source: rtems-libbsd/freebsd/netinet/tcp_hostcache.c @ 39292ce

#include <freebsd/machine/rtems-bsd-config.h>

/*-
 * Copyright (c) 2002 Andre Oppermann, Internet Business Solutions AG
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote
 *    products derived from this software without specific prior written
 *    permission.
 *
 * 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.
 */

/*
 * The tcp_hostcache moves the tcp-specific cached metrics from the routing
 * table to a dedicated structure indexed by the remote IP address.  It keeps
 * information on the measured TCP parameters of past TCP sessions to allow
 * better initial start values to be used with later connections to/from the
 * same source.  Depending on the network parameters (delay, bandwidth, max
 * MTU, congestion window) between local and remote sites, this can lead to
 * significant speed-ups for new TCP connections after the first one.
 *
 * Due to the tcp_hostcache, all TCP-specific metrics information in the
 * routing table have been removed.  The inpcb no longer keeps a pointer to
 * the routing entry, and protocol-initiated route cloning has been removed
 * as well.  With these changes, the routing table has gone back to being
 * more lightwight and only carries information related to packet forwarding.
 *
 * tcp_hostcache is designed for multiple concurrent access in SMP
 * environments and high contention.  All bucket rows have their own lock and
 * thus multiple lookups and modifies can be done at the same time as long as
 * they are in different bucket rows.  If a request for insertion of a new
 * record can't be satisfied, it simply returns an empty structure.  Nobody
 * and nothing outside of tcp_hostcache.c will ever point directly to any
 * entry in the tcp_hostcache.  All communication is done in an
 * object-oriented way and only functions of tcp_hostcache will manipulate
 * hostcache entries.  Otherwise, we are unable to achieve good behaviour in
 * concurrent access situations.  Since tcp_hostcache is only caching
 * information, there are no fatal consequences if we either can't satisfy
 * any particular request or have to drop/overwrite an existing entry because
 * of bucket limit memory constrains.
 */

/*
 * Many thanks to jlemon for basic structure of tcp_syncache which is being
 * followed here.
 */

#include <freebsd/sys/cdefs.h>
__FBSDID("$FreeBSD$");

#include <freebsd/local/opt_inet6.h>

#include <freebsd/sys/param.h>
#include <freebsd/sys/systm.h>
#include <freebsd/sys/kernel.h>
#include <freebsd/sys/lock.h>
#include <freebsd/sys/mutex.h>
#include <freebsd/sys/malloc.h>
#include <freebsd/sys/socket.h>
#include <freebsd/sys/socketvar.h>
#include <freebsd/sys/sysctl.h>

#include <freebsd/net/if.h>
#include <freebsd/net/route.h>
#include <freebsd/net/vnet.h>

#include <freebsd/netinet/in.h>
#include <freebsd/netinet/in_systm.h>
#include <freebsd/netinet/ip.h>
#include <freebsd/netinet/in_var.h>
#include <freebsd/netinet/in_pcb.h>
#include <freebsd/netinet/ip_var.h>
#ifdef INET6
#include <freebsd/netinet/ip6.h>
#include <freebsd/netinet6/ip6_var.h>
#endif
#include <freebsd/netinet/tcp.h>
#include <freebsd/netinet/tcp_var.h>
#include <freebsd/netinet/tcp_hostcache.h>
#ifdef INET6
#include <freebsd/netinet6/tcp6_var.h>
#endif

#include <freebsd/vm/uma.h>

/* Arbitrary values */
#define TCP_HOSTCACHE_HASHSIZE          512
#define TCP_HOSTCACHE_BUCKETLIMIT       30
#define TCP_HOSTCACHE_EXPIRE            60*60   /* one hour */
#define TCP_HOSTCACHE_PRUNE             5*60    /* every 5 minutes */

static VNET_DEFINE(struct tcp_hostcache, tcp_hostcache);
#define V_tcp_hostcache         VNET(tcp_hostcache)

static VNET_DEFINE(struct callout, tcp_hc_callout);
#define V_tcp_hc_callout        VNET(tcp_hc_callout)

static struct hc_metrics *tcp_hc_lookup(struct in_conninfo *);
static struct hc_metrics *tcp_hc_insert(struct in_conninfo *);
static int sysctl_tcp_hc_list(SYSCTL_HANDLER_ARGS);
static void tcp_hc_purge_internal(int);
static void tcp_hc_purge(void *);

