net/dccp/output.c - android_kernel_htc_msm8960 - Gitiles

 /*
  *  net/dccp/output.c
  *
  *  An implementation of the DCCP protocol
  *  Arnaldo Carvalho de Melo <acme@conectiva.com.br>
  *
  *	This program is free software; you can redistribute it and/or
  *	modify it under the terms of the GNU General Public License
  *	as published by the Free Software Foundation; either version
  *	2 of the License, or (at your option) any later version.
  */

 #include <linux/dccp.h>
 #include <linux/kernel.h>
 #include <linux/skbuff.h>
 #include <linux/slab.h>

 #include <net/inet_sock.h>
 #include <net/sock.h>

 #include "ackvec.h"
 #include "ccid.h"
 #include "dccp.h"

 static inline void dccp_event_ack_sent(struct sock *sk)
 {
 	inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
 }

 static void dccp_skb_entail(struct sock *sk, struct sk_buff *skb)
 {
 	skb_set_owner_w(skb, sk);
 	WARN_ON(sk->sk_send_head);
 	sk->sk_send_head = skb;
 }

 /*
  * All SKB's seen here are completely headerless. It is our
  * job to build the DCCP header, and pass the packet down to
  * IP so it can do the same plus pass the packet off to the
  * device.
  */
 static int dccp_transmit_skb(struct sock *sk, struct sk_buff *skb)
 {
 	if (likely(skb != NULL)) {
 		const struct inet_sock *inet = inet_sk(sk);
 		const struct inet_connection_sock *icsk = inet_csk(sk);
 		struct dccp_sock *dp = dccp_sk(sk);
 		struct dccp_skb_cb *dcb = DCCP_SKB_CB(skb);
 		struct dccp_hdr *dh;
 		/* XXX For now we're using only 48 bits sequence numbers */
 		const u32 dccp_header_size = sizeof(*dh) +
 					     sizeof(struct dccp_hdr_ext) +
 					  dccp_packet_hdr_len(dcb->dccpd_type);
 		int err, set_ack = 1;
 		u64 ackno = dp->dccps_gsr;
 		/*
 		 * Increment GSS here already in case the option code needs it.
 		 * Update GSS for real only if option processing below succeeds.
 		 */
 		dcb->dccpd_seq = ADD48(dp->dccps_gss, 1);

 		switch (dcb->dccpd_type) {
 		case DCCP_PKT_DATA:
 			set_ack = 0;
 			/* fall through */
 		case DCCP_PKT_DATAACK:
 		case DCCP_PKT_RESET:
 			break;

 		case DCCP_PKT_REQUEST:
 			set_ack = 0;
 			/* Use ISS on the first (non-retransmitted) Request. */
 			if (icsk->icsk_retransmits == 0)
 				dcb->dccpd_seq = dp->dccps_iss;
 			/* fall through */

 		case DCCP_PKT_SYNC:
 		case DCCP_PKT_SYNCACK:
 			ackno = dcb->dccpd_ack_seq;
 			/* fall through */
 		default:
 			/*
 			 * Set owner/destructor: some skbs are allocated via
 			 * alloc_skb (e.g. when retransmission may happen).
 			 * Only Data, DataAck, and Reset packets should come
 			 * through here with skb->sk set.
 			 */
 			WARN_ON(skb->sk);
 			skb_set_owner_w(skb, sk);
 			break;
 		}

 		if (dccp_insert_options(sk, skb)) {
 			kfree_skb(skb);
 			return -EPROTO;
 		}


 		/* Build DCCP header and checksum it. */
 		dh = dccp_zeroed_hdr(skb, dccp_header_size);
 		dh->dccph_type	= dcb->dccpd_type;
 		dh->dccph_sport	= inet->inet_sport;
 		dh->dccph_dport	= inet->inet_dport;
 		dh->dccph_doff	= (dccp_header_size + dcb->dccpd_opt_len) / 4;
 		dh->dccph_ccval	= dcb->dccpd_ccval;
 		dh->dccph_cscov = dp->dccps_pcslen;
 		/* XXX For now we're using only 48 bits sequence numbers */
 		dh->dccph_x	= 1;

 		dccp_update_gss(sk, dcb->dccpd_seq);
 		dccp_hdr_set_seq(dh, dp->dccps_gss);
 		if (set_ack)
 			dccp_hdr_set_ack(dccp_hdr_ack_bits(skb), ackno);

 		switch (dcb->dccpd_type) {
 		case DCCP_PKT_REQUEST:
 			dccp_hdr_request(skb)->dccph_req_service =
 							dp->dccps_service;
 			/*
 			 * Limit Ack window to ISS <= P.ackno <= GSS, so that
 			 * only Responses to Requests we sent are considered.
 			 */
 			dp->dccps_awl = dp->dccps_iss;
 			break;
 		case DCCP_PKT_RESET:
 			dccp_hdr_reset(skb)->dccph_reset_code =
 							dcb->dccpd_reset_code;
 			break;
 		}

 		icsk->icsk_af_ops->send_check(sk, skb);

 		if (set_ack)
 			dccp_event_ack_sent(sk);

 		DCCP_INC_STATS(DCCP_MIB_OUTSEGS);

 		err = icsk->icsk_af_ops->queue_xmit(skb);
 		return net_xmit_eval(err);
 	}
 	return -ENOBUFS;
 }

