On Tue, Apr 15, 2008 at 02:23:53PM -0700, Ryan Scott wrote:
Daniel P. Berrange wrote:
On Tue, Apr 15, 2008 at 11:31:32AM -0700, Ryan Scott wrote:
I'd like to get some comments on the following...
We would like to use libvirt to store some properties related to a domain. This can be done by adding a simple get/set API as follows:
What are the properties ? I'm not really very enthusiastic about the idea of adding API / XML for generic key,value properties. I think it will quickly be abused as a way to add arbitrary, non-standardized hypervisor / driver specific configuration which would be better represented with explicit schema.
One thing we have in mind is driver/software version numbers. For example, the control tools may change the domain configuration based on whether a certain driver has the support for a new feature. If we create the domain's xml with the driver information, we can make this decision quickly, on the fly, in dom0.
Taking the specific example of driver support I think it's far better to express that as part of the device description of the domain. If it's about the Guest OS currently we only have a generic <domain> <os> <type> ...</type> having a version attribute there sounds reasonable. If it's about the emulated hardware, for example the number of crypto engine like in the lDOM description the proper place would under <domain> <features>
While this information is related to domain configuration, it's not hypervisor-specific, so I'm not sure where else we would put it in the domain's XML description.
Domain configuration pertains to the XML domain description for sure but this need to be added in a structured way.
This gives the control tools someplace to store that information, rather than having to create some separate storage for each domain.
I think every new addition to the structure need to be examined on a case by case basis, in order to keep libvirt API and the tools buit on top of them coherent. It is certainly more complex than opening the gate to a completely unstructured mechanism but like any API design, it takes a bit of time and efforts to find the proper syntactic constructs. The effort pays off on the long term IMHO. Daniel -- Red Hat Virtualization group http://redhat.com/virtualization/ Daniel Veillard | virtualization library http://libvirt.org/ veillard@redhat.com | libxml GNOME XML XSLT toolkit http://xmlsoft.org/ http://veillard.com/ | Rpmfind RPM search engine http://rpmfind.net/