timedated: add SNTP client/query hookup (unused for now)

3 files changed, 792 insertions, 0 deletions

diff --git a/src/timedate/test-timedate-sntp.c b/src/timedate/test-timedate-sntp.c
new file mode 100644
index 0000000000..41999c85cb
--- /dev/null
+++ b/src/timedate/test-timedate-sntp.c
@@ -0,0 +1,107 @@
+/*-*- 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 <arpa/inet.h>
+#include <netinet/in.h>
+#include <netinet/ip.h>
+#include <sys/timex.h>
+#include <sys/socket.h>
+
+#include "sd-event.h"
+#include "util.h"
+#include "log.h"
+#include "timedate-sntp.h"
+
+typedef struct Manager Manager;
+struct Manager {
+        sd_event *event;
+        SNTPContext *sntp;
+};
+
+static void manager_free(Manager *m);
+DEFINE_TRIVIAL_CLEANUP_FUNC(Manager*, manager_free);
+#define _cleanup_manager_free_ _cleanup_(manager_freep)
+
+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;
+
+        *ret = m;
+        m = NULL;
+
+        return 0;
+}
+
+static void manager_free(Manager *m) {
+
+        if (!m)
+                return;
+
+        m->sntp = sntp_unref(m->sntp);
+        sd_event_unref(m->event);
+        free(m);
+}
+
+int main(int argc, char *argv[]) {
+        _cleanup_manager_free_ Manager *m = NULL;
+        const char *server;
+        int r;
+
+        if (argv[1])
+                log_set_max_level(LOG_DEBUG);
+
+        r = manager_new(&m);
+        if (r < 0)
+                goto out;
+
+        r = sntp_new(&m->sntp, m->event);
+        if (r < 0)
+                goto out;
+
+        //server = "216.239.32.15";       /* time1.google.com */
+        //server = "192.53.103.108";      /* ntp1.ptb.de */
+        server = "130.102.2.123";       /* 0.au.pool.ntp.org */
+        r = sntp_server_connect(m->sntp, server);
+
+        if (r < 0)
+                goto out;
+
+        r = sd_event_loop(m->event);
+        if (r < 0)
+                goto out;
+
+out:
+        return r < 0 ? EXIT_FAILURE : EXIT_SUCCESS;
+}
diff --git a/src/timedate/timedate-sntp.c b/src/timedate/timedate-sntp.c
new file mode 100644
index 0000000000..608177f662
--- /dev/null
+++ b/src/timedate/timedate-sntp.c
@@ -0,0 +1,652 @@
+/*-*- 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/>.
+***/
+
+/*
+ * "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 <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/timex.h>
+#include <sys/socket.h>
+
+#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_POLL_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 int log2i(int a) {
+        int exp = 0;
+
+        assert(a > 0);
+
+        while (a > 0) {
+                a >>= 1;
+                exp++;
+        }
+
+        return exp;
+}
+
+static double log2d(int a) {
+        if (a < 0)
+                return 1.0 / (1UL << - a);
+        return 1UL << a;
+}
+
+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 snmp_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_POLL_ACCURACY_SEC) {
+                sntp->poll_interval = NTP_POLL_INTERVAL_MIN_SEC * USEC_PER_SEC;
+                return;
+        }
+
+        /* increase polling interval */
+        if (delta < NTP_POLL_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_POLL_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, recv, 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;
+        recv = 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 = ((recv - origin) + (trans - dest)) / 2;
+        delay = (dest - origin) - (trans - recv);
+
+        spike = sntp_sample_spike_detection(sntp, offset, delay);
+
+        snmp_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"
+                  "  recv         : %f\n"
+                  "  transmit     : %f\n"
+                  "  dest         : %f\n"
+                  "  offset       : %+f sec\n"
+                  "  delay        : %+f sec\n"
+                  "  packet count : %llu\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,
+                  log2d(ntpmsg->precision), ntpmsg->precision,
+                  ntpmsg->stratum == 1 ? ntpmsg->refid : "n/a",
+                  origin - OFFSET_1900_1970,
+                  recv - OFFSET_1900_1970,
+                  trans - OFFSET_1900_1970,
+                  dest - OFFSET_1900_1970,
+                  offset, delay,
+                  (unsigned long long)sntp->packet_count,
+                  sntp->samples_jitter, spike ? "yes" : "no",
+                  sntp->poll_interval / USEC_PER_SEC);
+
+        log_info("%4llu %s %+12f", sntp->poll_interval / USEC_PER_SEC, spike ? "y" : "n", offset);
+
+        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;
+}
diff --git a/src/timedate/timedate-sntp.h b/src/timedate/timedate-sntp.h
new file mode 100644
index 0000000000..09107c72cf
--- /dev/null
+++ b/src/timedate/timedate-sntp.h
@@ -0,0 +1,33 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+#pragma once
+
+/***
+  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 "util.h"
+#include "sd-event.h"
+
+typedef struct SNTPContext SNTPContext;
+struct SNTPContext;
+
+int sntp_new(SNTPContext **sntp, sd_event *e);
+SNTPContext *sntp_unref(SNTPContext *sntp);
+int sntp_server_connect(SNTPContext *sntp, const char *server);
+void sntp_server_disconnect(SNTPContext *sntp);