frr/babeld/route.c

// SPDX-License-Identifier: MIT
/*
Copyright (c) 2007, 2008 by Juliusz Chroboczek
Copyright 2011 by Matthieu Boutier and Juliusz Chroboczek
*/

#include <zebra.h>
#include "if.h"

#include "babeld.h"
#include "util.h"
#include "kernel.h"
#include "babel_interface.h"
#include "source.h"
#include "neighbour.h"
#include "route.h"
#include "xroute.h"
#include "message.h"
#include "resend.h"
#include "babel_errors.h"

static void consider_route(struct babel_route *route);

struct babel_route **routes = NULL;
static int route_slots = 0, max_route_slots = 0;
int kernel_metric = 0;
enum babel_diversity diversity_kind = DIVERSITY_NONE;
int diversity_factor = BABEL_DEFAULT_DIVERSITY_FACTOR;
int keep_unfeasible = 0;

int smoothing_half_life = 0;
static int two_to_the_one_over_hl = 0; /* 2^(1/hl) * 0x10000 */

/* We maintain a list of "slots", ordered by prefix.  Every slot
   contains a linked list of the routes to this prefix, with the
   installed route, if any, at the head of the list. */

static int
route_compare(const unsigned char *prefix, unsigned char plen,
               struct babel_route *route)
{
    int i = memcmp(prefix, route->src->prefix, 16);
    if(i != 0)
        return i;

    if(plen < route->src->plen)
        return -1;
    else if(plen > route->src->plen)
        return 1;
    else
        return 0;
}

/* Performs binary search, returns -1 in case of failure.  In the latter
   case, new_return is the place where to insert the new element. */

static int
find_route_slot(const unsigned char *prefix, unsigned char plen,
                int *new_return)
{
    int p, m, g, c;

    if(route_slots < 1) {
        if(new_return)
            *new_return = 0;
        return -1;
    }

    p = 0; g = route_slots - 1;

    do {
        m = (p + g) / 2;
        c = route_compare(prefix, plen, routes[m]);
        if(c == 0)
            return m;
        else if(c < 0)
            g = m - 1;
        else
            p = m + 1;
    } while(p <= g);

    if(new_return)
        *new_return = p;

    return -1;
}

struct babel_route *
find_route(const unsigned char *prefix, unsigned char plen,
           struct neighbour *neigh, const unsigned char *nexthop)
{
    struct babel_route *route;
    int i = find_route_slot(prefix, plen, NULL);

    if(i < 0)
        return NULL;

    route = routes[i];

    while(route) {
        if(route->neigh == neigh && memcmp(route->nexthop, nexthop, 16) == 0)
            return route;
        route = route->next;
    }

    return NULL;
}

struct babel_route *
find_installed_route(const unsigned char *prefix, unsigned char plen)
{
    int i = find_route_slot(prefix, plen, NULL);

    if(i >= 0 && routes[i]->installed)
        return routes[i];

    return NULL;
}

/* Returns an overestimate of the number of installed routes. */
int
installed_routes_estimate(void)
{
    return route_slots;
}

static int
resize_route_table(int new_slots)
{
    struct babel_route **new_routes;
    assert(new_slots >= route_slots);

    if(new_slots == 0) {
        new_routes = NULL;
        free(routes);
    } else {
        new_routes = realloc(routes, new_slots * sizeof(struct babel_route*));
        if(new_routes == NULL)
            return -1;
    }

    max_route_slots = new_slots;
    routes = new_routes;
    return 1;
}

/* Insert a route into the table.  If successful, retains the route.
   On failure, caller must free the route. */
static struct babel_route *
insert_route(struct babel_route *route)
{
    int i, n = 0;

    assert(!route->installed);

    i = find_route_slot(route->src->prefix, route->src->plen, &n);

    if(i < 0) {
        if(route_slots >= max_route_slots)
            resize_route_table(max_route_slots < 1 ? 8 : 2 * max_route_slots);
        if(route_slots >= max_route_slots)
            return NULL;
        assert(routes);
        route->next = NULL;
        if(n < route_slots)
            memmove(routes + n + 1, routes + n,
                    (route_slots - n) * sizeof(struct babel_route*));
        route_slots++;
        routes[n] = route;
    } else {
        struct babel_route *r;
        r = routes[i];
        while(r->next)
            r = r->next;
        r->next = route;
        route->next = NULL;
    }

