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List:       debian-user
Subject:    Re: Screen scaling and 4k support in libvirt with qemu/kvm
From:       Linux-Fan <Ma_Sys.ma () web ! de>
Date:       2021-01-27 9:41:47
Message-ID: cone.1611740507.700662.33746.1000 () masysma-18
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Rainer Dorsch writes:

> Hi,
>
> with virtualbox, it is possible that the guest system rescales its screen if  
> I change the window for the guest (and virtualbox guest tools are installed at
> least). Does anybody know if that is possible with virt-manager/libvirt/qemu/
> kvm?

It is certainly possible to set the guest resolution to exactly match the  
window size. I am not sure if it can be configured to _automatically_ adjust  
the guest resolution upon window size change though.

The protocol must support it, because I know that for Windows guest systems,  
the Windows resolution adjusts to the window size. Unlike with Linux guests,  
it does this in fixed steps of "common" monitor resolutions and thus does  
not usually match the exact window size but something smaller.

If you find out how to apply the sizes automatically on Linux, I'd be  
interested to learn how that works :) If no „solution" exists yet, it might  
be easy to script (although I have not bothered to do that so far).

My usual approach to bypass guest system screen resolution issues is to use  
ssh -X from the host to the guest and then run the program under the host's  
X11 session.

> Also I noticed that I cannot scale my guest higher than 1920x1200. Is the max
> resolution configured somewhere or is this a fundamental limitation?

This very much sounds like you are either using the VGA video adapter or do  
not have `spice-vdagent` running in the guest system?

Set Video "Model" to either QXL or virtio in virt-manager and then in the  
guest system install and run `spice-vdagent`. This will not apply the  
resolution immediately, but invoking `xrandr` in the guest it should be  
possible to see a lot larger list of virtual screen resolutions including  
one to match the host window size and including sizes above 1920x1200.

HTH
Linux-Fan

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