On 7/30/07, Avi Kivity <[EMAIL PROTECTED]> wrote: > Jorge Lucángeli Obes wrote: > > Hi Avi, hi all, > > I believe that Laurent (copied) is also interested in this area.
Copied him. > > I've started some (very minor) groundwork for this task. My idea was > > to add an extra "annotation" field in qcow2 snapshots. In this way, a > > snapshot can hold abitrary information; for example, command line > > arguments. > > > > Before going any further, I wanted to validate the general idea with > > the list. > I've copied qemu-devel as well. This can benefit qemu as much as kvm > and I see no reasons that this shouldn't be merged into kvm through qemu > upstream. Furthermore, I'd very much hate to see qemu and kvm image > formats diverge, so I'd like to get the qemu maintainer's approval for > any format changes or extensions. Agreed. > > There's a slight overhead as now all qcow2 snapshots have to store a > > extra (probably) empty pointer. An alternative approach would be to > > somehow indicate that some snapshots are "descriptive" snapshots and > > others are "useful" snapshots; however, I felt that this would be more > > complicated. > > > > Will storing an extra pointer break existing qcow2 images? If so, we'd > better avoid it. It could be a problem, I agree. Maybe it's a better idea not to touch the on-disk format. That would mean leaving 'struct QCowSnapshotHeader' intact, and using existing fields to store our information. The header includes an "extra_data_size" field that can do the trick. This would of course need approval from qemu developers. Laurent, do you want the patches for the functionality that's working right now? We can divide the (not very big amount of) work that's left. It consists basically on teaching qemu how to look for command line options, if none are present on the current invocation. I don't mind doing it by myself if you want to keep working on the other stuff you've been posting patches about. Just to be clear, the actual "embedding" of command line options into the image would be done with qemu-img. It would be qemu's job to validate this when the image is loaded. Another way to do this could be to add an option to qemu that does the embedding. This would have the benefit of free option validation, but I felt that image-related operations should be used from qemu-img. Cheers, Jorge