    return route;
}

void
flush_route(struct babel_route *route)
{
    int i;
    struct source *src;
    unsigned oldmetric;
    int lost = 0;

    oldmetric = route_metric(route);
    src = route->src;

    if(route->installed) {
        uninstall_route(route);
        lost = 1;
    }

    i = find_route_slot(route->src->prefix, route->src->plen, NULL);
    assert(i >= 0 && i < route_slots);

    if(route == routes[i]) {
        routes[i] = route->next;
        route->next = NULL;
        free(route);

        if(routes[i] == NULL) {
            if(i < route_slots - 1)
                memmove(routes + i, routes + i + 1,
                        (route_slots - i - 1) * sizeof(struct babel_route*));
            routes[route_slots - 1] = NULL;
            route_slots--;
        }

        if(route_slots == 0)
            resize_route_table(0);
        else if(max_route_slots > 8 && route_slots < max_route_slots / 4)
            resize_route_table(max_route_slots / 2);
    } else {
        struct babel_route *r = routes[i];
        while(r->next != route)
            r = r->next;
        r->next = route->next;
        route->next = NULL;
        free(route);
    }

    if(lost)
        route_lost(src, oldmetric);

    release_source(src);
}

void
flush_all_routes(void)
{
    int i;

    /* Start from the end, to avoid shifting the table. */
    i = route_slots - 1;
    while(i >= 0) {
        while(i < route_slots) {
        /* Uninstall first, to avoid calling route_lost. */
            if(routes[i]->installed)
                uninstall_route(routes[i]);
            flush_route(routes[i]);
        }
        i--;
    }

    check_sources_released();
}

void
flush_neighbour_routes(struct neighbour *neigh)
{
    int i;

    i = 0;
    while(i < route_slots) {
        struct babel_route *r;
        r = routes[i];
        while(r) {
            if(r->neigh == neigh) {
                flush_route(r);
                goto again;
            }
            r = r->next;
        }
        i++;
    again:
        ;
    }
}

void
flush_interface_routes(struct interface *ifp, int v4only)
{
    int i;

    i = 0;
    while(i < route_slots) {
        struct babel_route *r;
        r = routes[i];
        while(r) {
            if(r->neigh->ifp == ifp &&
               (!v4only || v4mapped(r->nexthop))) {
                flush_route(r);
                goto again;
            }
            r = r->next;
        }
        i++;
    again:
        ;
    }
}

struct route_stream {
    int installed;
    int index;
    struct babel_route *next;
};


struct route_stream *
route_stream(int installed)
{
    struct route_stream *stream;

    stream = malloc(sizeof(struct route_stream));
    if(stream == NULL)
       return NULL;

    stream->installed = installed;
    stream->index = installed ? 0 : -1;
    stream->next = NULL;

    return stream;
}

struct babel_route *
route_stream_next(struct route_stream *stream)
{
    if(stream->installed) {
        while(stream->index < route_slots && !routes[stream->index]->installed)
            stream->index++;

        if(stream->index < route_slots)
            return routes[stream->index++];
        else
            return NULL;
    } else {
        struct babel_route *next;
        if(!stream->next) {
            stream->index++;
            if(stream->index >= route_slots)
                return NULL;
            stream->next = routes[stream->index];
        }
        next = stream->next;
        stream->next = next->next;
        return next;
    }
}

void
route_stream_done(struct route_stream *stream)
{
    free(stream);
}

static int
metric_to_kernel(int metric)
{
    return metric < INFINITY ? kernel_metric : KERNEL_INFINITY;
}

/* This is used to maintain the invariant that the installed route is at
   the head of the list. */
static void
move_installed_route(struct babel_route *route, int i)
{
    assert(i >= 0 && i < route_slots);
    assert(route->installed);

    if(route != routes[i]) {
        struct babel_route *r = routes[i];
        while(r->next != route)
            r = r->next;
        r->next = route->next;
        route->next = routes[i];
        routes[i] = route;
    }
}

void
install_route(struct babel_route *route)
{
    int i, rc;

    if(route->installed)
        return;

    if(!route_feasible(route))
	    flog_err(EC_BABEL_ROUTE,
		     "Installing unfeasible route (this shouldn't happen).");

    i = find_route_slot(route->src->prefix, route->src->plen, NULL);
    assert(i >= 0 && i < route_slots);

    if(routes[i] != route && routes[i]->installed) {
	    flog_err(
		    EC_BABEL_ROUTE,
		    "Attempting to install duplicate route (this shouldn't happen).");
	    return;
    }

    rc = kernel_route(ROUTE_ADD, route->src->prefix, route->src->plen,
                      route->nexthop,
                      route->neigh->ifp->ifindex,
                      metric_to_kernel(route_metric(route)), NULL, 0, 0);
    if(rc < 0) {
        int save = errno;
        flog_err(EC_BABEL_ROUTE, "kernel_route(ADD): %s",
		  safe_strerror(errno));
        if(save != EEXIST)
            return;
    }
    route->installed = 1;
    move_installed_route(route, i);

