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static void
tcp_conn_request(struct sock *sk, struct sk_buff *skb,
unsigned long daddr, unsigned long saddr,
struct options *opt, struct device *dev)
{
struct sk_buff *buff;
struct tcphdr *t1;
unsigned char *ptr;
struct sock *newsk;
struct tcphdr *th;
int tmp;
DPRINTF((DBG_TCP, "tcp_conn_request(sk = %X, skb = %X, daddr = %X, sadd4= %X, \n"
" opt = %X, dev = %X)\n",
sk, skb, daddr, saddr, opt, dev));
th = skb->h.th;
/* If the socket is dead, don't accept the connection. */
if (!sk->dead) {
sk->data_ready(sk,0);
} else {
DPRINTF((DBG_TCP, "tcp_conn_request on dead socket\n"));
tcp_reset(daddr, saddr, th, sk->prot, opt, dev, sk->ip_tos,sk->ip_ttl);
kfree_skb(skb, FREE_READ);
return;
}
/*
* Make sure we can accept more. This will prevent a
* flurry of syns from eating up all our memory.
*/
if (sk->ack_backlog >= sk->max_ack_backlog) {//这里，达到max，丢弃报文
kfree_skb(skb, FREE_READ);
return;
}
/*
* We need to build a new sock struct.
* It is sort of bad to have a socket without an inode attached
* to it, but the wake_up's will just wake up the listening socket,
* and if the listening socket is destroyed before this is taken
* off of the queue, this will take care of it.
*/
//复制一份新的sock
newsk = (struct sock *) kmalloc(sizeof(struct sock), GFP_ATOMIC);
if (newsk == NULL) {
/* just ignore the syn. It will get retransmitted. */
kfree_skb(skb, FREE_READ);
return;
}
DPRINTF((DBG_TCP, "newsk = %X\n", newsk));
memcpy((void *)newsk,(void *)sk, sizeof(*newsk));
newsk->wback = NULL;
newsk->wfront = NULL;
newsk->rqueue = NULL;
newsk->send_head = NULL;
newsk->send_tail = NULL;
newsk->back_log = NULL;
newsk->rtt = TCP_CONNECT_TIME << 3;
newsk->rto = TCP_CONNECT_TIME;
newsk->mdev = 0;
newsk->max_window = 0;
newsk->cong_window = 1;
newsk->cong_count = 0;
newsk->ssthresh = 0;
newsk->backoff = 0;
newsk->blog = 0;
newsk->intr = 0;
newsk->proc = 0;
newsk->done = 0;
newsk->partial = NULL;
newsk->pair = NULL;
newsk->wmem_alloc = 0;
newsk->rmem_alloc = 0;
newsk->max_unacked = MAX_WINDOW - TCP_WINDOW_DIFF;
newsk->err = 0;
newsk->shutdown = 0;
newsk->ack_backlog = 0;
newsk->acked_seq = skb->h.th->seq+1;
newsk->fin_seq = skb->h.th->seq;
newsk->copied_seq = skb->h.th->seq;
newsk->state = TCP_SYN_RECV;//设置状态，注意这个是newsk，原来的sk状态仍为LISTEN，这样在下一个tcp_rcv的处理中，会做进一步的处理
newsk->timeout = 0;
newsk->send_seq = jiffies * SEQ_TICK - seq_offset;//随机生成序列号算法
newsk->window_seq = newsk->send_seq;
newsk->rcv_ack_seq = newsk->send_seq;
newsk->urg =0;
newsk->retransmits = 0;
newsk->destroy = 0;
newsk->timer.data = (unsigned long)newsk;
newsk->timer.function = &net_timer;//协议用到的timer
newsk->dummy_th.source = skb->h.th->dest;
newsk->dummy_th.dest = skb->h.th->source;
/* Swap these two, they are from our point of view. */
newsk->daddr = saddr;
newsk->saddr = daddr;
