FreeBSD released 6.3

[dragonfly.git] / usr.sbin / dntpd / client.c

/*
 * Copyright (c) 2005 The DragonFly Project.  All rights reserved.
 * 
 * This code is derived from software contributed to The DragonFly Project
 * by Matthew Dillon <dillon@backplane.com>
 * 
 * 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. Neither the name of The DragonFly Project nor the names of its
 *    contributors may be used to endorse or promote products derived
 *    from this software without specific, prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS 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
 * COPYRIGHT HOLDERS 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.
 * 
 * $DragonFly: src/usr.sbin/dntpd/client.c,v 1.13 2007/06/26 02:40:20 dillon Exp $
 */

#include "defs.h"

static int client_insane(struct server_info **, int, server_info_t);

void
client_init(void)
{
}

int
client_main(struct server_info **info_ary, int count)
{
    struct server_info *best_off;
    struct server_info *best_freq;
    double last_freq;
    double freq;
    double offset;
    int calc_offset_correction;
    int didreconnect;
    int i;
    int insane;

    last_freq = 0.0;

    for (;;) {
        /*
         * Subtract the interval from poll_sleep and poll the client
         * if it reaches 0.
         *
         * Because we do not compensate for offset corrections which are
         * in progress, we cannot accumulate data for an offset correction
         * while a prior correction is still being worked through by the
         * system.
         */
        calc_offset_correction = !sysntp_offset_correction_is_running();
        for (i = 0; i < count; ++i)
            client_poll(info_ary[i], min_sleep_opt, calc_offset_correction);

        /*
         * Find the best client (or synthesize one).  A different client
         * can be chosen for frequency and offset.  Note in particular 
         * that offset counters and averaging code gets reset when an
         * offset correction is made (otherwise the averaging history will
         * cause later corrections to overshoot).  
         * 
         * The regression used to calculate the frequency is a much 
         * longer-term entity and is NOT reset, so it is still possible
         * for the offset correction code to make minor adjustments to
         * the frequency if it so desires.
         *
         * client_check may replace the server_info pointer with a new
         * one.
         */
        best_off = NULL;
        best_freq = NULL;
        for (i = 0; i < count; ++i)
            client_check(&info_ary[i], &best_off, &best_freq);

        /*
         * Check for server insanity.  In large NNTP pools some servers
         * may just be dead wrong, but report that they are right.
         */
        if (best_off) {
            insane = client_insane(info_ary, count, best_off);
            if (insane > 0) {
                /* 
                 * best_off meets the quorum requirements and is good
                 * (keep best_off)
                 */
                best_off->server_insane = 0;
            } else if (insane == 0) {
                /*
                 * best_off is probably good, but we do not have enough
                 * servers reporting yet to meet the quorum requirements.
                 */
                best_off = NULL;
            } else {
                /*
                 * best_off is ugly, mark the server as being insane for
                 * 60 minutes.
                 */
                best_off->server_insane = 60 * 60;
                logdebuginfo(best_off, 1, 
                             "excessive offset deviation, mapping out\n");
                best_off = NULL;
            }
        }

        /*
         * Offset correction.
         */
        if (best_off) {
            offset = best_off->lin_sumoffset / best_off->lin_countoffset;
            lin_resetalloffsets(info_ary, count);
            if (offset < -COURSE_OFFSET_CORRECTION_LIMIT ||
                offset > COURSE_OFFSET_CORRECTION_LIMIT ||
                quickset_opt
            ) {
                freq = sysntp_correct_course_offset(offset);
                quickset_opt = 0;
            } else {
                freq = sysntp_correct_offset(offset);
            }
        } else {
            freq = 0.0;
        }

        /*
         * Frequency correction (throw away minor freq adjusts from the
         * offset code if we can't do a frequency correction here).  Do
         * not reissue if it hasn't changed from the last issued correction.
         */
        if (best_freq) {
            freq += best_freq->lin_cache_freq;
            if (last_freq != freq) {
                sysntp_correct_freq(freq);
                last_freq = freq;
            }
        }

        /*
         * This function is responsible for managing the polling mode and
         * figures out how long we should sleep.
         */
        didreconnect = 0;
        for (i = 0; i < count; ++i)
            client_manage_polling_mode(info_ary[i], &didreconnect);
        if (didreconnect)
            client_check_duplicate_ips(info_ary, count);

