On Tue, 2016-07-19 at 16:17 +0200, Andrea Bolognani wrote:
Commit 8156493d8db9 changed libvirt so that '-device pci-ohci' would be used instead of '-usb' on ppc64 when no specific USB controller model had been specified in the guest configuration. While the device that ends up being presented by the guest is exactly the same, '-usb' causes it to be assigned to PCI address 00:00.0 while '-device pci-ohci', being subject to the regular PCI address assignment logic, will be at a different address. This PCI address mismatch breaks migration of existing guests to new libvirt versions. Luckily, when QEMU has switched its default '-usb' controller from pci-ohci to nec-usb-xhci (QEMU commit 57040d451315), it has done so without affecting older machine types, which means we can keep using '-usb' without risking guest ABI breakage. Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1357468 --- src/qemu/qemu_command.c | 8 +++++--- tests/qemuxml2argvdata/qemuxml2argv-ppc64-usb-controller.args | 2 +- tests/qemuxml2argvdata/qemuxml2argv-pseries-usb-default.args | 2 +- 3 files changed, 7 insertions(+), 5 deletions(-)
Ján pointed out that applying this would un-break migration for ppc64 guests created before 8156493d8db9, but at the same time break migration for those created since, eg. in the last ~6 months. I'm kinda out of ideas here, so if anyone has a brilliant plan to make migration work for both old and new guests, please do share :) -- Andrea Bolognani / Red Hat / Virtualization