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[Xen-users] Principal question: XEN 3.1.0 and initrd

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Subject: [Xen-users] Principal question: XEN 3.1.0 and initrd
From: Peter Pfannenschmid <lists@xxxxxxxxxx>
Date: Sun, 02 Dec 2007 16:14:44 +0100
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I would like to use XEN 3.1.0 on a debian etch system. I have downloaded
and installed the tarball from xen.org, but booting the xen kernel /
hypervisor (Dom0) failed.

The boot partition resides on a raid array (3ware 9650SE), so I started
the previous kernel (without xen) and did the following:

depmod -e -F /boot/System.map-2.6.18-xen 2.6.18-xen
mkinitrd -o /boot/initrd.img-2.6.18-xen 2.6.18-xen

My /etc/mkinitrd/modules looks like:

#<some comments>

My /etc/mkinitrd/mkinitrd.conf contains (besides other entries):

MODULES=all # for testing

My /boot/grub/menu.lst contains (besides other entries):

title           Xen 3.1.0 / Debian GNU/Linux, kernel 2.6.18-xen
root            (hd0,0)
kernel          /boot/xen-3.1.0.gz
module          /boot/vmlinuz-2.6.18-xen ramdisk_size=32768
root=/dev/sda1 ro console=tty0
module          /boot/initrd.img-2.6.18-xen

The depmod and mkinitrd commands did not produce any errors, so I am
quite sure the initrd img contains all neccessary drivers.

But when booting, the kernel says:

No filesystem could mount root. Tried: ext2

Then, some other error message, then panic. Why does it try ext2 instead
of ext3 although the latter is included in the ramdisk)? And even if
ext3 was not loaded for some reason: AFAIK, you can read ext3 partitions
with ext2 drivers... strange.

On http://gentoo-wiki.com/HOWTO_Xen_and_Gentoo, in the section about
building xen kernels, I have read a statement which finally leads me to
complete confusion:

"You can use modules, but all drivers required to boot must be builtin."

So my principal question is: If I want to boot a xen kernel from my
3ware controller, do I have to compile the driver for the controller
(and for ext3 etc) into the kernel directly? If yes, what sense does
initrd make anyway (when booting xen)?

Sorry for the long post, but during googling, rtfming and grouping I saw
that many other users have similar problems, so perhaps it would be
worth explaining the correlation between xen hypervisor, the xenidized
kernel and initrd from scratch, in easy words, by some expert....
especially what drivers can be loaded as modules from ramdisk image and
which drivers have definitely to be compiled into the kernel, and
finally, what are the general differences regarding initrd between a
standard kernel and an xen / dom0 kernel?

Thank you very much,


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