |    7 +
>  drivers/scsi/scsi_lib.c                    |    7 +
>  drivers/scsi/scsi_scan.c                   |    6 +
>  drivers/scsi/scsi_sysfs.c                  |    7 +-
>  include/scsi/scsi_alua.h                   |  103 ++
>  include/scsi/scsi_device.h                 |    1 +
>  12 files changed, 977 insertions(+), 924 deletions(-)
>  create mode 100644 drivers/scsi/scsi_alua.c
>  create mode 100644 include/scsi/scsi_alua.h
> 
> -- 
> 2.43.5