C++ ICMP_STATS_INC函数代码示例

void
icmp_dest_unreach(struct pbuf *p, enum icmp_dur_type t)
{
    struct pbuf *q;
    struct ip_hdr *iphdr;
    struct icmp_dur_hdr *idur;

    /* @todo: can this be PBUF_LINK instead of PBUF_IP? */
    q = pbuf_alloc(PBUF_IP, 8 + IP_HLEN + 8, PBUF_RAM);
    /* ICMP header + IP header + 8 bytes of data */
    if (q == NULL) {
        LWIP_DEBUGF(ICMP_DEBUG, ("icmp_dest_unreach: failed to allocate pbuf for ICMP packet.\n"));
        pbuf_free(p);
        return;
    }
    LWIP_ASSERT("check that first pbuf can hold icmp message",
                (q->len >= (8 + IP_HLEN + 8)));

    iphdr = p->payload;

    idur = q->payload;
    idur->type = (u8_t)ICMP6_DUR;
    idur->icode = (u8_t)t;

    SMEMCPY((u8_t *)q->payload + 8, p->payload, IP_HLEN + 8);

    /* calculate checksum */
    idur->chksum = 0;
    idur->chksum = inet_chksum(idur, q->len);
    ICMP_STATS_INC(icmp.xmit);

    ip_output(q, NULL,
              (struct ip_addr *)&(iphdr->src), ICMP_TTL, IP_PROTO_ICMP);
    pbuf_free(q);
}

void
icmp_time_exceeded(struct pbuf *p, enum icmp_te_type t)
{
  struct pbuf *q;
  struct ip_hdr *iphdr;
  struct icmp_te_hdr *tehdr;

  q = pbuf_alloc(PBUF_IP, 8 + IP_HLEN + 8, PBUF_RAM);

  iphdr = p->payload;
  LWIP_DEBUGF(ICMP_DEBUG, ("icmp_time_exceeded from "));
  ip_addr_debug_print(ICMP_DEBUG, &(iphdr->src));
  LWIP_DEBUGF(ICMP_DEBUG, (" to "));
  ip_addr_debug_print(ICMP_DEBUG, &(iphdr->dest));
  LWIP_DEBUGF(ICMP_DEBUG, ("\n"));

  tehdr = q->payload;
  ICMPH_TYPE_SET(tehdr, ICMP_TE);
  ICMPH_CODE_SET(tehdr, t);

  /* copy fields from original packet */
  memcpy((u8_t *)q->payload + 8, (u8_t *)p->payload, IP_HLEN + 8);

  /* calculate checksum */
  tehdr->chksum = 0;
  tehdr->chksum = inet_chksum(tehdr, q->len);
  ICMP_STATS_INC(icmp.xmit);
  /* increase number of messages attempted to send */
  snmp_inc_icmpoutmsgs();
  /* increase number of destination unreachable messages attempted to send */
  snmp_inc_icmpouttimeexcds();
  ip_output(q, NULL, &(iphdr->src),
	    ICMP_TTL, 0, IP_PROTO_ICMP);
  pbuf_free(q);
}

/* 发送一个ICMP差错报文 */
static void
icmp_send_response(struct pbuf *p, u8_t type, u8_t code)
{
  struct pbuf *q;
  struct ip_hdr *iphdr;
  /* we can use the echo header here */
	/* 用回显请求的首部描述差错报文首部 */
  struct icmp_echo_hdr *icmphdr;

  /* ICMP header + IP header + 8 bytes of data */
	/* 在IP层申请一个pbuf，会自动预留IP首部和以太网帧首部，
	 * 申请的大小是回显请求首部 + 引起差错的IP数据报首部大小 + IP数据报载荷的前8字节
	 */
  q = pbuf_alloc(PBUF_IP, sizeof(struct icmp_echo_hdr) + IP_HLEN + ICMP_DEST_UNREACH_DATASIZE,
                 PBUF_RAM);
  if (q == NULL) {
		/* 申请失败，则返回 */
    LWIP_DEBUGF(ICMP_DEBUG, ("icmp_time_exceeded: failed to allocate pbuf for ICMP packet.\n"));
    return;
  }
  LWIP_ASSERT("check that first pbuf can hold icmp message",
             (q->len >= (sizeof(struct icmp_echo_hdr) + IP_HLEN + ICMP_DEST_UNREACH_DATASIZE)));

	/* 指向引起差错的IP数据报 */
  iphdr = p->payload;
  LWIP_DEBUGF(ICMP_DEBUG, ("icmp_time_exceeded from "));
  ip_addr_debug_print(ICMP_DEBUG, &(iphdr->src));
  LWIP_DEBUGF(ICMP_DEBUG, (" to "));
  ip_addr_debug_print(ICMP_DEBUG, &(iphdr->dest));
  LWIP_DEBUGF(ICMP_DEBUG, ("\n"));

	/* 指向ICMP报文首部 */
  icmphdr = q->payload;
	/* 填写类型字段 */
  icmphdr->type = type;
	/* 填写代码字段 */
  icmphdr->code = code;
	/* ICMP首部第4-7字节填0 */
  icmphdr->id = 0;
  icmphdr->seqno = 0;

