/* SCTP kernel implementation
   * (C) Copyright IBM Corp. 2001, 2004
   * Copyright (c) 1999-2000 Cisco, Inc.
   * Copyright (c) 1999-2001 Motorola, Inc.
   * Copyright (c) 2001 Intel Corp.
   * Copyright (c) 2001 Nokia, Inc.
   * Copyright (c) 2001 La Monte H.P. Yarroll
   *
   * This abstraction carries sctp events to the ULP (sockets).
   *
   * This SCTP implementation 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, or (at your option)
   * any later version.
   *
   * This SCTP implementation is distributed in the hope that it
   * will be useful, but WITHOUT ANY WARRANTY; without even the implied
   *                 ************************
   * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
   * See the GNU General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with GNU CC; see the file COPYING.  If not, see
   * <http://www.gnu.org/licenses/>.
   *
   * Please send any bug reports or fixes you make to the
   * email address(es):
   *    lksctp developers <linux-sctp@vger.kernel.org>
   *
   * Written or modified by:
   *    Jon Grimm             <jgrimm@us.ibm.com>
   *    La Monte H.P. Yarroll <piggy@acm.org>
   *    Sridhar Samudrala     <sri@us.ibm.com>
   */
  
  #include <linux/slab.h>
  #include <linux/types.h>
  #include <linux/skbuff.h>
  #include <net/sock.h>
  #include <net/sctp/structs.h>
  #include <net/sctp/sctp.h>
  #include <net/sctp/sm.h>
  
  /* Forward declarations for internal helpers.  */
  static struct sctp_ulpevent *sctp_ulpq_reasm(struct sctp_ulpq *ulpq,
  					      struct sctp_ulpevent *);
  static struct sctp_ulpevent *sctp_ulpq_order(struct sctp_ulpq *,
  					      struct sctp_ulpevent *);
  static void sctp_ulpq_reasm_drain(struct sctp_ulpq *ulpq);
  
  /* 1st Level Abstractions */
  
  /* Initialize a ULP queue from a block of memory.  */
  struct sctp_ulpq *sctp_ulpq_init(struct sctp_ulpq *ulpq,
  				 struct sctp_association *asoc)
  {
  	memset(ulpq, 0, sizeof(struct sctp_ulpq));
  
  	ulpq->asoc = asoc;
  	skb_queue_head_init(&ulpq->reasm);
  	skb_queue_head_init(&ulpq->lobby);
  	ulpq->pd_mode  = 0;
  
  	return ulpq;
  }
  
  
  /* Flush the reassembly and ordering queues.  */
  void sctp_ulpq_flush(struct sctp_ulpq *ulpq)
  {
  	struct sk_buff *skb;
  	struct sctp_ulpevent *event;
  
  	while ((skb = __skb_dequeue(&ulpq->lobby)) != NULL) {
  		event = sctp_skb2event(skb);
  		sctp_ulpevent_free(event);
  	}
  
  	while ((skb = __skb_dequeue(&ulpq->reasm)) != NULL) {
  		event = sctp_skb2event(skb);
  		sctp_ulpevent_free(event);
  	}
  
  }
  
  /* Dispose of a ulpqueue.  */
  void sctp_ulpq_free(struct sctp_ulpq *ulpq)
  {
  	sctp_ulpq_flush(ulpq);
  }
  
  /* Process an incoming DATA chunk.  */
  int sctp_ulpq_tail_data(struct sctp_ulpq *ulpq, struct sctp_chunk *chunk,
  			gfp_t gfp)
  {
  	struct sk_buff_head temp;
  	struct sctp_ulpevent *event;
  	int event_eor = 0;
  
  	/* Create an event from the incoming chunk. */
  	event = sctp_ulpevent_make_rcvmsg(chunk->asoc, chunk, gfp);
  	if (!event)
  		return -ENOMEM;
  
  	/* Do reassembly if needed.  */
  	event = sctp_ulpq_reasm(ulpq, event);
  
  	/* Do ordering if needed.  */
  	if ((event) && (event->msg_flags & MSG_EOR)) {
  		/* Create a temporary list to collect chunks on.  */
  		skb_queue_head_init(&temp);
  		__skb_queue_tail(&temp, sctp_event2skb(event));
  
  		event = sctp_ulpq_order(ulpq, event);
  	}
  
  	/* Send event to the ULP.  'event' is the sctp_ulpevent for
  	 * very first SKB on the 'temp' list.
  	 */
  	if (event) {
  		event_eor = (event->msg_flags & MSG_EOR) ? 1 : 0;
  		sctp_ulpq_tail_event(ulpq, event);
  	}
  
  	return event_eor;
  }
  
  /* Add a new event for propagation to the ULP.  */
  /* Clear the partial delivery mode for this socket.   Note: This
   * assumes that no association is currently in partial delivery mode.
   */
  int sctp_clear_pd(struct sock *sk, struct sctp_association *asoc)
  {
  	struct sctp_sock *sp = sctp_sk(sk);
  
