On 1/17/19 4:37 PM, Laine Stump wrote:
When commit 361c8dc17 added support for hotplugging the i6300esb watchdog device (first in libvirt-3.9.0), it accidentally contstructed the commandline for the device_add command before allocating a PCI address for the device. With no PCI address specified in the command, the watchdog would simply be placed at the lowest unused PCI slot.
On a 440fx guest, this doesn't cause a problem, because libvirt's PCI address allocation algorithm would most likely give the same address anyway (usually a slot on pci-root), so nobody noticed the omission of address from the command.
But on a Q35 guest, the lowest unused PCI slot is on pcie-root, which doesn't support hotplug; libvirt knows enough to assign a PCI address that is on a pcie-to-pci-bridge (because its slots *do* support hotplug), but qemu doesn't, so if there is no PCI address in the command, qemu just tries to plug the new device into pcie-root, and fails because it doesn't support hotplug, e.g.:
error: Failed to attach device from watchdog.xml error: internal error: unable to execute QEMU command 'device_add': Bus 'pcie.0' does not support hotplugging
The solution is simply to build the command string after assigning a PCI address, not before.
Resolves: https://bugzilla.redhat.com/1666559 Signed-off-by: Laine Stump <laine@laine.org> --- src/qemu/qemu_hotplug.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
Reviewed-by: John Ferlan <jferlan@redhat.com> John