/*
 * Copyright (c) 2012-2014 The DragonFly Project.  All rights reserved.
 *
 * This code is derived from software contributed to The DragonFly Project
 * by Matthew Dillon <dillon@dragonflybsd.org>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name of The DragonFly Project nor the names of its
 *    contributors may be used to endorse or promote products derived
 *    from this software without specific, prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */
/*
 * LNK_SPAN PROTOCOL SUPPORT FUNCTIONS - Please see sys/dmsg.h for an
 * involved explanation of the protocol.
 */

#include "dmsg_local.h"

/*
 * Maximum spanning tree distance.  This has the practical effect of
 * stopping tail-chasing closed loops when a feeder span is lost.
 */
#define DMSG_SPAN_MAXDIST       16

/*
 * RED-BLACK TREE DEFINITIONS
 *
 * We need to track:
 *
 * (1) shared fsid's (a cluster).
 * (2) unique fsid's (a node in a cluster) <--- LNK_SPAN transactions.
 *
 * We need to aggegate all active LNK_SPANs, aggregate, and create our own
 * outgoing LNK_SPAN transactions on each of our connections representing
 * the aggregated state.
 *
 * h2span_conn          - list of iocom connections who wish to receive SPAN
 *                        propagation from other connections.  Might contain
 *                        a filter string.  Only iocom's with an open
 *                        LNK_CONN transactions are applicable for SPAN
 *                        propagation.
 *
 * h2span_relay         - List of links relayed (via SPAN).  Essentially
 *                        each relay structure represents a LNK_SPAN
 *                        transaction that we initiated, verses h2span_link
 *                        which is a LNK_SPAN transaction that we received.
 *
 * --
 *
 * h2span_cluster       - Organizes the shared fsid's.  One structure for
 *                        each cluster.
 *
 * h2span_node          - Organizes the nodes in a cluster.  One structure
 *                        for each unique {cluster,node}, aka {peer_id, pfs_id}.
 *
 * h2span_link          - Organizes all incoming and outgoing LNK_SPAN message
 *                        transactions related to a node.
 *
 *                        One h2span_link structure for each incoming LNK_SPAN
 *                        transaction.  Links selected for propagation back
 *                        out are also where the outgoing LNK_SPAN messages
 *                        are indexed into (so we can propagate changes).
 *
 *                        The h2span_link's use a red-black tree to sort the
 *                        distance hop metric for the incoming LNK_SPAN.  We
 *                        then select the top N for outgoing.  When the
 *                        topology changes the top N may also change and cause
 *                        new outgoing LNK_SPAN transactions to be opened
 *                        and less desireable ones to be closed, causing
 *                        transactional aborts within the message flow in
 *                        the process.
 *
 * Also note            - All outgoing LNK_SPAN message transactions are also
 *                        entered into a red-black tree for use by the routing
 *                        function.  This is handled by msg.c in the state
 *                        code, not here.
 */

struct h2span_link;
struct h2span_relay;
TAILQ_HEAD(h2span_conn_queue, h2span_conn);
TAILQ_HEAD(h2span_relay_queue, h2span_relay);

RB_HEAD(h2span_cluster_tree, h2span_cluster);
RB_HEAD(h2span_node_tree, h2span_node);
RB_HEAD(h2span_link_tree, h2span_link);
RB_HEAD(h2span_relay_tree, h2span_relay);
uint32_t DMsgRNSS;

/*
 * Received LNK_CONN transaction enables SPAN protocol over connection.
 * (may contain filter).  Typically one for each mount and several may
 * share the same media.
 */
struct h2span_conn {
        TAILQ_ENTRY(h2span_conn) entry;
        struct h2span_relay_tree tree;
        dmsg_state_t *state;
        dmsg_lnk_conn_t lnk_conn;
};

/*
 * All received LNK_SPANs are organized by peer id (peer_id),
 * node (pfs_id), and link (received LNK_SPAN transaction).
 */
struct h2span_cluster {
        RB_ENTRY(h2span_cluster) rbnode;
        struct h2span_node_tree tree;
        uuid_t  peer_id;                /* shared fsid */
        uint8_t peer_type;
        uint8_t reserved01[7];
        char    peer_label[128];        /* string identification */
        int     refs;                   /* prevents destruction */
};

struct h2span_node {
        RB_ENTRY(h2span_node) rbnode;
        struct h2span_link_tree tree;
        struct h2span_cluster *cls;
        uint8_t pfs_type;
        uint8_t reserved01[7];
        uuid_t  pfs_id;                 /* unique pfs id */
        char    pfs_label[128];         /* string identification */
        void    *opaque;
};

struct h2span_link {
        RB_ENTRY(h2span_link) rbnode;
        dmsg_state_t    *state;         /* state<->link */
        struct h2span_node *node;       /* related node */
        struct h2span_relay_queue relayq; /* relay out */
        dmsg_lnk_span_t lnk_span;
};

