The function realhostname converts ip to the corresponding host name. This is done by resolving ip to a host name and then ensuring that the host name resolves back to ip.
host must point to a buffer of at least hsize bytes, and will always be written to by this function.
If the name resolution does not work both ways or if the host name is longer than hsize bytes, inet_ntoa(3) is used to convert ip to an ASCII form.
If the string written to host is hsize bytes long, host will not be NUL terminated.
The realhostname function will return one of the following constants which are defined in
.In libutil.h :