On Fri, Oct 28, 2016 at 01:28:19PM +0200, Henning Schild wrote:
Hey,
i am running an unusual setup where i assign pci devices behind the back of libvirt. I have two options to do that: 1. a wrapper script for qemu that takes care of suid-root and appends arguments for pci-assign 2. virsh qemu-monitor-command ... 'device_add pci-assign...'
I know i should probably not be doing this, it is a workaround to introduce fine-grained pci-assignment in an openstack setup, where vendor and device id are not enough to pick the right device for a vm.
In both cases qemu will crash with the following output:
qemu: hardware error: pci read failed, ret = 0 errno = 22
followed by the usual machine state dump. With strace i found it to be a failing read on the config space file of my device. /sys/bus/pci/devices/0000:xx:xx.x/config A few reads out of that file succeeded, as well as accesses on vendor etc.
errno == 22, means EINVAL, so it feels unlikely to be a permissions problem unless the kernel or QEMU is reporting the wrong errno.
Manually launching a qemu with the pci-assign works without a problem, so i "blame" libvirt and the cgroup environment the qemu ends up in.
The 'config' file is a plain file, so not affected by cgroups - that only affects block devices. When libvirt runs QEMU, it runs unprivileged qemu:qemu user/group, so perhaps it is a permissions thing, despite the fact that you're getting EINVAL, not EACCESS. It would be interesting to know just what part of the config space QEMU was trying to read I guess, to better understand why it might be failing Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://entangle-photo.org -o- http://search.cpan.org/~danberr/ :|