  /* copy fields from original packet */
	/* 复制引起差错的IP数据报首部+8字节到ICMP数据字段 */
  SMEMCPY((u8_t *)q->payload + sizeof(struct icmp_echo_hdr), (u8_t *)p->payload,
          IP_HLEN + ICMP_DEST_UNREACH_DATASIZE);

  /* calculate checksum */
	/* 计算并填写校验和 */
  icmphdr->chksum = 0;
  icmphdr->chksum = inet_chksum(icmphdr, q->len);
  ICMP_STATS_INC(icmp.xmit);
  /* increase number of messages attempted to send */
  snmp_inc_icmpoutmsgs();
  /* increase number of destination unreachable messages attempted to send */
  snmp_inc_icmpouttimeexcds();
	/* 调用IP层函数输出ICMP报文 */
  ip_output(q, NULL, &(iphdr->src), ICMP_TTL, 0, IP_PROTO_ICMP);
	/* 发送完成，释放申请的ICMP用的pbuf */
  pbuf_free(q);
}

void
icmp_dest_unreach(struct pbuf *p, enum icmp_dur_type t)
{
  struct pbuf *q;
  struct ip_hdr *iphdr;
  struct icmp_dur_hdr *idur;

  q = pbuf_alloc(PBUF_IP, 8 + IP_HLEN + 8, PBUF_RAM);
  /* ICMP header + IP header + 8 bytes of data */

  iphdr = p->payload;

  idur = q->payload;
  ICMPH_TYPE_SET(idur, ICMP_DUR);
  ICMPH_CODE_SET(idur, t);

  memcpy((u8_t *)q->payload + 8, p->payload, IP_HLEN + 8);

  /* calculate checksum */
  idur->chksum = 0;
  idur->chksum = inet_chksum(idur, q->len);
  ICMP_STATS_INC(icmp.xmit);
  /* increase number of messages attempted to send */
  snmp_inc_icmpoutmsgs();
  /* increase number of destination unreachable messages attempted to send */
  snmp_inc_icmpoutdestunreachs();

  ip_output(q, NULL, &(iphdr->src),
	    ICMP_TTL, 0, IP_PROTO_ICMP);
  pbuf_free(q);
}

/**
 * Send an icmp packet in response to an incoming packet.
 *
 * @param p the input packet for which the 'unreachable' should be sent,
 *          p->payload pointing to the IP header
 * @param type Type of the ICMP header
 * @param code Code of the ICMP header
 */
static void icmp_send_response(struct pbuf *p, u8_t type, u8_t code)
{
    struct pbuf *q;
    struct ip_hdr *iphdr;

    /* we can use the echo header here */
    struct icmp_echo_hdr *icmphdr;

    /* ICMP header + IP header + 8 bytes of data */
    q =
      pbuf_alloc(PBUF_IP,
                 sizeof(struct icmp_echo_hdr) + IP_HLEN +
                 ICMP_DEST_UNREACH_DATASIZE, PBUF_RAM);
    if (q == NULL) {
        LWIP_DEBUGF(ICMP_DEBUG,
                    ("icmp_time_exceeded: failed to allocate pbuf for ICMP packet.\n"));
        return;
    }
    LWIP_ASSERT("check that first pbuf can hold icmp message",
                (q->len >=
                 (sizeof(struct icmp_echo_hdr) + IP_HLEN +
                  ICMP_DEST_UNREACH_DATASIZE)));

    iphdr = p->payload;
    LWIP_DEBUGF(ICMP_DEBUG, ("icmp_time_exceeded from "));
    ip_addr_debug_print(ICMP_DEBUG, &(iphdr->src));
    LWIP_DEBUGF(ICMP_DEBUG, (" to "));
    ip_addr_debug_print(ICMP_DEBUG, &(iphdr->dest));
    LWIP_DEBUGF(ICMP_DEBUG, ("\n"));

    icmphdr = q->payload;
    icmphdr->type = type;
    icmphdr->code = code;
    icmphdr->id = 0;
    icmphdr->seqno = 0;

    /* copy fields from original packet */
    SMEMCPY((u8_t *) q->payload + sizeof(struct icmp_echo_hdr),
            (u8_t *) p->payload, IP_HLEN + ICMP_DEST_UNREACH_DATASIZE);

    /* calculate checksum */
    icmphdr->chksum = 0;
    icmphdr->chksum = inet_chksum(icmphdr, q->len);
    ICMP_STATS_INC(icmp.xmit);
    /* increase number of messages attempted to send */
    snmp_inc_icmpoutmsgs();
    /* increase number of destination unreachable messages attempted to send */
    snmp_inc_icmpouttimeexcds();
    ip_output(q, NULL, &(iphdr->src), ICMP_TTL, 0, IP_PROTO_ICMP);
    pbuf_free(q);
}

void
icmp_input(struct pbuf *p, struct netif *inp)
{
    u8_t type;
    struct icmp_echo_hdr *iecho;
    struct ip_hdr *iphdr;
    struct ip_addr tmpaddr;

    ICMP_STATS_INC(icmp.recv);

