[libvirt-users] How to change libvirt / cgroup interaction?

Hi there, Do you know if there is a way to modify how libvirt interacts with the cgroup? Because, I successfully add the /dev/net/tun support in my LXC container by doing: echo c 10:200 rwm >> /cgroup/libvirt/lxc/instance-00000005/devices.allow But when I restart the instance/LXC container, this option has gone. How can I make this persistant? Is there a configuration file? Thanks for your answers. Best regards. Sam