>     mkfifo exits 0 if successful, and >0 if an error occurred.

As somebody pointed out, this is the shell program mkfifo.
The system call mkfifo returns -1 on error. I checked almost
everything out from the Stevens book Adv. Programming in the
Unix Environment, and the program works flawlessly on Linux...
(except of course the design flaws like nonblocking I/O
eating up 99% CPU all the time - I think I'll insert a select()
somewhere in there).

>     I haven't seen anything about fifofs in the GENERIC kernel configs on
> both vax and pmax. Try nm /netbsd | grep fifo and I get about 35 symbols on
> a custom kernel on my pmax.

Well, I would think that fifos are something that should be 
supported on any unixhy system that's been updated since 
the beginning of the 80's. Can you use mkfifo in a shell?
As in

$ mkfifo kikkeli
$ echo this text goes through the fifo > kikkeli &
$ cat kikkeli


- hautis