/*
 * Any LNK_SPAN transactions we receive which are relayed out other
 * connections utilize this structure to track the LNK_SPAN transactions
 * we initiate (relay out) on other connections.  We only relay out
 * LNK_SPANs on connections we have an open CONN transaction for.
 *
 * The relay structure points to the outgoing LNK_SPAN trans (out_state)
 * and to the incoming LNK_SPAN transaction (in_state).  The relay
 * structure holds refs on the related states.
 *
 * In many respects this is the core of the protocol... actually figuring
 * out what LNK_SPANs to relay.  The spanid used for relaying is the
 * address of the 'state' structure, which is why h2span_relay has to
 * be entered into a RB-TREE based at h2span_conn (so we can look
 * up the spanid to validate it).
 */
struct h2span_relay {
        TAILQ_ENTRY(h2span_relay) entry;        /* from link */
        RB_ENTRY(h2span_relay) rbnode;          /* from h2span_conn */
        struct h2span_conn      *conn;          /* related CONN transaction */
        dmsg_state_t            *source_rt;     /* h2span_link state */
        dmsg_state_t            *target_rt;     /* h2span_relay state */
};

typedef struct h2span_conn h2span_conn_t;
typedef struct h2span_cluster h2span_cluster_t;
typedef struct h2span_node h2span_node_t;
typedef struct h2span_link h2span_link_t;
typedef struct h2span_relay h2span_relay_t;

#define dmsg_termstr(array)     _dmsg_termstr((array), sizeof(array))

static h2span_relay_t *dmsg_generate_relay(h2span_conn_t *conn,
                                        h2span_link_t *slink);
static uint32_t dmsg_rnss(void);

static __inline
void
_dmsg_termstr(char *base, size_t size)
{
        base[size-1] = 0;
}

/*
 * Cluster peer_type, uuid, AND label must match for a match
 */
static
int
h2span_cluster_cmp(h2span_cluster_t *cls1, h2span_cluster_t *cls2)
{
        int r;

        if (cls1->peer_type < cls2->peer_type)
                return(-1);
        if (cls1->peer_type > cls2->peer_type)
                return(1);
        r = uuid_compare(&cls1->peer_id, &cls2->peer_id, NULL);
        if (r == 0)
                r = strcmp(cls1->peer_label, cls2->peer_label);

        return r;
}

/*
 * Match against pfs_label/pfs_id.  Together these two items represent a
 * unique node.  In most cases the primary differentiator is pfs_id but
 * we also string-match fs_label.
 */
static
int
h2span_node_cmp(h2span_node_t *node1, h2span_node_t *node2)
{
        int r;

        r = strcmp(node1->pfs_label, node2->pfs_label);
        if (r == 0)
                r = uuid_compare(&node1->pfs_id, &node2->pfs_id, NULL);
        return (r);
}

/*
 * Sort/subsort must match h2span_relay_cmp() under any given node
 * to make the aggregation algorithm easier, so the best links are
 * in the same sorted order as the best relays.
 *
 * NOTE: We cannot use link*->state->msgid because this msgid is created
 *       by each remote host and thus might wind up being the same.
 */
static
int
h2span_link_cmp(h2span_link_t *link1, h2span_link_t *link2)
{
        if (link1->lnk_span.dist < link2->lnk_span.dist)
                return(-1);
        if (link1->lnk_span.dist > link2->lnk_span.dist)
                return(1);
        if (link1->lnk_span.rnss < link2->lnk_span.rnss)
                return(-1);
        if (link1->lnk_span.rnss > link2->lnk_span.rnss)
                return(1);
#if 1
        if ((uintptr_t)link1->state < (uintptr_t)link2->state)
                return(-1);
        if ((uintptr_t)link1->state > (uintptr_t)link2->state)
                return(1);
#else
        if (link1->state->msgid < link2->state->msgid)
                return(-1);
        if (link1->state->msgid > link2->state->msgid)
                return(1);
#endif
        return(0);
}

/*
 * Relay entries are sorted by node, subsorted by distance and link
 * address (so we can match up the conn->tree relay topology with
 * a node's link topology).
 */
static
int
h2span_relay_cmp(h2span_relay_t *relay1, h2span_relay_t *relay2)
{
        h2span_link_t *link1 = relay1->source_rt->any.link;
        h2span_link_t *link2 = relay2->source_rt->any.link;

        if ((intptr_t)link1->node < (intptr_t)link2->node)
                return(-1);
        if ((intptr_t)link1->node > (intptr_t)link2->node)
                return(1);
        if (link1->lnk_span.dist < link2->lnk_span.dist)
                return(-1);
        if (link1->lnk_span.dist > link2->lnk_span.dist)
                return(1);
        if (link1->lnk_span.rnss < link2->lnk_span.rnss)
                return(-1);
        if (link1->lnk_span.rnss > link2->lnk_span.rnss)
                return(1);
#if 1
        if ((uintptr_t)link1->state < (uintptr_t)link2->state)
                return(-1);
        if ((uintptr_t)link1->state > (uintptr_t)link2->state)
                return(1);
#else
        if (link1->state->msgid < link2->state->msgid)
                return(-1);
        if (link1->state->msgid > link2->state->msgid)
                return(1);
#endif
        return(0);
}

RB_PROTOTYPE_STATIC(h2span_cluster_tree, h2span_cluster,
             rbnode, h2span_cluster_cmp);
RB_PROTOTYPE_STATIC(h2span_node_tree, h2span_node,
             rbnode, h2span_node_cmp);
RB_PROTOTYPE_STATIC(h2span_link_tree, h2span_link,
             rbnode, h2span_link_cmp);
RB_PROTOTYPE_STATIC(h2span_relay_tree, h2span_relay,
             rbnode, h2span_relay_cmp);

RB_GENERATE_STATIC(h2span_cluster_tree, h2span_cluster,
             rbnode, h2span_cluster_cmp);
RB_GENERATE_STATIC(h2span_node_tree, h2span_node,
             rbnode, h2span_node_cmp);
RB_GENERATE_STATIC(h2span_link_tree, h2span_link,
             rbnode, h2span_link_cmp);
RB_GENERATE_STATIC(h2span_relay_tree, h2span_relay,
             rbnode, h2span_relay_cmp);

