Re: [RFC] Unify KVM kernel-space and user-space code into a single project

Zachary Amsden
2010-03-18T21:02:12Z

On 03/18/2010 12:50 AM, Ingo Molnar wrote:
> * Avi Kivity<avi@redhat.com> wrote:
>
>
>>> The moment any change (be it as trivial as fixing a GUI detail or as
>>> complex as a new feature) involves two or more packages, development speed
>>> slows down to a crawl - while the complexity of the change might be very
>>> low!
>>>
>> Why is that?
>>
> It's very simple: because the contribution latencies and overhead compound,
> almost inevitably.
>
> If you ever tried to implement a combo GCC+glibc+kernel feature you'll know
> ...
>
> Even with the best-run projects in existence it takes forever and is very
> painful - and here i talk about first hand experience over many years.
>

Ingo, what you miss is that this is not a bad thing. Fact of the matter
is, it's not just painful, it downright sucks.

This is actually a Good Thing (tm). It means you have to get your
feature and its interfaces well defined and able to version forwards and
backwards independently from each other. And that introduces some
complexity and time and testing, but in the end it's what you want. You
don't introduce a requirement to have the feature, but take advantage of
it if it is there.

It may take everyone else a couple years to upgrade the compilers,
tools, libraries and kernel, and by that time any bugs introduced by
interacting with this feature will have been ironed out and their
patterns well known.

If you haven't well defined and carefully thought out the feature ahead
of time, you end up creating a giant mess, possibly the need for nasty
backwards compatibility (case in point: COMPAT_VDSO). But in the end,
you would have made those same mistakes on your internal tree anyway,
and then you (or likely, some other hapless project maintainer for the
project you forked) would have to go add the features, fixes and
workarounds back to the original project(s). However, since you
developed in an insulated sheltered environment, those fixes and
workarounds would not be robust and independently versionable from each
other.

The result is you've kept your codebase version-neutral, forked in
outside code, enhanced it, and left the hard work of backporting those
changes and keeping them version-safe to the original package
maintainers you forked from. What you've created is no longer a single
project, it is called a distro, and you're being short-sighted and
anti-social to think you can garner more support than all of those
individual packages you forked. This is why most developers work
upstream and let the goodness propagate down from the top like molten
sugar of each granular package on a flan where it is collected from the
rich custard channel sitting on a distribution plate below before the
big hungry mouth of the consumer devours it and incorporates it into
their infrastructure.

Or at least, something like that, until the last sentence. In short, if
project A has Y active developers, you better have Z >> Y active
developers to throw at project A when you fork it into project B.

Zach