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[Xen-users] Migrating from -xen guest kernel to unmodified guest kernel

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Subject: [Xen-users] Migrating from -xen guest kernel to unmodified guest kernel
From: Tom Haddon <tom@xxxxxxxxxxxxxxxxx>
Date: Thu, 10 Jul 2008 22:41:45 +0100
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Hi Folks,

I'm trying to switch a guest from using a -xen guest kernel to using an
unmodified guest kernel. Looking at the disk layout on my current guest
I see the following:

mthaddon@dapper:~$ sudo fdisk -l

Disk /dev/hda1: 4294 MB, 4294967296 bytes
255 heads, 63 sectors/track, 522 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Disk /dev/hda1 doesn't contain a valid partition table

Disk /dev/hda2: 268 MB, 268435456 bytes
255 heads, 63 sectors/track, 32 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Disk /dev/hda2 doesn't contain a valid partition table

My disk config looks like this:

disk = [ 'tap:aio:/srv/xen/domains/dapper/disk.img,hda1,w' ,
'tap:aio:/srv/xen/domains/dapper/swap.img,hda2,w' ]

As I understand it, there are a few things that I'd need to do to be
able to do this.

1) Install the kernel on the guest itself, and configure grub on the
guest itself to boot that kernel
2) Because I need to install grub, I need to switch from using
file-based partitions (/dev/hda1) to file-based disks (/dev/hda
with /dev/hda1 and /dev/hda2 as a partition within that).

I think that what I may need to do is build the whole /dev/hda disk
image from scratch, and then mount it as a loopback device, and create
the partition layout I want and format the partitions as ext3 and swap
respectively. Then I should also mount the current /dev/hda1 image as
loopback devices, and then copy everything into the first partition. 

Then I should be able to change my disk config to:

disk = [ 'tap:aio:/srv/xen/domains/dapper/new_disk.img,hda,w' ]

I'd then boot into it and install grub, shut it down, change the config
to use hvmloader, and then boot again. Does this sound sane?

Part of the reason I need to avoid just building a new unmodified kernel
guest from scratch is that I can't seem to get console access to the xen
guest when it's using hvm (I think this isn't supported from what I can
see), and I don't have firewall access to be able to get to the server
on a vnc port. I also can't get xen to work on my current laptop (kernel
panic), so I'm stuck with trying to do things directly on the server.

I did also try creating a VM in qemu on my local machine and then
copying that up to the server. It seems to boot, and xm list reports
it's running, but something seems to be messed up in the networking side
of things, as I can't connect to it via ssh (even though I can if I run
it locally in qemu), and xm console <guest_name> fails too.

Many thanks for any help.


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