/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 2020 Alexander V. Chernikov
 *
 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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.
 */

#include <sys/cdefs.h>
#include "opt_inet.h"
#include "opt_inet6.h"
#include "opt_route.h"

#include <sys/param.h>
#include <sys/eventhandler.h>
#include <sys/kernel.h>
#include <sys/sbuf.h>
#include <sys/lock.h>
#include <sys/rmlock.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/module.h>
#include <sys/kernel.h>
#include <sys/priv.h>
#include <sys/proc.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/stdarg.h>
#include <sys/sysctl.h>
#include <sys/syslog.h>
#include <sys/queue.h>
#include <net/vnet.h>

#include <net/if.h>
#include <net/if_var.h>

#include <netinet/in.h>
#include <netinet/in_var.h>
#include <netinet/ip.h>
#include <netinet/ip_var.h>
#ifdef INET6
#include <netinet/ip6.h>
#include <netinet6/ip6_var.h>
#endif

#include <net/route.h>
#include <net/route/nhop.h>
#include <net/route/route_ctl.h>
#include <net/route/route_var.h>
#include <net/route/fib_algo.h>

/*
 * Fib lookup framework.
 *
 * This framework enables accelerated longest-prefix-match lookups for the
 *  routing tables by adding the ability to dynamically attach/detach lookup
 *  algorithms implementation to/from the datapath.
 *
 * flm - fib lookup modules - implementation of particular lookup algorithm
 * fd - fib data - instance of an flm bound to specific routing table
 *
 * This file provides main framework functionality.
 *
 * The following are the features provided by the framework
 *
 * 1) nexhops abstraction -> provides transparent referencing, indexing
 *   and efficient idx->ptr mappings for nexthop and nexthop groups.
 * 2) Routing table synchronisation
 * 3) dataplane attachment points
 * 4) automatic algorithm selection based on the provided preference.
 *
 *
 * DATAPATH
 * For each supported address family, there is a an allocated array of fib_dp
 *  structures, indexed by fib number. Each array entry contains callback function
 *  and its argument. This function will be called with a family-specific lookup key,
 *  scope and provided argument. This array gets re-created every time when new algo
 *  instance gets created. Please take a look at the replace_rtables_family() function
 *  for more details.
 *
 */

SYSCTL_DECL(_net_route);
SYSCTL_NODE(_net_route, OID_AUTO, algo, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
    "Fib algorithm lookups");

/* Algorithm sync policy */

/* Time interval to bucket updates */
VNET_DEFINE_STATIC(unsigned int, update_bucket_time_ms) = 50;
#define V_update_bucket_time_ms VNET(update_bucket_time_ms)
SYSCTL_UINT(_net_route_algo, OID_AUTO, bucket_time_ms, CTLFLAG_RW | CTLFLAG_VNET,
    &VNET_NAME(update_bucket_time_ms), 0, "Time interval to calculate update rate");

/* Minimum update rate to delay sync */
VNET_DEFINE_STATIC(unsigned int, bucket_change_threshold_rate) = 500;
#define V_bucket_change_threshold_rate  VNET(bucket_change_threshold_rate)
SYSCTL_UINT(_net_route_algo, OID_AUTO, bucket_change_threshold_rate, CTLFLAG_RW | CTLFLAG_VNET,
    &VNET_NAME(bucket_change_threshold_rate), 0, "Minimum update rate to delay sync");

/* Max allowed delay to sync */
VNET_DEFINE_STATIC(unsigned int, fib_max_sync_delay_ms) = 1000;
#define V_fib_max_sync_delay_ms VNET(fib_max_sync_delay_ms)
SYSCTL_UINT(_net_route_algo, OID_AUTO, fib_max_sync_delay_ms, CTLFLAG_RW | CTLFLAG_VNET,
    &VNET_NAME(fib_max_sync_delay_ms), 0, "Maximum time to delay sync (ms)");


#ifdef INET6
VNET_DEFINE_STATIC(bool, algo_fixed_inet6) = false;
#define V_algo_fixed_inet6      VNET(algo_fixed_inet6)
SYSCTL_NODE(_net_route_algo, OID_AUTO, inet6, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
    "IPv6 longest prefix match lookups");
#endif
#ifdef INET
VNET_DEFINE_STATIC(bool, algo_fixed_inet) = false;
#define V_algo_fixed_inet       VNET(algo_fixed_inet)
SYSCTL_NODE(_net_route_algo, OID_AUTO, inet, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
    "IPv4 longest prefix match lookups");
#endif

/* Fib instance counter */
static uint32_t fib_gen = 0;

struct nhop_ref_table {
        uint32_t                count;
        int32_t                 refcnt[0];
};

enum fib_callout_action {
        FDA_NONE,       /* No callout scheduled */
        FDA_REBUILD,    /* Asks to rebuild algo instance */
        FDA_EVAL,       /* Asks to evaluate if the current algo is still be best */
        FDA_BATCH,      /* Asks to submit batch of updates to the algo */
};

struct fib_sync_status {
        struct timeval          diverge_time;   /* ts when diverged */
        uint32_t                num_changes;    /* number of changes since sync */
        uint32_t                bucket_changes; /* num changes within the current bucket */
        uint64_t                bucket_id;      /* 50ms bucket # */
        struct fib_change_queue fd_change_queue;/* list of scheduled entries */
};

/*
 * Data structure for the fib lookup instance tied to the particular rib.
 */
struct fib_data {
        uint32_t                number_nhops;   /* current # of nhops */
        uint8_t                 hit_nhops;      /* true if out of nhop limit */
        uint8_t                 init_done;      /* true if init is competed */
        uint32_t                fd_dead:1;      /* Scheduled for deletion */
        uint32_t                fd_linked:1;    /* true if linked */
        uint32_t                fd_need_rebuild:1;      /* true if rebuild scheduled */
        uint32_t                fd_batch:1;     /* true if batched notification scheduled */
        uint8_t                 fd_family;      /* family */
        uint32_t                fd_fibnum;      /* fibnum */
        uint32_t                fd_failed_rebuilds;     /* stat: failed rebuilds */
        uint32_t                fd_gen;         /* instance gen# */
        struct callout          fd_callout;     /* rebuild callout */
        enum fib_callout_action fd_callout_action;      /* Callout action to take */
        void                    *fd_algo_data;  /* algorithm data */
        struct nhop_object      **nh_idx;       /* nhop idx->ptr array */
        struct nhop_ref_table   *nh_ref_table;  /* array with # of nhop references */
        struct rib_head         *fd_rh;         /* RIB table we're attached to */
        struct rib_subscription *fd_rs;         /* storing table subscription */
        struct fib_dp           fd_dp;          /* fib datapath data */
        struct vnet             *fd_vnet;       /* vnet fib belongs to */
        struct epoch_context    fd_epoch_ctx;   /* epoch context for deletion */
        struct fib_lookup_module        *fd_flm;/* pointer to the lookup module */
        struct fib_sync_status  fd_ss;          /* State relevant to the rib sync  */
        uint32_t                fd_num_changes; /* number of changes since last callout */
        TAILQ_ENTRY(fib_data)   entries;        /* list of all fds in vnet */
};

static bool rebuild_fd(struct fib_data *fd, const char *reason);
static bool rebuild_fd_flm(struct fib_data *fd, struct fib_lookup_module *flm_new);
static void handle_fd_callout(void *_data);
static void destroy_fd_instance_epoch(epoch_context_t ctx);
static bool is_idx_free(struct fib_data *fd, uint32_t index);
static void set_algo_fixed(struct rib_head *rh);
static bool is_algo_fixed(struct rib_head *rh);

static uint32_t fib_ref_nhop(struct fib_data *fd, struct nhop_object *nh);
static void fib_unref_nhop(struct fib_data *fd, struct nhop_object *nh);

static struct fib_lookup_module *fib_check_best_algo(struct rib_head *rh,
    struct fib_lookup_module *orig_flm);
static void fib_unref_algo(struct fib_lookup_module *flm);
static bool flm_error_check(const struct fib_lookup_module *flm, uint32_t fibnum);

struct mtx fib_mtx;
#define FIB_MOD_LOCK()          mtx_lock(&fib_mtx)
#define FIB_MOD_UNLOCK()        mtx_unlock(&fib_mtx)
#define FIB_MOD_LOCK_ASSERT()   mtx_assert(&fib_mtx, MA_OWNED)

MTX_SYSINIT(fib_mtx, &fib_mtx, "algo list mutex", MTX_DEF);

