bridge_native_dahdi.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2013 Digium, Inc.
 *
 * Richard Mudgett <rmudgett@digium.com>
 *
 * See http://www.asterisk.org for more information about
 * the Asterisk project. Please do not directly contact
 * any of the maintainers of this project for assistance;
 * the project provides a web site, mailing lists and IRC
 * channels for your use.
 *
 * This program is free software, distributed under the terms of
 * the GNU General Public License Version 2. See the LICENSE file
 * at the top of the source tree.
 */
 
/*!
 * \file
 * \brief Native DAHDI bridging support.
 *
 * \author Richard Mudgett <rmudgett@digium.com>
 *
 * See Also:
 * \arg \ref AstCREDITS
 */
 
/*** MODULEINFO
    <support_level>core</support_level>
 ***/
 
#include "asterisk.h"
 
#include "../sig_analog.h"
#if defined(HAVE_PRI)
#include "../sig_pri.h"
#endif  /* defined(HAVE_PRI) */
#include "../chan_dahdi.h"
 
#include "bridge_native_dahdi.h"
#include "asterisk/bridge.h"
#include "asterisk/bridge_technology.h"
#include "asterisk/frame.h"
#include "asterisk/format_cache.h"
 
/* ------------------------------------------------------------------- */
 
static const struct ast_channel_tech *dahdi_tech;
 
struct native_pvt_chan {
    /*! Original private. */
    struct dahdi_pvt *pvt;
    /*! Original private owner. */
    struct ast_channel *owner;
    /*! Original owner index. */
    int index;
    /*! Original file descriptor 0. */
    int fd0;
    /*! Original channel state. */
    int state;
    /*! Original inthreeway. */
    unsigned int inthreeway:1;
};
 
struct native_pvt_bridge {
    /*! Master channel in the native bridge. */
    struct dahdi_pvt *master;
    /*! Slave channel in the native bridge. */
    struct dahdi_pvt *slave;
    /*! TRUE if the bridge can start when ready. */
    unsigned int saw_start:1;
    /*! TRUE if the channels are connected in a conference. */
    unsigned int connected:1;
#if defined(HAVE_PRI) && defined(PRI_2BCT)
    /*!
     * \brief TRUE if tried to eliminate possible PRI tromboned call.
     *
     * \note A tromboned call uses two B channels of the same ISDN
     * span.  One leg comes into Asterisk, the other leg goes out of
     * Asterisk, and Asterisk is natively bridging the two legs.
     */
    unsigned int tried_trombone_removal:1;
#endif  /* defined(HAVE_PRI) && defined(PRI_2BCT) */
};
 
/*!
 * \internal
 * \brief Create a bridge technology instance for a bridge.
 * \since 12.0.0
 *
 * \retval 0 on success
 * \retval -1 on failure
 *
 * \note On entry, bridge may or may not already be locked.
 * However, it can be accessed as if it were locked.
 */
static int native_bridge_create(struct ast_bridge *bridge)
{
    struct native_pvt_bridge *tech_pvt;
 
    ast_assert(!bridge->tech_pvt);
 
    tech_pvt = ast_calloc(1, sizeof(*tech_pvt));
    if (!tech_pvt) {
        return -1;
    }
 
    bridge->tech_pvt = tech_pvt;
    return 0;
}
 
/*!
 * \internal
 * \brief Destroy a bridging technology instance for a bridge.
 * \since 12.0.0
 *
 * \note On entry, bridge must NOT be locked.
 */
static void native_bridge_destroy(struct ast_bridge *bridge)
{
    struct native_pvt_bridge *tech_pvt;
 
    tech_pvt = bridge->tech_pvt;
    bridge->tech_pvt = NULL;
    ast_free(tech_pvt);
}
 
/*!
 * \internal
 * \brief Stop native bridging activity.
 * \since 12.0.0
 *
 * \param bridge What to operate upon.
 *
 * \note On entry, bridge is already locked.
 */
static void native_stop(struct ast_bridge *bridge)
{
    struct native_pvt_bridge *bridge_tech_pvt;
    struct ast_bridge_channel *cur;
 
    ast_assert(bridge->tech_pvt != NULL);
 
