Keyboard layout switching unreliable

[arkenoi]

Qubes OS version:

R4.1

Affected component(s) or functionality:

GUI

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Steps to reproduce the behavior:

keyboard layout switcher is ru++grp:shifts_toggle

Expected or desired behavior:

shift+shift consistently switches layouts in any VM

Actual behavior:

layout switcher is reliable in dom0 but not in domU, sometimes it is not changed at all and gets out of sync with xfce layout indicator if there is one in place.

General notes:

Apparently turning HT on makes things worse but I am not sure

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I have consulted the following relevant documentation:

I am aware of the following related, non-duplicate issues:

#1396

[arkenoi]

Don't know if it helps to diagnose, but it happens if you switch and type with no pause. If you switch, wait and type after a second or two, it works properly.

[arkenoi]

double checked, no, HT does not affect it. but i have the impression than it was better while on 3.x and 4.0

[DemiMarie]

Don't know if it helps to diagnose, but it happens if you switch and type with no pause. If you switch, wait and type after a second or two, it works properly.

This sounds like a race condition. I imagine that the keyboard layout switch is communicated via qrexec, which does not synchronize with the GUI daemon. Ideally, keyboard layout events would be sent via the GUI protocol instead.

If I am correct, what happens is that you start typing before the qube you are typing into has been notified of the changed keyboard layout. This should not be possible.

[hexagonrecursion]

Nitpick: the information is transferred not via qrexec, but via QubesDB
https://github.com/QubesOS/qubes-core-admin/blob/568908c8c628171a638e5b7a683aa55aeb33bc42/qubes/ext/gui.py#L92

vm.untrusted_qdb.write('/keyboard-layout', vm.keyboard_layout)