Using a Virtual Machine to develop sDDF components #

LionsOS drivers have two parts: a driver interface (that consists of the device registers and interrupts), and an sDDF interface that consists of ring buffers and microkit notifications.

The actual driver can be developed under Linux, by mapping both interfaces as UIO and writing a usermode program to do the work.

As a halfway point, one can use the Linux driver to develop the sDDF part. For complex drivers (like for Graphics), or if performance is not an issue, the resulting driver can be used in a production system. However, both performance and security will be enhanced with a native driver.

This tutorial leads you through the creation of a simple block interface to the sDDF.

Steps we’re going to take #

1. Get a virtual machine using LionsOS working on the target platform, with all devices passed through. This allows us to be sure the virtualisation system is working, and to set up a development environment using the target’s local storage.
2. Switch the virtual machine to use LionsOS sDDF for serial and ethernet. This shows how to set up the memory regions and use virtIO.
3. Create a second virtual machine using virtio-Network and serial; using a buildroot kernel and RAMdisk. This shows how to set up multiple virtual machines.
4. Set up a UIO region for the development VM that shares memory regions with the second (client) VM.
5. Set up an sDDF user-mode block device to feed virtIO-Block on the client VM, using only Linux user-space tools in the development VM. This shows how you can access sDDF rings from Linux user space in an appropriately configured VM.