    AST_LIST_TRAVERSE(&bridge->channels, cur, entry) {
        struct native_pvt_chan *chan_tech_pvt;
 
        chan_tech_pvt = cur->tech_pvt;
        if (!chan_tech_pvt) {
            continue;
        }
 
        ast_mutex_lock(&chan_tech_pvt->pvt->lock);
        if (chan_tech_pvt->pvt == ast_channel_tech_pvt(cur->chan)) {
            dahdi_ec_enable(chan_tech_pvt->pvt);
        }
        if (chan_tech_pvt->index == SUB_REAL) {
            dahdi_dtmf_detect_enable(chan_tech_pvt->pvt);
        }
        ast_mutex_unlock(&chan_tech_pvt->pvt->lock);
    }
 
    bridge_tech_pvt = bridge->tech_pvt;
    dahdi_master_slave_unlink(bridge_tech_pvt->slave, bridge_tech_pvt->master, 1);
 
    ast_debug(2, "Stop native bridging %s and %s\n",
        ast_channel_name(AST_LIST_FIRST(&bridge->channels)->chan),
        ast_channel_name(AST_LIST_LAST(&bridge->channels)->chan));
}
 
/*!
 * \internal
 * \brief Request to stop native bridging activity.
 * \since 12.0.0
 *
 * \param bridge What to operate upon.
 *
 * \note On entry, bridge is already locked.
 */
static void native_request_stop(struct ast_bridge *bridge)
{
    struct native_pvt_bridge *tech_pvt;
 
    ast_assert(bridge->tech_pvt != NULL);
 
    tech_pvt = bridge->tech_pvt;
    if (!tech_pvt->connected) {
        return;
    }
    tech_pvt->connected = 0;
 
    /* Now to actually stop the bridge. */
    native_stop(bridge);
}
 
/*!
 * \internal
 * \brief Start native bridging activity.
 * \since 12.0.0
 *
 * \param bridge What to operate upon.
 *
 * \retval 0 on success.
 * \retval -1 on error.  Could not start the bridge.
 *
 * \note On entry, bridge may or may not already be locked.
 * However, it can be accessed as if it were locked.
 */
static int native_start(struct ast_bridge *bridge)
{
    struct native_pvt_bridge *tech_pvt;
    struct ast_bridge_channel *bc0;
    struct ast_bridge_channel *bc1;
    struct native_pvt_chan *npc0;
    struct native_pvt_chan *npc1;
    struct ast_channel *c0;
    struct ast_channel *c1;
    struct dahdi_pvt *p0;
    struct dahdi_pvt *p1;
    struct dahdi_pvt *master;
    struct dahdi_pvt *slave;
    int inconf;
    int nothing_ok;
 
    ast_assert(bridge->tech_pvt != NULL);
 
    bc0 = AST_LIST_FIRST(&bridge->channels);
    bc1 = AST_LIST_LAST(&bridge->channels);
    c0 = bc0->chan;
    c1 = bc1->chan;
 
    /* Lock channels and privates */
    for (;;) {
        ast_channel_lock(c0);
        if (!ast_channel_trylock(c1)) {
            p0 = ast_channel_tech_pvt(c0);
            if (!ast_mutex_trylock(&p0->lock)) {
                p1 = ast_channel_tech_pvt(c1);
                if (!ast_mutex_trylock(&p1->lock)) {
                    /* Got all locks */
                    break;
                }
                ast_mutex_unlock(&p0->lock);
            }
            ast_channel_unlock(c1);
        }
        ast_channel_unlock(c0);
        sched_yield();
    }
 
    npc0 = bc0->tech_pvt;
    ast_assert(npc0 != NULL);
    npc0->pvt = p0;
    npc0->owner = p0->owner;
    npc0->index = dahdi_get_index(c0, p0, 0);
    npc0->fd0 = ast_channel_fd(c0, 0);
    npc0->state = -1;
    npc0->inthreeway = p0->subs[SUB_REAL].inthreeway;
 
    npc1 = bc1->tech_pvt;
    ast_assert(npc1 != NULL);
    npc1->pvt = p1;
    npc1->owner = p1->owner;
    npc1->index = dahdi_get_index(c1, p1, 0);
    npc1->fd0 = ast_channel_fd(c1, 0);
    npc1->state = -1;
    npc1->inthreeway = p1->subs[SUB_REAL].inthreeway;
 
