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ef6191945e
systemd/src/timesync/timesyncd.c
Kay Sievers ef6191945e timesyncd: log drift correction
2014-05-03 15:09:33 +02:00

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/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
/***
This file is part of systemd.
Copyright 2014 Kay Sievers
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
***/
#include <stdlib.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#include <time.h>
#include <math.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <sys/timerfd.h>
#include <sys/timex.h>
#include <sys/socket.h>
#include "missing.h"
#include "util.h"
#include "sparse-endian.h"
#include "log.h"
#include "sd-event.h"
#include "sd-daemon.h"
#define TIME_T_MAX (time_t)((1UL << ((sizeof(time_t) << 3) - 1)) - 1)
#ifndef ADJ_SETOFFSET
#define ADJ_SETOFFSET 0x0100 /* add 'time' to current time */
#endif
/* expected accuracy of time synchronization; used to adjust the poll interval */
#define NTP_ACCURACY_SEC 0.2
/*
* "A client MUST NOT under any conditions use a poll interval less
* than 15 seconds."
*/
#define NTP_POLL_INTERVAL_MIN_SEC 32
#define NTP_POLL_INTERVAL_MAX_SEC 2048
/*
* Maximum delta in seconds which the system clock is gradually adjusted
* (slew) to approach the network time. Deltas larger that this are set by
* letting the system time jump. The kernel's limit for adjtime is 0.5s.
*/
#define NTP_MAX_ADJUST 0.4
/* NTP protocol, packet header */
#define NTP_LEAP_PLUSSEC 1
#define NTP_LEAP_MINUSSEC 2
#define NTP_LEAP_NOTINSYNC 3
#define NTP_MODE_CLIENT 3
#define NTP_MODE_SERVER 4
#define NTP_FIELD_LEAP(f) (((f) >> 6) & 3)
#define NTP_FIELD_VERSION(f) (((f) >> 3) & 7)
#define NTP_FIELD_MODE(f) ((f) & 7)
#define NTP_FIELD(l, v, m) (((l) << 6) | ((v) << 3) | (m))
/*
* "NTP timestamps are represented as a 64-bit unsigned fixed-point number,
* in seconds relative to 0h on 1 January 1900."
*/
#define OFFSET_1900_1970 2208988800UL
struct ntp_ts {
be32_t sec;
be32_t frac;
} _packed_;
struct ntp_ts_short {
be16_t sec;
be16_t frac;
} _packed_;
struct ntp_msg {
uint8_t field;
uint8_t stratum;
int8_t poll;
int8_t precision;
struct ntp_ts_short root_delay;
struct ntp_ts_short root_dispersion;
char refid[4];
struct ntp_ts reference_time;
struct ntp_ts origin_time;
struct ntp_ts recv_time;
struct ntp_ts trans_time;
} _packed_;
typedef struct Manager Manager;
struct Manager {
sd_event *event;
/* peer */
sd_event_source *event_receive;
char *server;
struct sockaddr_in server_addr;
int server_socket;
uint64_t packet_count;
/* last sent packet */
struct timespec trans_time_mon;
struct timespec trans_time;
usec_t retry_interval;
bool pending;
/* poll timer */
sd_event_source *event_timer;
usec_t poll_interval_usec;
bool poll_resync;
/* history data */
struct {
double offset;
double delay;
} samples[8];
unsigned int samples_idx;
double samples_jitter;
/* last change */
bool jumped;
int drift_ppm;
/* watch for time changes */
sd_event_source *event_clock_watch;
int clock_watch_fd;
};
static void manager_free(Manager *m);
DEFINE_TRIVIAL_CLEANUP_FUNC(Manager*, manager_free);
#define _cleanup_manager_free_ _cleanup_(manager_freep)
static int sntp_arm_timer(Manager *m, usec_t next);
static int sntp_clock_watch_setup(Manager *m);
static void sntp_server_disconnect(Manager *m);
static double ntp_ts_to_d(const struct ntp_ts *ts) {
return be32toh(ts->sec) + ((double)be32toh(ts->frac) / UINT_MAX);
}
static double ts_to_d(const struct timespec *ts) {
return ts->tv_sec + (1.0e-9 * ts->tv_nsec);
}
static double tv_to_d(const struct timeval *tv) {
return tv->tv_sec + (1.0e-6 * tv->tv_usec);
}
static double square(double d) {
return d * d;
}
static int sntp_send_request(Manager *m) {
struct ntp_msg ntpmsg = {};
struct sockaddr_in addr = {};
ssize_t len;
int r;
/*
* "The client initializes the NTP message header, sends the request
* to the server, and strips the time of day from the Transmit
* Timestamp field of the reply. For this purpose, all the NTP
* header fields are set to 0, except the Mode, VN, and optional
* Transmit Timestamp fields."
