[libvirt] RFC: Drop unmaintained hv drivers? (phyp, xenapi, hyperv)

[Daniel P. Berrange]

On Mon, Apr 18, 2016 at 09:11:24AM -0400, Cole Robinson wrote:
> On 04/18/2016 08:58 AM, Daniel P. Berrange wrote:
> > On Mon, Apr 18, 2016 at 08:54:15AM -0400, Cole Robinson wrote:
> >> On 04/18/2016 05:21 AM, Daniel P. Berrange wrote:
> >>> On Fri, Apr 15, 2016 at 03:54:00PM -0400, Cole Robinson wrote:
> >>>
> >>>
> >>> In general I'm not really in favour of dropping virt drivers for hypervisor
> >>> platforms that still exist and have potential users, even if we don't hear
> >>> much about them. I don't think any of these drivers is really giving us a
> >>> significant maintenance headache to justify deletion.
> >>>
> >>
> >> It's just kind of a weird situation. We advertise support for these platforms,
> >> but if someone tries them and finds them lacking and reports an issue here,
> >> the only response they are going to get is 'no one has worked on it for years,
> >> no one here has a setup to test, sorry we cannot help you'. That's if they get
> >> a response at all. Seems bizarre to me...
> > 
> > This is implying that because we don't have an active maintainer who will
> > answer bug reports, then the driver is entirely useless to everybody. I
> > find that really dubious, because it ignores the possibility that people
> > are happily using the other parts of it that actually do work. Sure it
> > would be nice if we have active maintainers, but I don't think the lack
> > of an active maintainer means the driver is useless to all users.
> 
> My paragraph didn't fully describe all the assumptions; Those three drivers
> may have zero active users in the wild. Certainly there is no obvious evidence
> to the contrary. The most damning bit seems to be that there hasn't been a
> single targeted bug fix for those drivers in an average of 4 years; if someone
> was actively using those drivers I'm pretty sure we would have received a
> drive by patch at some point
> 
> Maybe someone will chime in to prove me wrong, but what if the situation is
> that there's no active maintainer, and no active users? Then it truly _is_
> serving no purpose, and IMO even advertising it is actively harmful since it
> may lead users down a dead end path
> 
> Removing a driver doesn't need to be the end either... if someone motivated
> shows up they can always revive the old code

As Jan points out though, that's not so easy in practice because the rest
of libvirt continues evolving and so the old code won't be re-creatable
without many fixups. With the current setup people who do refactoring
take responsibility for fixing up all drivers. Given the number of drivers
we have in tree, deleting a couple of drivers won't materially affect
that effort. Someone new to libvirt though who tries to restore the old
code will have to fight through all this subsequent refactoring with
little domain knowledge to help them. I don't think that's really a
positive tradeoff overall.

> ...now that I do some more targeted searches looking for patches, looks like
> someone from bull.net did try to massively expand the hyperv driver a few
> years back, but it was an awkward code dump:
> 
> https://www.redhat.com/archives/libvir-list/2014-October/msg00257.html

Oh wow, that is a huge set of enhancements - its a real shame we did not
apply those, as that'd be a big step forward for hyperv. I wonder how
easily they apply today....

Regards,
Daniel
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