[safe/jmp/linux-2.6] / net / sctp / associola.c

/* SCTP kernel reference 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 La Monte H.P. Yarroll
 *
 * This file is part of the SCTP kernel reference Implementation
 *
 * This module provides the abstraction for an SCTP association.
 *
 * The SCTP reference 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.
 *
 * The SCTP reference 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, write to
 * the Free Software Foundation, 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 *
 * Please send any bug reports or fixes you make to the
 * email address(es):
 *    lksctp developers <lksctp-developers@lists.sourceforge.net>
 *
 * Or submit a bug report through the following website:
 *    http://www.sf.net/projects/lksctp
 *
 * Written or modified by:
 *    La Monte H.P. Yarroll <piggy@acm.org>
 *    Karl Knutson          <karl@athena.chicago.il.us>
 *    Jon Grimm             <jgrimm@us.ibm.com>
 *    Xingang Guo           <xingang.guo@intel.com>
 *    Hui Huang             <hui.huang@nokia.com>
 *    Sridhar Samudrala     <sri@us.ibm.com>
 *    Daisy Chang           <daisyc@us.ibm.com>
 *    Ryan Layer            <rmlayer@us.ibm.com>
 *    Kevin Gao             <kevin.gao@intel.com>
 *
 * Any bugs reported given to us we will try to fix... any fixes shared will
 * be incorporated into the next SCTP release.
 */

#include <linux/types.h>
#include <linux/fcntl.h>
#include <linux/poll.h>
#include <linux/init.h>
#include <linux/sched.h>

#include <linux/slab.h>
#include <linux/in.h>
#include <net/ipv6.h>
#include <net/sctp/sctp.h>
#include <net/sctp/sm.h>

/* Forward declarations for internal functions. */
static void sctp_assoc_bh_rcv(struct sctp_association *asoc);


/* 1st Level Abstractions. */

/* Initialize a new association from provided memory. */
static struct sctp_association *sctp_association_init(struct sctp_association *asoc,
                                          const struct sctp_endpoint *ep,
                                          const struct sock *sk,
                                          sctp_scope_t scope,
                                          gfp_t gfp)
{
        struct sctp_sock *sp;
        int i;

        /* Retrieve the SCTP per socket area.  */
        sp = sctp_sk((struct sock *)sk);

        /* Init all variables to a known value.  */
        memset(asoc, 0, sizeof(struct sctp_association));

        /* Discarding const is appropriate here.  */
        asoc->ep = (struct sctp_endpoint *)ep;
        sctp_endpoint_hold(asoc->ep);

        /* Hold the sock.  */
        asoc->base.sk = (struct sock *)sk;
        sock_hold(asoc->base.sk);

        /* Initialize the common base substructure.  */
        asoc->base.type = SCTP_EP_TYPE_ASSOCIATION;

        /* Initialize the object handling fields.  */
        atomic_set(&asoc->base.refcnt, 1);
        asoc->base.dead = 0;
        asoc->base.malloced = 0;

        /* Initialize the bind addr area.  */
        sctp_bind_addr_init(&asoc->base.bind_addr, ep->base.bind_addr.port);
        rwlock_init(&asoc->base.addr_lock);

        asoc->state = SCTP_STATE_CLOSED;

        /* Set these values from the socket values, a conversion between
         * millsecons to seconds/microseconds must also be done.
         */
        asoc->cookie_life.tv_sec = sp->assocparams.sasoc_cookie_life / 1000;
        asoc->cookie_life.tv_usec = (sp->assocparams.sasoc_cookie_life % 1000)
                                        * 1000;
        asoc->frag_point = 0;

        /* Set the association max_retrans and RTO values from the
         * socket values.
         */
        asoc->max_retrans = sp->assocparams.sasoc_asocmaxrxt;
        asoc->rto_initial = msecs_to_jiffies(sp->rtoinfo.srto_initial);
        asoc->rto_max = msecs_to_jiffies(sp->rtoinfo.srto_max);
        asoc->rto_min = msecs_to_jiffies(sp->rtoinfo.srto_min);

        asoc->overall_error_count = 0;

        /* Initialize the association's heartbeat interval based on the
         * sock configured value.
         */
        asoc->hbinterval = msecs_to_jiffies(sp->hbinterval);

        /* Initialize path max retrans value. */
        asoc->pathmaxrxt = sp->pathmaxrxt;

        /* Initialize default path MTU. */
        asoc->pathmtu = sp->pathmtu;

        /* Set association default SACK delay */
        asoc->sackdelay = msecs_to_jiffies(sp->sackdelay);

        /* Set the association default flags controlling
         * Heartbeat, SACK delay, and Path MTU Discovery.
         */
        asoc->param_flags = sp->param_flags;

        /* Initialize the maximum mumber of new data packets that can be sent
         * in a burst.
         */
        asoc->max_burst = sctp_max_burst;

        /* initialize association timers */
        asoc->timeouts[SCTP_EVENT_TIMEOUT_NONE] = 0;
        asoc->timeouts[SCTP_EVENT_TIMEOUT_T1_COOKIE] = asoc->rto_initial;
        asoc->timeouts[SCTP_EVENT_TIMEOUT_T1_INIT] = asoc->rto_initial;
        asoc->timeouts[SCTP_EVENT_TIMEOUT_T2_SHUTDOWN] = asoc->rto_initial;
        asoc->timeouts[SCTP_EVENT_TIMEOUT_T3_RTX] = 0;
        asoc->timeouts[SCTP_EVENT_TIMEOUT_T4_RTO] = 0;