 /**
  * dccp_determine_ccmps  -  Find out about CCID-specfic packet-size limits
  * We only consider the HC-sender CCID for setting the CCMPS (RFC 4340, 14.),
  * since the RX CCID is restricted to feedback packets (Acks), which are small
  * in comparison with the data traffic. A value of 0 means "no current CCMPS".
  */
 static u32 dccp_determine_ccmps(const struct dccp_sock *dp)
 {
 	const struct ccid *tx_ccid = dp->dccps_hc_tx_ccid;

 	if (tx_ccid == NULL || tx_ccid->ccid_ops == NULL)
 		return 0;
 	return tx_ccid->ccid_ops->ccid_ccmps;
 }

 unsigned int dccp_sync_mss(struct sock *sk, u32 pmtu)
 {
 	struct inet_connection_sock *icsk = inet_csk(sk);
 	struct dccp_sock *dp = dccp_sk(sk);
 	u32 ccmps = dccp_determine_ccmps(dp);
 	u32 cur_mps = ccmps ? min(pmtu, ccmps) : pmtu;

 	/* Account for header lengths and IPv4/v6 option overhead */
 	cur_mps -= (icsk->icsk_af_ops->net_header_len + icsk->icsk_ext_hdr_len +
 		    sizeof(struct dccp_hdr) + sizeof(struct dccp_hdr_ext));

 	/*
 	 * Leave enough headroom for common DCCP header options.
 	 * This only considers options which may appear on DCCP-Data packets, as
 	 * per table 3 in RFC 4340, 5.8. When running out of space for other
 	 * options (eg. Ack Vector which can take up to 255 bytes), it is better
 	 * to schedule a separate Ack. Thus we leave headroom for the following:
 	 *  - 1 byte for Slow Receiver (11.6)
 	 *  - 6 bytes for Timestamp (13.1)
 	 *  - 10 bytes for Timestamp Echo (13.3)
 	 *  - 8 bytes for NDP count (7.7, when activated)
 	 *  - 6 bytes for Data Checksum (9.3)
 	 *  - %DCCPAV_MIN_OPTLEN bytes for Ack Vector size (11.4, when enabled)
 	 */
 	cur_mps -= roundup(1 + 6 + 10 + dp->dccps_send_ndp_count * 8 + 6 +
 			   (dp->dccps_hc_rx_ackvec ? DCCPAV_MIN_OPTLEN : 0), 4);

 	/* And store cached results */
 	icsk->icsk_pmtu_cookie = pmtu;
 	dp->dccps_mss_cache = cur_mps;

 	return cur_mps;
 }

 EXPORT_SYMBOL_GPL(dccp_sync_mss);

 void dccp_write_space(struct sock *sk)
 {
 	struct socket_wq *wq;

 	rcu_read_lock();
 	wq = rcu_dereference(sk->sk_wq);
 	if (wq_has_sleeper(wq))
 		wake_up_interruptible(&wq->wait);
 	/* Should agree with poll, otherwise some programs break */
 	if (sock_writeable(sk))
 		sk_wake_async(sk, SOCK_WAKE_SPACE, POLL_OUT);

 	rcu_read_unlock();
 }

 /**
  * 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_sleep(sk), &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_sleep(sk), &wait);
 	return rc;

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

 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_retransmit_skb  -  Retransmit Request, Close, or CloseReq packets
  * There are only four retransmittable packet types in DCCP:
  * - Request  in client-REQUEST  state (sec. 8.1.1),
  * - CloseReq in server-CLOSEREQ state (sec. 8.3),
  * - Close    in   node-CLOSING  state (sec. 8.3),
  * - Acks in client-PARTOPEN state (sec. 8.1.5, handled by dccp_delack_timer()).
  * This function expects sk->sk_send_head to contain the original skb.
  */
 int dccp_retransmit_skb(struct sock *sk)
 {
 	WARN_ON(sk->sk_send_head == NULL);

 	if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk) != 0)
 		return -EHOSTUNREACH; /* Routing failure or similar. */

 	/* this count is used to distinguish original and retransmitted skb */
 	inet_csk(sk)->icsk_retransmits++;

 	return dccp_transmit_skb(sk, skb_clone(sk->sk_send_head, GFP_ATOMIC));
 }

 struct sk_buff *dccp_make_response(struct sock *sk, struct dst_entry *dst,
 				   struct request_sock *req)
 {
 	struct dccp_hdr *dh;
 	struct dccp_request_sock *dreq;
 	const u32 dccp_header_size = sizeof(struct dccp_hdr) +
 				     sizeof(struct dccp_hdr_ext) +
 				     sizeof(struct dccp_hdr_response);
 	struct sk_buff *skb = sock_wmalloc(sk, sk->sk_prot->max_header, 1,
 					   GFP_ATOMIC);
 	if (skb == NULL)
 		return NULL;

 	/* Reserve space for headers. */
 	skb_reserve(skb, sk->sk_prot->max_header);

 	skb_dst_set(skb, dst_clone(dst));

 	dreq = dccp_rsk(req);
 	if (inet_rsk(req)->acked)	/* increase ISS upon retransmission */
 		dccp_inc_seqno(&dreq->dreq_iss);
 	DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_RESPONSE;
 	DCCP_SKB_CB(skb)->dccpd_seq  = dreq->dreq_iss;

 	/* Resolve feature dependencies resulting from choice of CCID */
 	if (dccp_feat_server_ccid_dependencies(dreq))
 		goto response_failed;

 	if (dccp_insert_options_rsk(dreq, skb))
 		goto response_failed;