SYSCTL_NODE(_net_inet_tcp, OID_AUTO, hostcache, CTLFLAG_RW, 0,
    "TCP Host cache");

SYSCTL_VNET_INT(_net_inet_tcp_hostcache, OID_AUTO, cachelimit, CTLFLAG_RDTUN,
    &VNET_NAME(tcp_hostcache.cache_limit), 0,
    "Overall entry limit for hostcache");

SYSCTL_VNET_INT(_net_inet_tcp_hostcache, OID_AUTO, hashsize, CTLFLAG_RDTUN,
    &VNET_NAME(tcp_hostcache.hashsize), 0,
    "Size of TCP hostcache hashtable");

SYSCTL_VNET_INT(_net_inet_tcp_hostcache, OID_AUTO, bucketlimit,
    CTLFLAG_RDTUN, &VNET_NAME(tcp_hostcache.bucket_limit), 0,
    "Per-bucket hash limit for hostcache");

SYSCTL_VNET_INT(_net_inet_tcp_hostcache, OID_AUTO, count, CTLFLAG_RD,
     &VNET_NAME(tcp_hostcache.cache_count), 0,
    "Current number of entries in hostcache");

SYSCTL_VNET_INT(_net_inet_tcp_hostcache, OID_AUTO, expire, CTLFLAG_RW,
    &VNET_NAME(tcp_hostcache.expire), 0,
    "Expire time of TCP hostcache entries");

SYSCTL_VNET_INT(_net_inet_tcp_hostcache, OID_AUTO, prune, CTLFLAG_RW,
    &VNET_NAME(tcp_hostcache.prune), 0,
    "Time between purge runs");

SYSCTL_VNET_INT(_net_inet_tcp_hostcache, OID_AUTO, purge, CTLFLAG_RW,
    &VNET_NAME(tcp_hostcache.purgeall), 0,
    "Expire all entires on next purge run");

SYSCTL_PROC(_net_inet_tcp_hostcache, OID_AUTO, list,
    CTLTYPE_STRING | CTLFLAG_RD | CTLFLAG_SKIP, 0, 0,
    sysctl_tcp_hc_list, "A", "List of all hostcache entries");


static MALLOC_DEFINE(M_HOSTCACHE, "hostcache", "TCP hostcache");

#define HOSTCACHE_HASH(ip) \
        (((ip)->s_addr ^ ((ip)->s_addr >> 7) ^ ((ip)->s_addr >> 17)) &  \
          V_tcp_hostcache.hashmask)

/* XXX: What is the recommended hash to get good entropy for IPv6 addresses? */
#define HOSTCACHE_HASH6(ip6)                            \
        (((ip6)->s6_addr32[0] ^                         \
          (ip6)->s6_addr32[1] ^                         \
          (ip6)->s6_addr32[2] ^                         \
          (ip6)->s6_addr32[3]) &                        \
         V_tcp_hostcache.hashmask)

#define THC_LOCK(lp)            mtx_lock(lp)
#define THC_UNLOCK(lp)          mtx_unlock(lp)

void
tcp_hc_init(void)
{
        int i;

        /*
         * Initialize hostcache structures.
         */
        V_tcp_hostcache.cache_count = 0;
        V_tcp_hostcache.hashsize = TCP_HOSTCACHE_HASHSIZE;
        V_tcp_hostcache.bucket_limit = TCP_HOSTCACHE_BUCKETLIMIT;
        V_tcp_hostcache.cache_limit =
            V_tcp_hostcache.hashsize * V_tcp_hostcache.bucket_limit;
        V_tcp_hostcache.expire = TCP_HOSTCACHE_EXPIRE;
        V_tcp_hostcache.prune = TCP_HOSTCACHE_PRUNE;