        /* sctpimpguide Section 2.12.2
         * If the 'T5-shutdown-guard' timer is used, it SHOULD be set to the
         * recommended value of 5 times 'RTO.Max'.
         */
        asoc->timeouts[SCTP_EVENT_TIMEOUT_T5_SHUTDOWN_GUARD]
                = 5 * asoc->rto_max;

        asoc->timeouts[SCTP_EVENT_TIMEOUT_HEARTBEAT] = 0;
        asoc->timeouts[SCTP_EVENT_TIMEOUT_SACK] = asoc->sackdelay;
        asoc->timeouts[SCTP_EVENT_TIMEOUT_AUTOCLOSE] =
                sp->autoclose * HZ;
        
        /* Initilizes the timers */
        for (i = SCTP_EVENT_TIMEOUT_NONE; i < SCTP_NUM_TIMEOUT_TYPES; ++i) {
                init_timer(&asoc->timers[i]);
                asoc->timers[i].function = sctp_timer_events[i];
                asoc->timers[i].data = (unsigned long) asoc;
        }

        /* Pull default initialization values from the sock options.
         * Note: This assumes that the values have already been
         * validated in the sock.
         */
        asoc->c.sinit_max_instreams = sp->initmsg.sinit_max_instreams;
        asoc->c.sinit_num_ostreams  = sp->initmsg.sinit_num_ostreams;
        asoc->max_init_attempts = sp->initmsg.sinit_max_attempts;

        asoc->max_init_timeo =
                 msecs_to_jiffies(sp->initmsg.sinit_max_init_timeo);

        /* Allocate storage for the ssnmap after the inbound and outbound
         * streams have been negotiated during Init.
         */
        asoc->ssnmap = NULL;

        /* Set the local window size for receive.
         * This is also the rcvbuf space per association.
         * RFC 6 - A SCTP receiver MUST be able to receive a minimum of
         * 1500 bytes in one SCTP packet.
         */
        if ((sk->sk_rcvbuf/2) < SCTP_DEFAULT_MINWINDOW)
                asoc->rwnd = SCTP_DEFAULT_MINWINDOW;
        else
                asoc->rwnd = sk->sk_rcvbuf/2;

        asoc->a_rwnd = asoc->rwnd;

        asoc->rwnd_over = 0;

        /* Use my own max window until I learn something better.  */
        asoc->peer.rwnd = SCTP_DEFAULT_MAXWINDOW;

        /* Set the sndbuf size for transmit.  */
        asoc->sndbuf_used = 0;

        /* Initialize the receive memory counter */
        atomic_set(&asoc->rmem_alloc, 0);

        init_waitqueue_head(&asoc->wait);

        asoc->c.my_vtag = sctp_generate_tag(ep);
        asoc->peer.i.init_tag = 0;     /* INIT needs a vtag of 0. */
        asoc->c.peer_vtag = 0;
        asoc->c.my_ttag   = 0;
        asoc->c.peer_ttag = 0;
        asoc->c.my_port = ep->base.bind_addr.port;

        asoc->c.initial_tsn = sctp_generate_tsn(ep);

        asoc->next_tsn = asoc->c.initial_tsn;

        asoc->ctsn_ack_point = asoc->next_tsn - 1;
        asoc->adv_peer_ack_point = asoc->ctsn_ack_point;
        asoc->highest_sacked = asoc->ctsn_ack_point;
        asoc->last_cwr_tsn = asoc->ctsn_ack_point;
        asoc->unack_data = 0;

        /* ADDIP Section 4.1 Asconf Chunk Procedures
         *
         * When an endpoint has an ASCONF signaled change to be sent to the
         * remote endpoint it should do the following:
         * ...
         * A2) a serial number should be assigned to the chunk. The serial
         * number SHOULD be a monotonically increasing number. The serial
         * numbers SHOULD be initialized at the start of the
         * association to the same value as the initial TSN.
         */
        asoc->addip_serial = asoc->c.initial_tsn;

        INIT_LIST_HEAD(&asoc->addip_chunk_list);

        /* Make an empty list of remote transport addresses.  */
        INIT_LIST_HEAD(&asoc->peer.transport_addr_list);
        asoc->peer.transport_count = 0;

        /* RFC 2960 5.1 Normal Establishment of an Association
         *
         * After the reception of the first data chunk in an
         * association the endpoint must immediately respond with a
         * sack to acknowledge the data chunk.  Subsequent
         * acknowledgements should be done as described in Section
         * 6.2.
         *
         * [We implement this by telling a new association that it
         * already received one packet.]
         */
        asoc->peer.sack_needed = 1;

        /* Assume that the peer recongizes ASCONF until reported otherwise
         * via an ERROR chunk.
         */
        asoc->peer.asconf_capable = 1;

        /* Create an input queue.  */
        sctp_inq_init(&asoc->base.inqueue);
        sctp_inq_set_th_handler(&asoc->base.inqueue,
                                    (void (*)(void *))sctp_assoc_bh_rcv,
                                    asoc);

        /* Create an output queue.  */
        sctp_outq_init(asoc, &asoc->outqueue);

        if (!sctp_ulpq_init(&asoc->ulpq, asoc))
                goto fail_init;

        /* Set up the tsn tracking. */
        sctp_tsnmap_init(&asoc->peer.tsn_map, SCTP_TSN_MAP_SIZE, 0);

        asoc->need_ecne = 0;

        asoc->assoc_id = 0;

        /* Assume that peer would support both address types unless we are
         * told otherwise.
         */
        asoc->peer.ipv4_address = 1;
        asoc->peer.ipv6_address = 1;
        INIT_LIST_HEAD(&asoc->asocs);

        asoc->autoclose = sp->autoclose;

        asoc->default_stream = sp->default_stream;
        asoc->default_ppid = sp->default_ppid;
        asoc->default_flags = sp->default_flags;
        asoc->default_context = sp->default_context;
        asoc->default_timetolive = sp->default_timetolive;

        return asoc;

fail_init:
        sctp_endpoint_put(asoc->ep);
        sock_put(asoc->base.sk);
        return NULL;
}

