[libvirt-users] how libvirt create virbr0

libvirt version: 3.4.0 architecture: x86_64 ubuntu16.04-server hypervisor: kvm,qemu when install libvirt from ubuntu distribution deb install libvirt, a virtual bridge virbr0 will be create . But when I build libvirt from souce code, how can I create a virbr0. If I want create another virtual bridge ,How can I create and start the virtual bridge. Thanks