On Fri, 2009-06-12 at 09:51 -0500, Anthony Liguori wrote: > Mark McLoughlin wrote: > > On Wed, 2009-06-10 at 20:27 +0100, Jamie Lokier wrote: > > > >> Michael S. Tsirkin wrote: > >> > >>>> I think the right long term answer to all this is a way to get QEMU to > >>>> dump it's current machine configuration in glorious detail as a file > >>>> which can be reloaded as a machine configuration. > >>>> > >>> And then we'll have the same set of problems there. > >>> > >> We will, and the solution will be the same: options to create devices > >> as they were in older versions of QEMU. It only needs to cover device > >> features which matter to guests, not every bug fix. > >> > >> However with a machine configuration which is generated by QEMU, > >> there's less worry about proliferation of obscure options, compared > >> with the command line. You don't necessarily have to document every > >> backward-compatibility option in any detail, you just have to make > >> sure it's written and read properly, which is much the same thing as > >> the snapshot code does. > >> > > > > This is a sensible plan, but I don't think we should mix these compat > > options in with the VM manager supplied configuration. > > > > There are two problems with that approach. > > > > = Problem 1 - VM manager needs to parse qemu config = > > > > Your proposal implies: > > > > - VM manager supplies a basic configuration to qemu > > > > - It then immediately asks qemu for a dump of the machine > > configuration in all its glorious detail and retains that > > config > > > > - If the VM manager wishes to add a new device it needs to parse the > > qemu config and add it, rather than just generate an entirely new > > config > > > > What's the problem with parsing the device config and modifying it? Is > it just complexity? Yes, complexity is the issue. > If we provided a mechanism to simplify manipulating a device config, > would that eliminate the concern here? In libvirt's case, a lot of the complexity would come from needing to figure out what to change. i.e. libvirt produces a qemu configuration (currently a command line) from a guest XML's configuration; with this idea, libvirt would probably compare the old XML config to the new XML config, and then apply those differences to the qemu configuration. Cheers, Mark. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