/* Allocate and initialize a new association */
struct sctp_association *sctp_association_new(const struct sctp_endpoint *ep,
                                         const struct sock *sk,
                                         sctp_scope_t scope,
                                         gfp_t gfp)
{
        struct sctp_association *asoc;

        asoc = t_new(struct sctp_association, gfp);
        if (!asoc)
                goto fail;

        if (!sctp_association_init(asoc, ep, sk, scope, gfp))
                goto fail_init;

        asoc->base.malloced = 1;
        SCTP_DBG_OBJCNT_INC(assoc);
        SCTP_DEBUG_PRINTK("Created asoc %p\n", asoc);

        return asoc;

fail_init:
        kfree(asoc);
fail:
        return NULL;
}

/* Free this association if possible.  There may still be users, so
 * the actual deallocation may be delayed.
 */
void sctp_association_free(struct sctp_association *asoc)
{
        struct sock *sk = asoc->base.sk;
        struct sctp_transport *transport;
        struct list_head *pos, *temp;
        int i;

        /* Only real associations count against the endpoint, so
         * don't bother for if this is a temporary association.
         */
        if (!asoc->temp) {
                list_del(&asoc->asocs);

                /* Decrement the backlog value for a TCP-style listening
                 * socket.
                 */
                if (sctp_style(sk, TCP) && sctp_sstate(sk, LISTENING))
                        sk->sk_ack_backlog--;
        }

        /* Mark as dead, so other users can know this structure is
         * going away.
         */
        asoc->base.dead = 1;

        /* Dispose of any data lying around in the outqueue. */
        sctp_outq_free(&asoc->outqueue);

        /* Dispose of any pending messages for the upper layer. */
        sctp_ulpq_free(&asoc->ulpq);

        /* Dispose of any pending chunks on the inqueue. */
        sctp_inq_free(&asoc->base.inqueue);

        /* Free ssnmap storage. */
        sctp_ssnmap_free(asoc->ssnmap);

        /* Clean up the bound address list. */
        sctp_bind_addr_free(&asoc->base.bind_addr);

        /* Do we need to go through all of our timers and
         * delete them?   To be safe we will try to delete all, but we
         * should be able to go through and make a guess based
         * on our state.
         */
        for (i = SCTP_EVENT_TIMEOUT_NONE; i < SCTP_NUM_TIMEOUT_TYPES; ++i) {
                if (timer_pending(&asoc->timers[i]) &&
                    del_timer(&asoc->timers[i]))
                        sctp_association_put(asoc);
        }

        /* Free peer's cached cookie. */
        kfree(asoc->peer.cookie);

        /* Release the transport structures. */
        list_for_each_safe(pos, temp, &asoc->peer.transport_addr_list) {
                transport = list_entry(pos, struct sctp_transport, transports);
                list_del(pos);
                sctp_transport_free(transport);
        }

        asoc->peer.transport_count = 0;

        /* Free any cached ASCONF_ACK chunk. */
        if (asoc->addip_last_asconf_ack)
                sctp_chunk_free(asoc->addip_last_asconf_ack);

        /* Free any cached ASCONF chunk. */
        if (asoc->addip_last_asconf)
                sctp_chunk_free(asoc->addip_last_asconf);

        sctp_association_put(asoc);
}

/* Cleanup and free up an association. */
static void sctp_association_destroy(struct sctp_association *asoc)
{
        SCTP_ASSERT(asoc->base.dead, "Assoc is not dead", return);

        sctp_endpoint_put(asoc->ep);
        sock_put(asoc->base.sk);

        if (asoc->assoc_id != 0) {
                spin_lock_bh(&sctp_assocs_id_lock);
                idr_remove(&sctp_assocs_id, asoc->assoc_id);
                spin_unlock_bh(&sctp_assocs_id_lock);
        }

        BUG_TRAP(!atomic_read(&asoc->rmem_alloc));

        if (asoc->base.malloced) {
                kfree(asoc);
                SCTP_DBG_OBJCNT_DEC(assoc);
        }
}

/* Change the primary destination address for the peer. */
void sctp_assoc_set_primary(struct sctp_association *asoc,
                            struct sctp_transport *transport)
{
        asoc->peer.primary_path = transport;

        /* Set a default msg_name for events. */
        memcpy(&asoc->peer.primary_addr, &transport->ipaddr,
               sizeof(union sctp_addr));

        /* If the primary path is changing, assume that the
         * user wants to use this new path.
         */
        if ((transport->state == SCTP_ACTIVE) ||
            (transport->state == SCTP_UNKNOWN))
                asoc->peer.active_path = transport;

        /*
         * SFR-CACC algorithm:
         * Upon the receipt of a request to change the primary
         * destination address, on the data structure for the new
         * primary destination, the sender MUST do the following:
         *
         * 1) If CHANGEOVER_ACTIVE is set, then there was a switch
         * to this destination address earlier. The sender MUST set
         * CYCLING_CHANGEOVER to indicate that this switch is a
         * double switch to the same destination address.
         */
        if (transport->cacc.changeover_active)
                transport->cacc.cycling_changeover = 1;

        /* 2) The sender MUST set CHANGEOVER_ACTIVE to indicate that
         * a changeover has occurred.
         */
        transport->cacc.changeover_active = 1;

        /* 3) The sender MUST store the next TSN to be sent in
         * next_tsn_at_change.
         */
        transport->cacc.next_tsn_at_change = asoc->next_tsn;
}

/* Remove a transport from an association.  */
void sctp_assoc_rm_peer(struct sctp_association *asoc,
                        struct sctp_transport *peer)
{
        struct list_head        *pos;
        struct sctp_transport   *transport;

        SCTP_DEBUG_PRINTK_IPADDR("sctp_assoc_rm_peer:association %p addr: ",
                                 " port: %d\n",
                                 asoc,
                                 (&peer->ipaddr),
                                 peer->ipaddr.v4.sin_port);

