On Sat, Oct 4, 2008 at 1:17 AM, Daniel P. Berrange <berrange@redhat.com> wrote:
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@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.
Please remember my words "if you ever find that you have a code base that looks like what we have in libcgroups, please remember to switch over to libcgroup". I fear that you will reach that stage, the code that is going in right now has too many things hard-coded and will need a lot of changes going forward, things like adding support for new controllers is not going to be straight forward, your assumption that only root can create a container might be broken and we'll build support for hierarchies, which will require further changes, etc. I am not scaring you, just trying to make sure we don't solve the same problems twice. Balbir