        /*
         * Polling loop sleep.
         */
        usleep(min_sleep_opt * 1000000 + random() % 500000);
    }
}

void
client_poll(server_info_t info, int poll_interval, int calc_offset_correction)
{
    struct timeval rtv;
    struct timeval ltv;
    struct timeval lbtv;
    double offset;

    /*
     * Adjust the insane-server countdown
     */
    if (info->server_insane > poll_interval)
        info->server_insane -= poll_interval;
    else
        info->server_insane = 0;

    /*
     * By default we always poll.  If the polling interval comes under
     * active management the poll_sleep will be non-zero.
     */
    if (info->poll_sleep > poll_interval) {
        info->poll_sleep -= poll_interval;
        return;
    }
    info->poll_sleep = 0;

    /*
     * If the client isn't open don't mess with the poll_failed count
     * or anything else.  We are left in the init or startup phase.
     */
    if (info->fd < 0) {
        if (info->poll_failed < 0x7FFFFFFF)
            ++info->poll_failed;
        return;
    }

    logdebuginfo(info, 4, "poll, ");
    if (udp_ntptimereq(info->fd, &rtv, &ltv, &lbtv) < 0) {
        ++info->poll_failed;
        logdebug(4, "no response (%d failures in a row)\n", info->poll_failed);
        if (info->poll_failed == POLL_FAIL_RESET) {
            if (info->lin_count != 0) {
                logdebuginfo(info, 4, "resetting regression due to failures\n");
            }
            lin_reset(info);
        }
        return;
    }

    /*
     * Successful query.  Update polling info for the polling mode manager.
     */
    ++info->poll_count;
    info->poll_failed = 0;

    /*
     * Figure out the offset (the difference between the reported
     * time and our current time) for linear regression purposes.
     */
    offset = tv_delta_double(&rtv, &ltv);

    while (info) {
        /*
         * Linear regression
         */
        if (debug_level >= 4) {
            struct tm *tp;
            char buf[64];
            time_t t;

            t = rtv.tv_sec;
            tp = localtime(&t);
            strftime(buf, sizeof(buf), "%d-%b-%Y %H:%M:%S", tp);
            logdebug(4, "%s.%03ld ", buf, rtv.tv_usec / 1000);
        }
        lin_regress(info, &ltv, &lbtv, offset, calc_offset_correction);
        info = info->altinfo;
        if (info && debug_level >= 4) {
            logdebug(4, "%*.*s: poll, ", 
                (int)strlen(info->target), 
                (int)strlen(info->target), "(alt)");
        }
    }
}

/*
 * Find the best client (or synthesize a fake info structure to return).
 * We can find separate best clients for offset and frequency.
 */
void
client_check(struct server_info **checkp, 
             struct server_info **best_off,
             struct server_info **best_freq)
{
    struct server_info *check = *checkp;
    struct server_info *info;

    /*
     * Start an alternate linear regression once our current one
     * has passed a certain point.
     */
    if (check->lin_count >= LIN_RESTART / 2 && check->altinfo == NULL) {
        info = malloc(sizeof(*info));
        assert(info != NULL);
        /* note: check->altinfo is NULL as of the bcopy */
        bcopy(check, info, sizeof(*info));
        check->altinfo = info;
        lin_reset(info);
    }

    /*
     * Replace our current linear regression with the alternate once
     * the current one has hit its limit (beyond a certain point the
     * linear regression starts to work against us, preventing us from
     * reacting to changing conditions).
     *
     * Report any significant change in the offset or ppm.
     */
    if (check->lin_count >= LIN_RESTART) {
        if ((info = check->altinfo) && info->lin_count >= LIN_RESTART / 2) {
            double freq_diff;

            freq_diff = info->lin_cache_freq - check->lin_cache_freq;
            logdebuginfo(info, 4, "Switching to alternate, Frequence "
                         "difference is %6.3f ppm\n",
                         freq_diff * 1.0E+6);
            *checkp = info;
            free(check);
            check = info;
        }
    }

    /*
     * BEST CLIENT FOR FREQUENCY CORRECTION:
     *
     *  8 samples and a correlation > 0.99, or
     * 16 samples and a correlation > 0.96
     */
    info = *best_freq;
    if ((check->lin_count >= 8 && fabs(check->lin_cache_corr) >= 0.99) ||
        (check->lin_count >= 16 && fabs(check->lin_cache_corr) >= 0.96)
    ) {
        if (info == NULL || 
            fabs(check->lin_cache_corr) > fabs(info->lin_cache_corr)
        ) {
            info = check;
            *best_freq = info;
        }

