【Linux4.1.12源码分析】协议栈gro收包之IP层处理

IP层的offload定义是ip_packet_offload

static struct packet_offload ip_packet_offload __read_mostly = {.type = cpu_to_be16(ETH_P_IP),.callbacks = {.gso_segment = inet_gso_segment,.gro_receive = inet_gro_receive,.gro_complete = inet_gro_complete,},};

inet_gro_receive函数

static struct sk_buff **inet_gro_receive(struct sk_buff **head, struct sk_buff *skb){const struct net_offload *ops;struct sk_buff **pp = NULL;struct sk_buff *p;const struct iphdr *iph;unsigned int hlen;unsigned int off;unsigned int id;int flush = 1;int proto;off = skb_gro_offset(skb);hlen = off + sizeof(*iph);iph = skb_gro_header_fast(skb, off);//得到IP头，内核支持两种skb，放在线性区和放在fragif (skb_gro_header_hard(skb, hlen)) {iph = skb_gro_header_slow(skb, hlen, off);if (unlikely(!iph))goto out;}proto = iph->protocol;//得到传输层协议rcu_read_lock();ops = rcu_dereference(inet_offloads[proto]);//得到传输层对应的offloadif (!ops || !ops->callbacks.gro_receive)//如果未找到对应的offload，则报文将被提交给协议栈goto out_unlock;if (*(u8 *)iph != 0x45)//IP报文的协议版本必须为4，且报文头长度为20（5*4），否则报文将被提交给协议栈goto out_unlock;if (unlikely(ip_fast_csum((u8 *)iph, 5)))//IP头csum校验，如果通不过，则flush置1，报文将被提交给协议栈goto out_unlock;id = ntohl(*(__be32 *)&iph->id);//得到16位的ID值，3位flag和13位分片偏移flush = (u16)((ntohl(*(__be32 *)iph) ^ skb_gro_len(skb)) | (id & ~IP_DF)); //IP报文数据长度不等于gro_len或者报文携带DF标记，flush置1id >>= 16;for (p = *head; p; p = p->next) {//遍历gro_list中的报文struct iphdr *iph2;if (!NAPI_GRO_CB(p)->same_flow)//same_flow为零说明MAC的流匹配未通过，不需要下一步处理continue;iph2 = (struct iphdr *)(p->data + off); //得到报文的IP头，此时采用线性区的方式，从当前报文的IP头获取方式，此处也将会改变/* The above works because, with the exception of the top * (inner most) layer, we only aggregate pkts with the same * hdr length so all the hdrs we'll need to verify will start * at the same offset. */if ((iph->protocol ^ iph2->protocol) |//IP层判断同一个流，要求：4层协议要相同    ((__force u32)iph->saddr ^ (__force u32)iph2->saddr) |//源地址要相同    ((__force u32)iph->daddr ^ (__force u32)iph2->daddr)) {//目标地址要相同NAPI_GRO_CB(p)->same_flow = 0;continue;}/* All fields must match except length and checksum. */NAPI_GRO_CB(p)->flush |=(iph->ttl ^ iph2->ttl) |//同一个流，但是ttl、tos、有一个报文包含DF标记，则需要flush当前该报文(iph->tos ^ iph2->tos) |((iph->frag_off ^ iph2->frag_off) & htons(IP_DF));/* Save the IP ID check to be included later when we get to * the transport layer so only the inner most IP ID is checked. * This is because some GSO/TSO implementations do not * correctly increment the IP ID for the outer hdrs. */NAPI_GRO_CB(p)->flush_id =    ((u16)(ntohs(iph2->id) + NAPI_GRO_CB(p)->count) ^ id);NAPI_GRO_CB(p)->flush |= flush;//刷新报文的flush}NAPI_GRO_CB(skb)->flush |= flush;//刷新当前报文的flushskb_set_network_header(skb, off);//设置network header，可以找到IP头/* The above will be needed by the transport layer if there is one * immediately following this IP hdr. *//* Note : No need to call skb_gro_postpull_rcsum() here, * as we already checked checksum over ipv4 header was 0 */skb_gro_pull(skb, sizeof(*iph));//报文移动到4层头skb_set_transport_header(skb, skb_gro_offset(skb));//设置传输层header值pp = ops->callbacks.gro_receive(head, skb);//调用4层的offloadout_unlock:rcu_read_unlock();out:NAPI_GRO_CB(skb)->flush |= flush;//刷新当前报文的flush，调用四层offload后，可能会刷新return pp;}

inet_gro_complete函数

static int inet_gro_complete(struct sk_buff *skb, int nhoff){__be16 newlen = htons(skb->len - nhoff);struct iphdr *iph = (struct iphdr *)(skb->data + nhoff);//找到IP头const struct net_offload *ops;int proto = iph->protocol;int err = -ENOSYS;if (skb->encapsulation)skb_set_inner_network_header(skb, nhoff);   //如果报文是封装报文，那么iph指向的就是内层报文csum_replace2(&iph->check, iph->tot_len, newlen);//由于长度变化，刷新csum值iph->tot_len = newlen;//指定IP头中的长度字段rcu_read_lock();ops = rcu_dereference(inet_offloads[proto]);//找到传输层的offloadif (WARN_ON(!ops || !ops->callbacks.gro_complete))goto out_unlock;/* Only need to add sizeof(*iph) to get to the next hdr below * because any hdr with option will have been flushed in * inet_gro_receive(). */err = ops->callbacks.gro_complete(skb, nhoff + sizeof(*iph));//调用传输层的gro_complete函数out_unlock:rcu_read_unlock();return err;}

inet_gro_receive函数完成same_flow和flush判断，inet_gro_complete用于刷新IP头信息。