chiark / gitweb /
timesyncd: make use of floating event sources for signal handling
[elogind.git] / src / timesync / timesyncd.c
index 7b7ec7ae9f5b15e11eb1afae5c7483beef354f78..19e6d67c63d6203c9221455420852b3eb5ce97cc 100644 (file)
@@ -3,7 +3,7 @@
 /***
   This file is part of systemd.
 
-  Copyright 2014 Kay Sievers
+  Copyright 2014 Kay Sievers, Lennart Poettering
 
   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
 #include <sys/timerfd.h>
 #include <sys/timex.h>
 #include <sys/socket.h>
+#include <resolv.h>
+#include <sys/prctl.h>
+#include <sys/types.h>
+#include <grp.h>
 
 #include "missing.h"
 #include "util.h"
 #include "sparse-endian.h"
 #include "log.h"
+#include "socket-util.h"
+#include "list.h"
+#include "ratelimit.h"
+#include "strv.h"
+#include "conf-parser.h"
 #include "sd-event.h"
+#include "sd-resolve.h"
 #include "sd-daemon.h"
+#include "sd-network.h"
+#include "event-util.h"
+#include "network-util.h"
+#include "capability.h"
+#include "timesyncd.h"
 
 #define TIME_T_MAX (time_t)((1UL << ((sizeof(time_t) << 3) - 1)) - 1)
 
  */
 #define OFFSET_1900_1970        2208988800UL
 
+#define RETRY_USEC (30*USEC_PER_SEC)
+#define RATELIMIT_INTERVAL_USEC (10*USEC_PER_SEC)
+#define RATELIMIT_BURST 10
+
+#define TIMEOUT_USEC (10*USEC_PER_SEC)
+
 struct ntp_ts {
         be32_t sec;
         be32_t frac;
@@ -104,93 +125,65 @@ struct ntp_msg {
         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;
-
-        /* 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 int manager_arm_timer(Manager *m, usec_t next);
+static int manager_clock_watch_setup(Manager *m);
+static int manager_connect(Manager *m);
+static void manager_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 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 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 = {};
+static int manager_timeout(sd_event_source *source, usec_t usec, void *userdata) {
+        _cleanup_free_ char *pretty = NULL;
+        Manager *m = userdata;
+
+        assert(m);
+        assert(m->current_server_name);
+        assert(m->current_server_address);
+
+        sockaddr_pretty(&m->current_server_address->sockaddr.sa, m->current_server_address->socklen, true, &pretty);
+        log_info("Timed out waiting for reply from %s (%s).", strna(pretty), m->current_server_name->string);
+
+        return manager_connect(m);
+}
+
+static int manager_send_request(Manager *m) {
+        _cleanup_free_ char *pretty = NULL;
+        struct ntp_msg ntpmsg = {
+                /*
+                 * "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."
+                 */
+                .field = NTP_FIELD(0, 4, NTP_MODE_CLIENT),
+        };
         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);
+        assert(m);
+        assert(m->current_server_name);
+        assert(m->current_server_address);
+
+        m->event_timeout = sd_event_source_unref(m->event_timeout);
 
         /*
          * Set transmit timestamp, remember it; the server will send that back
@@ -200,44 +193,58 @@ static int sntp_send_request(Manager *m) {
          * 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);
+        assert_se(clock_gettime(CLOCK_MONOTONIC, &m->trans_time_mon) >= 0);
+        assert_se(clock_gettime(CLOCK_REALTIME, &m->trans_time) >= 0);
         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));
+        sockaddr_pretty(&m->current_server_address->sockaddr.sa, m->current_server_address->socklen, true, &pretty);
+
+        len = sendto(m->server_socket, &ntpmsg, sizeof(ntpmsg), MSG_DONTWAIT, &m->current_server_address->sockaddr.sa, m->current_server_address->socklen);
         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);
+                log_debug("Sent NTP request to %s (%s).", strna(pretty), m->current_server_name->string);
+        } else {
+                log_debug("Sending NTP request to %s (%s) failed: %m", strna(pretty), m->current_server_name->string);
+                return manager_connect(m);
+        }
 
-        /* re-arm timer with incresing timeout, in case the packets never arrive back */
+        /* re-arm timer with increasing 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)
+
+        r = manager_arm_timer(m, m->retry_interval);
+        if (r < 0) {
+                log_error("Failed to rearm timer: %s", strerror(-r));
                 return r;
+        }
+
+        r = sd_event_add_time(
+                        m->event,
+                        &m->event_timeout,
+                        CLOCK_MONOTONIC,
+                        now(CLOCK_MONOTONIC) + TIMEOUT_USEC, 0,
+                        manager_timeout, m);
+        if (r < 0) {
+                log_error("Failed to arm timeout timer: %s", strerror(-r));
+                return r;
+        }
 
         return 0;
 }
 
-static int sntp_timer(sd_event_source *source, usec_t usec, void *userdata) {
+static int manager_timer(sd_event_source *source, usec_t usec, void *userdata) {
         Manager *m = userdata;
 
         assert(m);
 
