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On 09/17/2015 06:06 PM, John Griffith wrote:
> On Thu, Sep 17, 2015 at 11:31 AM, Eric Harney <eharney at redhat.com> wrote:
> 
>> On 09/17/2015 05:00 AM, Duncan Thomas wrote:
>>> On 16 September 2015 at 23:43, Eric Harney <eharney at redhat.com> wrote:
>>>
>>>> Currently, at least some options set in [DEFAULT] don't apply to
>>>> per-driver sections, and require you to set them in the driver section
>>>> as well.
>>>>
>>>
>>> This is extremely confusing behaviour. Do you have any examples? I'm not
>>> sure if we can fix it without breaking people's existing configs but I
>>> think it is worth trying. I'll add it to the list of things to talk about
>>> briefly in Tokyo.
>>>
>>
>> The most recent place this bit me was with iscsi_helper.
>>
>> If cinder.conf has:
>>
>> [DEFAULT]
>> iscsi_helper = lioadm
>> enabled_backends = lvm1
>>
>> [lvm1]
>> volume_driver = ...LVMISCSIDriver
>> # no iscsi_helper setting
>>
>>
>> You end up with c-vol showing "iscsi_helper = lioadm", and
>> "lvm1.iscsi_helper = tgtadm", which is the default in the code, and not
>> the default in the configuration file.
>>
>> I agree that this is confusing, I think it's also blatantly wrong.  I'm
>> not sure how to fix it, but I think it's some combination of your
>> suggestions above and possibly having to introduce new option names.
>>
> ​
> I'm not sure why that's "blatantly wrong', this is a side effect of having
> multiple backends enabled, it's by design really.  Any option that is
> defined in driver.py needs to be set in the actual enabled-backend stanza
> IIRC.  This includes iscsi_helper, volume_clear etc.
> 

I think it's wrong because it's not predictable for someone configuring
Cinder.  I understand that this is a side effect of multi-backend, but
I'm not sure what the reasoning is if it's intentional design.  I think
most people would expect a setting set in a [DEFAULT] section to be
treated as a default rather than being ignored.

This is particularly odd in the case of "iscsi_helper", where I want to
ship packages configured to use LIO since tgt doesn't exist on the
platform, and is never the right value for my packages.

This isn't possible without patching the code directly, which seems like
a shortfall in our configuration system.

> Having the "global conf" settings intermixed with the backend sections
> caused a number of issues when we first started working on this.  That's
> part of why we require the "self.configuration" usage all over in the
> drivers.  Each driver instantiation is it's own independent entity.
> 

Yes, each driver instantiation is independent, but that would still be
the case if these settings inherited values set in [DEFAULT] when they
aren't set in the backend section.

> I haven't looked at this for a long time, but if something has changed or
> I'm missing something my apologies.  We can certainly consider changing it,
> but because of the way we do multi-backend I'm not exactly sure how you
> would do this, or honestly why you would want to.
> 
> John
>