[Libguestfs] Xen drivers for virt-builder images

[George Dunlap]

On Wed, Jun 11, 2014 at 8:34 PM, Richard W.M. Jones <rjones at redhat.com> wrote:
> On Wed, Jun 11, 2014 at 06:15:33PM +0100, George Dunlap wrote:
>> I've just been playing around with virt-builder, and it seems like a
>> pretty useful tool.  However, it seems that in a number of the images,
>> the initrd file is missing drivers for Xen virtual block and network
>> devices.  This results in a VM that can't find its root device.
>>
>> The files needed are drivers/block/xen-blkfront.ko and
>> drivers/net/xen-netfront.ko.  They seem to be present in centos-6 and
>> ubuntu-14.04, but not in rhel-7rc or fedora-20.
>>
>> Whom would I contact to get these added?
>
> That would likely be me or Pino Toscano, but read on :-)
>
> Firstly I'd like to say that the current images shipped in
> http://libguestfs.org/download/builder/ are a temporary solution that
> has turned out to be more permanent than we wished for.  Eventually we
> want to simply use the cloud images shipped by the Linux distros, and
> just provide simple metadata and the virt-builder front end.  When we
> do that (and it's not a huge change) then the issue of drivers for
> Xen, VMware, virtio, etc will be up to the distros to solve.

Right -- that makes sense.  I'm helping out with the CentOS Virt SIG
at the moment, so I can try to make that happen for CentOS when the
time comes. :-)

> However at the moment we could add Xen drivers to our current scripts,
> located here:
>
> https://github.com/libguestfs/libguestfs/tree/master/builder/website (*.sh)
>
> For Fedora and RHEL, it would require a modest change to the kickstart
> embedded in those scripts, plus rebuilding the images and reuploading
> them.
>
> Do you know what extra packages have to be installed or commands need
> to be run to enable Xen drivers in Fedora?

The kernel already has a lot of the Xen stuff enabled.  AFAICT from
looking at the boot output it's just missing those two modules in the
initrd.  (Although it's possible you'll need more.)  I'm pretty sure
they should just come in the normal kernel rpm; there aren't really
any user-space components necessary for basic functionality of a Xen
guest.  (There are a few tools which someone might want to install for
one purpose or another -- tools for querying Xen state or acting as a
"driver domain" -- but they're something that should be added as
needed, not in the core.)

Dario has more familiarity with Fedora and Xen -- Dario, any comments?

Thanks for your help,

 -George