-        sntp_send_request(m);
-        return 0;
+        return manager_send_request(m);
 }
 
-static int sntp_arm_timer(Manager *m, usec_t next) {
+static int manager_arm_timer(Manager *m, usec_t next) {
         int r;
 
         assert(m);
@@ -256,26 +263,21 @@ static int sntp_arm_timer(Manager *m, usec_t next) {
                 return sd_event_source_set_enabled(m->event_timer, SD_EVENT_ONESHOT);
         }
 
-        r = sd_event_add_time(
+        return 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;
+                        manager_timer, m);
 }
 
-static int sntp_clock_watch(sd_event_source *source, int fd, uint32_t revents, void *userdata) {
+static int manager_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);
+        manager_clock_watch_setup(m);
 
         /* skip our own jumps */
         if (m->jumped) {
@@ -286,55 +288,49 @@ static int sntp_clock_watch(sd_event_source *source, int fd, uint32_t revents, v
         /* resync */
         log_info("System time changed. Resyncing.");
         m->poll_resync = true;
-        sntp_send_request(m);
-
-        return 0;
+        return manager_send_request(m);
 }
 
 /* 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 *e;
-        sd_event_source *source;
+static int manager_clock_watch_setup(Manager *m) {
+
+        struct itimerspec its = {
+                .it_value.tv_sec = TIME_T_MAX
+        };
+
         int r;
 
         assert(m);
-        assert(m->event_receive);
 
-        fd = timerfd_create(CLOCK_REALTIME, TFD_NONBLOCK|TFD_CLOEXEC);
-        if (fd < 0) {
+        m->event_clock_watch = sd_event_source_unref(m->event_clock_watch);
+        safe_close(m->clock_watch_fd);
+
+        m->clock_watch_fd = timerfd_create(CLOCK_REALTIME, TFD_NONBLOCK|TFD_CLOEXEC);
+        if (m->clock_watch_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) {
+        if (timerfd_settime(m->clock_watch_fd, TFD_TIMER_ABSTIME|TFD_TIMER_CANCEL_ON_SET, &its, NULL) < 0) {
                 log_error("Failed to set up timerfd: %m");
                 return -errno;
         }
 
-        e = sd_event_source_get_event(m->event_receive);
-        r = sd_event_add_io(e, &source, fd, EPOLLIN, sntp_clock_watch, m);
+        r = sd_event_add_io(m->event, &m->event_clock_watch, m->clock_watch_fd, EPOLLIN, manager_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) {
+static int manager_adjust_clock(Manager *m, double offset, int leap_sec) {
         struct timex tmx = {};
         int r;
 
+        assert(m);
+
         /*
          * For small deltas, tell the kernel to gradually adjust the system
          * clock to the NTP time, larger deltas are just directly set.
@@ -343,19 +339,28 @@ static int sntp_adjust_clock(Manager *m, double offset, int leap_sec) {
          * syncs the system time periodically to the hardware clock.
          */
         if (fabs(offset) < NTP_MAX_ADJUST) {
-                tmx.modes = ADJ_STATUS | ADJ_OFFSET | ADJ_TIMECONST | ADJ_MAXERROR | ADJ_ESTERROR;
+                tmx.modes = ADJ_STATUS | ADJ_NANO | ADJ_OFFSET | ADJ_TIMECONST | ADJ_MAXERROR | ADJ_ESTERROR;
                 tmx.status = STA_PLL;
-                tmx.offset = offset * USEC_PER_SEC;
-                tmx.constant = log2i(m->poll_interval_usec / USEC_PER_SEC) - 6;
+                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", (double)tmx.offset / USEC_PER_SEC);
+                log_debug("  adjust (slew): %+.3f sec\n", offset);
         } else {
-                tmx.modes = ADJ_SETOFFSET;
-                d_to_tv(offset, &tmx.time);
+                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", tv_to_d(&tmx.time));
+                log_debug("  adjust (jump): %+.3f sec\n", offset);
         }
 
         switch (leap_sec) {
@@ -371,25 +376,29 @@ static int sntp_adjust_clock(Manager *m, double offset, int leap_sec) {
         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 (%+.3f ppm)\n",
+                  "  freq offset  : %+li (%i ppm)\n",
                   tmx.status, tmx.status & STA_UNSYNC ? "" : "sync",
-                  tmx.time.tv_sec, tmx.time.tv_usec / USEC_PER_MSEC,
+                  tmx.time.tv_sec, tmx.time.tv_usec / NSEC_PER_MSEC,
                   tmx.constant,
-                  (double)tmx.offset / USEC_PER_SEC,
-                  tmx.freq, (double)tmx.freq / 65536);
+                  (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) {
+static bool manager_sample_spike_detection(Manager *m, double offset, double delay) {
         unsigned int i, idx_cur, idx_new, idx_min;
         double jitter;
         double j;
 
