libvirt users - Jan 2016 - "INTx fd" busy error on VM startup at boot, subsequent startup okay

Hey all,

I'm getting an error starting a libvirt managed qemu/kvm VM at physical 
host boot time, but manually starting it afterwards works fine. This is 
on a Ubuntu Wily i7-4790 box running Linux 4.2 and libvirt 1.2.16. 
There is a legacy (5V) PCI card being passed through to the VM, the 
error seems to relate to that.

The error that always appears at boot in 
`/var/log/libvirt/qemu/test-vm.log` is:
> 2016-01-11T05:29:28.487935Z qemu-system-x86_64: -device 
> vfio-pci,host=05:00.0,id=hostdev0,bus=pci.0,addr=0x4: vfio: Error: 
> Failed to setup INTx fd: Device or resource busy
> 2016-01-11T05:29:28.488148Z qemu-system-x86_64: -device 
> vfio-pci,host=05:00.0,id=hostdev0,bus=pci.0,addr=0x4: Device 
> initialization failed
> 2016-01-11T05:29:28.488169Z qemu-system-x86_64: -device 
> vfio-pci,host=05:00.0,id=hostdev0,bus=pci.0,addr=0x4: Device 
> 'vfio-pci' could not be initialized
After the physical machine has completed booting, starting the VM via 
virsh or virt-manager works fine.

The card is an old Firewire card. I have blacklisted the firewire 
modules on the physical machine so they aren't loaded, but is it 
possible that the kernel, udev or some other process still has access 
to the device when systemd starts the libvirt-bin service?

Any clues greatly appreciated.

Thanks,
//Mike

-- 
⊨ Michael Gratton, Percept Wrangler.
⚙ <http://mjog.vee.net/>