/* Algorithm has to be this percent better than the current to switch */
#define BEST_DIFF_PERCENT       (5 * 256 / 100)
/* Schedule algo re-evaluation X seconds after a change */
#define ALGO_EVAL_DELAY_MS      30000
/* Force algo re-evaluation after X changes */
#define ALGO_EVAL_NUM_ROUTES    100
/* Try to setup algorithm X times */
#define FIB_MAX_TRIES           32
/* Max amount of supported nexthops */
#define FIB_MAX_NHOPS           262144
#define FIB_CALLOUT_DELAY_MS    50


/* Debug */
static int flm_debug_level = LOG_NOTICE;
SYSCTL_INT(_net_route_algo, OID_AUTO, debug_level, CTLFLAG_RW | CTLFLAG_RWTUN,
    &flm_debug_level, 0, "debuglevel");
#define FLM_MAX_DEBUG_LEVEL     LOG_DEBUG
#ifndef LOG_DEBUG2
#define LOG_DEBUG2      8
#endif

#define _PASS_MSG(_l)   (flm_debug_level >= (_l))
#define ALGO_PRINTF(_l, _fmt, ...)      if (_PASS_MSG(_l)) {            \
        printf("[fib_algo] %s: " _fmt "\n", __func__, ##__VA_ARGS__);   \
}
#define _ALGO_PRINTF(_fib, _fam, _aname, _gen, _func, _fmt, ...) \
    printf("[fib_algo] %s.%u (%s#%u) %s: " _fmt "\n",\
    print_family(_fam), _fib, _aname, _gen, _func, ## __VA_ARGS__)
#define _RH_PRINTF(_fib, _fam, _func, _fmt, ...) \
    printf("[fib_algo] %s.%u %s: " _fmt "\n", print_family(_fam), _fib, _func, ## __VA_ARGS__)
#define RH_PRINTF(_l, _rh, _fmt, ...)   if (_PASS_MSG(_l)) {    \
    _RH_PRINTF(_rh->rib_fibnum, _rh->rib_family, __func__, _fmt, ## __VA_ARGS__);\
}
#define FD_PRINTF(_l, _fd, _fmt, ...)   FD_PRINTF_##_l(_l, _fd, _fmt, ## __VA_ARGS__)
#define _FD_PRINTF(_l, _fd, _fmt, ...)  if (_PASS_MSG(_l)) {            \
    _ALGO_PRINTF(_fd->fd_fibnum, _fd->fd_family, _fd->fd_flm->flm_name, \
    _fd->fd_gen, __func__, _fmt, ## __VA_ARGS__);                       \
}
#if FLM_MAX_DEBUG_LEVEL>=LOG_DEBUG2
#define FD_PRINTF_LOG_DEBUG2    _FD_PRINTF
#else
#define FD_PRINTF_LOG_DEBUG2(_l, _fd, _fmt, ...)
#endif
#if FLM_MAX_DEBUG_LEVEL>=LOG_DEBUG
#define FD_PRINTF_LOG_DEBUG     _FD_PRINTF
#else
#define FD_PRINTF_LOG_DEBUG()
#endif
#if FLM_MAX_DEBUG_LEVEL>=LOG_INFO
#define FD_PRINTF_LOG_INFO      _FD_PRINTF
#else
#define FD_PRINTF_LOG_INFO()
#endif
#define FD_PRINTF_LOG_NOTICE    _FD_PRINTF
#define FD_PRINTF_LOG_ERR       _FD_PRINTF
#define FD_PRINTF_LOG_WARNING   _FD_PRINTF


/* List of all registered lookup algorithms */
static TAILQ_HEAD(, fib_lookup_module) all_algo_list = TAILQ_HEAD_INITIALIZER(all_algo_list);

/* List of all fib lookup instances in the vnet */
VNET_DEFINE_STATIC(TAILQ_HEAD(fib_data_head, fib_data), fib_data_list);
#define V_fib_data_list VNET(fib_data_list)

/* Datastructure for storing non-transient fib lookup module failures */
struct fib_error {
        int                             fe_family;
        uint32_t                        fe_fibnum;      /* failed rtable */
        struct fib_lookup_module        *fe_flm;        /* failed module */
        TAILQ_ENTRY(fib_error)          entries;/* list of all errored entries */
};
VNET_DEFINE_STATIC(TAILQ_HEAD(fib_error_head, fib_error), fib_error_list);
#define V_fib_error_list VNET(fib_error_list)

/* Per-family array of fibnum -> {func, arg} mappings used in datapath */
struct fib_dp_header {
        struct epoch_context    fdh_epoch_ctx;
        uint32_t                fdh_num_tables;
        struct fib_dp           fdh_idx[0];
};

/*
 * Tries to add new non-transient algorithm error to the list of
 *  errors.
 * Returns true on success.
 */
static bool
flm_error_add(struct fib_lookup_module *flm, uint32_t fibnum)
{
        struct fib_error *fe;

        fe = malloc(sizeof(struct fib_error), M_TEMP, M_NOWAIT | M_ZERO);
        if (fe == NULL)
                return (false);
        fe->fe_flm = flm;
        fe->fe_family = flm->flm_family;
        fe->fe_fibnum = fibnum;

        FIB_MOD_LOCK();
        /* Avoid duplicates by checking if error already exists first */
        if (flm_error_check(flm, fibnum)) {
                FIB_MOD_UNLOCK();
                free(fe, M_TEMP);
                return (true);
        }
        TAILQ_INSERT_HEAD(&V_fib_error_list, fe, entries);
        FIB_MOD_UNLOCK();

        return (true);
}

/*
 * True if non-transient error has been registered for @flm in @fibnum.
 */
static bool
flm_error_check(const struct fib_lookup_module *flm, uint32_t fibnum)
{
        const struct fib_error *fe;

        TAILQ_FOREACH(fe, &V_fib_error_list, entries) {
                if ((fe->fe_flm == flm) && (fe->fe_fibnum == fibnum))
                        return (true);
        }

        return (false);
}

/*
 * Clear all errors of algo specified by @flm.
 */
static void
fib_error_clear_flm(struct fib_lookup_module *flm)
{
        struct fib_error *fe, *fe_tmp;

        FIB_MOD_LOCK_ASSERT();

        TAILQ_FOREACH_SAFE(fe, &V_fib_error_list, entries, fe_tmp) {
                if (fe->fe_flm == flm) {
                        TAILQ_REMOVE(&V_fib_error_list, fe, entries);
                        free(fe, M_TEMP);
                }
        }
}

/*
 * Clears all errors in current VNET.
 */
static void
fib_error_clear(void)
{
        struct fib_error *fe, *fe_tmp;

        FIB_MOD_LOCK_ASSERT();

        TAILQ_FOREACH_SAFE(fe, &V_fib_error_list, entries, fe_tmp) {
                TAILQ_REMOVE(&V_fib_error_list, fe, entries);
                free(fe, M_TEMP);
        }
}

static const char *
print_op_result(enum flm_op_result result)
{
        switch (result) {
        case FLM_SUCCESS:
                return "success";
        case FLM_REBUILD:
                return "rebuild";
        case FLM_BATCH:
                return "batch";
        case FLM_ERROR:
                return "error";
        }

        return "unknown";
}

static const char *
print_family(int family)
{

        if (family == AF_INET)
                return ("inet");
        else if (family == AF_INET6)
                return ("inet6");
        else
                return ("unknown");
}

/*
 * Debug function used by lookup algorithms.
 * Outputs message denoted by @fmt, prepended by "[fib_algo] inetX.Y (algo) "
 */
void
fib_printf(int level, struct fib_data *fd, const char *func, char *fmt, ...)
{
        char buf[128];
        va_list ap;

        if (level > flm_debug_level)
                return;

        va_start(ap, fmt);
        vsnprintf(buf, sizeof(buf), fmt, ap);
        va_end(ap);

        _ALGO_PRINTF(fd->fd_fibnum, fd->fd_family, fd->fd_flm->flm_name,
            fd->fd_gen, func, "%s", buf);
}

/*
 * Outputs list of algorithms supported by the provided address family.
 */
static int
print_algos_sysctl(struct sysctl_req *req, int family)
{
        struct fib_lookup_module *flm;
        struct sbuf sbuf;
        int error, count = 0;

        error = sysctl_wire_old_buffer(req, 0);
        if (error == 0) {
                sbuf_new_for_sysctl(&sbuf, NULL, 512, req);
                TAILQ_FOREACH(flm, &all_algo_list, entries) {
                        if (flm->flm_family == family) {
                                if (count++ > 0)
                                        sbuf_cat(&sbuf, ", ");
                                sbuf_cat(&sbuf, flm->flm_name);
                        }
                }
                error = sbuf_finish(&sbuf);
                sbuf_delete(&sbuf);
        }
        return (error);
}

