Xen users - Nov 2005 - Video output/graphics in virtualized OSs

How do the virtualized operating systems in XEN output video? I presume
at this point, it isn''t completely transparent - where they are writing
to what they consider to be video memory and the display of that virtual
buffer is somehow managed by Dom0. If that''s the case, then how at this
point is it handled? Specialized X Servers?

 

Is there a link to where I can find out more about how this works?

 

Thanks,

 

Curtis



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On Saturday 12 November 2005 21:42, Curtis Shipley
wrote:
> How do the virtualized operating systems in XEN output video? I presume
> at this point, it isn''t completely transparent - where they are
writing
> to what they consider to be video memory and the display of that virtual
> buffer is somehow managed by Dom0. If that''s the case, then how at
this
> point is it handled? Specialized X Servers?
Well, the answer is: It depends.

For example, dom0 (yes, thats a virtualized OS, too) simply accesses your VGA.
domUs are textmode only as far as xen is concerned, they only got a virtual 
terminal device. 
But since you have networking between them, you can use the standard unix 
stuff to get graphical apps working in domU, like X11, VNC, NX, ...

Now if you were asking about unmodified guests running with help of the next 
generation AMD/Intel CPUs, I think they''ll have a emulated SVGA card.


/Ernst

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>> How do the virtualized operating systems in XEN output video? I presume
>> at this point, it isn''t completely transparent - where they
are writing
>> to what they consider to be video memory and the display of that
virtual
>> buffer is somehow managed by Dom0. If that''s the case, then
how at this
>> point is it handled? Specialized X Servers?
>
>Well, the answer is: It depends.
>
> For example, dom0 (yes, thats a virtualized OS, too) simply accesses your 
> VGA. domUs are textmode only as far as xen is concerned, they only got a 
> virtual terminal device. But since you have networking between them, you 
> can use the standard unix stuff to get graphical apps working in domU, 
> like X11, VNC, NX, ...
>
> Now if you were asking about unmodified guests running with help of the 
> next generation AMD/Intel CPUs, I think they''ll have a emulated
SVGA
> card.
That''s about all I was going to say ;-)

I should also mention that it''s theoretically possible to give a domU 
access to a PCI video card and devote another physical monitor to the 
domain. Various people have fooled around with this; I''m not sure if it
works *yet* because there are lots of fiddly things in the console / X.org 
subsystems that need to be right. Hopefully this will be fully functional 
some time soon.

Cheers,
Mark

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M.A. Williamson wrote:
>>> How do the virtualized operating systems in XEN output video? I
presume
>>> at this point, it isn''t completely transparent - where
they are writing
>>> to what they consider to be video memory and the display of that
virtual
>>> buffer is somehow managed by Dom0. If that''s the case,
then how at this
>>> point is it handled? Specialized X Servers?
>>
>>
>> Well, the answer is: It depends.
>>
>> For example, dom0 (yes, thats a virtualized OS, too) simply accesses 
>> your VGA. domUs are textmode only as far as xen is concerned, they 
>> only got a virtual terminal device. But since you have networking 
>> between them, you can use the standard unix stuff to get graphical 
>> apps working in domU, like X11, VNC, NX, ...
>>
>> Now if you were asking about unmodified guests running with help of 
>> the next generation AMD/Intel CPUs, I think they''ll have a
emulated
>> SVGA card.
> 
> 
> That''s about all I was going to say ;-)
> 
> I should also mention that it''s theoretically possible to give a
domU
> access to a PCI video card and devote another physical monitor to the 
> domain. Various people have fooled around with this; I''m not sure
if it
> works *yet* because there are lots of fiddly things in the console / 
> X.org subsystems that need to be right. Hopefully this will be fully 
> functional some time soon.
 From which follows that it should - at some point in the future - be 
possible to use a mobo with onboard video for dom0, and a PCIx card in 
at least one domU, or maybe even more PCIx cards for different domU''s?

-- 
Kind regards,
Mogens Valentin


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On Sunday 13 November 2005 20:24, Mogens Valentin wrote:
...
> > I should also mention that it''s theoretically possible to
give a domU
> > access to a PCI video card and devote another physical monitor to the
> > domain. Various people have fooled around with this; I''m not
sure if it
> > works *yet* because there are lots of fiddly things in the console /
> > X.org subsystems that need to be right. Hopefully this will be fully
> > functional some time soon.
>
>  From which follows that it should - at some point in the future - be
> possible to use a mobo with onboard video for dom0, and a PCIx card in
> at least one domU, or maybe even more PCIx cards for different
domU''s?
No, that should work right now, but only with xen-2.* as xen-3 currently
can''t
pass arround PCI devices.

