void dccp_set_state(struct sock *sk, const int state)
{
	const int oldstate = sk->sk_state;

	dccp_pr_debug("%s(%p)  %s  -->  %s\n", dccp_role(sk), sk,
		      dccp_state_name(oldstate), dccp_state_name(state));
	WARN_ON(state == oldstate);

	switch (state) {
	case DCCP_OPEN:
		if (oldstate != DCCP_OPEN)
			DCCP_INC_STATS(DCCP_MIB_CURRESTAB);
		break;

	case DCCP_CLOSED:
		if (oldstate == DCCP_OPEN || oldstate == DCCP_ACTIVE_CLOSEREQ ||
		    oldstate == DCCP_CLOSING)
			DCCP_INC_STATS(DCCP_MIB_ESTABRESETS);

		sk->sk_prot->unhash(sk);
		if (inet_csk(sk)->icsk_bind_hash != NULL &&
		    !(sk->sk_userlocks & SOCK_BINDPORT_LOCK))
			inet_put_port(sk);
		/* fall through */
	default:
		if (oldstate == DCCP_OPEN)
			DCCP_DEC_STATS(DCCP_MIB_CURRESTAB);
	}

	/* Change state AFTER socket is unhashed to avoid closed
	 * socket sitting in hash tables.
	 */
	sk->sk_state = state;
}

static void dccp_terminate_connection(struct sock *sk)
{
	u8 next_state = DCCP_CLOSED;

	switch (sk->sk_state) {
	case DCCP_PASSIVE_CLOSE:
	case DCCP_PASSIVE_CLOSEREQ:
		dccp_finish_passive_close(sk);
		break;
	case DCCP_PARTOPEN:
		dccp_pr_debug("Stop PARTOPEN timer (%p)\n", sk);
		inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
		/* fall through */
	case DCCP_OPEN:
		dccp_send_close(sk, 1);

		if (dccp_sk(sk)->dccps_role == DCCP_ROLE_SERVER &&
		    !dccp_sk(sk)->dccps_server_timewait)
			next_state = DCCP_ACTIVE_CLOSEREQ;
		else
			next_state = DCCP_CLOSING;
		/* fall through */
	default:
		dccp_set_state(sk, next_state);
	}
}

void dccp_write_xmit(struct sock *sk, int block)
{
	struct dccp_sock *dp = dccp_sk(sk);
	struct sk_buff *skb;

	while ((skb = skb_peek(&sk->sk_write_queue))) {
		int err = ccid_hc_tx_send_packet(dp->dccps_hc_tx_ccid, sk, skb);

		if (err > 0) {
			if (!block) {
				sk_reset_timer(sk, &dp->dccps_xmit_timer,
						msecs_to_jiffies(err)+jiffies);
				break;
			} else
				err = dccp_wait_for_ccid(sk, skb, err);
			if (err && err != -EINTR)
				DCCP_BUG("err=%d after dccp_wait_for_ccid", err);
		}

		skb_dequeue(&sk->sk_write_queue);
		if (err == 0) {
			struct dccp_skb_cb *dcb = DCCP_SKB_CB(skb);
			const int len = skb->len;

			if (sk->sk_state == DCCP_PARTOPEN) {
				const u32 cur_mps = dp->dccps_mss_cache - DCCP_FEATNEG_OVERHEAD;
				/*
				 * See 8.1.5 - Handshake Completion.
				 *
				 * For robustness we resend Confirm options until the client has
				 * entered OPEN. During the initial feature negotiation, the MPS
				 * is smaller than usual, reduced by the Change/Confirm options.
				 */
				if (!list_empty(&dp->dccps_featneg) && len > cur_mps) {
					DCCP_WARN("Payload too large (%d) for featneg.\n", len);
					dccp_send_ack(sk);
					dccp_feat_list_purge(&dp->dccps_featneg);
				}

				inet_csk_schedule_ack(sk);
				inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
						  inet_csk(sk)->icsk_rto,
						  DCCP_RTO_MAX);
				dcb->dccpd_type = DCCP_PKT_DATAACK;
			} else if (dccp_ack_pending(sk))
				dcb->dccpd_type = DCCP_PKT_DATAACK;
			else
				dcb->dccpd_type = DCCP_PKT_DATA;

			err = dccp_transmit_skb(sk, skb);
			ccid_hc_tx_packet_sent(dp->dccps_hc_tx_ccid, sk, 0, len);
			if (err)
				DCCP_BUG("err=%d after ccid_hc_tx_packet_sent",
					 err);
		} else {
			dccp_pr_debug("packet discarded due to err=%d\n", err);
			kfree_skb(skb);
		}
	}
}

/**
 * dccp_xmit_packet  -  Send data packet under control of CCID
 * Transmits next-queued payload and informs CCID to account for the packet.
 */
static void dccp_xmit_packet(struct sock *sk)
{
	int err, len;
	struct dccp_sock *dp = dccp_sk(sk);
	struct sk_buff *skb = dccp_qpolicy_pop(sk);

	if (unlikely(skb == NULL))
		return;
	len = skb->len;

	if (sk->sk_state == DCCP_PARTOPEN) {
		const u32 cur_mps = dp->dccps_mss_cache - DCCP_FEATNEG_OVERHEAD;
		/*
		 * See 8.1.5 - Handshake Completion.
		 *
		 * For robustness we resend Confirm options until the client has
		 * entered OPEN. During the initial feature negotiation, the MPS
		 * is smaller than usual, reduced by the Change/Confirm options.
		 */
		if (!list_empty(&dp->dccps_featneg) && len > cur_mps) {
			DCCP_WARN("Payload too large (%d) for featneg.\n", len);
			dccp_send_ack(sk);
			dccp_feat_list_purge(&dp->dccps_featneg);
		}

