External MIDI Keyboard in Flatpak not detected

[helpsterTee]

Is the MIDI support also working in Flatpak? I do not see the permission in the context (only access to the pulseaudio socket).

Observed behaviour:

• no MIDI devices selectable, tried rescan

Expected behaviour:

• MIDI devices are available as soon as they are plugged in / re-scanned / application is restarted

Relevant log output:

[info] initializing MIDI.
ALSA lib ../../../src/seq/seq_hw.c:466:(snd_seq_hw_open) open /dev/snd/seq failed: No such file or directory

MidiInAlsa::initialize: error creating ALSA sequencer client object.

[warning] could not initialize RtMidi in! MidiInAlsa::initialize: error creating ALSA sequencer client object.
[warning] error while initializing MIDI!
[trace] no MIDI output device selected.

Flatpak context:

[Context]
shared=ipc;
sockets=x11;wayland;pulseaudio;fallback-x11;
devices=dri;
filesystems=xdg-run/pipewire-0;

Flatpak version of furnace:

v0.6.1

[helpsterTee]

Apparently it seems that would need --device=all, which is too much permissions in general (blockdevs, etc):

https://github.com/flathub/net.sourceforge.kmidimon/blob/master/net.sourceforge.kmidimon.json#L13

[tildearrow]

The wonders of sandboxing...

Assign to @ColinKinloch

[ColinKinloch]

It has access to the xdg-run/pipewire-0.
Pipewire provides a jack server implementation.
Though looking through the furnace options I can't find the setting for it.
I'm using SDL/pipewire for my audio output which works pretty well.

[tildearrow]

Furnace uses ALSA MIDI through RtMidi (yeah, I disabled JACK MIDI).

[ColinKinloch]

Ah, the flatpak builds RtMidi separately with jack support.
Is there a reason it's disabled? It seems to work well.

[tildearrow]

It is disabled because I plan to add a native JACK backend to Furnace.

[ColinKinloch]

Seems that Debian KDE doesn't use pipewire by default yet.
I guess I should add --device=all ☹️

[helpsterTee]

My recommendation would be to add this as a part of the installation documentation, so the users can override that behaviour themselves.

That way, the Flatpak is still contained in a sane way and if anybody needs to override this, until the Jack implementation is ready, they can do that, with all the possible repercussions.

sudo flatpak override --device=all org.tildearrow.furnace for systemwide
flatpak override --user --device=all org.tildearrow.furnace for user installations.

[ColinKinloch]

The flatpak currently supports jack via RTMidi and has permissions for specifically the pipewire implementation of jackd.

The issue is how do you display these suggestions to the user:

• I could add a flatpak specific patch to the appdata to put it here: https://flathub.org/en-GB/apps/org.tildearrow.furnace
• And add it to the README here: https://github.com/flathub/org.tildearrow.furnace/
• Also perhaps a patch to put it in the log when it fails to access the midi device

Out of interest what distro do you use?

[helpsterTee]

Maybe I don't understand, but do you mean MIDI should work currently with jack routing? Because it doesn't on my side:

This is on a Ubuntu system.

[ColinKinloch]

Which version of Ubuntu?
Ubuntu switched to pipewire on version 22.10.
Could you give me the output of pgrep -a pulse and pgrep -a jack

[helpsterTee]

Yeah, this is focal, but has added pipewire support and jack via pipewire works for other applications (Bitwig for example). So that's not the problem:

pgrep -a pulse:

1234 /usr/bin/pipewire-pulse
4567 /usr/lib/x86_64-linux-gnu/xfce4/panel/wrapper-2.0 /usr/lib/x86_64-linux-gnu/xfce4/panel/plugins/libpulseaudio-plugin.so

pgrep -a jack is empty

[ColinKinloch]

I feel it should work, I'll have a think and get back to you.

[ColinKinloch]

Mine is using ALSA for MIDI as it turns out (via) pipewire 🤷.
Maybe try dpkg -S '*libspa-alsa*' to figure out what package provides it.
or just update to a newer distro.

[helpsterTee]

Yeah, I can't figure it out in this setup. But it will work as intended, if I give it --device all access:

Will check on another system, as soon as the next LTS drops. Thanks so far for the help :)

[tildearrow]

It appears that Furnace does not allow you to choose which RtMidi::Api to use, so RtMidi falls back to trying all available APIs...

...starting with ALSA.

[tildearrow]

Are you sure Flatpak does not offer a way to only provide access to /dev/snd?

[ColinKinloch]

There's a discussion here: flatpak/xdg-desktop-portal#1142

I checked just now and if I run furnace with --nosocket=pulseaudio I retain jack / pipewire audio out and loose the ability to enumerate MIDI devices. It seems that access to ALSA midi (/dev/snd/seq) is controlled by that socket.

Here's the line in flatpak that gives access to /dev/snd: https://github.com/flatpak/flatpak/blob/2cb17b4eb82ecedaa98b5b7f954cf3e52fa95682/common/flatpak-run-pulseaudio.c#L331-L337

introduced in: flatpak/flatpak@4d1899b

Looks like flatpak 0.6.1 was 8 years ago https://github.com/flatpak/flatpak/tree/0.6.1

The version of flatpak included in 20.04 LTS is too old by 4 years. I guess the question is what does LTS mean? It's a promise made by Ubuntu so let them provide the support 😁.

[helpsterTee]

Looks like flatpak 0.6.1 was 8 years ago

I've updated the issue description to better reflect what v0.6.1 refers to.

[helpsterTee]

Can confirm it working on latest available Flatpak stable 1.14.4 👍

Thanks for the pointers :)