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

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?