https://libvirt.org/drvxen.html
libvirt is a generalized virtualization layer for managing various virtualization technlogies with a common toolkit (or toolstack).
The libvirt libxl driver uses Xen’s libxl API, also known as libxenlight, to implement libvirt’s hypervisor driver functionality.
Unlike old versions of Xen where applications often had to communicate with xend, xenstored, and the hypervisor itself via hypercalls. With libxl the only pre-requisit is a properly installed Xen host with the libxl toolstack running in a service domain (often Domain-0).