+        assert(m);
+
         m->packet_count++;
 
         /* ignore initial sample */
@@ -434,7 +443,9 @@ static bool sntp_sample_spike_detection(Manager *m, double offset, double delay)
         return fabs(offset - m->samples[idx_cur].offset) > 3 * jitter;
 }
 
-static void sntp_adjust_poll(Manager *m, double offset, bool spike) {
+static void manager_adjust_poll(Manager *m, double offset, bool spike) {
+        assert(m);
+
         if (m->poll_resync) {
                 m->poll_interval_usec = NTP_POLL_INTERVAL_MIN_SEC * USEC_PER_SEC;
                 m->poll_resync = false;
@@ -462,18 +473,35 @@ static void sntp_adjust_poll(Manager *m, double offset, bool spike) {
         }
 }
 
-static int sntp_receive_response(sd_event_source *source, int fd, uint32_t revents, void *userdata) {
+static bool sockaddr_equal(union sockaddr_union *a, union sockaddr_union *b) {
+        assert(a);
+        assert(b);
+
+        if (a->sa.sa_family != b->sa.sa_family)
+                return false;
+
+        if (a->sa.sa_family == AF_INET)
+                return a->in.sin_addr.s_addr == b->in.sin_addr.s_addr;
+
+        if (a->sa.sa_family == AF_INET6)
+                return memcmp(&a->in6.sin6_addr, &b->in6.sin6_addr, sizeof(a->in6.sin6_addr)) == 0;
+
+        return false;
+}
+
+static int manager_receive_response(sd_event_source *source, int fd, uint32_t revents, void *userdata) {
         Manager *m = userdata;
-        unsigned char buf[sizeof(struct ntp_msg)];
+        struct ntp_msg ntpmsg;
+
         struct iovec iov = {
-                .iov_base = buf,
-                .iov_len = sizeof(buf),
+                .iov_base = &ntpmsg,
+                .iov_len = sizeof(ntpmsg),
         };
         union {
                 struct cmsghdr cmsghdr;
                 uint8_t buf[CMSG_SPACE(sizeof(struct timeval))];
         } control;
-        struct sockaddr_in server_addr;
+        union sockaddr_union server_addr;
         struct msghdr msghdr = {
                 .msg_iov = &iov,
                 .msg_iovlen = 1,
@@ -486,33 +514,39 @@ static int sntp_receive_response(sd_event_source *source, int fd, uint32_t reven
         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;
 
+        assert(source);
+        assert(m);
+
         if (revents & (EPOLLHUP|EPOLLERR)) {
-                log_debug("Server connection returned error. Closing.");
-                sntp_server_disconnect(m);
-                return -ENOTCONN;
+                log_warning("Server connection returned error.");
+                return manager_connect(m);
         }
 
         len = recvmsg(fd, &msghdr, MSG_DONTWAIT);
         if (len < 0) {
-                log_debug("Error receiving message. Disconnecting.");
-                return -EINVAL;
+                if (errno == EAGAIN)
+                        return 0;
+
+                log_warning("Error receiving message. Disconnecting.");
+                return manager_connect(m);
         }
 
         if (iov.iov_len < sizeof(struct ntp_msg)) {
-                log_debug("Invalid response from server. Disconnecting.");
-                return -EINVAL;
+                log_warning("Invalid response from server. Disconnecting.");
+                return manager_connect(m);
         }
 
-        if (m->server_addr.sin_addr.s_addr != server_addr.sin_addr.s_addr) {
-                log_debug("Response from unknown server. Disconnecting.");
-                return -EINVAL;
+        if (!m->current_server_name ||
+            !m->current_server_address ||
+            !sockaddr_equal(&server_addr, &m->current_server_address->sockaddr)) {
+                log_debug("Response from unknown server.");
+                return 0;
         }
 
         recv_time = NULL;
@@ -527,36 +561,43 @@ static int sntp_receive_response(sd_event_source *source, int fd, uint32_t reven
                 }
         }
         if (!recv_time) {
-                log_debug("Invalid packet timestamp. Disconnecting.");
+                log_error("Invalid packet timestamp.");
                 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) {
+        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) {
+        m->event_timeout = sd_event_source_unref(m->event_timeout);
+
+        if (be32toh(ntpmsg.recv_time.sec) < TIME_EPOCH + OFFSET_1900_1970 ||
+            be32toh(ntpmsg.trans_time.sec) < TIME_EPOCH + OFFSET_1900_1970) {
+                log_debug("Invalid reply, returned times before epoch. Ignoring.");
+                return manager_connect(m);
+        }
+
+        if (NTP_FIELD_LEAP(ntpmsg.field) == NTP_LEAP_NOTINSYNC) {
                 log_debug("Server is not synchronized. Disconnecting.");
-                return -EINVAL;
+                return manager_connect(m);
         }
 
