xnu-4570.71.2.tar.gz

[apple/xnu.git] / bsd / netinet / tcp_cache.c

/*
 * Copyright (c) 2015-2017 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 *
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 *
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 *
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */

/* TCP-cache to store and retrieve TCP-related information */

#include <net/flowhash.h>
#include <net/route.h>
#include <net/necp.h>
#include <netinet/in_pcb.h>
#include <netinet/mptcp_var.h>
#include <netinet/tcp_cache.h>
#include <netinet/tcp_seq.h>
#include <netinet/tcp_var.h>
#include <kern/locks.h>
#include <sys/queue.h>
#include <dev/random/randomdev.h>

typedef union {
        struct in_addr addr;
        struct in6_addr addr6;
} in_4_6_addr;

struct tcp_heuristic_key {
        union {
                uint8_t thk_net_signature[IFNET_SIGNATURELEN];
                in_4_6_addr thk_ip;
        };
        sa_family_t     thk_family;
};

struct tcp_heuristic {
        SLIST_ENTRY(tcp_heuristic) list;

        uint32_t        th_last_access;

        struct tcp_heuristic_key        th_key;

        char            th_val_start[0]; /* Marker for memsetting to 0 */

        uint8_t         th_tfo_data_loss; /* The number of times a SYN+data has been lost */
        uint8_t         th_tfo_req_loss; /* The number of times a SYN+cookie-req has been lost */
        uint8_t         th_tfo_data_rst; /* The number of times a SYN+data has received a RST */
        uint8_t         th_tfo_req_rst; /* The number of times a SYN+cookie-req has received a RST */
        uint8_t         th_mptcp_loss; /* The number of times a SYN+MP_CAPABLE has been lost */
        uint8_t         th_ecn_loss; /* The number of times a SYN+ecn has been lost */
        uint8_t         th_ecn_aggressive; /* The number of times we did an aggressive fallback */
        uint8_t         th_ecn_droprst; /* The number of times ECN connections received a RST after first data pkt */
        uint8_t         th_ecn_droprxmt; /* The number of times ECN connection is dropped after multiple retransmits */
        uint8_t         th_ecn_synrst;  /* number of times RST was received in response to an ECN enabled SYN */
        uint32_t        th_tfo_enabled_time; /* The moment when we reenabled TFO after backing off */
        uint32_t        th_tfo_backoff_until; /* Time until when we should not try out TFO */
        uint32_t        th_tfo_backoff; /* Current backoff timer */
        uint32_t        th_mptcp_backoff; /* Time until when we should not try out MPTCP */
        uint32_t        th_ecn_backoff; /* Time until when we should not try out ECN */

        uint8_t         th_tfo_in_backoff:1, /* Are we avoiding TFO due to the backoff timer? */
                        th_mptcp_in_backoff:1; /* Are we avoiding MPTCP due to the backoff timer? */

        char            th_val_end[0]; /* Marker for memsetting to 0 */
};

struct tcp_heuristics_head {
        SLIST_HEAD(tcp_heur_bucket, tcp_heuristic) tcp_heuristics;

        /* Per-hashbucket lock to avoid lock-contention */
        lck_mtx_t       thh_mtx;
};

struct tcp_cache_key {
        sa_family_t     tck_family;

        struct tcp_heuristic_key tck_src;
        in_4_6_addr tck_dst;
};

struct tcp_cache {
        SLIST_ENTRY(tcp_cache) list;

        u_int32_t       tc_last_access;

        struct tcp_cache_key tc_key;

        u_int8_t        tc_tfo_cookie[TFO_COOKIE_LEN_MAX];
        u_int8_t        tc_tfo_cookie_len;
};

struct tcp_cache_head {
        SLIST_HEAD(tcp_cache_bucket, tcp_cache) tcp_caches;

        /* Per-hashbucket lock to avoid lock-contention */
        lck_mtx_t       tch_mtx;
};

struct tcp_cache_key_src {
        struct ifnet *ifp;
        in_4_6_addr laddr;
        in_4_6_addr faddr;
        int af;
};

static u_int32_t tcp_cache_hash_seed;

size_t tcp_cache_size;

/*
 * The maximum depth of the hash-bucket. This way we limit the tcp_cache to
 * TCP_CACHE_BUCKET_SIZE * tcp_cache_size and have "natural" garbage collection
 */
#define TCP_CACHE_BUCKET_SIZE 5

static struct tcp_cache_head *tcp_cache;

decl_lck_mtx_data(, tcp_cache_mtx);

static lck_attr_t       *tcp_cache_mtx_attr;
static lck_grp_t        *tcp_cache_mtx_grp;
static lck_grp_attr_t   *tcp_cache_mtx_grp_attr;

static struct tcp_heuristics_head *tcp_heuristics;

decl_lck_mtx_data(, tcp_heuristics_mtx);

static lck_attr_t       *tcp_heuristic_mtx_attr;
static lck_grp_t        *tcp_heuristic_mtx_grp;
static lck_grp_attr_t   *tcp_heuristic_mtx_grp_attr;

static uint32_t tcp_backoff_maximum = 65536;

SYSCTL_UINT(_net_inet_tcp, OID_AUTO, backoff_maximum, CTLFLAG_RW | CTLFLAG_LOCKED,
        &tcp_backoff_maximum, 0, "Maximum time for which we won't try TFO");

SYSCTL_SKMEM_TCP_INT(OID_AUTO, ecn_timeout, CTLFLAG_RW | CTLFLAG_LOCKED,
        static int, tcp_ecn_timeout, 60, "Initial minutes to wait before re-trying ECN");

SYSCTL_SKMEM_TCP_INT(OID_AUTO, disable_tcp_heuristics, CTLFLAG_RW | CTLFLAG_LOCKED,
    static int, disable_tcp_heuristics, 0, "Set to 1, to disable all TCP heuristics (TFO, ECN, MPTCP)");

static uint32_t tcp_min_to_hz(uint32_t minutes)
{
        if (minutes > 65536)
                return ((uint32_t)65536 * 60 * TCP_RETRANSHZ);

        return (minutes * 60 * TCP_RETRANSHZ);
}

/*
 * This number is coupled with tcp_ecn_timeout, because we want to prevent
 * integer overflow. Need to find an unexpensive way to prevent integer overflow
 * while still allowing a dynamic sysctl.
 */
#define TCP_CACHE_OVERFLOW_PROTECT      9