    /* TODO: check length before accessing payload! */

    type = ((u8_t *)p->payload)[0];

    switch (type) {
        case ICMP6_ECHO:
            LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: ping\n"));

            if (p->tot_len < sizeof(struct icmp_echo_hdr)) {
                LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: bad ICMP echo received\n"));

                pbuf_free(p);
                ICMP_STATS_INC(icmp.lenerr);
                return;
            }
            iecho = p->payload;
            iphdr = (struct ip_hdr *)((u8_t *)p->payload - IP_HLEN);
            if (inet_chksum_pbuf(p) != 0) {
                LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: checksum failed for received ICMP echo (%"X16_F")\n", inet_chksum_pseudo(p, &(iphdr->src), &(iphdr->dest), IP_PROTO_ICMP, p->tot_len)));
                ICMP_STATS_INC(icmp.chkerr);
                /*      return;*/
            }
            LWIP_DEBUGF(ICMP_DEBUG, ("icmp: p->len %"S16_F" p->tot_len %"S16_F"\n", p->len, p->tot_len));
            ip_addr_set(&tmpaddr, &(iphdr->src));
            ip_addr_set(&(iphdr->src), &(iphdr->dest));
            ip_addr_set(&(iphdr->dest), &tmpaddr);
            iecho->type = ICMP6_ER;
            /* adjust the checksum */
            if (iecho->chksum >= htons(0xffff - (ICMP6_ECHO << 8))) {
                iecho->chksum += htons(ICMP6_ECHO << 8) + 1;
            } else {
                iecho->chksum += htons(ICMP6_ECHO << 8);
            }
            LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: checksum failed for received ICMP echo (%"X16_F")\n", inet_chksum_pseudo(p, &(iphdr->src), &(iphdr->dest), IP_PROTO_ICMP, p->tot_len)));
            ICMP_STATS_INC(icmp.xmit);

            /*    LWIP_DEBUGF("icmp: p->len %"U16_F" p->tot_len %"U16_F"\n", p->len, p->tot_len);*/
            ip_output_if (p, &(iphdr->src), IP_HDRINCL,
                          iphdr->hoplim, IP_PROTO_ICMP, inp);
            break;
        default:
            LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: ICMP type %"S16_F" not supported.\n", (s16_t)type));
            ICMP_STATS_INC(icmp.proterr);
            ICMP_STATS_INC(icmp.drop);
    }

    pbuf_free(p);
}

/**
 * Send an icmp packet in response to an incoming packet.
 *
 * @param p the input packet for which the 'unreachable' should be sent,
 *          p->payload pointing to the IP header
 * @param type Type of the ICMP header
 * @param code Code of the ICMP header
 */
static void ICACHE_FLASH_ATTR
icmp_send_response(struct pbuf *p, u8_t type, u8_t code)
{
  struct pbuf *q;
  struct ip_hdr *iphdr;
  /* we can use the echo header here */
  struct icmp_echo_hdr *icmphdr;
  ip_addr_t iphdr_src;

  /* ICMP header + IP header + 8 bytes of data */
  //为差错报文申请pbuf空间，pbuf中预留IP首部和以太网首部空间，pbuf数据区
  //长度=差错报文首部+差错报文数据长度(IP首部长度+8)
  q = pbuf_alloc(PBUF_IP, sizeof(struct icmp_echo_hdr) + IP_HLEN + ICMP_DEST_UNREACH_DATASIZE,
                 PBUF_RAM);
  if (q == NULL) {//失败，返回
    LWIP_DEBUGF(ICMP_DEBUG, ("icmp_time_exceeded: failed to allocate pbuf for ICMP packet.\n"));
    return;
  }
  LWIP_ASSERT("check that first pbuf can hold icmp message",
             (q->len >= (sizeof(struct icmp_echo_hdr) + IP_HLEN + ICMP_DEST_UNREACH_DATASIZE)));

  iphdr = (struct ip_hdr *)p->payload;//指向引起差错的IP数据包首部
  LWIP_DEBUGF(ICMP_DEBUG, ("icmp_time_exceeded from "));
  ip_addr_debug_print(ICMP_DEBUG, &(iphdr->src));
  LWIP_DEBUGF(ICMP_DEBUG, (" to "));
  ip_addr_debug_print(ICMP_DEBUG, &(iphdr->dest));
  LWIP_DEBUGF(ICMP_DEBUG, ("\n"));

  icmphdr = (struct icmp_echo_hdr *)q->payload;//指向差错报文首部
  icmphdr->type = type;//填写类型字段
  icmphdr->code = code;//填写代码字段
  icmphdr->id = 0;//对于目的不可达和数据报超时
  icmphdr->seqno = 0;//报文，首部剩余的4个字节都为0

  /* copy fields from original packet 将引起差错的IP数据报的IP首部+8字节数据拷贝到差错报文数据区*/
  SMEMCPY((u8_t *)q->payload + sizeof(struct icmp_echo_hdr), (u8_t *)p->payload,
          IP_HLEN + ICMP_DEST_UNREACH_DATASIZE);

  /* calculate checksum */
  icmphdr->chksum = 0;//报文校验和字段清0
  icmphdr->chksum = inet_chksum(icmphdr, q->len);//计算填写校验和
  ICMP_STATS_INC(icmp.xmit);
  /* increase number of messages attempted to send */
  snmp_inc_icmpoutmsgs();
  /* increase number of destination unreachable messages attempted to send */
  snmp_inc_icmpouttimeexcds();
  ip_addr_copy(iphdr_src, iphdr->src);
  ip_output(q, NULL, &iphdr_src, ICMP_TTL, 0, IP_PROTO_ICMP);//调用IP层函数输出ICMP报文
  pbuf_free(q);
}