}

void
uninstall_route(struct babel_route *route)
{
    int rc;

    if(!route->installed)
        return;

    rc = kernel_route(ROUTE_FLUSH, route->src->prefix, route->src->plen,
                      route->nexthop,
                      route->neigh->ifp->ifindex,
                      metric_to_kernel(route_metric(route)), NULL, 0, 0);
    if(rc < 0)
        flog_err(EC_BABEL_ROUTE, "kernel_route(FLUSH): %s",
		  safe_strerror(errno));

    route->installed = 0;
}

/* This is equivalent to uninstall_route followed with install_route,
   but without the race condition.  The destination of both routes
   must be the same. */

static void
switch_routes(struct babel_route *old, struct babel_route *new)
{
    int rc;

    if(!old) {
        install_route(new);
        return;
    }

    if(!old->installed)
        return;

    if(!route_feasible(new))
	    flog_err(EC_BABEL_ROUTE,
		     "Switching to unfeasible route (this shouldn't happen).");

    rc = kernel_route(ROUTE_MODIFY, old->src->prefix, old->src->plen,
                      old->nexthop, old->neigh->ifp->ifindex,
                      metric_to_kernel(route_metric(old)),
                      new->nexthop, new->neigh->ifp->ifindex,
                      metric_to_kernel(route_metric(new)));
    if(rc < 0) {
        flog_err(EC_BABEL_ROUTE, "kernel_route(MODIFY): %s",
		  safe_strerror(errno));
        return;
    }

    old->installed = 0;
    new->installed = 1;
    move_installed_route(new, find_route_slot(new->src->prefix, new->src->plen,
                                              NULL));
}

static void
change_route_metric(struct babel_route *route,
                    unsigned refmetric, unsigned cost, unsigned add)
{
    int old, new;
    int newmetric = MIN(refmetric + cost + add, INFINITY);

    old = metric_to_kernel(route_metric(route));
    new = metric_to_kernel(newmetric);

    if(route->installed && old != new) {
        int rc;
        rc = kernel_route(ROUTE_MODIFY, route->src->prefix, route->src->plen,
                          route->nexthop, route->neigh->ifp->ifindex,
                          old,
                          route->nexthop, route->neigh->ifp->ifindex,
                          new);
        if(rc < 0) {
            flog_err(EC_BABEL_ROUTE, "kernel_route(MODIFY metric): %s",
		      safe_strerror(errno));
            return;
        }
    }

    /* Update route->smoothed_metric using the old metric. */
    route_smoothed_metric(route);

    route->refmetric = refmetric;
    route->cost = cost;
    route->add_metric = add;

    if(smoothing_half_life == 0) {
        route->smoothed_metric = route_metric(route);
        route->smoothed_metric_time = babel_now.tv_sec;
    }
}

static void
retract_route(struct babel_route *route)
{
    /* We cannot simply remove the route from the kernel, as that might
       cause a routing loop -- see RFC 6126 Sections 2.8 and 3.5.5. */
    change_route_metric(route, INFINITY, INFINITY, 0);
}

int
route_feasible(struct babel_route *route)
{
    return update_feasible(route->src, route->seqno, route->refmetric);
}

int
route_old(struct babel_route *route)
{
    return route->time < babel_now.tv_sec - route->hold_time * 7 / 8;
}

int
route_expired(struct babel_route *route)
{
    return route->time < babel_now.tv_sec - route->hold_time;
}

static int
channels_interfere(int ch1, int ch2)
{
    if(ch1 == BABEL_IF_CHANNEL_NONINTERFERING
       || ch2 == BABEL_IF_CHANNEL_NONINTERFERING)
        return 0;
    if(ch1 == BABEL_IF_CHANNEL_INTERFERING
       || ch2 == BABEL_IF_CHANNEL_INTERFERING)
        return 1;
    return ch1 == ch2;
}

