Fix network interface enumeration on Mono

[NattyNarwhal]

Right now Mono can't enumerate network interfaces; it assumes none are installed. What's happening is Mono assumes in the default Unix interface enumerator class that it can list them off with getifaddrs, which isn't present under AIX, and is available in a different form with a different name under i. What can be done is writing a backend or two using SIOCGIFCONF based enumeration for AIX; and perhaps one using Qp2getifaddrs under i. (Alternatively, we could point to a wrapper library, but this is a pain.)

This is of relatively high importance because the Socket class uses these to enumerate supported network protocols; and that is used by things like DNS. Fixing this will enable a huge swath of tests under AIX CI. Right now, upstream is in the middle of refactoring this, so I don't know if I should wait for them to finish or not.

In the mean time, our binary builds supply a patch to nop out the check for interfaces in Sockets init.

[kadler]

FYI, we have some code which implements a getifaddrs shim for PASE already that we're looking at open sourcing. I'm not sure if the same would work on AIX, though.

[NattyNarwhal]

Is that the same as Qp2getifaddrs? I know rsyslog implements a shim.

I have a SIOCGIFCONF based implementation of NetworkInterface running on AIX, but I haven't tested it under PASE yet. I assume it'd work except for maybe MTUs, but the incongruency between the ioctl and getifaddrs/if_nameindex functions for device names is annoying and prevents me from getting the index; not essential for the class I implemented but other stuff like in CoreFX PAL really wants the index. It seems the ioctl on AIX returns AF_LINK containing sockaddr_dls, but not under PASE, so that's not a workaround. Is there another method perhaps?

Interestingly, all methods seem to return the same stuff regardless of PASE or ILE.

[kadler]

No, it's through a different method and uses neither Qp2getifaddrs nor SIOCGIFCONF

[NattyNarwhal]

@kadler do you know what interface that was? I was skimming through AIX headers a while back and I noticed some interfaces for querying, but they didn't have any documentation and some seemed to be kernel internals related...

[NattyNarwhal]

An attempt but upstream is hesitant due to a future refactor Real Soon Now™.

[NattyNarwhal]

Upstream has merged the AIX patch for now. It won't work 100% on i, but enough to omit a patch. When upstream works on importing CoreFX NetworkInterface, I have an idea of the interface to use instead that works properly on both AIX and i.