The problem is the X Server which tries to allocate a virtual terminal to run 
on (vt7 usually) whereas the xenified domU linux only has a console, no 
terminals...

For Mouse+Keyboard you''ll also have to dedicate an USB HCD to the domU,
the
std PS/2 ports usually aren''t a PCI device and can''t be
shared.

So with some tweaks to the X11 config and maybe a patch or two to it, it 
should basically work right now.

/Ernst

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> >  From which follows that it should - at some point in the future - be
> > possible to use a mobo with onboard video for dom0, and a PCIx card in
> > at least one domU, or maybe even more PCIx cards for different
domU''s?
>
> No, that should work right now, but only with xen-2.* as xen-3 currently
> can''t pass arround PCI devices.
>
> The problem is the X Server which tries to allocate a virtual terminal to
> run on (vt7 usually) whereas the xenified domU linux only has a console, no
> terminals...
>
> For Mouse+Keyboard you''ll also have to dedicate an USB HCD to the
domU, the
> std PS/2 ports usually aren''t a PCI device and can''t be
shared.
>
> So with some tweaks to the X11 config and maybe a patch or two to it, it
> should basically work right now.
All it needs is someone with the appropriate skills (or willingness to learn 
them) and enough time ;-)  There will be some useful information on this in 
the mailing list archives.

A number of people have worked towards this goal but I''m not sure how
far they
got in the end.  It was never a question of fundamental technical issues, 
just of the software involved being rather unco-operative.

Although you can only do this sort of trick with 2.0 right now, the required 
PCI functionality should be coming back during the 3.x series.

Cheers,
Mark

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Hi folks,

if I understand this thread right then setting up an xserver to transfer 
video output to an external machine should be the same as without xen?

Has anyone already done so: set up domUs with an xserver to be used from 
an admin workstation?

Any hint or help is appreciated.

Dirk

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On Monday 14 November 2005 02:17, Dirk H. Schulz wrote:
> if I understand this thread right then setting up an xserver to transfer
> video output to an external machine should be the same as without xen?
yep... any of the traditional remote X methods: using ssh X-forwarding or 
xnest or a good old "X -query [FQDN-domU] ...".   Just think of the
guest
as a headless X-app server.

Xen delivers an ideal desktop dev cluster (on a shoestring budget).

- -- 
pea
319E 1969 C476 E38D 6133  D3B4 6314 A6A9 67B6 ABB9
- ---------------------------------
I''m going to cast my rocks to the wind. 
  -Farberism #362
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P.E.Ahlquist J wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> On Monday 14 November 2005 02:17, Dirk H. Schulz wrote:
> 
>>if I understand this thread right then setting up an xserver to transfer
>>video output to an external machine should be the same as without xen?
> 
> 
> yep... any of the traditional remote X methods: using ssh X-forwarding or 
> xnest or a good old "X -query [FQDN-domU] ...".   Just think of
the guest
> as a headless X-app server.
> 
> Xen delivers an ideal desktop dev cluster (on a shoestring budget).
> 
I''ve been playing with xf4vnc (via xinetd) as the xserver running on
the
domU (rather than your workstation).  I then connect to the xserver on 
the domU using a vnc client e.g. tightvnc.  This has the advantage of 
better remote access (less bandwidth required then X over the network) 
and access from pretty much any operating system.  I have a KDE desktop 
running on a domU that is indistinguishable from my workstation except 
for the lack of peripherals, e.g. USB flatbed scanner (I need to read up 
a bit more on SANE and it''s network features).

Below are a few notes on my setup.

Simon


Here''s my file in /etc/xinetd.d/ ...
(I just connect to a different port to get different resolution desktops.)

service vnc1024
{
         disable = no
         socket_type = stream
         protocol = tcp
         wait = no
         user = nobody
         server = /usr/bin/xf4vnc
         server_args = -inetd -once -query localhost -geometry 1024x768 
-depth 16
         port = 5900
}

service vnc1280
{
         disable = no
         socket_type = stream
         protocol = tcp
         wait = no
         user = nobody
         server = /usr/bin/xf4vnc
         server_args = -inetd -once -query localhost -geometry 1280x1024 
-depth 16
         port = 5901
}

To use KDE I had to enable XDMCP in /etc/kde3/kdm/kdmrc ...
[Xdmcp]
Enable=true


One gotcha (xen 2.0.7 stable) that I had was xf4vnc would only connect 
to kdm when the DomU had an entry in /etc/hosts for itself (not 
localhost but the hostname).  I''m probably just being stupid somewhere 
or kdm isn''t looking up the hostname (from dom0) correctly.

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