[libvirt] Trouble booting Xen VM with NFS root file system

Hi, I'm currently trying to boot a Xen VM with the root file system on NFS via libvirt. Previously we used a small python script and "xm create" to boot a number of VMs (which worked fine). Now I'm trying to integrate that functionality in a python project which uses libvirt, but sadly booting the VMs fail. The small script constructs a Xen command line which looks like the following: create =("/usr/sbin/xm create /foo.cfg \ kernel=%s ramdisk=%s memory=64\ root=/dev/nfs nfs_server=%s nfs_root=%s name=%s vif='mac=%s'\ dhcp='dhcp' vcpus=1 extra='init=/stateless.sh xencons=tty1'\ ")%(vm_kernel, vm_ramdisk, vm_nfs_server, vm_nfs_root, hostname, vif) kernel and ramdisk are the path to the installed version, vm_nfs_server is the IP address of the NFS server and vm_nfs_root the path to the operating system installation (which is a Debian Linux). Firing up the script brings up all VMs with a read-only NFS root file system. Now I tried to do this with libvirt, but all attempts failed with the following error popping up after the VM boots (after a certain time(out)): Gave up waiting for root device. Common problems: - Boot args (cat /proc/cmdline) - Check rootdelay= (did the system wait long enough?) - Check root= (did the system wait for the right device?) - Missing modules (cat /proc/modules; ls /dev) ALERT! /dev/nfs does not exist. Dropping to a shell! BusyBox v1.10.2 (Debian 1:1.10.2-2) built-in shell (ash) Enter 'help' for a list of built-in commands. /bin/sh: can't access tty; job control turned off (initramfs) cat /proc/cmdline root=/dev/nfs nfs_server=10.0.0.150 nfs_root=/opt/xge/util/ph vif="mac=1A:00:00:00:00:64" dhcp=dhcp extra="init=./stateless.sh xencons=tty" The cmdline looks the same as in the script, but booting won't work. I can provide the libvirt XML used to boot the VM and further information if that is necessary. Cheers Matthias PS: I'm using Xen 3.2.1, Kernel 2.6.26 and libvirt 0.6.3 from Debian here.