Using kqueue to poll for exceptional conditions

Question

I'm modifying an app in order to replace its use of select() with kqueue. select() allows one to poll for exceptional conditions:

int select(int nfds,
     fd_set *restrict readfds,
     fd_set *restrict writefds,
     fd_set *restrict errorfds,           <---- this thing here
     struct timeval *restrict timeout
);

After reading the kqueue documentation it looks like there's no way to do that. There's EVFILT_READ and EVFILT_WRITE but nothing along the lines of EVFILT_ERROR/EVFILT_EXCEPTIONAL. Is it possible to poll for exceptional conditions, and if so, how?

Answer 1

There is no such thing as exceptional state on FreeBSD, to quote man 2 select:

The only exceptional condition detectable is out-of-band data received on a socket.

So your question boils down to “How can I detect OOB-data on a socket with kqueue”, which I, to be honest, cannot answer without doing some research.