/* Number of SYN-losses we accept */
#define TFO_MAX_COOKIE_LOSS     2
#define ECN_MAX_SYN_LOSS        2
#define MPTCP_MAX_SYN_LOSS      2
#define ECN_MAX_DROPRST         1
#define ECN_MAX_DROPRXMT        4
#define ECN_MAX_SYNRST          4

/* Flags for setting/unsetting loss-heuristics, limited to 4 bytes */
#define TCPCACHE_F_TFO_REQ      0x01
#define TCPCACHE_F_TFO_DATA     0x02
#define TCPCACHE_F_ECN          0x04
#define TCPCACHE_F_MPTCP        0x08
#define TCPCACHE_F_ECN_DROPRST  0x10
#define TCPCACHE_F_ECN_DROPRXMT 0x20
#define TCPCACHE_F_TFO_REQ_RST  0x40
#define TCPCACHE_F_TFO_DATA_RST 0x80
#define TCPCACHE_F_ECN_SYNRST   0x100

/* Always retry ECN after backing off to this level for some heuristics */
#define ECN_RETRY_LIMIT 9

#define TCP_CACHE_INC_IFNET_STAT(_ifp_, _af_, _stat_) { \
        if ((_ifp_) != NULL) { \
                if ((_af_) == AF_INET6) { \
                        (_ifp_)->if_ipv6_stat->_stat_++;\
                } else { \
                        (_ifp_)->if_ipv4_stat->_stat_++;\
                }\
        }\
}

/*
 * Round up to next higher power-of 2.  See "Bit Twiddling Hacks".
 *
 * Might be worth moving this to a library so that others
 * (e.g., scale_to_powerof2()) can use this as well instead of a while-loop.
 */
static u_int32_t tcp_cache_roundup2(u_int32_t a)
{
        a--;
        a |= a >> 1;
        a |= a >> 2;
        a |= a >> 4;
        a |= a >> 8;
        a |= a >> 16;
        a++;

        return a;
}

static void tcp_cache_hash_src(struct tcp_cache_key_src *tcks, struct tcp_heuristic_key *key)
{
        struct ifnet *ifp = tcks->ifp;
        uint8_t len = sizeof(key->thk_net_signature);
        uint16_t flags;

        if (tcks->af == AF_INET6) {
                int ret;

                key->thk_family = AF_INET6;
                ret = ifnet_get_netsignature(ifp, AF_INET6, &len, &flags,
                    key->thk_net_signature);

                /*
                 * ifnet_get_netsignature only returns EINVAL if ifn is NULL
                 * (we made sure that in the other cases it does not). So,
                 * in this case we should take the connection's address.
                 */
                if (ret == ENOENT || ret == EINVAL)
                        memcpy(&key->thk_ip.addr6, &tcks->laddr.addr6, sizeof(struct in6_addr));
        } else {
                int ret;

                key->thk_family = AF_INET;
                ret = ifnet_get_netsignature(ifp, AF_INET, &len, &flags,
                     key->thk_net_signature);

                /*
                 * ifnet_get_netsignature only returns EINVAL if ifn is NULL
                 * (we made sure that in the other cases it does not). So,
                 * in this case we should take the connection's address.
                 */
                if (ret == ENOENT || ret == EINVAL)
                        memcpy(&key->thk_ip.addr, &tcks->laddr.addr, sizeof(struct in_addr));
        }
}

static u_int16_t tcp_cache_hash(struct tcp_cache_key_src *tcks, struct tcp_cache_key *key)
{
        u_int32_t hash;

        bzero(key, sizeof(struct tcp_cache_key));

        tcp_cache_hash_src(tcks, &key->tck_src);

        if (tcks->af == AF_INET6) {
                key->tck_family = AF_INET6;
                memcpy(&key->tck_dst.addr6, &tcks->faddr.addr6,
                    sizeof(struct in6_addr));
        } else {
                key->tck_family = AF_INET;
                memcpy(&key->tck_dst.addr, &tcks->faddr.addr,
                    sizeof(struct in_addr));
        }

        hash = net_flowhash(key, sizeof(struct tcp_cache_key),
            tcp_cache_hash_seed);

        return (hash & (tcp_cache_size - 1));
}

static void tcp_cache_unlock(struct tcp_cache_head *head)
{
        lck_mtx_unlock(&head->tch_mtx);
}

/*
 * Make sure that everything that happens after tcp_getcache_with_lock()
 * is short enough to justify that you hold the per-bucket lock!!!
 *
 * Otherwise, better build another lookup-function that does not hold the
 * lock and you copy out the bits and bytes.
 *
 * That's why we provide the head as a "return"-pointer so that the caller
 * can give it back to use for tcp_cache_unlock().
 */
static struct tcp_cache *tcp_getcache_with_lock(struct tcp_cache_key_src *tcks,
    int create, struct tcp_cache_head **headarg)
{
        struct tcp_cache *tpcache = NULL;
        struct tcp_cache_head *head;
        struct tcp_cache_key key;
        u_int16_t hash;
        int i = 0;

        hash = tcp_cache_hash(tcks, &key);
        head = &tcp_cache[hash];

        lck_mtx_lock(&head->tch_mtx);

        /*** First step: Look for the tcp_cache in our bucket ***/
        SLIST_FOREACH(tpcache, &head->tcp_caches, list) {
                if (memcmp(&tpcache->tc_key, &key, sizeof(key)) == 0)
                        break;

                i++;
        }

        /*** Second step: If it's not there, create/recycle it ***/
        if ((tpcache == NULL) && create) {
                if (i >= TCP_CACHE_BUCKET_SIZE) {
                        struct tcp_cache *oldest_cache = NULL;
                        u_int32_t max_age = 0;

                        /* Look for the oldest tcp_cache in the bucket */
                        SLIST_FOREACH(tpcache, &head->tcp_caches, list) {
                                u_int32_t age = tcp_now - tpcache->tc_last_access;
                                if (age > max_age) {
                                        max_age = age;
                                        oldest_cache = tpcache;
                                }
                        }
                        VERIFY(oldest_cache != NULL);

                        tpcache = oldest_cache;

