[dm-devel] Can we drop 'hardware_handler "1 alua"'?

[Martin Wilck]

hwtable.c has multiple entries that set 'hardware_handler "1 alua"'
explicitly. But the kernel has been auto-attaching the ALUA hwhandler
to devices that support it since 4.3, the only prerequisite being that
scsi_dh_alua is present at device probing time (kernel commits
d95dbff2, d6a32b98). "retain_attached_hwhandler" is also hard-wired
since 4.3. Thus if the above prerequisite is met, there's no point in
setting 'hardware_handler "1 alua"'.

We've recently seen problems with the explicit setting of the alua
hwhandler in the hwtable; if we do this and the device fails ALUA for
whatever reason, setting up the multipath map fails entirely.

Therefore we have reasons to try and remove 'hardware_handler "1 alua"'
from the hwtable. But it could cause regressions in some cases, e.g.
for distributions that don't force-load scsi_dh_alua before device
probing, or for kernels older than 4.3.

Opinions, please.

Martin

-- 
Dr. Martin Wilck <mwilck at suse.com>, Tel. +49 (0)911 74053 2107
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton
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