/*
 * Global mutex protects cluster_tree lookups, connq, mediaq.
 */
static pthread_mutex_t cluster_mtx;
static struct h2span_cluster_tree cluster_tree = RB_INITIALIZER(cluster_tree);
static struct h2span_conn_queue connq = TAILQ_HEAD_INITIALIZER(connq);
static struct dmsg_media_queue mediaq = TAILQ_HEAD_INITIALIZER(mediaq);

static void dmsg_lnk_span(dmsg_msg_t *msg);
static void dmsg_lnk_conn(dmsg_msg_t *msg);
static void dmsg_lnk_ping(dmsg_msg_t *msg);
static void dmsg_lnk_relay(dmsg_msg_t *msg);
static void dmsg_relay_scan(h2span_conn_t *conn, h2span_node_t *node);
static void dmsg_relay_delete(h2span_relay_t *relay);

void
dmsg_msg_lnk_signal(dmsg_iocom_t *iocom __unused)
{
        pthread_mutex_lock(&cluster_mtx);
        dmsg_relay_scan(NULL, NULL);
        pthread_mutex_unlock(&cluster_mtx);
}

/*
 * DMSG_PROTO_LNK - Generic DMSG_PROTO_LNK.
 *            (incoming iocom lock not held)
 *
 * This function is typically called for one-way and opening-transactions
 * since state->func is assigned after that, but it will also be called
 * if no state->func is assigned on transaction-open.
 */
void
dmsg_msg_lnk(dmsg_msg_t *msg)
{
        dmsg_iocom_t *iocom = msg->state->iocom;

        switch(msg->tcmd & DMSGF_BASECMDMASK) {
        case DMSG_LNK_CONN:
                dmsg_lnk_conn(msg);
                break;
        case DMSG_LNK_SPAN:
                dmsg_lnk_span(msg);
                break;
        case DMSG_LNK_PING:
                dmsg_lnk_ping(msg);
                break;
        default:
                iocom->usrmsg_callback(msg, 1);
                /* state invalid after reply */
                break;
        }
}

/*
 * LNK_CONN - iocom identify message reception.
 *            (incoming iocom lock not held)
 *
 * Remote node identifies itself to us, sets up a SPAN filter, and gives us
 * the ok to start transmitting SPANs.
 */
void
dmsg_lnk_conn(dmsg_msg_t *msg)
{
        dmsg_state_t *state = msg->state;
        dmsg_iocom_t *iocom = state->iocom;
        dmsg_media_t *media;
        h2span_conn_t *conn;
        h2span_relay_t *relay;
        char *alloc = NULL;

        pthread_mutex_lock(&cluster_mtx);

        dmio_printf(iocom, 3,
                "dmsg_lnk_conn: msg %p cmd %08x state %p "
                "txcmd %08x rxcmd %08x\n",
                msg, msg->any.head.cmd, state,
                state->txcmd, state->rxcmd);

        switch(msg->any.head.cmd & DMSGF_TRANSMASK) {
        case DMSG_LNK_CONN | DMSGF_CREATE:
        case DMSG_LNK_CONN | DMSGF_CREATE | DMSGF_DELETE:
                /*
                 * On transaction start we allocate a new h2span_conn and
                 * acknowledge the request, leaving the transaction open.
                 * We then relay priority-selected SPANs.
                 */
                dmio_printf(iocom, 3, "LNK_CONN(%08x): %s/%s\n",
                        (uint32_t)msg->any.head.msgid,
                        dmsg_uuid_to_str(&msg->any.lnk_conn.peer_id, &alloc),
                        msg->any.lnk_conn.peer_label);
                free(alloc);

                conn = dmsg_alloc(sizeof(*conn));
                assert(state->iocom->conn == NULL);

                RB_INIT(&conn->tree);
                state->iocom->conn = conn;      /* XXX only one */
                state->iocom->conn_msgid = state->msgid;
                dmsg_state_hold(state);
                conn->state = state;
                state->func = dmsg_lnk_conn;
                state->any.conn = conn;
                TAILQ_INSERT_TAIL(&connq, conn, entry);
                conn->lnk_conn = msg->any.lnk_conn;

                /*
                 * Set up media
                 */
                TAILQ_FOREACH(media, &mediaq, entry) {
                        if (uuid_compare(&msg->any.lnk_conn.media_id,
                                         &media->media_id, NULL) == 0) {
                                break;
                        }
                }
                if (media == NULL) {
                        media = dmsg_alloc(sizeof(*media));
                        media->media_id = msg->any.lnk_conn.media_id;
                        TAILQ_INSERT_TAIL(&mediaq, media, entry);
                }
                state->media = media;
                ++media->refs;

                if ((msg->any.head.cmd & DMSGF_DELETE) == 0) {
                        iocom->usrmsg_callback(msg, 0);
                        dmsg_msg_result(msg, 0);
                        dmsg_iocom_signal(iocom);
                        break;
                }
                /* FALL THROUGH */
        case DMSG_LNK_CONN | DMSGF_DELETE:
        case DMSG_LNK_ERROR | DMSGF_DELETE:
                /*
                 * On transaction terminate we clean out our h2span_conn
                 * and acknowledge the request, closing the transaction.
                 */
                dmio_printf(iocom, 3, "%s\n", "LNK_CONN: Terminated");
                conn = state->any.conn;
                assert(conn);