		inet_csk_schedule_ack(sk);
		inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
					      inet_csk(sk)->icsk_rto,
					      DCCP_RTO_MAX);
		DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_DATAACK;
	} else if (dccp_ack_pending(sk)) {
		DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_DATAACK;
	} else {
		DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_DATA;
	}

	err = dccp_transmit_skb(sk, skb);
	if (err)
		dccp_pr_debug("transmit_skb() returned err=%d\n", err);
	/*
	 * Register this one as sent even if an error occurred. To the remote
	 * end a local packet drop is indistinguishable from network loss, i.e.
	 * any local drop will eventually be reported via receiver feedback.
	 */
	ccid_hc_tx_packet_sent(dp->dccps_hc_tx_ccid, sk, len);

	/*
	 * If the CCID needs to transfer additional header options out-of-band
	 * (e.g. Ack Vectors or feature-negotiation options), it activates this
	 * flag to schedule a Sync. The Sync will automatically incorporate all
	 * currently pending header options, thus clearing the backlog.
	 */
	if (dp->dccps_sync_scheduled)
		dccp_send_sync(sk, dp->dccps_gsr, DCCP_PKT_SYNC);
}

static void dccp_insert_option_timestamp_echo(struct sock *sk,
					      struct sk_buff *skb)
{
	struct dccp_sock *dp = dccp_sk(sk);
#ifdef CONFIG_IP_DCCP_DEBUG
	const char *debug_prefix = dp->dccps_role == DCCP_ROLE_CLIENT ?
					"CLIENT TX opt: " : "server TX opt: ";
#endif
	struct timeval now;
	u32 tstamp_echo;
	u32 elapsed_time;
	int len, elapsed_time_len;
	unsigned char *to;

	dccp_timestamp(sk, &now);
	elapsed_time = timeval_delta(&now, &dp->dccps_timestamp_time) / 10;
	elapsed_time_len = dccp_elapsed_time_len(elapsed_time);
	len = 6 + elapsed_time_len;

	if (DCCP_SKB_CB(skb)->dccpd_opt_len + len > DCCP_MAX_OPT_LEN) {
		LIMIT_NETDEBUG(KERN_INFO "DCCP: packet too small to insert "
					 "timestamp echo!\n");
		return;
	}

	DCCP_SKB_CB(skb)->dccpd_opt_len += len;

	to    = skb_push(skb, len);
	*to++ = DCCPO_TIMESTAMP_ECHO;
	*to++ = len;

	tstamp_echo = htonl(dp->dccps_timestamp_echo);
	memcpy(to, &tstamp_echo, 4);
	to += 4;
	
	if (elapsed_time_len == 2) {
		const u16 var16 = htons((u16)elapsed_time);
		memcpy(to, &var16, 2);
	} else if (elapsed_time_len == 4) {
		const u32 var32 = htonl(elapsed_time);
		memcpy(to, &var32, 4);
	}

	dccp_pr_debug("%sTIMESTAMP_ECHO=%u, len=%d, seqno=%llu\n",
		      debug_prefix, dp->dccps_timestamp_echo,
		      len,
		      (unsigned long long) DCCP_SKB_CB(skb)->dccpd_seq);

	dp->dccps_timestamp_echo = 0;
	dp->dccps_timestamp_time.tv_sec = 0;
	dp->dccps_timestamp_time.tv_usec = 0;
}

void dccp_write_xmit(struct sock *sk, int block)
{
    struct dccp_sock *dp = dccp_sk(sk);
    struct sk_buff *skb;

    while ((skb = skb_peek(&sk->sk_write_queue))) {
        int err = ccid_hc_tx_send_packet(dp->dccps_hc_tx_ccid, sk, skb);

        if (err > 0) {
            if (!block) {
                sk_reset_timer(sk, &dp->dccps_xmit_timer,
                        msecs_to_jiffies(err)+jiffies);
                break;
            } else
                err = dccp_wait_for_ccid(sk, skb, err);
            if (err && err != -EINTR)
                DCCP_BUG("err=%d after dccp_wait_for_ccid", err);
        }

        skb_dequeue(&sk->sk_write_queue);
        if (err == 0) {
            struct dccp_skb_cb *dcb = DCCP_SKB_CB(skb);
            const int len = skb->len;

            if (sk->sk_state == DCCP_PARTOPEN) {
                /* See 8.1.5.  Handshake Completion */
                inet_csk_schedule_ack(sk);
                inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
                          inet_csk(sk)->icsk_rto,
                          DCCP_RTO_MAX);
                dcb->dccpd_type = DCCP_PKT_DATAACK;
            } else if (dccp_ack_pending(sk))
                dcb->dccpd_type = DCCP_PKT_DATAACK;
            else
                dcb->dccpd_type = DCCP_PKT_DATA;

            err = dccp_transmit_skb(sk, skb);
            ccid_hc_tx_packet_sent(dp->dccps_hc_tx_ccid, sk, 0, len);
            if (err)
                DCCP_BUG("err=%d after ccid_hc_tx_packet_sent",
                     err);
        } else {
            dccp_pr_debug("packet discarded due to err=%d\n", err);
            kfree_skb(skb);
        }
    }
}

