databuf
    Points to a buffer that contains an extension header. This is
    a pointer returned by a call to inet6_opt_find() or inet6_opt_
    next().
 offset
    Specifies the location in the data portion of the option from
    which to extract the data. You can access the first byte after
    the option type and length by specifying the offset of 0.
 val
    Points to a destination for the extracted data.
 vallen
    Specifies the length of the data, in bytes, to be extracted.