    }

    /*
     * BEST CLIENT FOR OFFSET CORRECTION:
     *
     * Use the standard-deviation and require at least 4 samples.  An
     * offset correction is valid if the standard deviation is less then
     * the average offset divided by 4.
     *
     * Servers marked as being insane are not allowed
     */
    info = *best_off;
    if (check->lin_countoffset >= 4 && 
        (check->lin_cache_stddev <
         fabs(check->lin_sumoffset / check->lin_countoffset / 4)) &&
        check->server_insane == 0
     ) {
        if (info == NULL || 
            fabs(check->lin_cache_stddev) < fabs(info->lin_cache_stddev)
        ) {
            info = check;
            *best_off = info;
        }
    }
}

/*
 * Actively manage the polling interval.  Note that the poll_* fields are
 * always transfered to the alternate regression when the check code replaces
 * the current regression with a new one.
 *
 * This routine is called from the main loop for each base info structure.
 * The polling mode applies to all alternates so we do not have to iterate
 * through the alt's.
 */
void
client_manage_polling_mode(struct server_info *info, int *didreconnect)
{
    /*
     * Permanently failed servers are ignored.
     */
    if (info->server_state == -2)
        return;

    /*
     * Our polling interval has not yet passed.
     */
    if (info->poll_sleep)
        return;

    /*
     * Standard polling mode progression
     */
    switch(info->poll_mode) {
    case POLL_FIXED:
        /*
         * Initial state after connect or when a reconnect is required.
         */
        if (info->fd < 0) {
            logdebuginfo(info, 2, "polling mode INIT, relookup & reconnect\n");
            reconnect_server(info);
            *didreconnect = 1;
            if (info->fd < 0) {
                if (info->poll_failed >= POLL_RECOVERY_RESTART * 5)
                    info->poll_sleep = max_sleep_opt;
                else if (info->poll_failed >= POLL_RECOVERY_RESTART)
                    info->poll_sleep = nom_sleep_opt;
                else
                    info->poll_sleep = min_sleep_opt;
                break;
            }

            /*
             * Transition the server to the DNS lookup successful state.
             * Note that the server state does not transition out of
             * lookup successful if we relookup after a packet failure
             * so the message is printed only once, usually.
             */
            client_setserverstate(info, 0, "DNS lookup success");

            /*
             * If we've failed many times switch to the startup state but
             * do not fall through into it.  break the switch and a single
             * poll will be made after the nominal polling interval.
             */
            if (info->poll_failed >= POLL_RECOVERY_RESTART * 5) {
                logdebuginfo(info, 2, "polling mode INIT->STARTUP (very slow)\n");
                info->poll_mode = POLL_STARTUP;
                info->poll_sleep = max_sleep_opt;
                info->poll_count = 0;
                break;
            } else if (info->poll_failed >= POLL_RECOVERY_RESTART) {
                logdebuginfo(info, 2, "polling mode INIT->STARTUP (slow)\n");
                info->poll_mode = POLL_STARTUP;
                info->poll_count = 0;
                break;
            }
        }

        /*
         * Fall through to the startup state.
         */
        info->poll_mode = POLL_STARTUP;
        logdebuginfo(info, 2, "polling mode INIT->STARTUP (normal)\n");
        /* fall through */
    case POLL_STARTUP:
        /*
         * Transition to a FAILED state if too many poll failures occured.
         */
        if (info->poll_failed >= POLL_FAIL_RESET) {
            logdebuginfo(info, 2, "polling mode STARTUP->FAILED\n");
            info->poll_mode = POLL_FAILED;
            info->poll_count = 0;
            break;
        }

        /*
         * Transition the server to operational.  Do a number of minimum
         * interval polls to try to get a good offset calculation quickly.
         */
        if (info->poll_count)
            client_setserverstate(info, 1, "connected ok");
        if (info->poll_count < POLL_STARTUP_MAX) {
            info->poll_sleep = min_sleep_opt;
            break;
        }