        /* If we are to remove the current retran_path, update it
         * to the next peer before removing this peer from the list.
         */
        if (asoc->peer.retran_path == peer)
                sctp_assoc_update_retran_path(asoc);

        /* Remove this peer from the list. */
        list_del(&peer->transports);

        /* Get the first transport of asoc. */
        pos = asoc->peer.transport_addr_list.next;
        transport = list_entry(pos, struct sctp_transport, transports);

        /* Update any entries that match the peer to be deleted. */
        if (asoc->peer.primary_path == peer)
                sctp_assoc_set_primary(asoc, transport);
        if (asoc->peer.active_path == peer)
                asoc->peer.active_path = transport;
        if (asoc->peer.last_data_from == peer)
                asoc->peer.last_data_from = transport;

        /* If we remove the transport an INIT was last sent to, set it to
         * NULL. Combined with the update of the retran path above, this
         * will cause the next INIT to be sent to the next available
         * transport, maintaining the cycle.
         */
        if (asoc->init_last_sent_to == peer)
                asoc->init_last_sent_to = NULL;

        asoc->peer.transport_count--;

        sctp_transport_free(peer);
}

/* Add a transport address to an association.  */
struct sctp_transport *sctp_assoc_add_peer(struct sctp_association *asoc,
                                           const union sctp_addr *addr,
                                           const gfp_t gfp,
                                           const int peer_state)
{
        struct sctp_transport *peer;
        struct sctp_sock *sp;
        unsigned short port;

        sp = sctp_sk(asoc->base.sk);

        /* AF_INET and AF_INET6 share common port field. */
        port = addr->v4.sin_port;

        SCTP_DEBUG_PRINTK_IPADDR("sctp_assoc_add_peer:association %p addr: ",
                                 " port: %d state:%d\n",
                                 asoc,
                                 addr,
                                 addr->v4.sin_port,
                                 peer_state);

        /* Set the port if it has not been set yet.  */
        if (0 == asoc->peer.port)
                asoc->peer.port = port;

        /* Check to see if this is a duplicate. */
        peer = sctp_assoc_lookup_paddr(asoc, addr);
        if (peer) {
                if (peer->state == SCTP_UNKNOWN) {
                        if (peer_state == SCTP_ACTIVE)
                                peer->state = SCTP_ACTIVE;
                        if (peer_state == SCTP_UNCONFIRMED)
                                peer->state = SCTP_UNCONFIRMED;
                }
                return peer;
        }

        peer = sctp_transport_new(addr, gfp);
        if (!peer)
                return NULL;

        sctp_transport_set_owner(peer, asoc);

        /* Initialize the peer's heartbeat interval based on the
         * association configured value.
         */
        peer->hbinterval = asoc->hbinterval;

        /* Set the path max_retrans.  */
        peer->pathmaxrxt = asoc->pathmaxrxt;

        /* Initialize the peer's SACK delay timeout based on the
         * association configured value.
         */
        peer->sackdelay = asoc->sackdelay;

        /* Enable/disable heartbeat, SACK delay, and path MTU discovery
         * based on association setting.
         */
        peer->param_flags = asoc->param_flags;

        /* Initialize the pmtu of the transport. */
        if (peer->param_flags & SPP_PMTUD_ENABLE)
                sctp_transport_pmtu(peer);
        else if (asoc->pathmtu)
                peer->pathmtu = asoc->pathmtu;
        else
                peer->pathmtu = SCTP_DEFAULT_MAXSEGMENT;

        /* If this is the first transport addr on this association,
         * initialize the association PMTU to the peer's PMTU.
         * If not and the current association PMTU is higher than the new
         * peer's PMTU, reset the association PMTU to the new peer's PMTU.
         */
        if (asoc->pathmtu)
                asoc->pathmtu = min_t(int, peer->pathmtu, asoc->pathmtu);
        else
                asoc->pathmtu = peer->pathmtu;

        SCTP_DEBUG_PRINTK("sctp_assoc_add_peer:association %p PMTU set to "
                          "%d\n", asoc, asoc->pathmtu);

        asoc->frag_point = sctp_frag_point(sp, asoc->pathmtu);

        /* The asoc->peer.port might not be meaningful yet, but
         * initialize the packet structure anyway.
         */
        sctp_packet_init(&peer->packet, peer, asoc->base.bind_addr.port,
                         asoc->peer.port);

        /* 7.2.1 Slow-Start
         *
         * o The initial cwnd before DATA transmission or after a sufficiently
         *   long idle period MUST be set to
         *      min(4*MTU, max(2*MTU, 4380 bytes))
         *
         * o The initial value of ssthresh MAY be arbitrarily high
         *   (for example, implementations MAY use the size of the
         *   receiver advertised window).
         */
        peer->cwnd = min(4*asoc->pathmtu, max_t(__u32, 2*asoc->pathmtu, 4380));

        /* At this point, we may not have the receiver's advertised window,
         * so initialize ssthresh to the default value and it will be set
         * later when we process the INIT.
         */
        peer->ssthresh = SCTP_DEFAULT_MAXWINDOW;

        peer->partial_bytes_acked = 0;
        peer->flight_size = 0;

        /* Set the transport's RTO.initial value */
        peer->rto = asoc->rto_initial;

        /* Set the peer's active state. */
        peer->state = peer_state;

        /* Attach the remote transport to our asoc.  */
        list_add_tail(&peer->transports, &asoc->peer.transport_addr_list);
        asoc->peer.transport_count++;