                /*
                 * Adjust media refs
                 *
                 * Callback will clean out media config / user-opaque state
                 */
                media = state->media;
                --media->refs;
                if (media->refs == 0) {
                        dmio_printf(iocom, 3, "%s\n", "Media shutdown");
                        TAILQ_REMOVE(&mediaq, media, entry);
                        pthread_mutex_unlock(&cluster_mtx);
                        iocom->usrmsg_callback(msg, 0);
                        pthread_mutex_lock(&cluster_mtx);
                        dmsg_free(media);
                }
                state->media = NULL;

                /*
                 * Clean out all relays.  This requires terminating each
                 * relay transaction.
                 */
                while ((relay = RB_ROOT(&conn->tree)) != NULL) {
                        dmsg_relay_delete(relay);
                }

                /*
                 * Clean out conn
                 */
                conn->state = NULL;
                msg->state->any.conn = NULL;
                msg->state->iocom->conn = NULL;
                TAILQ_REMOVE(&connq, conn, entry);
                dmsg_free(conn);

                dmsg_msg_reply(msg, 0);
                dmsg_state_drop(state);
                /* state invalid after reply */
                break;
        default:
                iocom->usrmsg_callback(msg, 1);
#if 0
                if (msg->any.head.cmd & DMSGF_DELETE)
                        goto deleteconn;
                dmsg_msg_reply(msg, DMSG_ERR_NOSUPP);
#endif
                break;
        }
        pthread_mutex_unlock(&cluster_mtx);
}

/*
 * LNK_SPAN - Spanning tree protocol message reception
 *            (incoming iocom lock not held)
 *
 * Receive a spanning tree transactional message, creating or destroying
 * a SPAN and propagating it to other iocoms.
 */
void
dmsg_lnk_span(dmsg_msg_t *msg)
{
        dmsg_state_t *state = msg->state;
        dmsg_iocom_t *iocom = state->iocom;
        h2span_cluster_t dummy_cls;
        h2span_node_t dummy_node;
        h2span_cluster_t *cls;
        h2span_node_t *node;
        h2span_link_t *slink;
        h2span_relay_t *relay;
        char *alloc = NULL;

        /*
         * XXX
         *
         * Ignore reply to LNK_SPAN.  The reply is expected and will commands
         * to flow in both directions on the open transaction.  This will also
         * ignore DMSGF_REPLY|DMSGF_DELETE messages.  Since we take no action
         * if the other end unexpectedly closes their side of the transaction,
         * we can ignore that too.
         */
        if (msg->any.head.cmd & DMSGF_REPLY) {
                dmio_printf(iocom, 2, "%s\n",
                            "Ignore reply to LNK_SPAN");
                return;
        }

        pthread_mutex_lock(&cluster_mtx);

        /*
         * On transaction start we initialize the tracking infrastructure
         */
        if (msg->any.head.cmd & DMSGF_CREATE) {
                assert(state->func == NULL);
                state->func = dmsg_lnk_span;

                dmsg_termstr(msg->any.lnk_span.peer_label);
                dmsg_termstr(msg->any.lnk_span.pfs_label);

                /*
                 * Find the cluster
                 */
                dummy_cls.peer_id = msg->any.lnk_span.peer_id;
                dummy_cls.peer_type = msg->any.lnk_span.peer_type;
                bcopy(msg->any.lnk_span.peer_label, dummy_cls.peer_label,
                      sizeof(dummy_cls.peer_label));
                cls = RB_FIND(h2span_cluster_tree, &cluster_tree, &dummy_cls);
                if (cls == NULL) {
                        cls = dmsg_alloc(sizeof(*cls));
                        cls->peer_id = msg->any.lnk_span.peer_id;
                        cls->peer_type = msg->any.lnk_span.peer_type;
                        bcopy(msg->any.lnk_span.peer_label,
                              cls->peer_label, sizeof(cls->peer_label));
                        RB_INIT(&cls->tree);
                        RB_INSERT(h2span_cluster_tree, &cluster_tree, cls);
                }

                /*
                 * Find the node
                 */
                dummy_node.pfs_id = msg->any.lnk_span.pfs_id;
                bcopy(msg->any.lnk_span.pfs_label, dummy_node.pfs_label,
                      sizeof(dummy_node.pfs_label));
                node = RB_FIND(h2span_node_tree, &cls->tree, &dummy_node);
                if (node == NULL) {
                        node = dmsg_alloc(sizeof(*node));
                        node->pfs_id = msg->any.lnk_span.pfs_id;
                        node->pfs_type = msg->any.lnk_span.pfs_type;
                        bcopy(msg->any.lnk_span.pfs_label, node->pfs_label,
                              sizeof(node->pfs_label));
                        node->cls = cls;
                        RB_INIT(&node->tree);
                        RB_INSERT(h2span_node_tree, &cls->tree, node);
                }

                /*
                 * Create the link
                 *
                 * NOTE: Sub-transactions on the incoming SPAN can be used
                 *       to talk to the originator.  We should not set-up
                 *       state->relay for incoming SPANs since our sub-trans
                 *       is running on the same interface (i.e. no actual
                 *       relaying need be done).
                 *
                 * NOTE: Later on when we relay the SPAN out the outgoing
                 *       SPAN state will be set up to relay back to this
                 *       state.
                 *
                 * NOTE: It is possible for SPAN targets to send one-way
                 *       messages to the originator but it is not possible
                 *       for the originator to (currently) broadcast one-way
                 *       messages to all of its SPAN targets.  The protocol
                 *       allows such a feature to be added in the future.
                 */
                assert(state->any.link == NULL);
                dmsg_state_hold(state);
                slink = dmsg_alloc(sizeof(*slink));
                TAILQ_INIT(&slink->relayq);
                slink->node = node;
                slink->state = state;
                state->any.link = slink;
                slink->lnk_span = msg->any.lnk_span;

