CGROUP means Control group.
In my case, usb-redir works fine while usb-host not.
Just do it
# sed -i 's/devices /#devices /' # reboot
Add fine control list
Review the rules to libvirt, and leave all the character device to it
# cgget libvirt To remove "c" device # echo c > /sys/fs/cgroup/libvirt/devices.deny To add all the "c" devices # echo "c *:* rwm" > /sys/fs/cgroup/libvirt/devices.allow
devices.deny/allow is something like end-point.
A child will not have more permission than its parent.