        /*
         * Once we've got our polls fall through to aquisition mode to
         * do aquisition processing.
         */
        info->poll_mode = POLL_ACQUIRE;
        info->poll_count = 0;
        logdebuginfo(info, 2, "polling mode STARTUP->ACQUIRE\n");
        /* fall through */
    case POLL_ACQUIRE:
        /*
         * Transition to a FAILED state if too many poll failures occured.
         */
        if (info->poll_failed >= POLL_FAIL_RESET) {
            logdebuginfo(info, 2, "polling mode STARTUP->FAILED\n");
            info->poll_mode = POLL_FAILED;
            info->poll_count = 0;
            break;
        }

        /*
         * Acquisition mode using the nominal timeout.  We do not shift
         * to maintainance mode unless the correlation is at least 0.90
         */
        if (info->poll_count < POLL_ACQUIRE_MAX ||
            info->lin_count < 8 ||
            fabs(info->lin_cache_corr) < 0.85
        ) {
            if (info->poll_count >= POLL_ACQUIRE_MAX && 
                info->lin_count == LIN_RESTART - 2
            ) {
                logdebuginfo(info, 2, 
                    "WARNING: Unable to shift this source to "
                    "maintenance mode.  Target correlation is aweful\n");
            }
            break;
        }
        info->poll_mode = POLL_MAINTAIN;
        info->poll_count = 0;
        logdebuginfo(info, 2, "polling mode ACQUIRE->MAINTAIN\n");
        /* fall through */
    case POLL_MAINTAIN:
        /*
         * Transition to a FAILED state if too many poll failures occured.
         */
        if (info->poll_failed >= POLL_FAIL_RESET) {
            logdebuginfo(info, 2, "polling mode STARTUP->FAILED\n");
            info->poll_mode = POLL_FAILED;
            info->poll_count = 0;
            break;
        }

        /*
         * Maintaince mode, max polling interval.
         *
         * Transition back to acquisition mode if we are unable to maintain
         * this mode due to the correlation going bad.
         */
        if (info->lin_count >= LIN_RESTART / 2 && 
            fabs(info->lin_cache_corr) < 0.70
        ) {
            logdebuginfo(info, 2, 
                "polling mode MAINTAIN->ACQUIRE.  Unable to maintain\n"
                "the maintenance mode because the correlation went"
                " bad!\n");
            info->poll_mode = POLL_ACQUIRE;
            info->poll_count = 0;
            break;
        }
        info->poll_sleep = max_sleep_opt;
        break;
    case POLL_FAILED:
        /*
         * We have a communications failure.  A late recovery is possible 
         * if we enter this state with a good poll.
         */
        if (info->poll_count != 0) {
            logdebuginfo(info, 2, "polling mode FAILED->ACQUIRE\n");
            if (info->poll_failed >= POLL_FAIL_RESET)
                info->poll_mode = POLL_STARTUP;
            else
                info->poll_mode = POLL_ACQUIRE;
            /* do not reset poll_count */
            break;
        }

        /*
         * If we have been failed too long, disconnect from the server
         * and start us all over again.  Note that the failed count is not
         * reset to 0.
         */
        if (info->poll_failed >= POLL_RECOVERY_RESTART) {
            logdebuginfo(info, 2, "polling mode FAILED->INIT\n");
            client_setserverstate(info, 0, "FAILED");
            disconnect_server(info);
            info->poll_mode = POLL_FIXED;
            break;
        }
        break;
    }

    /*
     * If the above state machine has not set a polling interval, set a
     * nominal polling interval.
     */
    if (info->poll_sleep == 0)
        info->poll_sleep = nom_sleep_opt;
}

/*
 * Look for duplicate IP addresses.  This is done very inoften, so we do
 * not use a particularly efficient algorithm.
 *
 * Only reconnect a client which has not done its initial poll.
 */
void
client_check_duplicate_ips(struct server_info **info_ary, int count)
{
    server_info_t info1;
    server_info_t info2;
    int tries;
    int i;
    int j;

    for (i = 0; i < count; ++i) {
        info1 = info_ary[i];
        if (info1->fd < 0 || info1->server_state != 0)
            continue;
        for (tries = 0; tries < 10; ++tries) {
            for (j = 0; j < count; ++j) {
                info2 = info_ary[j];
                if (i == j || info2->fd < 0)
                    continue;
                if (strcmp(info1->ipstr, info2->ipstr) == 0) {
                    reconnect_server(info1);
                    break;
                }
            }
            if (j == count)
                break;
        }
        if (tries == 10) {
            disconnect_server(info1);
            client_setserverstate(info1, -2,
                                  "permanently disabling duplicate server");
        }
    }
}