 	/* Build and checksum header */
 	dh = dccp_zeroed_hdr(skb, dccp_header_size);

 	dh->dccph_sport	= inet_rsk(req)->loc_port;
 	dh->dccph_dport	= inet_rsk(req)->rmt_port;
 	dh->dccph_doff	= (dccp_header_size +
 			   DCCP_SKB_CB(skb)->dccpd_opt_len) / 4;
 	dh->dccph_type	= DCCP_PKT_RESPONSE;
 	dh->dccph_x	= 1;
 	dccp_hdr_set_seq(dh, dreq->dreq_iss);
 	dccp_hdr_set_ack(dccp_hdr_ack_bits(skb), dreq->dreq_isr);
 	dccp_hdr_response(skb)->dccph_resp_service = dreq->dreq_service;

 	dccp_csum_outgoing(skb);

 	/* We use `acked' to remember that a Response was already sent. */
 	inet_rsk(req)->acked = 1;
 	DCCP_INC_STATS(DCCP_MIB_OUTSEGS);
 	return skb;
 response_failed:
 	kfree_skb(skb);
 	return NULL;
 }

 EXPORT_SYMBOL_GPL(dccp_make_response);

 /* answer offending packet in @rcv_skb with Reset from control socket @ctl */
 struct sk_buff *dccp_ctl_make_reset(struct sock *sk, struct sk_buff *rcv_skb)
 {
 	struct dccp_hdr *rxdh = dccp_hdr(rcv_skb), *dh;
 	struct dccp_skb_cb *dcb = DCCP_SKB_CB(rcv_skb);
 	const u32 dccp_hdr_reset_len = sizeof(struct dccp_hdr) +
 				       sizeof(struct dccp_hdr_ext) +
 				       sizeof(struct dccp_hdr_reset);
 	struct dccp_hdr_reset *dhr;
 	struct sk_buff *skb;

 	skb = alloc_skb(sk->sk_prot->max_header, GFP_ATOMIC);
 	if (skb == NULL)
 		return NULL;

 	skb_reserve(skb, sk->sk_prot->max_header);

 	/* Swap the send and the receive. */
 	dh = dccp_zeroed_hdr(skb, dccp_hdr_reset_len);
 	dh->dccph_type	= DCCP_PKT_RESET;
 	dh->dccph_sport	= rxdh->dccph_dport;
 	dh->dccph_dport	= rxdh->dccph_sport;
 	dh->dccph_doff	= dccp_hdr_reset_len / 4;
 	dh->dccph_x	= 1;

 	dhr = dccp_hdr_reset(skb);
 	dhr->dccph_reset_code = dcb->dccpd_reset_code;

 	switch (dcb->dccpd_reset_code) {
 	case DCCP_RESET_CODE_PACKET_ERROR:
 		dhr->dccph_reset_data[0] = rxdh->dccph_type;
 		break;
 	case DCCP_RESET_CODE_OPTION_ERROR:	/* fall through */
 	case DCCP_RESET_CODE_MANDATORY_ERROR:
 		memcpy(dhr->dccph_reset_data, dcb->dccpd_reset_data, 3);
 		break;
 	}
 	/*
 	 * From RFC 4340, 8.3.1:
 	 *   If P.ackno exists, set R.seqno := P.ackno + 1.
 	 *   Else set R.seqno := 0.
 	 */
 	if (dcb->dccpd_ack_seq != DCCP_PKT_WITHOUT_ACK_SEQ)
 		dccp_hdr_set_seq(dh, ADD48(dcb->dccpd_ack_seq, 1));
 	dccp_hdr_set_ack(dccp_hdr_ack_bits(skb), dcb->dccpd_seq);

 	dccp_csum_outgoing(skb);
 	return skb;
 }

 EXPORT_SYMBOL_GPL(dccp_ctl_make_reset);

 /* send Reset on established socket, to close or abort the connection */
 int dccp_send_reset(struct sock *sk, enum dccp_reset_codes code)
 {
 	struct sk_buff *skb;
 	/*
 	 * FIXME: what if rebuild_header fails?
 	 * Should we be doing a rebuild_header here?
 	 */
 	int err = inet_csk(sk)->icsk_af_ops->rebuild_header(sk);

 	if (err != 0)
 		return err;

 	skb = sock_wmalloc(sk, sk->sk_prot->max_header, 1, GFP_ATOMIC);
 	if (skb == NULL)
 		return -ENOBUFS;

 	/* Reserve space for headers and prepare control bits. */
 	skb_reserve(skb, sk->sk_prot->max_header);
 	DCCP_SKB_CB(skb)->dccpd_type	   = DCCP_PKT_RESET;
 	DCCP_SKB_CB(skb)->dccpd_reset_code = code;

 	return dccp_transmit_skb(sk, skb);
 }

 /*
  * Do all connect socket setups that can be done AF independent.
  */
 static inline void dccp_connect_init(struct sock *sk)
 {
 	struct dccp_sock *dp = dccp_sk(sk);
 	struct dst_entry *dst = __sk_dst_get(sk);
 	struct inet_connection_sock *icsk = inet_csk(sk);

 	sk->sk_err = 0;
 	sock_reset_flag(sk, SOCK_DONE);

 	dccp_sync_mss(sk, dst_mtu(dst));

