src/time-wait-sync/time-wait-sync.c

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2 /* systemd service to wait until kernel realtime clock is synchronized */
   3
   4 #include <errno.h>
   5 #include <stdbool.h>
   6 #include <stdio.h>
   7 #include <stdlib.h>
   8 #include <string.h>
   9 #include <sys/inotify.h>
  10 #include <sys/timerfd.h>
  11 #include <sys/timex.h>
  12 #include <unistd.h>
  13
  14 #include "sd-event.h"
  15
  16 #include "fd-util.h"
  17 #include "fs-util.h"
  18 #include "main-func.h"
  19 #include "signal-util.h"
  20 #include "time-util.h"
  21
  22 typedef struct ClockState {
  23         int timerfd_fd;                  /* non-negative is descriptor from timerfd_create */
  24         int adjtime_state;               /* return value from last adjtimex(2) call */
  25         sd_event_source *timerfd_event_source; /* non-null is the active io event source */
  26         int inotify_fd;
  27         sd_event_source *inotify_event_source;
  28         int run_systemd_wd;
  29         int run_systemd_timesync_wd;
  30         bool has_watchfile;
  31 } ClockState;
  32
  33 static void clock_state_release_timerfd(ClockState *sp) {
  34         sp->timerfd_event_source = sd_event_source_unref(sp->timerfd_event_source);
  35         sp->timerfd_fd = safe_close(sp->timerfd_fd);
  36 }
  37
  38 static void clock_state_release(ClockState *sp) {
  39         clock_state_release_timerfd(sp);
  40         sp->inotify_event_source = sd_event_source_unref(sp->inotify_event_source);
  41         sp->inotify_fd = safe_close(sp->inotify_fd);
  42 }
  43
  44 static int clock_state_update(ClockState *sp, sd_event *event);
  45
  46 static int update_notify_run_systemd_timesync(ClockState *sp) {
  47         sp->run_systemd_timesync_wd = inotify_add_watch(sp->inotify_fd, "/run/systemd/timesync", IN_CREATE|IN_DELETE_SELF);
  48         return sp->run_systemd_timesync_wd;
  49 }
  50
  51 static int timerfd_handler(sd_event_source *s,
  52                            int fd,
  53                            uint32_t revents,
  54                            void *userdata) {
  55         ClockState *sp = userdata;
  56
  57         return clock_state_update(sp, sd_event_source_get_event(s));
  58 }
  59
  60 static void process_inotify_event(sd_event *event, ClockState *sp, struct inotify_event *e) {
  61         if (e->wd == sp->run_systemd_wd) {
  62                 /* Only thing we care about is seeing if we can start watching /run/systemd/timesync. */
  63                 if (sp->run_systemd_timesync_wd < 0)
  64                         update_notify_run_systemd_timesync(sp);
  65         } else if (e->wd == sp->run_systemd_timesync_wd) {
  66                 if (e->mask & IN_DELETE_SELF) {
  67                         /* Somebody removed /run/systemd/timesync. */
  68                         (void) inotify_rm_watch(sp->inotify_fd, sp->run_systemd_timesync_wd);
  69                         sp->run_systemd_timesync_wd = -1;
  70                 } else
  71                         /* Somebody might have created /run/systemd/timesync/synchronized. */
  72                         clock_state_update(sp, event);
  73         }
  74 }
  75
  76 static int inotify_handler(sd_event_source *s,
  77                            int fd,
  78                            uint32_t revents,
  79                            void *userdata) {
  80         sd_event *event = sd_event_source_get_event(s);
  81         ClockState *sp = userdata;
  82         union inotify_event_buffer buffer;
  83         struct inotify_event *e;
  84         ssize_t l;
  85
  86         l = read(fd, &buffer, sizeof(buffer));
  87         if (l < 0) {
  88                 if (IN_SET(errno, EAGAIN, EINTR))
  89                         return 0;
  90
  91                 return log_warning_errno(errno, "Lost access to inotify: %m");
  92         }
  93         FOREACH_INOTIFY_EVENT(e, buffer, l)
  94                 process_inotify_event(event, sp, e);
  95
  96         return 0;
  97 }
  98
  99 static int clock_state_update(
 100                 ClockState *sp,
 101                 sd_event *event) {
 102
 103         char buf[MAX((size_t)FORMAT_TIMESTAMP_MAX, STRLEN("unrepresentable"))];
 104         struct timex tx = {};
 105         const char * ts;
 106         usec_t t;
 107         int r;
 108
 109         clock_state_release_timerfd(sp);
 110
 111         /* The kernel supports cancelling timers whenever its realtime clock is "set" (which can happen in a variety of
 112          * ways, generally adjustments of at least 500 ms). The way this module works is we set up a timerfd that will
 113          * wake when the clock is set, and when that happens we read the clock synchronization state from the return
 114          * value of adjtimex(2), which supports the NTP time adjustment protocol.
 115          *
 116          * The kernel determines whether the clock is synchronized using driver-specific tests, based on time
 117          * information passed by an application, generally through adjtimex(2). If the application asserts the clock is
 118          * synchronized, but does not also do something that "sets the clock", the timer will not be cancelled and
 119          * synchronization will not be detected.