    /*
     * Check things that can change on the privates while in native
     * bridging and cause native to not activate.
     */
    if (npc0->index < 0 || npc1->index < 0
#if defined(HAVE_PRI)
        /*
         * PRI nobch channels (hold and call waiting) are equivalent to
         * pseudo channels and cannot be natively bridged.
         */
        || (dahdi_sig_pri_lib_handles(p0->sig)
            && ((struct sig_pri_chan *) p0->sig_pvt)->no_b_channel)
        || (dahdi_sig_pri_lib_handles(p1->sig)
            && ((struct sig_pri_chan *) p1->sig_pvt)->no_b_channel)
#endif  /* defined(HAVE_PRI) */
        ) {
        ast_mutex_unlock(&p0->lock);
        ast_mutex_unlock(&p1->lock);
        ast_channel_unlock(c0);
        ast_channel_unlock(c1);
        return -1;
    }
 
    inconf = 0;
    nothing_ok = 1;
    master = NULL;
    slave = NULL;
    if (npc0->index == SUB_REAL && npc1->index == SUB_REAL) {
        if (p0->owner && p1->owner) {
            /*
             * If we don't have a call-wait in a 3-way, and we aren't in a
             * 3-way, we can be master.
             */
            if (!p0->subs[SUB_CALLWAIT].inthreeway && !p1->subs[SUB_REAL].inthreeway) {
                master = p0;
                slave = p1;
                inconf = 1;
            } else if (!p1->subs[SUB_CALLWAIT].inthreeway && !p0->subs[SUB_REAL].inthreeway) {
                master = p1;
                slave = p0;
                inconf = 1;
            } else {
                ast_log(LOG_WARNING, "Huh?  Both calls are callwaits or 3-ways?  That's clever...?\n");
                ast_log(LOG_WARNING, "p0: chan %d/%d/CW%d/3W%d, p1: chan %d/%d/CW%d/3W%d\n",
                    p0->channel,
                    npc0->index, (p0->subs[SUB_CALLWAIT].dfd > -1) ? 1 : 0,
                    p0->subs[SUB_REAL].inthreeway,
                    p0->channel,
                    npc0->index, (p1->subs[SUB_CALLWAIT].dfd > -1) ? 1 : 0,
                    p1->subs[SUB_REAL].inthreeway);
            }
            nothing_ok = 0;
        }
    } else if (npc0->index == SUB_REAL && npc1->index == SUB_THREEWAY) {
        if (p1->subs[SUB_THREEWAY].inthreeway) {
            master = p1;
            slave = p0;
            nothing_ok = 0;
        }
    } else if (npc0->index == SUB_THREEWAY && npc1->index == SUB_REAL) {
        if (p0->subs[SUB_THREEWAY].inthreeway) {
            master = p0;
            slave = p1;
            nothing_ok = 0;
        }
    } else if (npc0->index == SUB_REAL && npc1->index == SUB_CALLWAIT) {
        /*
         * We have a real and a call wait.  If we're in a three way
         * call, put us in it, otherwise, don't put us in anything.
         */
        if (p1->subs[SUB_CALLWAIT].inthreeway) {
            master = p1;
            slave = p0;
            nothing_ok = 0;
        }
    } else if (npc0->index == SUB_CALLWAIT && npc1->index == SUB_REAL) {
        /* Same as previous */
        if (p0->subs[SUB_CALLWAIT].inthreeway) {
            master = p0;
            slave = p1;
            nothing_ok = 0;
        }
    }
    ast_debug(3, "master: %d, slave: %d, nothing_ok: %d\n",
        master ? master->channel : 0,
        slave ? slave->channel : 0,
        nothing_ok);
    if (master && slave) {
        /*
         * Stop any tones, or play ringtone as appropriate.  If they are
         * bridged in an active threeway call with a channel that is
         * ringing, we should indicate ringing.
         */
        if (npc1->index == SUB_THREEWAY
            && p1->subs[SUB_THREEWAY].inthreeway
            && p1->subs[SUB_REAL].owner
            && p1->subs[SUB_REAL].inthreeway
            && ast_channel_state(p1->subs[SUB_REAL].owner) == AST_STATE_RINGING) {
            ast_debug(2,
                "Playing ringback on %d/%d(%s) since %d/%d(%s) is in a ringing three-way\n",
                p0->channel, npc0->index, ast_channel_name(c0),
                p1->channel, npc1->index, ast_channel_name(c1));
            tone_zone_play_tone(p0->subs[npc0->index].dfd, DAHDI_TONE_RINGTONE);
            npc1->state = ast_channel_state(p1->subs[SUB_REAL].owner);
        } else {
            ast_debug(2, "Stopping tones on %d/%d(%s) talking to %d/%d(%s)\n",
                p0->channel, npc0->index, ast_channel_name(c0),
                p1->channel, npc1->index, ast_channel_name(c1));
            tone_zone_play_tone(p0->subs[npc0->index].dfd, -1);
        }
 
