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.

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?

dracut --add-drivers "some list of xen kmods ..."

Hello everyone, On gio, 2014-06-12 at 08:20 +0100, Richard W.M. Jones wrote: > On Wed, Jun 11, 2014 at 10:02:22PM +0100, George Dunlap wrote: > > On Wed, Jun 11, 2014 at 8:34 PM, Richard W.M. Jones <rjones(a)redhat.com&gt; wrote: > > > 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.) > > I suspect we may need to run a dracut command in %post. Something > like: > > dracut --add-drivers "some list of xen kmods ..." > > I'm not sure which Xen drivers are required. The Fedora 21 kernel has > 13 files named 'xen*.ko.xz'. > So, first of all, forgive my libguestfs / virt-builder ignorance. :-) About the modules, what I know is that if I point virt-install to this location: http://mirror.euserv.net/linux/fedora/linux/releases/20/Fedora/x86_64/os/ it just works, i.e., the installer is able to see the virtual disk and network interface while running in a Xen (PV) guest. Looking inside the initrd.img that the above uses, here's what I find: $ find lib/modules/3.11.10-301.fc20.x86_64/ -iname xen* lib/modules/3.11.10-301.fc20.x86_64/kernel/drivers/block/xen-blkfront.ko lib/modules/3.11.10-301.fc20.x86_64/kernel/drivers/net/xen-netback lib/modules/3.11.10-301.fc20.x86_64/kernel/drivers/net/xen-netback/xen-netback.ko lib/modules/3.11.10-301.fc20.x86_64/kernel/drivers/net/xen-netfront.ko

On Thu, Jun 12, 2014 at 03:12:46PM +0100, Richard W.M. Jones wrote: > > Not quite as easy as I imagined. However by using the attached patch > I have managed to add the two Xen drivers to the initramfs. (I > haven't been able to test that it boots in Xen however) > > I'm just building an updated Fedora 20 image which I'll upload later > today. The F20 image has been uploaded. You should notice when you install it that it will download the full disk image again, and also that a file "fedora-20.x86_64.2" will be created in ~/.cache/virt-builder/ (.2 == revision 2) I tried various experiments, and it seems as if the Xen modules are included in the initramfs even if you upgrade the kernel when running virt-builder itself. So all looks good over here, but I didn't actually try booting the disk image on Xen itself.

While I have your attention ... It'd be great if libguestfs could use Xen as a backend (in addition to current qemu, KVM and UML backends). Most likely that would involve one of two approaches: (1) Modify the libvirt backend (src/launch-libvirt.c) so it works properly when the hypervisor is Xen. If you buy into libvirt, this one is probably going to be less code. (2) Add a new backend (src/launch-xl.c ?) which uses native Xen APIs to create the appliance.

Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com Fedora Windows cross-compiler. Compile Windows programs, test, and build Windows installers. Over 100 libraries supported. http://fedoraproject.org/wiki/MinGW _______________________________________________ Libguestfs mailing list Libguestfs(a)redhat.com https://www.redhat.com/mailman/listinfo/libguestfs

On Thu, Jun 12, 2014 at 07:04:06PM +0100, George Dunlap wrote: > Right, well after managing to work around our corporate transparent > caching proxy to actually get the new version, I've tested it and it > works great. Thanks. Thanks for testing. I'll make the same change to CentOS, but that will take a bit longer to build & upload.

> * On the other hand, I suspect most distros will have a > libguestfs->libvirt dependency anyway. Upstream, I have steered away from using the libvirt backend. Running qemu directly is the default. The reason is that the libvirt backend adds complexity without a great deal of benefit for most users. [That's less true if we're talking about supporting Xen because there it gives us benefit by moving much of the Xen support code into libvirt.] In Fedora & RHEL we are using the libvirt backend by default, partly because me & Dan Berrange are around to support it, and partly because it allows us to use SELinux + cgroups to contain the qemu process (somewhat analogous to driver-domains in Xen). AFAIK no other distro uses the libvirt backend by default, but they all ship it and you can switch to it by setting an environment variable (whether it actually works or not is another question). > So it seems like going with #1 is probably the best, overall. I'm not going to implement the Xen backend myself, but patches welcome as they say.

Not quite as easy as I imagined. However by using the attached patch I have managed to add the two Xen drivers to the initramfs. (I haven't been able to test that it boots in Xen however) I'm just building an updated Fedora 20 image which I'll upload later today. Are there other guests that need to be updated in the same way?