-        if (NTP_FIELD_VERSION(ntpmsg->field) != 4) {
-                log_debug("Response NTPv%d. Disconnecting.", NTP_FIELD_VERSION(ntpmsg->field));
-                return -EINVAL;
+        if (!IN_SET(NTP_FIELD_VERSION(ntpmsg.field), 3, 4)) {
+                log_debug("Response NTPv%d. Disconnecting.", NTP_FIELD_VERSION(ntpmsg.field));
+                return manager_connect(m);
         }
 
-        if (NTP_FIELD_MODE(ntpmsg->field) != NTP_MODE_SERVER) {
-                log_debug("Unsupported mode %d. Disconnecting.", NTP_FIELD_MODE(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 manager_connect(m);
         }
 
         /* valid packet */
@@ -564,9 +605,9 @@ static int sntp_receive_response(sd_event_source *source, int fd, uint32_t reven
         m->retry_interval = 0;
 
         /* announce leap seconds */
-        if (NTP_FIELD_LEAP(ntpmsg->field) & NTP_LEAP_PLUSSEC)
+        if (NTP_FIELD_LEAP(ntpmsg.field) & NTP_LEAP_PLUSSEC)
                 leap_sec = 1;
-        else if (NTP_FIELD_LEAP(ntpmsg->field) & NTP_LEAP_MINUSSEC)
+        else if (NTP_FIELD_LEAP(ntpmsg.field) & NTP_LEAP_MINUSSEC)
                 leap_sec = -1;
         else
                 leap_sec = 0;
@@ -582,25 +623,25 @@ static int sntp_receive_response(sd_event_source *source, int fd, uint32_t reven
          *  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);
+        assert_se(clock_gettime(CLOCK_MONOTONIC, &now_ts) >= 0);
         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);
+        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);
+        spike = manager_sample_spike_detection(m, offset, delay);
 
-        sntp_adjust_poll(m, offset, spike);
+        manager_adjust_poll(m, offset, spike);
 
         log_debug("NTP response:\n"
                   "  leap         : %u\n"
                   "  version      : %u\n"
                   "  mode         : %u\n"
                   "  stratum      : %u\n"
-                  "  precision    : %.3f sec (%d)\n"
+                  "  precision    : %.6f sec (%d)\n"
                   "  reference    : %.4s\n"
                   "  origin       : %.3f\n"
                   "  receive      : %.3f\n"
@@ -611,12 +652,12 @@ static int sntp_receive_response(sd_event_source *source, int fd, uint32_t reven
                   "  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",
+                  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,
@@ -626,102 +667,299 @@ static int sntp_receive_response(sd_event_source *source, int fd, uint32_t reven
                   m->samples_jitter, spike ? " spike" : "",
                   m->poll_interval_usec / USEC_PER_SEC);
 
-        log_info("%s: interval/delta/delay/jitter %llu/%+.3f/%.3f/%.3f%s",
-                 m->server, m->poll_interval_usec / USEC_PER_SEC, offset, delay, m->samples_jitter, spike ? " (ignored)" : "");
-
         if (!spike) {
-                r = sntp_adjust_clock(m, offset, leap_sec);
+                r = manager_adjust_clock(m, offset, leap_sec);
                 if (r < 0)
                         log_error("Failed to call clock_adjtime(): %m");
         }
 
-        r = sntp_arm_timer(m, m->poll_interval_usec);
-        if (r < 0)
+        log_info("interval/delta/delay/jitter/drift %llus/%+.3fs/%.3fs/%.3fs/%+ippm%s",
+                 m->poll_interval_usec / USEC_PER_SEC, offset, delay, m->samples_jitter, m->drift_ppm,
+                 spike ? " (ignored)" : "");
+
+        r = manager_arm_timer(m, m->poll_interval_usec);
+        if (r < 0) {
+                log_error("Failed to rearm timer: %s", strerror(-r));
                 return r;
+        }
 
         return 0;
 }
 
-static int sntp_server_connect(Manager *m, const char *server) {
-        _cleanup_free_ char *s = NULL;
+static int manager_listen_setup(Manager *m) {
+        union sockaddr_union addr = {};
+        static const int tos = IPTOS_LOWDELAY;
+        static const int on = 1;
+        int r;
 
         assert(m);
-        assert(server);
-        assert(m->server_socket >= 0);
 
-        s = strdup(server);
-        if (!s)
-                return -ENOMEM;
+        assert(m->server_socket < 0);
+        assert(!m->event_receive);
+        assert(m->current_server_address);
+
+        addr.sa.sa_family = m->current_server_address->sockaddr.sa.sa_family;
+
+        m->server_socket = socket(addr.sa.sa_family, SOCK_DGRAM | SOCK_CLOEXEC, 0);
+        if (m->server_socket < 0)
+                return -errno;
+
+        r = bind(m->server_socket, &addr.sa, m->current_server_address->socklen);
+        if (r < 0)
+                return -errno;
 