  	if (atomic_dec_and_test(&sp->pd_mode)) {
  		/* This means there are no other associations in PD, so
  		 * we can go ahead and clear out the lobby in one shot
  		 */
  		if (!skb_queue_empty(&sp->pd_lobby)) {
  			struct list_head *list;
  			sctp_skb_list_tail(&sp->pd_lobby, &sk->sk_receive_queue);
  			list = (struct list_head *)&sctp_sk(sk)->pd_lobby;
  			INIT_LIST_HEAD(list);
  			return 1;
  		}
  	} else {
  		/* There are other associations in PD, so we only need to
  		 * pull stuff out of the lobby that belongs to the
  		 * associations that is exiting PD (all of its notifications
  		 * are posted here).
  		 */
  		if (!skb_queue_empty(&sp->pd_lobby) && asoc) {
  			struct sk_buff *skb, *tmp;
  			struct sctp_ulpevent *event;
  
  			sctp_skb_for_each(skb, &sp->pd_lobby, tmp) {
  				event = sctp_skb2event(skb);
  				if (event->asoc == asoc) {
  					__skb_unlink(skb, &sp->pd_lobby);
  					__skb_queue_tail(&sk->sk_receive_queue,
  							 skb);
  				}
  			}
  		}
  	}
  
  	return 0;
  }
  
  /* Set the pd_mode on the socket and ulpq */
  static void sctp_ulpq_set_pd(struct sctp_ulpq *ulpq)
  {
  	struct sctp_sock *sp = sctp_sk(ulpq->asoc->base.sk);
  
  	atomic_inc(&sp->pd_mode);
  	ulpq->pd_mode = 1;
  }
  
  /* Clear the pd_mode and restart any pending messages waiting for delivery. */
  static int sctp_ulpq_clear_pd(struct sctp_ulpq *ulpq)
  {
  	ulpq->pd_mode = 0;
  	sctp_ulpq_reasm_drain(ulpq);
  	return sctp_clear_pd(ulpq->asoc->base.sk, ulpq->asoc);
  }
  
  /* If the SKB of 'event' is on a list, it is the first such member
   * of that list.
   */
  int sctp_ulpq_tail_event(struct sctp_ulpq *ulpq, struct sctp_ulpevent *event)
  {
  	struct sock *sk = ulpq->asoc->base.sk;
  	struct sk_buff_head *queue, *skb_list;
  	struct sk_buff *skb = sctp_event2skb(event);
  	int clear_pd = 0;
  
  	skb_list = (struct sk_buff_head *) skb->prev;
  
  	/* If the socket is just going to throw this away, do not
  	 * even try to deliver it.
  	 */
  	if (sock_flag(sk, SOCK_DEAD) || (sk->sk_shutdown & RCV_SHUTDOWN))
  		goto out_free;
  
  	/* Check if the user wishes to receive this event.  */
  	if (!sctp_ulpevent_is_enabled(event, &sctp_sk(sk)->subscribe))
  		goto out_free;
  
  	/* If we are in partial delivery mode, post to the lobby until
  	 * partial delivery is cleared, unless, of course _this_ is
  	 * the association the cause of the partial delivery.
  	 */
  
  	if (atomic_read(&sctp_sk(sk)->pd_mode) == 0) {
  		queue = &sk->sk_receive_queue;
  	} else {
  		if (ulpq->pd_mode) {
  			/* If the association is in partial delivery, we
  			 * need to finish delivering the partially processed
  			 * packet before passing any other data.  This is
  			 * because we don't truly support stream interleaving.
  			 */
  			if ((event->msg_flags & MSG_NOTIFICATION) ||
  			    (SCTP_DATA_NOT_FRAG ==
  				    (event->msg_flags & SCTP_DATA_FRAG_MASK)))
  				queue = &sctp_sk(sk)->pd_lobby;
  			else {
  				clear_pd = event->msg_flags & MSG_EOR;
  				queue = &sk->sk_receive_queue;
  			}
  		} else {
  			/*
  			 * If fragment interleave is enabled, we
  			 * can queue this to the receive queue instead
  			 * of the lobby.
  			 */
  			if (sctp_sk(sk)->frag_interleave)
  				queue = &sk->sk_receive_queue;
  			else
  				queue = &sctp_sk(sk)->pd_lobby;
  		}
  	}
  
  	/* If we are harvesting multiple skbs they will be
  	 * collected on a list.
  	 */
  	if (skb_list)
  		sctp_skb_list_tail(skb_list, queue);
  	else
  		__skb_queue_tail(queue, skb);
  
  	/* Did we just complete partial delivery and need to get
  	 * rolling again?  Move pending data to the receive
  	 * queue.
  	 */
  	if (clear_pd)
  		sctp_ulpq_clear_pd(ulpq);
  
  	if (queue == &sk->sk_receive_queue)
  		sk->sk_data_ready(sk, 0);
  	return 1;
  
  out_free:
  	if (skb_list)
  		sctp_queue_purge_ulpevents(skb_list);
  	else
  		sctp_ulpevent_free(event);
  
  	return 0;
  }
  
  /* 2nd Level Abstractions */
  
  /* Helper function to store chunks that need to be reassembled.  */
  static void sctp_ulpq_store_reasm(struct sctp_ulpq *ulpq,
  					 struct sctp_ulpevent *event)
  {
  	struct sk_buff *pos;
  	struct sctp_ulpevent *cevent;
  	__u32 tsn, ctsn;
  
  	tsn = event->tsn;
  
