lwip 分析一

一、接收端

  1、通过ehternetif_input

void ethernetif_input(struct netif *netif)
{
  struct ethernetif *ethernetif;
  struct eth_hdr *ethhdr;
  struct pbuf *p;

  ethernetif = netif->state;

  /* move received packet into a new pbuf */
  p = low_level_input(netif);   //接收数据
  /* no packet could be read, silently ignore this */
  if (p == NULL) return;
  /* points to packet payload, which starts with an Ethernet header */
  ethhdr = p->payload;

  switch (htons(ethhdr->type)) {
  /* IP or ARP packet? */
  case ETHTYPE_IP:
  case ETHTYPE_ARP:
#if PPPOE_SUPPORT
  /* PPPoE packet? */
  case ETHTYPE_PPPOEDISC:
  case ETHTYPE_PPPOE:
#endif /* PPPOE_SUPPORT */
    /* full packet send to tcpip_thread to process */
    if (netif->input(p, netif)!=ERR_OK)  //调用etharp.c里的ethnet_input函数
     { LWIP_DEBUGF(NETIF_DEBUG, ("ethernetif_input: IP input error "));
       pbuf_free(p);
       p = NULL;
     }
    break;

  default:
    pbuf_free(p);
    p = NULL;
    break;
  }
}

  接下来看ethernet_input函数

err_t
ethernet_input(struct pbuf *p, struct netif *netif)   //注意这里传递进来的netif以后会根据这个判断是不是我这个网卡的数据
{
  struct eth_hdr* ethhdr;

  /* points to packet payload, which starts with an Ethernet header */
  ethhdr = p->payload;
  
  switch (htons(ethhdr->type)) {   //不同协议调用不同函数 arp 0x0806  IP 0x0800  
    /* IP packet? */
    case ETHTYPE_IP: 
#if ETHARP_TRUST_IP_MAC  //如果使能了arp更新缓冲功能
      /* update ARP table */
      etharp_ip_input(netif, p);     //更新arp列表
#endif /* ETHARP_TRUST_IP_MAC */
      /* skip Ethernet header */
      if(pbuf_header(p, -(s16_t)sizeof(struct eth_hdr))) {
        LWIP_ASSERT("Can't move over header in packet", 0);
        pbuf_free(p);
        p = NULL;
      } else {
        /* pass to IP layer */
        ip_input(p, netif);   //ip协议，调用IP处理函数
      }
      break;
      
    case ETHTYPE_ARP:
      /* pass p to ARP module */
      etharp_arp_input(netif, (struct eth_addr*)(netif->hwaddr), p);    //arp协议，调用arp处理函数
      break;

#if PPPOE_SUPPORT
    case ETHTYPE_PPPOEDISC: /* PPP Over Ethernet Discovery Stage */
      pppoe_disc_input(netif, p);
      break;

    case ETHTYPE_PPPOE: /* PPP Over Ethernet Session Stage */
      pppoe_data_input(netif, p);
      break;
#endif /* PPPOE_SUPPORT */

    default:
      pbuf_free(p);
      p = NULL;
      break;
  }

  /* This means the pbuf is freed or consumed,
     so the caller doesn't have to free it again */
  return ERR_OK;
}

接下来看 ip_input();

err_t
ip_input(struct pbuf *p, struct netif *inp)
{
  struct ip_hdr *iphdr;
  struct netif *netif;
  u16_t iphdr_hlen;
  u16_t iphdr_len;
#if LWIP_DHCP
  int check_ip_src=1;
#endif /* LWIP_DHCP */

  IP_STATS_INC(ip.recv);
  snmp_inc_ipinreceives();

  /* identify the IP header */
  iphdr = p->payload;  //获取数据
  if (IPH_V(iphdr) != 4) {
    LWIP_DEBUGF(IP_DEBUG | 1, ("IP packet dropped due to bad version number %"U16_F" ", IPH_V(iphdr)));
    ip_debug_print(p);
    pbuf_free(p);
    IP_STATS_INC(ip.err);
    IP_STATS_INC(ip.drop);
    snmp_inc_ipinhdrerrors();
    return ERR_OK;
  }

