/*-*- 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 .
***/
/*
* "Simple Network Time Protocol Version 4 (SNTPv4) is a subset of the
* Network Time Protocol (NTP) used to synchronize computer clocks in
* the Internet. SNTPv4 can be used when the ultimate performance of
* a full NTP implementation based on RFC 1305 is neither needed nor
* justified."
*
* "Unlike most NTP clients, SNTP clients normally operate with only a
* single server at a time."
*
* http://tools.ietf.org/html/rfc4330
*/
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include "util.h"
#include "sparse-endian.h"
#include "log.h"
#include "sd-event.h"
#include "timedate-sntp.h"
#ifndef ADJ_SETOFFSET
#define ADJ_SETOFFSET 0x0100 /* add 'time' to current time */
#endif
/* Maximum delta in seconds which the system clock is gradually adjusted
* to approach the network time. Deltas larger that this are set by letting
* the system time jump. The maximum for adjtime is 500ms.
*/
#define NTP_MAX_ADJUST 0.2
/*
* "Define the required accuracy of the system clock, then calculate the
* maximum timeout. Use the longest maximum timeout possible given the system
* constraints to minimize time server aggregate load."
*
* "A client MUST NOT under any conditions use a poll interval less
* than 15 seconds."
*/
#define NTP_POLL_INTERVAL_MIN_SEC 16
#define NTP_POLL_INTERVAL_MAX_SEC 2048
#define NTP_ACCURACY_SEC 0.1
#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_;
struct SNTPContext {
sd_event_source *event_receive;
sd_event_source *event_timer;
char *server;
struct sockaddr_in server_addr;
int server_socket;
uint64_t packet_count;
struct timespec trans_time_mon;
struct timespec trans_time;
bool pending;
usec_t poll_interval;
struct {
double offset;
double delay;
} samples[8];
unsigned int samples_idx;
double samples_jitter;
};
static int sntp_arm_timer(SNTPContext *sntp);
static double ntp_ts_to_d(const struct ntp_ts *ts) {
return be32toh(ts->sec) + ((double)be32toh(ts->frac) / UINT_MAX);
}
static double tv_to_d(const struct timeval *tv) {
return tv->tv_sec + (1.0e-6 * tv->tv_usec);
}
static double ts_to_d(const struct timespec *ts) {
return ts->tv_sec + (1.0e-9 * ts->tv_nsec);
}
static void d_to_tv(double d, struct timeval *tv) {
tv->tv_sec = (long)d;
tv->tv_usec = (d - tv->tv_sec) * 1000 * 1000;
/* the kernel expects -0.3s as {-1, 7000.000} */
if (tv->tv_usec < 0) {
tv->tv_sec -= 1;
tv->tv_usec += 1000 * 1000;
}
}
static double square(double d) {
return d * d;
}
static int sntp_send_request(SNTPContext *sntp) {
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, &sntp->trans_time_mon);
clock_gettime(CLOCK_REALTIME, &sntp->trans_time);
ntpmsg.trans_time.sec = htobe32(sntp->trans_time.tv_sec + OFFSET_1900_1970);
ntpmsg.trans_time.frac = htobe32(sntp->trans_time.tv_nsec);
addr.sin_family = AF_INET;
addr.sin_port = htobe16(123);
addr.sin_addr.s_addr = inet_addr(sntp->server);
len = sendto(sntp->server_socket, &ntpmsg, sizeof(ntpmsg), MSG_DONTWAIT, &addr, sizeof(addr));
if (len < 0) {
log_debug("Sending NTP request to %s failed: %m", sntp->server);
return -errno;
}
sntp->pending = true;
/* re-arm timer for next poll interval, in case the packet never arrives back */
r = sntp_arm_timer(sntp);
if (r < 0)
return r;
log_debug("Sent NTP request to: %s", sntp->server);
return 0;
}
static int sntp_timer(sd_event_source *source, usec_t usec, void *userdata) {
