- int ip_push_pending_frames(struct sock *sk)
-
{
-
struct sk_buff *skb, *tmp_skb;
-
struct sk_buff **tail_skb;
-
struct inet_sock *inet = inet_sk(sk);
-
struct net *net = sock_net(sk);
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struct ip_options *opt = NULL;
-
struct rtable *rt = (struct rtable *)inet->cork.dst;
-
struct iphdr *iph;
-
__be16 df = 0;
-
__u8 ttl;
-
int err = 0;
/* 发送队列可能为空 */
-
if ((skb = __skb_dequeue(&sk->sk_write_queue)) == NULL)
-
goto out;
- /* 获得分片链表 */
-
tail_skb = &(skb_shinfo(skb)->frag_list);
-
-
/* move skb->data to ip header from ext header */
- /* 调整data指针位置 */
-
if (skb->data < skb_network_header(skb))
-
__skb_pull(skb, skb_network_offset(skb));
/* 调整所有发送缓冲中的sk_buff的data指针位置，并更新第一个sk_buff的数据长度 */
-
while ((tmp_skb = __skb_dequeue(&sk->sk_write_queue)) != NULL) {
-
__skb_pull(tmp_skb, skb_network_header_len(skb));
-
*tail_skb = tmp_skb;
-
tail_skb = &(tmp_skb->next);
-
skb->len = tmp_skb->len;
-
skb->data_len = tmp_skb->len;
-
skb->truesize = tmp_skb->truesize;
-
tmp_skb->destructor = NULL;
-
tmp_skb->sk = NULL;
-
}
-
-
/* Unless user demanded real pmtu discovery (IP_PMTUDISC_DO), we allow
-
* to fragment the frame generated here. No matter, what transforms
-
* how transforms change size of the packet, it will come out.
-
*/
- /* 允许本地分片 */
-
if (inet->pmtudisc < IP_PMTUDISC_DO)
-
skb->local_df = 1;
-
-
/* DF bit is set when we want to see DF on outgoing frames.
-
* If local_df is set too, we still allow to fragment this frame
-
* locally. */
- /* 不允许分片，或者不需要分片 */
-
if (inet->pmtudisc >= IP_PMTUDISC_DO ||
-
(skb->len <= dst_mtu(&rt->dst) &&
-
ip_dont_fragment(sk, &rt->dst)))
-
df = htons(IP_DF);
/* ip option 保存在cork中， 则使用cork中的option */
-
if (inet->cork.flags & IPCORK_OPT)
-
opt = inet->cork.opt;
/* 选择合适的TTL值 */
-
if (rt->rt_type == RTN_MULTICAST)
-
ttl = inet->mc_ttl;
-
else
-
ttl = ip_select_ttl(inet, &rt->dst);
/* 得到IP报文头的地址 */
-
iph = (struct iphdr *)skb->data;
- /* 初始化IP报文头的内容 */
-
iph->version = 4;
-
iph->ihl = 5;
-
if (opt) {
- /*
填充IP option - 看到这里，可以发现opt只可能从cork中获得
- */
-
iph->ihl = opt->optlen>>2;
-
ip_options_build(skb, opt, inet->cork.addr, rt, 0);
-
}
-
iph->tos = inet->tos;
-
iph->frag_off = df;
-
ip_select_ident(iph, &rt->dst, sk);
-
iph->ttl = ttl;
-
iph->protocol = sk->sk_protocol;
-
iph->saddr = rt->rt_src;
-
iph->daddr = rt->rt_dst;
-
-
skb->priority = sk->sk_priority;
-
skb->mark = sk->sk_mark;
-
/*
-
* Steal rt from cork.dst to avoid a pair of atomic_inc/atomic_dec
-
* on dst refcount
-
*/
-
inet->cork.dst = NULL;
-
skb_dst_set(skb, &rt->dst);
-
-
if (iph->protocol == IPPROTO_ICMP)
-
icmp_out_count(net, ((struct icmphdr *)
-
skb_transport_header(skb))->type);
-
-
/* Netfilter gets whole the not fragmented skb. */
- /* 发送数据 */
-
err = ip_local_out(skb);
-
if (err) {
-
if (err > 0)
-
err = net_xmit_errno(err);
-
if (err)
-
goto error;
-
}
-
-
out:
-
ip_cork_release(inet);
-
return err;
-
-
error:
-
IP_INC_STATS(net, IPSTATS_MIB_OUTDISCARDS);
-
goto out;
-
}
