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RE: [Xen-users] difference between Xen and Dom0 kernel

To: "'Fasiha Ashraf'" <feehapk@xxxxxxxxxxx>, "'Tapas Mishra'" <tapas@xxxxxxxxxxxx>, "'Fajar A. Nugraha'" <fajar@xxxxxxxxx>
Subject: RE: [Xen-users] difference between Xen and Dom0 kernel
From: "Bo Jiang" <bjiang@xxxxxx>
Date: Thu, 12 Nov 2009 15:09:15 -0500
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Hi All,


Yes, I also found the configuration harshly impacts the installation. I used several version of .config files for the compilation, and got various results. For example,

1)      sometimes there’ll be a kernel panic during boot;

2)      sometimes the compilation exits with errors on such as kvm.o, asm-offset.s (due to wrong subarchitecture); and

3)      sometimes the compiled kernel doesn’t boot because no root devices can be found, and http://lists.xensource.com/archives/html/xen-users/2009-06/msg00197.html doesn’t help, either.

4)      sometimes the make command “MAKE) -C $(LINUX_DIR) ARCH=$(LINUX_ARCH) INSTALL_PATH=$(DESTDIR) $(IMAGE_TARGET)” in buildconfigs/mk.linux-2.6-common exits with errors, thus there’s no vmlinuz image can be installed. (this was observed when I used ubuntu 9.04’s default config file, i.e., /boot/config-2.6.27…)

So far for some of these problems above, I still have no clue about which configuration options are the causes. The link that Tapas mentioned (http://wiki.xensource.com/xenwiki/XenParavirtOps) listed some configuration options, I’m trying it to see if it helps.


According to the selection order in line 73-90 in buildconfigs/mk.linux-2.6-common, the makefile will search the existing config file in the order of ${XEN_LINUX_CONFIG} -> the config file under /boot with the same version -> create one with the script linux/buildconfigs/create_config.sh -> make defconfig under linux/. To reuse the existing config file and have multiple tries compiling at the same time, I added “XEN_LINUX_CONFIG ?= ${XEN_ROOT}/.config” at the beginning of buildconfigs/mk.linux-2.6-common, though I’m not sure whether it’s a good idea.


In summary, .config for the installation is really confusing. Thus I’d really appreciate if Fajar could give us a working .config, or some advice on the installation.


P.S. I’m installing xen 3.4.1 on ubuntu 9.04/Intel Core2 6320, by compiling the source downloaded from http://www.xen.org/download/index_3.4.1.html. As Fajar mentioned, it’ll be easier to install on FC or RHEL, won’t it? Then Fajar, would you please tell me which distribution and which version you’re working on?


Thank you very much!





From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Fasiha Ashraf
Sent: Thursday, November 12, 2009 7:46 AM
To: Tapas Mishra; Fajar A. Nugraha
Cc: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] difference between Xen and Dom0 kernel


Fajar! can you please share .config for 2.6.18 kernel

Fasiha Ashraf

--- On Thu, 12/11/09, Fajar A. Nugraha <fajar@xxxxxxxxx> wrote:

From: Fajar A. Nugraha <fajar@xxxxxxxxx>
Subject: Re: [Xen-users] difference between Xen and Dom0 kernel
To: "Tapas Mishra" <tapas@xxxxxxxxxxxx>
Cc: xen-users@xxxxxxxxxxxxxxxxxxx
Date: Thursday, 12 November, 2009, 3:57 PM

On Thu, Nov 12, 2009 at 5:44 PM, Tapas Mishra <tapas@xxxxxxxxxxxx> wrote:
> Thanks for your reply .
> From your reply what I inferred is that to be able to use
> virtualization from XEN
> I need to install Hypervisor
> Xen tools and then I can start working on like installing guest
> operating systems
> in the installed hypervisor.

pretty much.

> Say for example I am having a laptop with Ubuntu installed.

The easiest way is tu start with RHEL/Centos5, and run "yum install
xen kernel-xen". After that you just edit /boot/grub/menu.lst to
choose newly installed kernel/hypevisor, reboot, and you're ready to

Once you have that working and able to start some domUs, you can try
compiling xen and kernels manually if you like.

> So I need to install Xen Hypervisor on it and
> then install a Dom0 kernel assuming that ( I downloaded the source
> hypervisor without linux-2.6.18 )
> from http://www.xen.org/products/xen_source.html

http://bits.xensource.com/oss-xen/release/3.4.2/xen-3.4.2.tar.gz will
get you the source for xen hypervisor and userland. However, if you
run "make" (or make world) it will download the kernel as well. If you
only want to compile the hypervisor and userland, look at the included
README and Makefile.

> then I need to compile one Dom0 kernel as per the instructions given
> http://wiki.xensource.com/xenwiki/XenParavirtOps

If you just run make you'd automatically get 2.6.18 kernel. I suggest
you start with that first.
The wiki page is useful if you want to compile newer pv_ops kernel.

> What does the following command do ?
> git clone git://git.kernel.org/pub/scm/linux/kernel/git/jeremy/xen.git
> linux-2.6-xen

That will download newest pv_ops kernel with xen support.

> Or I need to download a kernel from www.kernel.org and compile it so
> that I can use it as Dom0

vanilla kernel can't be used as dom0 kernel yet. You can use it as
domU kernel though.

> why can I not use the kernel present on my
> laptop in the installed Ubuntu as Dom0 and after installing hypervisor
> start working on it.

Because dom0 kernel needs to have xen support. Ubuntu's kernel does
not have that yet.
Jeremy's git tree (the git command you mentioned) has it.

> To be able to install hypervisor what do I need to do.

See what I wrote about RHEL/Centos and README/Makefile.


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