        TUNABLE_INT_FETCH("net.inet.tcp.hostcache.hashsize",
            &V_tcp_hostcache.hashsize);
        TUNABLE_INT_FETCH("net.inet.tcp.hostcache.cachelimit",
            &V_tcp_hostcache.cache_limit);
        TUNABLE_INT_FETCH("net.inet.tcp.hostcache.bucketlimit",
            &V_tcp_hostcache.bucket_limit);
        if (!powerof2(V_tcp_hostcache.hashsize)) {
                printf("WARNING: hostcache hash size is not a power of 2.\n");
                V_tcp_hostcache.hashsize = TCP_HOSTCACHE_HASHSIZE; /* default */
        }
        V_tcp_hostcache.hashmask = V_tcp_hostcache.hashsize - 1;

        /*
         * Allocate the hash table.
         */
        V_tcp_hostcache.hashbase = (struct hc_head *)
            malloc(V_tcp_hostcache.hashsize * sizeof(struct hc_head),
                   M_HOSTCACHE, M_WAITOK | M_ZERO);

        /*
         * Initialize the hash buckets.
         */
        for (i = 0; i < V_tcp_hostcache.hashsize; i++) {
                TAILQ_INIT(&V_tcp_hostcache.hashbase[i].hch_bucket);
                V_tcp_hostcache.hashbase[i].hch_length = 0;
                mtx_init(&V_tcp_hostcache.hashbase[i].hch_mtx, "tcp_hc_entry",
                          NULL, MTX_DEF);
        }

        /*
         * Allocate the hostcache entries.
         */
        V_tcp_hostcache.zone =
            uma_zcreate("hostcache", sizeof(struct hc_metrics),
            NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
        uma_zone_set_max(V_tcp_hostcache.zone, V_tcp_hostcache.cache_limit);

        /*
         * Set up periodic cache cleanup.
         */
        callout_init(&V_tcp_hc_callout, CALLOUT_MPSAFE);
        callout_reset(&V_tcp_hc_callout, V_tcp_hostcache.prune * hz,
            tcp_hc_purge, curvnet);
}

#ifdef VIMAGE
void
tcp_hc_destroy(void)
{
        int i;

        callout_drain(&V_tcp_hc_callout);

        /* Purge all hc entries. */
        tcp_hc_purge_internal(1);

        /* Free the uma zone and the allocated hash table. */
        uma_zdestroy(V_tcp_hostcache.zone);

        for (i = 0; i < V_tcp_hostcache.hashsize; i++)
                mtx_destroy(&V_tcp_hostcache.hashbase[i].hch_mtx);
        free(V_tcp_hostcache.hashbase, M_HOSTCACHE);
}
#endif

/*
 * Internal function: look up an entry in the hostcache or return NULL.
 *
 * If an entry has been returned, the caller becomes responsible for
 * unlocking the bucket row after he is done reading/modifying the entry.
 */
static struct hc_metrics *
tcp_hc_lookup(struct in_conninfo *inc)
{
        int hash;
        struct hc_head *hc_head;
        struct hc_metrics *hc_entry;

        KASSERT(inc != NULL, ("tcp_hc_lookup with NULL in_conninfo pointer"));

        /*
         * Hash the foreign ip address.
         */
        if (inc->inc_flags & INC_ISIPV6)
                hash = HOSTCACHE_HASH6(&inc->inc6_faddr);
        else
                hash = HOSTCACHE_HASH(&inc->inc_faddr);

        hc_head = &V_tcp_hostcache.hashbase[hash];

        /*
         * Acquire lock for this bucket row; we release the lock if we don't
         * find an entry, otherwise the caller has to unlock after he is
         * done.
         */
        THC_LOCK(&hc_head->hch_mtx);

