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Xen Pvops Dom0


pvops-based Package-x-generic-16.pngkernel to serve as Dom0 for a Xen-based system. Currently Fedora releases greater than 8 contain the Xen hypervisor and tools, but not a Xen Dom0-capable kernel.


  • Name: W. Michael Petullo
  • Email:
  • People Involved: Michael Young, Eduardo Habkost, Mark McLoughlin, Stephen Tweedie, Chris Wright, Juan Quintela, Markus Armbruster, Glauber Costa, Daniel Berrange et al.

Current status

  • Targeted release: Fedora 15
  • Last updated: 2010-10-29
  • Percentage of completion: 0%

Detailed Description

Xen is a hypervisor-based type-1 virtualization solution. The Xen hypervisor requires a standard operating system to run in a privileged domain, Dom0. The Dom0 operating system provides driver and guest management support to Xen and other guest operating systems running in the DomU domain. Fedora 8 provided a kernel that could serve as a Dom0 guest. However, newer Fedora releases dropped support for Dom0 (although they can run in DomU). The Xen project is presently pushing the features required for a Dom0 Linux kernel upstream. Once these features are available in a mainline kernel, it follows that Fedora could support Xen Dom0.

Benefit to Fedora

Fedora will benefit from a Xen Dom0-capable kernel. Xen has proven to be a competitive virtualization solution in real-world installations. Xen is different enough from KVM that the two technologies could complement each other within the Fedora Project. There are ongoing benchmarks that intend to define the relative performance of the two technologies.


  • Implement Dom0 support in upstream kernel (Xen / Jeremy Fitzhardinge)
  • Modify 'grubby' to support GRUB syntax required by Xen (Bugzilla #640486)
  • Make 'new-kernel-pkg' aware of Xen, possibly by a flag in /etc/sysconfig/kernel
  • Ensure Fedora's virtualization tools support Xen
  • Possibly implement support in Anaconda

How To Test

  • Install a Fedora Dom0 kernel
  • Turn on Xen Userspace by running 'chkconfig xend on'
  • Turn on Xen Hypervisor by setting 'HYPERVISOR=/boot/xen-4.0.gz' in /etc/sysconfig/kernel and running some tool (TBD)
  • Reboot
  • Observe presence of Xen via /sys/hypervisor/
  • Run 'xm list' and observe Domain-0
  • Use 'virt-install' to deploy a Fedora paravirtualized guest
  • Use 'virt-install' to deploy a Fedora fully virtualized guest
  • Use 'virsh' to save & restore guests
  • Balloon down memory of a guest with 'virsh'

User Experience

  • Stock Fedora kernel supports Xen dom0
  • All features and hardware supported on baremetal also work on Xen Dom0
  • Can enable and disable the use of hypervisor via a /etc/sysconfig/kernel setting


  • kernel
  • grubby
  • Fedora virtualization tools
  • (possibly) anaconda

Contingency Plan

There is presently some uncertainty as to when the Xen drivers will be upstream. They may make the 2.6.37 series and therefore Fedora 15 or they may not. Regardless, we will have to touch a lot of subsystems, so it makes sense to start early.

If the Xen drivers don't make Fedora 15, then little is lost. We can continue to test the Dom0 kernel (without DomU) and work on the supporting infrastructure. It would be useful for our effort to have a working Dom0, grubby, etc in Fedora 15 even if other features do not make it. In the worst case, we may delay the announcement of the Dom0 feature to Fedora 16, but can include all progress completed in Fedora 15. There is no shame in a delayed feature -- this happened to systemd during the preparation for Fedora 14.


See also:

Release Notes

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