from tcpip_priv.h:129
struct tcpip_msg
{
enum tcpip_msg_type type;
union {
#if !LWIP_TCPIP_CORE_LOCKING
struct {
tcpip_callback_fn function;
void* msg;
} api_msg;
struct {
tcpip_api_call_fn function;
struct tcpip_api_call_data *arg;
sys_sem_t *sem;
} api_call;
#endif
#if !LWIP_TCPIP_CORE_LOCKING_INPUT
struct {
struct pbuf *p;
struct netif *netif;
netif_input_fn input_fn;
} inp;
#endif
struct {
tcpip_callback_fn function;
void *ctx;
} cb;
#if LWIP_TCPIP_TIMEOUT && LWIP_TIMERS
struct {
u32_t msecs;
sys_timeout_handler h;
void *arg;
} tmo;
#endif
} msg;
};