I am writing a module for tcptrace. In that module I need to process payload. TCPTRACE _read function passes
struct ip *pip /* the packet */
as an argument.

how I can extract payload by using struct ip pointer.

there are multiple ip header structures. see /usr/include/netinet/ip.h for the details. 'struct ip' does not include any ip header options, so make sure that is what you want.

i don't know tcptrace, but in general, this is done through pointer math. for tcp/ip, the ip payload is the tcp header. so here some psuedo code:

struct tcphdr *tcpHdr;
struct ip *ipHdr;

ipHdr = /* some code that allocates memory & reads ip packet into it */

/* start of tcp header is the ip payload */
tcpHdr = (struct tcphdr)(ipHdr + sizeof( struct ip ));