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Re: [Libvir] Autostarting guests and networks





On 2/17/07, Daniel P. Berrange <berrange redhat com> wrote:
On Fri, Feb 16, 2007 at 02:51:07PM +0000, Mark McLoughlin wrote:
> Hey,
>       We need some way to have libvirtd automatically start guests and
> networks.
>
>       We had said we should have autostart directories containing config
> files of guests/networks which should be autostarted. One problem I see
> with that is that we'd need a new API to define autostart configs.
>
>       So, I suggest we add an "autostart" flag to the toplevel element of the
> configs.
>
>       We could discuss this one at length and I, for one, don't like using
> the XML format as an API like this, but ... comments?

I'm not sure that adding a flag to the XML is neccessarily the correct
way to do this. The XML is intended to be a description of the VM's
virtual hardware / resources. Whether a domain autostarts or not is really
administrator defined policy which doesn't match up with intended use of
the XML. Similar reason we don't put VCPU pinning information in the XML,
because its local machine / administrator defined policy rather than a
part of the VM hardware description.

I think I'd probably be more inclined to add a formal API for querying
whether a domain autostarts, and a second for setting the autostart
flag on/off.
 
Agreed let's not mix policies and data. However I assume the API would allow
to define directories for autostarted configs. I guess having predefined dirs for
such data is a common concept. And trying to hard code it like /etc/xen is
really not the best. IIRC we already have a config file now for some daemons,
can we have such directories entries in the config file ? I guess it would give
the flexibility required for most uses while keeping a relatively sane API and
avoiding putting the policy in the data themselve.
 
The old Xend just stuffs VM configs into a special directory to autostart,
so we can detect that by looking for appropriate symlins, and change it
by adding/removing the symlinks. The newer Xen 3.0.4 or later has a formal
API for setting/querying autostart I believe, but can't remember the details
just at the minute.
 
Do we need to match the new Xend mechanism ?

Daniel


 

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