On 06/28/2016 12:39 PM, Laine Stump wrote: > On 06/28/2016 01:39 PM, Jim Fehlig wrote: >> 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. > > Regardless of your current problem (as Dan says in his reply, this is kernel > breakage and should be fixed)... > > "Unsafe" was *one* of the words that came to my mind when I first saw the > new_id interface. These days there is a sysfs interface called driver_override > that seems much more thoughtfully designed - you just write the name of the > desired driver to /sys/devices/[rest of path to device]/driver_override. I > didn't check if this is the version of the patch that was pushed upstream, but > the commit log message does give a nice synopsis of its use: > > https://www.redhat.com/archives/libvir-list/2014-April/msg00382.html > > It would be nice to completely get rid of new_id in libvirt, but > driver_override doesn't exist in 2.6 kernels, so we have to keep it around for > compatibility with RHEL6/CentOS6. In the meantime, I wouldn't complain at all > if someone added support for driver_override that would fallback to new_id if > the driver_override node wasn't found. (A nice side effect would be that your > problem would be solved even when the kernel wasn't fixed - driver_override is > present at least as far back as kernel 3.10, and you say your problem doesn't > occur until 3.16). Sorry for the delay. I got sidetracked for a while but finally got around to adding support for driver_override, falling back to the existing new_id approach https://www.redhat.com/archives/libvir-list/2016-July/msg00370.html Regards, Jim -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list