  /* obtain IP header length in number of 32-bit words */
  iphdr_hlen = IPH_HL(iphdr);
  /* calculate IP header length in bytes */
  iphdr_hlen *= 4;
  /* obtain ip length in bytes */
  iphdr_len = ntohs(IPH_LEN(iphdr));

  /* header length exceeds first pbuf length, or ip length exceeds total pbuf length? */
  if ((iphdr_hlen > p->len) || (iphdr_len > p->tot_len)) {    //判断获取的数据是否正确IP报头，数据大小
    if (iphdr_hlen > p->len)
    LWIP_DEBUGF(IP_DEBUG | 2, ("IP header (len %"U16_F") does not fit in first pbuf (len %"U16_F"), IP packet dropped. ",
                               iphdr_hlen, p->len));
    if (iphdr_len > p->tot_len)
    LWIP_DEBUGF(IP_DEBUG | 2, ("IP (len %"U16_F") is longer than pbuf (len %"U16_F"), "
                               "IP packet dropped. ",
                               iphdr_len, p->tot_len));
    /* free (drop) packet pbufs */
    pbuf_free(p);
    IP_STATS_INC(ip.lenerr);
    IP_STATS_INC(ip.drop);
    snmp_inc_ipindiscards();
    return ERR_OK;
  }

  /* verify checksum */
#if CHECKSUM_CHECK_IP   //如果使能了IP校验和
  if (inet_chksum(iphdr, iphdr_hlen) != 0) {

    LWIP_DEBUGF(IP_DEBUG | 2, ("Checksum (0x%"X16_F") failed, IP packet dropped. ", inet_chksum(iphdr, iphdr_hlen)));
    ip_debug_print(p);
    pbuf_free(p);
    IP_STATS_INC(ip.chkerr);
    IP_STATS_INC(ip.drop);
    snmp_inc_ipinhdrerrors();
    return ERR_OK;
  }
#endif

  /* Trim pbuf. This should have been done at the netif layer,
   * but we'll do it anyway just to be sure that its done. */
  pbuf_realloc(p, iphdr_len);

  /* match packet against an interface, i.e. is this packet for us? */
#if LWIP_IGMP
  if (ip_addr_ismulticast(&(iphdr->dest))) {
    if ((inp->flags & NETIF_FLAG_IGMP) && (igmp_lookfor_group(inp, &(iphdr->dest)))) {
      netif = inp;
    } else {
      netif = NULL;
    }
  } else
#endif /* LWIP_IGMP */
  {
    /* start trying with inp. if that's not acceptable, start walking the
       list of configured netifs.
       'first' is used as a boolean to mark whether we started walking the list */
    int first = 1;
    netif = inp;
    do {     //在netif链上寻找合适的网络接口
      LWIP_DEBUGF(IP_DEBUG, ("ip_input: iphdr->dest 0x%"X32_F" netif->ip_addr 0x%"X32_F" (0x%"X32_F", 0x%"X32_F", 0x%"X32_F") ",
          iphdr->dest.addr, netif->ip_addr.addr,
          iphdr->dest.addr & netif->netmask.addr,
          netif->ip_addr.addr & netif->netmask.addr,
          iphdr->dest.addr & ~(netif->netmask.addr)));

      /* interface is up and configured? */
      if ((netif_is_up(netif)) && (!ip_addr_isany(&(netif->ip_addr)))) {   //这里判断接口是否是up状态，
        /* unicast to this interface address? */
        if (ip_addr_cmp(&(iphdr->dest), &(netif->ip_addr)) ||
            /* or broadcast on this interface network address? */
            ip_addr_isbroadcast(&(iphdr->dest), netif)) {    //这里判断是否是目标地址,如果是，就跳出while
          LWIP_DEBUGF(IP_DEBUG, ("ip_input: packet accepted on interface %c%c ",
              netif->name[0], netif->name[1]));
          /* break out of for loop */
          break;
        }
      }
      if (first) {
        first = 0;
        netif = netif_list;
      } else {
        netif = netif->next;
      }
      if (netif == inp) {
        netif = netif->next;
      }
    } while(netif != NULL);
  }

