Re: XL Console: Accessing DomU Guis?

[Paul Leiber <paul@xxxxxxxxxxxxxxxx>]

Hey John,

I have never used SDL so far and I am not an experienced KDE/Xfce user 
(my DomUs are mostly headless), so please take my reply with caution.
Am 04.01.2024 um 04:47 schrieb John L. Poole:
> Goal:
>
> I am trying to run 2 graphical environments ("guis"), KDE Plasma &
> Windows 7, on a machine where the Xen hypervisor runs and where I can
> access the guis on the monitor attached to the machine. I want to have
> the machine act as a workstation giving me the ability to switch between
> Gentoo & Win7 (Win for legacy Adobe products with I *own*) using the "xl
> console" command. I believe I want SDL. I do not want the VNC delay.
I don't think "xl console" works in the way you want to use it, see below.

> ============================================
>
> My guest VM, ryzdesk [desktop] herein "DomU" has KDE Plasma installed
> and I can successfully launch tiger VNC within DomU and access the KDE
> desktop through through VNC from a remote machine.
I assume from what you have written that you are running a TigerVNC 
server instance in the DomU. If you use the VNC option built into Xen 
(provided via QEMU, I belive), you don't need to use TigerVNC on the DomU.
> I have tried the following:
>
> 1) In Dom0, launch as root Xfce4
>
> 2) In a console within Xfce4,
>       start the DomU: "xl create ryzdesk.conf -c"
>
> 3) In the DomU console, log in as root. Run:
>      xinit
>     to launch the KDE desktop.
>
> 4) switch out of the DomU console with Ctrl+"]"
>
> 5) In the same Xfce4 console now activated in DomU,
>     use: "xl console [#]" to jump into DomU.
>
> When I am in the DomU session, nothing happens, there are only the
> messages from the start of xinit. No KDE desktop pops up and replaced my
> Xfce desktop. I then enter Ctrl + "c" to terminate the attempted launch
> of the KDE desktop.  Log is below.
My understanding is that the Dom0 _console_ simply can't display the GUI 
from the DomU. "xl console" does what it says, it shows the console of 
the DomU. The output of the DomU console after starting xinit shows that 
this is working as intended. "xl create" with the "-c" option is 
equivalent to using "xl console". Also, a Dom0 console is not 
"activated" by the DomU in any way, I think a DomU influencing the Dom0 
in such a way would violate the security aspect of virtualization.
GUI content from the DomU, be it transmitted via VNC or SDL or whatever, 
needs to be shown in a separate window in a GUI. Also, your Xfce desktop 
will not be "replaced" by anything. Xfce still is required for Dom0 to 
be able to render the windows in which the DomU GUI is shown.
If you have two DomUs you want to switch between (e. g. your Linux/KDE 
and your Windows DomU), you will have two separate Windows in your Dom0 
Xfce GUI between which you can switch.
> Xorg log file from an attempt to launch xinitc. In a prior attempt, I
> waited 3 minutes after output on the display before I executed
> Control-C; in this log, I only waited for about 20 seconds:
>
> https://salemdata.us/xen/guis/Xorg.0._20240103_1741PST.log
>
> I believe the ability to access the guis from Dom0 would be achieved by
> selecting SDL in the configuration and executing the "xl console"
> command from within a console on a gui. From my configurations file,
> ryzdesk.conf:
>
>
>     ...
>     vfb = [ 'type=sdl' ]
>     ...
>     # ref: https://www.youtube.com/watch?v=s1Ro0KxHooQ
>     #
>     videoram=16
>     stdvga=1
>     sdl = 1
>     vnc = 0

Two aspects come to my mind here:

1) There seem to be different options for SDL depending on the type of 
the DomU (PV or HVM). You seem to be setting options for both versions. 
Perhaps they get in the way of each other? See here: 
https://xenbits.xen.org/docs/unstable/man/xl.cfg.5.html
2) In the video you referenced, my point from above is confirmed: With 
starting the DomU, a separate X window opens automatically, the GUI of 
the DomU is _not_ shown in the terminal window. In fact, no "xl console" 
is ever executed.
> The new hardware consists of:
>
>    AMD Ryzen 7950+ processor
>    ASRock X670E motherboard
>    64 GB ram (non-ECC)
>
>    Video:
>      monitor: ViewSonic VA1655 15.6 Inch 1080p Portable IPS Monitor
>      port: HDMI of motherboard
>
> Operating system for Dom0 and DomU (same kernel)
>
>      Gentoo Linux: 6.1.67-gentoo-x86_64
>
> The VNC session demonstrates that the KDE Plasma desktop does work
> -- I have been using the KDE desktop through VNC.
>
> Here are links to the version of Xen (4.16.6_pre1) and Qemu I have
> installed:
>
> https://salemdata.us/xen/guis/qemu.script.202401031643PST.html
> https://salemdata.us/xen/guis/xen.script.202401031643PST.html
>
> Here is a dmesg listing with the Xorg.0.log of my attempt to
> to start the KDE desktop.
>
> https://salemdata.us/xen/guis/dmesg_ryzdesk_20240103_1936PST.script.html
>
> 1) Is my expectation that Xen will allow me to access guest desktops in
> a gui fashion from a Dom0 console unrealistic?
>
> 2) What can I reference and/or provide to help troubleshoot the failure
> to access a full gui of a guest VM on the hypervisor's monitor?
Do the Xen/QEMU logs on your Dom0 say anything relevant, e. g. about 
failing to start SDL?
Good luck!

Paul