*/
ntpmsg.field = NTP_FIELD(0, 4, NTP_MODE_CLIENT);
/*
* Set transmit timestamp, remember it; the server will send that back
* as the origin timestamp and we have an indication that this is the
* matching answer to our request.
*
* The actual value does not matter, We do not care about the correct
* NTP UINT_MAX fraction; we just pass the plain nanosecond value.
*/
clock_gettime(CLOCK_MONOTONIC, &m->trans_time_mon);
clock_gettime(CLOCK_REALTIME, &m->trans_time);
ntpmsg.trans_time.sec = htobe32(m->trans_time.tv_sec + OFFSET_1900_1970);
ntpmsg.trans_time.frac = htobe32(m->trans_time.tv_nsec);
addr.sin_family = AF_INET;
addr.sin_port = htobe16(123);
addr.sin_addr.s_addr = inet_addr(m->server);
len = sendto(m->server_socket, &ntpmsg, sizeof(ntpmsg), MSG_DONTWAIT, &addr, sizeof(addr));
if (len == sizeof(ntpmsg)) {
m->pending = true;
log_debug("Sent NTP request to: %s", m->server);
} else
log_debug("Sending NTP request to %s failed: %m", m->server);
/* re-arm timer with incresing timeout, in case the packets never arrive back */
if (m->retry_interval > 0) {
if (m->retry_interval < NTP_POLL_INTERVAL_MAX_SEC * USEC_PER_SEC)
m->retry_interval *= 2;
} else
m->retry_interval = NTP_POLL_INTERVAL_MIN_SEC * USEC_PER_SEC;
r = sntp_arm_timer(m, m->retry_interval);
if (r < 0)
return r;
return 0;
}
static int sntp_timer(sd_event_source *source, usec_t usec, void *userdata) {
Manager *m = userdata;
assert(m);
sntp_send_request(m);
return 0;
}
static int sntp_arm_timer(Manager *m, usec_t next) {
int r;
assert(m);
assert(m->event_receive);
if (next == 0) {
m->event_timer = sd_event_source_unref(m->event_timer);
return 0;
}
if (m->event_timer) {
r = sd_event_source_set_time(m->event_timer, now(CLOCK_MONOTONIC) + next);
if (r < 0)
return r;
return sd_event_source_set_enabled(m->event_timer, SD_EVENT_ONESHOT);
}
r = sd_event_add_time(
m->event,
&m->event_timer,
CLOCK_MONOTONIC,
now(CLOCK_MONOTONIC) + next, 0,
sntp_timer, m);
if (r < 0)
return r;
return 0;
}
static int sntp_clock_watch(sd_event_source *source, int fd, uint32_t revents, void *userdata) {
Manager *m = userdata;
assert(m);
assert(m->event_receive);
/* rearm timer */
sntp_clock_watch_setup(m);
/* skip our own jumps */
if (m->jumped) {
m->jumped = false;
return 0;
}
/* resync */
log_info("System time changed. Resyncing.");
m->poll_resync = true;
sntp_send_request(m);
return 0;
}
/* wake up when the system time changes underneath us */
static int sntp_clock_watch_setup(Manager *m) {
struct itimerspec its = { .it_value.tv_sec = TIME_T_MAX };
_cleanup_close_ int fd = -1;
sd_event_source *source;
int r;
assert(m);
assert(m->event_receive);
fd = timerfd_create(CLOCK_REALTIME, TFD_NONBLOCK|TFD_CLOEXEC);
if (fd < 0) {
log_error("Failed to create timerfd: %m");
return -errno;
}
if (timerfd_settime(fd, TFD_TIMER_ABSTIME|TFD_TIMER_CANCEL_ON_SET, &its, NULL) < 0) {
log_error("Failed to set up timerfd: %m");
return -errno;
}
r = sd_event_add_io(m->event, &source, fd, EPOLLIN, sntp_clock_watch, m);
if (r < 0) {
log_error("Failed to create clock watch event source: %s", strerror(-r));
return r;
}
sd_event_source_unref(m->event_clock_watch);
m->event_clock_watch = source;
if (m->clock_watch_fd >= 0)
close(m->clock_watch_fd);
m->clock_watch_fd = fd;
fd = -1;
return 0;
}
static int sntp_adjust_clock(Manager *m, double offset, int leap_sec) {
struct timex tmx = {};
int r;
/*
* For small deltas, tell the kernel to gradually adjust the system
* clock to the NTP time, larger deltas are just directly set.
