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

[Anton Protopopov]

2009/4/2 Daniel P. Berrange <berrange at 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'.


And in kvm/qemu case there is a lot of hidden information too :)
In OpenVZ case we don't loose any info (see below).



>
> 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.


It doesn't matter in OpenVZ case: template (or, "config", in openvz
terminology) is used only
once, when container is creating. But then per-container "copy" is created,
and it is already used by libvirt to keep information about container.
Per-container
OpenVZ config keeps the name of the original config (in ORIGIN_SAMPLE
variable).

Is there need for "Template API" in case of other hypervisors?
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