        /* If we do not yet have a primary path, set one.  */
        if (!asoc->peer.primary_path) {
                sctp_assoc_set_primary(asoc, peer);
                asoc->peer.retran_path = peer;
        }

        if (asoc->peer.active_path == asoc->peer.retran_path) {
                asoc->peer.retran_path = peer;
        }

        return peer;
}

/* Delete a transport address from an association.  */
void sctp_assoc_del_peer(struct sctp_association *asoc,
                         const union sctp_addr *addr)
{
        struct list_head        *pos;
        struct list_head        *temp;
        struct sctp_transport   *transport;

        list_for_each_safe(pos, temp, &asoc->peer.transport_addr_list) {
                transport = list_entry(pos, struct sctp_transport, transports);
                if (sctp_cmp_addr_exact(addr, &transport->ipaddr)) {
                        /* Do book keeping for removing the peer and free it. */
                        sctp_assoc_rm_peer(asoc, transport);
                        break;
                }
        }
}

/* Lookup a transport by address. */
struct sctp_transport *sctp_assoc_lookup_paddr(
                                        const struct sctp_association *asoc,
                                        const union sctp_addr *address)
{
        struct sctp_transport *t;
        struct list_head *pos;

        /* Cycle through all transports searching for a peer address. */

        list_for_each(pos, &asoc->peer.transport_addr_list) {
                t = list_entry(pos, struct sctp_transport, transports);
                if (sctp_cmp_addr_exact(address, &t->ipaddr))
                        return t;
        }

        return NULL;
}

/* Engage in transport control operations.
 * Mark the transport up or down and send a notification to the user.
 * Select and update the new active and retran paths.
 */
void sctp_assoc_control_transport(struct sctp_association *asoc,
                                  struct sctp_transport *transport,
                                  sctp_transport_cmd_t command,
                                  sctp_sn_error_t error)
{
        struct sctp_transport *t = NULL;
        struct sctp_transport *first;
        struct sctp_transport *second;
        struct sctp_ulpevent *event;
        struct list_head *pos;
        int spc_state = 0;

        /* Record the transition on the transport.  */
        switch (command) {
        case SCTP_TRANSPORT_UP:
                transport->state = SCTP_ACTIVE;
                spc_state = SCTP_ADDR_AVAILABLE;
                break;

        case SCTP_TRANSPORT_DOWN:
                transport->state = SCTP_INACTIVE;
                spc_state = SCTP_ADDR_UNREACHABLE;
                break;

        default:
                return;
        };

        /* Generate and send a SCTP_PEER_ADDR_CHANGE notification to the
         * user.
         */
        event = sctp_ulpevent_make_peer_addr_change(asoc,
                                (struct sockaddr_storage *) &transport->ipaddr,
                                0, spc_state, error, GFP_ATOMIC);
        if (event)
                sctp_ulpq_tail_event(&asoc->ulpq, event);

        /* Select new active and retran paths. */

        /* Look for the two most recently used active transports.
         *
         * This code produces the wrong ordering whenever jiffies
         * rolls over, but we still get usable transports, so we don't
         * worry about it.
         */
        first = NULL; second = NULL;

        list_for_each(pos, &asoc->peer.transport_addr_list) {
                t = list_entry(pos, struct sctp_transport, transports);

                if ((t->state == SCTP_INACTIVE) ||
                    (t->state == SCTP_UNCONFIRMED))
                        continue;
                if (!first || t->last_time_heard > first->last_time_heard) {
                        second = first;
                        first = t;
                }
                if (!second || t->last_time_heard > second->last_time_heard)
                        second = t;
        }

        /* RFC 2960 6.4 Multi-Homed SCTP Endpoints
         *
         * By default, an endpoint should always transmit to the
         * primary path, unless the SCTP user explicitly specifies the
         * destination transport address (and possibly source
         * transport address) to use.
         *
         * [If the primary is active but not most recent, bump the most
         * recently used transport.]
         */
        if (((asoc->peer.primary_path->state == SCTP_ACTIVE) ||
             (asoc->peer.primary_path->state == SCTP_UNKNOWN)) &&
            first != asoc->peer.primary_path) {
                second = first;
                first = asoc->peer.primary_path;
        }

        /* If we failed to find a usable transport, just camp on the
         * primary, even if it is inactive.
         */
        if (!first) {
                first = asoc->peer.primary_path;
                second = asoc->peer.primary_path;
        }

        /* Set the active and retran transports.  */
        asoc->peer.active_path = first;
        asoc->peer.retran_path = second;
}

/* Hold a reference to an association. */
void sctp_association_hold(struct sctp_association *asoc)
{
        atomic_inc(&asoc->base.refcnt);
}

/* Release a reference to an association and cleanup
 * if there are no more references.
 */
void sctp_association_put(struct sctp_association *asoc)
{
        if (atomic_dec_and_test(&asoc->base.refcnt))
                sctp_association_destroy(asoc);
}

/* Allocate the next TSN, Transmission Sequence Number, for the given
 * association.
 */
__u32 sctp_association_get_next_tsn(struct sctp_association *asoc)
{
        /* From Section 1.6 Serial Number Arithmetic:
         * Transmission Sequence Numbers wrap around when they reach
         * 2**32 - 1.  That is, the next TSN a DATA chunk MUST use
         * after transmitting TSN = 2*32 - 1 is TSN = 0.
         */
        __u32 retval = asoc->next_tsn;
        asoc->next_tsn++;
        asoc->unack_data++;

        return retval;
}

/* Compare two addresses to see if they match.  Wildcard addresses
 * only match themselves.
 */
int sctp_cmp_addr_exact(const union sctp_addr *ss1,
                        const union sctp_addr *ss2)
{
        struct sctp_af *af;

        af = sctp_get_af_specific(ss1->sa.sa_family);
        if (unlikely(!af))
                return 0;

        return af->cmp_addr(ss1, ss2);
}

/* Return an ecne chunk to get prepended to a packet.
 * Note:  We are sly and return a shared, prealloced chunk.  FIXME:
 * No we don't, but we could/should.
 */
struct sctp_chunk *sctp_get_ecne_prepend(struct sctp_association *asoc)
{
        struct sctp_chunk *chunk;

