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

[Hannes Reinecke <hare@suse.com>]

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
hare@suse.com                               +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
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