 	/* Initialise GAR as per 8.5; AWL/AWH are set in dccp_transmit_skb() */
 	dp->dccps_gar = dp->dccps_iss;

 	icsk->icsk_retransmits = 0;
 }

 int dccp_connect(struct sock *sk)
 {
 	struct sk_buff *skb;
 	struct inet_connection_sock *icsk = inet_csk(sk);

 	/* do not connect if feature negotiation setup fails */
 	if (dccp_feat_finalise_settings(dccp_sk(sk)))
 		return -EPROTO;

 	dccp_connect_init(sk);

 	skb = alloc_skb(sk->sk_prot->max_header, sk->sk_allocation);
 	if (unlikely(skb == NULL))
 		return -ENOBUFS;

 	/* Reserve space for headers. */
 	skb_reserve(skb, sk->sk_prot->max_header);

 	DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_REQUEST;

 	dccp_skb_entail(sk, skb);
 	dccp_transmit_skb(sk, skb_clone(skb, GFP_KERNEL));
 	DCCP_INC_STATS(DCCP_MIB_ACTIVEOPENS);

 	/* Timer for repeating the REQUEST until an answer. */
 	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
 				  icsk->icsk_rto, DCCP_RTO_MAX);
 	return 0;
 }

 EXPORT_SYMBOL_GPL(dccp_connect);

 void dccp_send_ack(struct sock *sk)
 {
 	/* If we have been reset, we may not send again. */
 	if (sk->sk_state != DCCP_CLOSED) {
 		struct sk_buff *skb = alloc_skb(sk->sk_prot->max_header,
 						GFP_ATOMIC);

 		if (skb == NULL) {
 			inet_csk_schedule_ack(sk);
 			inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN;
 			inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
 						  TCP_DELACK_MAX,
 						  DCCP_RTO_MAX);
 			return;
 		}

 		/* Reserve space for headers */
 		skb_reserve(skb, sk->sk_prot->max_header);
 		DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_ACK;
 		dccp_transmit_skb(sk, skb);
 	}
 }

 EXPORT_SYMBOL_GPL(dccp_send_ack);

 #if 0
 /* FIXME: Is this still necessary (11.3) - currently nowhere used by DCCP. */
 void dccp_send_delayed_ack(struct sock *sk)
 {
 	struct inet_connection_sock *icsk = inet_csk(sk);
 	/*
 	 * FIXME: tune this timer. elapsed time fixes the skew, so no problem
 	 * with using 2s, and active senders also piggyback the ACK into a
 	 * DATAACK packet, so this is really for quiescent senders.
 	 */
 	unsigned long timeout = jiffies + 2 * HZ;

 	/* Use new timeout only if there wasn't a older one earlier. */
 	if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
 		/* If delack timer was blocked or is about to expire,
 		 * send ACK now.
 		 *
 		 * FIXME: check the "about to expire" part
 		 */
 		if (icsk->icsk_ack.blocked) {
 			dccp_send_ack(sk);
 			return;
 		}

 		if (!time_before(timeout, icsk->icsk_ack.timeout))
 			timeout = icsk->icsk_ack.timeout;
 	}
 	icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
 	icsk->icsk_ack.timeout = timeout;
 	sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
 }
 #endif

 void dccp_send_sync(struct sock *sk, const u64 ackno,
 		    const enum dccp_pkt_type pkt_type)
 {
 	/*
 	 * We are not putting this on the write queue, so
 	 * dccp_transmit_skb() will set the ownership to this
 	 * sock.
 	 */
 	struct sk_buff *skb = alloc_skb(sk->sk_prot->max_header, GFP_ATOMIC);

 	if (skb == NULL) {
 		/* FIXME: how to make sure the sync is sent? */
 		DCCP_CRIT("could not send %s", dccp_packet_name(pkt_type));
 		return;
 	}

 	/* Reserve space for headers and prepare control bits. */
 	skb_reserve(skb, sk->sk_prot->max_header);
 	DCCP_SKB_CB(skb)->dccpd_type = pkt_type;
 	DCCP_SKB_CB(skb)->dccpd_ack_seq = ackno;

 	dccp_transmit_skb(sk, skb);
 }

 EXPORT_SYMBOL_GPL(dccp_send_sync);

 /*
  * Send a DCCP_PKT_CLOSE/CLOSEREQ. The caller locks the socket for us. This
  * cannot be allowed to fail queueing a DCCP_PKT_CLOSE/CLOSEREQ frame under
  * any circumstances.
  */
 void dccp_send_close(struct sock *sk, const int active)
 {
 	struct dccp_sock *dp = dccp_sk(sk);
 	struct sk_buff *skb;
 	const gfp_t prio = active ? GFP_KERNEL : GFP_ATOMIC;

 	skb = alloc_skb(sk->sk_prot->max_header, prio);
 	if (skb == NULL)
 		return;