        if (npc0->index == SUB_THREEWAY
            && p0->subs[SUB_THREEWAY].inthreeway
            && p0->subs[SUB_REAL].owner
            && p0->subs[SUB_REAL].inthreeway
            && ast_channel_state(p0->subs[SUB_REAL].owner) == AST_STATE_RINGING) {
            ast_debug(2,
                "Playing ringback on %d/%d(%s) since %d/%d(%s) is in a ringing three-way\n",
                p1->channel, npc1->index, ast_channel_name(c1),
                p0->channel, npc0->index, ast_channel_name(c0));
            tone_zone_play_tone(p1->subs[npc1->index].dfd, DAHDI_TONE_RINGTONE);
            npc0->state = ast_channel_state(p0->subs[SUB_REAL].owner);
        } else {
            ast_debug(2, "Stopping tones on %d/%d(%s) talking to %d/%d(%s)\n",
                p1->channel, npc1->index, ast_channel_name(c1),
                p0->channel, npc0->index, ast_channel_name(c0));
            tone_zone_play_tone(p1->subs[npc1->index].dfd, -1);
        }
 
        if (npc0->index == SUB_REAL && npc1->index == SUB_REAL) {
            if (!p0->echocanbridged || !p1->echocanbridged) {
                /* Disable echo cancellation if appropriate */
                dahdi_ec_disable(p0);
                dahdi_ec_disable(p1);
            }
        }
        dahdi_master_slave_link(slave, master);
        master->inconference = inconf;
    } else if (!nothing_ok) {
        ast_log(LOG_WARNING, "Can't link %d/%s with %d/%s\n",
            p0->channel, subnames[npc0->index],
            p1->channel, subnames[npc1->index]);
    }
    dahdi_conf_update(p0);
    dahdi_conf_update(p1);
 
    ast_channel_unlock(c0);
    ast_channel_unlock(c1);
 
    /* Native bridge failed */
    if ((!master || !slave) && !nothing_ok) {
        ast_mutex_unlock(&p0->lock);
        ast_mutex_unlock(&p1->lock);
        return -1;
    }
 
    if (npc0->index == SUB_REAL) {
        dahdi_dtmf_detect_disable(p0);
    }
    if (npc1->index == SUB_REAL) {
        dahdi_dtmf_detect_disable(p1);
    }
 
    ast_mutex_unlock(&p0->lock);
    ast_mutex_unlock(&p1->lock);
 
    tech_pvt = bridge->tech_pvt;
    tech_pvt->master = master;
    tech_pvt->slave = slave;
 
    ast_debug(2, "Start native bridging %s and %s\n",
        ast_channel_name(c0), ast_channel_name(c1));
 
#if defined(HAVE_PRI) && defined(PRI_2BCT)
    if (!tech_pvt->tried_trombone_removal) {
        tech_pvt->tried_trombone_removal = 1;
 
        if (p0->pri && p0->pri == p1->pri && p0->pri->transfer) {
            q931_call *q931_c0;
            q931_call *q931_c1;
 
            /* Try to eliminate the tromboned call. */
            ast_mutex_lock(&p0->pri->lock);
            ast_assert(dahdi_sig_pri_lib_handles(p0->sig));
            ast_assert(dahdi_sig_pri_lib_handles(p1->sig));
            q931_c0 = ((struct sig_pri_chan *) (p0->sig_pvt))->call;
            q931_c1 = ((struct sig_pri_chan *) (p1->sig_pvt))->call;
            if (q931_c0 && q931_c1) {
                pri_channel_bridge(q931_c0, q931_c1);
                ast_debug(2, "Attempt to eliminate tromboned call with %s and %s\n",
                    ast_channel_name(c0), ast_channel_name(c1));
            }
            ast_mutex_unlock(&p0->pri->lock);
        }
    }
#endif  /* defined(HAVE_PRI) && defined(PRI_2BCT) */
    return 0;
}
 
