Asynchronous user-space notification of interface address changes?

[Matthias Andree]

Greetings,

is there any sensible way to have a user-space application notified of
interface address changes (in the light of - but not limited to - IPv6
automatic configuration, with accept_rtadv or similar), preferably
without the application polling getifaddrs every five-ish seconds?

It does not appear kevent/kqueue, or devctl, are up to the task.

I am not asking for turnkey solutions (although I'll gladly take them),
a rough sketch or pointers will suffice.

Thanks.

Best regards
Matthias