[dm-devel] [PATCH 1/2] mpathpersist: add all_tg_pt option

[Martin Wilck]

On Fri, 2018-06-01 at 17:22 -0500, Benjamin Marzinski wrote:
> Some arrays, such as the EMC VNX, don't follow the scsi persistent
> reservations spec in making key registrations per I_T NEXUS. Instead,
> the registration is shared by all target ports connected to a given
> host.  This causes mpathpersist to fail whenever it tries to register
> a
> key, since it will receive a registration conflict on some of the
> paths.
> 
> To deal with this, mpathpersist needs to track the hosts that it has
> done a registration on, and only register once per host. The new
> "all_tg_pt" multipath.conf option is used to set which arrays need
> this
> feature.  I currently don't know if all EMC VNX arrays handle
> persistent
> reservations like this, or if it is configurable. A future patch will
> update the VNX built-in config, if this is indeed their default (or
> only) setting.
> 
> Multipathd doesn't need to worry about this. It is often the case
> that
> when a path device comes back, it will still have the keys registered
> to
> it. Because of this, multipathd uses register-and-ignore, which means
> that it won't cause an error if the registration has already happened
> down a different target port.
> 
> Signed-off-by: Benjamin Marzinski <bmarzins at redhat.com>
> ---
>  libmpathpersist/mpath_persist.c | 28 ++++++++++++++++++++++------
>  libmultipath/config.c           |  2 ++
>  libmultipath/config.h           |  2 ++
>  libmultipath/defaults.h         |  1 +
>  libmultipath/dict.c             | 10 ++++++++++
>  libmultipath/propsel.c          | 15 +++++++++++++++
>  libmultipath/propsel.h          |  1 +
>  libmultipath/structs.h          |  7 +++++++
>  multipath/multipath.conf.5      | 11 +++++++++++
>  9 files changed, 71 insertions(+), 6 deletions(-)

The patch looks good to me, but doesn't this mean that mpathpersist
would now also support persistent reservations with the ALL_TG_PT bit
set (IIUC, the VNX basically acts as if that bit was always set)? 

If yes, I think the warning in mpath_prout_reg() about this flag could
be dropped, and mpathpersist could be extended to support the -Y/
--param-alltgpt option, no?

Otherwise, I'd suggest to give this option a different name, because
it'd just too easily be confused with ALL_TG_PT from the spec.

Regards,
Martin

-- 
Dr. Martin Wilck <mwilck at suse.com>, Tel. +49 (0)911 74053 2107
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton
HRB 21284 (AG Nürnberg)