greedy auto-connect doesn't work with hotplug

[Ian Johnson]

The arduino snap has this declaration given to it via the store (see https://forum.snapcraft.io/t/auto-connection-request-for-arduino-raw-usb/15586):

plugs:
  raw-usb:
    allow-auto-connection: true
  serial-port:
    allow-auto-connection:
      slot-snap-type:
        - app
      slots-per-plug: *

and when installing the snap with no hotplug serial-port devices connected, it doesn't have any serial port interfaces connected (as expected). I then connected a physical Arduino (which shows up as a serial-port via USB), and I can see the hotplug interface show up under `snap interface serial-port`, but the slot does not get connected to the hotplug serial-port interface plug on the arduino snap.

I also tried just for kicks a similar situation, but where the hotplug device is connected before installing the snap (and thus auto-connect logic on install should process when the hotplug serial-port slot exists) and it also did not automatically get connected.

[Ian Johnson (anonymouse67)]

Pawel, could you take a look at this? I tried to look at overlord/ifacestate to see if it was trivial to fix the not auto-connecting on install when the slot already exists, and I don't see where this is going wrong which leads me to believe that the hotplug interfaces are maybe not showing up in the auto-connect candidates at all when we process the auto-connect event?

[Paweł Stołowski (stolowski)]

@Ian I had a quick look (with no way of reproducing easily due to specific setup) and I *think* this is because the declaration says slot-snap-type must be an app (for auto-connect to kick in). Hotplug slots are created on the system snap.

[Jamie Strandboge (jdstrand)]

This is a bug in the issued snap declaration, which is trying to work around: https://bugs.launchpad.net/snapstore/+bug/1873282 but did it wrong. I've updated the snap declaration to have:

plugs:
  raw-usb:
    allow-auto-connection: true
  serial-port:
    allow-auto-connection:
      slot-snap-type:
        - gadget
        - core
      slots-per-plug: *

I also did this for the s4a snap.

[Jamie Strandboge (jdstrand)]

@Pawel, should the above also include the 'snapd' as the slot-snap-type?

[Jamie Strandboge (jdstrand)]

(considering we use 'sudo snap set system experimental.hotplug=true' to set the feature and devices show up like 'core:ft232serialuartic' as opposed to 'snapd:foo', I didn't add 'snapd').

[Jamie Strandboge (jdstrand)]

FYI, it did auto connect here:

$ snap interface serial-port
name: serial-port
summary: allows accessing a specific serial port
plugs:
  - arduino
slots:
  - core:ft232serialuartic (allows accessing a specific serial port)

$ snap connections arduino|grep serial
serial-port arduino:serial-port :ft232serialuartic -

[Jamie Strandboge (jdstrand)]

I installed the snapd snap, made sure it was new enough to be re-execd into, and see:

$ snap interface serial-port
name: serial-port
summary: allows accessing a specific serial port
plugs:
  - arduino
slots:
  - snapd:ft232serialuartic (allows accessing a specific serial port)

$ snap connections arduino|grep serial
serial-port arduino:serial-port :ft232serialuartic -

So while I would want to use 'snapd' in the list for 'slot-snap-type', there is a store bug which prevents this, but thankfully snapd auto-connected the interfaces anyway.

[Ian Johnson (anonymouse67)]

I just confirmed locally that this now works, even with the snapd snap providing the slots, so I will close this as fix released.