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

[Hannes Reinecke]

On 3/26/26 13:16, John Garry wrote:
> On 26/03/2026 10:19, Hannes Reinecke wrote:
> > > @@ -80,6 +80,7 @@ config SCSI_MULTIPATH
> > >          bool "SCSI multipath support"
> > >          depends on SCSI_MOD
> > >          select LIBMULTIPATH
> > > +       select SCSI_DH_ALUA
> > >          help
> > >            This option enables support for native SCSI multipath 
> > > support for
> > >            SCSI host.
> > >
> > > And that is even enough, as Kconfigs should only specify build 
> > > requirements.
> > >
> > > We really should be also calling something like scsi_dh_attach() for 
> > > scsi multipath to ensure that DH is attached (and running to update 
> > > sdev->access_state).
> > >
> > > And I am not sure how the dh alua module is even autoloaded. I think 
> > > that on my ubuntu machine the multipath-tools.service does it - 
> > > something like this would not be nice for native SCSI multipath support.
> > Gnaa. But then we don't need this patchset at all.
> > Main point was that we _do not_ need to hook into scsi dh for implicit
> > ALUA.
>
> But again I don't think that this is good enough. Native SCSI 
> multipathing will read sdev->access_state to know ALUA state. We can't 
> just rely on dh alua module running and doing what we need to know that 
> this value is valid. AFAICS, dm mpath relies on dh alua module to even 
> work at all:
>
> device-mapper: table: 252:1: multipath: error attaching hardware
> handler (-EINVAL)
>
> At this point I am more inclined to just have a small SCSI core ALUA 
> support for implicit ALUA, and allow scsi_dh_alua.c reuse functions from 
> that but not use sdev->alua structure, like in this series - trying that 
> is turning into a mess, I am finding.
... where one finds himself inclined to think: 'told you so' :-)

And really, the SCSI alua handling doesn't need to be precise, in the
sense that the state is always up-to-date. It should be sufficient to
read the state once during startup, and then resend RTPG whenever we
get a sense code indicating that the ALUA state doesn't match.
We will be missing any changes between non-optimized and optimized,
but they are meaningless for the SCSI core anyway.

Cheers,

Hannes
--
Dr. Hannes Reinecke                  Kernel Storage Architect
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