diff options
Diffstat (limited to 'src/time-wait-sync/time-wait-sync.c')
| -rw-r--r-- | src/time-wait-sync/time-wait-sync.c | 244 |
1 files changed, 244 insertions, 0 deletions
diff --git a/src/time-wait-sync/time-wait-sync.c b/src/time-wait-sync/time-wait-sync.c new file mode 100644 index 0000000..df34541 --- /dev/null +++ b/src/time-wait-sync/time-wait-sync.c @@ -0,0 +1,244 @@ +/* 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) { + clock_state_release_timerfd(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) + update_notify_run_systemd_timesync(sp); + } 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"); + } + FOREACH_INOTIFY_EVENT(e, buffer, l) + 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; + + clock_state_release_timerfd(sp); + + /* 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; + + finish: + 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; + _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; +} + +DEFINE_MAIN_FUNCTION(run); |