Re: [libvirt] Re: [discuss] The new cgroup patches for libvirt
On Sat, Oct 04, 2008 at 12:13:38AM +0530, Balbir Singh wrote:
On Fri, Oct 3, 2008 at 11:43 PM, Daniel P. Berrange
<berrange(a)redhat.com> wrote:
True, it definitely does and the way I look at APIs is that they are
layers. We've built the first layer that abstracts permissions, paths
and strings into a set of useful API. The second layer does things
that you say, the question then is why don't we have it yet?
Let me try and answer that question
1. We've been trying to build configuration, classification and the
low level plumbing
2. We've been planning to build the exact same thing that you say, we
call that the pluggable architecture, where controller plug in their
logic and provide the abstractions you need, but not gotten there yet.
When you announced cgroup support in libvirt, it was definitely going
to be a user and we hoped that you would come to us with your exact
requirements that you've mentioned now (believe me, your feedback is
very useful). The question then to ask is, is it cheaper for you to
build these abstractions into libvirt or either helped us or asked us
to do so, we would have gladly obliged. You might say that the onus is
on the maintainers to do the right thing without feedback, but I would
beg to differ.
The thing I didn't mention, is that until Dan posted his current patches
actually implementing the cgroups stuff in LXC driver, I didn't have a
good picture of what the ideal higher level interface would look like.
If you try and imagine high level APIs, without having an app actually
using them, its all too easy to design something that turns out to not
be useful.
So while I know the low level cgroups API isn't what we need, it needs
the current proof of concept in the libvirt LXC driver to discover what
is an effective approach for libcgroups. I suspect our code will evolve
further as we learn from what we've got now. By doing this entirely
within libvirt we can experiment with effective implementation strategies
without having to lockdown a formally supported API immediately. Once
things settle down, it'll easier for libcgroups to see exactly what is
important for a high level API and thus make one that's useful to more
apps in the long term.
Daniel
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