void dccp_insert_option_elapsed_time(struct sock *sk,
				     struct sk_buff *skb,
				     u32 elapsed_time)
{
#ifdef CONFIG_IP_DCCP_DEBUG
	struct dccp_sock *dp = dccp_sk(sk);
	const char *debug_prefix = dp->dccps_role == DCCP_ROLE_CLIENT ?
					"CLIENT TX opt: " : "server TX opt: ";
#endif
	const int elapsed_time_len = dccp_elapsed_time_len(elapsed_time);
	const int len = 2 + elapsed_time_len;
	unsigned char *to;

	if (elapsed_time_len == 0)
		return;

	if (DCCP_SKB_CB(skb)->dccpd_opt_len + len > DCCP_MAX_OPT_LEN) {
		LIMIT_NETDEBUG(KERN_INFO "DCCP: packet too small to "
					 "insert elapsed time!\n");
		return;
	}

	DCCP_SKB_CB(skb)->dccpd_opt_len += len;

	to    = skb_push(skb, len);
	*to++ = DCCPO_ELAPSED_TIME;
	*to++ = len;

	if (elapsed_time_len == 2) {
		const u16 var16 = htons((u16)elapsed_time);
		memcpy(to, &var16, 2);
	} else {
		const u32 var32 = htonl(elapsed_time);
		memcpy(to, &var32, 4);
	}

	dccp_pr_debug("%sELAPSED_TIME=%u, len=%d, seqno=%llu\n",
		      debug_prefix, elapsed_time,
		      len,
		      (unsigned long long) DCCP_SKB_CB(skb)->dccpd_seq);
}

/**
 * dccp_flush_write_queue  -  Drain queue at end of connection
 * Since dccp_sendmsg queues packets without waiting for them to be sent, it may
 * happen that the TX queue is not empty at the end of a connection. We give the
 * HC-sender CCID a grace period of up to @time_budget jiffies. If this function
 * returns with a non-empty write queue, it will be purged later.
 */
void dccp_flush_write_queue(struct sock *sk, long *time_budget)
{
	struct dccp_sock *dp = dccp_sk(sk);
	struct sk_buff *skb;
	long delay, rc;

	while (*time_budget > 0 && (skb = skb_peek(&sk->sk_write_queue))) {
		rc = ccid_hc_tx_send_packet(dp->dccps_hc_tx_ccid, sk, skb);

		switch (ccid_packet_dequeue_eval(rc)) {
		case CCID_PACKET_WILL_DEQUEUE_LATER:
			/*
			 * If the CCID determines when to send, the next sending
			 * time is unknown or the CCID may not even send again
			 * (e.g. remote host crashes or lost Ack packets).
			 */
			DCCP_WARN("CCID did not manage to send all packets\n");
			return;
		case CCID_PACKET_DELAY:
			delay = msecs_to_jiffies(rc);
			if (delay > *time_budget)
				return;
			rc = dccp_wait_for_ccid(sk, delay);
			if (rc < 0)
				return;
			*time_budget -= (delay - rc);
			/* check again if we can send now */
			break;
		case CCID_PACKET_SEND_AT_ONCE:
			dccp_xmit_packet(sk);
			break;
		case CCID_PACKET_ERR:
			skb_dequeue(&sk->sk_write_queue);
			kfree_skb(skb);
			dccp_pr_debug("packet discarded due to err=%ld\n", rc);
		}
	}
}

/**
 * dccp_wait_for_ccid - Wait for ccid to tell us we can send a packet
 * @sk:    socket to wait for
 * @skb:   current skb to pass on for waiting
 * @delay: sleep timeout in milliseconds (> 0)
 * This function is called by default when the socket is closed, and
 * when a non-zero linger time is set on the socket. For consistency
 */
static int dccp_wait_for_ccid(struct sock *sk, struct sk_buff *skb, int delay)
{
    struct dccp_sock *dp = dccp_sk(sk);
    DEFINE_WAIT(wait);
    unsigned long jiffdelay;
    int rc;

    do {
        dccp_pr_debug("delayed send by %d msec\n", delay);
        jiffdelay = msecs_to_jiffies(delay);

        prepare_to_wait(sk->sk_sleep, &wait, TASK_INTERRUPTIBLE);

        sk->sk_write_pending++;
        release_sock(sk);
        schedule_timeout(jiffdelay);
        lock_sock(sk);
        sk->sk_write_pending--;

        if (sk->sk_err)
            goto do_error;
        if (signal_pending(current))
            goto do_interrupted;

        rc = ccid_hc_tx_send_packet(dp->dccps_hc_tx_ccid, sk, skb);
    } while ((delay = rc) > 0);
out:
    finish_wait(sk->sk_sleep, &wait);
    return rc;

do_error:
    rc = -EPIPE;
    goto out;
do_interrupted:
    rc = -EINTR;
    goto out;
}

void dccp_write_xmit(struct sock *sk)
{
	struct dccp_sock *dp = dccp_sk(sk);
	struct sk_buff *skb;

	while ((skb = dccp_qpolicy_top(sk))) {
		int rc = ccid_hc_tx_send_packet(dp->dccps_hc_tx_ccid, sk, skb);

		switch (ccid_packet_dequeue_eval(rc)) {
		case CCID_PACKET_WILL_DEQUEUE_LATER:
			return;
		case CCID_PACKET_DELAY:
			sk_reset_timer(sk, &dp->dccps_xmit_timer,
				       jiffies + msecs_to_jiffies(rc));
			return;
		case CCID_PACKET_SEND_AT_ONCE:
			dccp_xmit_packet(sk);
			break;
		case CCID_PACKET_ERR:
			dccp_qpolicy_drop(sk, skb);
			dccp_pr_debug("packet discarded due to err=%d\n", rc);
		}
	}
}

