Xen users - Aug 2008 - Converting full virtualized Linux domUs to use paravirtualized drivers

Hi

Is there any docs, howtos, etc, if i am installed eg. CentOS 5 to as domU 
as fully virtualized and now i am wanting to use it PV drivers. 
Any help how migration can be done?

Terveisin/Regards,
   Pekka Panula, Net Servant Oy - A Sofor company
   pekka.panula@sofor.fi


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On Tue, Aug 12, 2008 at 02:12:57PM +0300, Pekka.Panula@sofor.fi
wrote:
> Hi
> 
> Is there any docs, howtos, etc, if i am installed eg. CentOS 5 to as domU 
> as fully virtualized and now i am wanting to use it PV drivers. 
> Any help how migration can be done?
> 
If you want to run paravirtualized network/block drivers in fully
virtualized (HVM) guest, try these:

http://www.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/5.2/html/Virtualization/chap-Virtualization-Introduction_to_Para_virtualized_Drivers.html
http://www.centos.org/docs/5/html/5.2/Virtualization/chap-Virtualization-Introduction_to_Para_virtualized_Drivers.html

http://lists.centos.org/pipermail/centos-devel/2008-June/004797.html

ftp://ftp.redhat.com/pub/redhat/linux/enterprise/5Server/en/os/SRPMS/xenpv-0.1-9.el5.src.rpm

Other option is to convert the HVM guest to paravirtual domU.

-- Pasi

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On Tue, Aug 12, 2008 at 03:16:28PM +0300, Pekka.Panula@sofor.fi
wrote:
> Pasi Kärkkäinen <pasik@iki.fi> wrote on 12.08.2008 14:47:02:
> 
> > Other option is to convert the HVM guest to paravirtual domU.
> 
> I am mainly wanting to convert HVM as para domU, is there any docs about 
> that?
> 
Hmm.. basicly it should be something like:

- in HVM guest: yum install kernel-xen
- in HVM guest: make sure /boot/grub/menu.lst contains kernel-xen as a kernel to
boot
- in dom0: update your guest/domU cfgfile, make sure you use pygrub to load the
kernel+initrd from domU.

That should be it.. 

-- Pasi

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>> I am mainly wanting to convert HVM as para domU, is there any docs
about
>> that?
>>
>
> Hmm.. basicly it should be something like:
>
> - in HVM guest: yum install kernel-xen
> - in HVM guest: make sure /boot/grub/menu.lst contains kernel-xen as a
kernel to boot
> - in dom0: update your guest/domU cfgfile, make sure you use pygrub to load
the kernel+initrd from domU.
>
> That should be it..
>
> -- Pasi
>
I have converted a HVM installation of Trixbox(based on CentOS) to a
PVM running on Ubuntu 8.04 Dom0.
I didn''t use pygrub as that doesn''t play with DRBD. So below
is
another method. After doing the first two steps above you can follow
my installation notes below. Sorry if it is a bit messy, am about to
put it into a howto but haven''t found the time yet...

CONVERT TRIXBOX HVM to PVM
apt-get install kpartx

losetup /dev/loop0 /dev/drbd6
kpartx -av /dev/loop0
mount /dev/mapper/loop0p2 /mnt/

Create an LVM for root and swap.
mkfs.ext3 and
rsync -a /dev/mapper/loop0p2 to new LVM

Edit /etc/fstab on the DomU disk to map /dev/xvda to root and /dev/xvdb to swap

Ran the following within the HVM to create new initrd which loads xen
drivers. otherwise kernel panic.:
mkinitrd /boot/initrd-2.6.18-92.1.6.el5xenU2.img 2.6.18-92.1.6.el5xen
--with=xenblk --with=xennet --preload=xenblk --preload=xennet

Copy kernel and initrd from HVM to Dom0.

Modified the xen config file with the kernel and initrd above.

Removed: xencons=tty1 from the "extra=" line. like this:
extra="clock=jiffies"
as needed in other configs.

Problem with network, DomU tried to start eth1 only.
Modified: /etc/sysconfig/network-scripts like this:

# Realtek Semiconductor Co., Ltd. RTL-8139/8139C/8139C+
DEVICE=eth0
ONBOOT=yes
BOOTPROTO=none
NETWORK=10.111.1.0
NETMASK=255.255.255.0
IPADDR=10.111.1.160
GATEWAY=10.111.1.254
MACADDR=00:16:3E:AA:35:32

/etc/init.d/network restart
---------
I actually had a problem using the original kernel. Performing a live
migration or even shutting down the DomU made it hang. It couldn''t not
unload one or two block devices.
So I ended up using the Dom0 kernel instead. I copied the modules from
Dom0 to the DomU as usual.

To early to say if this is really stable, but at least it works. ;)

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