                RB_INSERT(h2span_link_tree, &node->tree, slink);

                dmio_printf(iocom, 3,
                            "LNK_SPAN(thr %p): %p %s cl=%s fs=%s dist=%d\n",
                            iocom, slink,
                            dmsg_uuid_to_str(&msg->any.lnk_span.peer_id,
                                             &alloc),
                            msg->any.lnk_span.peer_label,
                            msg->any.lnk_span.pfs_label,
                            msg->any.lnk_span.dist);
                free(alloc);
#if 0
                dmsg_relay_scan(NULL, node);
#endif
                /*
                 * Ack the open, which will issue a CREATE on our side, and
                 * leave the transaction open.  Necessary to allow the
                 * transaction to be used as a virtual circuit.
                 */
                dmsg_state_result(state, 0);
                dmsg_iocom_signal(iocom);
        }

        /*
         * On transaction terminate we remove the tracking infrastructure.
         */
        if (msg->any.head.cmd & DMSGF_DELETE) {
                slink = state->any.link;
                assert(slink->state == state);
                assert(slink != NULL);
                node = slink->node;
                cls = node->cls;

                dmio_printf(iocom, 3,
                            "LNK_DELE(thr %p): %p %s cl=%s fs=%s\n",
                            iocom, slink,
                            dmsg_uuid_to_str(&cls->peer_id, &alloc),
                            cls->peer_label,
                            node->pfs_label);
                free(alloc);

                /*
                 * Clean out all relays.  This requires terminating each
                 * relay transaction.
                 */
                while ((relay = TAILQ_FIRST(&slink->relayq)) != NULL) {
                        dmsg_relay_delete(relay);
                }

                /*
                 * Clean out the topology
                 */
                RB_REMOVE(h2span_link_tree, &node->tree, slink);
                if (RB_EMPTY(&node->tree)) {
                        RB_REMOVE(h2span_node_tree, &cls->tree, node);
                        if (RB_EMPTY(&cls->tree) && cls->refs == 0) {
                                RB_REMOVE(h2span_cluster_tree,
                                          &cluster_tree, cls);
                                dmsg_free(cls);
                        }
                        node->cls = NULL;
                        dmsg_free(node);
                        node = NULL;
                }
                state->any.link = NULL;
                slink->state = NULL;
                slink->node = NULL;
                dmsg_state_drop(state);
                dmsg_free(slink);

                /*
                 * We have to terminate the transaction
                 */
                dmsg_state_reply(state, 0);
                /* state invalid after reply */

                /*
                 * If the node still exists issue any required updates.  If
                 * it doesn't then all related relays have already been
                 * removed and there's nothing left to do.
                 */
#if 0
                if (node)
                        dmsg_relay_scan(NULL, node);
#endif
                if (node)
                        dmsg_iocom_signal(iocom);
        }

        pthread_mutex_unlock(&cluster_mtx);
}

/*
 * Respond to a PING with a PING|REPLY, forward replies to the usermsg
 * callback.
 */
static
void
dmsg_lnk_ping(dmsg_msg_t *msg)
{
        dmsg_msg_t *rep;

        if (msg->any.head.cmd & DMSGF_REPLY) {
                msg->state->iocom->usrmsg_callback(msg, 1);
        } else {
                rep = dmsg_msg_alloc(msg->state, 0,
                                     DMSG_LNK_PING | DMSGF_REPLY,
                                     NULL, NULL);
                dmsg_msg_write(rep);
        }
}

/*
 * Update relay transactions for SPANs.
 *
 * Called with cluster_mtx held.
 */
static void dmsg_relay_scan_specific(h2span_node_t *node,
                                        h2span_conn_t *conn);

static void
dmsg_relay_scan(h2span_conn_t *conn, h2span_node_t *node)
{
        h2span_cluster_t *cls;

        if (node) {
                /*
                 * Iterate specific node
                 */
                TAILQ_FOREACH(conn, &connq, entry)
                        dmsg_relay_scan_specific(node, conn);
        } else {
                /*
                 * Full iteration.
                 *
                 * Iterate cluster ids, nodes, and either a specific connection
                 * or all connections.
                 */
                RB_FOREACH(cls, h2span_cluster_tree, &cluster_tree) {
                        /*
                         * Iterate node ids
                         */
                        RB_FOREACH(node, h2span_node_tree, &cls->tree) {
                                /*
                                 * Synchronize the node's link (received SPANs)
                                 * with each connection's relays.
                                 */
                                if (conn) {
                                        dmsg_relay_scan_specific(node, conn);
                                } else {
                                        TAILQ_FOREACH(conn, &connq, entry) {
                                            dmsg_relay_scan_specific(node,
                                                                        conn);
                                        }
                                        assert(conn == NULL);
                                }
                        }
                }
        }
}