#ifdef INET6
static int
print_algos_sysctl_inet6(SYSCTL_HANDLER_ARGS)
{

        return (print_algos_sysctl(req, AF_INET6));
}
SYSCTL_PROC(_net_route_algo_inet6, OID_AUTO, algo_list,
    CTLTYPE_STRING | CTLFLAG_RD | CTLFLAG_MPSAFE, NULL, 0,
    print_algos_sysctl_inet6, "A", "List of IPv6 lookup algorithms");
#endif

#ifdef INET
static int
print_algos_sysctl_inet(SYSCTL_HANDLER_ARGS)
{

        return (print_algos_sysctl(req, AF_INET));
}
SYSCTL_PROC(_net_route_algo_inet, OID_AUTO, algo_list,
    CTLTYPE_STRING | CTLFLAG_RD | CTLFLAG_MPSAFE, NULL, 0,
    print_algos_sysctl_inet, "A", "List of IPv4 lookup algorithms");
#endif

/*
 * Calculate delay between repeated failures.
 * Returns current delay in milliseconds.
 */
static uint32_t
callout_calc_delay_ms(struct fib_data *fd)
{
        uint32_t shift;

        if (fd->fd_failed_rebuilds > 10)
                shift = 10;
        else
                shift = fd->fd_failed_rebuilds;

        return ((1 << shift) * FIB_CALLOUT_DELAY_MS);
}

static void
schedule_callout(struct fib_data *fd, enum fib_callout_action action, int delay_ms)
{

        FD_PRINTF(LOG_DEBUG, fd, "delay=%d action=%d", delay_ms, action);
        fd->fd_callout_action = action;
        callout_reset_sbt(&fd->fd_callout, SBT_1MS * delay_ms, 0,
            handle_fd_callout, fd, 0);
}

static void
schedule_fd_rebuild(struct fib_data *fd, const char *reason)
{

        RIB_WLOCK_ASSERT(fd->fd_rh);

        if (!fd->fd_need_rebuild) {
                fd->fd_need_rebuild = true;
                /* Stop batch updates */
                fd->fd_batch = false;

                /*
                 * Potentially re-schedules pending callout
                 *  initiated by schedule_algo_eval.
                 */
                FD_PRINTF(LOG_INFO, fd, "Scheduling rebuild: %s (failures=%d)",
                    reason, fd->fd_failed_rebuilds);
                schedule_callout(fd, FDA_REBUILD, callout_calc_delay_ms(fd));
        }
}

static void
sync_rib_gen(struct fib_data *fd)
{
        FD_PRINTF(LOG_DEBUG, fd, "Sync gen %u -> %u", fd->fd_rh->rnh_gen, fd->fd_rh->rnh_gen_rib);
        fd->fd_rh->rnh_gen = fd->fd_rh->rnh_gen_rib;
}

static int64_t
get_tv_diff_ms(const struct timeval *old_tv, const struct timeval *new_tv)
{
        int64_t diff = 0;

        diff = ((int64_t)(new_tv->tv_sec - old_tv->tv_sec)) * 1000;
        diff += (new_tv->tv_usec - old_tv->tv_usec) / 1000;

        return (diff);
}

static void
add_tv_diff_ms(struct timeval *tv, int ms)
{
        tv->tv_sec += ms / 1000;
        ms = ms % 1000;
        if (ms * 1000 + tv->tv_usec < 1000000)
                tv->tv_usec += ms * 1000;
        else {
                tv->tv_sec += 1;
                tv->tv_usec = ms * 1000 + tv->tv_usec - 1000000;
        }
}

/*
 * Marks the time when algo state diverges from the rib state.
 */
static void
mark_diverge_time(struct fib_data *fd)
{
        struct fib_sync_status *fd_ss = &fd->fd_ss;

        getmicrouptime(&fd_ss->diverge_time);
        fd_ss->bucket_id = 0;
        fd_ss->bucket_changes = 0;
}

/*
 * Calculates and updates the next algorithm sync time, based on the current activity.
 *
 * The intent is to provide reasonable balance between the update
 *  latency and efficient batching when changing large amount of routes.
 *
 * High-level algorithm looks the following:
 * 1) all changes are bucketed in 50ms intervals
 * 2) If amount of changes within the bucket is greater than the threshold,
 *   the update gets delayed, up to maximum delay threshold.
 */
static void
update_rebuild_delay(struct fib_data *fd, enum fib_callout_action action)
{
        uint32_t bucket_id, new_delay = 0;
        struct timeval tv;

        /* Fetch all variables at once to ensure consistent reads */
        uint32_t bucket_time_ms = V_update_bucket_time_ms;
        uint32_t threshold_rate = V_bucket_change_threshold_rate;
        uint32_t max_delay_ms = V_fib_max_sync_delay_ms;

        if (bucket_time_ms == 0)
                bucket_time_ms = 50;
        /* calculate per-bucket threshold rate */
        threshold_rate = threshold_rate * bucket_time_ms / 1000;

        getmicrouptime(&tv);

        struct fib_sync_status *fd_ss = &fd->fd_ss;

        bucket_id = get_tv_diff_ms(&fd_ss->diverge_time, &tv) / bucket_time_ms;

        if (fd_ss->bucket_id == bucket_id) {
                fd_ss->bucket_changes++;
                if (fd_ss->bucket_changes == threshold_rate) {
                        new_delay = (bucket_id + 2) * bucket_time_ms;
                        if (new_delay <= max_delay_ms) {
                                FD_PRINTF(LOG_DEBUG, fd,
                                    "hit threshold of %u routes, delay update,"
                                    "bucket: %u, total delay: %u",
                                    threshold_rate, bucket_id + 1, new_delay);
                        } else {
                                new_delay = 0;
                                FD_PRINTF(LOG_DEBUG, fd,
                                    "maximum sync delay (%u ms) reached", max_delay_ms);
                        }
                } else if ((bucket_id == 0) && (fd_ss->bucket_changes == 1))
                        new_delay = bucket_time_ms;
        } else {
                fd_ss->bucket_id = bucket_id;
                fd_ss->bucket_changes = 1;
        }

        if (new_delay > 0) {
                /* Calculated time has been updated */
                struct timeval new_tv = fd_ss->diverge_time;
                add_tv_diff_ms(&new_tv, new_delay);

                int32_t delay_ms = get_tv_diff_ms(&tv, &new_tv);
                schedule_callout(fd, action, delay_ms);
        }
}

static void
update_algo_state(struct fib_data *fd)
{

        RIB_WLOCK_ASSERT(fd->fd_rh);

        if (fd->fd_batch || fd->fd_need_rebuild) {
                enum fib_callout_action action = fd->fd_need_rebuild ? FDA_REBUILD : FDA_BATCH;
                update_rebuild_delay(fd, action);
                return;
        }

        if (fd->fd_num_changes++ == 0) {
                /* Start callout to consider switch */
                if (!callout_pending(&fd->fd_callout))
                        schedule_callout(fd, FDA_EVAL, ALGO_EVAL_DELAY_MS);
        } else if (fd->fd_num_changes == ALGO_EVAL_NUM_ROUTES) {
                /* Reset callout to exec immediately */
                if (fd->fd_callout_action == FDA_EVAL)
                        schedule_callout(fd, FDA_EVAL, 1);
        }
}

static bool
need_immediate_sync(struct fib_data *fd, struct rib_cmd_info *rc)
{
        struct nhop_object *nh;

        /* Sync addition/removal of interface routes */
        switch (rc->rc_cmd) {
        case RTM_ADD:
                nh = rc->rc_nh_new;
                if (!NH_IS_NHGRP(nh)) {
                        if (!(nh->nh_flags & NHF_GATEWAY))
                                return (true);
                        if (nhop_get_rtflags(nh) & RTF_STATIC)
                                return (true);
                }
                break;
        case RTM_DELETE:
                nh = rc->rc_nh_old;
                if (!NH_IS_NHGRP(nh)) {
                        if (!(nh->nh_flags & NHF_GATEWAY))
                                return (true);
                        if (nhop_get_rtflags(nh) & RTF_STATIC)
                                return (true);
                }
                break;
        }

        return (false);
}

static bool
apply_rtable_changes(struct fib_data *fd)
{
        enum flm_op_result result;
        struct fib_change_queue *q = &fd->fd_ss.fd_change_queue;

        result = fd->fd_flm->flm_change_rib_items_cb(fd->fd_rh, q, fd->fd_algo_data);

        if (result == FLM_SUCCESS) {
                sync_rib_gen(fd);
                for (int i = 0; i < q->count; i++)
                        if (q->entries[i].nh_old)
                                fib_unref_nhop(fd, q->entries[i].nh_old);
                q->count = 0;
        }
        fd->fd_batch = false;

        return (result == FLM_SUCCESS);
}

static bool
fill_change_entry(struct fib_data *fd, struct fib_change_entry *ce, struct rib_cmd_info *rc)
{
        int plen = 0;