/**
 * Send a 'time exceeded' packet, called from ip_forward() if TTL is 0.
 *
 * @param p the input packet for which the 'time exceeded' should be sent,
 *          p->payload pointing to the IP header
 * @param t type of the 'time exceeded' packet
 */
void
icmp_time_exceeded(struct pbuf *p, enum icmp_te_type t)
{
  struct pbuf *q;
  struct ip_hdr *iphdr;
  struct icmp_te_hdr *tehdr;

  /* ICMP header + IP header + 8 bytes of data */
  q = pbuf_alloc(PBUF_IP, sizeof(struct icmp_dur_hdr) + IP_HLEN + ICMP_DEST_UNREACH_DATASIZE,
                 PBUF_RAM);
  if (q == NULL) {
    LWIP_DEBUGF(ICMP_DEBUG, ("icmp_time_exceeded: failed to allocate pbuf for ICMP packet.\n"));
    return;
  }
  LWIP_ASSERT("check that first pbuf can hold icmp message",
             (q->len >= (sizeof(struct icmp_dur_hdr) + IP_HLEN + ICMP_DEST_UNREACH_DATASIZE)));

  iphdr = (struct ip_hdr *) p->payload;
  LWIP_DEBUGF(ICMP_DEBUG, ("icmp_time_exceeded from "));
  ip_addr_debug_print(ICMP_DEBUG, &(iphdr->src));
  LWIP_DEBUGF(ICMP_DEBUG, (" to "));
  ip_addr_debug_print(ICMP_DEBUG, &(iphdr->dest));
  LWIP_DEBUGF(ICMP_DEBUG, ("\n"));

  tehdr = (struct icmp_te_hdr *) q->payload;
  ICMPH_TYPE_SET(tehdr, ICMP_TE);
  ICMPH_CODE_SET(tehdr, t);

  /* copy fields from original packet */
  SMEMCPY((u8_t *)q->payload + sizeof(struct icmp_dur_hdr), (u8_t *)p->payload,
          IP_HLEN + ICMP_DEST_UNREACH_DATASIZE);

  /* calculate checksum */
  tehdr->chksum = 0;
  tehdr->chksum = inet_chksum(tehdr, q->len);
  ICMP_STATS_INC(icmp.xmit);
  /* increase number of messages attempted to send */
  snmp_inc_icmpoutmsgs();
  /* increase number of destination unreachable messages attempted to send */
  snmp_inc_icmpouttimeexcds();
  ip_output(q, NULL, &(iphdr->src), ICMP_TTL, 0, IP_PROTO_ICMP);
  pbuf_free(q);
}

/**
 * Send an icmp 'destination unreachable' packet, called from ip_input() if
 * the transport layer protocol is unknown and from udp_input() if the local
 * port is not bound.
 *
 * @param p the input packet for which the 'unreachable' should be sent,
 *          p->payload pointing to the IP header
 * @param t type of the 'unreachable' packet
 */
void
icmp_dest_unreach(struct pbuf *p, enum icmp_dur_type t)
{
  struct pbuf *q;
  struct ip_hdr *iphdr;
  struct icmp_dur_hdr *idur;

  /* ICMP header + IP header + 8 bytes of data */
  q = pbuf_alloc(PBUF_IP, sizeof(struct icmp_dur_hdr) + IP_HLEN + ICMP_DEST_UNREACH_DATASIZE,
                 PBUF_RAM);
  if (q == NULL) {
    LWIP_DEBUGF(ICMP_DEBUG, ("icmp_dest_unreach: failed to allocate pbuf for ICMP packet.\n"));
    return;
  }
  LWIP_ASSERT("check that first pbuf can hold icmp message",
             (q->len >= (sizeof(struct icmp_dur_hdr) + IP_HLEN + ICMP_DEST_UNREACH_DATASIZE)));

  iphdr = p->payload;

  idur = q->payload;
  ICMPH_TYPE_SET(idur, ICMP_DUR);
  ICMPH_CODE_SET(idur, t);

  SMEMCPY((u8_t *)q->payload + sizeof(struct icmp_dur_hdr), p->payload,
          IP_HLEN + ICMP_DEST_UNREACH_DATASIZE);

  /* calculate checksum */
  idur->chksum = 0;
  idur->chksum = inet_chksum(idur, q->len);
  ICMP_STATS_INC(icmp.xmit);
  /* increase number of messages attempted to send */
  snmp_inc_icmpoutmsgs();
  /* increase number of destination unreachable messages attempted to send */
  snmp_inc_icmpoutdestunreachs();

  ip_output(q, NULL, &(iphdr->src), ICMP_TTL, 0, IP_PROTO_ICMP);
  pbuf_free(q);
}

/**
 * Processes ICMP input packets, called from ip_input().
 *
 * Currently only processes icmp echo requests and sends
 * out the echo response.
 *
 * @param p the icmp echo request packet, p->payload pointing to the icmp header
 * @param inp the netif on which this packet was received
 */
void
icmp_input(struct pbuf *p, struct netif *inp)
{
  u8_t type;
#ifdef LWIP_DEBUG
  u8_t code;
#endif /* LWIP_DEBUG */
  struct icmp_echo_hdr *iecho;
  struct ip_hdr *iphdr;
  s16_t hlen;

