Re: XL Console: Accessing DomU Guis?

[zithro <slack@xxxxxxxxx>]

Hi,

On 06 Jan 2024 20:18, John L. Poole wrote:

>  > 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.
> Correct.  I have not be careful with my terminology.  What I envision
> is running Xfce in Dom0 as user jlpoole, and then within the Xfce
> session, launching a console within and executing the command:
> "sudo xl console [X]".  This procedure should be distinguished
> from being in the console window at boot time and trying therein
> "sudo xl console [X]" where I am not operating over an
> already-launched gui.
I think you misunderstand the way it works.
"xl console", or more generally a "console", is just a *text* interface, 
it cannot display a GUI, only a TUI (Text User Interface).
In a way, the console can only display what would be displayed on 
tty1-tty6, but not tty7 (where the GUI usually resides).
(In effect, [xl] console displays tty1, and tty1 only).

For graphics *and* without installing anything in the domU, you have 2 
choices: VNC or SDL.
Xen (for PV) or QEMU (for HVM) provide a VNC server to access the video 
output of your domU, but VNC is not installed in the domU !
Some analogy: a real computer has a videocard, a cable and a monitor, 
whereas virtualized hosts have a virtual videocard (vfb or emulated), 
and VNC or SDL "replace/virtualize" the cable and the monitor.
If you want to access the VNC display with the Xen commands, run :
    xl vncviewer $domU_id_or_name

Of course, you need at least one VNC *viewer* installed in dom0 
(gvncviewer, tigervnc, virt-viewer, etc).
With SDL, the (GUI) window starts automatically with the domU, but 
remember that closing the SDL window will shutdown the domU !
>  >>     ...
>  >>     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
>
> I will look into this more and try to figure out the nuances.
> I was hoping by posting here I might garner the attention
> of somebody who runs the kind of configuration I want to do
> and I would be directed with some simple instructions or
> someone would point out what I have missed or overlooked.
As Paul wrote, the configuration depends if your domUs are HVM or PV.
The "vfb" stanza is used for PV/PVH guests *only*, not HVM.
"vfb" means Virtual FrameBuffer, it is the PV equivalent of the emulated 
videocard of the HVM domUs.
So, config stanzas :
    PV/H -> vfb =
    HVM  -> vga =

For Windows, which has to be HVM, your config for SDL would be :
# VIDEO CARD
vga = "stdvga"
videoram = 128
# REMOTE ACCESS
sdl = 1
opengl = 1

If you want VNC instead :
# VIDEO CARD
vga = "stdvga"
videoram = 128
# REMOTE ACCESS
vnc = 1
vnclisten = "127.0.0.1:7"
# OR, if you want to access the domU GUI from your network, use the IP 
of the dom0 NIC connected to your local network, for example :
# vnclisten = "192.168.1.1:7"

AFAIK, QEMU provides *either* VNC *or* SDL, but not both at the same 
time, so if you want to use SDL from your dom0 *and* be able to connect 
to your domU from remote hosts as well, then you'd have to also install 
VNC *within* the domU (like you would do with any non-virtualized host).
>  >
>  > 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.
>
> Correct.  I tried to launch my Windows 7 ISO, but have run into
> other problems with my qemu complaining about being unable
> to find i386 stuff... I think it is a bug Gentoo's distribution
> has caused and need to file a bug according for the
> file complained of is, in fact, present on my system, it just
> is in another directory.
> Gentoo often has these kind of change-the-directory to suit Gentoo's
> philosophy and then some other software expect to find a file in a
> directory where Gentoo's installer changed it.
You seem to know what the problem is, so just a remark: did you install 
the correct QEMU packages ? I'm using Debian so I don't know how it's 
handled in Gentoo, but at some point the QEMU packages in Debian have 
been split between GUI and non-GUI packages (to reduce the number of 
dependencies on X/GUI stuff for servers).
For example on Debian, to use the SDL you need the package 
"qemu-system-gui". YMMV !
Hope it helps.

--
++
zithro / Cyril