.TH io_fd 3
.SH NAME
io_fd \- prepare descriptor for io_wait
.SH SYNTAX
.B #include <libowfat/io.h>

int \fBio_fd\fP(int64 fd);
.SH DESCRIPTION
If you want to use io_canread() and io_canwrite() on a descriptor, you
have to use io_wait() on it first, and io_wait() has to know which
descriptors you are interested in. io_fd() informs io_wait() that you
are interested in this fd.

If you know that the descriptor is writable, call io_fd_canwrite()
instead. Most fresh descriptors are writable, e.g. if it came from
pipe(2) or socketpair(2) or accept(2). This will save one syscall.

io_pipe and io_socketpair already call io_fd_canwrite() for you.

Waiting on descriptors only works for sockets, fifos and pipes.  It may
also work on devices and TTYs, but that is platform dependent -- you
should not rely on that.  It does not work on files.
.SH "RETURN VALUE"
io_fd returns 1 on success, 0 on error.
.SH "SEE ALSO"
io_fd_canwrite(3), io_wait(3), io_wantread(3), io_canread(3), io_eagain(3), io_nonblock(3)