  ICMP_STATS_INC(icmp.recv);
  snmp_inc_icmpinmsgs();

  iphdr = (struct ip_hdr *)ip_current_header();
  hlen = IPH_HL(iphdr) * 4;
  if (p->len < sizeof(u16_t)*2) {
    LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: short ICMP (%"U16_F" bytes) received\n", p->tot_len));
    goto lenerr;
  }

  type = *((u8_t *)p->payload);
#ifdef LWIP_DEBUG
  code = *(((u8_t *)p->payload)+1);
#endif /* LWIP_DEBUG */
  switch (type) {
  case ICMP_ER:
    /* This is OK, echo reply might have been parsed by a raw PCB
       (as obviously, an echo request has been sent, too). */
    break; 
  case ICMP_ECHO:
#if !LWIP_MULTICAST_PING || !LWIP_BROADCAST_PING
    {
      int accepted = 1;
#if !LWIP_MULTICAST_PING
      /* multicast destination address? */
      if (ip_addr_ismulticast(ip_current_dest_addr())) {
        accepted = 0;
      }
#endif /* LWIP_MULTICAST_PING */
#if !LWIP_BROADCAST_PING
      /* broadcast destination address? */
      if (ip_addr_isbroadcast(ip_current_dest_addr(), inp)) {
        accepted = 0;
      }
#endif /* LWIP_BROADCAST_PING */
      /* broadcast or multicast destination address not acceptd? */
      if (!accepted) {
        LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: Not echoing to multicast or broadcast pings\n"));
        ICMP_STATS_INC(icmp.err);
        pbuf_free(p);
        return;
      }
    }
#endif /* !LWIP_MULTICAST_PING || !LWIP_BROADCAST_PING */
    LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: ping\n"));
    if (p->tot_len < sizeof(struct icmp_echo_hdr)) {
      LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: bad ICMP echo received\n"));
      goto lenerr;
    }
#if CHECKSUM_CHECK_ICMP
    if (inet_chksum_pbuf(p) != 0) {
      LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: checksum failed for received ICMP echo\n"));
      pbuf_free(p);
      ICMP_STATS_INC(icmp.chkerr);
      snmp_inc_icmpinerrors();
      return;
    }
#endif
#if LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN
    if (pbuf_header(p, (PBUF_IP_HLEN + PBUF_LINK_HLEN))) {
      /* p is not big enough to contain link headers
       * allocate a new one and copy p into it
       */
      struct pbuf *r;
      /* switch p->payload to ip header */
      if (pbuf_header(p, hlen)) {
        LWIP_ASSERT("icmp_input: moving p->payload to ip header failed\n", 0);
        goto memerr;
      }
      /* allocate new packet buffer with space for link headers */
      r = pbuf_alloc(PBUF_LINK, p->tot_len, PBUF_RAM);
      if (r == NULL) {
        LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: allocating new pbuf failed\n"));
        goto memerr;
      }
      LWIP_ASSERT("check that first pbuf can hold struct the ICMP header",
                  (r->len >= hlen + sizeof(struct icmp_echo_hdr)));
      /* copy the whole packet including ip header */
      if (pbuf_copy(r, p) != ERR_OK) {
        LWIP_ASSERT("icmp_input: copying to new pbuf failed\n", 0);
//.........这里部分代码省略.........

/**
 * Proxy ICMP input packets, called from ip_input().
 *
 * @param p the icmp echo request packet, p->payload pointing to the icmp header
 * @param inp the netif on which this packet was received
 */
void
icmp_proxy_input(struct pbuf *p, struct netif *inp)
{
  u8_t type, code;
# ifdef VBOX
  (void)inp;
# endif

  ICMP_STATS_INC(icmp.recv);
  snmp_inc_icmpinmsgs();

  if (p->tot_len < 4) {         /* type(1), code(1), checksum(2) */
    LWIP_DEBUGF(ICMP_DEBUG,
      ("icmp_proxy_input: short ICMP (%"U16_F" bytes) received\n",
       p->tot_len));
    goto lenerr;
  }

  if (inet_chksum_pbuf(p) != 0) {
    LWIP_DEBUGF(ICMP_DEBUG, ("icmp_proxy_input: bad checksum\n"));
    pbuf_free(p);
    ICMP_STATS_INC(icmp.chkerr);
    snmp_inc_icmpinerrors();
    return;
  }

  type = *((u8_t *)p->payload);
  code = *(((u8_t *)p->payload)+1);
  switch (type) {

  case ICMP_ER:
    /* ignore silently */
    pbuf_free(p);
    break;

  case ICMP_DUR:
    /* TODO: anything useful we can do? */
    pbuf_free(p);
    break;

  case ICMP_ECHO:
    if (code != 0) {
      goto proterr;
    }
    if (p->tot_len < 8) {
      goto lenerr;
    }

    if (ping_proxy_accept_callback != NULL) {
      (*ping_proxy_accept_callback)(ping_proxy_accept_arg, p);
    }
    break;

  default:
    goto proterr;
  }
  return;

 lenerr:  
  ICMP_STATS_INC(icmp.lenerr);
  goto drop;

 proterr:
  LWIP_DEBUGF(ICMP_DEBUG,
              ("icmp_proxy_input: ICMP type %"S16_F" code %"S16_F
               " not supported.\n",
               (s16_t)type, (s16_t)code));
  ICMP_STATS_INC(icmp.proterr);
  goto drop;

 drop:
  pbuf_free(p);
  ICMP_STATS_INC(icmp.drop);
  snmp_inc_icmpinerrors();
  return;
}

