[Xen-users] Windows XP HVM on qcow diskfile and snapshots

[Geert Janssens <info@xxxxxxxxxxxx>]

Dom0: CentOS 5.2 i386, with gitco Xen 3.3.1 i386.

I have successfully managed to setup a Windows XP HVM guest domain, starting 
from a qcow disk image I was using with plain qemu so far. Even without GPLV 
drivers, there's already a noticeable speed increase. Yay!

As a next step, for several reasons I would like to have my base disk image 
immutable.

I have tried two different approaches, but both failed:
* Enable the 'snapshot=1' configuration parameter in my hvm config file. This 
doesn't seem to have any effect on my system (or maybe I misunderstand the 
option). All modifications to the disk image (like creating a new directory) 
are preserved after a complete shutdown of the guest and the recreating it.

* Created a copy-on-write disk image, based on my original image with
qemu-img create -b <original image> -fmt qcow <new image>
and changed the blockdevice line in my config file to
disk = [ 'tap:qcow:<new image>,hda,w', ',hdc:cdrom,r' ]

However, this configuration won't boot. To be exact, the guest aborts very 
shortly after the bios hard drive discovery. So I presume the copy-on-write 
disk image is somehow not working.

Any hints on what goes wrong here ?

Some more info on my system:
xm info
host                   : aragorn.vialila.lan
release                : 2.6.18-92.1.22.el5.centos.plusxen
version                : #1 SMP Wed Dec 17 12:11:57 EST 2008
machine                : i686
nr_cpus                : 4
nr_nodes               : 1
cores_per_socket       : 2
threads_per_core       : 1
cpu_mhz                : 2211
hw_caps                : 
178bfbff:ebd3fbff:00000000:00000010:00002001:00000000:0000001f:00000000
virt_caps              : hvm
total_memory           : 8191
free_memory            : 1026
node_to_cpu            : node0:0-3
node_to_memory         : node0:1026
xen_major              : 3
xen_minor              : 3
xen_extra              : .1
xen_caps               : xen-3.0-x86_32p hvm-3.0-x86_32 hvm-3.0-x86_32p
xen_scheduler          : credit
xen_pagesize           : 4096
platform_params        : virt_start=0xf5800000
xen_changeset          : unavailable
cc_compiler            : gcc version 4.1.2 20071124 (Red Hat 4.1.2-42)
cc_compile_by          : root
cc_compile_domain      : gitco.tld
cc_compile_date        : Tue Jan 20 23:35:28 CET 2009
xend_config_format     : 4

Below is my current hvm config file:
import os, re
arch = os.uname()[4]
if re.search('64', arch):
    arch_libdir = 'lib64'
else:
    arch_libdir = 'lib'
/var/lib/xen/images/WinXPViaLila.qcow')
kernel = "/usr/lib/xen/boot/hvmloader"
builder='hvm'
memory = 512
name = "WinXPViaLila"
acpi=0
vif = [ 'type=ioemu, mac=00:16:3e:4a:33:c6, bridge=xenbr0' ]
disk = [ 'tap:qcow:/var/lib/xen/images/WinXP-noacpi.qcow,hda,w', 
',hdc:cdrom,r' ]
device_model = '/usr/' + arch_libdir + '/xen/bin/qemu-dm'
snapshot=1
sdl=1
opengl=1
vnc=0
vnclisten="0.0.0.0"
vncdisplay=100
vncpasswd=''
serial='pty'
monitor=1
soundhw='sb16'
usb=1
usbdevice='tablet'

-- 
Kobalt W.I.T.
Web & Information Technology
Brusselsesteenweg 152
1850 Grimbergen

Tel  : +32 479 339 655
Email: info@xxxxxxxxxxxx


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