 	/* Reserve space for headers and prepare control bits. */
 	skb_reserve(skb, sk->sk_prot->max_header);
 	if (dp->dccps_role == DCCP_ROLE_SERVER && !dp->dccps_server_timewait)
 		DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_CLOSEREQ;
 	else
 		DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_CLOSE;

 	if (active) {
 		dccp_write_xmit(sk, 1);
 		dccp_skb_entail(sk, skb);
 		dccp_transmit_skb(sk, skb_clone(skb, prio));
 		/*
 		 * Retransmission timer for active-close: RFC 4340, 8.3 requires
 		 * to retransmit the Close/CloseReq until the CLOSING/CLOSEREQ
 		 * state can be left. The initial timeout is 2 RTTs.
 		 * Since RTT measurement is done by the CCIDs, there is no easy
 		 * way to get an RTT sample. The fallback RTT from RFC 4340, 3.4
 		 * is too low (200ms); we use a high value to avoid unnecessary
 		 * retransmissions when the link RTT is > 0.2 seconds.
 		 * FIXME: Let main module sample RTTs and use that instead.
 		 */
 		inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
 					  DCCP_TIMEOUT_INIT, DCCP_RTO_MAX);
 	} else
 		dccp_transmit_skb(sk, skb);
 }
	/*
	* net/dccp/output.c
	*
	* An implementation of the DCCP protocol
	* Arnaldo Carvalho de Melo <acme@conectiva.com.br>
	*
	* This program is free software; you can redistribute it and/or
	* modify it under the terms of the GNU General Public License
	* as published by the Free Software Foundation; either version
	* 2 of the License, or (at your option) any later version.
	*/

	#include <linux/dccp.h>
	#include <linux/kernel.h>
	#include <linux/skbuff.h>
	#include <linux/slab.h>

	#include <net/inet_sock.h>
	#include <net/sock.h>

	#include "ackvec.h"
	#include "ccid.h"
	#include "dccp.h"

	static inline void dccp_event_ack_sent(struct sock *sk)
	{
	inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
	}

	static void dccp_skb_entail(struct sock sk, struct sk_buff skb)
	{
	skb_set_owner_w(skb, sk);
	WARN_ON(sk->sk_send_head);
	sk->sk_send_head = skb;
	}

	/*
	* All SKB's seen here are completely headerless. It is our
	* job to build the DCCP header, and pass the packet down to
	* IP so it can do the same plus pass the packet off to the
	* device.
	*/
	static int dccp_transmit_skb(struct sock sk, struct sk_buff skb)
	{
	if (likely(skb != NULL)) {
	const struct inet_sock *inet = inet_sk(sk);
	const struct inet_connection_sock *icsk = inet_csk(sk);
	struct dccp_sock *dp = dccp_sk(sk);
	struct dccp_skb_cb *dcb = DCCP_SKB_CB(skb);
	struct dccp_hdr *dh;
	/* XXX For now we're using only 48 bits sequence numbers */
	const u32 dccp_header_size = sizeof(*dh) +
	sizeof(struct dccp_hdr_ext) +
	dccp_packet_hdr_len(dcb->dccpd_type);
	int err, set_ack = 1;
	u64 ackno = dp->dccps_gsr;
	/*
	* Increment GSS here already in case the option code needs it.
	* Update GSS for real only if option processing below succeeds.
	*/
	dcb->dccpd_seq = ADD48(dp->dccps_gss, 1);

	switch (dcb->dccpd_type) {
	case DCCP_PKT_DATA:
	set_ack = 0;
	/* fall through */
	case DCCP_PKT_DATAACK:
	case DCCP_PKT_RESET:
	break;

	case DCCP_PKT_REQUEST:
	set_ack = 0;
	/* Use ISS on the first (non-retransmitted) Request. */
	if (icsk->icsk_retransmits == 0)
	dcb->dccpd_seq = dp->dccps_iss;
	/* fall through */

	case DCCP_PKT_SYNC:
	case DCCP_PKT_SYNCACK:
	ackno = dcb->dccpd_ack_seq;
	/* fall through */
	default:
	/*
	* Set owner/destructor: some skbs are allocated via
	* alloc_skb (e.g. when retransmission may happen).
	* Only Data, DataAck, and Reset packets should come
	* through here with skb->sk set.
	*/
	WARN_ON(skb->sk);
	skb_set_owner_w(skb, sk);
	break;
	}

	if (dccp_insert_options(sk, skb)) {
	kfree_skb(skb);
	return -EPROTO;
	}


	/* Build DCCP header and checksum it. */
	dh = dccp_zeroed_hdr(skb, dccp_header_size);
	dh->dccph_type = dcb->dccpd_type;
	dh->dccph_sport = inet->inet_sport;
	dh->dccph_dport = inet->inet_dport;
	dh->dccph_doff = (dccp_header_size + dcb->dccpd_opt_len) / 4;
	dh->dccph_ccval = dcb->dccpd_ccval;
	dh->dccph_cscov = dp->dccps_pcslen;
	/* XXX For now we're using only 48 bits sequence numbers */
	dh->dccph_x = 1;

	dccp_update_gss(sk, dcb->dccpd_seq);
	dccp_hdr_set_seq(dh, dp->dccps_gss);
	if (set_ack)
	dccp_hdr_set_ack(dccp_hdr_ack_bits(skb), ackno);

	switch (dcb->dccpd_type) {
	case DCCP_PKT_REQUEST:
	dccp_hdr_request(skb)->dccph_req_service =
	dp->dccps_service;
	/*
	* Limit Ack window to ISS <= P.ackno <= GSS, so that
	* only Responses to Requests we sent are considered.
	*/
	dp->dccps_awl = dp->dccps_iss;
	break;
	case DCCP_PKT_RESET:
	dccp_hdr_reset(skb)->dccph_reset_code =
	dcb->dccpd_reset_code;
	break;
	}

	icsk->icsk_af_ops->send_check(sk, skb);

	if (set_ack)
	dccp_event_ack_sent(sk);