/* this is called when real data arrives */
static int dccp_v4_rcv(struct sk_buff *skb)
{
	const struct dccp_hdr *dh;
	const struct iphdr *iph;
	struct sock *sk;
	int min_cov;

	/* Step 1: Check header basics */

	if (dccp_invalid_packet(skb))
		goto discard_it;

	iph = ip_hdr(skb);
	/* Step 1: If header checksum is incorrect, drop packet and return */
	if (dccp_v4_csum_finish(skb, iph->saddr, iph->daddr)) {
		DCCP_WARN("dropped packet with invalid checksum\n");
		goto discard_it;
	}

	dh = dccp_hdr(skb);

	DCCP_SKB_CB(skb)->dccpd_seq  = dccp_hdr_seq(dh);
	DCCP_SKB_CB(skb)->dccpd_type = dh->dccph_type;

	dccp_pr_debug("%8.8s src=%[email protected]%-5d dst=%[email protected]%-5d seq=%llu",
		      dccp_packet_name(dh->dccph_type),
		      &iph->saddr, ntohs(dh->dccph_sport),
		      &iph->daddr, ntohs(dh->dccph_dport),
		      (unsigned long long) DCCP_SKB_CB(skb)->dccpd_seq);

	if (dccp_packet_without_ack(skb)) {
		DCCP_SKB_CB(skb)->dccpd_ack_seq = DCCP_PKT_WITHOUT_ACK_SEQ;
		dccp_pr_debug_cat("\n");
	} else {
		DCCP_SKB_CB(skb)->dccpd_ack_seq = dccp_hdr_ack_seq(skb);
		dccp_pr_debug_cat(", ack=%llu\n", (unsigned long long)
				  DCCP_SKB_CB(skb)->dccpd_ack_seq);
	}

lookup:
	sk = __inet_lookup_skb(&dccp_hashinfo, skb, __dccp_hdr_len(dh),
			       dh->dccph_sport, dh->dccph_dport);
	if (!sk) {
		dccp_pr_debug("failed to look up flow ID in table and "
			      "get corresponding socket\n");
		goto no_dccp_socket;
	}

	/*
	 * Step 2:
	 *	... or S.state == TIMEWAIT,
	 *		Generate Reset(No Connection) unless P.type == Reset
	 *		Drop packet and return
	 */
	if (sk->sk_state == DCCP_TIME_WAIT) {
		dccp_pr_debug("sk->sk_state == DCCP_TIME_WAIT: do_time_wait\n");
		inet_twsk_put(inet_twsk(sk));
		goto no_dccp_socket;
	}

	if (sk->sk_state == DCCP_NEW_SYN_RECV) {
		struct request_sock *req = inet_reqsk(sk);
		struct sock *nsk;

		sk = req->rsk_listener;
		if (unlikely(sk->sk_state != DCCP_LISTEN)) {
			inet_csk_reqsk_queue_drop_and_put(sk, req);
			goto lookup;
		}
		sock_hold(sk);
		nsk = dccp_check_req(sk, skb, req);
		if (!nsk) {
			reqsk_put(req);
			goto discard_and_relse;
		}
		if (nsk == sk) {
			reqsk_put(req);
		} else if (dccp_child_process(sk, nsk, skb)) {
			dccp_v4_ctl_send_reset(sk, skb);
			goto discard_and_relse;
		} else {
			sock_put(sk);
			return 0;
		}
	}
	/*
	 * RFC 4340, sec. 9.2.1: Minimum Checksum Coverage
	 *	o if MinCsCov = 0, only packets with CsCov = 0 are accepted
	 *	o if MinCsCov > 0, also accept packets with CsCov >= MinCsCov
	 */
	min_cov = dccp_sk(sk)->dccps_pcrlen;
	if (dh->dccph_cscov && (min_cov == 0 || dh->dccph_cscov < min_cov))  {
		dccp_pr_debug("Packet CsCov %d does not satisfy MinCsCov %d\n",
			      dh->dccph_cscov, min_cov);
		/* FIXME: "Such packets SHOULD be reported using Data Dropped
		 *         options (Section 11.7) with Drop Code 0, Protocol
		 *         Constraints."                                     */
		goto discard_and_relse;
	}
//.........这里部分代码省略.........

/**
 * dccp_parse_options  -  Parse DCCP options present in @skb
 * @sk: client|server|listening dccp socket (when @dreq != NULL)
 * @dreq: request socket to use during connection setup, or NULL
 */
int dccp_parse_options(struct sock *sk, struct dccp_request_sock *dreq,
                       struct sk_buff *skb)
{
    struct dccp_sock *dp = dccp_sk(sk);
    const struct dccp_hdr *dh = dccp_hdr(skb);
    const u8 pkt_type = DCCP_SKB_CB(skb)->dccpd_type;
    unsigned char *options = (unsigned char *)dh + dccp_hdr_len(skb);
    unsigned char *opt_ptr = options;
    const unsigned char *opt_end = (unsigned char *)dh +
                                   (dh->dccph_doff * 4);
    struct dccp_options_received *opt_recv = &dp->dccps_options_received;
    unsigned char opt, len;
    unsigned char *uninitialized_var(value);
    u32 elapsed_time;
    __be32 opt_val;
    int rc;
    int mandatory = 0;

    memset(opt_recv, 0, sizeof(*opt_recv));

    opt = len = 0;
    while (opt_ptr != opt_end) {
        opt   = *opt_ptr++;
        len   = 0;
        value = NULL;

