[gentoo-amd64] AMD64, Nvidia Graphics, Xen -- Xorg on DomU Only

[Samir Mishra]

Hello.

I posted this on the Xen Users mailing list, thought I'd try for a 
different perspective from Gentoo users.

I'm doing a fresh install of Xen on an AMD64 using Gentoo. I have an 
nvidia graphics card. I want Dom0 to be a minimal system, installed 
without Xorg or any other GUI applications. I'm hoping to set up Xen 
with (at least) 3 guest domains -- one running servers for the network 
(ntp, dhcp, bind, yp, etc.), one guest domain running my desktop with 
Xorg and the third guest domain to be used for development & testing.

What I'm hoping to find out is --
1. does the above make sense?
2. I want to access the X-server on the desktop domU directly on tty7. 
Is this possible? If so, how can I do this?
3. what are the things I need to watch out for?
4. Any list members running Xen?

I've done some research and I'm aware I have to disable tls and compile 
the system with specific compiler flags. If anyone has pointers to 
documentation specific to what I want to do, that would be much 
appreciated.

One of the responses I received on the Xen-Users mailing list (from 
Matts Peterssons, quote) --
| No. The X-server needs to be the OWNER of all the graphics card, and 
your Dom0 takes ownership of
| the graphics card very early on. There is two solutions that come to 
mind:
| You could perhaps use a simple PCI graphics card for the Dom0 console, 
and then give the DomU the
| nvidia card, but any shared hardware must be managed by one Domain 
only (and everyone else talking
| through that domain to get access). Of course, this assumes that there 
is an nVidia driver that works
| under Xen, which I don't think exists (yet) - and I very much doubt 
that native kernel graphics drivers
| will work "out of the box" - as they probably do all sorts of "nasty" 
things that Xen needs to be aware of.
|
| Or you can use vncserver/vncviewer to access your desktop machine.

In one of the documents, I read, it indicated that, for example, if I 
had 2 PCI network cards, and I wanted to have domU manage one of the 
cards directly, there's a way of telling Dom0 to leave the management of 
a particular PCI bus/device alone. Is it possible to do something 
similar with the AGP adapter bus/card? But, given that I actually get 
this to work, how do I go about getting desktop domU to gain control of 
tty7 (or whatever, since all consoles are (I believe) controlled by 
dom0. In other words, I'd like to have a direct pass-through, or 
whatever one might call it.

Could I achieve something similar by installing Xorg in dom0 and domU 
and running XDMCP to connect to domU? This would mean a more complicated 
package management scenario since Dom0 won't be a minimalist 
installation anymore. I guess it all depends on how well the nvidia 
drivers play with Xen.

A later response (again from Matts Peterssons, quote) -- 
| I very much doubt this [having DomU control the nvidia card] will work in actual 
| practice [as I once read: In theory, there's no difference between theory and 
| practice - in practice there is...] The difficulty would be to have a driver that
| is "Xen-clean" or "Xen-aware". Since the low-level driver for the graphics card
| is a kernel driver, it will have access to all sorts of kernel-internal information,
| and some of this is managed by Xen and should not be used directly by for instance 
| a driver. Xen fixes this by patching [changing some macros in header-files is the 
| key part of this] the kernel drivers that are included in the kernel itself. But
| the nVidia drivers are closed source, so they are not patchable by this method...

I'd rather have DomU have control of my graphics card and have the 
output of Dom0 be redirected to DomU via XDMCP or VNC (for X-Server) and 
to virtual network consoles for the rest.

But is this possible?

TIA.

Samir
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