                        /* We recycle, thus let's indicate that there is no cookie */
                        tpcache->tc_tfo_cookie_len = 0;
                } else {
                        /* Create a new cache and add it to the list */
                        tpcache = _MALLOC(sizeof(struct tcp_cache), M_TEMP,
                            M_NOWAIT | M_ZERO);
                        if (tpcache == NULL)
                                goto out_null;

                        SLIST_INSERT_HEAD(&head->tcp_caches, tpcache, list);
                }

                memcpy(&tpcache->tc_key, &key, sizeof(key));
        }

        if (tpcache == NULL)
                goto out_null;

        /* Update timestamp for garbage collection purposes */
        tpcache->tc_last_access = tcp_now;
        *headarg = head;

        return (tpcache);

out_null:
        tcp_cache_unlock(head);
        return (NULL);
}

static void tcp_cache_key_src_create(struct tcpcb *tp, struct tcp_cache_key_src *tcks)
{
        struct inpcb *inp = tp->t_inpcb;
        memset(tcks, 0, sizeof(*tcks));

        tcks->ifp = inp->inp_last_outifp;

        if (inp->inp_vflag & INP_IPV6) {
                memcpy(&tcks->laddr.addr6, &inp->in6p_laddr, sizeof(struct in6_addr));
                memcpy(&tcks->faddr.addr6, &inp->in6p_faddr, sizeof(struct in6_addr));
                tcks->af = AF_INET6;
        } else {
                memcpy(&tcks->laddr.addr, &inp->inp_laddr, sizeof(struct in_addr));
                memcpy(&tcks->faddr.addr, &inp->inp_faddr, sizeof(struct in_addr));
                tcks->af = AF_INET;
        }

        return;
}

static void tcp_cache_set_cookie_common(struct tcp_cache_key_src *tcks, u_char *cookie, u_int8_t len)
{
        struct tcp_cache_head *head;
        struct tcp_cache *tpcache;

        /* Call lookup/create function */
        tpcache = tcp_getcache_with_lock(tcks, 1, &head);
        if (tpcache == NULL)
                return;

        tpcache->tc_tfo_cookie_len = len > TFO_COOKIE_LEN_MAX ?
                TFO_COOKIE_LEN_MAX : len;
        memcpy(tpcache->tc_tfo_cookie, cookie, tpcache->tc_tfo_cookie_len);

        tcp_cache_unlock(head);
}

void tcp_cache_set_cookie(struct tcpcb *tp, u_char *cookie, u_int8_t len)
{
        struct tcp_cache_key_src tcks;

        tcp_cache_key_src_create(tp, &tcks);
        tcp_cache_set_cookie_common(&tcks, cookie, len);
}

static int tcp_cache_get_cookie_common(struct tcp_cache_key_src *tcks, u_char *cookie, u_int8_t *len)
{
        struct tcp_cache_head *head;
        struct tcp_cache *tpcache;

        /* Call lookup/create function */
        tpcache = tcp_getcache_with_lock(tcks, 1, &head);
        if (tpcache == NULL) {
                return (0);
        }

        if (tpcache->tc_tfo_cookie_len == 0) {
                tcp_cache_unlock(head);
                return (0);
        }

        /*
         * Not enough space - this should never happen as it has been checked
         * in tcp_tfo_check. So, fail here!
         */
        VERIFY(tpcache->tc_tfo_cookie_len <= *len);

        memcpy(cookie, tpcache->tc_tfo_cookie, tpcache->tc_tfo_cookie_len);
        *len = tpcache->tc_tfo_cookie_len;

        tcp_cache_unlock(head);

        return (1);
}

/*
 * Get the cookie related to 'tp', and copy it into 'cookie', provided that len
 * is big enough (len designates the available memory.
 * Upon return, 'len' is set to the cookie's length.
 *
 * Returns 0 if we should request a cookie.
 * Returns 1 if the cookie has been found and written.
 */
int tcp_cache_get_cookie(struct tcpcb *tp, u_char *cookie, u_int8_t *len)
{
        struct tcp_cache_key_src tcks;

        tcp_cache_key_src_create(tp, &tcks);
        return tcp_cache_get_cookie_common(&tcks, cookie, len);
}

static unsigned int tcp_cache_get_cookie_len_common(struct tcp_cache_key_src *tcks)
{
        struct tcp_cache_head *head;
        struct tcp_cache *tpcache;
        unsigned int cookie_len;

        /* Call lookup/create function */
        tpcache = tcp_getcache_with_lock(tcks, 1, &head);
        if (tpcache == NULL)
                return (0);

        cookie_len = tpcache->tc_tfo_cookie_len;

        tcp_cache_unlock(head);

        return cookie_len;
}

unsigned int tcp_cache_get_cookie_len(struct tcpcb *tp)
{
        struct tcp_cache_key_src tcks;

        tcp_cache_key_src_create(tp, &tcks);
        return tcp_cache_get_cookie_len_common(&tcks);
}

static u_int16_t tcp_heuristics_hash(struct tcp_cache_key_src *tcks, struct tcp_heuristic_key *key)
{
        u_int32_t hash;

        bzero(key, sizeof(struct tcp_heuristic_key));

        tcp_cache_hash_src(tcks, key);

        hash = net_flowhash(key, sizeof(struct tcp_heuristic_key),
            tcp_cache_hash_seed);

        return (hash & (tcp_cache_size - 1));
}

static void tcp_heuristic_unlock(struct tcp_heuristics_head *head)
{
        lck_mtx_unlock(&head->thh_mtx);
}

/*
 * Make sure that everything that happens after tcp_getheuristic_with_lock()
 * is short enough to justify that you hold the per-bucket lock!!!
 *
 * Otherwise, better build another lookup-function that does not hold the
 * lock and you copy out the bits and bytes.
 *
 * That's why we provide the head as a "return"-pointer so that the caller
 * can give it back to use for tcp_heur_unlock().
 *
 *
 * ToDo - way too much code-duplication. We should create an interface to handle
 * bucketized hashtables with recycling of the oldest element.
 */
static struct tcp_heuristic *tcp_getheuristic_with_lock(struct tcp_cache_key_src *tcks,
    int create, struct tcp_heuristics_head **headarg)
{
        struct tcp_heuristic *tpheur = NULL;
        struct tcp_heuristics_head *head;
        struct tcp_heuristic_key key;
        u_int16_t hash;
        int i = 0;

        hash = tcp_heuristics_hash(tcks, &key);
        head = &tcp_heuristics[hash];

        lck_mtx_lock(&head->thh_mtx);