        /* Check if this isn't a single byte option */
        if (opt > DCCPO_MAX_RESERVED) {
            if (opt_ptr == opt_end)
                goto out_nonsensical_length;

            len = *opt_ptr++;
            if (len < 2)
                goto out_nonsensical_length;
            /*
             * Remove the type and len fields, leaving
             * just the value size
             */
            len	-= 2;
            value	= opt_ptr;
            opt_ptr += len;

            if (opt_ptr > opt_end)
                goto out_nonsensical_length;
        }

        /*
         * CCID-specific options are ignored during connection setup, as
         * negotiation may still be in progress (see RFC 4340, 10.3).
         * The same applies to Ack Vectors, as these depend on the CCID.
         */
        if (dreq != NULL && (opt >= DCCPO_MIN_RX_CCID_SPECIFIC ||
                             opt == DCCPO_ACK_VECTOR_0 || opt == DCCPO_ACK_VECTOR_1))
            goto ignore_option;

        switch (opt) {
        case DCCPO_PADDING:
            break;
        case DCCPO_MANDATORY:
            if (mandatory)
                goto out_invalid_option;
            if (pkt_type != DCCP_PKT_DATA)
                mandatory = 1;
            break;
        case DCCPO_NDP_COUNT:
            if (len > 6)
                goto out_invalid_option;

            opt_recv->dccpor_ndp = dccp_decode_value_var(value, len);
            dccp_pr_debug("%s opt: NDP count=%llu\n", dccp_role(sk),
                          (unsigned long long)opt_recv->dccpor_ndp);
            break;
        case DCCPO_CHANGE_L ... DCCPO_CONFIRM_R:
            if (pkt_type == DCCP_PKT_DATA)      /* RFC 4340, 6 */
                break;
            if (len == 0)
                goto out_invalid_option;
            rc = dccp_feat_parse_options(sk, dreq, mandatory, opt,
                                         *value, value + 1, len - 1);
            if (rc)
                goto out_featneg_failed;
            break;
        case DCCPO_TIMESTAMP:
            if (len != 4)
                goto out_invalid_option;
            /*
             * RFC 4340 13.1: "The precise time corresponding to
             * Timestamp Value zero is not specified". We use
             * zero to indicate absence of a meaningful timestamp.
             */
            opt_val = get_unaligned((__be32 *)value);
            if (unlikely(opt_val == 0)) {
                DCCP_WARN("Timestamp with zero value\n");
                break;
            }
//.........这里部分代码省略.........

static int dccp_rcv_request_sent_state_process(struct sock *sk,
					       struct sk_buff *skb,
					       const struct dccp_hdr *dh,
					       const unsigned len)
{
	/*
	 *  Step 4: Prepare sequence numbers in REQUEST
	 *     If S.state == REQUEST,
	 *	  If (P.type == Response or P.type == Reset)
	 *		and S.AWL <= P.ackno <= S.AWH,
	 *	     / * Set sequence number variables corresponding to the
	 *		other endpoint, so P will pass the tests in Step 6 * /
	 *	     Set S.GSR, S.ISR, S.SWL, S.SWH
	 *	     / * Response processing continues in Step 10; Reset
	 *		processing continues in Step 9 * /
	*/
	if (dh->dccph_type == DCCP_PKT_RESPONSE) {
		const struct inet_connection_sock *icsk = inet_csk(sk);
		struct dccp_sock *dp = dccp_sk(sk);

		/* Stop the REQUEST timer */
		inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
		BUG_TRAP(sk->sk_send_head != NULL);
		__kfree_skb(sk->sk_send_head);
		sk->sk_send_head = NULL;

		if (!between48(DCCP_SKB_CB(skb)->dccpd_ack_seq,
			       dp->dccps_awl, dp->dccps_awh)) {
			dccp_pr_debug("invalid ackno: S.AWL=%llu, "
				      "P.ackno=%llu, S.AWH=%llu \n",
				      (unsigned long long)dp->dccps_awl,
			   (unsigned long long)DCCP_SKB_CB(skb)->dccpd_ack_seq,
				      (unsigned long long)dp->dccps_awh);
			goto out_invalid_packet;
		}

		if (dccp_parse_options(sk, skb))
			goto out_invalid_packet;

                if (dccp_msk(sk)->dccpms_send_ack_vector &&
                    dccp_ackvec_add(dp->dccps_hc_rx_ackvec, sk,
                                    DCCP_SKB_CB(skb)->dccpd_seq,
                                    DCCP_ACKVEC_STATE_RECEIVED))
                        goto out_invalid_packet; /* FIXME: change error code */

		dp->dccps_isr = DCCP_SKB_CB(skb)->dccpd_seq;
		dccp_update_gsr(sk, dp->dccps_isr);
		/*
		 * SWL and AWL are initially adjusted so that they are not less than
		 * the initial Sequence Numbers received and sent, respectively:
		 *	SWL := max(GSR + 1 - floor(W/4), ISR),
		 *	AWL := max(GSS - W' + 1, ISS).
		 * These adjustments MUST be applied only at the beginning of the
		 * connection.
		 *
		 * AWL was adjusted in dccp_v4_connect -acme
		 */
		dccp_set_seqno(&dp->dccps_swl,
			       max48(dp->dccps_swl, dp->dccps_isr));

		dccp_sync_mss(sk, icsk->icsk_pmtu_cookie);