int
route_interferes(struct babel_route *route, struct interface *ifp)
{
    struct babel_interface *babel_ifp = NULL;
    switch(diversity_kind) {
    case DIVERSITY_NONE:
        return 1;
    case DIVERSITY_INTERFACE_1:
        return route->neigh->ifp == ifp;
    case DIVERSITY_CHANNEL_1:
    case DIVERSITY_CHANNEL:
        if(route->neigh->ifp == ifp)
            return 1;
        babel_ifp = babel_get_if_nfo(ifp);
        if(channels_interfere(babel_ifp->channel,
                              babel_get_if_nfo(route->neigh->ifp)->channel))
            return 1;
        if(diversity_kind == DIVERSITY_CHANNEL) {
            int i;
            for(i = 0; i < DIVERSITY_HOPS; i++) {
                if(route->channels[i] == 0)
                    break;
                if(channels_interfere(babel_ifp->channel, route->channels[i]))
                    return 1;
            }
        }
        return 0;
    }

    return 1;
}

int
update_feasible(struct source *src,
                unsigned short seqno, unsigned short refmetric)
{
    if(src == NULL)
        return 1;

    if(src->time < babel_now.tv_sec - SOURCE_GC_TIME)
        /* Never mind what is probably stale data */
        return 1;

    if(refmetric >= INFINITY)
        /* Retractions are always feasible */
        return 1;

    return (seqno_compare(seqno, src->seqno) > 0 ||
            (src->seqno == seqno && refmetric < src->metric));
}

void
change_smoothing_half_life(int half_life)
{
    if(half_life <= 0) {
        smoothing_half_life = 0;
        two_to_the_one_over_hl = 0;
        return;
    }

    smoothing_half_life = half_life;
    switch(smoothing_half_life) {
    case 1: two_to_the_one_over_hl = 131072; break;
    case 2: two_to_the_one_over_hl = 92682; break;
    case 3: two_to_the_one_over_hl = 82570; break;
    case 4: two_to_the_one_over_hl = 77935; break;
    default:
        /* 2^(1/x) is 1 + log(2)/x + O(1/x^2) at infinity. */
        two_to_the_one_over_hl = 0x10000 + 45426 / half_life;
    }
}

/* Update the smoothed metric, return the new value. */
int
route_smoothed_metric(struct babel_route *route)
{
    int metric = route_metric(route);

    if(smoothing_half_life <= 0 ||                 /* no smoothing */
       metric >= INFINITY ||                       /* route retracted */
       route->smoothed_metric_time > babel_now.tv_sec || /* clock stepped */
       route->smoothed_metric == metric) {         /* already converged */
        route->smoothed_metric = metric;
        route->smoothed_metric_time = babel_now.tv_sec;
    } else {
        int diff;
        /* We randomise the computation, to minimise global synchronisation
           and hence oscillations. */
        while(route->smoothed_metric_time <=
              babel_now.tv_sec - smoothing_half_life) {
            diff = metric - route->smoothed_metric;
            route->smoothed_metric += roughly(diff) / 2;
            route->smoothed_metric_time += smoothing_half_life;
        }
        while(route->smoothed_metric_time < babel_now.tv_sec) {
            diff = metric - route->smoothed_metric;
            route->smoothed_metric +=
                roughly(diff) * (two_to_the_one_over_hl - 0x10000) / 0x10000;
            route->smoothed_metric_time++;
        }

        diff = metric - route->smoothed_metric;
        if(diff > -4 && diff < 4)
            route->smoothed_metric = metric;
    }

    /* change_route_metric relies on this */
    assert(route->smoothed_metric_time == babel_now.tv_sec);
    return route->smoothed_metric;
}

static int
route_acceptable(struct babel_route *route, int feasible,
                 struct neighbour *exclude)
{
    if(route_expired(route))
        return 0;
    if(feasible && !route_feasible(route))
        return 0;
    if(exclude && route->neigh == exclude)
        return 0;
    return 1;
}