SNTPContext *sntp = userdata;
assert(sntp);
sntp_send_request(sntp);
return 0;
}
static int sntp_arm_timer(SNTPContext *sntp) {
sd_event *e;
int r;
assert(sntp);
assert(sntp->event_receive);
if (sntp->poll_interval <= 0) {
sntp->event_timer = sd_event_source_unref(sntp->event_timer);
return 0;
}
if (sntp->event_timer) {
r = sd_event_source_set_time(sntp->event_timer, now(CLOCK_MONOTONIC) + sntp->poll_interval);
if (r < 0)
return r;
return sd_event_source_set_enabled(sntp->event_timer, SD_EVENT_ONESHOT);
}
e = sd_event_source_get_event(sntp->event_receive);
r = sd_event_add_monotonic(e, &sntp->event_timer, now(CLOCK_MONOTONIC) + sntp->poll_interval, 0, sntp_timer, sntp);
if (r < 0)
return r;
return 0;
}
static int sntp_adjust_clock(SNTPContext *sntp, 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 (offset < NTP_MAX_ADJUST && offset > -NTP_MAX_ADJUST) {
int constant;
constant = log2i(sntp->poll_interval / USEC_PER_SEC) - 5;
tmx.modes |= ADJ_STATUS | ADJ_OFFSET | ADJ_TIMECONST;
tmx.status = STA_PLL;
tmx.offset = offset * 1000 * 1000;
tmx.constant = constant;
log_debug(" adjust (slew): %+f sec\n", (double)tmx.offset / USEC_PER_SEC);
} else {
tmx.modes = ADJ_SETOFFSET;
d_to_tv(offset, &tmx.time);
log_debug(" adjust (jump): %+f sec\n", tv_to_d(&tmx.time));
}
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;
log_debug(" status : %04i %s\n"
" time now : %li.%06li\n"
" constant : %li\n"
" offset : %+f sec\n"
" freq offset : %+li (%+.3f ppm)\n",
tmx.status, tmx.status & STA_UNSYNC ? "" : "sync",
tmx.time.tv_sec, tmx.time.tv_usec,
tmx.constant,
(double)tmx.offset / USEC_PER_SEC,
tmx.freq, (double)tmx.freq / 65536);
return 0;
}
static bool sntp_sample_spike_detection(SNTPContext *sntp, double offset, double delay) {
unsigned int i, idx_cur, idx_new, idx_min;
double jitter;
bool spike;
/* store the current data in our samples array */
idx_cur = sntp->samples_idx;
idx_new = (idx_cur + 1) % ELEMENTSOF(sntp->samples);
sntp->samples_idx = idx_new;
sntp->samples[idx_new].offset = offset;
sntp->samples[idx_new].delay = delay;
sntp->packet_count++;
/*
* Spike detection; compare the difference between the
* current offset to the previous offset and jitter.
*/
spike = sntp->packet_count > 2 && fabs(offset - sntp->samples[idx_cur].offset) > sntp->samples_jitter * 3;
/* calculate new jitter value from the RMS differences relative to the lowest delay sample */
for (idx_min = idx_cur, i = 0; i < ELEMENTSOF(sntp->samples); i++)
if (sntp->samples[i].delay > 0 && sntp->samples[i].delay < sntp->samples[idx_min].delay)
idx_min = i;
for (jitter = 0, i = 0; i < ELEMENTSOF(sntp->samples); i++)
jitter += square(sntp->samples[i].offset - sntp->samples[idx_min].offset);
sntp->samples_jitter = sqrt(jitter / (ELEMENTSOF(sntp->samples) - 1));
return spike;
}
static void sntp_adjust_poll(SNTPContext *sntp, double offset, bool spike) {
double delta;
if (spike) {
if (sntp->poll_interval > NTP_POLL_INTERVAL_MIN_SEC * USEC_PER_SEC)
sntp->poll_interval /= 2;
return;
}
delta = fabs(offset);
/* set to minimal poll interval */
if (delta > NTP_ACCURACY_SEC) {
sntp->poll_interval = NTP_POLL_INTERVAL_MIN_SEC * USEC_PER_SEC;
return;
}
/* increase polling interval */
if (delta < NTP_ACCURACY_SEC * 0.25) {
if (sntp->poll_interval < NTP_POLL_INTERVAL_MAX_SEC * USEC_PER_SEC)
sntp->poll_interval *= 2;
