Efficient way to display domU output in dom0 panel?

[qubist]

Hi,

What would be an efficient and correct way to display info from a domU
on dom0's XFCE panel?

I have tried using a generic monitor widget polling a script in the
domU but it seems too laggy (qvm-run introduces about 200-300ms delay).
Additionally, synchronizing the reading of script output and its
writing is somewhat challenging in such a setup.

I see that sys-net displays its own network manager applet in dom0's
panel. I wonder how this is done and if something similar is
possible/suitalbe.

XY: I am trying to create a simple network monitor.
https://github.com/QubesOS/qubes-issues/issues/8948

[Marek Marczykowski-Górecki]

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Any status widget running in a domU should show up in dom0, you don't
need to change anything in dom0.

- --
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab
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[qubist]

Thanks for the quick reply!

On Tue, 13 May 2025 16:59:31 +0200 Marek Marczykowski-Górecki wrote:

> Any status widget running in a domU should show up in dom0, you don't
> need to change anything in dom0.

In case you mean running a panel in the domU itself (and a widget in
that panel), I am already using that. The problem is that this domU
panel is:

- a second panel (using extra space)
- is challenging to position correctly (so I use a custom script in
dom0 for that part)
- is actually a window - with a title, frame and everything

i.e. not really a seamlessly integrated UI element.

In case you mean something else, could you please explain?

[Marek Marczykowski-Górecki]

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I meant just an application that dock itself in the tray area ("status
icon"?), just like network manager.

- --
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab
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[qubist]

How can I display domU's bash script output (short text) in dom0 panel,
without the mentioned lag?

[Marek Marczykowski-Górecki]

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On Tue, May 13, 2025 at 04:33:52PM -0000, qubist wrote:
> How can I display domU's bash script output (short text) in dom0 panel,
> without the mentioned lag?

I don't know any specific app doing that, but if you want to reduce lag,
IMO trying with bash is not the best idea. Try to search for a tray
widget showing network traffic stats already, I'm pretty sure you are
not the first person wanting this.

- --
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab
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[qubist]

On Tue, 13 May 2025 18:57:18 +0200 Marek Marczykowski-Górecki wrote:

> I don't know any specific app doing that, but if you want to reduce lag,
> IMO trying with bash is not the best idea.

It is not bash that introduces the lag but qvm-run.

My script completes in about 20ms, i.e. x10-15 faster than the
200-300ms lag which qvm-run adds. So, the bottleneck is qvm-run.

> Try to search for a tray widget showing network traffic stats
> already, I'm pretty sure you are not the first person wanting this.

I have done that multiple times recently and in the past, w/o success.

[qubist]

Marek,

Is there a way to reduce the lag and load of qvm-run?

user@dom0:~ > time qvm-run --pass-io --no-color-output -- sys-net 'true'

real 0m0.218s
user 0m0.098s
sys 0m0.061s

Running this every second adds about 6% CPU load.

That is too much.

[Marek Marczykowski-Górecki]

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Simply don't run it every second... If you really need to, make a script
that runs continuously and outputs new info every second.

- --
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab
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[qubist]

On Wed, 14 May 2025 19:02:03 +0200 Marek Marczykowski-Górecki wrote:

> Simply don't run it every second... If you really need to, make a
> script that runs continuously and outputs new info every second.

But that is not possible. The data (RX/TX transfer bytes) is in sys-net
and needs to be read frequently to make realtime monitoring.
Calculations can happen either in dom0 or in sys-net.

If in dom0: There need to be at least 4 polls (4 x qvm-run), i.e. even
worse.
If in sys-net: There will be only one poll per cycle (one qvm-run),
pulling the result only (what I use).

The only problem is the slowness of qvm-run.

Or... I don't understand your idea. I hope you can clarify.

[Marek Marczykowski-Górecki]

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qvm-run -p sys-net "while sleep 1; do your-magic-commands; done"

And then handle incoming data as it goes.

- --
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab
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[qubist]

On Wed, 14 May 2025 21:11:08 +0200 Marek Marczykowski-Górecki wrote:

> qvm-run -p sys-net "while sleep 1; do your-magic-commands; done"

Interesting. I didn't know that was possible. Thanks!

Is there a way to capture only the last line of qvm-run's output?

'>' acts strangely, always appending (like '>>'). Piping through tail
doesn't seem to work at all. I have been fighting with --localcmd as
well but can't get my head around how it works. Can't find more
detailed docs as well.

XFCE's generic monitor seems to expect a static string, not a stream
(which qvm-run generates through this remote loop).

[qubist]

I think I made it:

https://forum.qubes-os.org/t/network-monitor-widget-for-xfce-panel/33946

You are welcome to use it for the project, if you find it appropriate.

It may need some polishing and optimization, as handling the stream
data is somewhat tricky to me.