/**
 * Processes ICMP input packets, called from ip_input().
 *
 * Currently only processes icmp echo requests and sends
 * out the echo response.
 *
 * @param p the icmp echo request packet, p->payload pointing to the ip header
 * @param inp the netif on which this packet was received
 */
void
icmp_input(struct pbuf *p, struct netif *inp)
{
  u8_t type;
#ifdef LWIP_DEBUG
  u8_t code;
#endif /* LWIP_DEBUG */
  struct icmp_echo_hdr *iecho;
  struct ip_hdr *iphdr;
  struct ip_addr tmpaddr;
  s16_t hlen;

  u8_t iptxt[20];
  volatile u8_t iptab[4];
  u32_t IPaddress;
  
  ICMP_STATS_INC(icmp.recv);
  snmp_inc_icmpinmsgs();


  iphdr = p->payload;
  hlen = IPH_HL(iphdr) * 4;
  if (pbuf_header(p, -hlen) || (p->tot_len < sizeof(u16_t)*2)) {
    LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: short ICMP (%"U16_F" bytes) received\n", p->tot_len));
    goto lenerr;
  }

  IPaddress = iphdr->src.addr;
  
  /* read its IP address */
  iptab[0] = (u8_t)(IPaddress >> 24);
  iptab[1] = (u8_t)(IPaddress >> 16);
  iptab[2] = (u8_t)(IPaddress >> 8);
  iptab[3] = (u8_t)(IPaddress);

  sprintf((char*)iptxt, "Ping: %d.%d.%d.%d   ", iptab[3], iptab[2], iptab[1], iptab[0]);	
  
  LCD_DisplayStringLine(Line4, iptxt);

  printf("\n\r%s", iptxt);
  
  
  type = *((u8_t *)p->payload);
#ifdef LWIP_DEBUG
  code = *(((u8_t *)p->payload)+1);
#endif /* LWIP_DEBUG */
  switch (type) {
  case ICMP_ECHO:
#if !LWIP_MULTICAST_PING || !LWIP_BROADCAST_PING
    {
      int accepted = 1;
#if !LWIP_MULTICAST_PING
      /* multicast destination address? */
      if (ip_addr_ismulticast(&iphdr->dest)) {
        accepted = 0;
      }
#endif /* LWIP_MULTICAST_PING */
#if !LWIP_BROADCAST_PING
      /* broadcast destination address? */
      if (ip_addr_isbroadcast(&iphdr->dest, inp)) {
        accepted = 0;
      }
#endif /* LWIP_BROADCAST_PING */
      /* broadcast or multicast destination address not acceptd? */
      if (!accepted) {
        LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: Not echoing to multicast or broadcast pings\n"));
        ICMP_STATS_INC(icmp.err);
        pbuf_free(p);
        return;
      }
    }
#endif /* !LWIP_MULTICAST_PING || !LWIP_BROADCAST_PING */
    LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: ping\n"));
    if (p->tot_len < sizeof(struct icmp_echo_hdr)) {
      LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: bad ICMP echo received\n"));
      goto lenerr;
    }
    if (inet_chksum_pbuf(p) != 0) {
      LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: checksum failed for received ICMP echo\n"));
      pbuf_free(p);
      ICMP_STATS_INC(icmp.chkerr);
      snmp_inc_icmpinerrors();
      return;
    }
#if LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN
    if (pbuf_header(p, (PBUF_IP_HLEN + PBUF_LINK_HLEN))) {
      /* p is not big enough to contain link headers
       * allocate a new one and copy p into it
       */
      struct pbuf *r;
      /* switch p->payload to ip header */
//.........这里部分代码省略.........

/* 调用途径：ethernetif_input() -> ethernet_input() -> ip_input() -> icmp_input()*/
void
icmp_input(struct pbuf *p, struct netif *inp)
{
  u8_t type;
#ifdef LWIP_DEBUG
  u8_t code;
#endif /* LWIP_DEBUG */
  struct icmp_echo_hdr *iecho;
  struct ip_hdr *iphdr;
	/* IP 地址 */
  struct ip_addr tmpaddr;
  s16_t hlen;

  ICMP_STATS_INC(icmp.recv);
  snmp_inc_icmpinmsgs();


	/* 指向IP首部 */
  iphdr = p->payload;
	/* 获得IP报头长度 */
  hlen = IPH_HL(iphdr) * 4;
	/* pbuf的payload向后移动到IP载荷，即ICMP报头处
	 * 如果IP的载荷小于4字节，则跳到lenerr处，释放pbuf
	 */
  if (pbuf_header(p, -hlen) || (p->tot_len < sizeof(u16_t)*2)) {
    LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: short ICMP (%"U16_F" bytes) received\n", p->tot_len));
    goto lenerr;
  }

