On 03/20/2015 08:19 AM, Markus Armbruster wrote: The real libvirt requirement is that the new option is accessible via _some_ QMP command (doesn't have to be query-command-line-options, but that is the most obvious). Makes sense, and is certainly easier than figuring out an alternative QMP probing mechanism. Mostly agree; --machine is more for what the guest sees, while this has no impact on the guest ABI. On the other hand, things like -machine accel=[tcg|kvm] aren't necessarily guest visible either, so -machine has tended to be a catch-all for other things. But that doesn't mean it should continue to be one. The only clients using the new option will be machine generated, so I don't think ugly appearance is a show-stopper. And -misc really does sound like it is the most amenable to adding other random flags in the future, so I can live with that name. Unless anyone else has a better idea, '-misc format-probing=off' has my vote and works for libvirt; it is only a two-line change to my libvirt RFC patch: diff --git i/src/qemu/qemu_capabilities.c w/src/qemu/qemu_capabilities.c index b452a75..f7a46c1 100644 --- i/src/qemu/qemu_capabilities.c +++ w/src/qemu/qemu_capabilities.c @@ -2517,7 +2517,7 @@ static struct virQEMUCapsCommandLineProps virQEMUCapsCommandLine[] = { { "msg", "timestamp", QEMU_CAPS_MSG_TIMESTAMP }, { "numa", NULL, QEMU_CAPS_NUMA }, { "drive", "throttling.bps-total-max", QEMU_CAPS_DRIVE_IOTUNE_MAX }, - { "no-format-probing", NULL, QEMU_CAPS_NO_FORMAT_PROBING }, + { "misc", "format-probing", QEMU_CAPS_NO_FORMAT_PROBING }, }; static int diff --git i/src/qemu/qemu_command.c w/src/qemu/qemu_command.c index 1085639..08f6560 100644 --- i/src/qemu/qemu_command.c +++ w/src/qemu/qemu_command.c @@ -8674,7 +8674,7 @@ qemuBuildCommandLine(virConnectPtr conn, } if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_NO_FORMAT_PROBING) && !cfg->allowDiskFormatProbing) - virCommandAddArg(cmd, "-no-format-probing"); + virCommandAddArgList(cmd, "-misc", "format-probing=off", NULL); /* Serial graphics adapter */ if (def->os.bios.useserial == VIR_TRISTATE_BOOL_YES) { Nice way to plan for future cleanups. I also agree that while this one option about format-probing is reasonable to get into 2.3, that any other sugar cleanups are better deferred until after the freeze. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org