put_sock(newsk->num,newsk);
newsk->dummy_th.res1 = 0;
newsk->dummy_th.doff = 6;
newsk->dummy_th.fin = 0;
newsk->dummy_th.syn = 0;
newsk->dummy_th.rst = 0;
newsk->dummy_th.psh = 0;
newsk->dummy_th.ack = 0;
newsk->dummy_th.urg = 0;
newsk->dummy_th.res2 = 0;
newsk->acked_seq = skb->h.th->seq + 1;
newsk->copied_seq = skb->h.th->seq;
/* Grab the ttl and tos values and use them */
newsk->ip_ttl=sk->ip_ttl;
newsk->ip_tos=skb->ip_hdr->tos;
/* use 512 or whatever user asked for */
/* note use of sk->user_mss, since user has no direct access to newsk */
if (sk->user_mss)
newsk->mtu = sk->user_mss;
else {
#ifdef SUBNETSARELOCAL
if ((saddr ^ daddr) & default_mask(saddr))
#else
if ((saddr ^ daddr) & dev->pa_mask)
#endif
newsk->mtu = 576 - HEADER_SIZE;
else
newsk->mtu = MAX_WINDOW;
}
/* but not bigger than device MTU */
newsk->mtu = min(newsk->mtu, dev->mtu - HEADER_SIZE);
/* this will min with what arrived in the packet */
tcp_options(newsk,skb->h.th);
//准备发送sync&ack的报文
buff = newsk->prot->wmalloc(newsk, MAX_SYN_SIZE, 1, GFP_ATOMIC);
if (buff == NULL) {
sk->err = -ENOMEM;
newsk->dead = 1;
release_sock(newsk);
kfree_skb(skb, FREE_READ);
return;
}
buff->mem_addr = buff;
buff->mem_len = MAX_SYN_SIZE;
buff->len = sizeof(struct tcphdr)+4;
buff->sk = newsk;
t1 =(struct tcphdr *) buff->data;
/* Put in the IP header and routing stuff. */
tmp = sk->prot->build_header(buff, newsk->saddr, newsk->daddr, &dev,
IPPROTO_TCP, NULL, MAX_SYN_SIZE,sk->ip_tos,sk->ip_ttl);
/* Something went wrong. */
if (tmp < 0) {
sk->err = tmp;
buff->free=1;
kfree_skb(buff,FREE_WRITE);
newsk->dead = 1;
release_sock(newsk);
skb->sk = sk;
kfree_skb(skb, FREE_READ);
return;
}
buff->len += tmp;
t1 =(struct tcphdr *)((char *)t1 +tmp);
memcpy(t1, skb->h.th, sizeof(*t1));
buff->h.seq = newsk->send_seq;
/* Swap the send and the receive. */
t1->dest = skb->h.th->source;
t1->source = newsk->dummy_th.source;
t1->seq = ntohl(newsk->send_seq++);
t1->ack = 1;//设置ACK标志
newsk->window = tcp_select_window(newsk);/*newsk->prot->rspace(newsk);*/
t1->window = ntohs(newsk->window);
t1->res1 = 0;
t1->res2 = 0;
t1->rst = 0;
t1->urg = 0;
t1->psh = 0;
t1->syn = 1;//设置SYNC标志
t1->ack_seq = ntohl(skb->h.th->seq+1);
t1->doff = sizeof(*t1)/4+1;
ptr =(unsigned char *)(t1+1);
ptr[0] = 2;
ptr[1] = 4;
ptr[2] = ((newsk->mtu) >> 8) & 0xff;
ptr[3] =(newsk->mtu) & 0xff;
tcp_send_check(t1, daddr, saddr, sizeof(*t1)+4, newsk);
newsk->prot->queue_xmit(newsk, dev, buff, 0);//在这里发送SYNC/ACK报文
reset_timer(newsk, TIME_WRITE /* -1 ? FIXME ??? */, TCP_CONNECT_TIME);
skb->sk = newsk;
/* Charge the sock_buff to newsk. */
sk->rmem_alloc -= skb->mem_len;
newsk->rmem_alloc += skb->mem_len;
skb_queue_tail(&sk->rqueue,skb);//同时把接收的这个报文上加入到sock接收队列中
sk->ack_backlog++;
release_sock(newsk);
}
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