*
* Clear STA_UNSYNC, it will enable the kernel's 11-minute mode, which
* syncs the system time periodically to the hardware clock.
*/
if (fabs(offset) < NTP_MAX_ADJUST) {
tmx.modes = ADJ_STATUS | ADJ_NANO | ADJ_OFFSET | ADJ_TIMECONST | ADJ_MAXERROR | ADJ_ESTERROR;
tmx.status = STA_PLL;
tmx.offset = offset * NSEC_PER_SEC;
tmx.constant = log2i(m->poll_interval_usec / USEC_PER_SEC) - 4;
tmx.maxerror = 0;
tmx.esterror = 0;
log_debug(" adjust (slew): %+.3f sec\n", offset);
} else {
tmx.modes = ADJ_SETOFFSET | ADJ_NANO;
/* ADJ_NANO uses nanoseconds in the microseconds field */
tmx.time.tv_sec = (long)offset;
tmx.time.tv_usec = (offset - tmx.time.tv_sec) * NSEC_PER_SEC;
/* the kernel expects -0.3s as {-1, 7000.000.000} */
if (tmx.time.tv_usec < 0) {
tmx.time.tv_sec -= 1;
tmx.time.tv_usec += NSEC_PER_SEC;
}
m->jumped = true;
log_debug(" adjust (jump): %+.3f sec\n", offset);
}
switch (leap_sec) {
case 1:
tmx.status |= STA_INS;
break;
case -1:
tmx.status |= STA_DEL;
break;
}
r = clock_adjtime(CLOCK_REALTIME, &tmx);
if (r < 0)
return r;
m->drift_ppm = tmx.freq / 65536;
log_debug(" status : %04i %s\n"
" time now : %li.%03lli\n"
" constant : %li\n"
" offset : %+.3f sec\n"
" freq offset : %+li (%i ppm)\n",
tmx.status, tmx.status & STA_UNSYNC ? "" : "sync",
tmx.time.tv_sec, tmx.time.tv_usec / NSEC_PER_MSEC,
tmx.constant,
(double)tmx.offset / NSEC_PER_SEC,
tmx.freq, m->drift_ppm);
return 0;
}
static bool sntp_sample_spike_detection(Manager *m, double offset, double delay) {
unsigned int i, idx_cur, idx_new, idx_min;
double jitter;
double j;
m->packet_count++;
/* ignore initial sample */
if (m->packet_count == 1)
return false;
/* store the current data in our samples array */
idx_cur = m->samples_idx;
idx_new = (idx_cur + 1) % ELEMENTSOF(m->samples);
m->samples_idx = idx_new;
m->samples[idx_new].offset = offset;
m->samples[idx_new].delay = delay;
/* calculate new jitter value from the RMS differences relative to the lowest delay sample */
jitter = m->samples_jitter;
for (idx_min = idx_cur, i = 0; i < ELEMENTSOF(m->samples); i++)
if (m->samples[i].delay > 0 && m->samples[i].delay < m->samples[idx_min].delay)
idx_min = i;
j = 0;
for (i = 0; i < ELEMENTSOF(m->samples); i++)
j += square(m->samples[i].offset - m->samples[idx_min].offset);
m->samples_jitter = sqrt(j / (ELEMENTSOF(m->samples) - 1));
/* ignore samples when resyncing */
if (m->poll_resync)
return false;
/* always accept offset if we are farther off than the round-trip delay */
if (fabs(offset) > delay)
return false;
/* we need a few samples before looking at them */
if (m->packet_count < 4)
return false;
/* do not accept anything worse than the maximum possible error of the best sample */
if (fabs(offset) > m->samples[idx_min].delay)
return true;