        /*** First step: Look for the tcp_heur in our bucket ***/
        SLIST_FOREACH(tpheur, &head->tcp_heuristics, list) {
                if (memcmp(&tpheur->th_key, &key, sizeof(key)) == 0)
                        break;

                i++;
        }

        /*** Second step: If it's not there, create/recycle it ***/
        if ((tpheur == NULL) && create) {
                if (i >= TCP_CACHE_BUCKET_SIZE) {
                        struct tcp_heuristic *oldest_heur = NULL;
                        u_int32_t max_age = 0;

                        /* Look for the oldest tcp_heur in the bucket */
                        SLIST_FOREACH(tpheur, &head->tcp_heuristics, list) {
                                u_int32_t age = tcp_now - tpheur->th_last_access;
                                if (age > max_age) {
                                        max_age = age;
                                        oldest_heur = tpheur;
                                }
                        }
                        VERIFY(oldest_heur != NULL);

                        tpheur = oldest_heur;

                        /* We recycle - set everything to 0 */
                        bzero(tpheur->th_val_start,
                              tpheur->th_val_end - tpheur->th_val_start);
                } else {
                        /* Create a new heuristic and add it to the list */
                        tpheur = _MALLOC(sizeof(struct tcp_heuristic), M_TEMP,
                            M_NOWAIT | M_ZERO);
                        if (tpheur == NULL)
                                goto out_null;

                        SLIST_INSERT_HEAD(&head->tcp_heuristics, tpheur, list);
                }

                /*
                 * Set to tcp_now, to make sure it won't be > than tcp_now in the
                 * near future.
                 */
                tpheur->th_ecn_backoff = tcp_now;
                tpheur->th_tfo_backoff_until = tcp_now;
                tpheur->th_mptcp_backoff = tcp_now;
                tpheur->th_tfo_backoff = tcp_min_to_hz(tcp_ecn_timeout);

                memcpy(&tpheur->th_key, &key, sizeof(key));
        }

        if (tpheur == NULL)
                goto out_null;

        /* Update timestamp for garbage collection purposes */
        tpheur->th_last_access = tcp_now;
        *headarg = head;

        return (tpheur);

out_null:
        tcp_heuristic_unlock(head);
        return (NULL);
}

static void tcp_heuristic_reset_counters(struct tcp_cache_key_src *tcks, u_int8_t flags)
{
        struct tcp_heuristics_head *head;
        struct tcp_heuristic *tpheur;

        /*
         * Don't attempt to create it! Keep the heuristics clean if the
         * server does not support TFO. This reduces the lookup-cost on
         * our side.
         */
        tpheur = tcp_getheuristic_with_lock(tcks, 0, &head);
        if (tpheur == NULL)
                return;

        if (flags & TCPCACHE_F_TFO_DATA) {
                tpheur->th_tfo_data_loss = 0;
        }

        if (flags & TCPCACHE_F_TFO_REQ) {
                tpheur->th_tfo_req_loss = 0;
        }

        if (flags & TCPCACHE_F_TFO_DATA_RST) {
                tpheur->th_tfo_data_rst = 0;
        }

        if (flags & TCPCACHE_F_TFO_REQ_RST) {
                tpheur->th_tfo_req_rst = 0;
        }

        if (flags & TCPCACHE_F_ECN) {
                tpheur->th_ecn_loss = 0;
                tpheur->th_ecn_synrst = 0;
        }

        if (flags & TCPCACHE_F_MPTCP)
                tpheur->th_mptcp_loss = 0;

        tcp_heuristic_unlock(head);
}

void tcp_heuristic_tfo_success(struct tcpcb *tp)
{
        struct tcp_cache_key_src tcks;
        uint8_t flag = 0;

        tcp_cache_key_src_create(tp, &tcks);

        if (tp->t_tfo_stats & TFO_S_SYN_DATA_SENT)
                flag = (TCPCACHE_F_TFO_DATA | TCPCACHE_F_TFO_REQ |
                        TCPCACHE_F_TFO_DATA_RST | TCPCACHE_F_TFO_REQ_RST );
        if (tp->t_tfo_stats & TFO_S_COOKIE_REQ)
                flag = (TCPCACHE_F_TFO_REQ | TCPCACHE_F_TFO_REQ_RST);

        tcp_heuristic_reset_counters(&tcks, flag);
}

void tcp_heuristic_mptcp_success(struct tcpcb *tp)
{
        struct tcp_cache_key_src tcks;

        tcp_cache_key_src_create(tp, &tcks);
        tcp_heuristic_reset_counters(&tcks, TCPCACHE_F_MPTCP);
}

void tcp_heuristic_ecn_success(struct tcpcb *tp)
{
        struct tcp_cache_key_src tcks;

        tcp_cache_key_src_create(tp, &tcks);
        tcp_heuristic_reset_counters(&tcks, TCPCACHE_F_ECN);
}

static void __tcp_heuristic_tfo_middlebox_common(struct tcp_heuristic *tpheur)
{
        if (tpheur->th_tfo_in_backoff)
                return;

        tpheur->th_tfo_in_backoff = 1;

        if (tpheur->th_tfo_enabled_time) {
                uint32_t old_backoff = tpheur->th_tfo_backoff;

                tpheur->th_tfo_backoff -= (tcp_now - tpheur->th_tfo_enabled_time);
                if (tpheur->th_tfo_backoff > old_backoff)
                        tpheur->th_tfo_backoff = tcp_min_to_hz(tcp_ecn_timeout);
        }

        tpheur->th_tfo_backoff_until = tcp_now + tpheur->th_tfo_backoff;

        /* Then, increase the backoff time */
        tpheur->th_tfo_backoff *= 2;

        if (tpheur->th_tfo_backoff > tcp_min_to_hz(tcp_backoff_maximum))
                tpheur->th_tfo_backoff = tcp_min_to_hz(tcp_ecn_timeout);
}

static void tcp_heuristic_tfo_middlebox_common(struct tcp_cache_key_src *tcks)
{
        struct tcp_heuristics_head *head;
        struct tcp_heuristic *tpheur;

        tpheur = tcp_getheuristic_with_lock(tcks, 1, &head);
        if (tpheur == NULL)
                return;

