[Xen-users] hiccups in adopting xen in my desktop...

[S.P.T.Krishnan <sptkrishnan@xxxxxxxxx>]

Hi,

This is my first post to this mailing list, therefore appreciate your patience.

I have been having these xen questions for quite some time... tried googling around but didn't get answers.

My scenario is this.

1. I am not new to linux.
2. I have been using VMware, Qemu, Argos, Bochs for some time there fore I am not new to virtualisation as well.
3.
Currently, I use VMware on a Linux host to run Windows XP;

What do I lack and why I want Xen (in the hope that Xen will fill in the gaps) ?

Currently,
VMware virtualises the hardware, say HDD, eth, floppy, HDD, USB,
monitor, keyboard, mouse and presents it to the guest OS.

I think the following translations occur for any command to run in a guest OS.  (Please correct me if I am wrong).

guest.app <-> guest.os <-> vmware <-> host.os <-> hw

a. By using xen, we can eliminate 1 or 2 layers of translations and naturally get better response.
b. the memory limitations of the host os on its processes will no
longer be applicable to the guest os.  currently, vmware workstation
runs as host process.
c. all the other benefits applicable in vmware case also applies here.

What I want or wish ?
(these are the real questions)

A. Does Xen allow me to partition the physical hw for different virtual OS ?
Let me explain.  say I have 8 usb ports... and 3 guest OS... can I ask xen to assign 4 ports to 
guest.os-1 and 2 each to 2 other OS ? so that each OS doesn't trip on each other... 
currently,
when you install vmware in windows, during installation, the installer
will highly recommend that the user disable auto-play feature of cdrom
drive in windows.  The reason for this, I think, is that vmware is
neither not able to virtualise the hw as in hdd, eth or restrict the
hw(cdrom) to one OS.  Part of the problem could be that vmware itself
is running as a process in the host os.  This scenario actually embeds
a serious security risk.

B.
In general, I would like to know if the same be applied to any hardware
device in the system ? like serial ports, parallel ports, and most
importantly wifi interfaces.  wifi is very interesting in that where
eth allows for multiple associations and thereby multiple IP address
per physical interface, wifi currently allows only one association
therefore 1 IP address only.  In this case, I would then say, for
example assign wifi to WindowsXP and assign eth to Linux VM
respectively.

C. My final question for this round is more of an understanding one, on how things actually work in xen.
Let me first state my understanding of VMware and Qemu.
(I
think) VMware virtualises the real hardware into multiple instances of
virtual hardware.  For example, if you have a network card from
companyX, then it will create multiple virtual companyX eth one for
each VM.  It is still upto the guest OS to have the respective
drivers...
Qemu, on the other hand, will always create virtual interface that
are very old so that all major OS are likely to carry the driver
software for the hardware irrespective of the card you have.

Now,
for a transaction, the guest.app does a hand-over to guest.os, which
hands over to vmware and which hands over to guest.os and then runs in
the hardware.

My
understanding of xen is that, xen does not provide a virtual driver
connecting the virtual hardware to the the real hardware.  Instead it
merely transports the guest OS instructions to the real hardware.

If my view is correct, then in Xen, if a new hardware is
installed and say only one OS supports it and if that hw is assigned to
(if that's possible) another os, the os will complain...

-----

I
hope my email is not long enough to annoy you.  Overall, I am thinking
of having a desktop setup where I run Xen and then I run multiple OS as
VMs.  However, before I make the jump I want to make sure it is a
long-term solution.

Thank you for your time

regards,
Krishnan
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