		/*
		 *    Step 10: Process REQUEST state (second part)
		 *       If S.state == REQUEST,
		 *	  / * If we get here, P is a valid Response from the
		 *	      server (see Step 4), and we should move to
		 *	      PARTOPEN state. PARTOPEN means send an Ack,
		 *	      don't send Data packets, retransmit Acks
		 *	      periodically, and always include any Init Cookie
		 *	      from the Response * /
		 *	  S.state := PARTOPEN
		 *	  Set PARTOPEN timer
		 *	  Continue with S.state == PARTOPEN
		 *	  / * Step 12 will send the Ack completing the
		 *	      three-way handshake * /
		 */
		dccp_set_state(sk, DCCP_PARTOPEN);

		/* Make sure socket is routed, for correct metrics. */
		icsk->icsk_af_ops->rebuild_header(sk);

		if (!sock_flag(sk, SOCK_DEAD)) {
			sk->sk_state_change(sk);
			sk_wake_async(sk, 0, POLL_OUT);
		}

		if (sk->sk_write_pending || icsk->icsk_ack.pingpong ||
		    icsk->icsk_accept_queue.rskq_defer_accept) {
			/* Save one ACK. Data will be ready after
			 * several ticks, if write_pending is set.
			 *
			 * It may be deleted, but with this feature tcpdumps
			 * look so _wonderfully_ clever, that I was not able
			 * to stand against the temptation 8)     --ANK
			 */
			/*
			 * OK, in DCCP we can as well do a similar trick, its
			 * even in the draft, but there is no need for us to
			 * schedule an ack here, as dccp_sendmsg does this for
//.........这里部分代码省略.........

int dccp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
		 size_t len, int nonblock, int flags, int *addr_len)
{
	const struct dccp_hdr *dh;
	long timeo;

	lock_sock(sk);

	if (sk->sk_state == DCCP_LISTEN) {
		len = -ENOTCONN;
		goto out;
	}

	timeo = sock_rcvtimeo(sk, nonblock);

	do {
		struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);

		if (skb == NULL)
			goto verify_sock_status;

		dh = dccp_hdr(skb);

		switch (dh->dccph_type) {
		case DCCP_PKT_DATA:
		case DCCP_PKT_DATAACK:
			goto found_ok_skb;

		case DCCP_PKT_CLOSE:
		case DCCP_PKT_CLOSEREQ:
			if (!(flags & MSG_PEEK))
				dccp_finish_passive_close(sk);
			/* fall through */
		case DCCP_PKT_RESET:
			dccp_pr_debug("found fin (%s) ok!\n",
				      dccp_packet_name(dh->dccph_type));
			len = 0;
			goto found_fin_ok;
		default:
			dccp_pr_debug("packet_type=%s\n",
				      dccp_packet_name(dh->dccph_type));
			sk_eat_skb(sk, skb, false);
		}
verify_sock_status:
		if (sock_flag(sk, SOCK_DONE)) {
			len = 0;
			break;
		}

		if (sk->sk_err) {
			len = sock_error(sk);
			break;
		}

		if (sk->sk_shutdown & RCV_SHUTDOWN) {
			len = 0;
			break;
		}

		if (sk->sk_state == DCCP_CLOSED) {
			if (!sock_flag(sk, SOCK_DONE)) {
				/* This occurs when user tries to read
				 * from never connected socket.
				 */
				len = -ENOTCONN;
				break;
			}
			len = 0;
			break;
		}

		if (!timeo) {
			len = -EAGAIN;
			break;
		}

		if (signal_pending(current)) {
			len = sock_intr_errno(timeo);
			break;
		}

		sk_wait_data(sk, &timeo);
		continue;
	found_ok_skb:
		if (len > skb->len)
			len = skb->len;
		else if (len < skb->len)
			msg->msg_flags |= MSG_TRUNC;

		if (skb_copy_datagram_iovec(skb, 0, msg->msg_iov, len)) {
			/* Exception. Bailout! */
			len = -EFAULT;
			break;
		}
		if (flags & MSG_TRUNC)
			len = skb->len;
	found_fin_ok:
		if (!(flags & MSG_PEEK))
			sk_eat_skb(sk, skb, false);
		break;
//.........这里部分代码省略.........

void dccp_shutdown(struct sock *sk, int how)
{
	dccp_pr_debug("called shutdown(%x)\n", how);
}

void dccp_shutdown(struct sock *sk, int how)
{
	dccp_pr_debug("entry\n");
}

int dccp_ioctl(struct sock *sk, int cmd, unsigned long arg)
{
	dccp_pr_debug("entry\n");
	return -ENOIOCTLCMD;
}

static int dccp_v6_rcv(struct sk_buff *skb)
{
	const struct dccp_hdr *dh;
	bool refcounted;
	struct sock *sk;
	int min_cov;

	/* Step 1: Check header basics */

	if (dccp_invalid_packet(skb))
		goto discard_it;

	/* Step 1: If header checksum is incorrect, drop packet and return. */
	if (dccp_v6_csum_finish(skb, &ipv6_hdr(skb)->saddr,
				     &ipv6_hdr(skb)->daddr)) {
		DCCP_WARN("dropped packet with invalid checksum\n");
		goto discard_it;
	}

	dh = dccp_hdr(skb);

