Early GUI connection to preloaded disposables

[ben-grande]

Checkout other implementation that might make this one partially or totally obsolete:

• Delay connecting with gui-daemon until after starting Xorg qubes-gui-agent-linux#251

---

When the GUI session is established before being paused, the preloaded disposables can use the same GUI session after requesting the qube, thus the time to connect to the session is offset from the request stage to the preload stage.

Reverting initial iteration: 212b148

It isn't the default because it comes with various disadvantages:

• Depends on apps not autostarting, else they may appear before the qube is paused and can cause confusion;
• Cannot adapt to monitor changes, screen resize, plugging external monitor;
• Cannot survive display manager logout+login;
• Only works after using has logged in to GUI session;

For: QubesOS/qubes-issues#10230
For: QubesOS/qubes-issues#1512

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TODO:

• test how the installer reacts when attempting to preload while there is no display, or is there a display at that time? Still has to pass display manager login screen.

[codecov]

Codecov Report

❌ Patch coverage is 70.96774% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.67%. Comparing base (6b978a3) to head (32a2dc0).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
qubes/vm/mix/dvmtemplate.py	69.23%	4 Missing ⚠️
qubes/api/admin.py	70.00%	3 Missing ⚠️
qubes/vm/dispvm.py	75.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #752      +/-   ##
==========================================
- Coverage   70.68%   70.67%   -0.02%     
==========================================
  Files          61       61              
  Lines       13809    13831      +22     
==========================================
+ Hits         9761     9775      +14     
- Misses       4048     4056       +8     

Flag	Coverage Δ
unittests	70.67% <70.96%> (-0.02%)	⬇️

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[ben-grande]

QubesOS/qubes-gui-agent-linux#251

With all the patches accompanying that PR, waiting for GUI agent is done on the preload stage while GUID is established only after the preload is used, this connection is quite fast. The slow part always was the GUI agent startup. Therefore, this PR is superseded.

One thing that is still a bit problematic but not much is that preloaded disposables started before there is a GUI session on the GUIVM will have a delayed startup because qubes.Notifications uses wait-for-session. The default systemd start timeout is 45s. The notification agent will only start after the preload is marked as used, which is not problematic, but if made like this:

qvm-run -p --dispvm -- 'notify-send hey'

It will fail as the qubes-notification-agent may not be ready yet. It will be restarted automatically and that will be solved. This seems to be the only problem, very small.