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Re: [Xen-devel] paravirtualized guest OS

On Tue, 2007-02-13 at 05:41 +0000, rahul gundecha wrote:
> hi,
> 1) When we install guest linux inside Xen using paravirtualization,
> how actually guest linux code is modified. Whats the actual process.

not sure whether i understand your question correctly, but it might be

the passably witty answer would probably be 'manually'.

paravirtualization is based on the assumption that system virtualization
is well worth the effort of _modifying_ systems to suit a virtual
environment better. this leads to improved efficiency, and is thereby in
contrast to the more traditional (and technically challenging) method of
making unmodified operating systems think they actually _own_ the
hardware they operate on. which they don't. xen does now.

the linux kernel is a very portable thing, and used to run on different
platforms since its earliest revisions. so there's x86, powerpc, mips
and so on. xen-linux is basically a port to yet another platform, with
the major difference being that this platform does not an interface
defined by hardware, but in software.

d'you know what a system call is? user programs you run on linux use
them to acquire resources (e.g. storage or IPC). xen is very similar in
that respect. a (comparatively small) set of well-defined functions
needed to supplement a whole bunch of operating systems on top of it.

> 2) I am using suse 10.2. After installing xen package which comes with
> it, the new boot menu "SUSE (XEN)" gets added up. What are the
> difference between the kernel which runs this SUSE-XEN & original
> kernel.

in the case of the kernel mentioned by your grub.conf, comparatively

as you might have noticed you get to boot xen, and xen boots on into a
special VM commonly called 'dom0'. dom0 hosts a paravirtual kernel as
described above, but additionally armed with the typical set of device
drivers necessary to put your peripheral hardware work, and privileged
enough by xen to apply them.

additional guest systems booted are even different. they don't require
hardware device drivers, since the first one already does that. instead,
they communicate with dom0 for peripheral I/O.

xen maintains cpu(s) and memory. linux in dom0 almost anything else, so
xen does not have to (because writing device drivers is such an
expensive business).


Daniel Stodden
LRR     -      Lehrstuhl fÃr Rechnertechnik und Rechnerorganisation
Institut fÃr Informatik der TU MÃnchen             D-85748 Garching
http://www.lrr.in.tum.de/~stodden         mailto:stodden@xxxxxxxxxx
PGP Fingerprint: F5A4 1575 4C56 E26A 0B33  3D80 457E 82AE B0D8 735B

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