* Eric Blake (ebl...@redhat.com) wrote: > On 03/29/2016 09:38 AM, Max Reitz wrote: > > On 17.03.2016 10:56, Wen Congyang wrote: > >> On 03/17/2016 05:48 PM, Dr. David Alan Gilbert wrote: > > > > [...] > > > >>> The children.0 notation is really confusing in the way that Berto > >>> describes; I hit this a couple of months ago and it really doesn't > >>> make sense. > >> > >> Do you mean: read from children.1 first, and then read from children.0 in > >> fifo mode? Yes, the behavior is very strange. > > > > So is this intended or is it not? In > > http://lists.nongnu.org/archive/html/qemu-block/2016-03/msg00526.html > > you said that it is. > > > > I myself would indeed say it is very strange. If I were a user, I would > > not expect this behavior. And as I developer, I think that how a BDS's > > child is used by its parent should solely depend on its role (e.g. > > whether it is "children.0" or "children.1"). > > It sounds like the argument here, and in Max's thread on > query-block-node-tree, is that we DO have cases where order matters, and > so we need a way for the hot-add operation to explicitly specify where > in the list a child is inserted (whether it is being inserted as the new > primary image, or explicitly as the last resort, or somewhere in the > middle). An optional parameter, that defaults to appending, may be ok, > but we definitely need to consider how the order of children is affected > by hot-add.
Certainly in the COLO case the two children are not identical; and IMHO we need to get away from thinking about ordering and start thinking about functional namingd - children.0/children.1 doesn't suggest the fact they behave differently. Dave > > -- > Eric Blake eblake redhat com +1-919-301-3266 > Libvirt virtualization library http://libvirt.org > -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
