Comment 40 for bug 1674509

For the slot Permanent policy I think it is fine to allow the bluez interface access to /dev/ttyAMA0. ofono, ppp, et al are in similar situations.

That said, if I understand this bug correctly, the most correct solution would seem to be for the pi gadget snap to declare the serial-port interface, eg:

slots:
  pi-bluetooth:
    interface: serial-port
    path: /dev/ttyAMA0

such that the bluez snap would do:

apps:
  bluez:
    daemon: simple
    plugs:
    - serial-port

The question of which to do is I think dependent on how often this situation occurs. If there are many gadgets that have different /dev entries, then having gadget yaml expose this seems the right choice-- the bluez snap need only 'plugs: serial-port' on any device that has a gadget that exposes it and it is connected (in this way there are no snapd changes required for new devices/etc-- gadgets are updated to expose the correct device and bluez picks them up as it gains support for the device).

If the pi is the only gadget out there that does this, then I think it also makes sense to go the gadget route.

Adding to the permanent slot policy probably only makes sense if /dev/ttyAMA0 specifically is a common access across a wide variety of devices. Even then it could be argued the gadget route is the way to go, but in this particular case putting it in the permanent slot policy could remove a small stumbling block for gadget developers.