libguestfs appliances launched by nova will attempt to use KVM even if libvirt_type=qemu in nova.conf

[Lars Kellogg-Stedman]

The value of libvirt_type in nova.conf is not respected when Nova launches libguestfs appliances. This can cause problems were an administrator has explicitly set libvirt_type=qemu to work around KVM issues (or to test qemu). Newer versions of libguestfs support the 'force_tcg' option to disable the use of hardware emulation.

[Lars Kellogg-Stedman (larsks)]

Where "newer versions" means >= 1.25.23 (force_tcg introduced in libguestfs commit 11ac9f7).

[Kashyap Chamarthy (kashyapc)]

@Lars: Just to clarify: 'force_tcg' doesn't _disable_ use of hardware acceleration. It's an environment variable that will force libguestfs appliance to use software emulation.

From its man page[1]

    export LIBGUESTFS_BACKEND_SETTINGS=force_tcg

    which will force the 'direct' and 'libvirt' backends to use TCG (software emulation) instead of KVM (hardware accelerated virtualization).

  [1] http://libguestfs.org/guestfs.3.html#guestfs_set_backend_settings

[Dmitry Guryanov (dguryanov)]

The same issue has been resolved - https://bugs.launchpad.net/nova/+bug/1286256