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

[John Garry]

On 24/03/2026 15:48, Benjamin Marzinski wrote:
> > We would need something like the following to ensure that DH ALUA is present
> > to update sdev access_state:
> >
> > @@ -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.
> DM_MULTIPATH doesn't force the device handlers to be built. You just
> don't have their support if they aren't there. Granted, it does make
> sure that if they are built, you can't build dm-multipath directly into
> the kernel, if the device handlers are built as modules.

Note that dm-mpath does not even work without DH ALUA module:

device-mapper: table: 252:1: multipath: error attaching hardware
handler (-EINVAL)

> > 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).
> That isn't necessary. If there is an alua device handler, kernel will
> auto-attach it to any device that supports alua (see scsi_dh_add_device
> and scsi_dh_find_driver). DM-multipath's calling of scsi_dh_attach() is
> mostly a historical relic.

We still need to know that DH is attached to know that whatever is in 
sdev->access_state is valid for scsi multipath.

> > 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.
> Fair point. Depending on how the kernel is built, there could be system
> configuration work that needs to happen if implicit alua support
> wasn't in the generic scsi code. But as far as the kernel code goes, I
> still see them as parallel efforts.

I see what you are saying, I'll defer to Martin/Hannes on this.

Thanks,
John