        /*
         * Iterate through entries in bucket row looking for a match.
         */
        TAILQ_FOREACH(hc_entry, &hc_head->hch_bucket, rmx_q) {
                if (inc->inc_flags & INC_ISIPV6) {
                        if (memcmp(&inc->inc6_faddr, &hc_entry->ip6,
                            sizeof(inc->inc6_faddr)) == 0)
                                return hc_entry;
                } else {
                        if (memcmp(&inc->inc_faddr, &hc_entry->ip4,
                            sizeof(inc->inc_faddr)) == 0)
                                return hc_entry;
                }
        }

        /*
         * We were unsuccessful and didn't find anything.
         */
        THC_UNLOCK(&hc_head->hch_mtx);
        return NULL;
}

/*
 * Internal function: insert an entry into the hostcache or return NULL if
 * unable to allocate a new one.
 *
 * If an entry has been returned, the caller becomes responsible for
 * unlocking the bucket row after he is done reading/modifying the entry.
 */
static struct hc_metrics *
tcp_hc_insert(struct in_conninfo *inc)
{
        int hash;
        struct hc_head *hc_head;
        struct hc_metrics *hc_entry;

        KASSERT(inc != NULL, ("tcp_hc_insert with NULL in_conninfo pointer"));

        /*
         * Hash the foreign ip address.
         */
        if (inc->inc_flags & INC_ISIPV6)
                hash = HOSTCACHE_HASH6(&inc->inc6_faddr);
        else
                hash = HOSTCACHE_HASH(&inc->inc_faddr);

        hc_head = &V_tcp_hostcache.hashbase[hash];

        /*
         * Acquire lock for this bucket row; we release the lock if we don't
         * find an entry, otherwise the caller has to unlock after he is
         * done.
         */
        THC_LOCK(&hc_head->hch_mtx);

        /*
         * If the bucket limit is reached, reuse the least-used element.
         */
        if (hc_head->hch_length >= V_tcp_hostcache.bucket_limit ||
            V_tcp_hostcache.cache_count >= V_tcp_hostcache.cache_limit) {
                hc_entry = TAILQ_LAST(&hc_head->hch_bucket, hc_qhead);
                /*
                 * At first we were dropping the last element, just to
                 * reacquire it in the next two lines again, which isn't very
                 * efficient.  Instead just reuse the least used element.
                 * We may drop something that is still "in-use" but we can be
                 * "lossy".
                 * Just give up if this bucket row is empty and we don't have
                 * anything to replace.
                 */
                if (hc_entry == NULL) {
                        THC_UNLOCK(&hc_head->hch_mtx);
                        return NULL;
                }
                TAILQ_REMOVE(&hc_head->hch_bucket, hc_entry, rmx_q);
                V_tcp_hostcache.hashbase[hash].hch_length--;
                V_tcp_hostcache.cache_count--;
                TCPSTAT_INC(tcps_hc_bucketoverflow);
#if 0
                uma_zfree(V_tcp_hostcache.zone, hc_entry);
#endif
        } else {
                /*
                 * Allocate a new entry, or balk if not possible.
                 */
                hc_entry = uma_zalloc(V_tcp_hostcache.zone, M_NOWAIT);
                if (hc_entry == NULL) {
                        THC_UNLOCK(&hc_head->hch_mtx);
                        return NULL;
                }
        }

        /*
         * Initialize basic information of hostcache entry.
         */
        bzero(hc_entry, sizeof(*hc_entry));
        if (inc->inc_flags & INC_ISIPV6)
                bcopy(&inc->inc6_faddr, &hc_entry->ip6, sizeof(hc_entry->ip6));
        else
                hc_entry->ip4 = inc->inc_faddr;
        hc_entry->rmx_head = hc_head;
        hc_entry->rmx_expire = V_tcp_hostcache.expire;

