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

[Didier Roche]

Le 06/11/2016 à 11:50, Jacques Supcik a écrit :
> 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.

Hey Jacques,

I think we did discuss about GPIO support in confined mode, but there is
no interface for this today AFAIK (CCing Jamie who can confirm and maybe
give a path/ETA forward).

Meanwhile, you can still install your snap in devmode to bypass
security, and that should do it in your case, mind confirming?
Cheers,
Didier
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