  	/* See if it belongs at the end. */
  	pos = skb_peek_tail(&ulpq->reasm);
  	if (!pos) {
  		__skb_queue_tail(&ulpq->reasm, sctp_event2skb(event));
  		return;
  	}
  
  	/* Short circuit just dropping it at the end. */
  	cevent = sctp_skb2event(pos);
  	ctsn = cevent->tsn;
  	if (TSN_lt(ctsn, tsn)) {
  		__skb_queue_tail(&ulpq->reasm, sctp_event2skb(event));
  		return;
  	}
  
  	/* Find the right place in this list. We store them by TSN.  */
  	skb_queue_walk(&ulpq->reasm, pos) {
  		cevent = sctp_skb2event(pos);
  		ctsn = cevent->tsn;
  
  		if (TSN_lt(tsn, ctsn))
  			break;
  	}
  
  	/* Insert before pos. */
  	__skb_queue_before(&ulpq->reasm, pos, sctp_event2skb(event));
  
  }
  
  /* Helper function to return an event corresponding to the reassembled
   * datagram.
   * This routine creates a re-assembled skb given the first and last skb's
   * as stored in the reassembly queue. The skb's may be non-linear if the sctp
   * payload was fragmented on the way and ip had to reassemble them.
   * We add the rest of skb's to the first skb's fraglist.
   */
  static struct sctp_ulpevent *sctp_make_reassembled_event(struct net *net,
  	struct sk_buff_head *queue, struct sk_buff *f_frag,
  	struct sk_buff *l_frag)
  {
  	struct sk_buff *pos;
  	struct sk_buff *new = NULL;
  	struct sctp_ulpevent *event;
  	struct sk_buff *pnext, *last;
  	struct sk_buff *list = skb_shinfo(f_frag)->frag_list;
  
  	/* Store the pointer to the 2nd skb */
  	if (f_frag == l_frag)
  		pos = NULL;
  	else
  		pos = f_frag->next;
  
  	/* Get the last skb in the f_frag's frag_list if present. */
  	for (last = list; list; last = list, list = list->next)
  		;
  
  	/* Add the list of remaining fragments to the first fragments
  	 * frag_list.
  	 */
  	if (last)
  		last->next = pos;
  	else {
  		if (skb_cloned(f_frag)) {
  			/* This is a cloned skb, we can't just modify
  			 * the frag_list.  We need a new skb to do that.
  			 * Instead of calling skb_unshare(), we'll do it
  			 * ourselves since we need to delay the free.
  			 */
  			new = skb_copy(f_frag, GFP_ATOMIC);
  			if (!new)
  				return NULL;	/* try again later */
  
  			sctp_skb_set_owner_r(new, f_frag->sk);
  
  			skb_shinfo(new)->frag_list = pos;
  		} else
  			skb_shinfo(f_frag)->frag_list = pos;
  	}
  
  	/* Remove the first fragment from the reassembly queue.  */
  	__skb_unlink(f_frag, queue);
  
  	/* if we did unshare, then free the old skb and re-assign */
  	if (new) {
  		kfree_skb(f_frag);
  		f_frag = new;
  	}
  
  	while (pos) {
  
  		pnext = pos->next;
  
  		/* Update the len and data_len fields of the first fragment. */
  		f_frag->len += pos->len;
  		f_frag->data_len += pos->len;
  
  		/* Remove the fragment from the reassembly queue.  */
  		__skb_unlink(pos, queue);
  
  		/* Break if we have reached the last fragment.  */
  		if (pos == l_frag)
  			break;
  		pos->next = pnext;
  		pos = pnext;
  	}
  
  	event = sctp_skb2event(f_frag);
  	SCTP_INC_STATS(net, SCTP_MIB_REASMUSRMSGS);
  
  	return event;
  }
  
  
  /* Helper function to check if an incoming chunk has filled up the last
   * missing fragment in a SCTP datagram and return the corresponding event.
   */
  static struct sctp_ulpevent *sctp_ulpq_retrieve_reassembled(struct sctp_ulpq *ulpq)
  {
  	struct sk_buff *pos;
  	struct sctp_ulpevent *cevent;
  	struct sk_buff *first_frag = NULL;
  	__u32 ctsn, next_tsn;
  	struct sctp_ulpevent *retval = NULL;
  	struct sk_buff *pd_first = NULL;
  	struct sk_buff *pd_last = NULL;
  	size_t pd_len = 0;
  	struct sctp_association *asoc;
  	u32 pd_point;
  
  	/* Initialized to 0 just to avoid compiler warning message.  Will
  	 * never be used with this value. It is referenced only after it
  	 * is set when we find the first fragment of a message.
  	 */
  	next_tsn = 0;
  