        switch (fd->fd_family) {
#ifdef INET
        case AF_INET:
                rt_get_inet_prefix_plen(rc->rc_rt, &ce->addr4, &plen, &ce->scopeid);
                break;
#endif
#ifdef INET6
        case AF_INET6:
                rt_get_inet6_prefix_plen(rc->rc_rt, &ce->addr6, &plen, &ce->scopeid);
                break;
#endif
        }

        ce->plen = plen;
        ce->nh_old = rc->rc_nh_old;
        ce->nh_new = rc->rc_nh_new;
        if (ce->nh_new != NULL) {
                if (fib_ref_nhop(fd, ce->nh_new) == 0)
                        return (false);
        }

        return (true);
}

static bool
queue_rtable_change(struct fib_data *fd, struct rib_cmd_info *rc)
{
        struct fib_change_queue *q = &fd->fd_ss.fd_change_queue;

        if (q->count >= q->size) {
                uint32_t q_size;

                if (q->size == 0)
                        q_size = 256; /* ~18k memory */
                else
                        q_size = q->size * 2;

                size_t size = q_size * sizeof(struct fib_change_entry);
                void *a = realloc(q->entries, size, M_TEMP, M_NOWAIT | M_ZERO);
                if (a == NULL) {
                        FD_PRINTF(LOG_INFO, fd, "Unable to realloc queue for %u elements",
                            q_size);
                        return (false);
                }
                q->entries = a;
                q->size = q_size;
        }

        return (fill_change_entry(fd, &q->entries[q->count++], rc));
}

/*
 * Rib subscription handler. Checks if the algorithm is ready to
 *  receive updates, handles nexthop refcounting and passes change
 *  data to the algorithm callback.
 */
static void
handle_rtable_change_cb(struct rib_head *rnh, struct rib_cmd_info *rc,
    void *_data)
{
        struct fib_data *fd = (struct fib_data *)_data;
        enum flm_op_result result;

        RIB_WLOCK_ASSERT(rnh);

        /*
         * There is a small gap between subscribing for route changes
         *  and initiating rtable dump. Avoid receiving route changes
         *  prior to finishing rtable dump by checking `init_done`.
         */
        if (!fd->init_done)
                return;

        bool immediate_sync = need_immediate_sync(fd, rc);

        /* Consider scheduling algorithm re-evaluation */
        update_algo_state(fd);

        /*
         * If algo requested rebuild, stop sending updates by default.
         * This simplifies nexthop refcount handling logic.
         */
        if (fd->fd_need_rebuild) {
                if (immediate_sync)
                        rebuild_fd(fd, "rtable change type enforced sync");
                return;
        }

        /*
         * Algo requested updates to be delivered in batches.
         * Add the current change to the queue and return.
         */
        if (fd->fd_batch) {
                if (immediate_sync) {
                        if (!queue_rtable_change(fd, rc) || !apply_rtable_changes(fd))
                                rebuild_fd(fd, "batch sync failed");
                } else {
                        if (!queue_rtable_change(fd, rc))
                                schedule_fd_rebuild(fd, "batch queue failed");
                }
                return;
        }

        /*
         * Maintain guarantee that every nexthop returned by the dataplane
         *  lookup has > 0 refcount, so can be safely referenced within current
         *  epoch.
         */
        if (rc->rc_nh_new != NULL) {
                if (fib_ref_nhop(fd, rc->rc_nh_new) == 0) {
                        /* ran out of indexes */
                        schedule_fd_rebuild(fd, "ran out of nhop indexes");
                        return;
                }
        }

        result = fd->fd_flm->flm_change_rib_item_cb(rnh, rc, fd->fd_algo_data);

        switch (result) {
        case FLM_SUCCESS:
                sync_rib_gen(fd);
                /* Unref old nexthop on success */
                if (rc->rc_nh_old != NULL)
                        fib_unref_nhop(fd, rc->rc_nh_old);
                break;
        case FLM_BATCH:

                /*
                 * Algo asks to batch the changes.
                 */
                if (queue_rtable_change(fd, rc)) {
                        if (!immediate_sync) {
                                fd->fd_batch = true;
                                mark_diverge_time(fd);
                                update_rebuild_delay(fd, FDA_BATCH);
                                break;
                        }
                        if (apply_rtable_changes(fd))
                                break;
                }
                FD_PRINTF(LOG_ERR, fd, "batched sync failed, force the rebuild");

        case FLM_REBUILD:

                /*
                 * Algo is not able to apply the update.
                 * Schedule algo rebuild.
                 */
                if (!immediate_sync) {
                        mark_diverge_time(fd);
                        schedule_fd_rebuild(fd, "algo requested rebuild");
                        break;
                }

                FD_PRINTF(LOG_INFO, fd, "running sync rebuild");
                rebuild_fd(fd, "rtable change type enforced sync");
                break;
        case FLM_ERROR:

                /*
                 * Algo reported a non-recoverable error.
                 * Record the error and schedule rebuild, which will
                 *  trigger best algo selection.
                 */
                FD_PRINTF(LOG_ERR, fd, "algo reported non-recoverable error");
                if (!flm_error_add(fd->fd_flm, fd->fd_fibnum))
                        FD_PRINTF(LOG_ERR, fd, "failed to ban algo");
                schedule_fd_rebuild(fd, "algo reported non-recoverable error");
        }
}

static void
estimate_nhop_scale(const struct fib_data *old_fd, struct fib_data *fd)
{

        if (old_fd == NULL) {
                // TODO: read from rtable
                fd->number_nhops = 16;
                return;
        }

        if (old_fd->hit_nhops && old_fd->number_nhops < FIB_MAX_NHOPS)
                fd->number_nhops = 2 * old_fd->number_nhops;
        else
                fd->number_nhops = old_fd->number_nhops;
}

struct walk_cbdata {
        struct fib_data         *fd;
        flm_dump_t              *func;
        enum flm_op_result      result;
};

/*
 * Handler called after all rtenties have been dumped.
 * Performs post-dump framework checks and calls
 * algo:flm_dump_end_cb().
 *
 * Updates walk_cbdata result.
 */
static void
sync_algo_end_cb(struct rib_head *rnh, enum rib_walk_hook stage, void *_data)
{
        struct walk_cbdata *w = (struct walk_cbdata *)_data;
        struct fib_data *fd = w->fd;

        RIB_WLOCK_ASSERT(w->fd->fd_rh);

        if (rnh->rib_dying) {
                w->result = FLM_ERROR;
                return;
        }

        if (fd->hit_nhops) {
                FD_PRINTF(LOG_INFO, fd, "ran out of nexthops at %u nhops",
                    fd->nh_ref_table->count);
                if (w->result == FLM_SUCCESS)
                        w->result = FLM_REBUILD;
                return;
        }

        if (stage != RIB_WALK_HOOK_POST || w->result != FLM_SUCCESS)
                return;

        /* Post-dump hook, dump successful */
        w->result = fd->fd_flm->flm_dump_end_cb(fd->fd_algo_data, &fd->fd_dp);

        if (w->result == FLM_SUCCESS) {
                /* Mark init as done to allow routing updates */
                fd->init_done = 1;
        }
}

/*
 * Callback for each entry in rib.
 * Calls algo:flm_dump_rib_item_cb func as a part of initial
 *  route table synchronisation.
 */
static int
sync_algo_cb(struct rtentry *rt, void *_data)
{
        struct walk_cbdata *w = (struct walk_cbdata *)_data;

        RIB_WLOCK_ASSERT(w->fd->fd_rh);

        if (w->result == FLM_SUCCESS && w->func) {

                /*
                 * Reference nexthops to maintain guarantee that
                 *  each nexthop returned by datapath has > 0 references
                 *  and can be safely referenced within current epoch.
                 */
                struct nhop_object *nh = rt_get_raw_nhop(rt);
                if (fib_ref_nhop(w->fd, nh) != 0)
                        w->result = w->func(rt, w->fd->fd_algo_data);
                else
                        w->result = FLM_REBUILD;
        }

        return (0);
}

/*
 * Dump all routing table state to the algo instance.
 */
static enum flm_op_result
sync_algo(struct fib_data *fd)
{
        struct walk_cbdata w = {
                .fd = fd,
                .func = fd->fd_flm->flm_dump_rib_item_cb,
                .result = FLM_SUCCESS,
        };

        rib_walk_ext_locked(fd->fd_rh, sync_algo_cb, sync_algo_end_cb, &w);

        FD_PRINTF(LOG_INFO, fd,
            "initial dump completed (rtable version: %d), result: %s",
            fd->fd_rh->rnh_gen, print_op_result(w.result));

        return (w.result);
}

/*
 * Schedules epoch-backed @fd instance deletion.
 * * Unlinks @fd from the list of active algo instances.
 * * Removes rib subscription.
 * * Stops callout.
 * * Schedules actual deletion.
 *
 * Assume @fd is already unlinked from the datapath.
 */
static int
schedule_destroy_fd_instance(struct fib_data *fd, bool in_callout)
{
        bool is_dead;