/* compare the difference between the current offset to the previous offset and jitter */
return fabs(offset - m->samples[idx_cur].offset) > 3 * jitter;
}
static void sntp_adjust_poll(Manager *m, double offset, bool spike) {
if (m->poll_resync) {
m->poll_interval_usec = NTP_POLL_INTERVAL_MIN_SEC * USEC_PER_SEC;
m->poll_resync = false;
return;
}
/* set to minimal poll interval */
if (!spike && fabs(offset) > NTP_ACCURACY_SEC) {
m->poll_interval_usec = NTP_POLL_INTERVAL_MIN_SEC * USEC_PER_SEC;
return;
}
/* increase polling interval */
if (fabs(offset) < NTP_ACCURACY_SEC * 0.25) {
if (m->poll_interval_usec < NTP_POLL_INTERVAL_MAX_SEC * USEC_PER_SEC)
m->poll_interval_usec *= 2;
return;
}
/* decrease polling interval */
if (spike || fabs(offset) > NTP_ACCURACY_SEC * 0.75) {
if (m->poll_interval_usec > NTP_POLL_INTERVAL_MIN_SEC * USEC_PER_SEC)
m->poll_interval_usec /= 2;
return;
}
}
static int sntp_receive_response(sd_event_source *source, int fd, uint32_t revents, void *userdata) {
Manager *m = userdata;
unsigned char buf[sizeof(struct ntp_msg)];
struct iovec iov = {
.iov_base = buf,
.iov_len = sizeof(buf),
};
union {
struct cmsghdr cmsghdr;
uint8_t buf[CMSG_SPACE(sizeof(struct timeval))];
} control;
struct sockaddr_in server_addr;
struct msghdr msghdr = {
.msg_iov = &iov,
.msg_iovlen = 1,
.msg_control = &control,
.msg_controllen = sizeof(control),
.msg_name = &server_addr,
.msg_namelen = sizeof(server_addr),
};
struct cmsghdr *cmsg;
struct timespec now_ts;
struct timeval *recv_time;
ssize_t len;
struct ntp_msg *ntpmsg;
double origin, receive, trans, dest;
double delay, offset;
bool spike;
int leap_sec;
int r;
if (revents & (EPOLLHUP|EPOLLERR)) {
log_debug("Server connection returned error. Closing.");
sntp_server_disconnect(m);
return -ENOTCONN;
}
len = recvmsg(fd, &msghdr, MSG_DONTWAIT);
if (len < 0) {
log_debug("Error receiving message. Disconnecting.");
return -EINVAL;
}
if (iov.iov_len < sizeof(struct ntp_msg)) {
log_debug("Invalid response from server. Disconnecting.");
return -EINVAL;
}
if (m->server_addr.sin_addr.s_addr != server_addr.sin_addr.s_addr) {
log_debug("Response from unknown server. Disconnecting.");
return -EINVAL;
}
recv_time = NULL;
for (cmsg = CMSG_FIRSTHDR(&msghdr); cmsg; cmsg = CMSG_NXTHDR(&msghdr, cmsg)) {
if (cmsg->cmsg_level != SOL_SOCKET)
continue;
switch (cmsg->cmsg_type) {
case SCM_TIMESTAMP:
recv_time = (struct timeval *) CMSG_DATA(cmsg);
break;
}
}
if (!recv_time) {
log_debug("Invalid packet timestamp. Disconnecting.");
return -EINVAL;
}
ntpmsg = iov.iov_base;
if (!m->pending) {
log_debug("Unexpected reply. Ignoring.");
return 0;
}
/* check our "time cookie" (we just stored nanoseconds in the fraction field) */
if (be32toh(ntpmsg->origin_time.sec) != m->trans_time.tv_sec + OFFSET_1900_1970 ||