        __tcp_heuristic_tfo_middlebox_common(tpheur);

        tcp_heuristic_unlock(head);
}

static void tcp_heuristic_inc_counters(struct tcp_cache_key_src *tcks,
    u_int32_t flags)
{
        struct tcp_heuristics_head *head;
        struct tcp_heuristic *tpheur;

        tpheur = tcp_getheuristic_with_lock(tcks, 1, &head);
        if (tpheur == NULL)
                return;

        /* Limit to prevent integer-overflow during exponential backoff */
        if ((flags & TCPCACHE_F_TFO_DATA) && tpheur->th_tfo_data_loss < TCP_CACHE_OVERFLOW_PROTECT) {
                tpheur->th_tfo_data_loss++;

                if (tpheur->th_tfo_data_loss >= TFO_MAX_COOKIE_LOSS)
                        __tcp_heuristic_tfo_middlebox_common(tpheur);
        }

        if ((flags & TCPCACHE_F_TFO_REQ) && tpheur->th_tfo_req_loss < TCP_CACHE_OVERFLOW_PROTECT) {
                tpheur->th_tfo_req_loss++;

                if (tpheur->th_tfo_req_loss >= TFO_MAX_COOKIE_LOSS)
                        __tcp_heuristic_tfo_middlebox_common(tpheur);
        }

        if ((flags & TCPCACHE_F_TFO_DATA_RST) && tpheur->th_tfo_data_rst < TCP_CACHE_OVERFLOW_PROTECT) {
                tpheur->th_tfo_data_rst++;

                if (tpheur->th_tfo_data_rst >= TFO_MAX_COOKIE_LOSS)
                        __tcp_heuristic_tfo_middlebox_common(tpheur);
        }

        if ((flags & TCPCACHE_F_TFO_REQ_RST) && tpheur->th_tfo_req_rst < TCP_CACHE_OVERFLOW_PROTECT) {
                tpheur->th_tfo_req_rst++;

                if (tpheur->th_tfo_req_rst >= TFO_MAX_COOKIE_LOSS)
                        __tcp_heuristic_tfo_middlebox_common(tpheur);
        }

        if ((flags & TCPCACHE_F_ECN) && tpheur->th_ecn_loss < TCP_CACHE_OVERFLOW_PROTECT) {
                tpheur->th_ecn_loss++;
                if (tpheur->th_ecn_loss >= ECN_MAX_SYN_LOSS) {
                        tcpstat.tcps_ecn_fallback_synloss++;
                        TCP_CACHE_INC_IFNET_STAT(tcks->ifp, tcks->af, ecn_fallback_synloss);
                        tpheur->th_ecn_backoff = tcp_now +
                            (tcp_min_to_hz(tcp_ecn_timeout) <<
                            (tpheur->th_ecn_loss - ECN_MAX_SYN_LOSS));
                }
        }

        if ((flags & TCPCACHE_F_MPTCP) &&
            tpheur->th_mptcp_loss < TCP_CACHE_OVERFLOW_PROTECT) {
                tpheur->th_mptcp_loss++;
                if (tpheur->th_mptcp_loss >= MPTCP_MAX_SYN_LOSS) {
                        /*
                         * Yes, we take tcp_ecn_timeout, to avoid adding yet
                         * another sysctl that is just used for testing.
                         */
                        tpheur->th_mptcp_backoff = tcp_now +
                            (tcp_min_to_hz(tcp_ecn_timeout) <<
                            (tpheur->th_mptcp_loss - MPTCP_MAX_SYN_LOSS));
                }
        }

        if ((flags & TCPCACHE_F_ECN_DROPRST) &&
            tpheur->th_ecn_droprst < TCP_CACHE_OVERFLOW_PROTECT) {
                tpheur->th_ecn_droprst++;
                if (tpheur->th_ecn_droprst >= ECN_MAX_DROPRST) {
                        tcpstat.tcps_ecn_fallback_droprst++;
                        TCP_CACHE_INC_IFNET_STAT(tcks->ifp, tcks->af,
                            ecn_fallback_droprst);
                        tpheur->th_ecn_backoff = tcp_now +
                            (tcp_min_to_hz(tcp_ecn_timeout) <<
                            (tpheur->th_ecn_droprst - ECN_MAX_DROPRST));

                }
        }

        if ((flags & TCPCACHE_F_ECN_DROPRXMT) &&
            tpheur->th_ecn_droprxmt < TCP_CACHE_OVERFLOW_PROTECT) {
                tpheur->th_ecn_droprxmt++;
                if (tpheur->th_ecn_droprxmt >= ECN_MAX_DROPRXMT) {
                        tcpstat.tcps_ecn_fallback_droprxmt++;
                        TCP_CACHE_INC_IFNET_STAT(tcks->ifp, tcks->af,
                            ecn_fallback_droprxmt);
                        tpheur->th_ecn_backoff = tcp_now +
                            (tcp_min_to_hz(tcp_ecn_timeout) <<
                            (tpheur->th_ecn_droprxmt - ECN_MAX_DROPRXMT));
                }
        }
        if ((flags & TCPCACHE_F_ECN_SYNRST) &&
            tpheur->th_ecn_synrst < TCP_CACHE_OVERFLOW_PROTECT) {
                tpheur->th_ecn_synrst++;
                if (tpheur->th_ecn_synrst >= ECN_MAX_SYNRST) {
                        tcpstat.tcps_ecn_fallback_synrst++;
                        TCP_CACHE_INC_IFNET_STAT(tcks->ifp, tcks->af,
                            ecn_fallback_synrst);
                        tpheur->th_ecn_backoff = tcp_now +
                            (tcp_min_to_hz(tcp_ecn_timeout) <<
                            (tpheur->th_ecn_synrst - ECN_MAX_SYNRST));
                }
        }
        tcp_heuristic_unlock(head);
}

void tcp_heuristic_tfo_loss(struct tcpcb *tp)
{
        struct tcp_cache_key_src tcks;
        uint32_t flag = 0;

        tcp_cache_key_src_create(tp, &tcks);

        if (tp->t_tfo_stats & TFO_S_SYN_DATA_SENT)
                flag = (TCPCACHE_F_TFO_DATA | TCPCACHE_F_TFO_REQ);
        if (tp->t_tfo_stats & TFO_S_COOKIE_REQ)
                flag = TCPCACHE_F_TFO_REQ;