  	/* The chunks are held in the reasm queue sorted by TSN.
  	 * Walk through the queue sequentially and look for a sequence of
  	 * fragmented chunks that complete a datagram.
  	 * 'first_frag' and next_tsn are reset when we find a chunk which
  	 * is the first fragment of a datagram. Once these 2 fields are set
  	 * we expect to find the remaining middle fragments and the last
  	 * fragment in order. If not, first_frag is reset to NULL and we
  	 * start the next pass when we find another first fragment.
  	 *
  	 * There is a potential to do partial delivery if user sets
  	 * SCTP_PARTIAL_DELIVERY_POINT option. Lets count some things here
  	 * to see if can do PD.
  	 */
  	skb_queue_walk(&ulpq->reasm, pos) {
  		cevent = sctp_skb2event(pos);
  		ctsn = cevent->tsn;
  
  		switch (cevent->msg_flags & SCTP_DATA_FRAG_MASK) {
  		case SCTP_DATA_FIRST_FRAG:
  			/* If this "FIRST_FRAG" is the first
  			 * element in the queue, then count it towards
  			 * possible PD.
  			 */
  			if (pos == ulpq->reasm.next) {
  			    pd_first = pos;
  			    pd_last = pos;
  			    pd_len = pos->len;
  			} else {
  			    pd_first = NULL;
  			    pd_last = NULL;
  			    pd_len = 0;
  			}
  
  			first_frag = pos;
  			next_tsn = ctsn + 1;
  			break;
  
  		case SCTP_DATA_MIDDLE_FRAG:
  			if ((first_frag) && (ctsn == next_tsn)) {
  				next_tsn++;
  				if (pd_first) {
  				    pd_last = pos;
  				    pd_len += pos->len;
  				}
  			} else
  				first_frag = NULL;
  			break;
  
  		case SCTP_DATA_LAST_FRAG:
  			if (first_frag && (ctsn == next_tsn))
  				goto found;
  			else
  				first_frag = NULL;
  			break;
  		}
  	}
  
  	asoc = ulpq->asoc;
  	if (pd_first) {
  		/* Make sure we can enter partial deliver.
  		 * We can trigger partial delivery only if framgent
  		 * interleave is set, or the socket is not already
  		 * in  partial delivery.
  		 */
  		if (!sctp_sk(asoc->base.sk)->frag_interleave &&
  		    atomic_read(&sctp_sk(asoc->base.sk)->pd_mode))
  			goto done;
  
  		cevent = sctp_skb2event(pd_first);
  		pd_point = sctp_sk(asoc->base.sk)->pd_point;
  		if (pd_point && pd_point <= pd_len) {
  			retval = sctp_make_reassembled_event(sock_net(asoc->base.sk),
  							     &ulpq->reasm,
  							     pd_first,
  							     pd_last);
  			if (retval)
  				sctp_ulpq_set_pd(ulpq);
  		}
  	}
  done:
  	return retval;
  found:
  	retval = sctp_make_reassembled_event(sock_net(ulpq->asoc->base.sk),
  					     &ulpq->reasm, first_frag, pos);
  	if (retval)
  		retval->msg_flags |= MSG_EOR;
  	goto done;
  }
  
  /* Retrieve the next set of fragments of a partial message. */
  static struct sctp_ulpevent *sctp_ulpq_retrieve_partial(struct sctp_ulpq *ulpq)
  {
  	struct sk_buff *pos, *last_frag, *first_frag;
  	struct sctp_ulpevent *cevent;
  	__u32 ctsn, next_tsn;
  	int is_last;
  	struct sctp_ulpevent *retval;
  
  	/* The chunks are held in the reasm queue sorted by TSN.
  	 * Walk through the queue sequentially and look for the first
  	 * sequence of fragmented chunks.
  	 */
  
  	if (skb_queue_empty(&ulpq->reasm))
  		return NULL;
  
  	last_frag = first_frag = NULL;
  	retval = NULL;
  	next_tsn = 0;
  	is_last = 0;
  
  	skb_queue_walk(&ulpq->reasm, pos) {
  		cevent = sctp_skb2event(pos);
  		ctsn = cevent->tsn;
  
  		switch (cevent->msg_flags & SCTP_DATA_FRAG_MASK) {
  		case SCTP_DATA_FIRST_FRAG:
  			if (!first_frag)
  				return NULL;
  			goto done;
  		case SCTP_DATA_MIDDLE_FRAG:
  			if (!first_frag) {
  				first_frag = pos;
  				next_tsn = ctsn + 1;
  				last_frag = pos;
  			} else if (next_tsn == ctsn) {
  				next_tsn++;
  				last_frag = pos;
  			} else
  				goto done;
  			break;
  		case SCTP_DATA_LAST_FRAG:
  			if (!first_frag)
  				first_frag = pos;
  			else if (ctsn != next_tsn)
  				goto done;
  			last_frag = pos;
  			is_last = 1;
  			goto done;
  		default:
  			return NULL;
  		}
  	}
  