/*
 * Update the relay'd SPANs for this (node, conn).
 *
 * Iterate links and adjust relays to match.  We only propagate the top link
 * for now (XXX we want to propagate the top two).
 *
 * The dmsg_relay_scan_cmp() function locates the first relay element
 * for any given node.  The relay elements will be sub-sorted by dist.
 */
struct relay_scan_info {
        h2span_node_t *node;
        h2span_relay_t *relay;
};

static int
dmsg_relay_scan_cmp(h2span_relay_t *relay, void *arg)
{
        struct relay_scan_info *info = arg;

        if ((intptr_t)relay->source_rt->any.link->node < (intptr_t)info->node)
                return(-1);
        if ((intptr_t)relay->source_rt->any.link->node > (intptr_t)info->node)
                return(1);
        return(0);
}

static int
dmsg_relay_scan_callback(h2span_relay_t *relay, void *arg)
{
        struct relay_scan_info *info = arg;

        info->relay = relay;
        return(-1);
}

static void
dmsg_relay_scan_specific(h2span_node_t *node, h2span_conn_t *conn)
{
        struct relay_scan_info info;
        h2span_relay_t *relay;
        h2span_relay_t *next_relay;
        h2span_link_t *slink;
        dmsg_lnk_conn_t *lconn;
        dmsg_lnk_span_t *lspan;
        int count;
        int maxcount = 2;
#ifdef REQUIRE_SYMMETRICAL
        uint32_t lastdist = DMSG_SPAN_MAXDIST;
        uint32_t lastrnss = 0;
#endif

        info.node = node;
        info.relay = NULL;

        /*
         * Locate the first related relay for the node on this connection.
         * relay will be NULL if there were none.
         */
        RB_SCAN(h2span_relay_tree, &conn->tree,
                dmsg_relay_scan_cmp, dmsg_relay_scan_callback, &info);
        relay = info.relay;
        info.relay = NULL;
        if (relay)
                assert(relay->source_rt->any.link->node == node);

        dm_printf(9, "relay scan for connection %p\n", conn);

        /*
         * Iterate the node's links (received SPANs) in distance order,
         * lowest (best) dist first.
         *
         * PROPAGATE THE BEST LINKS OVER THE SPECIFIED CONNECTION.
         *
         * Track relays while iterating the best links and construct
         * missing relays when necessary.
         *
         * (If some prior better link was removed it would have also
         *  removed the relay, so the relay can only match exactly or
         *  be worse).
         */
        count = 0;
        RB_FOREACH(slink, h2span_link_tree, &node->tree) {
                /*
                 * Increment count of successful relays.  This isn't
                 * quite accurate if we break out but nothing after
                 * the loop uses (count).
                 *
                 * If count exceeds the maximum number of relays we desire
                 * we normally want to break out.  However, in order to
                 * guarantee a symmetric path we have to continue if both
                 * (dist) and (rnss) continue to match.  Otherwise the SPAN
                 * propagation in the reverse direction may choose different
                 * routes and we will not have a symmetric path.
                 *
                 * NOTE: Spanning tree does not have to be symmetrical so
                 *       this code is not currently enabled.
                 */
                if (++count >= maxcount) {
#ifdef REQUIRE_SYMMETRICAL
                        if (lastdist != slink->lnk_span.dist ||
                            lastrnss != slink->lnk_span.rnss) {
                                break;
                        }
#else
                        break;
#endif
                        /* go beyond the nominal maximum desired relays */
                }

                /*
                 * Match, relay already in-place, get the next
                 * relay to match against the next slink.
                 */
                if (relay && relay->source_rt->any.link == slink) {
                        relay = RB_NEXT(h2span_relay_tree, &conn->tree, relay);
                        continue;
                }

                /*
                 * We might want this SLINK, if it passes our filters.
                 *
                 * The spanning tree can cause closed loops so we have
                 * to limit slink->dist.
                 */
                if (slink->lnk_span.dist > DMSG_SPAN_MAXDIST)
                        break;

                /*
                 * Don't bother transmitting a LNK_SPAN out the same
                 * connection it came in on.  Trivial optimization.
                 */
                if (slink->state->iocom == conn->state->iocom)
                        break;

                /*
                 * NOTE ON FILTERS: The protocol spec allows non-requested
                 * SPANs to be transmitted, the other end is expected to
                 * leave their transactions open but otherwise ignore them.
                 *
                 * Don't bother transmitting if the remote connection
                 * is not accepting this SPAN's peer_type.
                 */
                lspan = &slink->lnk_span;
                lconn = &conn->lnk_conn;
                if (((1LLU << lspan->peer_type) & lconn->peer_mask) == 0)
                        break;

                /*
                 * Do not give pure clients visibility to other pure clients
                 */
                if (lconn->peer_type == DMSG_PEER_CLIENT &&
                    lspan->peer_type == DMSG_PEER_CLIENT) {
                        break;
                }

                /*
                 * Clients can set peer_id to filter the peer_id of incoming
                 * spans.  Other peer types set peer_id to advertising their
                 * peer_id. XXX
                 *
                 * NOTE: peer_label is not a filter on clients, it identifies 
                 *       the client just as it identifies other peer types.
                 */
                if (lconn->peer_type == DMSG_PEER_CLIENT &&
                    !uuid_is_nil(&lconn->peer_id, NULL) &&
                    uuid_compare(&slink->node->cls->peer_id,
                                 &lconn->peer_id, NULL)) {
                        break;
                }

                /*
                 * NOTE! pfs_id differentiates nodes within the same cluster
                 *       so we obviously don't want to match those.  Similarly
                 *       for pfs_label.
                 */

                /*
                 * Ok, we've accepted this SPAN for relaying.
                 */
                assert(relay == NULL ||
                       relay->source_rt->any.link->node != slink->node ||
                       relay->source_rt->any.link->lnk_span.dist >=
                        slink->lnk_span.dist);
                relay = dmsg_generate_relay(conn, slink);
#ifdef REQUIRE_SYMMETRICAL
                lastdist = slink->lnk_span.dist;
                lastrnss = slink->lnk_span.rnss;
#endif

