/* 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/busy_poll.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)) {
                        skb_queue_splice_tail_init(&sp->pd_lobby,
                                                   &sk->sk_receive_queue);
                        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 sctp_sock *sp = sctp_sk(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 (sk->sk_shutdown & RCV_SHUTDOWN &&
            (sk->sk_shutdown & SEND_SHUTDOWN ||
             !sctp_ulpevent_is_notification(event)))
                goto out_free;

        if (!sctp_ulpevent_is_notification(event)) {
                sk_mark_napi_id(sk, skb);
                sk_incoming_cpu_update(sk);
        }
        /* Check if the user wishes to receive this event.  */
        if (!sctp_ulpevent_is_enabled(event, &sp->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(&sp->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 = &sp->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 (sp->frag_interleave)
                                queue = &sk->sk_receive_queue;
                        else
                                queue = &sp->pd_lobby;
                }
        }

        /* If we are harvesting multiple skbs they will be
         * collected on a list.
         */
        if (skb_list)
                skb_queue_splice_tail_init(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 && !sp->data_ready_signalled) {
                sp->data_ready_signalled = 1;
                sk->sk_data_ready(sk);
        }
        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;
        struct sctp_sock *sp;

        if (!ulpq->pd_mode)
                return;

        sk = ulpq->asoc->base.sk;
        sp = sctp_sk(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) && !sp->data_ready_signalled) {
                sp->data_ready_signalled = 1;
                sk->sk_data_ready(sk);
        }
}