libvirt User Mode Linux driver and other new features

It has been a while since I reported on libvirt development news, but that doesn’t mean we’ve been idle. The big news is the introduction of another new hypervisor driver in libvirt, this time for User Mode Linux. While Xen / KVM get all the press these days, UML has been quietly providing virtualization for Linux users for many years – until very recently nearly all Linux virtual server providers were deploying User Mode Linux guests. libvirt aims to be the universal management API for all virtualization technologies, and UML has no formal API of its own, so it is only natural that we provide a UML driver in libvirt. It is still at a fairly basic level of functionality, only supporting disks & paravirt consoles, but it is enough to get a guest booted & interact locally. The next step is adding networking support at which point it’ll be genuinely useful. To recap, libvirt now has drivers for Xen, QEMU, KVM, OpenVZ, LXC (LinuX native Containers) and UML, as well as a test driver & RPC support.

In other news, a couple of developers at VirtualIron have recently contributed some major new features to libvirt. The first set of APIs provides the ability to register for lifecycle events against domains, allowing an application to be notified whenever a domain stops, starts, migrates, etc, rather than having to continually poll for status changes. This is implemented for KVM and Xen so far. The second huge set of APIs provide a way to query a host for details of all the hardware devices it has. This is a key building block to allow remote management tools to assign PCI/USB devices directly to guest VMs, and to more intelligently configure networking and storage. Think of it as a remotely accessible version of HAL. In fact, we use HAL as one of the backend implementations for the API, or as an alternative, the new DeviceKit service.