        NET_EPOCH_ASSERT();
        RIB_WLOCK_ASSERT(fd->fd_rh);

        FIB_MOD_LOCK();
        is_dead = fd->fd_dead;
        if (!is_dead)
                fd->fd_dead = true;
        if (fd->fd_linked) {
                TAILQ_REMOVE(&V_fib_data_list, fd, entries);
                fd->fd_linked = false;
        }
        FIB_MOD_UNLOCK();
        if (is_dead)
                return (0);

        FD_PRINTF(LOG_INFO, fd, "DETACH");

        if (fd->fd_rs != NULL)
                rib_unsubscribe_locked(fd->fd_rs);

        /*
         * After rib_unsubscribe() no _new_ handle_rtable_change_cb() calls
         * will be executed, hence no _new_ callout schedules will happen.
         */
        callout_stop(&fd->fd_callout);

        fib_epoch_call(destroy_fd_instance_epoch, &fd->fd_epoch_ctx);

        return (0);
}

/*
 * Wipe all fd instances from the list matching rib specified by @rh.
 * If @keep_first is set, remove all but the first record.
 */
static void
fib_cleanup_algo(struct rib_head *rh, bool keep_first, bool in_callout)
{
        struct fib_data_head tmp_head = TAILQ_HEAD_INITIALIZER(tmp_head);
        struct fib_data *fd, *fd_tmp;
        struct epoch_tracker et;

        FIB_MOD_LOCK();
        TAILQ_FOREACH_SAFE(fd, &V_fib_data_list, entries, fd_tmp) {
                if (fd->fd_rh == rh) {
                        if (keep_first) {
                                keep_first = false;
                                continue;
                        }
                        TAILQ_REMOVE(&V_fib_data_list, fd, entries);
                        fd->fd_linked = false;
                        TAILQ_INSERT_TAIL(&tmp_head, fd, entries);
                }
        }
        FIB_MOD_UNLOCK();

        /* Pass 2: remove each entry */
        NET_EPOCH_ENTER(et);
        TAILQ_FOREACH_SAFE(fd, &tmp_head, entries, fd_tmp) {
                if (!in_callout)
                        RIB_WLOCK(fd->fd_rh);
                schedule_destroy_fd_instance(fd, in_callout);
                if (!in_callout)
                        RIB_WUNLOCK(fd->fd_rh);
        }
        NET_EPOCH_EXIT(et);
}

void
fib_destroy_rib(struct rib_head *rh)
{

        /*
         * rnh has `is_dying` flag set, so setup of new fd's will fail at
         *  sync_algo() stage, preventing new entries to be added to the list
         *  of active algos. Remove all existing entries for the particular rib.
         */
        fib_cleanup_algo(rh, false, false);
}

/*
 * Finalises fd destruction by freeing all fd resources.
 */
static void
destroy_fd_instance(struct fib_data *fd)
{

        FD_PRINTF(LOG_INFO, fd, "destroy fd %p", fd);

        /* Call destroy callback first */
        if (fd->fd_algo_data != NULL)
                fd->fd_flm->flm_destroy_cb(fd->fd_algo_data);

        /* Nhop table */
        if ((fd->nh_idx != NULL) && (fd->nh_ref_table != NULL)) {
                for (int i = 0; i < fd->number_nhops; i++) {
                        if (!is_idx_free(fd, i)) {
                                FD_PRINTF(LOG_DEBUG2, fd, " FREE nhop %d %p",
                                    i, fd->nh_idx[i]);
                                nhop_free_any(fd->nh_idx[i]);
                        }
                }
                free(fd->nh_idx, M_RTABLE);
        }
        if (fd->nh_ref_table != NULL)
                free(fd->nh_ref_table, M_RTABLE);

        if (fd->fd_ss.fd_change_queue.entries != NULL)
                free(fd->fd_ss.fd_change_queue.entries, M_TEMP);

        fib_unref_algo(fd->fd_flm);

        free(fd, M_RTABLE);
}

/*
 * Epoch callback indicating fd is safe to destroy
 */
static void
destroy_fd_instance_epoch(epoch_context_t ctx)
{
        struct fib_data *fd;

        fd = __containerof(ctx, struct fib_data, fd_epoch_ctx);

        CURVNET_SET(fd->fd_vnet);
        destroy_fd_instance(fd);
        CURVNET_RESTORE();
}

/*
 * Tries to setup fd instance.
 * - Allocates fd/nhop table
 * - Runs algo:flm_init_cb algo init
 * - Subscribes fd to the rib
 * - Runs rtable dump
 * - Adds instance to the list of active instances.
 *
 * Returns: operation result. Fills in @pfd with resulting fd on success.
 *
 */
static enum flm_op_result
try_setup_fd_instance(struct fib_lookup_module *flm, struct rib_head *rh,
    struct fib_data *old_fd, struct fib_data **pfd)
{
        struct fib_data *fd;
        size_t size;
        enum flm_op_result result;

        /* Allocate */
        fd = malloc(sizeof(struct fib_data), M_RTABLE, M_NOWAIT | M_ZERO);
        if (fd == NULL)  {
                *pfd = NULL;
                RH_PRINTF(LOG_INFO, rh, "Unable to allocate fib_data structure");
                return (FLM_REBUILD);
        }
        *pfd = fd;

        estimate_nhop_scale(old_fd, fd);

        fd->fd_rh = rh;
        fd->fd_family = rh->rib_family;
        fd->fd_fibnum = rh->rib_fibnum;
        callout_init_rm(&fd->fd_callout, &rh->rib_lock, 0);
        fd->fd_vnet = curvnet;
        fd->fd_flm = flm;

        FIB_MOD_LOCK();
        flm->flm_refcount++;
        fd->fd_gen = ++fib_gen;
        FIB_MOD_UNLOCK();

        FD_PRINTF(LOG_DEBUG, fd, "allocated fd %p", fd);

        /* Allocate nhidx -> nhop_ptr table */
        size = fd->number_nhops * sizeof(void *);
        fd->nh_idx = malloc(size, M_RTABLE, M_NOWAIT | M_ZERO);
        if (fd->nh_idx == NULL) {
                FD_PRINTF(LOG_INFO, fd, "Unable to allocate nhop table idx (sz:%zu)", size);
                return (FLM_REBUILD);
        }

        /* Allocate nhop index refcount table */
        size = sizeof(struct nhop_ref_table);
        size += fd->number_nhops * sizeof(uint32_t);
        fd->nh_ref_table = malloc(size, M_RTABLE, M_NOWAIT | M_ZERO);
        if (fd->nh_ref_table == NULL) {
                FD_PRINTF(LOG_INFO, fd, "Unable to allocate nhop refcount table (sz:%zu)", size);
                return (FLM_REBUILD);
        }
        FD_PRINTF(LOG_DEBUG, fd, "Allocated %u nhop indexes", fd->number_nhops);

        /* Okay, we're ready for algo init */
        void *old_algo_data = (old_fd != NULL) ? old_fd->fd_algo_data : NULL;
        result = flm->flm_init_cb(fd->fd_fibnum, fd, old_algo_data, &fd->fd_algo_data);
        if (result != FLM_SUCCESS) {
                FD_PRINTF(LOG_INFO, fd, "%s algo init failed", flm->flm_name);
                return (result);
        }

        /* Try to subscribe */
        if (flm->flm_change_rib_item_cb != NULL) {
                fd->fd_rs = rib_subscribe_locked(fd->fd_rh,
                    handle_rtable_change_cb, fd, RIB_NOTIFY_IMMEDIATE);
                if (fd->fd_rs == NULL) {
                        FD_PRINTF(LOG_INFO, fd, "failed to subscribe to the rib changes");
                        return (FLM_REBUILD);
                }
        }

        /* Dump */
        result = sync_algo(fd);
        if (result != FLM_SUCCESS) {
                FD_PRINTF(LOG_INFO, fd, "rib sync failed");
                return (result);
        }
        FD_PRINTF(LOG_INFO, fd, "DUMP completed successfully.");

        FIB_MOD_LOCK();
        /*
         * Insert fd in the beginning of a list, to maintain invariant
         *  that first matching entry for the AF/fib is always the active
         *  one.
         */
        TAILQ_INSERT_HEAD(&V_fib_data_list, fd, entries);
        fd->fd_linked = true;
        FIB_MOD_UNLOCK();

        return (FLM_SUCCESS);
}

/*
 * Sets up algo @flm for table @rh and links it to the datapath.
 *
 */
static enum flm_op_result
setup_fd_instance(struct fib_lookup_module *flm, struct rib_head *rh,
    struct fib_data *orig_fd, struct fib_data **pfd, bool attach)
{
        struct fib_data *prev_fd, *new_fd;
        enum flm_op_result result;