        /* Send ECNE if needed.
         * Not being able to allocate a chunk here is not deadly.
         */
        if (asoc->need_ecne)
                chunk = sctp_make_ecne(asoc, asoc->last_ecne_tsn);
        else
                chunk = NULL;

        return chunk;
}

/*
 * Find which transport this TSN was sent on.
 */
struct sctp_transport *sctp_assoc_lookup_tsn(struct sctp_association *asoc,
                                             __u32 tsn)
{
        struct sctp_transport *active;
        struct sctp_transport *match;
        struct list_head *entry, *pos;
        struct sctp_transport *transport;
        struct sctp_chunk *chunk;
        __u32 key = htonl(tsn);

        match = NULL;

        /*
         * FIXME: In general, find a more efficient data structure for
         * searching.
         */

        /*
         * The general strategy is to search each transport's transmitted
         * list.   Return which transport this TSN lives on.
         *
         * Let's be hopeful and check the active_path first.
         * Another optimization would be to know if there is only one
         * outbound path and not have to look for the TSN at all.
         *
         */

        active = asoc->peer.active_path;

        list_for_each(entry, &active->transmitted) {
                chunk = list_entry(entry, struct sctp_chunk, transmitted_list);

                if (key == chunk->subh.data_hdr->tsn) {
                        match = active;
                        goto out;
                }
        }

        /* If not found, go search all the other transports. */
        list_for_each(pos, &asoc->peer.transport_addr_list) {
                transport = list_entry(pos, struct sctp_transport, transports);

                if (transport == active)
                        break;
                list_for_each(entry, &transport->transmitted) {
                        chunk = list_entry(entry, struct sctp_chunk,
                                           transmitted_list);
                        if (key == chunk->subh.data_hdr->tsn) {
                                match = transport;
                                goto out;
                        }
                }
        }
out:
        return match;
}

/* Is this the association we are looking for? */
struct sctp_transport *sctp_assoc_is_match(struct sctp_association *asoc,
                                           const union sctp_addr *laddr,
                                           const union sctp_addr *paddr)
{
        struct sctp_transport *transport;

        sctp_read_lock(&asoc->base.addr_lock);

        if ((asoc->base.bind_addr.port == laddr->v4.sin_port) &&
            (asoc->peer.port == paddr->v4.sin_port)) {
                transport = sctp_assoc_lookup_paddr(asoc, paddr);
                if (!transport)
                        goto out;

                if (sctp_bind_addr_match(&asoc->base.bind_addr, laddr,
                                         sctp_sk(asoc->base.sk)))
                        goto out;
        }
        transport = NULL;

out:
        sctp_read_unlock(&asoc->base.addr_lock);
        return transport;
}

/* Do delayed input processing.  This is scheduled by sctp_rcv(). */
static void sctp_assoc_bh_rcv(struct sctp_association *asoc)
{
        struct sctp_endpoint *ep;
        struct sctp_chunk *chunk;
        struct sock *sk;
        struct sctp_inq *inqueue;
        int state;
        sctp_subtype_t subtype;
        int error = 0;

        /* The association should be held so we should be safe. */
        ep = asoc->ep;
        sk = asoc->base.sk;

        inqueue = &asoc->base.inqueue;
        sctp_association_hold(asoc);
        while (NULL != (chunk = sctp_inq_pop(inqueue))) {
                state = asoc->state;
                subtype = SCTP_ST_CHUNK(chunk->chunk_hdr->type);

                /* Remember where the last DATA chunk came from so we
                 * know where to send the SACK.
                 */
                if (sctp_chunk_is_data(chunk))
                        asoc->peer.last_data_from = chunk->transport;
                else
                        SCTP_INC_STATS(SCTP_MIB_INCTRLCHUNKS);

                if (chunk->transport)
                        chunk->transport->last_time_heard = jiffies;

                /* Run through the state machine. */
                error = sctp_do_sm(SCTP_EVENT_T_CHUNK, subtype,
                                   state, ep, asoc, chunk, GFP_ATOMIC);

                /* Check to see if the association is freed in response to
                 * the incoming chunk.  If so, get out of the while loop.
                 */
                if (asoc->base.dead)
                        break;

                /* If there is an error on chunk, discard this packet. */
                if (error && chunk)
                        chunk->pdiscard = 1;
        }
        sctp_association_put(asoc);
}

/* This routine moves an association from its old sk to a new sk.  */
void sctp_assoc_migrate(struct sctp_association *assoc, struct sock *newsk)
{
        struct sctp_sock *newsp = sctp_sk(newsk);
        struct sock *oldsk = assoc->base.sk;

        /* Delete the association from the old endpoint's list of
         * associations.
         */
        list_del_init(&assoc->asocs);

        /* Decrement the backlog value for a TCP-style socket. */
        if (sctp_style(oldsk, TCP))
                oldsk->sk_ack_backlog--;

        /* Release references to the old endpoint and the sock.  */
        sctp_endpoint_put(assoc->ep);
        sock_put(assoc->base.sk);

        /* Get a reference to the new endpoint.  */
        assoc->ep = newsp->ep;
        sctp_endpoint_hold(assoc->ep);

        /* Get a reference to the new sock.  */
        assoc->base.sk = newsk;
        sock_hold(assoc->base.sk);

        /* Add the association to the new endpoint's list of associations.  */
        sctp_endpoint_add_asoc(newsp->ep, assoc);
}

/* Update an association (possibly from unexpected COOKIE-ECHO processing).  */
void sctp_assoc_update(struct sctp_association *asoc,
                       struct sctp_association *new)
{
        struct sctp_transport *trans;
        struct list_head *pos, *temp;

