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?