-        free(m->server);
-        m->server = s;
-        s = NULL;
+        r = setsockopt(m->server_socket, SOL_SOCKET, SO_TIMESTAMP, &on, sizeof(on));
+        if (r < 0)
+                return -errno;
 
-        zero(m->server_addr);
-        m->server_addr.sin_family = AF_INET;
-        m->server_addr.sin_addr.s_addr = inet_addr(server);
+        setsockopt(m->server_socket, IPPROTO_IP, IP_TOS, &tos, sizeof(tos));
+
+        return sd_event_add_io(m->event, &m->event_receive, m->server_socket, EPOLLIN, manager_receive_response, m);
+}
+
+static int manager_begin(Manager *m) {
+        _cleanup_free_ char *pretty = NULL;
+        int r;
+
+        assert(m);
+        assert_return(m->current_server_name, -EHOSTUNREACH);
+        assert_return(m->current_server_address, -EHOSTUNREACH);
 
         m->poll_interval_usec = NTP_POLL_INTERVAL_MIN_SEC * USEC_PER_SEC;
 
-        return sntp_send_request(m);
+        sockaddr_pretty(&m->current_server_address->sockaddr.sa, m->current_server_address->socklen, true, &pretty);
+        log_info("Using NTP server %s (%s).", strna(pretty), m->current_server_name->string);
+        sd_notifyf(false, "STATUS=Using Time Server %s (%s).", strna(pretty), m->current_server_name->string);
+
+        r = manager_listen_setup(m);
+        if (r < 0) {
+                log_warning("Failed to setup connection socket: %s", strerror(-r));
+                return r;
+        }
+
+        r = manager_clock_watch_setup(m);
+        if (r < 0)
+                return r;
+
+        return manager_send_request(m);
 }
 
-static void sntp_server_disconnect(Manager *m) {
-        if (!m->server)
-                return;
+static void server_name_flush_addresses(ServerName *n) {
+        ServerAddress *a;
 
-        m->event_timer = sd_event_source_unref(m->event_timer);
+        assert(n);
 
-        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;
+        while ((a = n->addresses)) {
+                LIST_REMOVE(addresses, n->addresses, a);
+                free(a);
+        }
+}
 
-        m->event_receive = sd_event_source_unref(m->event_receive);
-        if (m->server_socket > 0)
-                close(m->server_socket);
-        m->server_socket = -1;
+static void manager_flush_names(Manager *m) {
+        ServerName *n;
+
+        assert(m);
 
-        zero(m->server_addr);
-        free(m->server);
-        m->server = NULL;
+        while ((n = m->servers)) {
+                LIST_REMOVE(names, m->servers, n);
+                free(n->string);
+                server_name_flush_addresses(n);
+                free(n);
+        }
 }
 
-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;
+static int manager_resolve_handler(sd_resolve_query *q, int ret, const struct addrinfo *ai, void *userdata) {
+        Manager *m = userdata;
+        ServerAddress *a, *last = NULL;
+
+        assert(q);
+        assert(m);
+        assert(m->current_server_name);
+
+        m->resolve_query = sd_resolve_query_unref(m->resolve_query);
+
+        if (ret != 0) {
+                log_info("Failed to resolve %s: %s", m->current_server_name->string, gai_strerror(ret));
+
+                /* Try next host */
+                return manager_connect(m);
+        }
+
+        server_name_flush_addresses(m->current_server_name);
+
+        for (; ai; ai = ai->ai_next) {
+                _cleanup_free_ char *pretty = NULL;
+
+                assert(ai->ai_addr);
+                assert(ai->ai_addrlen >= offsetof(struct sockaddr, sa_data));
+                assert(ai->ai_addrlen <= sizeof(union sockaddr_union));
+
+                if (!IN_SET(ai->ai_addr->sa_family, AF_INET, AF_INET6)) {
+                        log_warning("Unsuitable address protocol for %s", m->current_server_name->string);
+                        continue;
+                }
+
+                a = new0(ServerAddress, 1);
+                if (!a)
+                        return log_oom();
+
+                memcpy(&a->sockaddr, ai->ai_addr, ai->ai_addrlen);
+                a->socklen = ai->ai_addrlen;
+
+                LIST_INSERT_AFTER(addresses, m->current_server_name->addresses, last, a);
+                last = a;
+
+                sockaddr_pretty(&a->sockaddr.sa, a->socklen, true, &pretty);
+                log_debug("Resolved address %s for %s.", pretty, m->current_server_name->string);
+        }
+
+        if (!m->current_server_name->addresses) {
+                log_error("Failed to find suitable address for host %s.", m->current_server_name->string);
+
+                /* Try next host */
+                return manager_connect(m);
+        }
+
+        m->current_server_address = m->current_server_name->addresses;
+
+        return manager_begin(m);
+}
+
+static int manager_retry(sd_event_source *source, usec_t usec, void *userdata) {
+        Manager *m = userdata;
+
+        assert(m);
+
+        return manager_connect(m);
+}
+
+static int manager_connect(Manager *m) {
+
+        struct addrinfo hints = {
+                .ai_flags = AI_NUMERICSERV|AI_ADDRCONFIG,
+                .ai_socktype = SOCK_DGRAM,
+        };
         int r;
 
