Mar
22
2009
2

Fedora 11 will likely not include Xen Dom0 (virtualization) support

xen logo

I (like many of you) have been patiently waiting since Fedora 8 for Dom0(Domain 0) Xen support in Fedora.  Why hasn’t Red Hat or the Fedora Project made an announcement? Haven’t we been good? I mean libvirtd is great and all, but Xen PV(paravirtualized) VM’s destroy. I did some googling to get to the bottom of this. I found a fedora project page with a January 2009 status update.

Here is a snipit:

“Currently, the Fedora kernel-xen package is based on forward-porting of the XenSource patches from 2.6.18 to more recent kernel versions. This has many problems, including:

  • XenSource code has no chance of being merged upstream, in the near future, making the forward-porting work needed for all new kernel versions.
  • Lots of porting work for each new kernel version
  • Because of the above, kernel-xen has been some releases behind the non-xen kernel package, and the lag between kernel and kernel-xen has been increasing constantly”

And also:

“As of November 2007, the kernel-xen forward-porting was being finished for 2.6.22, and Linux 2.6.24 was about to be released. The effort needed for 2.6.23, 2.6.24 and later would have been even bigger with the introduction of paravirt_ops and the i386-x86_64 merge upstream. Thus, the decision was made to abandon the forward-porting effort and focus on upstream paravirt_ops.”

So where does this leave us?  Unmodified guest are old news.  Even Microsoft can do that.  Well not really, as I understand it, Microsoft’s HyperV platform contains Xensource licensed code.  But a customer of the company I work for likes HyperV a lot(incidently).  On the Xen Wiki it says that Paravirt_ops will be ported to the 2.6.30 kernel.  My prediction, Xen Dom0 support will be available toward the end of Fedora 11’s cycle or Fedora 12.

Why does Dom0 matter?  Dom0 is the specially modifed Xen-linux kernel that sits on top of the hypervisor. From Dom0 you can run fully virtualized guest and partially virtualized guest (paravirtualization).  Paravirtualized guest enjoy a method for allowing the use of a set of generic virtual device drivers provided by Dom0.  PV guest are known to have outstanding perfomance compared to their fully virtualized counterpart.  Paravirt_ops refers to Dom0 integration with the Linux kernel.