        /*
         * Put it upfront.
         */
        TAILQ_INSERT_HEAD(&hc_head->hch_bucket, hc_entry, rmx_q);
        V_tcp_hostcache.hashbase[hash].hch_length++;
        V_tcp_hostcache.cache_count++;
        TCPSTAT_INC(tcps_hc_added);

        return hc_entry;
}

/*
 * External function: look up an entry in the hostcache and fill out the
 * supplied TCP metrics structure.  Fills in NULL when no entry was found or
 * a value is not set.
 */
void
tcp_hc_get(struct in_conninfo *inc, struct hc_metrics_lite *hc_metrics_lite)
{
        struct hc_metrics *hc_entry;

        /*
         * Find the right bucket.
         */
        hc_entry = tcp_hc_lookup(inc);

        /*
         * If we don't have an existing object.
         */
        if (hc_entry == NULL) {
                bzero(hc_metrics_lite, sizeof(*hc_metrics_lite));
                return;
        }
        hc_entry->rmx_hits++;
        hc_entry->rmx_expire = V_tcp_hostcache.expire; /* start over again */

        hc_metrics_lite->rmx_mtu = hc_entry->rmx_mtu;
        hc_metrics_lite->rmx_ssthresh = hc_entry->rmx_ssthresh;
        hc_metrics_lite->rmx_rtt = hc_entry->rmx_rtt;
        hc_metrics_lite->rmx_rttvar = hc_entry->rmx_rttvar;
        hc_metrics_lite->rmx_bandwidth = hc_entry->rmx_bandwidth;
        hc_metrics_lite->rmx_cwnd = hc_entry->rmx_cwnd;
        hc_metrics_lite->rmx_sendpipe = hc_entry->rmx_sendpipe;
        hc_metrics_lite->rmx_recvpipe = hc_entry->rmx_recvpipe;

        /*
         * Unlock bucket row.
         */
        THC_UNLOCK(&hc_entry->rmx_head->hch_mtx);
}

/*
 * External function: look up an entry in the hostcache and return the
 * discovered path MTU.  Returns NULL if no entry is found or value is not
 * set.
 */
u_long
tcp_hc_getmtu(struct in_conninfo *inc)
{
        struct hc_metrics *hc_entry;
        u_long mtu;

        hc_entry = tcp_hc_lookup(inc);
        if (hc_entry == NULL) {
                return 0;
        }
        hc_entry->rmx_hits++;
        hc_entry->rmx_expire = V_tcp_hostcache.expire; /* start over again */

        mtu = hc_entry->rmx_mtu;
        THC_UNLOCK(&hc_entry->rmx_head->hch_mtx);
        return mtu;
}

/*
 * External function: update the MTU value of an entry in the hostcache.
 * Creates a new entry if none was found.
 */
void
tcp_hc_updatemtu(struct in_conninfo *inc, u_long mtu)
{
        struct hc_metrics *hc_entry;

        /*
         * Find the right bucket.
         */
        hc_entry = tcp_hc_lookup(inc);

        /*
         * If we don't have an existing object, try to insert a new one.
         */
        if (hc_entry == NULL) {
                hc_entry = tcp_hc_insert(inc);
                if (hc_entry == NULL)
                        return;
        }
        hc_entry->rmx_updates++;
        hc_entry->rmx_expire = V_tcp_hostcache.expire; /* start over again */

        hc_entry->rmx_mtu = mtu;

        /*
         * Put it upfront so we find it faster next time.
         */
        TAILQ_REMOVE(&hc_entry->rmx_head->hch_bucket, hc_entry, rmx_q);
        TAILQ_INSERT_HEAD(&hc_entry->rmx_head->hch_bucket, hc_entry, rmx_q);

        /*
         * Unlock bucket row.
         */
        THC_UNLOCK(&hc_entry->rmx_head->hch_mtx);
}