return;
}
/* decrease polling interval */
if (delta > NTP_ACCURACY_SEC * 0.75) {
if (sntp->poll_interval > NTP_POLL_INTERVAL_MIN_SEC * USEC_PER_SEC)
sntp->poll_interval /= 2;
return;
}
}
static int sntp_receive_response(sd_event_source *source, int fd, uint32_t revents, void *userdata) {
SNTPContext *sntp = 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;
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(sntp);
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 (sntp->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 (!sntp->pending) {
log_debug("Unexpected reply, ignoring");
return 0;
}
sntp->pending = false;
/* check our "time cookie" (we just stored nanoseconds in the fraction field) */
if (be32toh(ntpmsg->origin_time.sec) != sntp->trans_time.tv_sec + OFFSET_1900_1970||
be32toh(ntpmsg->origin_time.frac) != sntp->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;
}
/* 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 roundtrip 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);
origin = tv_to_d(recv_time) - (ts_to_d(&now) - ts_to_d(&sntp->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(sntp, offset, delay);
sntp_adjust_poll(sntp, offset, spike);
log_debug("NTP response:\n"
" leap : %u\n"
" version : %u\n"
" mode : %u\n"
" stratum : %u\n"
" precision : %f sec (%d)\n"
" reference : %.4s\n"
" origin : %f\n"
" receive : %f\n"
" transmit : %f\n"
" dest : %f\n"
" offset : %+f sec\n"
" delay : %+f sec\n"
" packet count : %"PRIu64"\n"
" jitter/spike : %f (%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,
sntp->packet_count,
sntp->samples_jitter, spike ? "yes" : "no",
sntp->poll_interval / USEC_PER_SEC);
log_info("%4llu %+10f %10f %10f %s",
sntp->poll_interval / USEC_PER_SEC, offset, delay, sntp->samples_jitter, spike ? "spike" : "");
if (!spike) {
r = sntp_adjust_clock(sntp, offset, leap_sec);
if (r < 0)
log_error("Failed to call clock_adjtime(): %m");
}
r = sntp_arm_timer(sntp);
if (r < 0)
return r;
return 0;
}
int sntp_server_connect(SNTPContext *sntp, const char *server) {
_cleanup_free_ char *s = NULL;
assert(sntp);
assert(server);
assert(sntp->server_socket >= 0);
s = strdup(server);
if (!s)
return -ENOMEM;
free(sntp->server);
sntp->server = s;
s = NULL;
zero(sntp->server_addr);
sntp->server_addr.sin_family = AF_INET;
sntp->server_addr.sin_addr.s_addr = inet_addr(server);
sntp->poll_interval = 2 * NTP_POLL_INTERVAL_MIN_SEC * USEC_PER_SEC;
return sntp_send_request(sntp);
}
void sntp_server_disconnect(SNTPContext *sntp) {
if (!sntp->server)
return;
sntp->event_timer = sd_event_source_unref(sntp->event_timer);
sntp->event_receive = sd_event_source_unref(sntp->event_receive);
if (sntp->server_socket > 0)
close(sntp->server_socket);
sntp->server_socket = -1;
zero(sntp->server_addr);
free(sntp->server);
sntp->server = NULL;
}
int sntp_new(SNTPContext **sntp, sd_event *e) {
_cleanup_free_ SNTPContext *c;
_cleanup_close_ int fd = -1;
struct sockaddr_in addr;
const int on = 1;
const int tos = IPTOS_LOWDELAY;
int r;
c = new0(SNTPContext, 1);
if (!c)
return -ENOMEM;
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(e, &c->event_receive, fd, EPOLLIN, sntp_receive_response, c);
if (r < 0)
return r;
c->server_socket = fd;
fd = -1;
*sntp = c;
c = NULL;
return 0;
}
SNTPContext *sntp_unref(SNTPContext *sntp) {
sntp_server_disconnect(sntp);
free(sntp);
return NULL;
}