RE: [Xen-users] how to compile a dom0 kernel

[Mike Viau <viaum@xxxxxxxxxxxxxxx>]

> On Wed, 2 Mar 2011 08:54:50 +0530 <abhidixit87@xxxxxxxxx> wrote:
> >
> >> On Tue, 1 Mar 2011 18:13:36 +0530  wrote:
> >>
> >> Hi,
> >> I was wondering on internet if there is any guide that mentions how to
> >> compile a Dom0 kernel for a Ubuntu 10.04 64 bit system.
> >> What I came across after a lot of Googling were some Debian guides
> >> here and there and most of the guides on Xen's wiki are to make
> >> a pv-ops Dom0 kernel.No where I see how can you compile your own Dom0
> >> for a distribution such as Ubuntu .
> >> Can any one clarify my doubt?
> >>
> >
> > I might be mistaken, but if you take you pv-ops sources, you should be able 
> > to build a Debian based dom0 based kernel
> You mean to say a kernel that was for pv-ops sources would run like a
> normal Dom0 kernel (no pv-ops)
> what is the difference between a Dom0 kernel which runs on Xen and
> pv-ops Dom0 kernel.

A pv-ops kernel may be used to boot linux natively as well as a Xen domU 
depending on how the pv-ops kernel is booted with your bootloader. That said, I 
am fan of the pv-ops Linux kernel not only because I use Xen to manage some 
virtual machines, but also because I do not need to be boot Linux through the 
Xen hypervisor in order to get full functionality of my host Linux.

> Both run on Xen.If I am not mistaken then pv-ops Dom0 kernel is built
> using jeremy's tree and is itself a para virtualized Dom0 kernel.

This is true, and also current development branch based on Linux 2.6.38 is 
apparently available from konrad's git repository 
(linux/kernel/git/konrad/xen.git)


> Where as in case of non pv-ops Dom0 kernel they are not para
> virtualized i.e. normal Dom0 kernel which runs on Xen is
> HVM.Correct me if I am wrong.

I believe you are referring to old-sytle or Xenlinux dom0 kernels, and yes 
these kernel are capable of running HVM VMs as well as pv-ops dom0 kernels. [1]
A note about: Linux Xen PV guest kernel availability
Upstream
kernel.org Linux kernels contain "pv_ops" Xen paravirtual guest support
out-of-the-box since Linux 2.6.23, so all the latest Linux kernels have
Xen PV domU support available. See [XenParavirtOps] wiki page for more 
information [2]


> Well thanks for the guide.What this link mentions is if I understand
> correctly is to compile a kernel the Debian way.
> What my understanding upto now about Xen is If I just install
> Xen-4.0.1 on my system then (and I do not compile a Kernel with Xen
> options for Dom0) then Xen won't work.

This is correct, you can not create or manage virtual machine with tools like 
xm or xl that are part of Xen without booting youe Xen dom0 kernel via the Xen 
hypervisor. As you may come across guides to setup Xen you might see a grub 
example like this:

menuentry "Xen 3.4.0 / Debian GNU/Linux, Linux 2.6.31-1-xen-amd64" {

     insmod xfs

     set root=(hd0,2)

     multiboot /boot/xen-3.4-amd64.gz

     module /boot/vmlinuz-2.6.31-1-xen-amd64 dummy=dummy 

root=UUID=e9ed5af4-0503-4314-9d28-415a0eb7b0a0 ro quiet

     module /boot/initrd.img-2.6.31-1-xen-amd64

}


See: http://wiki.xensource.com/xenwiki/XenCommonProblems ; for relevant links 
and useful tip when using Xen


>So what I am curious to know is
> how can I or how should I go to compile a kernel so that when I
> install Xen
> I can use Dom0 also.
>

I am not away of Ubuntu's packages which are available for Xen. Debian Squeeze 
which is now stable includes a 2.6.32 pv-ops xen dom0 kernel out-of-the-box.

> Or do I not need to go through this painful process and simply
> installing Xen and making changes in Grub (no new Dom0 kernel)
> to use xen.gz with the kernel which was installed from the Ubuntu CD
> is sufficient.
>

The alternative is to go through a similar process of compiling a
kernel from sources (using the sources obtained from Jeremy's or
Konrad's git repositories) to compile the pv-ops kernel.


[1] - http://wiki.xensource.com/xenwiki/XenParavirtOps
[2] - http://wiki.xensource.com/xenwiki/XenOverview
                                          
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