/*
 * External function: update the TCP metrics of an entry in the hostcache.
 * Creates a new entry if none was found.
 */
void
tcp_hc_update(struct in_conninfo *inc, struct hc_metrics_lite *hcml)
{
        struct hc_metrics *hc_entry;

        hc_entry = tcp_hc_lookup(inc);
        if (hc_entry == NULL) {
                hc_entry = tcp_hc_insert(inc);
                if (hc_entry == NULL)
                        return;
        }
        hc_entry->rmx_updates++;
        hc_entry->rmx_expire = V_tcp_hostcache.expire; /* start over again */

        if (hcml->rmx_rtt != 0) {
                if (hc_entry->rmx_rtt == 0)
                        hc_entry->rmx_rtt = hcml->rmx_rtt;
                else
                        hc_entry->rmx_rtt =
                            (hc_entry->rmx_rtt + hcml->rmx_rtt) / 2;
                TCPSTAT_INC(tcps_cachedrtt);
        }
        if (hcml->rmx_rttvar != 0) {
                if (hc_entry->rmx_rttvar == 0)
                        hc_entry->rmx_rttvar = hcml->rmx_rttvar;
                else
                        hc_entry->rmx_rttvar =
                            (hc_entry->rmx_rttvar + hcml->rmx_rttvar) / 2;
                TCPSTAT_INC(tcps_cachedrttvar);
        }
        if (hcml->rmx_ssthresh != 0) {
                if (hc_entry->rmx_ssthresh == 0)
                        hc_entry->rmx_ssthresh = hcml->rmx_ssthresh;
                else
                        hc_entry->rmx_ssthresh =
                            (hc_entry->rmx_ssthresh + hcml->rmx_ssthresh) / 2;
                TCPSTAT_INC(tcps_cachedssthresh);
        }
        if (hcml->rmx_bandwidth != 0) {
                if (hc_entry->rmx_bandwidth == 0)
                        hc_entry->rmx_bandwidth = hcml->rmx_bandwidth;
                else
                        hc_entry->rmx_bandwidth =
                            (hc_entry->rmx_bandwidth + hcml->rmx_bandwidth) / 2;
                /* TCPSTAT_INC(tcps_cachedbandwidth); */
        }
        if (hcml->rmx_cwnd != 0) {
                if (hc_entry->rmx_cwnd == 0)
                        hc_entry->rmx_cwnd = hcml->rmx_cwnd;
                else
                        hc_entry->rmx_cwnd =
                            (hc_entry->rmx_cwnd + hcml->rmx_cwnd) / 2;
                /* TCPSTAT_INC(tcps_cachedcwnd); */
        }
        if (hcml->rmx_sendpipe != 0) {
                if (hc_entry->rmx_sendpipe == 0)
                        hc_entry->rmx_sendpipe = hcml->rmx_sendpipe;
                else
                        hc_entry->rmx_sendpipe =
                            (hc_entry->rmx_sendpipe + hcml->rmx_sendpipe) /2;
                /* TCPSTAT_INC(tcps_cachedsendpipe); */
        }
        if (hcml->rmx_recvpipe != 0) {
                if (hc_entry->rmx_recvpipe == 0)
                        hc_entry->rmx_recvpipe = hcml->rmx_recvpipe;
                else
                        hc_entry->rmx_recvpipe =
                            (hc_entry->rmx_recvpipe + hcml->rmx_recvpipe) /2;
                /* TCPSTAT_INC(tcps_cachedrecvpipe); */
        }

        TAILQ_REMOVE(&hc_entry->rmx_head->hch_bucket, hc_entry, rmx_q);
        TAILQ_INSERT_HEAD(&hc_entry->rmx_head->hch_bucket, hc_entry, rmx_q);
        THC_UNLOCK(&hc_entry->rmx_head->hch_mtx);
}