/*
 * Calculate whether the server pointed to by *bestp is insane or not.
 * For some reason some servers in e.g. the ntp pool are sometimes an hour
 * off.  If we have at least three servers in the pool require that a
 * quorum agree that the current best server's offset is reasonable.
 *
 * Allow +/- 0.5 seconds of error for now (settable with option).
 *
 * Returns -1 if insane, 0 if not enough samples, and 1 if ok
 */
static
int
client_insane(struct server_info **info_ary, int count, server_info_t best)
{
    server_info_t info;
    double best_offset;
    double info_offset;
    int good;
    int bad;
    int skip;
    int quorum;
    int i;

    /*
     * If only one ntp server we cannot check to see if it is insane
     */
    if (count < 2)
            return(1);
    best_offset = best->lin_sumoffset / best->lin_countoffset;

    /*
     * Calculated the quorum.  Do not count permanently failed servers
     * in the calculation.
     *
     * adjusted count   quorum
     *   2                2
     *   3                2
     *   4                3
     *   5                3
     */
    quorum = count;
    for (i = 0; i < count; ++i) {
        info = info_ary[i];
        if (info->server_state == -2)
            --quorum;
    }

    quorum = quorum / 2 + 1;
    good = 0;
    bad = 0;
    skip = 0;

    /*
     * Find the good, the bad, and the ugly.  We need at least four samples
     * and a stddev within the deviation being checked to count a server
     * in the calculation.
     */
    for (i = 0; i < count; ++i) {
        info = info_ary[i];
        if (info->lin_countoffset < 4 ||
            info->lin_cache_stddev > insane_deviation
        ) {
            ++skip;
            continue;
        }

        info_offset = info->lin_sumoffset / info->lin_countoffset;
        info_offset -= best_offset;
        if (info_offset < -insane_deviation || info_offset > insane_deviation)
                ++bad;
        else
                ++good;
    }

    /*
     * Did we meet our quorum?
     */
    logdebuginfo(best, 5, "insanecheck good=%d bad=%d skip=%d "
                          "quorum=%d (allowed=%-+8.6f)\n",
                 good, bad, skip, quorum, insane_deviation);
    if (good >= quorum)
        return(1);
    if (good + skip >= quorum)
        return(0);
    return(-1);
}

/*
 * Linear regression.
 *
 *      ltv     local time as of when the offset error was calculated between
 *              local time and remote time.
 *
 *      lbtv    base time as of when local time was obtained.  Used to
 *              calculate the cumulative corrections made to the system's
 *              real time clock so we can de-correct the offset for the
 *              linear regression.
 *
 * X is the time axis, in seconds.
 * Y is the uncorrected offset, in seconds.
 */
void
lin_regress(server_info_t info, struct timeval *ltv, struct timeval *lbtv,
            double offset, int calc_offset_correction)
{
    double time_axis;
    double uncorrected_offset;

    /*
     * De-correcting the offset:
     *
     *  The passed offset is (our_real_time - remote_real_time).  To remove
     *  corrections from our_real_time we take the difference in the basetime
     *  (new_base_time - old_base_time) and subtract that from the offset.
     *  That is, if the basetime goesup, the uncorrected offset goes down.
     */
    if (info->lin_count == 0) {
        info->lin_tv = *ltv;
        info->lin_btv = *lbtv;
        time_axis = 0;
        uncorrected_offset = offset;
    } else {
        time_axis = tv_delta_double(&info->lin_tv, ltv);
        uncorrected_offset = offset - tv_delta_double(&info->lin_btv, lbtv);
    }

    /*
     * We have to use the uncorrected offset for frequency calculations.
     */
    ++info->lin_count;
    info->lin_sumx += time_axis;
    info->lin_sumx2 += time_axis * time_axis;
    info->lin_sumy += uncorrected_offset;
    info->lin_sumy2 += uncorrected_offset * uncorrected_offset;
    info->lin_sumxy += time_axis * uncorrected_offset;

    /*
     * We have to use the corrected offset for offset calculations.
     */
    if (calc_offset_correction) {
        ++info->lin_countoffset;
        info->lin_sumoffset += offset;
        info->lin_sumoffset2 += offset * offset;
    }

