title: implementation of ioctl in freebsd
body: <p>I want to know how to implement <code>ioctl</code> command for a character device in FreeBSD.
  I already write a character device with <code>open()</code> <code>close()</code> <code>read()</code> <code>write()</code> but I don't know what argument should I pass to <code>ioctl_handler</code>. Does anybody know the prototype of <code>d_ioctl_t</code>?</p>