After updating the dom0 kernel on one of my Xen test hosts, I noticed problems with PCI hostdev management. E.g # virsh nodedev-detach pci_0000_07_10_1 error: Failed to detach device pci_0000_07_10_1 error: Failed to add PCI device ID '8086 1520' to pciback: File exists It turns out there was a small interface change to new_id with the following commit to 3.16 kernel https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/drivers/pci/pci-driver.c?h=v3.16&id=8895d3bcb8ba960b1b83f95d772b641352ea8e51 which now causes xen_pciback to fail writes of "vendorid productid" to new_id. e.g. # echo "8086 1520" > /sys/bus/pci/drivers/pciback/new_id -bash: echo: write error: File exists Interestingly, vfio doesn't encounter the same error # echo "8086 1520" > /sys/bus/pci/drivers/vfio-pci/new_id # echo $? 0 vfio-pci has: static struct pci_driver vfio_pci_driver = { .name = "vfio-pci", .id_table = NULL, /* only dynamic ids */ while xen-pciback has: static const struct pci_device_id pcistub_ids[] = { { .vendor = PCI_ANY_ID, .device = PCI_ANY_ID, .subvendor = PCI_ANY_ID, .subdevice = PCI_ANY_ID, }, {0,}, }; static struct pci_driver xen_pcibk_pci_driver = { .name = "pciback", .id_table = pcistub_ids, So any vendor/device pair will match for xen-pciback, while none will match for vfio-pci. But after reading that commit and the associated thread, it is not clear to me how to best fix this. Options are 1. set .id_table to NULL for xen-pciback 2. drop using the new_id interface from libvirt 3. pass more values (subvendor, subdevice, class, etc) to the new_id interface I'm not sure what problems, if any, options 1 and 2 might cause. Option 2 seems the best approach since new_id seems to be a rather unsafe interface. Thanks for your opinions! Regards, Jim