POSIX requires the NI_NUMERICSCOPE flag to be defined for use with getnameinfo. glibc is missing it. I propose defining it as 256 (the next available value); ignoring it should produce perfectly conformant behavior as far as I can tell.
Ping. This seems like a really simple issue to resolve. I'm waiting for a decision because musl libc is also missing it and we want to use the same number glibc ends up choosing to avoid gratuitous incompatibility.
For issues like these a fastest way is to send patch to libc-alpha.
Created attachment 7627 [details]
Here's a patch; I also sent it to the list.