        tcp_heuristic_inc_counters(&tcks, flag);
}

void tcp_heuristic_tfo_rst(struct tcpcb *tp)
{
        struct tcp_cache_key_src tcks;
        uint32_t flag = 0;

        tcp_cache_key_src_create(tp, &tcks);

        if (tp->t_tfo_stats & TFO_S_SYN_DATA_SENT)
                flag = (TCPCACHE_F_TFO_DATA_RST | TCPCACHE_F_TFO_REQ_RST);
        if (tp->t_tfo_stats & TFO_S_COOKIE_REQ)
                flag = TCPCACHE_F_TFO_REQ_RST;

        tcp_heuristic_inc_counters(&tcks, flag);
}

void tcp_heuristic_mptcp_loss(struct tcpcb *tp)
{
        struct tcp_cache_key_src tcks;

        tcp_cache_key_src_create(tp, &tcks);

        tcp_heuristic_inc_counters(&tcks, TCPCACHE_F_MPTCP);
}

void tcp_heuristic_ecn_loss(struct tcpcb *tp)
{
        struct tcp_cache_key_src tcks;

        tcp_cache_key_src_create(tp, &tcks);

        tcp_heuristic_inc_counters(&tcks, TCPCACHE_F_ECN);
}

void tcp_heuristic_ecn_droprst(struct tcpcb *tp)
{
        struct tcp_cache_key_src tcks;

        tcp_cache_key_src_create(tp, &tcks);

        tcp_heuristic_inc_counters(&tcks, TCPCACHE_F_ECN_DROPRST);
}

void tcp_heuristic_ecn_droprxmt(struct tcpcb *tp)
{
        struct tcp_cache_key_src tcks;

        tcp_cache_key_src_create(tp, &tcks);

        tcp_heuristic_inc_counters(&tcks, TCPCACHE_F_ECN_DROPRXMT);
}

void tcp_heuristic_ecn_synrst(struct tcpcb *tp)
{
        struct tcp_cache_key_src tcks;

        tcp_cache_key_src_create(tp, &tcks);

        tcp_heuristic_inc_counters(&tcks, TCPCACHE_F_ECN_SYNRST);
}

void tcp_heuristic_tfo_middlebox(struct tcpcb *tp)
{
        struct tcp_cache_key_src tcks;

        tp->t_tfo_flags |= TFO_F_HEURISTIC_DONE;

        tcp_cache_key_src_create(tp, &tcks);
        tcp_heuristic_tfo_middlebox_common(&tcks);
}

static void tcp_heuristic_ecn_aggressive_common(struct tcp_cache_key_src *tcks)
{
        struct tcp_heuristics_head *head;
        struct tcp_heuristic *tpheur;

        tpheur = tcp_getheuristic_with_lock(tcks, 1, &head);
        if (tpheur == NULL)
                return;

        /* Must be done before, otherwise we will start off with expo-backoff */
        tpheur->th_ecn_backoff = tcp_now +
                (tcp_min_to_hz(tcp_ecn_timeout) << (tpheur->th_ecn_aggressive));

        /*
         * Ugly way to prevent integer overflow... limit to prevent in
         * overflow during exp. backoff.
         */
        if (tpheur->th_ecn_aggressive < TCP_CACHE_OVERFLOW_PROTECT)
                tpheur->th_ecn_aggressive++;

        tcp_heuristic_unlock(head);
}

void tcp_heuristic_ecn_aggressive(struct tcpcb *tp)
{
        struct tcp_cache_key_src tcks;

        tcp_cache_key_src_create(tp, &tcks);
        tcp_heuristic_ecn_aggressive_common(&tcks);
}

static boolean_t tcp_heuristic_do_tfo_common(struct tcp_cache_key_src *tcks)
{
        struct tcp_heuristics_head *head;
        struct tcp_heuristic *tpheur;

        if (disable_tcp_heuristics)
                return (TRUE);

        /* Get the tcp-heuristic. */
        tpheur = tcp_getheuristic_with_lock(tcks, 0, &head);
        if (tpheur == NULL)
                return (TRUE);

        if (tpheur->th_tfo_in_backoff == 0)
                goto tfo_ok;

        if (TSTMP_GT(tcp_now, tpheur->th_tfo_backoff_until)) {
                tpheur->th_tfo_in_backoff = 0;
                tpheur->th_tfo_enabled_time = tcp_now;

                goto tfo_ok;
        }

        tcp_heuristic_unlock(head);
        return (FALSE);

tfo_ok:
        tcp_heuristic_unlock(head);
        return (TRUE);
}

boolean_t tcp_heuristic_do_tfo(struct tcpcb *tp)
{
        struct tcp_cache_key_src tcks;

        tcp_cache_key_src_create(tp, &tcks);
        if (tcp_heuristic_do_tfo_common(&tcks))
                return (TRUE);

        return (FALSE);
}

boolean_t tcp_heuristic_do_mptcp(struct tcpcb *tp)
{
        struct tcp_cache_key_src tcks;
        struct tcp_heuristics_head *head = NULL;
        struct tcp_heuristic *tpheur;

        if (disable_tcp_heuristics)
                return (TRUE);

        tcp_cache_key_src_create(tp, &tcks);

        /* Get the tcp-heuristic. */
        tpheur = tcp_getheuristic_with_lock(&tcks, 0, &head);
        if (tpheur == NULL)
                return (TRUE);

        if (TSTMP_GT(tpheur->th_mptcp_backoff, tcp_now))
                goto fallback;

        tcp_heuristic_unlock(head);

        return (TRUE);

fallback:
        if (head)
                tcp_heuristic_unlock(head);

        if (tptomptp(tp)->mpt_mpte->mpte_flags & MPTE_FIRSTPARTY)
                tcpstat.tcps_mptcp_fp_heuristic_fallback++;
        else
                tcpstat.tcps_mptcp_heuristic_fallback++;

        return (FALSE);
}

static boolean_t tcp_heuristic_do_ecn_common(struct tcp_cache_key_src *tcks)
{
        struct tcp_heuristics_head *head;
        struct tcp_heuristic *tpheur;
        boolean_t ret = TRUE;

        if (disable_tcp_heuristics)
                return (TRUE);