        NET_EPOCH_ASSERT();
        RIB_WLOCK_ASSERT(rh);

        prev_fd = orig_fd;
        new_fd = NULL;
        for (int i = 0; i < FIB_MAX_TRIES; i++) {
                result = try_setup_fd_instance(flm, rh, prev_fd, &new_fd);

                if ((result == FLM_SUCCESS) && attach) {
                        if (fib_set_datapath_ptr(new_fd, &new_fd->fd_dp))
                                sync_rib_gen(new_fd);
                        else
                                result = FLM_REBUILD;
                }

                if ((prev_fd != NULL) && (prev_fd != orig_fd)) {
                        schedule_destroy_fd_instance(prev_fd, false);
                        prev_fd = NULL;
                }

                RH_PRINTF(LOG_INFO, rh, "try %d: fib algo result: %s", i,
                    print_op_result(result));

                if (result == FLM_REBUILD) {
                        prev_fd = new_fd;
                        new_fd = NULL;
                        continue;
                }

                break;
        }

        if (result != FLM_SUCCESS) {
                RH_PRINTF(LOG_WARNING, rh,
                    "%s algo instance setup failed, failures=%d", flm->flm_name,
                    orig_fd ? orig_fd->fd_failed_rebuilds + 1 : 0);
                /* update failure count */
                FIB_MOD_LOCK();
                if (orig_fd != NULL)
                        orig_fd->fd_failed_rebuilds++;
                FIB_MOD_UNLOCK();

                /* Ban algo on non-recoverable error */
                if (result == FLM_ERROR)
                        flm_error_add(flm, rh->rib_fibnum);

                if ((prev_fd != NULL) && (prev_fd != orig_fd))
                        schedule_destroy_fd_instance(prev_fd, false);
                if (new_fd != NULL) {
                        schedule_destroy_fd_instance(new_fd, false);
                        new_fd = NULL;
                }
        }

        *pfd = new_fd;
        return (result);
}

/*
 * Tries to sync algo with the current rtable state, either
 * by executing batch update or rebuilding.
 * Returns true on success.
 */
static bool
execute_callout_action(struct fib_data *fd)
{
        enum fib_callout_action action = fd->fd_callout_action;
        struct fib_lookup_module *flm_new = NULL;
        bool result = true;

        NET_EPOCH_ASSERT();
        RIB_WLOCK_ASSERT(fd->fd_rh);

        fd->fd_need_rebuild = false;
        fd->fd_batch = false;
        fd->fd_num_changes = 0;

        /* First, check if we're still OK to use this algo */
        if (!is_algo_fixed(fd->fd_rh))
                flm_new = fib_check_best_algo(fd->fd_rh, fd->fd_flm);
        if (flm_new != NULL)
                action = FDA_REBUILD;

        if (action == FDA_BATCH) {
                /* Try to sync */
                if (!apply_rtable_changes(fd))
                        action = FDA_REBUILD;
        }

        if (action == FDA_REBUILD)
                result = rebuild_fd_flm(fd, flm_new != NULL ? flm_new : fd->fd_flm);
        if (flm_new != NULL)
                fib_unref_algo(flm_new);

        return (result);
}

/*
 * Callout for all scheduled fd-related work.
 * - Checks if the current algo is still the best algo
 * - Synchronises algo instance to the rtable (batch usecase)
 * - Creates a new instance of an algo for af/fib if desired.
 */
static void
handle_fd_callout(void *_data)
{
        struct fib_data *fd = (struct fib_data *)_data;
        struct epoch_tracker et;

        FD_PRINTF(LOG_INFO, fd, "running callout type=%d", fd->fd_callout_action);

        NET_EPOCH_ENTER(et);
        CURVNET_SET(fd->fd_vnet);
        execute_callout_action(fd);
        CURVNET_RESTORE();
        NET_EPOCH_EXIT(et);
}

/*
 * Tries to create new algo instance based on @fd data.
 * Returns true on success.
 */
static bool
rebuild_fd_flm(struct fib_data *fd, struct fib_lookup_module *flm_new)
{
        struct fib_data *fd_new, *fd_tmp = NULL;
        bool result;

        if (flm_new == fd->fd_flm)
                fd_tmp = fd;
        else
                FD_PRINTF(LOG_INFO, fd, "switching algo to %s", flm_new->flm_name);

        result = setup_fd_instance(flm_new, fd->fd_rh, fd_tmp, &fd_new, true);
        if (result != FLM_SUCCESS) {
                FD_PRINTF(LOG_NOTICE, fd, "table rebuild failed");
                return (false);
        }
        FD_PRINTF(LOG_INFO, fd_new, "switched to new instance");

        /* Remove old instance */
        schedule_destroy_fd_instance(fd, true);

        return (true);
}

static bool
rebuild_fd(struct fib_data *fd, const char *reason)
{
        struct fib_lookup_module *flm_new = NULL;
        bool result;

        if (!is_algo_fixed(fd->fd_rh))
                flm_new = fib_check_best_algo(fd->fd_rh, fd->fd_flm);

        FD_PRINTF(LOG_INFO, fd, "running sync rebuild: %s", reason);
        result = rebuild_fd_flm(fd, flm_new != NULL ? flm_new : fd->fd_flm);
        if (flm_new != NULL)
                fib_unref_algo(flm_new);

        if (!result) {
                FD_PRINTF(LOG_ERR, fd, "sync rebuild failed");
                schedule_fd_rebuild(fd, "sync rebuild failed");
        }

        return (result);
}

/*
 * Finds algo by name/family.
 * Returns referenced algo or NULL.
 */
static struct fib_lookup_module *
fib_find_algo(const char *algo_name, int family)
{
        struct fib_lookup_module *flm;

        FIB_MOD_LOCK();
        TAILQ_FOREACH(flm, &all_algo_list, entries) {
                if ((strcmp(flm->flm_name, algo_name) == 0) &&
                    (family == flm->flm_family)) {
                        flm->flm_refcount++;
                        FIB_MOD_UNLOCK();
                        return (flm);
                }
        }
        FIB_MOD_UNLOCK();

        return (NULL);
}

static void
fib_unref_algo(struct fib_lookup_module *flm)
{

        FIB_MOD_LOCK();
        flm->flm_refcount--;
        FIB_MOD_UNLOCK();
}

static int
set_fib_algo(uint32_t fibnum, int family, struct sysctl_oid *oidp, struct sysctl_req *req)
{
        struct fib_lookup_module *flm = NULL;
        struct fib_data *fd = NULL;
        char old_algo_name[32], algo_name[32];
        struct rib_head *rh = NULL;
        enum flm_op_result result;
        struct epoch_tracker et;
        int error;

        /* Fetch current algo/rib for af/family */
        FIB_MOD_LOCK();
        TAILQ_FOREACH(fd, &V_fib_data_list, entries) {
                if ((fd->fd_family == family) && (fd->fd_fibnum == fibnum))
                        break;
        }
        if (fd == NULL) {
                FIB_MOD_UNLOCK();
                return (ENOENT);
        }
        rh = fd->fd_rh;
        strlcpy(old_algo_name, fd->fd_flm->flm_name,
            sizeof(old_algo_name));
        FIB_MOD_UNLOCK();

        strlcpy(algo_name, old_algo_name, sizeof(algo_name));
        error = sysctl_handle_string(oidp, algo_name, sizeof(algo_name), req);
        if (error != 0 || req->newptr == NULL)
                return (error);

        if (strcmp(algo_name, old_algo_name) == 0)
                return (0);

        /* New algorithm name is different */
        flm = fib_find_algo(algo_name, family);
        if (flm == NULL) {
                RH_PRINTF(LOG_INFO, rh, "unable to find algo %s", algo_name);
                return (ESRCH);
        }

        fd = NULL;
        NET_EPOCH_ENTER(et);
        RIB_WLOCK(rh);
        result = setup_fd_instance(flm, rh, NULL, &fd, true);
        RIB_WUNLOCK(rh);
        NET_EPOCH_EXIT(et);
        fib_unref_algo(flm);
        if (result != FLM_SUCCESS)
                return (EINVAL);

        /* Disable automated jumping between algos */
        FIB_MOD_LOCK();
        set_algo_fixed(rh);
        FIB_MOD_UNLOCK();
        /* Remove old instance(s) */
        fib_cleanup_algo(rh, true, false);

