Introduction to Xen Source Code Structure

The Xen hypervisor is a powerful virtualization solution that provides virtualization capabilities for x86, x86-64, and ARM architectures. The source code structure of Xen is organized into several directories, each of which contains a specific set of files. The backend and frontend drivers are an important part of the Xen hypervisor, and they provide a mechanism for virtualizing physical devices and communicating with the hypervisor. By understanding the source code structure of Xen and the backend and frontend drivers, you can gain a deeper understanding of how the Xen hypervisor works and how to develop applications and drivers for Xen.

Xen Source Code Structure

The Xen source code is organized into several directories, each of which contains a specific set of files. The top-level directories are:

• docs: Contains documentation and user manuals for Xen.
• tools: Contains various tools for managing and monitoring Xen, such as xl, xm, and xentop.
• xen: Contains the source code for the Xen hypervisor.
• linux-2.6.xx-xen: Contains the source code for the Linux kernel with Xen support.
• extras: Contains extra tools and utilities for Xen.

The xen directory contains the core source code for the Xen hypervisor, which is written in C. The source code is organized into several subdirectories, each of which contains a specific set of files:

• common: Contains common code used by both the Xen hypervisor and the backend and frontend drivers.
• arch: Contains architecture-specific code for x86, x86-64, and ARM architectures.
• drivers: Contains backend and frontend drivers for various devices, such as disk, network, and input devices.
• xsm: Contains code for the Xen Security Modules (XSM), which implements mandatory access control policies for Xen.
• tools: Contains tools for managing and monitoring Xen, such as xenstore, xenbus, and event_channels.

Backend and Frontend Drivers

The backend and frontend drivers are an important part of the Xen hypervisor. The backend drivers run in the domain 0 (dom0) and provide access to physical devices, such as disks and network interfaces. The frontend drivers run in the guest domains (domU) and provide a virtual representation of the physical devices.

The backend and frontend drivers communicate with each other using a shared memory area called the XenBus. The XenBus provides a mechanism for the backend and frontend drivers to exchange messages and negotiate the configuration of the devices.

The backend drivers are responsible for handling the physical devices and providing a virtual interface to the frontend drivers. The backend drivers are implemented as kernel modules in the Linux kernel, and they communicate with the hypervisor using the xenbus interface.

The frontend drivers are responsible for handling the virtual devices and communicating with the backend drivers using the XenBus. The frontend drivers are implemented as drivers in the guest operating system, and they communicate with the hypervisor using the xenstore interface.

A slides deck

I have created slides from introducing Xen’s source code structure and backend and frontend drivers in Xen. Please note these slides on Xen was made in around 2013 and the Xen source code structure might have already changed a lot. Please check this as a reference to the Xen source structure only.