#if LWIP_DHCP
  /* Pass DHCP messages regardless of destination address. DHCP traffic is addressed
   * using link layer addressing (such as Ethernet MAC) so we must not filter on IP.
   * According to RFC 1542 section 3.1.1, referred by RFC 2131).
   */
  if (netif == NULL) {
    /* remote port is DHCP server? */
    if (IPH_PROTO(iphdr) == IP_PROTO_UDP) {
      LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_TRACE | 1, ("ip_input: UDP packet to DHCP client port %"U16_F" ",
        ntohs(((struct udp_hdr *)((u8_t *)iphdr + iphdr_hlen))->dest)));
      if (ntohs(((struct udp_hdr *)((u8_t *)iphdr + iphdr_hlen))->dest) == DHCP_CLIENT_PORT) {
        LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_TRACE | 1, ("ip_input: DHCP packet accepted. "));
        netif = inp;
        check_ip_src = 0;
      }
    }
  }
#endif /* LWIP_DHCP */

  /* broadcast or multicast packet source address? Compliant with RFC 1122: 3.2.1.3 */
#if LWIP_DHCP
  if (check_ip_src)
#endif /* LWIP_DHCP */
  {  if ((ip_addr_isbroadcast(&(iphdr->src), inp)) ||
         (ip_addr_ismulticast(&(iphdr->src)))) {  //判断是否是广播或多播，如果是，丢弃
      /* packet source is not valid */
      LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_TRACE | 1, ("ip_input: packet source is not valid. "));
      /* free (drop) packet pbufs */
      pbuf_free(p);
      IP_STATS_INC(ip.drop);
      snmp_inc_ipinaddrerrors();
      snmp_inc_ipindiscards();
      return ERR_OK;
    }
  }

  /* packet not for us? */
  if (netif == NULL) {
    /* packet not for us, route or discard */
    LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_TRACE | 1, ("ip_input: packet not for us. "));
#if IP_FORWARD    //如果只有一个网络接口卡，这里为0
    /* non-broadcast packet? */
    if (!ip_addr_isbroadcast(&(iphdr->dest), inp)) {
      /* try to forward IP packet on (other) interfaces */
      ip_forward(p, iphdr, inp);
    } else
#endif /* IP_FORWARD */
    {
      snmp_inc_ipinaddrerrors();
      snmp_inc_ipindiscards();
    }
    pbuf_free(p);
    return ERR_OK;
  }
  /* packet consists of multiple fragments? */
  if ((IPH_OFFSET(iphdr) & htons(IP_OFFMASK | IP_MF)) != 0) {
#if IP_REASSEMBLY /* packet fragment reassembly code present? */
    LWIP_DEBUGF(IP_DEBUG, ("IP packet is a fragment (id=0x%04"X16_F" tot_len=%"U16_F" len=%"U16_F" MF=%"U16_F" offset=%"U16_F"), calling ip_reass() ",
      ntohs(IPH_ID(iphdr)), p->tot_len, ntohs(IPH_LEN(iphdr)), !!(IPH_OFFSET(iphdr) & htons(IP_MF)), (ntohs(IPH_OFFSET(iphdr)) & IP_OFFMASK)*8));
    /* reassemble the packet*/
    p = ip_reass(p);
    /* packet not fully reassembled yet? */
    if (p == NULL) {
      return ERR_OK;
    }
    iphdr = p->payload;
#else /* IP_REASSEMBLY == 0, no packet fragment reassembly code present */
    pbuf_free(p);
    LWIP_DEBUGF(IP_DEBUG | 2, ("IP packet dropped since it was fragmented (0x%"X16_F") (while IP_REASSEMBLY == 0). ",
      ntohs(IPH_OFFSET(iphdr))));
    IP_STATS_INC(ip.opterr);
    IP_STATS_INC(ip.drop);
    /* unsupported protocol feature */
    snmp_inc_ipinunknownprotos();
    return ERR_OK;
#endif /* IP_REASSEMBLY */
  }