	DCCP_SKB_CB(skb)->dccpd_seq  = dccp_hdr_seq(dh);
	DCCP_SKB_CB(skb)->dccpd_type = dh->dccph_type;

	if (dccp_packet_without_ack(skb))
		DCCP_SKB_CB(skb)->dccpd_ack_seq = DCCP_PKT_WITHOUT_ACK_SEQ;
	else
		DCCP_SKB_CB(skb)->dccpd_ack_seq = dccp_hdr_ack_seq(skb);

lookup:
	sk = __inet6_lookup_skb(&dccp_hashinfo, skb, __dccp_hdr_len(dh),
			        dh->dccph_sport, dh->dccph_dport,
				inet6_iif(skb), 0, &refcounted);
	if (!sk) {
		dccp_pr_debug("failed to look up flow ID in table and "
			      "get corresponding socket\n");
		goto no_dccp_socket;
	}

	/*
	 * Step 2:
	 *	... or S.state == TIMEWAIT,
	 *		Generate Reset(No Connection) unless P.type == Reset
	 *		Drop packet and return
	 */
	if (sk->sk_state == DCCP_TIME_WAIT) {
		dccp_pr_debug("sk->sk_state == DCCP_TIME_WAIT: do_time_wait\n");
		inet_twsk_put(inet_twsk(sk));
		goto no_dccp_socket;
	}

	if (sk->sk_state == DCCP_NEW_SYN_RECV) {
		struct request_sock *req = inet_reqsk(sk);
		struct sock *nsk;

		sk = req->rsk_listener;
		if (unlikely(sk->sk_state != DCCP_LISTEN)) {
			inet_csk_reqsk_queue_drop_and_put(sk, req);
			goto lookup;
		}
		sock_hold(sk);
		refcounted = true;
		nsk = dccp_check_req(sk, skb, req);
		if (!nsk) {
			reqsk_put(req);
			goto discard_and_relse;
		}
		if (nsk == sk) {
			reqsk_put(req);
		} else if (dccp_child_process(sk, nsk, skb)) {
			dccp_v6_ctl_send_reset(sk, skb);
			goto discard_and_relse;
		} else {
			sock_put(sk);
			return 0;
		}
	}
	/*
	 * RFC 4340, sec. 9.2.1: Minimum Checksum Coverage
	 *	o if MinCsCov = 0, only packets with CsCov = 0 are accepted
	 *	o if MinCsCov > 0, also accept packets with CsCov >= MinCsCov
	 */
	min_cov = dccp_sk(sk)->dccps_pcrlen;
	if (dh->dccph_cscov  &&  (min_cov == 0 || dh->dccph_cscov < min_cov))  {
		dccp_pr_debug("Packet CsCov %d does not satisfy MinCsCov %d\n",
			      dh->dccph_cscov, min_cov);
		/* FIXME: send Data Dropped option (see also dccp_v4_rcv) */
		goto discard_and_relse;
	}

	if (!xfrm6_policy_check(sk, XFRM_POLICY_IN, skb))
		goto discard_and_relse;

	return __sk_receive_skb(sk, skb, 1, dh->dccph_doff * 4,
				refcounted) ? -1 : 0;

no_dccp_socket:
	if (!xfrm6_policy_check(NULL, XFRM_POLICY_IN, skb))
		goto discard_it;
	/*
//.........这里部分代码省略.........

int dccp_parse_options(struct sock *sk, struct sk_buff *skb)
{
	struct dccp_sock *dp = dccp_sk(sk);
#ifdef CONFIG_IP_DCCP_DEBUG
	const char *debug_prefix = dp->dccps_role == DCCP_ROLE_CLIENT ?
					"CLIENT rx opt: " : "server rx opt: ";
#endif
	const struct dccp_hdr *dh = dccp_hdr(skb);
	const u8 pkt_type = DCCP_SKB_CB(skb)->dccpd_type;
	unsigned char *options = (unsigned char *)dh + dccp_hdr_len(skb);
	unsigned char *opt_ptr = options;
	const unsigned char *opt_end = (unsigned char *)dh +
					(dh->dccph_doff * 4);
	struct dccp_options_received *opt_recv = &dp->dccps_options_received;
	unsigned char opt, len;
	unsigned char *value;
	u32 elapsed_time;

	memset(opt_recv, 0, sizeof(*opt_recv));

	while (opt_ptr != opt_end) {
		opt   = *opt_ptr++;
		len   = 0;
		value = NULL;

		/* Check if this isn't a single byte option */
		if (opt > DCCPO_MAX_RESERVED) {
			if (opt_ptr == opt_end)
				goto out_invalid_option;

			len = *opt_ptr++;
			if (len < 3)
				goto out_invalid_option;
			/*
			 * Remove the type and len fields, leaving
			 * just the value size
			 */
			len	-= 2;
			value	= opt_ptr;
			opt_ptr += len;

			if (opt_ptr > opt_end)
				goto out_invalid_option;
		}

		switch (opt) {
		case DCCPO_PADDING:
			break;
		case DCCPO_NDP_COUNT:
			if (len > 3)
				goto out_invalid_option;

			opt_recv->dccpor_ndp = dccp_decode_value_var(value, len);
			dccp_pr_debug("%sNDP count=%d\n", debug_prefix,
				      opt_recv->dccpor_ndp);
			break;
		case DCCPO_ACK_VECTOR_0:
		case DCCPO_ACK_VECTOR_1:
			if (pkt_type == DCCP_PKT_DATA)
				continue;