/* Find the best route according to the weak ordering.  Any
   linearisation of the strong ordering (see consider_route) will do,
   we use sm <= sm'.  We could probably use a lexical ordering, but
   that's probably overkill. */

struct babel_route *
find_best_route(const unsigned char *prefix, unsigned char plen, int feasible,
                struct neighbour *exclude)
{
    struct babel_route *route = NULL, *r = NULL;
    int i = find_route_slot(prefix, plen, NULL);

    if(i < 0)
        return NULL;

    route = routes[i];
    while(route && !route_acceptable(route, feasible, exclude))
        route = route->next;

    if(!route)
        return NULL;

    r = route->next;
    while(r) {
        if(route_acceptable(r, feasible, exclude) &&
           (route_smoothed_metric(r) < route_smoothed_metric(route)))
            route = r;
        r = r->next;
    }

    return route;
}

void
update_route_metric(struct babel_route *route)
{
    int oldmetric = route_metric(route);
    int old_smoothed_metric = route_smoothed_metric(route);

    if(route_expired(route)) {
        if(route->refmetric < INFINITY) {
            route->seqno = seqno_plus(route->src->seqno, 1);
            retract_route(route);
            if(oldmetric < INFINITY)
                route_changed(route, route->src, oldmetric);
        }
    } else {
        struct neighbour *neigh = route->neigh;
        int add_metric = input_filter(route->src->id,
                                      route->src->prefix, route->src->plen,
                                      neigh->address,
                                      neigh->ifp->ifindex);
        change_route_metric(route, route->refmetric,
                            neighbour_cost(route->neigh), add_metric);
        if(route_metric(route) != oldmetric ||
           route_smoothed_metric(route) != old_smoothed_metric)
            route_changed(route, route->src, oldmetric);
    }
}

/* Called whenever a neighbour's cost changes, to update the metric of
   all routes through that neighbour. */
void
update_neighbour_metric(struct neighbour *neigh, int changed)
{

    if(changed) {
        int i;

        for(i = 0; i < route_slots; i++) {
            struct babel_route *r = routes[i];
            while(r) {
                if(r->neigh == neigh)
                    update_route_metric(r);
                r = r->next;
            }
        }
    }
}

void
update_interface_metric(struct interface *ifp)
{
    int i;

    for(i = 0; i < route_slots; i++) {
        struct babel_route *r = routes[i];
        while(r) {
            if(r->neigh->ifp == ifp)
                update_route_metric(r);
            r = r->next;
        }
    }
}

/* This is called whenever we receive an update. */
struct babel_route *
update_route(const unsigned char *router_id,
             const unsigned char *prefix, unsigned char plen,
             unsigned short seqno, unsigned short refmetric,
             unsigned short interval,
             struct neighbour *neigh, const unsigned char *nexthop,
             const unsigned char *channels, int channels_len)
{
    struct babel_route *route;
    struct source *src;
    int metric, feasible;
    int add_metric;
    int hold_time = MAX((4 * interval) / 100 + interval / 50, 15);

    if(memcmp(router_id, myid, 8) == 0)
        return NULL;

    if(martian_prefix(prefix, plen)) {
        flog_err(EC_BABEL_ROUTE, "Rejecting martian route to %s through %s.",
                 format_prefix(prefix, plen), format_address(nexthop));
        return NULL;
    }

    add_metric = input_filter(router_id, prefix, plen,
                              neigh->address, neigh->ifp->ifindex);
    if(add_metric >= INFINITY)
        return NULL;

    route = find_route(prefix, plen, neigh, nexthop);

    if(route && memcmp(route->src->id, router_id, 8) == 0)
        /* Avoid scanning the source table. */
        src = route->src;
    else
        src = find_source(router_id, prefix, plen, 1, seqno);

    if(src == NULL)
        return NULL;

    feasible = update_feasible(src, seqno, refmetric);
    metric = MIN((int)refmetric + neighbour_cost(neigh) + add_metric, INFINITY);

    if(route) {
        struct source *oldsrc;
        unsigned short oldmetric;
        int lost = 0;

        oldsrc = route->src;
        oldmetric = route_metric(route);

        /* If a successor switches sources, we must accept his update even
           if it makes a route unfeasible in order to break any routing loops
           in a timely manner.  If the source remains the same, we ignore
           the update. */
        if(!feasible && route->installed) {
            debugf(BABEL_DEBUG_COMMON,"Unfeasible update for installed route to %s (%s %d %d -> %s %d %d).",
                   format_prefix(src->prefix, src->plen),
                   format_eui64(route->src->id),
                   route->seqno, route->refmetric,
                   format_eui64(src->id), seqno, refmetric);
            if(src != route->src) {
                uninstall_route(route);
                lost = 1;
            }
        }

