原文地址为:http://blog.csdn.net/yuzhihui_no1/article/details/39481745
其实想了很久要不要去分析下key值得提取,因为key值的提取是比较简单的,而且没多大实用。因为你不可能去修改key的结构,也不可能去修改key值得提取函数(当然了除非你想重构openVswitch整个项目),更不可能在key提取函数中添加自己的代码。因此对于分析key值没有多大的实用性。但我依然去简单分析key值得提取函数,有两个原因:第一、key值作为数据结构在openVswitch中是非常重要的,后期的一些流表查询和匹配都要用到key值;第二、想借机复习下内核网络协议栈的各层协议信息;
首先来看下各层协议的协议信息:
第一、二层帧头信息
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struct ethhdr {
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unsigned char h_dest[ETH_ALEN]; /*目标Mac地址 6个字节*/
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unsigned char h_source[ETH_ALEN]; /*源Mac地址*/
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__be16 h_proto; /*包的协议类型 IP包:0x800;ARP包:0x806;IPV6:0x86DD*/
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} __attribute__((packed));
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/*从skb网络数据包中获取到帧头*/
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static inline struct ethhdr *eth_hdr(const struct sk_buff *skb)
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{
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return (struct ethhdr *)skb_mac_header(skb);
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}
第二、三层网络层IP头信息
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/*IPV4头结构体*/
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struct iphdr {
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#if defined(__LITTLE_ENDIAN_BITFIELD)
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__u8 ihl:4, // 报文头部长度
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version:4; // 版本IPv4
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#elif defined (__BIG_ENDIAN_BITFIELD)
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__u8 version:4,
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ihl:4;
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#else
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#error "Please fix "
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#endif
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__u8 tos; // 服务类型
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__be16 tot_len; // 报文总长度
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__be16 id; // 标志符
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__be16 frag_off; // 片偏移量
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__u8 ttl; // 生存时间
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__u8 protocol; // 协议类型 TCP:6;UDP:17
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__sum16 check; // 报头校验和
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__be32 saddr; // 源IP地址
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__be32 daddr; // 目的IP地址
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/*The options start here. */
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};
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#ifdef __KERNEL__
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#include <linux/skbuff.h>
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/*通过数据包skb获取到IP头部结构体指针*/
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static inline struct iphdr *ip_hdr(const struct sk_buff *skb)
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{
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return (struct iphdr *)skb_network_header(skb);
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}
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/*通过数据包skb获取到二层帧头结构体指针*/
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static inline struct iphdr *ipip_hdr(const struct sk_buff *skb)
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{
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return (struct iphdr *)skb_transport_header(skb);
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}
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第三、ARP协议头信息
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struct arphdr
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{
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__be16 ar_hrd; /* format of hardware address硬件类型 */
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__be16 ar_pro; /* format of protocol address协议类型 */
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unsigned char ar_hln; /* length of hardware address硬件长度 */
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unsigned char ar_pln; /* length of protocol address协议长度 */
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__be16 ar_op; /* ARP opcode (command)操作,请求:1;应答:2;*/
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#if 0 //下面被注释掉了,使用时要自己定义结构体
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/*
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* Ethernet looks like this : This bit is variable sized however...
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*/
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unsigned char ar_sha[ETH_ALEN]; /* sender hardware address源Mac */
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unsigned char ar_sip[4]; /* sender IP address源IP */
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unsigned char ar_tha[ETH_ALEN]; /* target hardware address目的Mac */
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unsigned char ar_tip[4]; /* target IP address 目的IP */
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#endif
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};
对于传输层协议信息TCP/UDP协议头信息比较多,这里就不分析了。下面直接来看key值提取代码:
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int ovs_flow_extract(struct sk_buff *skb, u16 in_port, struct sw_flow_key *key)
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{
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int error;
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struct ethhdr *eth; //帧头协议结构指针
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memset(key, 0, sizeof(*key));// 初始化key为0
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key->phy.priority = skb->priority;//赋值skb数据包的优先级
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if (OVS_CB(skb)->tun_key)
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memcpy(&key->tun_key, OVS_CB(skb)->tun_key, sizeof(key->tun_key));
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key->phy.in_port = in_port;// 端口成员的设置
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key->phy.skb_mark = skb_get_mark(skb);//默认为0
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skb_reset_mac_header(skb);//该函数的实现skb->mac_header = skb->data;
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/* Link layer. We are guaranteed to have at least the 14 byte Ethernet
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* header in the linear data area.