                /*
                 * Match (created new relay), get the next relay to
                 * match against the next slink.
                 */
                relay = RB_NEXT(h2span_relay_tree, &conn->tree, relay);
        }

        /*
         * Any remaining relay's belonging to this connection which match
         * the node are in excess of the current aggregate spanning state
         * and should be removed.
         */
        while (relay && relay->source_rt->any.link->node == node) {
                next_relay = RB_NEXT(h2span_relay_tree, &conn->tree, relay);
                dm_printf(9, "%s\n", "RELAY DELETE FROM EXTRAS");
                dmsg_relay_delete(relay);
                relay = next_relay;
        }
}

/*
 * Find the slink associated with the msgid and return its state,
 * so the caller can issue a transaction.
 */
dmsg_state_t *
dmsg_findspan(const char *label)
{
        dmsg_state_t *state;
        h2span_cluster_t *cls;
        h2span_node_t *node;
        h2span_link_t *slink;
        uint64_t msgid = strtoull(label, NULL, 16);

        pthread_mutex_lock(&cluster_mtx);

        state = NULL;
        RB_FOREACH(cls, h2span_cluster_tree, &cluster_tree) {
                RB_FOREACH(node, h2span_node_tree, &cls->tree) {
                        RB_FOREACH(slink, h2span_link_tree, &node->tree) {
                                if (slink->state->msgid == msgid) {
                                        state = slink->state;
                                        goto done;
                                }
                        }
                }
        }
done:
        pthread_mutex_unlock(&cluster_mtx);

        dm_printf(8, "findspan: %p\n", state);

        return state;
}


/*
 * Helper function to generate missing relay on target connection.
 *
 * cluster_mtx must be held
 */
static
h2span_relay_t *
dmsg_generate_relay(h2span_conn_t *conn, h2span_link_t *slink)
{
        h2span_relay_t *relay;
        dmsg_msg_t *msg;

        dmsg_state_hold(slink->state);
        relay = dmsg_alloc(sizeof(*relay));
        relay->conn = conn;
        relay->source_rt = slink->state;
        /* relay->source_rt->any.link = slink; */

        /*
         * NOTE: relay->target_rt->any.relay set to relay by alloc.
         *
         * NOTE: LNK_SPAN is transmitted as a top-level transaction.
         */
        msg = dmsg_msg_alloc(&conn->state->iocom->state0,
                             0, DMSG_LNK_SPAN | DMSGF_CREATE,
                             dmsg_lnk_relay, relay);
        dmsg_state_hold(msg->state);
        relay->target_rt = msg->state;

        msg->any.lnk_span = slink->lnk_span;
        msg->any.lnk_span.dist = slink->lnk_span.dist + 1;
        msg->any.lnk_span.rnss = slink->lnk_span.rnss + dmsg_rnss();

        RB_INSERT(h2span_relay_tree, &conn->tree, relay);
        TAILQ_INSERT_TAIL(&slink->relayq, relay, entry);

        /*
         * Seed the relay so new sub-transactions received on the outgoing
         * SPAN circuit are relayed back to the originator.
         */
        msg->state->relay = relay->source_rt;
        dmsg_state_hold(msg->state->relay);

        dmsg_msg_write(msg);

        return (relay);
}

/*
 * Messages received on relay SPANs.  These are open transactions so it is
 * in fact possible for the other end to close the transaction.
 *
 * XXX MPRACE on state structure
 */
static void
dmsg_lnk_relay(dmsg_msg_t *msg)
{
        dmsg_state_t *state = msg->state;
        h2span_relay_t *relay;

        assert(msg->any.head.cmd & DMSGF_REPLY);

        if (msg->any.head.cmd & DMSGF_DELETE) {
                pthread_mutex_lock(&cluster_mtx);
                dm_printf(8, "%s\n", "RELAY DELETE FROM LNK_RELAY MSG");
                if ((relay = state->any.relay) != NULL) {
                        dmsg_relay_delete(relay);
                } else {
                        dmsg_state_reply(state, 0);
                }
                pthread_mutex_unlock(&cluster_mtx);
        }
}

/*
 * cluster_mtx held by caller
 */
static
void
dmsg_relay_delete(h2span_relay_t *relay)
{
        dm_printf(8,
                  "RELAY DELETE %p RELAY %p ON CLS=%p NODE=%p "
                  "DIST=%d FD %d STATE %p\n",
                  relay->source_rt->any.link,
                  relay,
                  relay->source_rt->any.link->node->cls,
                  relay->source_rt->any.link->node,
                  relay->source_rt->any.link->lnk_span.dist,
                  relay->conn->state->iocom->sock_fd,
                  relay->target_rt);

        RB_REMOVE(h2span_relay_tree, &relay->conn->tree, relay);
        TAILQ_REMOVE(&relay->source_rt->any.link->relayq, relay, entry);

        if (relay->target_rt) {
                relay->target_rt->any.relay = NULL;
                dmsg_state_reply(relay->target_rt, 0);
                dmsg_state_drop(relay->target_rt);
                /* state invalid after reply */
                relay->target_rt = NULL;
        }

        /*
         * NOTE: relay->source_rt->refs is held by the relay SPAN
         *       state, not by this relay structure.
         */
        relay->conn = NULL;
        if (relay->source_rt) {
                dmsg_state_drop(relay->source_rt);
                relay->source_rt = NULL;
        }
        dmsg_free(relay);
}

