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Re: [Xen-API] Re: XSDL schemas for Xen virtual machine configurations

Well, I was going to keep quiet rather than risk forever being labelled (and dismissed?) as a "CIM bigot", but ... :-)

As Mike implies, there is today already a "pseudo-standard" XML based format for fully describing a virtual system configuration, namely the array of CIM_SettingData that is passed into the DefineVirtualSystem() extrinsic method in the DMTF System Virtualization profile. Basically, this contains all the important data describing what you want in your VM, shoved into a CIM-XML extrinsic method call. The *actual* settings of the eventual new VM may differ somewhat, since the virtualization platform may apply some internal defaults, etc, but you still basically end up with a set of CIM_SettingData objects that fully describe the VM, all of which can be translated in a well-defined manner to CIM-XML. Whilst we don't pass in any associations defining structural relations between the components of the new VM, these are generated as part of the DefineVirtualSystem process to tie things together and exist as internal CIM objects (aka CIM_Dependency subclasses) and have a well-defined CIM-XML representation too.

I'm not suggesting that we must adopt CIM-XML because it is undoubtedly the best format to persist DomU config data - it probably isn't the 'best' - but the reality is that we effectively have all the data in this specific XML format already, independent of anything else, by virtue of the CIM mgmt stuff. And by definition, we - Xen CIM folk - are going to have to make sure everything we need to express for a DomU config can be expressed via CIM classes, and hence representable in CIM-XML, in order for us to do basic CIM-based lifecycle management of Xen; ie we're already effectively having to invent this wheel, albeit primarily for our CIM mgmt! :-)

Just something to keep in mind.

- Gareth

Dr. Gareth S. Bestor
IBM Linux Technology Center
M/S DES2-01
15300 SW Koll Parkway, Beaverton, OR 97006
503-578-3186, T/L 775-3186, Fax 503-578-3186

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          08/02/06 07:30 AM






[Xen-API] Re: XSDL schemas for Xen virtual machine configurations

On 02/08/06 09:57 -0400, Andrew D. Ball wrote:
>You're most welcome to kick this off which whichever type of schema you
>think is appropriate.  I think [without lots of experience to back it
>up, mind you] that something simple would be fine for now, leaving the
>more complicated contraints to domain logic.

Please don't ignore the DMTF modelling work that is going on right now. CIM
technology is not elegant but standard xml schemata are truly horrid - there
are no elegant options.

CIM schemata are very good a expressing conditions and relationships, despite
their clumsy notation.


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