        route->src = retain_source(src);
        if((feasible || keep_unfeasible) && refmetric < INFINITY)
            route->time = babel_now.tv_sec;
        route->seqno = seqno;

        memset(&route->channels, 0, sizeof(route->channels));
        if(channels_len > 0)
            memcpy(&route->channels, channels,
                   MIN(channels_len, DIVERSITY_HOPS));

        change_route_metric(route,
                            refmetric, neighbour_cost(neigh), add_metric);
        route->hold_time = hold_time;

        route_changed(route, oldsrc, oldmetric);
        if(lost)
            route_lost(oldsrc, oldmetric);

        if(!feasible)
            send_unfeasible_request(neigh, route->installed && route_old(route),
                                    seqno, metric, src);
        release_source(oldsrc);
    } else {
        struct babel_route *new_route;

        if(refmetric >= INFINITY)
            /* Somebody's retracting a route we never saw. */
            return NULL;
        if(!feasible) {
            send_unfeasible_request(neigh, 0, seqno, metric, src);
            if(!keep_unfeasible)
                return NULL;
        }

        route = malloc(sizeof(struct babel_route));
        if(route == NULL) {
            perror("malloc(route)");
            return NULL;
        }

        route->src = retain_source(src);
        route->refmetric = refmetric;
        route->cost = neighbour_cost(neigh);
        route->add_metric = add_metric;
        route->seqno = seqno;
        route->neigh = neigh;
        memcpy(route->nexthop, nexthop, 16);
        route->time = babel_now.tv_sec;
        route->hold_time = hold_time;
        route->smoothed_metric = MAX(route_metric(route), INFINITY / 2);
        route->smoothed_metric_time = babel_now.tv_sec;
        route->installed = 0;
        memset(&route->channels, 0, sizeof(route->channels));
        if(channels_len > 0)
            memcpy(&route->channels, channels,
                   MIN(channels_len, DIVERSITY_HOPS));
        route->next = NULL;
        new_route = insert_route(route);
        if(new_route == NULL) {
            flog_err(EC_BABEL_ROUTE, "Couldn't insert route.");
            free(route);
            return NULL;
        }
        consider_route(route);
    }
    return route;
}

/* We just received an unfeasible update.  If it's any good, send
   a request for a new seqno. */
void
send_unfeasible_request(struct neighbour *neigh, int force,
                        unsigned short seqno, unsigned short metric,
                        struct source *src)
{
    struct babel_route *route = find_installed_route(src->prefix, src->plen);

    if(seqno_minus(src->seqno, seqno) > 100) {
        /* Probably a source that lost its seqno.  Let it time-out. */
        return;
    }

    if(force || !route || route_metric(route) >= metric + 512) {
        send_unicast_multihop_request(neigh, src->prefix, src->plen,
                                      src->metric >= INFINITY ?
                                      src->seqno :
                                      seqno_plus(src->seqno, 1),
                                      src->id, 127);
    }
}

/* This takes a feasible route and decides whether to install it.
   This uses the strong ordering, which is defined by sm <= sm' AND
   m <= m'.  This ordering is not total, which is what causes
   hysteresis. */

static void
consider_route(struct babel_route *route)
{
    struct babel_route *installed;
    struct xroute *xroute;

    if(route->installed)
        return;

    if(!route_feasible(route))
        return;

    xroute = find_xroute(route->src->prefix, route->src->plen);
    if(xroute)
        return;

    installed = find_installed_route(route->src->prefix, route->src->plen);

    if(installed == NULL)
        goto install;

    if(route_metric(route) >= INFINITY)
        return;

    if(route_metric(installed) >= INFINITY)
        goto install;

    if(route_metric(installed) >= route_metric(route) &&
       route_smoothed_metric(installed) > route_smoothed_metric(route))
        goto install;

    return;

 install:
    switch_routes(installed, route);
    if(installed && route->installed)
        send_triggered_update(route, installed->src, route_metric(installed));
    else
        send_update(NULL, 1, route->src->prefix, route->src->plen);
    return;
}

void
retract_neighbour_routes(struct neighbour *neigh)
{
    int i;

    for(i = 0; i < route_slots; i++) {
        struct babel_route *r = routes[i];
        while(r) {
            if(r->neigh == neigh) {
                if(r->refmetric != INFINITY) {
                    unsigned short oldmetric = route_metric(r);
                    retract_route(r);
                    if(oldmetric != INFINITY)
                        route_changed(r, r->src, oldmetric);
                }
            }
            r = r->next;
        }
    }
}

