Someone

#  -*- mode: python; -*-
kernel = "/boot/vmlinuz-2.6-xenU"
memory = 256
name = "test_xen1"
vif = [ 'mac=00:16:3e:10:10:11, bridge=xenbr0' ]
disk = [ 'phy:/dev/xen_disk/xen1,sda1,w', 'phy:/dev/xen_disk/xen1_swap,sda2,w' ]
root = "/dev/sda1 ro"
extra = "4 fastboot"
#============================================================================

for a file :

disk = [ 'file:/xen_disks/active.img,ioemu:hda,w' ]