LRO -- skb_buff->frags[] & skb_buff->frag_list

/*更新整個lro skb的相關數據*/
static void lro_add_common(struct net_lro_desc *lro_desc, struct iphdr *iph,
			   struct tcphdr *tcph, int tcp_data_len)
{
	struct sk_buff *parent = lro_desc->parent;
	__be32 *topt;

	lro_desc->pkt_aggr_cnt++;
	lro_desc->ip_tot_len += tcp_data_len;
	lro_desc->tcp_next_seq += tcp_data_len;
	lro_desc->tcp_window = tcph->window;
	lro_desc->tcp_ack = tcph->ack_seq;

	/* don't update tcp_rcv_tsval, would not work with PAWS */
	if (lro_desc->tcp_saw_tstamp) {
		topt = (__be32 *) (tcph + 1);
		lro_desc->tcp_rcv_tsecr = *(topt + 2);
	}

	lro_desc->data_csum = csum_block_add(lro_desc->data_csum,
					     lro_tcp_data_csum(iph, tcph,
							       tcp_data_len),
					     parent->len);

	parent->len += tcp_data_len;
	parent->data_len += tcp_data_len;
	if (tcp_data_len > lro_desc->mss)
		lro_desc->mss = tcp_data_len;
}

/*向LRO skb中添加一個新的skb*/
static void lro_add_packet(struct net_lro_desc *lro_desc, struct sk_buff *skb,
			   struct iphdr *iph, struct tcphdr *tcph)
{
	struct sk_buff *parent = lro_desc->parent;
	int tcp_data_len = TCP_PAYLOAD_LENGTH(iph, tcph);

	lro_add_common(lro_desc, iph, tcph, tcp_data_len);

	/*更新該skb的data 長度，需要除去header部分長度*/
	skb_pull(skb, (skb->len - tcp_data_len));

	/*更新整個lro skb的總長度*/
	parent->truesize += skb->truesize;

	/*將skb掛接在lro skb的 frag_list上面。*/
	if (lro_desc->last_skb)
		lro_desc->last_skb->next = skb;
	else
		skb_shinfo(parent)->frag_list = skb;

	lro_desc->last_skb = skb;
}

/*向一個skb添加帶frags的數據包； 支持分散、聚合的dma， 一個數據可能由多個skb_frags組成。*/
static void lro_add_frags(struct net_lro_desc *lro_desc,
			  int len, int hlen, int truesize,
			  struct skb_frag_struct *skb_frags,
			  struct iphdr *iph, struct tcphdr *tcph)
{
	struct sk_buff *skb = lro_desc->parent;
	int tcp_data_len = TCP_PAYLOAD_LENGTH(iph, tcph);

	lro_add_common(lro_desc, iph, tcph, tcp_data_len);

	skb->truesize += truesize;

	/*去掉該skb包的header部分， 而該header應該保存在第一個frags數據中。*/
	skb_frags[0].page_offset += hlen;
	skb_frags[0].size -= hlen;

	/*將page部分的數據，直接保存到skb的frags中*/
	while (tcp_data_len > 0) {
		*(lro_desc->next_frag) = *skb_frags;
		tcp_data_len -= skb_frags->size;
		lro_desc->next_frag++;
		skb_frags++;
		skb_shinfo(skb)->nr_frags++;
	}
}