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*/
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eth = eth_hdr(skb); //获取到以太网帧头信息
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memcpy(key->eth.src, eth->h_source, ETH_ALEN);// 源地址成员赋值
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memcpy(key->eth.dst, eth->h_dest, ETH_ALEN);// 目的地址成员赋值
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__skb_pull(skb, 2 * ETH_ALEN);//这是移动skb结构中指针
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if (vlan_tx_tag_present(skb))// 数据包的类型判断设置
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key->eth.tci = htons(vlan_get_tci(skb));
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else if (eth->h_proto == htons(ETH_P_8021Q))// 协议类型设置
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if (unlikely(parse_vlan(skb, key)))
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return -ENOMEM;
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key->eth.type = parse_ethertype(skb);//包的类型设置,即是IP包还是ARP包
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if (unlikely(key->eth.type == htons(0)))
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return -ENOMEM;
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skb_reset_network_header(skb);// 函数实现:skb->nh.raw = skb->data;
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__skb_push(skb, skb->data - skb_mac_header(skb));// 移动skb中的指针
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/* Network layer. */
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// 判断是否是邋IP数据包,如果是则设置IP相关字段
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if (key->eth.type == htons(ETH_P_IP)) {
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struct iphdr *nh;//设置IP协议头信息结构体指针
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__be16 offset;// 大端格式short类型变量
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error = check_iphdr(skb);// 检测IP协议头信息
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if (unlikely(error)) {
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if (error == -EINVAL) {
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skb->transport_header = skb->network_header;
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error = 0;
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}
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return error;
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}
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nh = ip_hdr(skb);// 函数实现:return (struct iphdr *)skb_network_header(skb);
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// 下面就是IP协议头的一些字段的赋值
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key->ipv4.addr.src = nh->saddr;
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key->ipv4.addr.dst = nh->daddr;
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key->ip.proto = nh->protocol;
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key->ip.tos = nh->tos;
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key->ip.ttl = nh->ttl;
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offset = nh->frag_off & htons(IP_OFFSET);
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if (offset) {
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key->ip.frag = OVS_FRAG_TYPE_LATER;
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return 0;
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}
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if (nh->frag_off & htons(IP_MF) ||
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skb_shinfo(skb)->gso_type & SKB_GSO_UDP)
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key->ip.frag = OVS_FRAG_TYPE_FIRST;
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/* Transport layer. */
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if (key->ip.proto == IPPROTO_TCP) {
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if (tcphdr_ok(skb)) {
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struct tcphdr *tcp = tcp_hdr(skb);
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key->ipv4.tp.src = tcp->source;
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key->ipv4.tp.dst = tcp->dest;
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}
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} else if (key->ip.proto == IPPROTO_UDP) {
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if (udphdr_ok(skb)) {
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struct udphdr *udp = udp_hdr(skb);
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key->ipv4.tp.src = udp->source;
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key->ipv4.tp.dst = udp->dest;
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}
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} else if (key->ip.proto == IPPROTO_ICMP) {
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if (icmphdr_ok(skb)) {
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struct icmphdr *icmp = icmp_hdr(skb);
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/* The ICMP type and code fields use the 16-bit
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* transport port fields, so we need to store
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* them in 16-bit network byte order. */
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key->ipv4.tp.src = htons(icmp->type);
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key->ipv4.tp.dst = htons(icmp->code);
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}
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}
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// 判断是否是ARP数据包,设置ARP数据包字段
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} else if ((key->eth.type == htons(ETH_P_ARP) ||
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key->eth.type == htons(ETH_P_RARP)) && arphdr_ok(skb)) {
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struct arp_eth_header *arp; // 定义ARP协议头结构体指针
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arp = (struct arp_eth_header *)skb_network_header(skb);// return skb->nh.raw;
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// 下面就是一些ARP数据包字段的设置
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if (arp->ar_hrd == htons(ARPHRD_ETHER)
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&& arp->ar_pro == htons(ETH_P_IP)
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&& arp->ar_hln == ETH_ALEN
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&& arp->ar_pln == 4) {
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/* We only match on the lower 8 bits of the opcode. */
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if (ntohs(arp->ar_op) <= 0xff)
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key->ip.proto = ntohs(arp->ar_op);
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memcpy(&key->ipv4.addr.src, arp->ar_sip, sizeof(key->ipv4.addr.src));
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memcpy(&key->ipv4.addr.dst, arp->ar_tip, sizeof(key->ipv4.addr.dst));
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memcpy(key->ipv4.arp.sha, arp->ar_sha, ETH_ALEN);
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memcpy(key->ipv4.arp.tha, arp->ar_tha, ETH_ALEN);
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}
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//判断是否是IPV6数据包,设置IPV6数据包字段
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} else if (key->eth.type == htons(ETH_P_IPV6)) {
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int nh_len; /* IPv6 Header + Extensions */
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// IPV6就不分析了
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nh_len = parse_ipv6hdr(skb, key);
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if (unlikely(nh_len < 0)) {
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if (nh_len == -EINVAL) {
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skb->transport_header = skb->network_header;
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error = 0;
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} else {
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error = nh_len;
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}
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return error;
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}
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if (key->ip.frag == OVS_FRAG_TYPE_LATER)
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return 0;
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if (skb_shinfo(skb)->gso_type & SKB_GSO_UDP)
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key->ip.frag = OVS_FRAG_TYPE_FIRST;
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/* Transport layer. */
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if (key->ip.proto == NEXTHDR_TCP) {
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if (tcphdr_ok(skb)) {
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struct tcphdr *tcp = tcp_hdr(skb);
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key->ipv6.tp.src = tcp->source;
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key->ipv6.tp.dst = tcp->dest;
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}
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} else if (key->ip.proto == NEXTHDR_UDP) {
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if (udphdr_ok(skb)) {
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struct udphdr *udp = udp_hdr(skb);
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key->ipv6.tp.src = udp->source;
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key->ipv6.tp.dst = udp->dest;
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}
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} else if (key->ip.proto == NEXTHDR_ICMP) {
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if (icmp6hdr_ok(skb)) {
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error = parse_icmpv6(skb, key, nh_len);
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if (error)
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return error;
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}
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}
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}
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return 0;
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}
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