    /*
     * Calculate various derived values.   This gets us slope, y-intercept,
     * and correlation from the linear regression.
     */
    if (info->lin_count > 1) {
        info->lin_cache_slope = 
         (info->lin_count * info->lin_sumxy - info->lin_sumx * info->lin_sumy) /
         (info->lin_count * info->lin_sumx2 - info->lin_sumx * info->lin_sumx);

        info->lin_cache_yint = 
         (info->lin_sumy - info->lin_cache_slope * info->lin_sumx) /
         (info->lin_count);

        info->lin_cache_corr =
         (info->lin_count * info->lin_sumxy - info->lin_sumx * info->lin_sumy) /
         sqrt((info->lin_count * info->lin_sumx2 - 
                      info->lin_sumx * info->lin_sumx) *
             (info->lin_count * info->lin_sumy2 - 
                      info->lin_sumy * info->lin_sumy)
         );
    }

    /*
     * Calculate more derived values.  This gets us the standard-deviation
     * of offsets.  The standard deviation approximately means that 68%
     * of the samples fall within the calculated stddev of the mean.
     */
    if (info->lin_countoffset > 1) {
         info->lin_cache_stddev = 
             sqrt((info->lin_sumoffset2 - 
                 ((info->lin_sumoffset * info->lin_sumoffset / 
                   info->lin_countoffset))) /
                 (info->lin_countoffset - 1.0));
    }

    /*
     * Save the most recent offset, we might use it in the future.
     * Save the frequency correction (we might scale the slope later so
     * we have a separate field for the actual frequency correction in
     * seconds per second).
     */
    info->lin_cache_offset = offset;
    info->lin_cache_freq = info->lin_cache_slope;

    if (debug_level >= 4) {
        logdebuginfo(info, 4, "iter=%2d time=%7.3f off=%+.6f uoff=%+.6f",
            (int)info->lin_count,
            time_axis, offset, uncorrected_offset);
        if (info->lin_count > 1) {
            logdebug(4, " slope %+7.6f"
                            " yint %+3.2f corr %+7.6f freq_ppm %+4.2f", 
                info->lin_cache_slope,
                info->lin_cache_yint,
                info->lin_cache_corr,
                info->lin_cache_freq * 1000000.0);
        }
        if (info->lin_countoffset > 1) {
            logdebug(4, " stddev %7.6f", info->lin_cache_stddev);
        } else if (calc_offset_correction == 0) {
            /* cannot calculate offset correction due to prior correction */
            logdebug(4, " offset_ignored");
        }
        logdebug(4, "\n");
    }
}

/*
 * Reset the linear regression data.  The info structure will not again be
 * a candidate for frequency or offset correction until sufficient data
 * has been accumulated to make a decision.
 */
void
lin_reset(server_info_t info)
{
    server_info_t scan;

    info->lin_count = 0;
    info->lin_sumx = 0;
    info->lin_sumy = 0;
    info->lin_sumxy = 0;
    info->lin_sumx2 = 0;
    info->lin_sumy2 = 0;

    info->lin_countoffset = 0;
    info->lin_sumoffset = 0;
    info->lin_sumoffset2 = 0;

    info->lin_cache_slope = 0;
    info->lin_cache_yint = 0;
    info->lin_cache_corr = 0;
    info->lin_cache_offset = 0;
    info->lin_cache_freq = 0;

    /*
     * Destroy any additional alternative regressions.
     */
    while ((scan = info->altinfo) != NULL) {
        info->altinfo = scan->altinfo;
        free(scan);
    }
}

/*
 * Sometimes we want to clean out the offset calculations without
 * destroying the linear regression used to figure out the frequency
 * correction.  This usually occurs whenever we issue an offset
 * adjustment to the system, which invalidates any offset data accumulated
 * up to that point.
 */
void
lin_resetalloffsets(struct server_info **info_ary, int count)
{
    server_info_t info;
    int i;

    for (i = 0; i < count; ++i) {
        for (info = info_ary[i]; info; info = info->altinfo)
            lin_resetoffsets(info);
    }
}

void
lin_resetoffsets(server_info_t info)
{
    info->lin_countoffset = 0;
    info->lin_sumoffset = 0;
    info->lin_sumoffset2 = 0;
}

void
client_setserverstate(server_info_t info, int state, const char *str)
{
    if (info->server_state != state) {
        info->server_state = state;
        logdebuginfo(info, 1, "%s\n", str);
    }
}