/*!
 * \internal
 * \brief Request to start native bridging activity.
 * \since 12.0.0
 *
 * \param bridge What to operate upon.
 *
 * \note On entry, bridge may or may not already be locked.
 * However, it can be accessed as if it were locked.
 */
static void native_request_start(struct ast_bridge *bridge)
{
    struct native_pvt_bridge *tech_pvt;
    struct ast_bridge_channel *cur;
 
    ast_assert(bridge->tech_pvt != NULL);
 
    tech_pvt = bridge->tech_pvt;
 
    if (bridge->num_channels != 2 || !tech_pvt->saw_start || tech_pvt->connected) {
        return;
    }
    AST_LIST_TRAVERSE(&bridge->channels, cur, entry) {
        if (cur->suspended || !cur->tech_pvt) {
            return;
        }
    }
 
    /* Actually try starting the native bridge. */
    if (native_start(bridge)) {
        return;
    }
    tech_pvt->connected = 1;
}
 
/*!
 * \internal
 * \brief Request a bridge technology instance start operations.
 * \since 12.0.0
 *
 * \retval 0 on success
 * \retval -1 on failure
 *
 * \note On entry, bridge may or may not already be locked.
 * However, it can be accessed as if it were locked.
 */
static int native_bridge_start(struct ast_bridge *bridge)
{
    struct native_pvt_bridge *tech_pvt;
 
    ast_assert(bridge->tech_pvt != NULL);
 
    tech_pvt = bridge->tech_pvt;
    tech_pvt->saw_start = 1;
 
    native_request_start(bridge);
    return 0;
}
 
/*!
 * \internal
 * \brief Request a bridge technology instance stop in preparation for being destroyed.
 * \since 12.0.0
 *
 * \note On entry, bridge is already locked.
 */
static void native_bridge_stop(struct ast_bridge *bridge)
{
    struct native_pvt_bridge *tech_pvt;
 
    tech_pvt = bridge->tech_pvt;
    if (!tech_pvt) {
        return;
    }
 
    tech_pvt->saw_start = 0;
    native_request_stop(bridge);
}
 
/*!
 * \internal
 * \brief Add a channel to a bridging technology instance for a bridge.
 * \since 12.0.0
 *
 * \retval 0 on success
 * \retval -1 on failure
 *
 * \note On entry, bridge is already locked.
 */
static int native_bridge_join(struct ast_bridge *bridge, struct ast_bridge_channel *bridge_channel)
{
    struct native_pvt_chan *tech_pvt;
    struct ast_channel *c0;
    struct ast_channel *c1;
 
    ast_assert(!bridge_channel->tech_pvt);
 
    tech_pvt = ast_calloc(1, sizeof(*tech_pvt));
    if (!tech_pvt) {
        return -1;
    }
 
    bridge_channel->tech_pvt = tech_pvt;
    native_request_start(bridge);
 
    /*
     * Make the channels compatible in case the native bridge did
     * not start for some reason and we need to fallback to 1-1
     * bridging.
     */
    c0 = AST_LIST_FIRST(&bridge->channels)->chan;
    c1 = AST_LIST_LAST(&bridge->channels)->chan;
    if (c0 == c1) {
        return 0;
    }
    return ast_channel_make_compatible(c0, c1);
}
 
/*!
 * \internal
 * \brief Remove a channel from a bridging technology instance for a bridge.
 * \since 12.0.0
 *
 * \note On entry, bridge is already locked.
 */
static void native_bridge_leave(struct ast_bridge *bridge, struct ast_bridge_channel *bridge_channel)
{
    struct native_pvt_chan *tech_pvt;
 
    native_request_stop(bridge);
 
    tech_pvt = bridge_channel->tech_pvt;
    bridge_channel->tech_pvt = NULL;
    ast_free(tech_pvt);
}
 
/*!
 * \internal
 * \brief Suspend a channel on a bridging technology instance for a bridge.
 * \since 12.0.0
 *
 * \note On entry, bridge is already locked.
 */
static void native_bridge_suspend(struct ast_bridge *bridge, struct ast_bridge_channel *bridge_channel)
{
    native_request_stop(bridge);
}
 
/*!
 * \internal
 * \brief Unsuspend a channel on a bridging technology instance for a bridge.
 * \since 12.0.0
 *
 * \note On entry, bridge is already locked.
 */
static void native_bridge_unsuspend(struct ast_bridge *bridge, struct ast_bridge_channel *bridge_channel)
{
    native_request_start(bridge);
}
 
