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

[Richard W.M. Jones]

On Fri, Mar 14, 2014 at 10:53:48AM +0000, Daniel P. Berrange wrote:
> On Wed, Mar 12, 2014 at 05:34:17PM -0600, Eric Blake wrote:
> > Hmm.  Another feature coming down the pipes in qemu 2.0 is the ability
> > to give an alias to any portion of the backing chain.  Right now, we
> > have an <alias> element tied to the <disk> as a whole (in qemu parlance,
> > the device id), but some qemu operations will be easier if we also have
> > a name tied to each file in the chain (in qemu parlance, a node id for
> > the bd [block driver structure]).  Maybe we kill two birds with one
> > stone, by having each <backingStore> track an <alias> sub-element with
> > the name of the node, when communicating with qemu 2.0 and newer.
> 
> I like the idea of having a string-alias against each node to  allow
> unambigously references to it. We could do an integer index, but a
> string alias is a bit more flexible, allowing us to tie the alias value
> to the QEMU name if desired.

You either have to force the caller to provide an alias for each node,
or you have to auto-assign them.  But if you auto-assign them (say
"node123"), what if the user provides a label for that node later on?
What if the user gives that label to a different node?

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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