  	/* We have the reassembled event. There is no need to look
  	 * further.
  	 */
  done:
  	retval = sctp_make_reassembled_event(sock_net(ulpq->asoc->base.sk),
  					&ulpq->reasm, first_frag, last_frag);
  	if (retval && is_last)
  		retval->msg_flags |= MSG_EOR;
  
  	return retval;
  }
  
  
  /* Helper function to reassemble chunks.  Hold chunks on the reasm queue that
   * need reassembling.
   */
  static struct sctp_ulpevent *sctp_ulpq_reasm(struct sctp_ulpq *ulpq,
  						struct sctp_ulpevent *event)
  {
  	struct sctp_ulpevent *retval = NULL;
  
  	/* Check if this is part of a fragmented message.  */
  	if (SCTP_DATA_NOT_FRAG == (event->msg_flags & SCTP_DATA_FRAG_MASK)) {
  		event->msg_flags |= MSG_EOR;
  		return event;
  	}
  
  	sctp_ulpq_store_reasm(ulpq, event);
  	if (!ulpq->pd_mode)
  		retval = sctp_ulpq_retrieve_reassembled(ulpq);
  	else {
  		__u32 ctsn, ctsnap;
  
  		/* Do not even bother unless this is the next tsn to
  		 * be delivered.
  		 */
  		ctsn = event->tsn;
  		ctsnap = sctp_tsnmap_get_ctsn(&ulpq->asoc->peer.tsn_map);
  		if (TSN_lte(ctsn, ctsnap))
  			retval = sctp_ulpq_retrieve_partial(ulpq);
  	}
  
  	return retval;
  }
  
  /* Retrieve the first part (sequential fragments) for partial delivery.  */
  static struct sctp_ulpevent *sctp_ulpq_retrieve_first(struct sctp_ulpq *ulpq)
  {
  	struct sk_buff *pos, *last_frag, *first_frag;
  	struct sctp_ulpevent *cevent;
  	__u32 ctsn, next_tsn;
  	struct sctp_ulpevent *retval;
  
  	/* The chunks are held in the reasm queue sorted by TSN.
  	 * Walk through the queue sequentially and look for a sequence of
  	 * fragmented chunks that start a datagram.
  	 */
  
  	if (skb_queue_empty(&ulpq->reasm))
  		return NULL;
  
  	last_frag = first_frag = NULL;
  	retval = NULL;
  	next_tsn = 0;
  
  	skb_queue_walk(&ulpq->reasm, pos) {
  		cevent = sctp_skb2event(pos);
  		ctsn = cevent->tsn;
  
  		switch (cevent->msg_flags & SCTP_DATA_FRAG_MASK) {
  		case SCTP_DATA_FIRST_FRAG:
  			if (!first_frag) {
  				first_frag = pos;
  				next_tsn = ctsn + 1;
  				last_frag = pos;
  			} else
  				goto done;
  			break;
  
  		case SCTP_DATA_MIDDLE_FRAG:
  			if (!first_frag)
  				return NULL;
  			if (ctsn == next_tsn) {
  				next_tsn++;
  				last_frag = pos;
  			} else
  				goto done;
  			break;
  
  		case SCTP_DATA_LAST_FRAG:
  			if (!first_frag)
  				return NULL;
  			else
  				goto done;
  			break;
  
  		default:
  			return NULL;
  		}
  	}
  
  	/* We have the reassembled event. There is no need to look
  	 * further.
  	 */
  done:
  	retval = sctp_make_reassembled_event(sock_net(ulpq->asoc->base.sk),
  					&ulpq->reasm, first_frag, last_frag);
  	return retval;
  }
  
  /*
   * Flush out stale fragments from the reassembly queue when processing
   * a Forward TSN.
   *
   * RFC 3758, Section 3.6
   *
   * After receiving and processing a FORWARD TSN, the data receiver MUST
   * take cautions in updating its re-assembly queue.  The receiver MUST
   * remove any partially reassembled message, which is still missing one
   * or more TSNs earlier than or equal to the new cumulative TSN point.
   * In the event that the receiver has invoked the partial delivery API,
   * a notification SHOULD also be generated to inform the upper layer API
   * that the message being partially delivered will NOT be completed.
   */
  void sctp_ulpq_reasm_flushtsn(struct sctp_ulpq *ulpq, __u32 fwd_tsn)
  {
  	struct sk_buff *pos, *tmp;
  	struct sctp_ulpevent *event;
  	__u32 tsn;
  
  	if (skb_queue_empty(&ulpq->reasm))
  		return;
  
  	skb_queue_walk_safe(&ulpq->reasm, pos, tmp) {
  		event = sctp_skb2event(pos);
  		tsn = event->tsn;
  
  		/* Since the entire message must be abandoned by the
  		 * sender (item A3 in Section 3.5, RFC 3758), we can
  		 * free all fragments on the list that are less then
  		 * or equal to ctsn_point
  		 */
  		if (TSN_lte(tsn, fwd_tsn)) {
  			__skb_unlink(pos, &ulpq->reasm);
  			sctp_ulpevent_free(event);
  		} else
  			break;
  	}
  }
  
