Xen will never be part of Linux

Recently ZDNet published a skirmish of words between Ian Pratt, Xen founder and chief architect, and Benny Schnaider, CEO of Qumranet (supporting the development of KVM), about the destiny of Xen and the right to be called hypervisor of KVM.

While the debate itself is not too much interesting, one of the reactions that it provoked is much more.

Anthony Liguori, Software Engineer at Linux Technology Center, contributor for both Xen and KVM ( and of Debunking Blue Pill Myth fame), used his personal blog to provide some interesting perspectives of why KVM was preferred over Xen for the integration in the Linux kernel:

Xen is a hypervisor that is based on the Nemesis microkernel. Linux distributions ship Xen today and by default install a Linux guest (known as domain-0) and do their best to hide the fact that Xen is not a part of Linux. They’ve done a good job, most users won’t even notice that they are running an entirely different Operating System. The whole situation is somewhat absurd though. It’s like if the distributions shipped a NetBSD kernel automatically and switched to using it when you wanted to run a LAMP stack. We don’t ship a plethora of purpose-built kernels in a distribution. We ship one kernel and make sure that it works well for all users. That’s what makes a Linux distribution Linux. When you take away the Linux kernel, it’s not Linux any more.

When people talk about Xen not being merged into Linux, I don’t think they realize that Xen will *never* be merged into Linux. Xen will always be a separate, purpose-built kernel. There are patches to Linux that enable it to run well as a guest under Xen. These patches are likely to be merged in the future, but Xen will never been a part of the Linux kernel…