/*!
 * \internal
 * \brief Check if channel is compatible.
 * \since 12.0.0
 *
 * \param bridge_channel Is this channel compatible.
 *
 * \retval TRUE if channel is compatible with native DAHDI bridge.
 */
static int native_bridge_is_capable(struct ast_bridge_channel *bridge_channel)
{
    struct ast_channel *chan = bridge_channel->chan;
    struct dahdi_pvt *pvt;
    int is_capable;
 
    if (ao2_container_count(bridge_channel->features->dtmf_hooks)) {
        ast_debug(2, "Channel '%s' has DTMF hooks.\n", ast_channel_name(chan));
        return 0;
    }
 
    ast_channel_lock(chan);
 
    if (dahdi_tech != ast_channel_tech(chan)) {
        ast_debug(2, "Channel '%s' is not %s.\n",
            ast_channel_name(chan), dahdi_tech->type);
        ast_channel_unlock(chan);
        return 0;
    }
    if (ast_channel_has_audio_frame_or_monitor(chan)) {
        ast_debug(2, "Channel '%s' has an active monitor, audiohook, or framehook.\n",
            ast_channel_name(chan));
        ast_channel_unlock(chan);
        return 0;
    }
    pvt = ast_channel_tech_pvt(chan);
    if (!pvt || !pvt->sig) {
        /* No private; or signaling is for a pseudo channel. */
        ast_channel_unlock(chan);
        return 0;
    }
 
    is_capable = 1;
    ast_mutex_lock(&pvt->lock);
 
    if (pvt->callwaiting && pvt->callwaitingcallerid) {
        /*
         * Call Waiting Caller ID requires DTMF detection to know if it
         * can send the CID spill.
         */
        ast_debug(2, "Channel '%s' has call waiting caller ID enabled.\n",
            ast_channel_name(chan));
        is_capable = 0;
    }
 
    ast_mutex_unlock(&pvt->lock);
    ast_channel_unlock(chan);
 
    return is_capable;
}
 
/*!
 * \internal
 * \brief Check if a bridge is compatible with the bridging technology.
 * \since 12.0.0
 *
 * \retval 0 if not compatible
 * \retval non-zero if compatible
 *
 * \note On entry, bridge may or may not already be locked.
 * However, it can be accessed as if it were locked.
 */
static int native_bridge_compatible(struct ast_bridge *bridge)
{
    struct ast_bridge_channel *cur;
 
    /* We require two channels before even considering native bridging. */
    if (bridge->num_channels != 2) {
        ast_debug(1, "Bridge %s: Cannot use native DAHDI.  Must have two channels.\n",
            bridge->uniqueid);
        return 0;
    }
 
    AST_LIST_TRAVERSE(&bridge->channels, cur, entry) {
        if (!native_bridge_is_capable(cur)) {
            ast_debug(1, "Bridge %s: Cannot use native DAHDI.  Channel '%s' not compatible.\n",
                bridge->uniqueid, ast_channel_name(cur->chan));
            return 0;
        }
    }
 
    return -1;
}
 
/*!
 * \internal
 * \brief Check if something changed on the channel.
 * \since 12.0.0
 *
 * \param bridge_channel What to operate upon.
 *
 * \retval 0 Nothing changed.
 * \retval -1 Something changed.
 *
 * \note On entry, bridge_channel->bridge is already locked.
 */
static int native_chan_changed(struct ast_bridge_channel *bridge_channel)
{
    struct native_pvt_chan *tech_pvt;
    struct ast_channel *chan;
    struct dahdi_pvt *pvt;
    int idx = -1;
 
    ast_assert(bridge_channel->tech_pvt != NULL);
 
    tech_pvt = bridge_channel->tech_pvt;
 
    chan = bridge_channel->chan;
    ast_channel_lock(chan);
    pvt = ast_channel_tech_pvt(chan);
    if (tech_pvt->pvt == pvt) {
        idx = dahdi_get_index(chan, pvt, 1);
    }
    ast_channel_unlock(chan);
 
