Snap hangs when accessing a special /dev/file (/dev/vcio) [ubuntu-core 16 / RaspberryPi2]

[Jacques Supcik]

Dear community.

I have a program <https://gitlab.com/telecom-tower/tower>, written in go,
and running on a raspberry Pi 2, which displays messages on a LED panel.
The panel <https://www.adafruit.com/product/2294> is made of "neo pixels"
and is connected to the GPIO of the raspberry Pi. Internally, it uses the
DMA and PWM to generate and accurate signals.

The program currently runs well on a Raspbian system and I would like to
move to ubuntu-core. I was able to build the snap and to deploy it on a
raspberry Pi 2 running Core version 16. I installed the snap with
"--dangerous", but as soon as the system configure the DMA/PWM/GPIO, it
just freezes.

I installed snappy-debug to check the logs and this is what I get:

= AppArmor =
Time: Nov  6 09:28:45
Log: apparmor="DENIED" operation="open" profile="snap.telecom-tower.daemon"
name="/dev/vcio" pid=4441 comm="tower" requested_mask="r" denied_mask="r"
fsuid=0 ouid=0
File: /dev/vcio (read)

= Seccomp =
Time: Nov  6 09:28:45
Log: auid=4294967295 uid=0 gid=0 ses=4294967295 pid=4441 comm="tower"
exe="/snap/telecom-tower/x1/bin/tower" sig=31 arch=40000028 14(mknod)
compat=0 ip=0x76e3aaf6 code=0x0
Syscall: mknod

Note that if I scp the binary file and run on ubuntu core as root, then the
program runs fine. (I don't install the snap, I just run the binary from
the home directory.)

Does someone have an idea about what I can do to make my snap run?

Thank you very much in advance for your support.

Best regards,

█  Jacques
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