Descriptorless files for io_uring

Well, RIO is kinda a completely separate API from regular IOCP and overlapped IO. It is indeed similar to io_uring, albeit more limited.

IOCP is pretty well designed, actually. It's a way better design than the classic POSIX asynchronous APIs, but it's around 20 years old by now and its age is showing.

> I haven't tried using Windows's "registered IO", their equivalent to io_uring's ring buffer and registered buffers... is it particularly broken somehow?

Well, it's not really IOCP network IO, but something that can be bolted sideways to iocp :). But yes, fair enough.

> > readiness style notification (not building data to send out before socket is ready is useful for efficiency, even if one otherwise uses completion notification), ...

> FWIW, IOCP actually does support readiness-style notification -- the windows kernel only understands IOCP, not `select`, so Winsock `select` is actually using IOCP syscalls underneath. The API for this was supposed to be completely internal and undocumented, but someone (@piscisaureus) reverse-engineered it, and it's now used in a number of modern event-loop libraries like libuv, tokio, trio, etc. (And also apparently "Starcraft: Remastered", according to the wine issue tracker.) It's awkward and janky and has some outright bugs you have to work around, but it's so much better than dealing with `select` that it's worth it.

That is *very* interesting. I've occasionally looked in that space because the winsock restrictions are problematic for some things in postgres..