	/* 获取ICMP报头中的类型 */
  type = *((u8_t *)p->payload);
#ifdef LWIP_DEBUG
  code = *(((u8_t *)p->payload)+1);
#endif /* LWIP_DEBUG */
  switch (type) {
	/* 如果ICMP类型是回显请求 */
  case ICMP_ECHO:
		/* 先检查目的IP地址是否合法 */
#if !LWIP_MULTICAST_PING || !LWIP_BROADCAST_PING
    {
			/* accepted表示是否对ICMP回显请求进行回应 */
      int accepted = 1;
#if !LWIP_MULTICAST_PING
      /* multicast destination address? */
			/* 如果目的IP地址是多播地址，则不回应 */
      if (ip_addr_ismulticast(&iphdr->dest)) {
        accepted = 0;
      }
#endif /* LWIP_MULTICAST_PING */
#if !LWIP_BROADCAST_PING
      /* broadcast destination address? */
			/* 如果目的IP地址是广播地址，则不回应 */
      if (ip_addr_isbroadcast(&iphdr->dest, inp)) {
        accepted = 0;
      }
#endif /* LWIP_BROADCAST_PING */
      /* broadcast or multicast destination address not acceptd? */
			/* 如果不回应，则释放pbuf后，返回 */
      if (!accepted) {
        LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: Not echoing to multicast or broadcast pings\n"));
        ICMP_STATS_INC(icmp.err);
        pbuf_free(p);
        return;
      }
    }
#endif /* !LWIP_MULTICAST_PING || !LWIP_BROADCAST_PING */
    LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: ping\n"));
		/* 检查ICMP报文长度是否合法,ICMP报文总长度不能小于ICMP报头长度8字节 */
    if (p->tot_len < sizeof(struct icmp_echo_hdr)) {
      LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: bad ICMP echo received\n"));
			/* 跳到lenerr处执行返回操作 */
      goto lenerr;
    }
		/* 计算ICMP的校验和是否正确 */
    if (inet_chksum_pbuf(p) != 0) {
      LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: checksum failed for received ICMP echo\n"));
			/* ICMP校验和错误，则释放pbuf，并返回 */
      pbuf_free(p);
      ICMP_STATS_INC(icmp.chkerr);
      snmp_inc_icmpinerrors();
      return;
    }
#if LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN
    if (pbuf_header(p, (PBUF_IP_HLEN + PBUF_LINK_HLEN))) {
      /* p is not big enough to contain link headers
       * allocate a new one and copy p into it
       */
      struct pbuf *r;
      /* switch p->payload to ip header */
      if (pbuf_header(p, hlen)) {
        LWIP_ASSERT("icmp_input: moving p->payload to ip header failed\n", 0);
        goto memerr;
      }
      /* allocate new packet buffer with space for link headers */
      r = pbuf_alloc(PBUF_LINK, p->tot_len, PBUF_RAM);
      if (r == NULL) {
        LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: allocating new pbuf failed\n"));
        goto memerr;
      }
//.........这里部分代码省略.........

void
icmp_input(struct pbuf *p, struct netif *inp)
{
  u8_t type;
  u8_t code;
  struct icmp_echo_hdr *iecho;
  struct ip_hdr *iphdr;
  struct ip_addr tmpaddr;
  u16_t hlen;
  u8_t   *payload = NULL;

  ICMP_STATS_INC(icmp.recv);
  snmp_inc_icmpinmsgs();


  iphdr = p->payload;
  hlen = IPH_HL(iphdr) * 4;
  if (p->tot_len < sizeof(u16_t)*2) {
    LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: short ICMP (%"U16_F" bytes) received\n", p->tot_len));
    pbuf_free(p);
    ICMP_STATS_INC(icmp.lenerr);
    snmp_inc_icmpinerrors();
    return;
  }

  payload = (u8_t *)p->payload + hlen;

  type = *payload;
  code = *(payload+1);
  switch (type) {
  case ICMP_ECHO:
    /* broadcast or multicast destination address? */
    if (ip_addr_isbroadcast(&iphdr->dest, inp) || ip_addr_ismulticast(&iphdr->dest)) {
      LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: Not echoing to multicast or broadcast pings\n"));
      ICMP_STATS_INC(icmp.err);
      pbuf_free(p);
      return;
    }
    LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: ping\n"));
    if (p->tot_len < sizeof(struct icmp_echo_hdr)) {
      LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: bad ICMP echo received\n"));
      pbuf_free(p);
      ICMP_STATS_INC(icmp.lenerr);
      snmp_inc_icmpinerrors();

      return;
    }
    iecho = (struct icmp_echo_hdr *)payload;
    if (inet_chksum_pbuf(p) != 0) {
      LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: checksum failed for received ICMP echo\n"));
      pbuf_free(p);
      ICMP_STATS_INC(icmp.chkerr);
      snmp_inc_icmpinerrors();
      return;
    }
    tmpaddr.addr = iphdr->src.addr;
    iphdr->src.addr = iphdr->dest.addr;
    iphdr->dest.addr = tmpaddr.addr;
    ICMPH_TYPE_SET(iecho, ICMP_ER);
    /* adjust the checksum */
    if (iecho->chksum >= htons(0xffff - (ICMP_ECHO << 8))) {
      iecho->chksum += htons(ICMP_ECHO << 8) + 1;
    } else {
      iecho->chksum += htons(ICMP_ECHO << 8);
    }
    ICMP_STATS_INC(icmp.xmit);
    /* increase number of messages attempted to send */
    snmp_inc_icmpoutmsgs();
    /* increase number of echo replies attempted to send */
    snmp_inc_icmpoutechoreps();

