Anatomy of the libvirt virtualization library

"When it comes to scale-out computing (such as cloud computing), libvirt may be one of the most important libraries you've never heard of. Libvirt provides a hypervisor-agnostic API to securely manage guest operating systems running on a host. Libvirt isn't a tool per se but an API to build tools to manage guest operating systems. Libvirt itself is built on the idea of abstraction. It provides a common API for common functionality that the supported hypervisors implement. Libvirt was originally designed as a management API for Xen, but it has since been extended to support a number of hypervisors.

"Let's start our discussion of libvirt with a view of the use model, then dig into its architecture and use. Libvirt exists as a set of APIs designed to be used by a management application (see Figure 1). Libvirt, through a hypervisor-specific mechanism, communicates with each available hypervisor to perform the API requests. I explore how this is done with QEMU later in the article.

"Also shown is a comparison of the terminology that libvirt uses. This terminology is important, as these terms are used in API naming. The two fundamental differences are that libvirt calls the physical host a node, and the guest operating system is called a domain. Note here that libvirt (and its application) runs in the domain of the host Linux operating system (domain 0)."

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