Re: [libvirt] [PATCH] Openvz: how to use a nondefault config

["Daniel P. Berrange" <berrange redhat com>]

On Thu, Apr 02, 2009 at 06:36:15PM +0400, Evgeniy Sokolov wrote:
> 
> Config /etc/vz/conf/ve-XXX.conf-sample define there are many parameters 
> like  memory, CPU etc. This parameters are not properties of <filesystem>.
> 
> Daniel, usage of pre-defined configs in really usefull. Can we create 
> additional tag inside <domain></domain>?

The trouble with this is that given the XML config of a guest, you can
no longer determine what its configuration is, because a large amount
of configuration is hidden in this opaque 'template'.

If we're to support templates, I think we need to make them first class
objects, so you can query what templates exist, and see their associated
config settings. 

eg, expose a simple API

   virDomainTemplatePtr;

   int virConnectListDomainTemplates(virConnectPtr conn, const char **names);
   virDomainTemplatePtr virDomainTemplateLookupbyName(virConnectPtr con, const char *name)
   char *virDomainTemplateGetXMLDesc(virDomainTemplatePtr tmpl);
   virDomainTemplatePtr virDomainTemplateDefineXML(virConnectPtr conn, const char *xml)
   int virDomainTemplateUndefine(virDomainTemplatePtr tmpl);
   int virDomainTemplateFree(virDomainTemplatePtr tmpl);


Then, we could either include a <template>$NAME</template> parameter in 
the XML for a guest. Or have an alternate API for creating guests

   virDomainCreateXMLWithTemplate(virConnectPtr conn,
                                  const char *xmlDesc,
                                  const char *template)

It depends whether we'd want to track the template <-> guest association
forever, or just use it once to fill-in the guest XML and then forget
about the template after that.


Daniel
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