Hotplug arsenal is incomplete

I've developed my own firewall script, which needs to read the addresses from pppoe-wan (that works sufficiently) and br-lan. I'm getting only an ifup event for br-lan. I need to act on the assignment of an IPv6 global address to br-lan.

For now, I'm using a /40 address in my script, but I'd rather use the assigned /60 address. While hotplug is designed to generate ifupdate events, they are only generated for the wan interface. wan_6 is missing, too.

Is there any chance to add more hotplug events to OpenWRT?

I've posted this question in the forum and made some progress with the help of brada4, but we both lack insight into the current mechanism that generates hotplug events. I found some hints to a transition to procd, but nothing pointing to specific code.

I'm willing to contribute, but I need pointers to the places in the code that could use some love.

It was suggested to me that this should not be an enhancement request but filed against netifd. I politely disagree because I found some mentions of procd being involved in hotplug events. But the entire hotplug generation mechanism is unclear to me and I have yet to find somebody or some document who/that explains that. So here we are...

Start by tracing the hotplug event generation path in netifd and the mentioned procd transition, comparing events for br-lan, pppoe-wan, and wan_6. Done means the mechanism is understood and the requested IPv6 global-address assignment produces the appropriate hotplug event, with the behavior verified for the affected interfaces.