[libvirt] RFC: Exposing backing chains in <domain> XML

[Daniel P. Berrange]

On Fri, Mar 14, 2014 at 02:05:49PM +0000, Richard W.M. Jones wrote:
> On Fri, Mar 14, 2014 at 11:07:21AM +0000, Daniel P. Berrange wrote:
> > I understand why you chose to use nesting, but I can't say I like
> > the appearance of nesting. I think that in the common case where
> > we have a single non-branching chain, the XML structure is kind of
> > unpleasant and would be nicer if just a flat list. Using nesting
> > makes it harder to extract info about backing files from the XML
> > structure with XPath because you can't simply ask for all <source>
> > elements at a given location.
> 
> OTOH, with nesting, existing XPath queries keep working.
> 
> https://github.com/libguestfs/libguestfs/blob/master/src/libvirt-domain.c#L445
> 
> Have a look in this file for existing XPath queries involving /source
> 
> However a flat list of backingStore nodes (as you suggested later)
> would not break anything.
> 
> > I don't think we want todo that - there are genuine use cases where
> > that is a reasonable thing todo. eg you can provide a raw file to a
> > guest and that guest may genuinely want to format the virtual disk
> > it received with some other format. We don't want to taint such use
> > cases.
> 
> Ewww by formatting you mean turning raw into qcow2??

Yes, RHEV for example formats block devices as QCow2. I'm not saying
this is a good idea, but we know of apps which do this and so we
shouldn't taint this.


Regards,
Daniel
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