-        fd = socket(PF_INET, SOCK_DGRAM | SOCK_CLOEXEC, 0);
-        if (fd < 0)
-                return -errno;
+        assert(m);
 
-        zero(addr);
-        addr.sin_family = AF_INET;
-        r = bind(fd, (struct sockaddr *)&addr, sizeof(addr));
-        if (r < 0)
-                return -errno;
+        manager_disconnect(m);
 
-        r = setsockopt(fd, SOL_SOCKET, SO_TIMESTAMP, &on, sizeof(on));
-        if (r < 0)
-                return -errno;
+        m->event_retry = sd_event_source_unref(m->event_retry);
+        if (!ratelimit_test(&m->ratelimit)) {
+                log_debug("Slowing down attempts to contact servers.");
 
-        r = setsockopt(fd, IPPROTO_IP, IP_TOS, &tos, sizeof(tos));
-        if (r < 0)
-                return -errno;
+                r = sd_event_add_time(m->event, &m->event_retry, CLOCK_MONOTONIC, now(CLOCK_MONOTONIC) + RETRY_USEC, 0, manager_retry, m);
+                if (r < 0) {
+                        log_error("Failed to create retry timer: %s", strerror(-r));
+                        return r;
+                }
 
-        r = sd_event_add_io(m->event, &m->event_receive, fd, EPOLLIN, sntp_receive_response, m);
+                return 0;
+        }
+
+        /* If we already are operating on some address, switch to the
+         * next one. */
+        if (m->current_server_address && m->current_server_address->addresses_next)
+                m->current_server_address = m->current_server_address->addresses_next;
+        else {
+                /* Hmm, we are through all addresses, let's look for the next host instead */
+                m->current_server_address = NULL;
+
+                if (m->current_server_name && m->current_server_name->names_next)
+                        m->current_server_name = m->current_server_name->names_next;
+                else {
+                        if (!m->servers) {
+                                m->current_server_name = NULL;
+                                log_debug("No server found.");
+                                return 0;
+                        }
+
+                        m->current_server_name = m->servers;
+                }
+
+                /* Tell the resolver to reread /etc/resolv.conf, in
+                 * case it changed. */
+                res_init();
+
+                r = sd_resolve_getaddrinfo(m->resolve, &m->resolve_query, m->current_server_name->string, "123", &hints, manager_resolve_handler, m);
+                if (r < 0) {
+                        log_error("Failed to create resolver: %s", strerror(-r));
+                        return r;
+                }
+
+                return 1;
+        }
+
+        r = manager_begin(m);
         if (r < 0)
                 return r;
 
-        m->server_socket = fd;
-        fd = -1;
+        return 1;
+}
+
+static int manager_add_server(Manager *m, const char *server) {
+        ServerName *n, *tail;
+
+        assert(m);
+        assert(server);
+
+        n = new0(ServerName, 1);
+        if (!n)
+                return -ENOMEM;
+
+        n->string = strdup(server);
+        if (!n->string) {
+                free(n);
+                return -ENOMEM;
+        }
+
+        LIST_FIND_TAIL(names, m->servers, tail);
+        LIST_INSERT_AFTER(names, m->servers, tail, n);
 
         return 0;
 }
 
+static int manager_add_server_string(Manager *m, const char *string) {
+        char *w, *state;
+        size_t l;
+        int r;
+
+        assert(m);
+        assert(string);
+
+        FOREACH_WORD_QUOTED(w, l, string, state) {
+                char t[l+1];
+
+                memcpy(t, w, l);
+                t[l] = 0;
+
+                r = manager_add_server(m, t);
+                if (r < 0)
+                        log_error("Failed to add server %s to configuration, ignoring: %s", t, strerror(-r));
+        }
+
+        return 0;
+}
+
+static void manager_disconnect(Manager *m) {
+        assert(m);
+
+        m->resolve_query = sd_resolve_query_unref(m->resolve_query);
+
+        m->event_timer = sd_event_source_unref(m->event_timer);
+
+        m->event_receive = sd_event_source_unref(m->event_receive);
+        m->server_socket = safe_close(m->server_socket);
+
+        m->event_clock_watch = sd_event_source_unref(m->event_clock_watch);
+        m->clock_watch_fd = safe_close(m->clock_watch_fd);
+
+        m->event_timeout = sd_event_source_unref(m->event_timeout);
+
+        sd_notifyf(false, "STATUS=Idle.");
+}
+
 static int manager_new(Manager **ret) {
         _cleanup_manager_free_ Manager *m = NULL;
         int r;
@@ -730,15 +968,28 @@ static int manager_new(Manager **ret) {
         if (!m)
                 return -ENOMEM;
 