  /*
   * Drain the reassembly queue.  If we just cleared parted delivery, it
   * is possible that the reassembly queue will contain already reassembled
   * messages.  Retrieve any such messages and give them to the user.
   */
  static void sctp_ulpq_reasm_drain(struct sctp_ulpq *ulpq)
  {
  	struct sctp_ulpevent *event = NULL;
  	struct sk_buff_head temp;
  
  	if (skb_queue_empty(&ulpq->reasm))
  		return;
  
  	while ((event = sctp_ulpq_retrieve_reassembled(ulpq)) != NULL) {
  		/* Do ordering if needed.  */
  		if ((event) && (event->msg_flags & MSG_EOR)) {
  			skb_queue_head_init(&temp);
  			__skb_queue_tail(&temp, sctp_event2skb(event));
  
  			event = sctp_ulpq_order(ulpq, event);
  		}
  
  		/* Send event to the ULP.  'event' is the
  		 * sctp_ulpevent for  very first SKB on the  temp' list.
  		 */
  		if (event)
  			sctp_ulpq_tail_event(ulpq, event);
  	}
  }
  
  
  /* Helper function to gather skbs that have possibly become
   * ordered by an an incoming chunk.
   */
  static void sctp_ulpq_retrieve_ordered(struct sctp_ulpq *ulpq,
  					      struct sctp_ulpevent *event)
  {
  	struct sk_buff_head *event_list;
  	struct sk_buff *pos, *tmp;
  	struct sctp_ulpevent *cevent;
  	struct sctp_stream *in;
  	__u16 sid, csid, cssn;
  
  	sid = event->stream;
  	in  = &ulpq->asoc->ssnmap->in;
  
  	event_list = (struct sk_buff_head *) sctp_event2skb(event)->prev;
  
  	/* We are holding the chunks by stream, by SSN.  */
  	sctp_skb_for_each(pos, &ulpq->lobby, tmp) {
  		cevent = (struct sctp_ulpevent *) pos->cb;
  		csid = cevent->stream;
  		cssn = cevent->ssn;
  
  		/* Have we gone too far?  */
  		if (csid > sid)
  			break;
  
  		/* Have we not gone far enough?  */
  		if (csid < sid)
  			continue;
  
  		if (cssn != sctp_ssn_peek(in, sid))
  			break;
  
  		/* Found it, so mark in the ssnmap. */
  		sctp_ssn_next(in, sid);
  
  		__skb_unlink(pos, &ulpq->lobby);
  
  		/* Attach all gathered skbs to the event.  */
  		__skb_queue_tail(event_list, pos);
  	}
  }
  
  /* Helper function to store chunks needing ordering.  */
  static void sctp_ulpq_store_ordered(struct sctp_ulpq *ulpq,
  					   struct sctp_ulpevent *event)
  {
  	struct sk_buff *pos;
  	struct sctp_ulpevent *cevent;
  	__u16 sid, csid;
  	__u16 ssn, cssn;
  
  	pos = skb_peek_tail(&ulpq->lobby);
  	if (!pos) {
  		__skb_queue_tail(&ulpq->lobby, sctp_event2skb(event));
  		return;
  	}
  
  	sid = event->stream;
  	ssn = event->ssn;
  
  	cevent = (struct sctp_ulpevent *) pos->cb;
  	csid = cevent->stream;
  	cssn = cevent->ssn;
  	if (sid > csid) {
  		__skb_queue_tail(&ulpq->lobby, sctp_event2skb(event));
  		return;
  	}
  
  	if ((sid == csid) && SSN_lt(cssn, ssn)) {
  		__skb_queue_tail(&ulpq->lobby, sctp_event2skb(event));
  		return;
  	}
  
  	/* Find the right place in this list.  We store them by
  	 * stream ID and then by SSN.
  	 */
  	skb_queue_walk(&ulpq->lobby, pos) {
  		cevent = (struct sctp_ulpevent *) pos->cb;
  		csid = cevent->stream;
  		cssn = cevent->ssn;
  
  		if (csid > sid)
  			break;
  		if (csid == sid && SSN_lt(ssn, cssn))
  			break;
  	}
  
  
  	/* Insert before pos. */
  	__skb_queue_before(&ulpq->lobby, pos, sctp_event2skb(event));
  }
  
  static struct sctp_ulpevent *sctp_ulpq_order(struct sctp_ulpq *ulpq,
  					     struct sctp_ulpevent *event)
  {
  	__u16 sid, ssn;
  	struct sctp_stream *in;
  
  	/* Check if this message needs ordering.  */
  	if (SCTP_DATA_UNORDERED & event->msg_flags)
  		return event;
  
  	/* Note: The stream ID must be verified before this routine.  */
  	sid = event->stream;
  	ssn = event->ssn;
  	in  = &ulpq->asoc->ssnmap->in;
  
  	/* Is this the expected SSN for this stream ID?  */
  	if (ssn != sctp_ssn_peek(in, sid)) {
  		/* We've received something out of order, so find where it
  		 * needs to be placed.  We order by stream and then by SSN.
  		 */
  		sctp_ulpq_store_ordered(ulpq, event);
  		return NULL;
  	}
  
  	/* Mark that the next chunk has been found.  */
  	sctp_ssn_next(in, sid);
  