#if IP_OPTIONS_ALLOWED == 0 /* no support for IP options in the IP header? */

#if LWIP_IGMP
  /* there is an extra "router alert" option in IGMP messages which we allow for but do not police */
  if((iphdr_hlen > IP_HLEN &&  (IPH_PROTO(iphdr) != IP_PROTO_IGMP)) {
#else
  if (iphdr_hlen > IP_HLEN) {
#endif /* LWIP_IGMP */
    LWIP_DEBUGF(IP_DEBUG | 2, ("IP packet dropped since there were IP options (while IP_OPTIONS_ALLOWED == 0). "));
    pbuf_free(p);
    IP_STATS_INC(ip.opterr);
    IP_STATS_INC(ip.drop);
    /* unsupported protocol feature */
    snmp_inc_ipinunknownprotos();
    return ERR_OK;
  }
#endif /* IP_OPTIONS_ALLOWED == 0 */

  /* send to upper layers */
  LWIP_DEBUGF(IP_DEBUG, ("ip_input: "));
  ip_debug_print(p);
  LWIP_DEBUGF(IP_DEBUG, ("ip_input: p->len %"U16_F" p->tot_len %"U16_F" ", p->len, p->tot_len));

#if LWIP_RAW
  /* raw input did not eat the packet? */
  if (raw_input(p, inp) == 0)
#endif /* LWIP_RAW */
  {

    switch (IPH_PROTO(iphdr)) {   //判断传输层用什么协议
#if LWIP_UDP
    case IP_PROTO_UDP:
#if LWIP_UDPLITE
    case IP_PROTO_UDPLITE:
#endif /* LWIP_UDPLITE */
      snmp_inc_ipindelivers();
      udp_input(p, inp);   //UDP协议，调用UDP处理函数
      break;
#endif /* LWIP_UDP */
#if LWIP_TCP
    case IP_PROTO_TCP:
      snmp_inc_ipindelivers();
      tcp_input(p, inp); //TCP协议，调用TCP处理函数
      break;
#endif /* LWIP_TCP */
#if LWIP_ICMP
    case IP_PROTO_ICMP:
      snmp_inc_ipindelivers();
      icmp_input(p, inp);   //ICMP协议，调用ICMP处理函数
      break;
#endif /* LWIP_ICMP */
#if LWIP_IGMP
    case IP_PROTO_IGMP:
      igmp_input(p,inp,&(iphdr->dest));
      break;
#endif /* LWIP_IGMP */
    default:
#if LWIP_ICMP
      /* send ICMP destination protocol unreachable unless is was a broadcast */
      if (!ip_addr_isbroadcast(&(iphdr->dest), inp) &&
          !ip_addr_ismulticast(&(iphdr->dest))) {
        p->payload = iphdr;
        icmp_dest_unreach(p, ICMP_DUR_PROTO);  //发送ICMP报文，通知主机，有问题 

  ICMP_DUR_NET = 0,    /* net unreachable */
  ICMP_DUR_HOST = 1,   /* host unreachable */
  ICMP_DUR_PROTO = 2,  /* protocol unreachable */
  ICMP_DUR_PORT = 3,   /* port unreachable */
  ICMP_DUR_FRAG = 4,   /* fragmentation needed and DF set */
  ICMP_DUR_SR = 5      /* source route failed */

      }
#endif /* LWIP_ICMP */
      pbuf_free(p);

      LWIP_DEBUGF(IP_DEBUG | 2, ("Unsupported transport protocol %"U16_F" ", IPH_PROTO(iphdr)));

      IP_STATS_INC(ip.proterr);
      IP_STATS_INC(ip.drop);
      snmp_inc_ipinunknownprotos();
    }
  }

  return ERR_OK;
}

接下来该分析一下udp_input了