be32toh(ntpmsg->origin_time.frac) != m->trans_time.tv_nsec) {
log_debug("Invalid reply; not our transmit time. Ignoring.");
return 0;
}
if (NTP_FIELD_LEAP(ntpmsg->field) == NTP_LEAP_NOTINSYNC) {
log_debug("Server is not synchronized. Disconnecting.");
return -EINVAL;
}
if (NTP_FIELD_VERSION(ntpmsg->field) != 4) {
log_debug("Response NTPv%d. Disconnecting.", NTP_FIELD_VERSION(ntpmsg->field));
return -EINVAL;
}
if (NTP_FIELD_MODE(ntpmsg->field) != NTP_MODE_SERVER) {
log_debug("Unsupported mode %d. Disconnecting.", NTP_FIELD_MODE(ntpmsg->field));
return -EINVAL;
}
/* valid packet */
m->pending = false;
m->retry_interval = 0;
/* announce leap seconds */
if (NTP_FIELD_LEAP(ntpmsg->field) & NTP_LEAP_PLUSSEC)
leap_sec = 1;
else if (NTP_FIELD_LEAP(ntpmsg->field) & NTP_LEAP_MINUSSEC)
leap_sec = -1;
else
leap_sec = 0;
/*
* "Timestamp Name ID When Generated
* ------------------------------------------------------------
* Originate Timestamp T1 time request sent by client
* Receive Timestamp T2 time request received by server
* Transmit Timestamp T3 time reply sent by server
* Destination Timestamp T4 time reply received by client
*
* The round-trip delay, d, and system clock offset, t, are defined as:
* d = (T4 - T1) - (T3 - T2) t = ((T2 - T1) + (T3 - T4)) / 2"
*/
clock_gettime(CLOCK_MONOTONIC, &now_ts);
origin = tv_to_d(recv_time) - (ts_to_d(&now_ts) - ts_to_d(&m->trans_time_mon)) + OFFSET_1900_1970;
receive = ntp_ts_to_d(&ntpmsg->recv_time);
trans = ntp_ts_to_d(&ntpmsg->trans_time);
dest = tv_to_d(recv_time) + OFFSET_1900_1970;
offset = ((receive - origin) + (trans - dest)) / 2;
delay = (dest - origin) - (trans - receive);
spike = sntp_sample_spike_detection(m, offset, delay);
sntp_adjust_poll(m, offset, spike);
log_debug("NTP response:\n"
" leap : %u\n"
" version : %u\n"
" mode : %u\n"
" stratum : %u\n"
" precision : %.6f sec (%d)\n"
" reference : %.4s\n"
" origin : %.3f\n"
" receive : %.3f\n"
" transmit : %.3f\n"
" dest : %.3f\n"
" offset : %+.3f sec\n"
" delay : %+.3f sec\n"
" packet count : %"PRIu64"\n"
" jitter : %.3f%s\n"
" poll interval: %llu\n",
NTP_FIELD_LEAP(ntpmsg->field),
NTP_FIELD_VERSION(ntpmsg->field),
NTP_FIELD_MODE(ntpmsg->field),
ntpmsg->stratum,
exp2(ntpmsg->precision), ntpmsg->precision,
ntpmsg->stratum == 1 ? ntpmsg->refid : "n/a",
origin - OFFSET_1900_1970,
receive - OFFSET_1900_1970,
trans - OFFSET_1900_1970,
dest - OFFSET_1900_1970,
offset, delay,
m->packet_count,
m->samples_jitter, spike ? " spike" : "",
m->poll_interval_usec / USEC_PER_SEC);
if (!spike) {
r = sntp_adjust_clock(m, offset, leap_sec);
if (r < 0)
log_error("Failed to call clock_adjtime(): %m");
}
log_info("%s: interval/delta/delay/jitter/drift %llus/%+.3fs/%.3fs/%.3fs/%uppm%s",
