[openstack-dev] [cinder] Target classes in Cinder

Kendall Nelson kennelson11 at gmail.com
Fri Jun 2 20:05:28 UTC 2017

I personally agree that the target classes route is a much cleaner and more
efficient way of doing it.  Also, that it doesn't make sense to have all
the code duplication to support doing it both ways.

If other people agree with that- maybe we can start with not taking new
drivers that do it the common/iscsi/fc way? And then pick a release to
refactor drivers and make that the focus kind of like we did with ocata
being a stabilization release? Assuming that asking the larger number of
drivers to switch formats isn't asking the impossible. I dunno, just a
thought :)

-Kendall (diablo_rojo)

On Fri, Jun 2, 2017 at 2:48 PM John Griffith <john.griffith8 at gmail.com>

> Hey Everyone,
> So quite a while back we introduced a new model for dealing with target
> management in the drivers (ie initialize_connection, ensure_export etc).
> Just to summarize a bit:  The original model was that all of the target
> related stuff lived in a base class of the base drivers.  Folks would
> inherit from said base class and off they'd go.  This wasn't very flexible,
> and it's why we ended up with things like two drivers per backend in the
> case of FibreChannel support.  So instead of just say having "driver-foo",
> we ended up with "driver-foo-iscsi" and "driver-foo-fc", each with their
> own CI, configs etc.  Kind of annoying.
> So we introduced this new model for targets, independent connectors or
> fabrics so to speak that live in `cinder/volume/targets`.  The idea being
> that drivers were no longer locked in to inheriting from a base class to
> get the transport layer they wanted, but instead, the targets class was
> decoupled, and your driver could just instantiate whichever type they
> needed and use it.  This was great in theory for folks like me that if I
> ever did FC, rather than create a second driver (the pattern of 3 classes:
> common, iscsi and FC), it would just be a config option for my driver, and
> I'd use the one you selected in config (or both).
> Anyway, I won't go too far into the details around the concept (unless
> somebody wants to hear more), but the reality is it's been a couple years
> now and currently it looks like there are a total of 4 out of the 80+
> drivers in Cinder using this design, blockdevice, solidfire, lvm and drbd
> (and I implemented 3 of them I think... so that's not good).
> What I'm wondering is, even though I certainly think this is a FAR
> SUPERIOR design to what we had, I don't like having both code-paths and
> designs in the code base.  Should we consider reverting the drivers that
> are using the new model back and remove cinder/volume/targets?  Or should
> we start flagging those new drivers that don't use the new model during
> review?  Also, what about the legacy/burden of all the other drivers that
> are already in place?
> Like I said, I'm biased and I think the new approach is much better in a
> number of ways, but that's a different debate.  I'd be curious to see what
> others think and what might be the best way to move forward.
> Thanks,
> John
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