  	/* Go find any other chunks that were waiting for
  	 * ordering.
  	 */
  	sctp_ulpq_retrieve_ordered(ulpq, event);
  
  	return event;
  }
  
  /* Helper function to gather skbs that have possibly become
   * ordered by forward tsn skipping their dependencies.
   */
  static void sctp_ulpq_reap_ordered(struct sctp_ulpq *ulpq, __u16 sid)
  {
  	struct sk_buff *pos, *tmp;
  	struct sctp_ulpevent *cevent;
  	struct sctp_ulpevent *event;
  	struct sctp_stream *in;
  	struct sk_buff_head temp;
  	struct sk_buff_head *lobby = &ulpq->lobby;
  	__u16 csid, cssn;
  
  	in  = &ulpq->asoc->ssnmap->in;
  
  	/* We are holding the chunks by stream, by SSN.  */
  	skb_queue_head_init(&temp);
  	event = NULL;
  	sctp_skb_for_each(pos, lobby, tmp) {
  		cevent = (struct sctp_ulpevent *) pos->cb;
  		csid = cevent->stream;
  		cssn = cevent->ssn;
  
  		/* Have we gone too far?  */
  		if (csid > sid)
  			break;
  
  		/* Have we not gone far enough?  */
  		if (csid < sid)
  			continue;
  
  		/* see if this ssn has been marked by skipping */
  		if (!SSN_lt(cssn, sctp_ssn_peek(in, csid)))
  			break;
  
  		__skb_unlink(pos, lobby);
  		if (!event)
  			/* Create a temporary list to collect chunks on.  */
  			event = sctp_skb2event(pos);
  
  		/* Attach all gathered skbs to the event.  */
  		__skb_queue_tail(&temp, pos);
  	}
  
  	/* If we didn't reap any data, see if the next expected SSN
  	 * is next on the queue and if so, use that.
  	 */
  	if (event == NULL && pos != (struct sk_buff *)lobby) {
  		cevent = (struct sctp_ulpevent *) pos->cb;
  		csid = cevent->stream;
  		cssn = cevent->ssn;
  
  		if (csid == sid && cssn == sctp_ssn_peek(in, csid)) {
  			sctp_ssn_next(in, csid);
  			__skb_unlink(pos, lobby);
  			__skb_queue_tail(&temp, pos);
  			event = sctp_skb2event(pos);
  		}
  	}
  
  	/* Send event to the ULP.  'event' is the sctp_ulpevent for
  	 * very first SKB on the 'temp' list.
  	 */
  	if (event) {
  		/* see if we have more ordered that we can deliver */
  		sctp_ulpq_retrieve_ordered(ulpq, event);
  		sctp_ulpq_tail_event(ulpq, event);
  	}
  }
  
  /* Skip over an SSN. This is used during the processing of
   * Forwared TSN chunk to skip over the abandoned ordered data
   */
  void sctp_ulpq_skip(struct sctp_ulpq *ulpq, __u16 sid, __u16 ssn)
  {
  	struct sctp_stream *in;
  
  	/* Note: The stream ID must be verified before this routine.  */
  	in  = &ulpq->asoc->ssnmap->in;
  
  	/* Is this an old SSN?  If so ignore. */
  	if (SSN_lt(ssn, sctp_ssn_peek(in, sid)))
  		return;
  
  	/* Mark that we are no longer expecting this SSN or lower. */
  	sctp_ssn_skip(in, sid, ssn);
  
  	/* Go find any other chunks that were waiting for
  	 * ordering and deliver them if needed.
  	 */
  	sctp_ulpq_reap_ordered(ulpq, sid);
  }
  
  static __u16 sctp_ulpq_renege_list(struct sctp_ulpq *ulpq,
  		struct sk_buff_head *list, __u16 needed)
  {
  	__u16 freed = 0;
  	__u32 tsn, last_tsn;
  	struct sk_buff *skb, *flist, *last;
  	struct sctp_ulpevent *event;
  	struct sctp_tsnmap *tsnmap;
  
  	tsnmap = &ulpq->asoc->peer.tsn_map;
  
  	while ((skb = skb_peek_tail(list)) != NULL) {
  		event = sctp_skb2event(skb);
  		tsn = event->tsn;
  
  		/* Don't renege below the Cumulative TSN ACK Point. */
  		if (TSN_lte(tsn, sctp_tsnmap_get_ctsn(tsnmap)))
  			break;
  
  		/* Events in ordering queue may have multiple fragments
  		 * corresponding to additional TSNs.  Sum the total
  		 * freed space; find the last TSN.
  		 */
  		freed += skb_headlen(skb);
  		flist = skb_shinfo(skb)->frag_list;
  		for (last = flist; flist; flist = flist->next) {
  			last = flist;
  			freed += skb_headlen(last);
  		}
  		if (last)
  			last_tsn = sctp_skb2event(last)->tsn;
  		else
  			last_tsn = tsn;
  
