blob: 2a9b113ff484128840d6b090666826b3a8926ea3 [file] [log] [blame]
/* SPDX-License-Identifier: LGPL-2.1-or-later */
/* systemd service to wait until kernel realtime clock is synchronized */
#include <errno.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/inotify.h>
#include <sys/timerfd.h>
#include <sys/timex.h>
#include <unistd.h>
#include "sd-event.h"
#include "fd-util.h"
#include "fs-util.h"
#include "main-func.h"
#include "signal-util.h"
#include "time-util.h"
typedef struct ClockState {
int timerfd_fd; /* non-negative is descriptor from timerfd_create */
int adjtime_state; /* return value from last adjtimex(2) call */
sd_event_source *timerfd_event_source; /* non-null is the active io event source */
int inotify_fd;
sd_event_source *inotify_event_source;
int run_systemd_wd;
int run_systemd_timesync_wd;
bool has_watchfile;
} ClockState;
static void clock_state_release_timerfd(ClockState *sp) {
sp->timerfd_event_source = sd_event_source_unref(sp->timerfd_event_source);
sp->timerfd_fd = safe_close(sp->timerfd_fd);
static void clock_state_release(ClockState *sp) {
sp->inotify_event_source = sd_event_source_unref(sp->inotify_event_source);
sp->inotify_fd = safe_close(sp->inotify_fd);
static int clock_state_update(ClockState *sp, sd_event *event);
static int update_notify_run_systemd_timesync(ClockState *sp) {
sp->run_systemd_timesync_wd = inotify_add_watch(sp->inotify_fd, "/run/systemd/timesync", IN_CREATE|IN_DELETE_SELF);
return sp->run_systemd_timesync_wd;
static int timerfd_handler(sd_event_source *s,
int fd,
uint32_t revents,
void *userdata) {
ClockState *sp = userdata;
return clock_state_update(sp, sd_event_source_get_event(s));
static void process_inotify_event(sd_event *event, ClockState *sp, struct inotify_event *e) {
if (e->wd == sp->run_systemd_wd) {
/* Only thing we care about is seeing if we can start watching /run/systemd/timesync. */
if (sp->run_systemd_timesync_wd < 0)
} else if (e->wd == sp->run_systemd_timesync_wd) {
if (e->mask & IN_DELETE_SELF) {
/* Somebody removed /run/systemd/timesync. */
(void) inotify_rm_watch(sp->inotify_fd, sp->run_systemd_timesync_wd);
sp->run_systemd_timesync_wd = -1;
} else
/* Somebody might have created /run/systemd/timesync/synchronized. */
clock_state_update(sp, event);
static int inotify_handler(sd_event_source *s,
int fd,
uint32_t revents,
void *userdata) {
sd_event *event = sd_event_source_get_event(s);
ClockState *sp = userdata;
union inotify_event_buffer buffer;
struct inotify_event *e;
ssize_t l;
l = read(fd, &buffer, sizeof(buffer));
if (l < 0) {
if (IN_SET(errno, EAGAIN, EINTR))
return 0;
return log_warning_errno(errno, "Lost access to inotify: %m");
process_inotify_event(event, sp, e);
return 0;
static int clock_state_update(
ClockState *sp,
sd_event *event) {
char buf[MAX((size_t)FORMAT_TIMESTAMP_MAX, STRLEN("unrepresentable"))];
struct timex tx = {};
const char * ts;
usec_t t;
int r;
/* The kernel supports cancelling timers whenever its realtime clock is "set" (which can happen in a variety of
* ways, generally adjustments of at least 500 ms). The way this module works is we set up a timerfd that will
* wake when the clock is set, and when that happens we read the clock synchronization state from the return
* value of adjtimex(2), which supports the NTP time adjustment protocol.
* The kernel determines whether the clock is synchronized using driver-specific tests, based on time
* information passed by an application, generally through adjtimex(2). If the application asserts the clock is
* synchronized, but does not also do something that "sets the clock", the timer will not be cancelled and
* synchronization will not be detected.
* Similarly, this service will never complete if the application sets the time without also providing
* information that adjtimex(2) can use to determine that the clock is synchronized. This generally doesn't
* happen, but can if the system has a hardware clock that is accurate enough that the adjustment is too small
* to be a "set".