    if (/* Did chan get masqueraded or PRI change associated B channel? */
        tech_pvt->pvt != pvt
        /* Did the pvt active owner change? */
        || tech_pvt->owner != pvt->owner
        /* Did the pvt three way call status change? */
        || tech_pvt->inthreeway != pvt->subs[SUB_REAL].inthreeway
        /* Did the owner index change? */
        || tech_pvt->index != idx
        /*
         * Did chan file descriptor change? (This seems redundant with
         * masquerade and active owner change checks.)
         */
        || tech_pvt->fd0 != ast_channel_fd(chan, 0)
        /* Did chan state change? i.e. Did it stop ringing? */
        || (pvt->subs[SUB_REAL].owner
            && tech_pvt->state > -1
            && tech_pvt->state != ast_channel_state(pvt->subs[SUB_REAL].owner))) {
        return -1;
    }
 
    return 0;
}
 
/*!
 * \internal
 * \brief Check if something changed on the bridge channels.
 * \since 12.0.0
 *
 * \param bridge What to operate upon.
 *
 * \retval 0 Nothing changed.
 * \retval -1 Something changed.
 *
 * \note On entry, bridge is already locked.
 */
static int native_bridge_changed(struct ast_bridge *bridge)
{
    struct ast_bridge_channel *cur;
 
    AST_LIST_TRAVERSE(&bridge->channels, cur, entry) {
        if (native_chan_changed(cur)) {
            ast_debug(1, "Bridge %s: Something changed on channel '%s'.\n",
                bridge->uniqueid, ast_channel_name(cur->chan));
            return -1;
        }
    }
    return 0;
}
 
/*!
 * \internal
 * \brief Write a frame into the bridging technology instance for a bridge.
 * \since 12.0.0
 *
 * \note The bridge must be tolerant of bridge_channel being NULL.
 *
 * \retval 0 Frame accepted into the bridge.
 * \retval -1 Frame needs to be deferred.
 *
 * \note On entry, bridge is already locked.
 */
static int native_bridge_write(struct ast_bridge *bridge, struct ast_bridge_channel *bridge_channel, struct ast_frame *frame)
{
    struct native_pvt_bridge *tech_pvt;
 
    /*
     * When we are not native bridged by DAHDI, we are like a normal
     * 1-1 bridge.
     */
 
    ast_assert(bridge->tech_pvt != NULL);
 
    /* Recheck native bridging validity. */
    tech_pvt = bridge->tech_pvt;
    switch (frame->frametype) {
    case AST_FRAME_VOICE:
    case AST_FRAME_VIDEO:
        if (!tech_pvt->connected) {
            /* Don't try to start native mode on media frames. */
            break;
        }
        if (native_bridge_changed(bridge)) {
            native_request_stop(bridge);
            native_request_start(bridge);
            if (!tech_pvt->connected) {
                break;
            }
        }
 
        /*
         * Native bridge handles voice frames in hardware.  However, it
         * also passes the frames up to Asterisk anyway.  Discard the
         * media frames.
         */
        return 0;
    default:
        if (!tech_pvt->connected) {
            native_request_start(bridge);
            break;
        }
        if (native_bridge_changed(bridge)) {
            native_request_stop(bridge);
            native_request_start(bridge);
        }
        break;
    }
 
    return ast_bridge_queue_everyone_else(bridge, bridge_channel, frame);
}
 
static struct ast_bridge_technology native_bridge = {
    .name = "native_dahdi",
    .capabilities = AST_BRIDGE_CAPABILITY_NATIVE,
    .preference = AST_BRIDGE_PREFERENCE_BASE_NATIVE,
    .create = native_bridge_create,
    .start = native_bridge_start,
    .stop = native_bridge_stop,
    .destroy = native_bridge_destroy,
    .join = native_bridge_join,
    .leave = native_bridge_leave,
    .suspend = native_bridge_suspend,
    .unsuspend = native_bridge_unsuspend,
    .compatible = native_bridge_compatible,
    .write = native_bridge_write,
};
 
/*!
 * \internal
 * \brief Destroy the DAHDI native bridge support.
 * \since 12.0.0
 */
void dahdi_native_unload(void)
{
    ast_bridge_technology_unregister(&native_bridge);
}
 
/*!
 * \internal
 * \brief Initialize the DAHDI native bridge support.
 * \since 12.0.0
 *
 * \retval 0 on success.
 * \retval -1 on error.
 */
int dahdi_native_load(const struct ast_channel_tech *tech)
{
    dahdi_tech = tech;
 
    if (ast_bridge_technology_register(&native_bridge)) {
        dahdi_native_unload();
        return -1;
    }
 
    return 0;
}