        /* Drain cb so user can unload the module after userret if so desired */
        NET_EPOCH_DRAIN_CALLBACKS();

        return (0);
}

#ifdef INET
static int
set_algo_inet_sysctl_handler(SYSCTL_HANDLER_ARGS)
{

        return (set_fib_algo(curthread->td_proc->p_fibnum, AF_INET, oidp, req));
}
SYSCTL_PROC(_net_route_algo_inet, OID_AUTO, algo,
    CTLFLAG_VNET | CTLTYPE_STRING | CTLFLAG_RW | CTLFLAG_MPSAFE, NULL, 0,
    set_algo_inet_sysctl_handler, "A", "Set IPv4 lookup algo");
#endif

#ifdef INET6
static int
set_algo_inet6_sysctl_handler(SYSCTL_HANDLER_ARGS)
{

        return (set_fib_algo(curthread->td_proc->p_fibnum, AF_INET6, oidp, req));
}
SYSCTL_PROC(_net_route_algo_inet6, OID_AUTO, algo,
    CTLFLAG_VNET | CTLTYPE_STRING | CTLFLAG_RW | CTLFLAG_MPSAFE, NULL, 0,
    set_algo_inet6_sysctl_handler, "A", "Set IPv6 lookup algo");
#endif

static struct nhop_object *
dummy_lookup(void *algo_data, const struct flm_lookup_key key, uint32_t scopeid)
{
        return (NULL);
}

static void
destroy_fdh_epoch(epoch_context_t ctx)
{
        struct fib_dp_header *fdh;

        fdh = __containerof(ctx, struct fib_dp_header, fdh_epoch_ctx);
        free(fdh, M_RTABLE);
}

static struct fib_dp_header *
alloc_fib_dp_array(uint32_t num_tables, bool waitok)
{
        size_t sz;
        struct fib_dp_header *fdh;

        sz = sizeof(struct fib_dp_header);
        sz += sizeof(struct fib_dp) * num_tables;
        fdh = malloc(sz, M_RTABLE, (waitok ? M_WAITOK : M_NOWAIT) | M_ZERO);
        if (fdh != NULL) {
                fdh->fdh_num_tables = num_tables;
                /*
                 * Set dummy lookup function ptr always returning NULL, so
                 * we can delay algo init.
                 */
                for (uint32_t i = 0; i < num_tables; i++)
                        fdh->fdh_idx[i].f = dummy_lookup;
        }
        return (fdh);
}

static struct fib_dp_header *
get_fib_dp_header(struct fib_dp *dp)
{

        return (__containerof((void *)dp, struct fib_dp_header, fdh_idx));
}

/*
 * Replace per-family index pool @pdp with a new one which
 * contains updated callback/algo data from @fd.
 * Returns true on success.
 */
static bool
replace_rtables_family(struct fib_dp **pdp, struct fib_data *fd, struct fib_dp *dp)
{
        struct fib_dp_header *new_fdh, *old_fdh;

        NET_EPOCH_ASSERT();

        FD_PRINTF(LOG_DEBUG, fd, "[vnet %p] replace with f:%p arg:%p",
            curvnet, dp->f, dp->arg);

        FIB_MOD_LOCK();
        old_fdh = get_fib_dp_header(*pdp);

        if (old_fdh->fdh_idx[fd->fd_fibnum].f == dp->f) {
                /*
                 * Function is the same, data pointer needs update.
                 * Perform in-line replace without reallocation.
                 */
                old_fdh->fdh_idx[fd->fd_fibnum].arg = dp->arg;
                FD_PRINTF(LOG_DEBUG, fd, "FDH %p inline update", old_fdh);
                FIB_MOD_UNLOCK();
                return (true);
        }

        new_fdh = alloc_fib_dp_array(old_fdh->fdh_num_tables, false);
        FD_PRINTF(LOG_DEBUG, fd, "OLD FDH: %p NEW FDH: %p", old_fdh, new_fdh);
        if (new_fdh == NULL) {
                FIB_MOD_UNLOCK();
                FD_PRINTF(LOG_WARNING, fd, "error attaching datapath");
                return (false);
        }

        memcpy(&new_fdh->fdh_idx[0], &old_fdh->fdh_idx[0],
            old_fdh->fdh_num_tables * sizeof(struct fib_dp));
        /* Update relevant data structure for @fd */
        new_fdh->fdh_idx[fd->fd_fibnum] = *dp;

        /* Ensure memcpy() writes have completed */
        atomic_thread_fence_rel();
        /* Set new datapath pointer */
        *pdp = &new_fdh->fdh_idx[0];
        FIB_MOD_UNLOCK();
        FD_PRINTF(LOG_DEBUG, fd, "update %p -> %p", old_fdh, new_fdh);

        fib_epoch_call(destroy_fdh_epoch, &old_fdh->fdh_epoch_ctx);

        return (true);
}

static struct fib_dp **
get_family_dp_ptr(int family)
{
        switch (family) {
#ifdef INET
        case AF_INET:
                return (&V_inet_dp);
#endif
#ifdef INET6
        case AF_INET6:
                return (&V_inet6_dp);
#endif
        }
        return (NULL);
}

/*
 * Make datapath use fib instance @fd
 */
bool
fib_set_datapath_ptr(struct fib_data *fd, struct fib_dp *dp)
{
        struct fib_dp **pdp;

        pdp = get_family_dp_ptr(fd->fd_family);
        return (replace_rtables_family(pdp, fd, dp));
}

/*
 * Grow datapath pointers array.
 * Called from sysctl handler on growing number of routing tables.
 */
static void
grow_rtables_family(struct fib_dp **pdp, uint32_t new_num_tables)
{
        struct fib_dp_header *new_fdh, *old_fdh = NULL;

        new_fdh = alloc_fib_dp_array(new_num_tables, true);

        FIB_MOD_LOCK();
        if (*pdp != NULL) {
                old_fdh = get_fib_dp_header(*pdp);
                memcpy(&new_fdh->fdh_idx[0], &old_fdh->fdh_idx[0],
                    old_fdh->fdh_num_tables * sizeof(struct fib_dp));
        }

        /* Wait till all writes completed */
        atomic_thread_fence_rel();

        *pdp = &new_fdh->fdh_idx[0];
        FIB_MOD_UNLOCK();

        if (old_fdh != NULL)
                fib_epoch_call(destroy_fdh_epoch, &old_fdh->fdh_epoch_ctx);
}

/*
 * Grows per-AF arrays of datapath pointers for each supported family.
 * Called from fibs resize sysctl handler.
 */
void
fib_grow_rtables(uint32_t new_num_tables)
{

#ifdef INET
        grow_rtables_family(get_family_dp_ptr(AF_INET), new_num_tables);
#endif
#ifdef INET6
        grow_rtables_family(get_family_dp_ptr(AF_INET6), new_num_tables);
#endif
}

void
fib_get_rtable_info(struct rib_head *rh, struct rib_rtable_info *rinfo)
{

        bzero(rinfo, sizeof(struct rib_rtable_info));
        rinfo->num_prefixes = rh->rnh_prefixes;
        rinfo->num_nhops = nhops_get_count(rh);
        rinfo->num_nhgrp = nhgrp_get_count(rh);
}

/*
 * Updates pointer to the algo data for the @fd.
 */
void
fib_set_algo_ptr(struct fib_data *fd, void *algo_data)
{
        RIB_WLOCK_ASSERT(fd->fd_rh);

        fd->fd_algo_data = algo_data;
}

/*
 * Calls @callback with @ctx after the end of a current epoch.
 */
void
fib_epoch_call(epoch_callback_t callback, epoch_context_t ctx)
{
        NET_EPOCH_CALL(callback, ctx);
}

/*
 * Accessor to get rib instance @fd is attached to.
 */
struct rib_head *
fib_get_rh(struct fib_data *fd)
{

        return (fd->fd_rh);
}

/*
 * Accessor to export idx->nhop array
 */
struct nhop_object **
fib_get_nhop_array(struct fib_data *fd)
{

        return (fd->nh_idx);
}

static uint32_t
get_nhop_idx(struct nhop_object *nh)
{
        if (NH_IS_NHGRP(nh))
                return (nhgrp_get_idx((struct nhgrp_object *)nh));

        return (nhop_get_idx(nh));
}

uint32_t
fib_get_nhop_idx(struct fib_data *fd, struct nhop_object *nh)
{

        return (get_nhop_idx(nh));
}

static bool
is_idx_free(struct fib_data *fd, uint32_t index)
{

        return (fd->nh_ref_table->refcnt[index] == 0);
}

static uint32_t
fib_ref_nhop(struct fib_data *fd, struct nhop_object *nh)
{
        uint32_t idx = get_nhop_idx(nh);

        if (idx >= fd->number_nhops) {
                fd->hit_nhops = 1;
                return (0);
        }

        if (is_idx_free(fd, idx)) {
                nhop_ref_any(nh);
                fd->nh_idx[idx] = nh;
                fd->nh_ref_table->count++;
                FD_PRINTF(LOG_DEBUG2, fd, " REF nhop %u %p", idx, fd->nh_idx[idx]);
        }
        fd->nh_ref_table->refcnt[idx]++;

        return (idx);
}

struct nhop_release_data {
        struct nhop_object      *nh;
        struct epoch_context    ctx;
};

static void
release_nhop_epoch(epoch_context_t ctx)
{
        struct nhop_release_data *nrd;

        nrd = __containerof(ctx, struct nhop_release_data, ctx);
        nhop_free_any(nrd->nh);
        free(nrd, M_TEMP);
}