			if (dp->dccps_options.dccpo_send_ack_vector &&
			    dccp_ackvec_parse(sk, skb, opt, value, len))
				goto out_invalid_option;
			break;
		case DCCPO_TIMESTAMP:
			if (len != 4)
				goto out_invalid_option;

			opt_recv->dccpor_timestamp = ntohl(*(u32 *)value);

			dp->dccps_timestamp_echo = opt_recv->dccpor_timestamp;
			dccp_timestamp(sk, &dp->dccps_timestamp_time);

			dccp_pr_debug("%sTIMESTAMP=%u, ackno=%llu\n",
				      debug_prefix, opt_recv->dccpor_timestamp,
				      (unsigned long long)
				      DCCP_SKB_CB(skb)->dccpd_ack_seq);
			break;
		case DCCPO_TIMESTAMP_ECHO:
			if (len != 4 && len != 6 && len != 8)
				goto out_invalid_option;

			opt_recv->dccpor_timestamp_echo = ntohl(*(u32 *)value);

			dccp_pr_debug("%sTIMESTAMP_ECHO=%u, len=%d, ackno=%llu, ",
				      debug_prefix,
				      opt_recv->dccpor_timestamp_echo,
				      len + 2,
				      (unsigned long long)
				      DCCP_SKB_CB(skb)->dccpd_ack_seq);


			if (len == 4)
				break;

			if (len == 6)
				elapsed_time = ntohs(*(u16 *)(value + 4));
			else
				elapsed_time = ntohl(*(u32 *)(value + 4));
//.........这里部分代码省略.........

int dccp_parse_options(struct sock *sk, struct dccp_request_sock *dreq,
		       struct sk_buff *skb)
{
	struct dccp_sock *dp = dccp_sk(sk);
	const struct dccp_hdr *dh = dccp_hdr(skb);
	const u8 pkt_type = DCCP_SKB_CB(skb)->dccpd_type;
	unsigned char *options = (unsigned char *)dh + dccp_hdr_len(skb);
	unsigned char *opt_ptr = options;
	const unsigned char *opt_end = (unsigned char *)dh +
					(dh->dccph_doff * 4);
	struct dccp_options_received *opt_recv = &dp->dccps_options_received;
	unsigned char opt, len;
	unsigned char *uninitialized_var(value);
	u32 elapsed_time;
	__be32 opt_val;
	int rc;
	int mandatory = 0;

	memset(opt_recv, 0, sizeof(*opt_recv));

	opt = len = 0;
	while (opt_ptr != opt_end) {
		opt   = *opt_ptr++;
		len   = 0;
		value = NULL;

		
		if (opt > DCCPO_MAX_RESERVED) {
			if (opt_ptr == opt_end)
				goto out_nonsensical_length;

			len = *opt_ptr++;
			if (len < 2)
				goto out_nonsensical_length;
			len	-= 2;
			value	= opt_ptr;
			opt_ptr += len;

			if (opt_ptr > opt_end)
				goto out_nonsensical_length;
		}

		if (dreq != NULL && (opt >= DCCPO_MIN_RX_CCID_SPECIFIC ||
		    opt == DCCPO_ACK_VECTOR_0 || opt == DCCPO_ACK_VECTOR_1))
			goto ignore_option;

		switch (opt) {
		case DCCPO_PADDING:
			break;
		case DCCPO_MANDATORY:
			if (mandatory)
				goto out_invalid_option;
			if (pkt_type != DCCP_PKT_DATA)
				mandatory = 1;
			break;
		case DCCPO_NDP_COUNT:
			if (len > 6)
				goto out_invalid_option;

			opt_recv->dccpor_ndp = dccp_decode_value_var(value, len);
			dccp_pr_debug("%s opt: NDP count=%llu\n", dccp_role(sk),
				      (unsigned long long)opt_recv->dccpor_ndp);
			break;
		case DCCPO_CHANGE_L ... DCCPO_CONFIRM_R:
			if (pkt_type == DCCP_PKT_DATA)      
				break;
			if (len == 0)
				goto out_invalid_option;
			rc = dccp_feat_parse_options(sk, dreq, mandatory, opt,
						    *value, value + 1, len - 1);
			if (rc)
				goto out_featneg_failed;
			break;
		case DCCPO_TIMESTAMP:
			if (len != 4)
				goto out_invalid_option;
			opt_val = get_unaligned((__be32 *)value);
			if (unlikely(opt_val == 0)) {
				DCCP_WARN("Timestamp with zero value\n");
				break;
			}

			if (dreq != NULL) {
				dreq->dreq_timestamp_echo = ntohl(opt_val);
				dreq->dreq_timestamp_time = dccp_timestamp();
			} else {
				opt_recv->dccpor_timestamp =
					dp->dccps_timestamp_echo = ntohl(opt_val);
				dp->dccps_timestamp_time = dccp_timestamp();
			}
			dccp_pr_debug("%s rx opt: TIMESTAMP=%u, ackno=%llu\n",
				      dccp_role(sk), ntohl(opt_val),
				      (unsigned long long)
				      DCCP_SKB_CB(skb)->dccpd_ack_seq);
			
			inet_csk_schedule_ack(sk);
			break;
		case DCCPO_TIMESTAMP_ECHO:
			if (len != 4 && len != 6 && len != 8)
				goto out_invalid_option;
//.........这里部分代码省略.........