    pbuf_header(p, hlen);
    ip_output_if(p, &(iphdr->src), IP_HDRINCL,
		 IPH_TTL(iphdr), 0, IP_PROTO_ICMP, inp);
    break;
  default:
  LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: ICMP type %"S16_F" code %"S16_F" not supported.\n", (s16_t)type, (s16_t)code));
    ICMP_STATS_INC(icmp.proterr);
    ICMP_STATS_INC(icmp.drop);
  }

  pbuf_free(p);
}

/**
 * Processes ICMP input packets, called from ip_input().
 *
 * Currently only processes icmp echo requests and sends
 * out the echo response.
 *
 * @param p the icmp echo request packet, p->payload pointing to the icmp header
 * @param inp the netif on which this packet was received
 */
void
icmp_input(struct pbuf *p, struct netif *inp)
{
  u8_t type;
#ifdef LWIP_DEBUG
  u8_t code;
#endif /* LWIP_DEBUG */
  struct icmp_echo_hdr *iecho;
  const struct ip_hdr *iphdr_in;
  s16_t hlen;
  const ip4_addr_t* src;

  ICMP_STATS_INC(icmp.recv);
  MIB2_STATS_INC(mib2.icmpinmsgs);

  iphdr_in = ip4_current_header();
  hlen = IPH_HL(iphdr_in) * 4;
  if (hlen < IP_HLEN) {
    LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: short IP header (%"S16_F" bytes) received\n", hlen));
    goto lenerr;
  }
  if (p->len < sizeof(u16_t)*2) {
    LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: short ICMP (%"U16_F" bytes) received\n", p->tot_len));
    goto lenerr;
  }

  type = *((u8_t *)p->payload);
#ifdef LWIP_DEBUG
  code = *(((u8_t *)p->payload)+1);
#endif /* LWIP_DEBUG */
  switch (type) {
  case ICMP_ER:
    /* This is OK, echo reply might have been parsed by a raw PCB
       (as obviously, an echo request has been sent, too). */
    MIB2_STATS_INC(mib2.icmpinechoreps);
    break;
  case ICMP_ECHO:
    MIB2_STATS_INC(mib2.icmpinechos);
    src = ip4_current_dest_addr();
    /* multicast destination address? */
    if (ip4_addr_ismulticast(ip4_current_dest_addr())) {
#if LWIP_MULTICAST_PING
      /* For multicast, use address of receiving interface as source address */
      src = netif_ip4_addr(inp);
#else /* LWIP_MULTICAST_PING */
      LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: Not echoing to multicast pings\n"));
      goto icmperr;
#endif /* LWIP_MULTICAST_PING */
    }
    /* broadcast destination address? */
    if (ip4_addr_isbroadcast(ip4_current_dest_addr(), ip_current_netif())) {
#if LWIP_BROADCAST_PING
      /* For broadcast, use address of receiving interface as source address */
      src = netif_ip4_addr(inp);
#else /* LWIP_BROADCAST_PING */
      LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: Not echoing to broadcast pings\n"));
      goto icmperr;
#endif /* LWIP_BROADCAST_PING */
    }
    LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: ping\n"));
    if (p->tot_len < sizeof(struct icmp_echo_hdr)) {
      LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: bad ICMP echo received\n"));
      goto lenerr;
    }
#if CHECKSUM_CHECK_ICMP
    IF__NETIF_CHECKSUM_ENABLED(inp, NETIF_CHECKSUM_CHECK_ICMP) {
      if (inet_chksum_pbuf(p) != 0) {
        LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: checksum failed for received ICMP echo\n"));
        pbuf_free(p);
        ICMP_STATS_INC(icmp.chkerr);
        MIB2_STATS_INC(mib2.icmpinerrors);
        return;
      }
    }
#endif
#if LWIP_ICMP_ECHO_CHECK_INPUT_PBUF_LEN
    if (pbuf_header(p, (hlen + PBUF_LINK_HLEN + PBUF_LINK_ENCAPSULATION_HLEN))) {
      /* p is not big enough to contain link headers
       * allocate a new one and copy p into it
       */
      struct pbuf *r;
      /* allocate new packet buffer with space for link headers */
      r = pbuf_alloc(PBUF_LINK, p->tot_len + hlen, PBUF_RAM);
      if (r == NULL) {
        LWIP_DEBUGF(ICMP_DEBUG, ("icmp_input: allocating new pbuf failed\n"));
        goto icmperr;
      }
      if (r->len < hlen + sizeof(struct icmp_echo_hdr)) {
        LWIP_DEBUGF(ICMP_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("first pbuf cannot hold the ICMP header"));
        pbuf_free(r);
        goto icmperr;
//.........这里部分代码省略.........