* Both these failure-to-detect situations are covered by having the presence/creation of
* /run/systemd/timesync/synchronized, which is considered sufficient to indicate a synchronized clock even if
* the kernel has not been updated.
* For timesyncd the initial setting of the time uses settimeofday(2), which sets the clock but does not mark
* it synchronized. When an NTP source is selected it sets the clock again with clock_adjtime(2) which marks it
* synchronized and also touches /run/systemd/timesync/synchronized which covers the case when the clock wasn't
* "set". */
r = time_change_fd();
if (r < 0) {
log_error_errno(r, "Failed to create timerfd: %m");
goto finish;
sp->timerfd_fd = r;
r = adjtimex(&tx);
if (r < 0) {
log_error_errno(errno, "Failed to read adjtimex state: %m");
goto finish;
sp->adjtime_state = r;
if (tx.status & STA_NANO)
tx.time.tv_usec /= 1000;
t = timeval_load(&tx.time);
ts = format_timestamp_style(buf, sizeof(buf), t, TIMESTAMP_US_UTC);
if (!ts)
strcpy(buf, "unrepresentable");
log_info("adjtime state %d status %x time %s", sp->adjtime_state, tx.status, ts);
sp->has_watchfile = access("/run/systemd/timesync/synchronized", F_OK) >= 0;
if (sp->has_watchfile)
/* Presence of watch file overrides adjtime_state */
r = 0;
else if (sp->adjtime_state == TIME_ERROR) {
/* Not synchronized. Do a one-shot wait on the descriptor and inform the caller we need to keep
* running. */
r = sd_event_add_io(event, &sp->timerfd_event_source, sp->timerfd_fd,
EPOLLIN, timerfd_handler, sp);
if (r < 0) {
log_error_errno(r, "Failed to create time change monitor source: %m");
goto finish;
r = 1;
} else
/* Synchronized; we can exit. */
r = 0;
if (r <= 0)
(void) sd_event_exit(event, r);
return r;
static int run(int argc, char * argv[]) {
_cleanup_(sd_event_unrefp) sd_event *event = NULL;
_cleanup_(clock_state_release) ClockState state = {
.timerfd_fd = -1,
.inotify_fd = -1,
.run_systemd_wd = -1,
.run_systemd_timesync_wd = -1,
int r;
assert_se(sigprocmask_many(SIG_BLOCK, NULL, SIGTERM, SIGINT, -1) >= 0);
r = sd_event_default(&event);
if (r < 0)
return log_error_errno(r, "Failed to allocate event loop: %m");
r = sd_event_add_signal(event, NULL, SIGTERM, NULL, NULL);
if (r < 0)
return log_error_errno(r, "Failed to create sigterm event source: %m");
r = sd_event_add_signal(event, NULL, SIGINT, NULL, NULL);
if (r < 0)
return log_error_errno(r, "Failed to create sigint event source: %m");
r = sd_event_set_watchdog(event, true);
if (r < 0)
return log_error_errno(r, "Failed to create watchdog event source: %m");
r = inotify_init1(IN_NONBLOCK|IN_CLOEXEC);
if (r < 0)
return log_error_errno(errno, "Failed to create inotify descriptor: %m");
state.inotify_fd = r;
r = sd_event_add_io(event, &state.inotify_event_source, state.inotify_fd,
EPOLLIN, inotify_handler, &state);
if (r < 0)
return log_error_errno(r, "Failed to create notify event source: %m");
r = inotify_add_watch_and_warn(state.inotify_fd, "/run/systemd/", IN_CREATE);
if (r < 0)
return r;
state.run_systemd_wd = r;
(void) update_notify_run_systemd_timesync(&state);
r = clock_state_update(&state, event);
if (r > 0) {
r = sd_event_loop(event);
if (r < 0)
log_error_errno(r, "Failed in event loop: %m");
if (state.has_watchfile)
log_debug("Exit enabled by: /run/systemd/timesync/synchronized");
if (state.adjtime_state == TIME_ERROR)
log_info("Exit without adjtimex synchronized.");
return r;