/************************************************************************
 *                      ROUTER AND MESSAGING HANDLES                    *
 ************************************************************************
 *
 * Basically the idea here is to provide a stable data structure which
 * can be localized to the caller for higher level protocols to work with.
 * Depends on the context, these dmsg_handle's can be pooled by use-case
 * and remain persistent through a client (or mount point's) life.
 */

#if 0
/*
 * Obtain a stable handle on a cluster given its uuid.  This ties directly
 * into the global cluster topology, creating the structure if necessary
 * (even if the uuid does not exist or does not exist yet), and preventing
 * the structure from getting ripped out from under us while we hold a
 * pointer to it.
 */
h2span_cluster_t *
dmsg_cluster_get(uuid_t *peer_id)
{
        h2span_cluster_t dummy_cls;
        h2span_cluster_t *cls;

        dummy_cls.peer_id = *peer_id;
        pthread_mutex_lock(&cluster_mtx);
        cls = RB_FIND(h2span_cluster_tree, &cluster_tree, &dummy_cls);
        if (cls)
                ++cls->refs;
        pthread_mutex_unlock(&cluster_mtx);
        return (cls);
}

void
dmsg_cluster_put(h2span_cluster_t *cls)
{
        pthread_mutex_lock(&cluster_mtx);
        assert(cls->refs > 0);
        --cls->refs;
        if (RB_EMPTY(&cls->tree) && cls->refs == 0) {
                RB_REMOVE(h2span_cluster_tree,
                          &cluster_tree, cls);
                dmsg_free(cls);
        }
        pthread_mutex_unlock(&cluster_mtx);
}

/*
 * Obtain a stable handle to a specific cluster node given its uuid.
 * This handle does NOT lock in the route to the node and is typically
 * used as part of the dmsg_handle_*() API to obtain a set of
 * stable nodes.
 */
h2span_node_t *
dmsg_node_get(h2span_cluster_t *cls, uuid_t *pfs_id)
{
}

#endif

/*
 * Dumps the spanning tree
 *
 * DEBUG ONLY
 */
void
dmsg_shell_tree(dmsg_iocom_t *iocom, char *cmdbuf __unused)
{
        h2span_cluster_t *cls;
        h2span_node_t *node;
        h2span_link_t *slink;
        h2span_relay_t *relay;
        char *uustr = NULL;

        pthread_mutex_lock(&cluster_mtx);
        RB_FOREACH(cls, h2span_cluster_tree, &cluster_tree) {
                dmsg_printf(iocom, "Cluster %s %s (%s)\n",
                                  dmsg_peer_type_to_str(cls->peer_type),
                                  dmsg_uuid_to_str(&cls->peer_id, &uustr),
                                  cls->peer_label);
                RB_FOREACH(node, h2span_node_tree, &cls->tree) {
                        dmsg_printf(iocom, "    Node %02x %s (%s)\n",
                                node->pfs_type,
                                dmsg_uuid_to_str(&node->pfs_id, &uustr),
                                node->pfs_label);
                        RB_FOREACH(slink, h2span_link_tree, &node->tree) {
                                dmsg_printf(iocom,
                                            "\tSLink msgid %016jx "
                                            "dist=%d via %d\n",
                                            (intmax_t)slink->state->msgid,
                                            slink->lnk_span.dist,
                                            slink->state->iocom->sock_fd);
                                TAILQ_FOREACH(relay, &slink->relayq, entry) {
                                        dmsg_printf(iocom,
                                            "\t    Relay-out msgid %016jx "
                                            "via %d\n",
                                            (intmax_t)relay->target_rt->msgid,
                                            relay->target_rt->iocom->sock_fd);
                                }
                        }
                }
        }
        pthread_mutex_unlock(&cluster_mtx);
        if (uustr)
                free(uustr);
#if 0
        TAILQ_FOREACH(conn, &connq, entry) {
        }
#endif
}

/*
 * DEBUG ONLY
 *
 * Locate the state representing an incoming LNK_SPAN given its msgid.
 */
int
dmsg_debug_findspan(uint64_t msgid, dmsg_state_t **statep)
{
        h2span_cluster_t *cls;
        h2span_node_t *node;
        h2span_link_t *slink;

        pthread_mutex_lock(&cluster_mtx);
        RB_FOREACH(cls, h2span_cluster_tree, &cluster_tree) {
                RB_FOREACH(node, h2span_node_tree, &cls->tree) {
                        RB_FOREACH(slink, h2span_link_tree, &node->tree) {
                                if (slink->state->msgid == msgid) {
                                        *statep = slink->state;
                                        goto found;
                                }
                        }
                }
        }
        pthread_mutex_unlock(&cluster_mtx);
        *statep = NULL;
        return(ENOENT);
found:
        pthread_mutex_unlock(&cluster_mtx);
        return(0);
}

/*
 * Random number sub-sort value to add to SPAN rnss fields on relay.
 * This allows us to differentiate spans with the same <dist> field
 * for relaying purposes.  We must normally limit the number of relays
 * for any given SPAN origination but we must also guarantee that a
 * symmetric reverse path exists, so we use the rnss field as a sub-sort
 * (since there can be thousands or millions if we only match on <dist>),
 * and if there STILL too many spans we go past the limit.
 */
static
uint32_t
dmsg_rnss(void)
{
        if (DMsgRNSS == 0) {
                pthread_mutex_lock(&cluster_mtx);
                while (DMsgRNSS == 0) {
                        srandomdev();
                        DMsgRNSS = random();
                }
                pthread_mutex_unlock(&cluster_mtx);
        }
        return(DMsgRNSS);
}