the inheriting of linux sock type

0.0.1. Data Structure

Every xsock has parent sock as its first filed.

1. sock_common

157 struct sock_common {
...
}

2. sock

 288 struct sock {
 289         /*
 290          * Now struct inet_timewait_sock also uses sock_common, so please just
 291          * don't add nothing before this first member (__sk_common) --acme
 292          */
 293         struct sock_common      __sk_common;
...

3. inet_sock

37 struct inet_sock {
138         /* sk and pinet6 has to be the first two members of inet_sock */
139         struct sock             sk;
...

4. inet_connection_sock

 87 struct inet_connection_sock {
 88         /* inet_sock has to be the first member! */
 89         struct inet_sock          icsk_inet;
...

5. tcp_sock

133 struct tcp_sock {
134         /* inet_connection_sock has to be the first member of tcp_sock */
135         struct inet_connection_sock     inet_conn;
...

0.0.1.1. 转换函数：

0.0.1.1.1. sk to inet_sock

213 static inline struct inet_sock *inet_sk(const struct sock *sk)
214 {
215         return (struct inet_sock *)sk;
216 }

0.0.1.1.2. sk to inet_connection_sock

145 static inline struct inet_connection_sock *inet_csk(const struct sock *sk)
146 {
147         return (struct inet_connection_sock *)sk;
148 }

0.0.1.1.3. sk to tcp_sk

351 static inline struct tcp_sock *tcp_sk(const struct sock *sk)
352 {
353         return (struct tcp_sock *)sk;
354 }