Xen 4.2 brings new default tool stack
After approximately 18 months of development, the creators of the open source Xen hypervisor have released Xen 4.2 – changing almost 300,000 lines of code. The new release features "much improved" documentation and the default collection of tools for interacting with the software have also been changed.
The XL tool collection replaces the xend daemon and the xm management interface which are planned to be deprecated in the future; a feature comparison between both stacks is available on the Xen wiki. XL will hand the network configuration over to distribution-specific tools and the developers state that existing configuration files should be supported by the new tools. Embedded Python code is no longer supported, however.
Xen 4.2 increases the performance limits of the hypervisor in several respects. The new version supports 4,095 physical CPUs, 5TB of RAM, 512 guest CPUs with paravirtualised VMs (PV) and 256 guest CPUs with fully virtualised VMs (HVM). This is increased from more than 255 physical CPUs, 5TB of RAM, more than 255 PV guests and 128 HVM guests in the previous version.
Many changes developed by the Xen project are now moving upstream to other projects. Xen's HVM device model is now supported by QEMU and the next version of Xen is supposed to use this code by default. Using the XL stack, it is already available as an option. Through the harmonisation with the upstream projects, Xen has also gained support for SeaBIOS and the tianocore UEFI implementation for VMs. The dom0 code which is needed to use Linux kernels as hosts with the hypervisor was already merged in Linux 3.0 and has been used since Xen 4.1.