	DCCP_INC_STATS(DCCP_MIB_OUTSEGS);

	err = icsk->icsk_af_ops->queue_xmit(skb);
	return net_xmit_eval(err);
	}
	return -ENOBUFS;
	}

	/**
	* dccp_determine_ccmps - Find out about CCID-specfic packet-size limits
	* We only consider the HC-sender CCID for setting the CCMPS (RFC 4340, 14.),
	* since the RX CCID is restricted to feedback packets (Acks), which are small
	* in comparison with the data traffic. A value of 0 means "no current CCMPS".
	*/
	static u32 dccp_determine_ccmps(const struct dccp_sock *dp)
	{
	const struct ccid *tx_ccid = dp->dccps_hc_tx_ccid;

	if (tx_ccid == NULL \|\| tx_ccid->ccid_ops == NULL)
	return 0;
	return tx_ccid->ccid_ops->ccid_ccmps;
	}

	unsigned int dccp_sync_mss(struct sock *sk, u32 pmtu)
	{
	struct inet_connection_sock *icsk = inet_csk(sk);
	struct dccp_sock *dp = dccp_sk(sk);
	u32 ccmps = dccp_determine_ccmps(dp);
	u32 cur_mps = ccmps ? min(pmtu, ccmps) : pmtu;

	/* Account for header lengths and IPv4/v6 option overhead */
	cur_mps -= (icsk->icsk_af_ops->net_header_len + icsk->icsk_ext_hdr_len +
	sizeof(struct dccp_hdr) + sizeof(struct dccp_hdr_ext));

	/*
	* Leave enough headroom for common DCCP header options.
	* This only considers options which may appear on DCCP-Data packets, as
	* per table 3 in RFC 4340, 5.8. When running out of space for other
	* options (eg. Ack Vector which can take up to 255 bytes), it is better
	* to schedule a separate Ack. Thus we leave headroom for the following:
	* - 1 byte for Slow Receiver (11.6)
	* - 6 bytes for Timestamp (13.1)
	* - 10 bytes for Timestamp Echo (13.3)
	* - 8 bytes for NDP count (7.7, when activated)
	* - 6 bytes for Data Checksum (9.3)
	* - %DCCPAV_MIN_OPTLEN bytes for Ack Vector size (11.4, when enabled)
	*/
	cur_mps -= roundup(1 + 6 + 10 + dp->dccps_send_ndp_count * 8 + 6 +
	(dp->dccps_hc_rx_ackvec ? DCCPAV_MIN_OPTLEN : 0), 4);

	/* And store cached results */
	icsk->icsk_pmtu_cookie = pmtu;
	dp->dccps_mss_cache = cur_mps;

	return cur_mps;
	}

	EXPORT_SYMBOL_GPL(dccp_sync_mss);

	void dccp_write_space(struct sock *sk)
	{
	struct socket_wq *wq;

	rcu_read_lock();
	wq = rcu_dereference(sk->sk_wq);
	if (wq_has_sleeper(wq))
	wake_up_interruptible(&wq->wait);
	/* Should agree with poll, otherwise some programs break */
	if (sock_writeable(sk))
	sk_wake_async(sk, SOCK_WAKE_SPACE, POLL_OUT);

	rcu_read_unlock();
	}

	/**
	* 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_sleep(sk), &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_sleep(sk), &wait);
	return rc;

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

	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_retransmit_skb - Retransmit Request, Close, or CloseReq packets
	* There are only four retransmittable packet types in DCCP:
	* - Request in client-REQUEST state (sec. 8.1.1),
	* - CloseReq in server-CLOSEREQ state (sec. 8.3),
	* - Close in node-CLOSING state (sec. 8.3),
	* - Acks in client-PARTOPEN state (sec. 8.1.5, handled by dccp_delack_timer()).
	* This function expects sk->sk_send_head to contain the original skb.
	*/
	int dccp_retransmit_skb(struct sock *sk)
	{
	WARN_ON(sk->sk_send_head == NULL);

	if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk) != 0)
	return -EHOSTUNREACH; /* Routing failure or similar. */

	/* this count is used to distinguish original and retransmitted skb */
	inet_csk(sk)->icsk_retransmits++;

	return dccp_transmit_skb(sk, skb_clone(sk->sk_send_head, GFP_ATOMIC));
	}

	struct sk_buff dccp_make_response(struct sock sk, struct dst_entry *dst,
	struct request_sock *req)
	{
	struct dccp_hdr *dh;
	struct dccp_request_sock *dreq;
	const u32 dccp_header_size = sizeof(struct dccp_hdr) +
	sizeof(struct dccp_hdr_ext) +
	sizeof(struct dccp_hdr_response);
	struct sk_buff *skb = sock_wmalloc(sk, sk->sk_prot->max_header, 1,
	GFP_ATOMIC);
	if (skb == NULL)
	return NULL;

	/* Reserve space for headers. */
	skb_reserve(skb, sk->sk_prot->max_header);

	skb_dst_set(skb, dst_clone(dst));

	dreq = dccp_rsk(req);
	if (inet_rsk(req)->acked) /* increase ISS upon retransmission */
	dccp_inc_seqno(&dreq->dreq_iss);
	DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_RESPONSE;
	DCCP_SKB_CB(skb)->dccpd_seq = dreq->dreq_iss;

	/* Resolve feature dependencies resulting from choice of CCID */
	if (dccp_feat_server_ccid_dependencies(dreq))
	goto response_failed;

	if (dccp_insert_options_rsk(dreq, skb))
	goto response_failed;

