BSD sockets API extensions that would be nice for real-time apps

• make my UDP sendto()'s block if there's no buffer space, like writing to a pipe or a TCP socket
• how much buffer space is available - used = free on this socket? This has to be carefully-defined because that equation does not hold. There are headers on datagrams. If you have 64kByte available, you can't send 65536 one-byte datagrams. There's already an API to change this available size, though I'm not sure it's consistent across BSD, Linux, Solaris.
• to what point in this TCP stream have we received acknowledgements? I would like this. There ought to be a blocking version of this question, too---shutdown() this socket for sending, wait as long as you're going to wait, and then tell me how much (if not all) of the data I wrote to the socket was acknowledged by the other end.
• What is the statistically estimated latency and jitter of this TCP stream, and are these numbers you're giving me actually any good, or has the socket just opened?
• There should be a multicast datagram socket in the Unix domain. :)