+        m->server_socket = m->clock_watch_fd = -1;
+
+        RATELIMIT_INIT(m->ratelimit, RATELIMIT_INTERVAL_USEC, RATELIMIT_BURST);
+
         r = sd_event_default(&m->event);
         if (r < 0)
                 return r;
 
-        r = sntp_listen_setup(m);
+        sd_event_set_watchdog(m->event, true);
+
+        sd_event_add_signal(m->event, NULL, SIGTERM, NULL,  NULL);
+        sd_event_add_signal(m->event, NULL, SIGINT, NULL, NULL);
+
+        r = sd_resolve_default(&m->resolve);
         if (r < 0)
                 return r;
 
-        r = sntp_clock_watch_setup(m);
+        r = sd_resolve_attach_event(m->resolve, m->event, 0);
+        if (r < 0)
+                return r;
+
+        r = manager_clock_watch_setup(m);
         if (r < 0)
                 return r;
 
@@ -749,44 +1000,277 @@ static int manager_new(Manager **ret) {
 }
 
 static void manager_free(Manager *m) {
-
         if (!m)
                 return;
 
+        manager_disconnect(m);
+        manager_flush_names(m);
+
+        sd_event_source_unref(m->event_retry);
+
+        sd_event_source_unref(m->network_event_source);
+        sd_network_monitor_unref(m->network_monitor);
+
+        sd_resolve_unref(m->resolve);
         sd_event_unref(m->event);
+
         free(m);
 }
 
+int config_parse_servers(
+                const char *unit,
+                const char *filename,
+                unsigned line,
+                const char *section,
+                unsigned section_line,
+                const char *lvalue,
+                int ltype,
+                const char *rvalue,
+                void *data,
+                void *userdata) {
+
+        Manager *m = userdata;
+
+        assert(filename);
+        assert(lvalue);
+        assert(rvalue);
+
+        manager_flush_names(m);
+        manager_add_server_string(m, rvalue);
+
+        return 0;
+}
+
+static int manager_parse_config_file(Manager *m) {
+        static const char fn[] = "/etc/systemd/timesyncd.conf";
+        _cleanup_fclose_ FILE *f = NULL;
+        int r;
+
+        assert(m);
+
+        f = fopen(fn, "re");
+        if (!f) {
+                if (errno == ENOENT)
+                        return 0;
+
+                log_warning("Failed to open configuration file %s: %m", fn);
+                return -errno;
+        }
+
+        r = config_parse(NULL, fn, f, "Time\0", config_item_perf_lookup,
+                         (void*) timesyncd_gperf_lookup, false, false, m);
+        if (r < 0)
+                log_warning("Failed to parse configuration file: %s", strerror(-r));
+
+        return r;
+}
+
+static bool network_is_online(void) {
+        _cleanup_free_ char *state = NULL;
+        int r;
+
+        r = sd_network_get_operational_state(&state);
+        if (r >= 0 && streq("carrier", state))
+                return true;
+        else
+                return false;
+}
+
+static int manager_network_event_handler(sd_event_source *s, int fd, uint32_t revents,
+                                         void *userdata) {
+        Manager *m = userdata;
+        bool connected, online;
+        int r;
+
+        assert(m);
+
+        /* check if the machine is online */
+        online = network_is_online();
+
+        /* check if the client is currently connected */
+        connected = (m->server_socket != -1);
+
+        if (connected && !online) {
+                log_info("No network connectivity. Suspending.");
+                manager_disconnect(m);
+        } else if (!connected && online) {
+                log_info("Network connectivity detected. Resuming.");
+                if (m->current_server_address) {
+                        r = manager_begin(m);
+                        if (r < 0)
+                                return r;
+                } else {
+                        r = manager_connect(m);
+                        if (r < 0)
+                                return r;
+                }
+        }
+
+        sd_network_monitor_flush(m->network_monitor);
+
+        return 0;
+}
+
+static int manager_network_monitor_listen(Manager *m) {
+        _cleanup_event_source_unref_ sd_event_source *event_source = NULL;
+        _cleanup_network_monitor_unref_ sd_network_monitor *monitor = NULL;
+        int r, fd, events;
+
+        r = sd_network_monitor_new(NULL, &monitor);
+        if (r < 0)
+                return r;
+
+        fd = sd_network_monitor_get_fd(monitor);
+        if (fd < 0)
+                return fd;
+
+        events = sd_network_monitor_get_events(monitor);
+        if (events < 0)
+                return events;
+
+        r = sd_event_add_io(m->event, &event_source, fd, events,
+                            &manager_network_event_handler, m);
+        if (r < 0)
+                return r;
+
+        m->network_monitor = monitor;
+        m->network_event_source = event_source;
+        monitor = NULL;
+        event_source = NULL;
+
+        return 0;
+}
+
+static int drop_priviliges(void) {
+        static const cap_value_t bits[] = {
+                CAP_SYS_TIME,
+        };
+
+        _cleanup_cap_free_ cap_t d = NULL;
+        const char *name = "systemd-timesync";
+        uid_t uid;
+        gid_t gid;
+        int r;
+
+        /* Unfortunately we cannot leave privilige dropping to PID 1
+         * here, since we want to run as user but want to keep te
+         * CAP_SYS_TIME capability. Since file capabilities have been
+         * introduced this cannot be done across exec() anymore,
+         * unless our binary has the capability configured in the file
+         * system, which we want to avoid. */
+
+        r = get_user_creds(&name, &uid, &gid, NULL, NULL);
+        if (r < 0) {
+                log_error("Cannot resolve user name %s: %s", name, strerror(-r));
+                return r;
+        }
+
+        if (setresgid(gid, gid, gid) < 0) {
+                log_error("Failed change group ID: %m");
+                return -errno;
+        }
+
+        if (setgroups(0, NULL) < 0) {
+                log_error("Failed to drop auxiliary groups list: %m");
+                return -errno;
+        }
+
+        if (prctl(PR_SET_KEEPCAPS, 1) < 0) {
+                log_error("Failed to enable keep capabilities flag: %m");
+                return -errno;
+        }
+
+        r = setresuid(uid, uid, uid);
+        if (r < 0) {
+                log_error("Failed change user ID: %m");
+                return -errno;
+        }
+
+        if (prctl(PR_SET_KEEPCAPS, 0) < 0) {
+                log_error("Failed to disable keep capabilities flag: %m");
+                return -errno;
+        }
+
+        r = capability_bounding_set_drop(~(1ULL << CAP_SYS_TIME), true);
+        if (r < 0) {
+                log_error("Failed to drop capabilities: %s", strerror(-r));
+                return r;
+        }
+
+        d = cap_init();
+        if (!d)
+                return log_oom();
+
+        if (cap_set_flag(d, CAP_EFFECTIVE, ELEMENTSOF(bits), bits, CAP_SET) < 0 ||
+            cap_set_flag(d, CAP_PERMITTED, ELEMENTSOF(bits), bits, CAP_SET) < 0) {
+                log_error("Failed to enable capabilities bits: %m");
+                return -errno;
+        }
+
+        if (cap_set_proc(d) < 0) {
+                log_error("Failed to increase capabilities: %m");
+                return -errno;
+        }
+
+        return 0;
+}
+
 int main(int argc, char *argv[]) {
         _cleanup_manager_free_ Manager *m = NULL;
-        const char *server;
         int r;
 
