How do I get the original TCP sequence number from user space in Linux?

In order to keep track of a TCP session as it traverses the network, I would like to know the starting sequence number of the session. I wrote some code to just copy the ISN into the tcp_sock structure when creating a TCP session, and then add code to copy that value into the tcp_info structure returned by getsockopt (). This seems to work, but I was wondering if there is a better way. I can see that snt_isn and rcv_isn are stored in the tcp_request_sock structure. Is there a way to access the tcp_request_sock structure from the tp structure in getsockopt ()?

thanks in advance bws