[libvirt] Domain XML format using defined storage volume + RFC

[Daniel P. Berrange]

On Thu, May 15, 2008 at 03:20:06PM +0200, Stefan de Konink wrote:
> On Thu, 15 May 2008, Stefan de Konink wrote:
> 
> > Now I wonder, is it possible to have here
> > somethinglike storage://netapp/lun-0?
> >
> 
> [snip]
> 
> > From the standpoint: we make it easy for the user I would prefer not to
> > provide a Linux specific path.
> 
> http://libvirt.org/formatdomain.html#elementsDisks
> 
> I propose an extension to the current <source> tag specifying where a disk
> should come from. In my humble opinion something that is already available
> inside libvirt should be reused.
> 
> Therefore:
> 
> source
>     If the disk type is "file", then the file attribute specifies the
> fully-qualified path to the file holding the disk. If the disk type is
> "block", then the dev attribute specifies the path to the host device to
> serve as the disk.
> 
>     If the disk type is "pool", then the pool attribute and the volume
> attibute specify what volume should be used for this disk.

I'd support a syntax like this:

    <disk type="pool">
      <source pool="myfiler" vol="lun-4"/>
      <target dev="xvda"/>
    </disk>

Since this mirrors the concept we use for mapping virtual networks into
the domain <interface> element.

> I'm currently playing with xml.c to get it supported. One thing
> that would be interesting is a 'start' parameter, so when the
> pool is defined but not yet started it should start. Any comments
> to the idea?

No, lifecycle changes in one object (the domain) should not effect lifecycle
changes on another (the storage). We already provide ability for pools to
be auto-started at time libvirtd starts.  Pools will typically be serving more 
than one guest anyway, so starting a pool upon starting a domain is a niche
use case. Management tools can provide policy such as auto-starting pools 
in this scenario if desired. 

Regards,
Daniel.
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