  		/* Unlink the event, then renege all applicable TSNs. */
  		__skb_unlink(skb, list);
  		sctp_ulpevent_free(event);
  		while (TSN_lte(tsn, last_tsn)) {
  			sctp_tsnmap_renege(tsnmap, tsn);
  			tsn++;
  		}
  		if (freed >= needed)
  			return freed;
  	}
  
  	return freed;
  }
  
  /* Renege 'needed' bytes from the ordering queue. */
  static __u16 sctp_ulpq_renege_order(struct sctp_ulpq *ulpq, __u16 needed)
  {
  	return sctp_ulpq_renege_list(ulpq, &ulpq->lobby, needed);
  }
  
  /* Renege 'needed' bytes from the reassembly queue. */
  static __u16 sctp_ulpq_renege_frags(struct sctp_ulpq *ulpq, __u16 needed)
  {
  	return sctp_ulpq_renege_list(ulpq, &ulpq->reasm, needed);
  }
  
  /* Partial deliver the first message as there is pressure on rwnd. */
  void sctp_ulpq_partial_delivery(struct sctp_ulpq *ulpq,
  				gfp_t gfp)
  {
  	struct sctp_ulpevent *event;
  	struct sctp_association *asoc;
  	struct sctp_sock *sp;
  	__u32 ctsn;
  	struct sk_buff *skb;
  
  	asoc = ulpq->asoc;
  	sp = sctp_sk(asoc->base.sk);
  
  	/* If the association is already in Partial Delivery mode
  	 * we have nothing to do.
  	 */
  	if (ulpq->pd_mode)
  		return;
  
  	/* Data must be at or below the Cumulative TSN ACK Point to
  	 * start partial delivery.
  	 */
  	skb = skb_peek(&asoc->ulpq.reasm);
  	if (skb != NULL) {
  		ctsn = sctp_skb2event(skb)->tsn;
  		if (!TSN_lte(ctsn, sctp_tsnmap_get_ctsn(&asoc->peer.tsn_map)))
  			return;
  	}
  
  	/* If the user enabled fragment interleave socket option,
  	 * multiple associations can enter partial delivery.
  	 * Otherwise, we can only enter partial delivery if the
  	 * socket is not in partial deliver mode.
  	 */
  	if (sp->frag_interleave || atomic_read(&sp->pd_mode) == 0) {
  		/* Is partial delivery possible?  */
  		event = sctp_ulpq_retrieve_first(ulpq);
  		/* Send event to the ULP.   */
  		if (event) {
  			sctp_ulpq_tail_event(ulpq, event);
  			sctp_ulpq_set_pd(ulpq);
  			return;
  		}
  	}
  }
  
  /* Renege some packets to make room for an incoming chunk.  */
  void sctp_ulpq_renege(struct sctp_ulpq *ulpq, struct sctp_chunk *chunk,
  		      gfp_t gfp)
  {
  	struct sctp_association *asoc;
  	__u16 needed, freed;
  
  	asoc = ulpq->asoc;
  
  	if (chunk) {
  		needed = ntohs(chunk->chunk_hdr->length);
  		needed -= sizeof(sctp_data_chunk_t);
  	} else
  		needed = SCTP_DEFAULT_MAXWINDOW;
  
  	freed = 0;
  
  	if (skb_queue_empty(&asoc->base.sk->sk_receive_queue)) {
  		freed = sctp_ulpq_renege_order(ulpq, needed);
  		if (freed < needed) {
  			freed += sctp_ulpq_renege_frags(ulpq, needed - freed);
  		}
  	}
  	/* If able to free enough room, accept this chunk. */
  	if (chunk && (freed >= needed)) {
  		int retval;
  		retval = sctp_ulpq_tail_data(ulpq, chunk, gfp);
  		/*
  		 * Enter partial delivery if chunk has not been
  		 * delivered; otherwise, drain the reassembly queue.
  		 */
  		if (retval <= 0)
  			sctp_ulpq_partial_delivery(ulpq, gfp);
  		else if (retval == 1)
  			sctp_ulpq_reasm_drain(ulpq);
  	}
  
  	sk_mem_reclaim(asoc->base.sk);
  }
  
  
  
  /* Notify the application if an association is aborted and in
   * partial delivery mode.  Send up any pending received messages.
   */
  void sctp_ulpq_abort_pd(struct sctp_ulpq *ulpq, gfp_t gfp)
  {
  	struct sctp_ulpevent *ev = NULL;
  	struct sock *sk;
  
  	if (!ulpq->pd_mode)
  		return;
  
  	sk = ulpq->asoc->base.sk;
  	if (sctp_ulpevent_type_enabled(SCTP_PARTIAL_DELIVERY_EVENT,
  				       &sctp_sk(sk)->subscribe))
  		ev = sctp_ulpevent_make_pdapi(ulpq->asoc,
  					      SCTP_PARTIAL_DELIVERY_ABORTED,
  					      gfp);
  	if (ev)
  		__skb_queue_tail(&sk->sk_receive_queue, sctp_event2skb(ev));
  
  	/* If there is data waiting, send it up the socket now. */
  	if (sctp_ulpq_clear_pd(ulpq) || ev)
  		sk->sk_data_ready(sk, 0);
  }