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

[Matthias Schmidt]

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.