[9fans] csipinfo

[Joel “chesky” Salomon <chesky@plan9.jp>]

My homework assignment reads:
> Write a program to receive multiple UDP messages ...  Print to
> standard output the remote host and port from which the message
> originated (print the dotted decimal IP address and also use
> gethostbyaddr to print a textual host name), followed by the message
> itself.

I’ve got everything but the gethostbyaddr equivalent code.  From
cpu% sig csipinfo
	Ndbtuple* csipinfo(char *netroot, char *attr, char *val, char **attrs, int nattr)
it looks as if I should do something like:
	lfd = listen(adir, ldir);
	if (lfd < 0) sysfatal("listen: %r");
	dfd = accept(lfd, ldir);
	if (dfd < 0) sysfatal("can't accept: %r");
	NetConnInfo	*i = getnetconninfo(nil, lfd);
	Ndbtuple		*t = csipinfo(nil, "????", "????", ["ip", "dns"], 2);
	...
— but what’re the attr and val arguments to csipinfo?  I’ve read
ndb(2) and been thoroughly confused, and
http://www.google.com/codesearch turns up no uses of csipinfo, only
its implementation on Plan 9 and plan9ports.

Specifically, what attribute=value pair do I know about for this
remotely-initiated connection?

Thanks,
--Joel