	/* Build and checksum header */
	dh = dccp_zeroed_hdr(skb, dccp_header_size);

	dh->dccph_sport = inet_rsk(req)->loc_port;
	dh->dccph_dport = inet_rsk(req)->rmt_port;
	dh->dccph_doff = (dccp_header_size +
	DCCP_SKB_CB(skb)->dccpd_opt_len) / 4;
	dh->dccph_type = DCCP_PKT_RESPONSE;
	dh->dccph_x = 1;
	dccp_hdr_set_seq(dh, dreq->dreq_iss);
	dccp_hdr_set_ack(dccp_hdr_ack_bits(skb), dreq->dreq_isr);
	dccp_hdr_response(skb)->dccph_resp_service = dreq->dreq_service;

	dccp_csum_outgoing(skb);

	/* We use `acked' to remember that a Response was already sent. */
	inet_rsk(req)->acked = 1;
	DCCP_INC_STATS(DCCP_MIB_OUTSEGS);
	return skb;
	response_failed:
	kfree_skb(skb);
	return NULL;
	}

	EXPORT_SYMBOL_GPL(dccp_make_response);

	/* answer offending packet in @rcv_skb with Reset from control socket @ctl */
	struct sk_buff dccp_ctl_make_reset(struct sock sk, struct sk_buff *rcv_skb)
	{
	struct dccp_hdr rxdh = dccp_hdr(rcv_skb), dh;
	struct dccp_skb_cb *dcb = DCCP_SKB_CB(rcv_skb);
	const u32 dccp_hdr_reset_len = sizeof(struct dccp_hdr) +
	sizeof(struct dccp_hdr_ext) +
	sizeof(struct dccp_hdr_reset);
	struct dccp_hdr_reset *dhr;
	struct sk_buff *skb;

	skb = alloc_skb(sk->sk_prot->max_header, GFP_ATOMIC);
	if (skb == NULL)
	return NULL;

	skb_reserve(skb, sk->sk_prot->max_header);

	/* Swap the send and the receive. */
	dh = dccp_zeroed_hdr(skb, dccp_hdr_reset_len);
	dh->dccph_type = DCCP_PKT_RESET;
	dh->dccph_sport = rxdh->dccph_dport;
	dh->dccph_dport = rxdh->dccph_sport;
	dh->dccph_doff = dccp_hdr_reset_len / 4;
	dh->dccph_x = 1;

	dhr = dccp_hdr_reset(skb);
	dhr->dccph_reset_code = dcb->dccpd_reset_code;

	switch (dcb->dccpd_reset_code) {
	case DCCP_RESET_CODE_PACKET_ERROR:
	dhr->dccph_reset_data[0] = rxdh->dccph_type;
	break;
	case DCCP_RESET_CODE_OPTION_ERROR: /* fall through */
	case DCCP_RESET_CODE_MANDATORY_ERROR:
	memcpy(dhr->dccph_reset_data, dcb->dccpd_reset_data, 3);
	break;
	}
	/*
	* From RFC 4340, 8.3.1:
	* If P.ackno exists, set R.seqno := P.ackno + 1.
	* Else set R.seqno := 0.
	*/
	if (dcb->dccpd_ack_seq != DCCP_PKT_WITHOUT_ACK_SEQ)
	dccp_hdr_set_seq(dh, ADD48(dcb->dccpd_ack_seq, 1));
	dccp_hdr_set_ack(dccp_hdr_ack_bits(skb), dcb->dccpd_seq);

	dccp_csum_outgoing(skb);
	return skb;
	}

	EXPORT_SYMBOL_GPL(dccp_ctl_make_reset);

	/* send Reset on established socket, to close or abort the connection */
	int dccp_send_reset(struct sock *sk, enum dccp_reset_codes code)
	{
	struct sk_buff *skb;
	/*
	* FIXME: what if rebuild_header fails?
	* Should we be doing a rebuild_header here?
	*/
	int err = inet_csk(sk)->icsk_af_ops->rebuild_header(sk);

	if (err != 0)
	return err;

	skb = sock_wmalloc(sk, sk->sk_prot->max_header, 1, GFP_ATOMIC);
	if (skb == NULL)
	return -ENOBUFS;

	/* Reserve space for headers and prepare control bits. */
	skb_reserve(skb, sk->sk_prot->max_header);
	DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_RESET;
	DCCP_SKB_CB(skb)->dccpd_reset_code = code;

	return dccp_transmit_skb(sk, skb);
	}

	/*
	* Do all connect socket setups that can be done AF independent.
	*/
	static inline void dccp_connect_init(struct sock *sk)
	{
	struct dccp_sock *dp = dccp_sk(sk);
	struct dst_entry *dst = __sk_dst_get(sk);
	struct inet_connection_sock *icsk = inet_csk(sk);

	sk->sk_err = 0;
	sock_reset_flag(sk, SOCK_DONE);

	dccp_sync_mss(sk, dst_mtu(dst));

	/* Initialise GAR as per 8.5; AWL/AWH are set in dccp_transmit_skb() */
	dp->dccps_gar = dp->dccps_iss;

	icsk->icsk_retransmits = 0;
	}

	int dccp_connect(struct sock *sk)
	{
	struct sk_buff *skb;
	struct inet_connection_sock *icsk = inet_csk(sk);

