利用C语言预处理器的顺序Parse特性形成了一个链表。
技巧都在IPPROTO_PREVIOUS 宏，引用#define以及#undefine,形成一个链表赋值给inet_protocol_base .
#define IPPROTO_PREVIOUS NULL
#ifdef CONFIG_IP_MULTICAST
static struct inet_protocol igmp_protocol =
{
igmp_rcv, /* IGMP handler */
NULL, /* IGMP error control */
IPPROTO_PREVIOUS, /* next */
IPPROTO_IGMP, /* protocol ID */
0, /* copy */
NULL, /* data */
"IGMP" /* name */
};
#undef IPPROTO_PREVIOUS
#define IPPROTO_PREVIOUS &igmp_protocol
#endif
static struct inet_protocol tcp_protocol =
{
tcp_v4_rcv, /* TCP handler */
tcp_v4_err, /* TCP error control */
IPPROTO_PREVIOUS,
IPPROTO_TCP, /* protocol ID */
0, /* copy */
NULL, /* data */
"TCP" /* name */
};
#undef IPPROTO_PREVIOUS
#define IPPROTO_PREVIOUS &tcp_protocol
static struct inet_protocol udp_protocol =
{
udp_rcv, /* UDP handler */
udp_err, /* UDP error control */
IPPROTO_PREVIOUS, /* next */
IPPROTO_UDP, /* protocol ID */
0, /* copy */
NULL, /* data */
"UDP" /* name */
};
#undef IPPROTO_PREVIOUS
#define IPPROTO_PREVIOUS &udp_protocol
static struct inet_protocol icmp_protocol =
{
icmp_rcv, /* ICMP handler */
NULL, /* ICMP error control */
IPPROTO_PREVIOUS, /* next */
IPPROTO_ICMP, /* protocol ID */
0, /* copy */
NULL, /* data */
"ICMP" /* name */
};
#undef IPPROTO_PREVIOUS
#define IPPROTO_PREVIOUS &icmp_protocol
struct inet_protocol *inet_protocol_base = IPPROTO_PREVIOUS;