m->server, m->poll_interval_usec / USEC_PER_SEC, offset, delay, m->samples_jitter, m->drift_ppm,
spike ? " (ignored)" : "");
r = sntp_arm_timer(m, m->poll_interval_usec);
if (r < 0)
return r;
return 0;
}
static int sntp_server_connect(Manager *m, const char *server) {
_cleanup_free_ char *s = NULL;
assert(m);
assert(server);
assert(m->server_socket >= 0);
s = strdup(server);
if (!s)
return -ENOMEM;
free(m->server);
m->server = s;
s = NULL;
zero(m->server_addr);
m->server_addr.sin_family = AF_INET;
m->server_addr.sin_addr.s_addr = inet_addr(server);
m->poll_interval_usec = NTP_POLL_INTERVAL_MIN_SEC * USEC_PER_SEC;
return sntp_send_request(m);
}
static void sntp_server_disconnect(Manager *m) {
if (!m->server)
return;
m->event_timer = sd_event_source_unref(m->event_timer);
m->event_clock_watch = sd_event_source_unref(m->event_clock_watch);
if (m->clock_watch_fd > 0)
close(m->clock_watch_fd);
m->clock_watch_fd = -1;
m->event_receive = sd_event_source_unref(m->event_receive);
if (m->server_socket > 0)
close(m->server_socket);
m->server_socket = -1;
zero(m->server_addr);
free(m->server);
m->server = NULL;
}
static int sntp_listen_setup(Manager *m) {
_cleanup_close_ int fd = -1;
struct sockaddr_in addr;
const int on = 1;
const int tos = IPTOS_LOWDELAY;
int r;
fd = socket(PF_INET, SOCK_DGRAM | SOCK_CLOEXEC, 0);
if (fd < 0)
return -errno;
zero(addr);
addr.sin_family = AF_INET;
r = bind(fd, (struct sockaddr *)&addr, sizeof(addr));
if (r < 0)
return -errno;
r = setsockopt(fd, SOL_SOCKET, SO_TIMESTAMP, &on, sizeof(on));
if (r < 0)
return -errno;
r = setsockopt(fd, IPPROTO_IP, IP_TOS, &tos, sizeof(tos));
if (r < 0)
return -errno;
r = sd_event_add_io(m->event, &m->event_receive, fd, EPOLLIN, sntp_receive_response, m);
if (r < 0)
return r;
m->server_socket = fd;
fd = -1;
return 0;
}
static int manager_new(Manager **ret) {
_cleanup_manager_free_ Manager *m = NULL;
int r;
m = new0(Manager, 1);
if (!m)
return -ENOMEM;
r = sd_event_default(&m->event);
if (r < 0)
return r;
r = sntp_listen_setup(m);
if (r < 0)
return r;
r = sntp_clock_watch_setup(m);
if (r < 0)
return r;
*ret = m;
m = NULL;
return 0;
}
static void manager_free(Manager *m) {
if (!m)
return;
sd_event_unref(m->event);
free(m);
}
int main(int argc, char *argv[]) {
_cleanup_manager_free_ Manager *m = NULL;
const char *server;
int r;
log_set_target(LOG_TARGET_AUTO);
log_parse_environment();
log_open();
r = manager_new(&m);
if (r < 0)
goto out;
server = "216.239.32.15"; /* time1.google.com */
sd_notify(false, "READY=1");
r = sntp_server_connect(m, server);
if (r < 0)
goto out;
sd_notifyf(false, "STATUS=Using Time Server: %s", server);
r = sd_event_loop(m->event);
if (r < 0)
goto out;
out:
return r < 0 ? EXIT_FAILURE : EXIT_SUCCESS;
}
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