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Re: [libvirt] Question about supporting other hypervisor



On Fri, Oct 17, 2008 at 10:42:25AM +0100, Daniel P. Berrange wrote:
> On Fri, Oct 17, 2008 at 09:38:35AM +0900, Atsushi SAKAI wrote:
> > Hello,

  hi Atsushi,

> > I have a simple question raised yesterday.

  I got your question spinning on the back of my head since this
morning, but it's really hard to come up with good answers, maybe
peopel with more knowledge of CIM could give informations.

> > CIM(Common Information Model) is a kind of good I/F
> > (to support VMware, Hyper-V and other platform).

  The question really is is it a good interface ? In theory it sounds
like it could help us, but I wonder how that actually works in practice.

> > As a CIM Provider, libvirt-cim is going on.
> > But for CIM Client, Is not going on.
> > 
> > Is there any reason for not supporting CIM on libvirt driver layer?
> > I am thinking about cim-xml driver (like remote driver) in libvirt.
> 
> It is certainly a possibility, but personally I'd prefer native drivers
> for each hypervisor - there is only VMWare & Hyper-V left that are the
> main players with no driver support. Having an abstraction layer like
> libvirt run over an abstraction layer like CIM, in turn over the native 
> layer will make quite a complex system to debug & be inherantly less
> efficient than taking to the native APIs. So although it'd probably 
> be more work to write a separate VMWare & Hyper-V driver, I think that
> it'd result in better drivers for each in the long term.

  I agree that an abstraction layer doesn't sounds a good thing, *but*
since there hasn't been that many volunteers to implement VMWare or
Hyper-V, the fact that Hyper-V native would certainly have to be working
locally on the Windows machine and be compiled with MSC [1], the fact
that for VMWare we would have to do remote access with SOAP anyway for
deployment issues, that all considered maybe a client CIM remote driver
may not be that bad in comparison.
  Also having looked at the VMWare vix and SOAP APIs I'm not sure that
CIM can really be that much worse (but I'm certainly biased).

  Atsushi do you know if by default VMWare ESX and Hyper-V allow CIM
XML access, or if some 'additional' software need to be installed to
get this to work ? Also if you have feedback about the quality of the
client CIM APIs implemented (completeness, interoperability ...) that's
good to know too,

Daniel

[1] there is a collection of horror stories for libxml2 compiled with a
    given toolchain and linked with library built differently on Windows,
    I would not raise hope for mixing compiler environments

-- 
Daniel Veillard      | libxml Gnome XML XSLT toolkit  http://xmlsoft.org/
daniel veillard com  | Rpmfind RPM search engine http://rpmfind.net/
http://veillard.com/ | virtualization library  http://libvirt.org/


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