/*
 * Sysctl function: prints the list and values of all hostcache entries in
 * unsorted order.
 */
static int
sysctl_tcp_hc_list(SYSCTL_HANDLER_ARGS)
{
        int bufsize;
        int linesize = 128;
        char *p, *buf;
        int len, i, error;
        struct hc_metrics *hc_entry;
#ifdef INET6
        char ip6buf[INET6_ADDRSTRLEN];
#endif

        bufsize = linesize * (V_tcp_hostcache.cache_count + 1);

        p = buf = (char *)malloc(bufsize, M_TEMP, M_WAITOK|M_ZERO);

        len = snprintf(p, linesize,
                "\nIP address        MTU  SSTRESH      RTT   RTTVAR BANDWIDTH "
                "    CWND SENDPIPE RECVPIPE HITS  UPD  EXP\n");
        p += len;

#define msec(u) (((u) + 500) / 1000)
        for (i = 0; i < V_tcp_hostcache.hashsize; i++) {
                THC_LOCK(&V_tcp_hostcache.hashbase[i].hch_mtx);
                TAILQ_FOREACH(hc_entry, &V_tcp_hostcache.hashbase[i].hch_bucket,
                              rmx_q) {
                        len = snprintf(p, linesize,
                            "%-15s %5lu %8lu %6lums %6lums %9lu %8lu %8lu %8lu "
                            "%4lu %4lu %4i\n",
                            hc_entry->ip4.s_addr ? inet_ntoa(hc_entry->ip4) :
#ifdef INET6
                                ip6_sprintf(ip6buf, &hc_entry->ip6),
#else
                                "IPv6?",
#endif
                            hc_entry->rmx_mtu,
                            hc_entry->rmx_ssthresh,
                            msec(hc_entry->rmx_rtt *
                                (RTM_RTTUNIT / (hz * TCP_RTT_SCALE))),
                            msec(hc_entry->rmx_rttvar *
                                (RTM_RTTUNIT / (hz * TCP_RTT_SCALE))),
                            hc_entry->rmx_bandwidth * 8,
                            hc_entry->rmx_cwnd,
                            hc_entry->rmx_sendpipe,
                            hc_entry->rmx_recvpipe,
                            hc_entry->rmx_hits,
                            hc_entry->rmx_updates,
                            hc_entry->rmx_expire);
                        p += len;
                }
                THC_UNLOCK(&V_tcp_hostcache.hashbase[i].hch_mtx);
        }
#undef msec
        error = SYSCTL_OUT(req, buf, p - buf);
        free(buf, M_TEMP);
        return(error);
}

/*
 * Caller has to make sure the curvnet is set properly.
 */
static void
tcp_hc_purge_internal(int all)
{
        struct hc_metrics *hc_entry, *hc_next;
        int i;

        for (i = 0; i < V_tcp_hostcache.hashsize; i++) {
                THC_LOCK(&V_tcp_hostcache.hashbase[i].hch_mtx);
                TAILQ_FOREACH_SAFE(hc_entry,
                    &V_tcp_hostcache.hashbase[i].hch_bucket, rmx_q, hc_next) {
                        if (all || hc_entry->rmx_expire <= 0) {
                                TAILQ_REMOVE(&V_tcp_hostcache.hashbase[i].hch_bucket,
                                              hc_entry, rmx_q);
                                uma_zfree(V_tcp_hostcache.zone, hc_entry);
                                V_tcp_hostcache.hashbase[i].hch_length--;
                                V_tcp_hostcache.cache_count--;
                        } else
                                hc_entry->rmx_expire -= V_tcp_hostcache.prune;
                }
                THC_UNLOCK(&V_tcp_hostcache.hashbase[i].hch_mtx);
        }
}

/*
 * Expire and purge (old|all) entries in the tcp_hostcache.  Runs
 * periodically from the callout.
 */
static void
tcp_hc_purge(void *arg)
{
        CURVNET_SET((struct vnet *) arg);
        int all = 0;

        if (V_tcp_hostcache.purgeall) {
                all = 1;
                V_tcp_hostcache.purgeall = 0;
        }

        tcp_hc_purge_internal(all);

        callout_reset(&V_tcp_hc_callout, V_tcp_hostcache.prune * hz,
            tcp_hc_purge, arg);
        CURVNET_RESTORE();
}