下面这些宏对代码有影响：
LWIP_SOCKET
LWIP_ARP
LWIP_RAW
LWIP_UDP
LWIP_TCP
LWIP_SNMP
LWIP_AUTOIP
LWIP_IGMP
LWIP_DNS
LWIP_TIMERS
void lwip_init(void) { /* Sanity check user-configurable values */ lwip_sanity_check(); /* Modules initialization */ stats_init(); #if !NO_SYS sys_init(); #endif /* !NO_SYS */ mem_init(); memp_init(); pbuf_init(); netif_init(); #if LWIP_SOCKET lwip_socket_init(); #endif /* LWIP_SOCKET */ ip_init(); #if LWIP_ARP etharp_init(); #endif /* LWIP_ARP */ #if LWIP_RAW raw_init(); #endif /* LWIP_RAW */ #if LWIP_UDP udp_init(); #endif /* LWIP_UDP */ #if LWIP_TCP tcp_init(); #endif /* LWIP_TCP */ #if LWIP_SNMP snmp_init(); #endif /* LWIP_SNMP */ #if LWIP_AUTOIP autoip_init(); #endif /* LWIP_AUTOIP */ #if LWIP_IGMP igmp_init(); #endif /* LWIP_IGMP */ #if LWIP_DNS dns_init(); #endif /* LWIP_DNS */ #if LWIP_TIMERS sys_timeouts_init(); #endif /* LWIP_TIMERS */ }
netif_add函数
它添加一个网络接口到lwip，一个网卡应该是一个网络接口。本地回环也是一个网络接口，它已经在tcpip_init中的lwip_init调用netif_init被添加。
/** * Add a network interface to the list of lwIP netifs. * * @param netif a pre-allocated netif structure * @param ipaddr IP address for the new netif * @param netmask network mask for the new netif * @param gw default gateway IP address for the new netif * @param state opaque data passed to the new netif * @param init callback function that initializes the interface * @param input callback function that is called to pass * ingress packets up in the protocol layer stack. * * @return netif, or NULL if failed. */ struct netif * netif_add(struct netif *netif, ip_addr_t *ipaddr, ip_addr_t *netmask, ip_addr_t *gw, void *state, netif_init_fn init, netif_input_fn input)
Struct net_if
在初始化用netif_add添加到lwip中。
/** Generic data structure used for all lwIP network interfaces. * The following fields should be filled in by the initialization * function for the device driver: hwaddr_len, hwaddr[], mtu, flags */ struct netif { /** pointer to next in linked list */ struct netif *next; /** IP address configuration in network byte order */ ip_addr_t ip_addr; ip_addr_t netmask; ip_addr_t gw; /** This function is called by the network device driver * to pass a packet up the TCP/IP stack. */ netif_input_fn input; // 网卡数据接收函数，自定义设置 /** This function is called by the IP module when it wants * to send a packet on the interface. This function typically * first resolves the hardware address, then sends the packet. */ netif_output_fn output; //发送无连接的数据包，如广播包，多播包，最终还是调用下面的linkoutput函数。固定设置为etharp_output。 /** This function is called by the ARP module when it wants * to send a packet on the interface. This function outputs * the pbuf as-is on the link medium. */ netif_linkoutput_fn linkoutput; //发送有连接的数据包，已经包含MAC，类型等数据。 #if LWIP_NETIF_STATUS_CALLBACK /** This function is called when the netif state is set to up or down */ netif_status_callback_fn status_callback; #endif /* LWIP_NETIF_STATUS_CALLBACK */ #if LWIP_NETIF_LINK_CALLBACK /** This function is called when the netif link is set to up or down */ netif_status_callback_fn link_callback; #endif /* LWIP_NETIF_LINK_CALLBACK */ /** This field can be set by the device driver and could point * to state information for the device. */ void *state; //一般设置为网卡的私有数据，如netif->state = ethernetif; #if LWIP_DHCP /** the DHCP client state information for this netif */ struct dhcp *dhcp; #endif /* LWIP_DHCP */ #if LWIP_AUTOIP /** the AutoIP client state information for this netif */ struct autoip *autoip; #endif #if LWIP_NETIF_HOSTNAME /* the hostname for this netif, NULL is a valid value */ char* hostname; #endif /* LWIP_NETIF_HOSTNAME */ /** maximum transfer unit (in bytes) */ u16_t mtu; /** number of bytes used in hwaddr */ u8_t hwaddr_len; /** link level hardware address of this interface */ u8_t hwaddr[NETIF_MAX_HWADDR_LEN]; /** flags (see NETIF_FLAG_ above) */ u8_t flags; /** descriptive abbreviation */ char name[2]; /** number of this interface */ u8_t num; #if LWIP_SNMP