        /* Copy in new parameters of peer. */
        asoc->c = new->c;
        asoc->peer.rwnd = new->peer.rwnd;
        asoc->peer.sack_needed = new->peer.sack_needed;
        asoc->peer.i = new->peer.i;
        sctp_tsnmap_init(&asoc->peer.tsn_map, SCTP_TSN_MAP_SIZE,
                         asoc->peer.i.initial_tsn);

        /* Remove any peer addresses not present in the new association. */
        list_for_each_safe(pos, temp, &asoc->peer.transport_addr_list) {
                trans = list_entry(pos, struct sctp_transport, transports);
                if (!sctp_assoc_lookup_paddr(new, &trans->ipaddr))
                        sctp_assoc_del_peer(asoc, &trans->ipaddr);
        }

        /* If the case is A (association restart), use
         * initial_tsn as next_tsn. If the case is B, use
         * current next_tsn in case data sent to peer
         * has been discarded and needs retransmission.
         */
        if (asoc->state >= SCTP_STATE_ESTABLISHED) {
                asoc->next_tsn = new->next_tsn;
                asoc->ctsn_ack_point = new->ctsn_ack_point;
                asoc->adv_peer_ack_point = new->adv_peer_ack_point;

                /* Reinitialize SSN for both local streams
                 * and peer's streams.
                 */
                sctp_ssnmap_clear(asoc->ssnmap);

        } else {
                /* Add any peer addresses from the new association. */
                list_for_each(pos, &new->peer.transport_addr_list) {
                        trans = list_entry(pos, struct sctp_transport,
                                           transports);
                        if (!sctp_assoc_lookup_paddr(asoc, &trans->ipaddr))
                                sctp_assoc_add_peer(asoc, &trans->ipaddr,
                                                    GFP_ATOMIC, trans->state);
                }

                asoc->ctsn_ack_point = asoc->next_tsn - 1;
                asoc->adv_peer_ack_point = asoc->ctsn_ack_point;
                if (!asoc->ssnmap) {
                        /* Move the ssnmap. */
                        asoc->ssnmap = new->ssnmap;
                        new->ssnmap = NULL;
                }
        }
}

/* Update the retran path for sending a retransmitted packet.
 * Round-robin through the active transports, else round-robin
 * through the inactive transports as this is the next best thing
 * we can try.
 */
void sctp_assoc_update_retran_path(struct sctp_association *asoc)
{
        struct sctp_transport *t, *next;
        struct list_head *head = &asoc->peer.transport_addr_list;
        struct list_head *pos;

        /* Find the next transport in a round-robin fashion. */
        t = asoc->peer.retran_path;
        pos = &t->transports;
        next = NULL;

        while (1) {
                /* Skip the head. */
                if (pos->next == head)
                        pos = head->next;
                else
                        pos = pos->next;

                t = list_entry(pos, struct sctp_transport, transports);

                /* Try to find an active transport. */

                if ((t->state == SCTP_ACTIVE) ||
                    (t->state == SCTP_UNKNOWN)) {
                        break;
                } else {
                        /* Keep track of the next transport in case
                         * we don't find any active transport.
                         */
                        if (!next)
                                next = t;
                }

                /* We have exhausted the list, but didn't find any
                 * other active transports.  If so, use the next
                 * transport.
                 */
                if (t == asoc->peer.retran_path) {
                        t = next;
                        break;
                }
        }

        asoc->peer.retran_path = t;

        SCTP_DEBUG_PRINTK_IPADDR("sctp_assoc_update_retran_path:association"
                                 " %p addr: ",
                                 " port: %d\n",
                                 asoc,
                                 (&t->ipaddr),
                                 t->ipaddr.v4.sin_port);
}

/* Choose the transport for sending a INIT packet.  */
struct sctp_transport *sctp_assoc_choose_init_transport(
        struct sctp_association *asoc)
{
        struct sctp_transport *t;

        /* Use the retran path. If the last INIT was sent over the
         * retran path, update the retran path and use it.
         */
        if (!asoc->init_last_sent_to) {
                t = asoc->peer.active_path;
        } else {
                if (asoc->init_last_sent_to == asoc->peer.retran_path)
                        sctp_assoc_update_retran_path(asoc);
                t = asoc->peer.retran_path;
        }

        SCTP_DEBUG_PRINTK_IPADDR("sctp_assoc_update_retran_path:association"
                                 " %p addr: ",
                                 " port: %d\n",
                                 asoc,
                                 (&t->ipaddr),
                                 t->ipaddr.v4.sin_port);

        return t;
}

/* Choose the transport for sending a SHUTDOWN packet.  */
struct sctp_transport *sctp_assoc_choose_shutdown_transport(
        struct sctp_association *asoc)
{
        /* If this is the first time SHUTDOWN is sent, use the active path,
         * else use the retran path. If the last SHUTDOWN was sent over the
         * retran path, update the retran path and use it.
         */
        if (!asoc->shutdown_last_sent_to)
                return asoc->peer.active_path;
        else {
                if (asoc->shutdown_last_sent_to == asoc->peer.retran_path)
                        sctp_assoc_update_retran_path(asoc);
                return asoc->peer.retran_path;
        }

}

/* Update the association's pmtu and frag_point by going through all the
 * transports. This routine is called when a transport's PMTU has changed.
 */
void sctp_assoc_sync_pmtu(struct sctp_association *asoc)
{
        struct sctp_transport *t;
        struct list_head *pos;
        __u32 pmtu = 0;

        if (!asoc)
                return;

        /* Get the lowest pmtu of all the transports. */
        list_for_each(pos, &asoc->peer.transport_addr_list) {
                t = list_entry(pos, struct sctp_transport, transports);
                if (!pmtu || (t->pathmtu < pmtu))
                        pmtu = t->pathmtu;
        }

        if (pmtu) {
                struct sctp_sock *sp = sctp_sk(asoc->base.sk);
                asoc->pathmtu = pmtu;
                asoc->frag_point = sctp_frag_point(sp, pmtu);
        }