/*
 * Delays nexthop refcount release.
 * Datapath may have the datastructures not updated yet, so the old
 *  nexthop may still be returned till the end of current epoch. Delay
 *  refcount removal, as we may be removing the last instance, which will
 *  trigger nexthop deletion, rendering returned nexthop invalid.
 */
static void
fib_schedule_release_nhop(struct fib_data *fd, struct nhop_object *nh)
{
        struct nhop_release_data *nrd;

        nrd = malloc(sizeof(struct nhop_release_data), M_TEMP, M_NOWAIT | M_ZERO);
        if (nrd != NULL) {
                nrd->nh = nh;
                fib_epoch_call(release_nhop_epoch, &nrd->ctx);
        } else {
                /*
                 * Unable to allocate memory. Leak nexthop to maintain guarantee
                 *  that each nhop can be referenced.
                 */
                FD_PRINTF(LOG_ERR, fd, "unable to schedule nhop %p deletion", nh);
        }
}

static void
fib_unref_nhop(struct fib_data *fd, struct nhop_object *nh)
{
        uint32_t idx = get_nhop_idx(nh);

        KASSERT((idx < fd->number_nhops), ("invalid nhop index"));
        KASSERT((nh == fd->nh_idx[idx]), ("index table contains whong nh"));

        fd->nh_ref_table->refcnt[idx]--;
        if (fd->nh_ref_table->refcnt[idx] == 0) {
                FD_PRINTF(LOG_DEBUG, fd, " FREE nhop %d %p", idx, fd->nh_idx[idx]);
                fib_schedule_release_nhop(fd, fd->nh_idx[idx]);
        }
}

static void
set_algo_fixed(struct rib_head *rh)
{
        switch (rh->rib_family) {
#ifdef INET
        case AF_INET:
                V_algo_fixed_inet = true;
                break;
#endif
#ifdef INET6
        case AF_INET6:
                V_algo_fixed_inet6 = true;
                break;
#endif
        }
}

static bool
is_algo_fixed(struct rib_head *rh)
{

        switch (rh->rib_family) {
#ifdef INET
        case AF_INET:
                return (V_algo_fixed_inet);
#endif
#ifdef INET6
        case AF_INET6:
                return (V_algo_fixed_inet6);
#endif
        }
        return (false);
}

/*
 * Runs the check on what would be the best algo for rib @rh, assuming
 *  that the current algo is the one specified by @orig_flm. Note that
 *  it can be NULL for initial selection.
 *
 * Returns referenced new algo or NULL if the current one is the best.
 */
static struct fib_lookup_module *
fib_check_best_algo(struct rib_head *rh, struct fib_lookup_module *orig_flm)
{
        uint8_t preference, curr_preference = 0, best_preference = 0;
        struct fib_lookup_module *flm, *best_flm = NULL;
        struct rib_rtable_info rinfo;
        int candidate_algos = 0;

        fib_get_rtable_info(rh, &rinfo);

        FIB_MOD_LOCK();
        TAILQ_FOREACH(flm, &all_algo_list, entries) {
                if (flm->flm_family != rh->rib_family)
                        continue;
                candidate_algos++;
                preference = flm->flm_get_pref(&rinfo);
                if (preference > best_preference) {
                        if (!flm_error_check(flm, rh->rib_fibnum)) {
                                best_preference = preference;
                                best_flm = flm;
                        }
                }
                if (flm == orig_flm)
                        curr_preference = preference;
        }
        if ((best_flm != NULL) && (curr_preference + BEST_DIFF_PERCENT < best_preference))
                best_flm->flm_refcount++;
        else
                best_flm = NULL;
        FIB_MOD_UNLOCK();

        RH_PRINTF(LOG_DEBUG, rh, "candidate_algos: %d, curr: %s(%d) result: %s(%d)",
            candidate_algos, orig_flm ? orig_flm->flm_name : "NULL", curr_preference,
            best_flm ? best_flm->flm_name : (orig_flm ? orig_flm->flm_name : "NULL"),
            best_preference);

        return (best_flm);
}

/*
 * Called when new route table is created.
 * Selects, allocates and attaches fib algo for the table.
 */
static bool
fib_select_algo_initial(struct rib_head *rh, struct fib_dp *dp)
{
        struct fib_lookup_module *flm;
        struct fib_data *fd = NULL;
        enum flm_op_result result;
        struct epoch_tracker et;

        flm = fib_check_best_algo(rh, NULL);
        if (flm == NULL) {
                RH_PRINTF(LOG_CRIT, rh, "no algo selected");
                return (false);
        }
        RH_PRINTF(LOG_INFO, rh, "selected algo %s", flm->flm_name);

        NET_EPOCH_ENTER(et);
        RIB_WLOCK(rh);
        result = setup_fd_instance(flm, rh, NULL, &fd, false);
        RIB_WUNLOCK(rh);
        NET_EPOCH_EXIT(et);

        RH_PRINTF(LOG_DEBUG, rh, "result=%d fd=%p", result, fd);
        if (result == FLM_SUCCESS)
                *dp = fd->fd_dp;
        else
                RH_PRINTF(LOG_CRIT, rh, "unable to setup algo %s", flm->flm_name);

        fib_unref_algo(flm);

        return (result == FLM_SUCCESS);
}

/*
 * Sets up fib algo instances for the non-initialized RIBs in the @family.
 * Allocates temporary datapath index to amortize datapaint index updates
 * with large @num_tables.
 */
void
fib_setup_family(int family, uint32_t num_tables)
{
        struct fib_dp_header *new_fdh = alloc_fib_dp_array(num_tables, false);
        if (new_fdh == NULL) {
                ALGO_PRINTF(LOG_CRIT, "Unable to setup framework for %s", print_family(family));
                return;
        }

        for (int i = 0; i < num_tables; i++) {
                struct rib_head *rh = rt_tables_get_rnh(i, family);
                if (rh->rib_algo_init)
                        continue;
                if (!fib_select_algo_initial(rh, &new_fdh->fdh_idx[i]))
                        continue;

                rh->rib_algo_init = true;
        }

        FIB_MOD_LOCK();
        struct fib_dp **pdp = get_family_dp_ptr(family);
        struct fib_dp_header *old_fdh = get_fib_dp_header(*pdp);

        /* Update the items not touched by the new init, from the old data pointer */
        for (int i = 0; i < num_tables; i++) {
                if (new_fdh->fdh_idx[i].f == dummy_lookup)
                        new_fdh->fdh_idx[i] = old_fdh->fdh_idx[i];
        }

        /* Ensure all index writes have completed */
        atomic_thread_fence_rel();
        /* Set new datapath pointer */
        *pdp = &new_fdh->fdh_idx[0];

        FIB_MOD_UNLOCK();

        fib_epoch_call(destroy_fdh_epoch, &old_fdh->fdh_epoch_ctx);
}

/*
 * Registers fib lookup module within the subsystem.
 */
int
fib_module_register(struct fib_lookup_module *flm)
{

        FIB_MOD_LOCK();
        ALGO_PRINTF(LOG_INFO, "attaching %s to %s", flm->flm_name,
            print_family(flm->flm_family));
        TAILQ_INSERT_TAIL(&all_algo_list, flm, entries);
        FIB_MOD_UNLOCK();

        return (0);
}

/*
 * Tries to unregister fib lookup module.
 *
 * Returns 0 on success, EBUSY if module is still used
 *  by some of the tables.
 */
int
fib_module_unregister(struct fib_lookup_module *flm)
{

        FIB_MOD_LOCK();
        if (flm->flm_refcount > 0) {
                FIB_MOD_UNLOCK();
                return (EBUSY);
        }
        fib_error_clear_flm(flm);
        ALGO_PRINTF(LOG_INFO, "detaching %s from %s", flm->flm_name,
            print_family(flm->flm_family));
        TAILQ_REMOVE(&all_algo_list, flm, entries);
        FIB_MOD_UNLOCK();

        return (0);
}

void
vnet_fib_init(void)
{

        TAILQ_INIT(&V_fib_data_list);
}

void
vnet_fib_destroy(void)
{

        FIB_MOD_LOCK();
        fib_error_clear();
        FIB_MOD_UNLOCK();
}