        /* Get the tcp-heuristic. */
        tpheur = tcp_getheuristic_with_lock(tcks, 0, &head);
        if (tpheur == NULL)
                return ret;

        if (TSTMP_GT(tpheur->th_ecn_backoff, tcp_now)) {
                ret = FALSE;
        } else {
                /* Reset the following counters to start re-evaluating */
                if (tpheur->th_ecn_droprst >= ECN_RETRY_LIMIT)
                        tpheur->th_ecn_droprst = 0;
                if (tpheur->th_ecn_droprxmt >= ECN_RETRY_LIMIT)
                        tpheur->th_ecn_droprxmt = 0;
                if (tpheur->th_ecn_synrst >= ECN_RETRY_LIMIT)
                        tpheur->th_ecn_synrst = 0;
        }

        tcp_heuristic_unlock(head);

        return (ret);
}

boolean_t tcp_heuristic_do_ecn(struct tcpcb *tp)
{
        struct tcp_cache_key_src tcks;

        tcp_cache_key_src_create(tp, &tcks);
        return tcp_heuristic_do_ecn_common(&tcks);
}

boolean_t tcp_heuristic_do_ecn_with_address(struct ifnet *ifp,
    union sockaddr_in_4_6 *local_address)
{
        struct tcp_cache_key_src tcks;

        memset(&tcks, 0, sizeof(tcks));
        tcks.ifp = ifp;

        calculate_tcp_clock();

        if (local_address->sa.sa_family == AF_INET6) {
                memcpy(&tcks.laddr.addr6, &local_address->sin6.sin6_addr, sizeof(struct in6_addr));
                tcks.af = AF_INET6;
        } else if (local_address->sa.sa_family == AF_INET) {
                memcpy(&tcks.laddr.addr, &local_address->sin.sin_addr, sizeof(struct in_addr));
                tcks.af = AF_INET;
        }

        return tcp_heuristic_do_ecn_common(&tcks);
}

void tcp_heuristics_ecn_update(struct necp_tcp_ecn_cache *necp_buffer,
    struct ifnet *ifp, union sockaddr_in_4_6 *local_address)
{
        struct tcp_cache_key_src tcks;

        memset(&tcks, 0, sizeof(tcks));
        tcks.ifp = ifp;

        calculate_tcp_clock();

        if (local_address->sa.sa_family == AF_INET6) {
                memcpy(&tcks.laddr.addr6, &local_address->sin6.sin6_addr, sizeof(struct in6_addr));
                tcks.af = AF_INET6;
        } else if (local_address->sa.sa_family == AF_INET) {
                memcpy(&tcks.laddr.addr, &local_address->sin.sin_addr, sizeof(struct in_addr));
                tcks.af = AF_INET;
        }

        if (necp_buffer->necp_tcp_ecn_heuristics_success) {
                tcp_heuristic_reset_counters(&tcks, TCPCACHE_F_ECN);
        } else if (necp_buffer->necp_tcp_ecn_heuristics_loss) {
                tcp_heuristic_inc_counters(&tcks, TCPCACHE_F_ECN);
        } else if (necp_buffer->necp_tcp_ecn_heuristics_drop_rst) {
                tcp_heuristic_inc_counters(&tcks, TCPCACHE_F_ECN_DROPRST);
        } else if (necp_buffer->necp_tcp_ecn_heuristics_drop_rxmt) {
                tcp_heuristic_inc_counters(&tcks, TCPCACHE_F_ECN_DROPRXMT);
        } else if (necp_buffer->necp_tcp_ecn_heuristics_syn_rst) {
                tcp_heuristic_inc_counters(&tcks, TCPCACHE_F_ECN_SYNRST);
        } else if (necp_buffer->necp_tcp_ecn_heuristics_aggressive) {
                tcp_heuristic_ecn_aggressive_common(&tcks);
        }

        return;
}

boolean_t tcp_heuristic_do_tfo_with_address(struct ifnet *ifp,
    union sockaddr_in_4_6 *local_address, union sockaddr_in_4_6 *remote_address,
    u_int8_t *cookie, u_int8_t *cookie_len)
{
        struct tcp_cache_key_src tcks;

        memset(&tcks, 0, sizeof(tcks));
        tcks.ifp = ifp;

        calculate_tcp_clock();

        if (remote_address->sa.sa_family == AF_INET6) {
                memcpy(&tcks.laddr.addr6, &local_address->sin6.sin6_addr, sizeof(struct in6_addr));
                memcpy(&tcks.faddr.addr6, &remote_address->sin6.sin6_addr, sizeof(struct in6_addr));
                tcks.af = AF_INET6;
        } else if (remote_address->sa.sa_family == AF_INET) {
                memcpy(&tcks.laddr.addr, &local_address->sin.sin_addr, sizeof(struct in_addr));
                memcpy(&tcks.faddr.addr, &remote_address->sin.sin_addr, sizeof(struct in_addr));
                tcks.af = AF_INET;
        }

        if (tcp_heuristic_do_tfo_common(&tcks)) {
                if (!tcp_cache_get_cookie_common(&tcks, cookie, cookie_len)) {
                    *cookie_len = 0;
                }
                return TRUE;
        }

        return FALSE;
}

void tcp_heuristics_tfo_update(struct necp_tcp_tfo_cache *necp_buffer,
    struct ifnet *ifp, union sockaddr_in_4_6 *local_address,
    union sockaddr_in_4_6 *remote_address)
{
        struct tcp_cache_key_src tcks;

        memset(&tcks, 0, sizeof(tcks));
        tcks.ifp = ifp;

        calculate_tcp_clock();

        if (remote_address->sa.sa_family == AF_INET6) {
                memcpy(&tcks.laddr.addr6, &local_address->sin6.sin6_addr, sizeof(struct in6_addr));
                memcpy(&tcks.faddr.addr6, &remote_address->sin6.sin6_addr, sizeof(struct in6_addr));
                tcks.af = AF_INET6;
        } else if (remote_address->sa.sa_family == AF_INET) {
                memcpy(&tcks.laddr.addr, &local_address->sin.sin_addr, sizeof(struct in_addr));
                memcpy(&tcks.faddr.addr, &remote_address->sin.sin_addr, sizeof(struct in_addr));
                tcks.af = AF_INET;
        }