+        if (argc > 1) {
+                log_error("This program does not take arguments.");
+                return EXIT_FAILURE;
+        }
+
         log_set_target(LOG_TARGET_AUTO);
+        log_set_facility(LOG_CRON);
         log_parse_environment();
         log_open();
 
-        r = manager_new(&m);
+        umask(0022);
+
+        r = drop_priviliges();
         if (r < 0)
                 goto out;
 
-        server = "216.239.32.15";       /* time1.google.com */
+        assert_se(sigprocmask_many(SIG_BLOCK, SIGTERM, SIGINT, -1) == 0);
 
-        sd_notifyf(false,
-                  "READY=1\n"
-                  "STATUS=Connecting to %s", server);
+        r = manager_new(&m);
+        if (r < 0) {
+                log_error("Failed to allocate manager: %s", strerror(-r));
+                goto out;
+        }
 
-        r = sntp_server_connect(m, server);
-        if (r < 0)
+        manager_add_server_string(m, NTP_SERVERS);
+        manager_parse_config_file(m);
+
+        r = manager_network_monitor_listen(m);
+        if (r < 0) {
+                log_error("Failed to listen to networkd events: %s", strerror(-r));
                 goto out;
+        }
+
+        log_debug("systemd-timesyncd running as pid %lu", (unsigned long) getpid());
+        sd_notify(false, "READY=1");
 
-        sd_notifyf(false,
-                  "STATUS=Connected to %s", server);
+        if (network_is_online()) {
+                r = manager_connect(m);
+                if (r < 0)
+                        goto out;
+        }
 
         r = sd_event_loop(m->event);
-        if (r < 0)
+        if (r < 0) {
+                log_error("Failed to run event loop: %s", strerror(-r));
                 goto out;
+        }
+
+        sd_event_get_exit_code(m->event, &r);
 
 out:
+        sd_notify(false, "STATUS=Shutting down...");
+
         return r < 0 ? EXIT_FAILURE : EXIT_SUCCESS;
 }