qemu-bridge-helper: failed to create tun device: Operation not permitted

virsh start deepin

error: Failed to start domain deepin
error: internal error: /usr/lib/qemu/qemu-bridge-helper --use-vnet --br=br0 --fd=30: failed to communicate with bridge helper: 传输端点尚未连接
stderr=failed to create tun device: Operation not permitted

原因：qemu-bridge-helper需要set uid，但是deepin的apt没有自动设置这个权限。需要手动设置：

sudo chmod 4755 /usr/lib/qemu/qemu-bridge-helper

原文：https://listman.redhat.com/archives/libvirt-users/2014-June/msg00094.html