[libvirt] guest band width setting

Hi All, I am new to QEMU/libvirt I was starting to learn the libvirt code,I was browsing the code how the guest network bandwidth to be set like we mention <inbound> <outbound> tags in the xml,but where in code exactly these values set to the guest interface. I browsed the code a lot could not find it.Please help to understand how this works. Thanks in advance Pradeep