	/* do not connect if feature negotiation setup fails */
	if (dccp_feat_finalise_settings(dccp_sk(sk)))
	return -EPROTO;

	dccp_connect_init(sk);

	skb = alloc_skb(sk->sk_prot->max_header, sk->sk_allocation);
	if (unlikely(skb == NULL))
	return -ENOBUFS;

	/* Reserve space for headers. */
	skb_reserve(skb, sk->sk_prot->max_header);

	DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_REQUEST;

	dccp_skb_entail(sk, skb);
	dccp_transmit_skb(sk, skb_clone(skb, GFP_KERNEL));
	DCCP_INC_STATS(DCCP_MIB_ACTIVEOPENS);

	/* Timer for repeating the REQUEST until an answer. */
	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
	icsk->icsk_rto, DCCP_RTO_MAX);
	return 0;
	}

	EXPORT_SYMBOL_GPL(dccp_connect);

	void dccp_send_ack(struct sock *sk)
	{
	/* If we have been reset, we may not send again. */
	if (sk->sk_state != DCCP_CLOSED) {
	struct sk_buff *skb = alloc_skb(sk->sk_prot->max_header,
	GFP_ATOMIC);

	if (skb == NULL) {
	inet_csk_schedule_ack(sk);
	inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN;
	inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
	TCP_DELACK_MAX,
	DCCP_RTO_MAX);
	return;
	}

	/* Reserve space for headers */
	skb_reserve(skb, sk->sk_prot->max_header);
	DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_ACK;
	dccp_transmit_skb(sk, skb);
	}
	}

	EXPORT_SYMBOL_GPL(dccp_send_ack);

	#if 0
	/* FIXME: Is this still necessary (11.3) - currently nowhere used by DCCP. */
	void dccp_send_delayed_ack(struct sock *sk)
	{
	struct inet_connection_sock *icsk = inet_csk(sk);
	/*
	* FIXME: tune this timer. elapsed time fixes the skew, so no problem
	* with using 2s, and active senders also piggyback the ACK into a
	* DATAACK packet, so this is really for quiescent senders.
	*/
	unsigned long timeout = jiffies + 2 * HZ;

	/* Use new timeout only if there wasn't a older one earlier. */
	if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
	/* If delack timer was blocked or is about to expire,
	* send ACK now.
	*
	* FIXME: check the "about to expire" part
	*/
	if (icsk->icsk_ack.blocked) {
	dccp_send_ack(sk);
	return;
	}

	if (!time_before(timeout, icsk->icsk_ack.timeout))
	timeout = icsk->icsk_ack.timeout;
	}
	icsk->icsk_ack.pending \|= ICSK_ACK_SCHED \| ICSK_ACK_TIMER;
	icsk->icsk_ack.timeout = timeout;
	sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
	}
	#endif

	void dccp_send_sync(struct sock *sk, const u64 ackno,
	const enum dccp_pkt_type pkt_type)
	{
	/*
	* We are not putting this on the write queue, so
	* dccp_transmit_skb() will set the ownership to this
	* sock.
	*/
	struct sk_buff *skb = alloc_skb(sk->sk_prot->max_header, GFP_ATOMIC);

	if (skb == NULL) {
	/* FIXME: how to make sure the sync is sent? */
	DCCP_CRIT("could not send %s", dccp_packet_name(pkt_type));
	return;
	}

	/* Reserve space for headers and prepare control bits. */
	skb_reserve(skb, sk->sk_prot->max_header);
	DCCP_SKB_CB(skb)->dccpd_type = pkt_type;
	DCCP_SKB_CB(skb)->dccpd_ack_seq = ackno;

	dccp_transmit_skb(sk, skb);
	}

	EXPORT_SYMBOL_GPL(dccp_send_sync);

	/*
	* Send a DCCP_PKT_CLOSE/CLOSEREQ. The caller locks the socket for us. This
	* cannot be allowed to fail queueing a DCCP_PKT_CLOSE/CLOSEREQ frame under
	* any circumstances.
	*/
	void dccp_send_close(struct sock *sk, const int active)
	{
	struct dccp_sock *dp = dccp_sk(sk);
	struct sk_buff *skb;
	const gfp_t prio = active ? GFP_KERNEL : GFP_ATOMIC;

	skb = alloc_skb(sk->sk_prot->max_header, prio);
	if (skb == NULL)
	return;

	/* Reserve space for headers and prepare control bits. */
	skb_reserve(skb, sk->sk_prot->max_header);
	if (dp->dccps_role == DCCP_ROLE_SERVER && !dp->dccps_server_timewait)
	DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_CLOSEREQ;
	else
	DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_CLOSE;

	if (active) {
	dccp_write_xmit(sk, 1);
	dccp_skb_entail(sk, skb);
	dccp_transmit_skb(sk, skb_clone(skb, prio));
	/*
	* Retransmission timer for active-close: RFC 4340, 8.3 requires
	* to retransmit the Close/CloseReq until the CLOSING/CLOSEREQ
	* state can be left. The initial timeout is 2 RTTs.
	* Since RTT measurement is done by the CCIDs, there is no easy
	* way to get an RTT sample. The fallback RTT from RFC 4340, 3.4
	* is too low (200ms); we use a high value to avoid unnecessary
	* retransmissions when the link RTT is > 0.2 seconds.
	* FIXME: Let main module sample RTTs and use that instead.
	*/
	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
	DCCP_TIMEOUT_INIT, DCCP_RTO_MAX);
	} else
	dccp_transmit_skb(sk, skb);
	}