Re: [libvirt] [RFC] Per machine type qemu capability detection

On 04/04/2013 01:13 PM, Viktor Mihajlovski wrote: At one time we requested that of qemu, and learned that, due to the way qemu is internally organized, that would be next to impossible to provide (it turns out that type of information isn't available in a data table, but is constructed on the fly as a machine is instantiated, and one a machine is instantiated, qemu can't tear it down and instantiate a new/different machine without completely shutting down). However, as Dan pointed out in a previous message, relying on such information for definition-time validation would be flawed anyway, because there is no guarantee that what was available in the qemu binary at the time of definition (on the host where the definition is done) would be the same as what was available at runtime. Now that pkrempa's patches to support domain post-parse callback functions are going in, we can add in qemu-specific callbacks that do extra validation of devices depending on the setting of machinetype. This will be a big win not only for s390, but also for ARM and q35; we'll be able to remove all of the x86 (i.e. "pc") specific stuff that's automatically added to domains from the generic parser, and put it in a callback to only be added for pc-* machine types. Likewise you'll be able to do the same thing for any devices/controllers specific to s390. It won't allow *exact* validation for exactly what is supported by the binary on the current machine, but it will at least allow getting extremely close, and any final minute differences can be handled when the guest is actually started up.