        if (necp_buffer->necp_tcp_tfo_heuristics_success)
                tcp_heuristic_reset_counters(&tcks, TCPCACHE_F_TFO_REQ | TCPCACHE_F_TFO_DATA |
                                                    TCPCACHE_F_TFO_REQ_RST | TCPCACHE_F_TFO_DATA_RST);

        if (necp_buffer->necp_tcp_tfo_heuristics_success_req)
                tcp_heuristic_reset_counters(&tcks, TCPCACHE_F_TFO_REQ | TCPCACHE_F_TFO_REQ_RST);

        if (necp_buffer->necp_tcp_tfo_heuristics_loss)
                tcp_heuristic_inc_counters(&tcks, TCPCACHE_F_TFO_REQ | TCPCACHE_F_TFO_DATA);

        if (necp_buffer->necp_tcp_tfo_heuristics_loss_req)
                tcp_heuristic_inc_counters(&tcks, TCPCACHE_F_TFO_REQ);

        if (necp_buffer->necp_tcp_tfo_heuristics_rst_data)
                tcp_heuristic_inc_counters(&tcks, TCPCACHE_F_TFO_REQ_RST | TCPCACHE_F_TFO_DATA_RST);

        if (necp_buffer->necp_tcp_tfo_heuristics_rst_req)
                tcp_heuristic_inc_counters(&tcks, TCPCACHE_F_TFO_REQ_RST);

        if (necp_buffer->necp_tcp_tfo_heuristics_middlebox)
                tcp_heuristic_tfo_middlebox_common(&tcks);

        if (necp_buffer->necp_tcp_tfo_cookie_len != 0) {
                tcp_cache_set_cookie_common(&tcks,
                        necp_buffer->necp_tcp_tfo_cookie, necp_buffer->necp_tcp_tfo_cookie_len);
        }

        return;
}

static void sysctl_cleartfocache(void)
{
        int i;

        for (i = 0; i < tcp_cache_size; i++) {
                struct tcp_cache_head *head = &tcp_cache[i];
                struct tcp_cache *tpcache, *tmp;
                struct tcp_heuristics_head *hhead = &tcp_heuristics[i];
                struct tcp_heuristic *tpheur, *htmp;

                lck_mtx_lock(&head->tch_mtx);
                SLIST_FOREACH_SAFE(tpcache, &head->tcp_caches, list, tmp) {
                        SLIST_REMOVE(&head->tcp_caches, tpcache, tcp_cache, list);
                        _FREE(tpcache, M_TEMP);
                }
                lck_mtx_unlock(&head->tch_mtx);

                lck_mtx_lock(&hhead->thh_mtx);
                SLIST_FOREACH_SAFE(tpheur, &hhead->tcp_heuristics, list, htmp) {
                        SLIST_REMOVE(&hhead->tcp_heuristics, tpheur, tcp_heuristic, list);
                        _FREE(tpheur, M_TEMP);
                }
                lck_mtx_unlock(&hhead->thh_mtx);
        }
}

/* This sysctl is useful for testing purposes only */
static int tcpcleartfo = 0;

static int sysctl_cleartfo SYSCTL_HANDLER_ARGS
{
#pragma unused(arg1, arg2)
        int error = 0, val, oldval = tcpcleartfo;

        val = oldval;
        error = sysctl_handle_int(oidp, &val, 0, req);
        if (error || !req->newptr)
                return (error);

        /*
         * The actual value does not matter. If the value is set, it triggers
         * the clearing of the TFO cache. If a future implementation does not
         * use the route entry to hold the TFO cache, replace the route sysctl.
         */

        if (val != oldval)
                sysctl_cleartfocache();

        tcpcleartfo = val;

        return (error);
}

SYSCTL_PROC(_net_inet_tcp, OID_AUTO, clear_tfocache, CTLTYPE_INT | CTLFLAG_RW |
        CTLFLAG_LOCKED, &tcpcleartfo, 0, &sysctl_cleartfo, "I",
        "Toggle to clear the TFO destination based heuristic cache");

void tcp_cache_init(void)
{
        uint64_t sane_size_meg = sane_size / 1024 / 1024;
        int i;

        /*
         * On machines with <100MB of memory this will result in a (full) cache-size
         * of 32 entries, thus 32 * 5 * 64bytes = 10KB. (about 0.01 %)
         * On machines with > 4GB of memory, we have a cache-size of 1024 entries,
         * thus about 327KB.
         *
         * Side-note: we convert to u_int32_t. If sane_size is more than
         * 16000 TB, we loose precision. But, who cares? :)
         */
        tcp_cache_size = tcp_cache_roundup2((u_int32_t)(sane_size_meg >> 2));
        if (tcp_cache_size < 32)
                tcp_cache_size = 32;
        else if (tcp_cache_size > 1024)
                tcp_cache_size = 1024;

        tcp_cache = _MALLOC(sizeof(struct tcp_cache_head) * tcp_cache_size,
            M_TEMP, M_ZERO);
        if (tcp_cache == NULL)
                panic("Allocating tcp_cache failed at boot-time!");

        tcp_cache_mtx_grp_attr = lck_grp_attr_alloc_init();
        tcp_cache_mtx_grp = lck_grp_alloc_init("tcpcache", tcp_cache_mtx_grp_attr);
        tcp_cache_mtx_attr = lck_attr_alloc_init();

        tcp_heuristics = _MALLOC(sizeof(struct tcp_heuristics_head) * tcp_cache_size,
            M_TEMP, M_ZERO);
        if (tcp_heuristics == NULL)
                panic("Allocating tcp_heuristic failed at boot-time!");

        tcp_heuristic_mtx_grp_attr = lck_grp_attr_alloc_init();
        tcp_heuristic_mtx_grp = lck_grp_alloc_init("tcpheuristic", tcp_heuristic_mtx_grp_attr);
        tcp_heuristic_mtx_attr = lck_attr_alloc_init();

        for (i = 0; i < tcp_cache_size; i++) {
                lck_mtx_init(&tcp_cache[i].tch_mtx, tcp_cache_mtx_grp,
                    tcp_cache_mtx_attr);
                SLIST_INIT(&tcp_cache[i].tcp_caches);

                lck_mtx_init(&tcp_heuristics[i].thh_mtx, tcp_heuristic_mtx_grp,
                    tcp_heuristic_mtx_attr);
                SLIST_INIT(&tcp_heuristics[i].tcp_heuristics);
        }

        tcp_cache_hash_seed = RandomULong();
}