 120          *
 121          * Similarly, this service will never complete if the application sets the time without also providing
 122          * information that adjtimex(2) can use to determine that the clock is synchronized. This generally doesn't
 123          * happen, but can if the system has a hardware clock that is accurate enough that the adjustment is too small
 124          * to be a "set".
 125          *
 126          * Both these failure-to-detect situations are covered by having the presence/creation of
 127          * /run/systemd/timesync/synchronized, which is considered sufficient to indicate a synchronized clock even if
 128          * the kernel has not been updated.
 129          *
 130          * For timesyncd the initial setting of the time uses settimeofday(2), which sets the clock but does not mark
 131          * it synchronized. When an NTP source is selected it sets the clock again with clock_adjtime(2) which marks it
 132          * synchronized and also touches /run/systemd/timesync/synchronized which covers the case when the clock wasn't
 133          * "set". */
 134
 135         r = time_change_fd();
 136         if (r < 0) {
 137                 log_error_errno(r, "Failed to create timerfd: %m");
 138                 goto finish;
 139         }
 140         sp->timerfd_fd = r;
 141
 142         r = adjtimex(&tx);
 143         if (r < 0) {
 144                 log_error_errno(errno, "Failed to read adjtimex state: %m");
 145                 goto finish;
 146         }
 147         sp->adjtime_state = r;
 148
 149         if (tx.status & STA_NANO)
 150                 tx.time.tv_usec /= 1000;
 151         t = timeval_load(&tx.time);
 152         ts = format_timestamp_style(buf, sizeof(buf), t, TIMESTAMP_US_UTC);
 153         if (!ts)
 154                 strcpy(buf, "unrepresentable");
 155         log_info("adjtime state %d status %x time %s", sp->adjtime_state, tx.status, ts);
 156
 157         sp->has_watchfile = access("/run/systemd/timesync/synchronized", F_OK) >= 0;
 158         if (sp->has_watchfile)
 159                 /* Presence of watch file overrides adjtime_state */
 160                 r = 0;
 161         else if (sp->adjtime_state == TIME_ERROR) {
 162                 /* Not synchronized.  Do a one-shot wait on the descriptor and inform the caller we need to keep
 163                  * running. */
 164                 r = sd_event_add_io(event, &sp->timerfd_event_source, sp->timerfd_fd,
 165                                     EPOLLIN, timerfd_handler, sp);
 166                 if (r < 0) {
 167                         log_error_errno(r, "Failed to create time change monitor source: %m");
 168                         goto finish;
 169                 }
 170                 r = 1;
 171         } else
 172                 /* Synchronized; we can exit. */
 173                 r = 0;
 174
 175  finish:
 176         if (r <= 0)
 177                 (void) sd_event_exit(event, r);
 178         return r;
 179 }
 180
 181 static int run(int argc, char * argv[]) {
 182         _cleanup_(sd_event_unrefp) sd_event *event;
 183         _cleanup_(clock_state_release) ClockState state = {
 184                 .timerfd_fd = -1,
 185                 .inotify_fd = -1,
 186                 .run_systemd_wd = -1,
 187                 .run_systemd_timesync_wd = -1,
 188         };
 189         int r;
 190
 191         assert_se(sigprocmask_many(SIG_BLOCK, NULL, SIGTERM, SIGINT, -1) >= 0);
 192
 193         r = sd_event_default(&event);
 194         if (r < 0)
 195                 return log_error_errno(r, "Failed to allocate event loop: %m");
 196
 197         r = sd_event_add_signal(event, NULL, SIGTERM, NULL, NULL);
 198         if (r < 0)
 199                 return log_error_errno(r, "Failed to create sigterm event source: %m");
 200
 201         r = sd_event_add_signal(event, NULL, SIGINT, NULL, NULL);
 202         if (r < 0)
 203                 return log_error_errno(r, "Failed to create sigint event source: %m");
 204
 205         r = sd_event_set_watchdog(event, true);
 206         if (r < 0)
 207                 return log_error_errno(r, "Failed to create watchdog event source: %m");
 208
 209         r = inotify_init1(IN_NONBLOCK|IN_CLOEXEC);
 210         if (r < 0)
 211                 return log_error_errno(errno, "Failed to create inotify descriptor: %m");
 212
 213         state.inotify_fd = r;
 214
 215         r = sd_event_add_io(event, &state.inotify_event_source, state.inotify_fd,
 216                             EPOLLIN, inotify_handler, &state);
 217         if (r < 0)
 218                 return log_error_errno(r, "Failed to create notify event source: %m");
 219
 220         r = inotify_add_watch_and_warn(state.inotify_fd, "/run/systemd/", IN_CREATE);
 221         if (r < 0)
 222                 return r;
 223
 224         state.run_systemd_wd = r;
 225
 226         (void) update_notify_run_systemd_timesync(&state);
 227
 228         r = clock_state_update(&state, event);
 229         if (r > 0) {
 230                 r = sd_event_loop(event);
 231                 if (r < 0)
 232                         log_error_errno(r, "Failed in event loop: %m");
 233         }
 234
 235         if (state.has_watchfile)
 236                 log_debug("Exit enabled by: /run/systemd/timesync/synchronized");
 237
 238         if (state.adjtime_state == TIME_ERROR)
 239                 log_info("Exit without adjtimex synchronized.");
 240
 241         return r;
 242 }
 243
 244 DEFINE_MAIN_FUNCTION(run);