lwip 分析一

爱被打了一巴掌 2022-03-16 04:10 310阅读 0赞

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\\n"));  
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"\\n", 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.\\n",  
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.\\n",  
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.\\n", 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")\\n",  
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\\n",  
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"\\n",  
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.\\n"));  
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.\\n"));  
/\* 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.\\n"));  
\#if IP\_FORWARD //如果只有一个[网络接口卡][Link 1]，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()\\n",  
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).\\n",  
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).\\n"));  
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: \\n"));  
ip\_debug\_print(p);  
LWIP\_DEBUGF(IP\_DEBUG, ("ip\_input: p->len %"U16\_F" p->tot\_len %"U16\_F"\\n", 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"\\n", 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

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