void
send_triggered_update(struct babel_route *route, struct source *oldsrc,
                      unsigned oldmetric)
{
    unsigned newmetric, diff;
    /* 1 means send speedily, 2 means resend */
    int urgent;

    if(!route->installed)
        return;

    newmetric = route_metric(route);
    diff =
        newmetric >= oldmetric ? newmetric - oldmetric : oldmetric - newmetric;

    if(route->src != oldsrc || (oldmetric < INFINITY && newmetric >= INFINITY))
        /* Switching sources can cause transient routing loops.
           Retractions can cause blackholes. */
        urgent = 2;
    else if(newmetric > oldmetric && oldmetric < 6 * 256 && diff >= 512)
        /* Route getting significantly worse */
        urgent = 1;
    else if(unsatisfied_request(route->src->prefix, route->src->plen,
                                route->seqno, route->src->id))
        /* Make sure that requests are satisfied speedily */
        urgent = 1;
    else if(oldmetric >= INFINITY && newmetric < INFINITY)
        /* New route */
        urgent = 0;
    else if(newmetric < oldmetric && diff < 1024)
        /* Route getting better.  This may be a transient fluctuation, so
           don't advertise it to avoid making routes unfeasible later on. */
        return;
    else if(diff < 384)
        /* Don't fret about trivialities */
        return;
    else
        urgent = 0;

    if(urgent >= 2)
        send_update_resend(NULL, route->src->prefix, route->src->plen);
    else
        send_update(NULL, urgent, route->src->prefix, route->src->plen);

    if(oldmetric < INFINITY) {
        if(newmetric >= oldmetric + 512) {
            send_request_resend(NULL, route->src->prefix, route->src->plen,
                                route->src->metric >= INFINITY ?
                                route->src->seqno :
                                seqno_plus(route->src->seqno, 1),
                                route->src->id);
        } else if(newmetric >= oldmetric + 288) {
            send_request(NULL, route->src->prefix, route->src->plen);
        }
    }
}

/* A route has just changed.  Decide whether to switch to a different route or
   send an update. */
void
route_changed(struct babel_route *route,
              struct source *oldsrc, unsigned short oldmetric)
{
    if(route->installed) {
        struct babel_route *better_route;
        /* Do this unconditionally -- microoptimisation is not worth it. */
        better_route =
            find_best_route(route->src->prefix, route->src->plen, 1, NULL);
        if(better_route && route_metric(better_route) < route_metric(route))
            consider_route(better_route);
    }

    if(route->installed) {
        /* We didn't change routes after all. */
        send_triggered_update(route, oldsrc, oldmetric);
    } else {
        /* Reconsider routes even when their metric didn't decrease,
           they may not have been feasible before. */
        consider_route(route);
    }
}

/* We just lost the installed route to a given destination. */
void
route_lost(struct source *src, unsigned oldmetric)
{
    struct babel_route *new_route;
    new_route = find_best_route(src->prefix, src->plen, 1, NULL);
    if(new_route) {
        consider_route(new_route);
    } else if(oldmetric < INFINITY) {
        /* Avoid creating a blackhole. */
        send_update_resend(NULL, src->prefix, src->plen);
        /* If the route was usable enough, try to get an alternate one.
           If it was not, we could be dealing with oscillations around
           the value of INFINITY. */
        if(oldmetric <= INFINITY / 2)
            send_request_resend(NULL, src->prefix, src->plen,
                                src->metric >= INFINITY ?
                                src->seqno : seqno_plus(src->seqno, 1),
                                src->id);
    }
}

/* This is called periodically to flush old routes.  It will also send
   requests for routes that are about to expire. */
void
expire_routes(void)
{
    struct babel_route *r;
    int i;

    debugf(BABEL_DEBUG_COMMON,"Expiring old routes.");

    i = 0;
    while(i < route_slots) {
        r = routes[i];
        while(r) {
            /* Protect against clock being stepped. */
            if(r->time > babel_now.tv_sec || route_old(r)) {
                flush_route(r);
                goto again;
            }

            update_route_metric(r);

            if(r->installed && r->refmetric < INFINITY) {
                if(route_old(r))
                    /* Route about to expire, send a request. */
                    send_unicast_request(r->neigh,
                                         r->src->prefix, r->src->plen);
            }
            r = r->next;
        }
        i++;
    again:
        ;
    }
}