Hi, maybe it's a naive question. But I am confused here. For the options field of an IP header, as for the data in this field, according to document and the code in the method of "ip_options_compile", the first byte is the options type data and the second byte is the length of the option. But I traced back the method of "ip_options_get_from_user", there is no place that assign these two values to the __data field. I checked some example of socket API "setsockopt", it also just converts the target options data pointer into a char * pointer and passes down to " ip_options_get_from_user", still it doesn't set these two values. Can anyone help me on this? Because I am trying to add my own options to IP header at the IP layer for some experiment purposes. struct linger linger = { 0 }; linger.l_onoff = 1; linger.l_linger = 30; status = setsockopt(serverSocket, SOL_SOCKET, SO_LINGER, (const char *) &linger, sizeof(linger));