Incompatibility and pain - a perspective from Xen upstream

Xen is a complicated system. It contains both loosely- and tightly-coupled relationships between its components.

In this talk I will discuss some of the version compatibility problems we have faced, and how they have been solved (if indeed they have been solved).

I'm looking to present some of the problems and ask for feedback (and hopefully solutions from the Debian Xen community.)

Notable examples are:

• The very loose coupling of guest VMs, based on a very stable and long-term supported guest interface (ABI/API).

• The strict coupling of hypervisor version with the version of the low-level domain management code, which runs in userspace in the management VM. (The "tools".)

• The loose coupling between the management domain kernel(s) and both tools and hypervisor.

• The transition from xm/xend to xl/libxl.

• Development of the libxl stable API. ABI stability considerations.

• The coupling between infrastructure such as libxl and higher-level management/provisioning systems such as xen-tools, libvirt, XenServer, Openstack, etc.