        SCTP_DEBUG_PRINTK("%s: asoc:%p, pmtu:%d, frag_point:%d\n",
                          __FUNCTION__, asoc, asoc->pathmtu, asoc->frag_point);
}

/* Should we send a SACK to update our peer? */
static inline int sctp_peer_needs_update(struct sctp_association *asoc)
{
        switch (asoc->state) {
        case SCTP_STATE_ESTABLISHED:
        case SCTP_STATE_SHUTDOWN_PENDING:
        case SCTP_STATE_SHUTDOWN_RECEIVED:
        case SCTP_STATE_SHUTDOWN_SENT:
                if ((asoc->rwnd > asoc->a_rwnd) &&
                    ((asoc->rwnd - asoc->a_rwnd) >=
                     min_t(__u32, (asoc->base.sk->sk_rcvbuf >> 1), asoc->pathmtu)))
                        return 1;
                break;
        default:
                break;
        }
        return 0;
}

/* Increase asoc's rwnd by len and send any window update SACK if needed. */
void sctp_assoc_rwnd_increase(struct sctp_association *asoc, unsigned len)
{
        struct sctp_chunk *sack;
        struct timer_list *timer;

        if (asoc->rwnd_over) {
                if (asoc->rwnd_over >= len) {
                        asoc->rwnd_over -= len;
                } else {
                        asoc->rwnd += (len - asoc->rwnd_over);
                        asoc->rwnd_over = 0;
                }
        } else {
                asoc->rwnd += len;
        }

        SCTP_DEBUG_PRINTK("%s: asoc %p rwnd increased by %d to (%u, %u) "
                          "- %u\n", __FUNCTION__, asoc, len, asoc->rwnd,
                          asoc->rwnd_over, asoc->a_rwnd);

        /* Send a window update SACK if the rwnd has increased by at least the
         * minimum of the association's PMTU and half of the receive buffer.
         * The algorithm used is similar to the one described in
         * Section 4.2.3.3 of RFC 1122.
         */
        if (sctp_peer_needs_update(asoc)) {
                asoc->a_rwnd = asoc->rwnd;
                SCTP_DEBUG_PRINTK("%s: Sending window update SACK- asoc: %p "
                                  "rwnd: %u a_rwnd: %u\n", __FUNCTION__,
                                  asoc, asoc->rwnd, asoc->a_rwnd);
                sack = sctp_make_sack(asoc);
                if (!sack)
                        return;

                asoc->peer.sack_needed = 0;

                sctp_outq_tail(&asoc->outqueue, sack);

                /* Stop the SACK timer.  */
                timer = &asoc->timers[SCTP_EVENT_TIMEOUT_SACK];
                if (timer_pending(timer) && del_timer(timer))
                        sctp_association_put(asoc);
        }
}

/* Decrease asoc's rwnd by len. */
void sctp_assoc_rwnd_decrease(struct sctp_association *asoc, unsigned len)
{
        SCTP_ASSERT(asoc->rwnd, "rwnd zero", return);
        SCTP_ASSERT(!asoc->rwnd_over, "rwnd_over not zero", return);
        if (asoc->rwnd >= len) {
                asoc->rwnd -= len;
        } else {
                asoc->rwnd_over = len - asoc->rwnd;
                asoc->rwnd = 0;
        }
        SCTP_DEBUG_PRINTK("%s: asoc %p rwnd decreased by %d to (%u, %u)\n",
                          __FUNCTION__, asoc, len, asoc->rwnd,
                          asoc->rwnd_over);
}

/* Build the bind address list for the association based on info from the
 * local endpoint and the remote peer.
 */
int sctp_assoc_set_bind_addr_from_ep(struct sctp_association *asoc,
                                     gfp_t gfp)
{
        sctp_scope_t scope;
        int flags;

        /* Use scoping rules to determine the subset of addresses from
         * the endpoint.
         */
        scope = sctp_scope(&asoc->peer.active_path->ipaddr);
        flags = (PF_INET6 == asoc->base.sk->sk_family) ? SCTP_ADDR6_ALLOWED : 0;
        if (asoc->peer.ipv4_address)
                flags |= SCTP_ADDR4_PEERSUPP;
        if (asoc->peer.ipv6_address)
                flags |= SCTP_ADDR6_PEERSUPP;

        return sctp_bind_addr_copy(&asoc->base.bind_addr,
                                   &asoc->ep->base.bind_addr,
                                   scope, gfp, flags);
}

/* Build the association's bind address list from the cookie.  */
int sctp_assoc_set_bind_addr_from_cookie(struct sctp_association *asoc,
                                         struct sctp_cookie *cookie,
                                         gfp_t gfp)
{
        int var_size2 = ntohs(cookie->peer_init->chunk_hdr.length);
        int var_size3 = cookie->raw_addr_list_len;
        __u8 *raw = (__u8 *)cookie->peer_init + var_size2;

        return sctp_raw_to_bind_addrs(&asoc->base.bind_addr, raw, var_size3,
                                      asoc->ep->base.bind_addr.port, gfp);
}

/* Lookup laddr in the bind address list of an association. */ 
int sctp_assoc_lookup_laddr(struct sctp_association *asoc, 
                            const union sctp_addr *laddr)
{
        int found;

        sctp_read_lock(&asoc->base.addr_lock);
        if ((asoc->base.bind_addr.port == ntohs(laddr->v4.sin_port)) &&
            sctp_bind_addr_match(&asoc->base.bind_addr, laddr,
                                 sctp_sk(asoc->base.sk))) {
                found = 1;
                goto out;
        }

        found = 0;
out:
        sctp_read_unlock(&asoc->base.addr_lock);
        return found;
}