1 files changed, 167 insertions, 0 deletions
diff --git a/src/shared/clock-util.c b/src/shared/clock-util.c
new file mode 100644
index 0000000..a4c00d7
--- /dev/null
+++ b/src/shared/clock-util.c
@@ -0,0 +1,167 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <stdbool.h>
+#include <time.h>
+#include <linux/rtc.h>
+#include <stdio.h>
+#include <sys/ioctl.h>
+#include <sys/time.h>
+
+#include "alloc-util.h"
+#include "clock-util.h"
+#include "errno-util.h"
+#include "fd-util.h"
+#include "fileio.h"
+#include "macro.h"
+#include "string-util.h"
+
+int clock_get_hwclock(struct tm *tm) {
+        _cleanup_close_ int fd = -1;
+
+        assert(tm);
+
+        fd = open("/dev/rtc", O_RDONLY|O_CLOEXEC);
+        if (fd < 0)
+                return -errno;
+
+        /* This leaves the timezone fields of struct tm
+         * uninitialized! */
+        if (ioctl(fd, RTC_RD_TIME, tm) < 0)
+                return -errno;
+
+        /* We don't know daylight saving, so we reset this in order not
+         * to confuse mktime(). */
+        tm->tm_isdst = -1;
+
+        return 0;
+}
+
+int clock_set_hwclock(const struct tm *tm) {
+        _cleanup_close_ int fd = -1;
+
+        assert(tm);
+
+        fd = open("/dev/rtc", O_RDONLY|O_CLOEXEC);
+        if (fd < 0)
+                return -errno;
+
+        return RET_NERRNO(ioctl(fd, RTC_SET_TIME, tm));
+}
+
+int clock_is_localtime(const char* adjtime_path) {
+        _cleanup_fclose_ FILE *f = NULL;
+        int r;
+
+        if (!adjtime_path)
+                adjtime_path = "/etc/adjtime";
+
+        /*
+         * The third line of adjtime is "UTC" or "LOCAL" or nothing.
+         *   # /etc/adjtime
+         *   0.0 0 0
+         *   0
+         *   UTC
+         */
+        f = fopen(adjtime_path, "re");
+        if (f) {
+                _cleanup_free_ char *line = NULL;
+                unsigned i;
+
+                for (i = 0; i < 2; i++) { /* skip the first two lines */
+                        r = read_line(f, LONG_LINE_MAX, NULL);
+                        if (r < 0)
+                                return r;
+                        if (r == 0)
+                                return false; /* less than three lines → default to UTC */
+                }
+
+                r = read_line(f, LONG_LINE_MAX, &line);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        return false; /* less than three lines → default to UTC */
+
+                return streq(line, "LOCAL");
+
+        } else if (errno != ENOENT)
+                return -errno;
+
+        /* adjtime not present → default to UTC */
+        return false;
+}
+
+int clock_set_timezone(int *ret_minutesdelta) {
+        struct timespec ts;
+        struct tm tm;
+        int minutesdelta;
+        struct timezone tz;
+
+        assert_se(clock_gettime(CLOCK_REALTIME, &ts) == 0);
+        assert_se(localtime_r(&ts.tv_sec, &tm));
+        minutesdelta = tm.tm_gmtoff / 60;
+
+        tz = (struct timezone) {
+                .tz_minuteswest = -minutesdelta,
+                .tz_dsttime = 0, /* DST_NONE */
+        };
+
+        /* If the RTC does not run in UTC but in local time, the very first call to settimeofday() will set
+         * the kernel's timezone and will warp the system clock, so that it runs in UTC instead of the local
+         * time we have read from the RTC. */
+        if (settimeofday(NULL, &tz) < 0)
+                return -errno;
+
+        if (ret_minutesdelta)
+                *ret_minutesdelta = minutesdelta;
+
+        return 0;
+}
+
+int clock_reset_timewarp(void) {
+        static const struct timezone tz = {
+                .tz_minuteswest = 0,
+                .tz_dsttime = 0, /* DST_NONE */
+        };
+
+        /* The very first call to settimeofday() does time warp magic. Do a dummy call here, so the time
+         * warping is sealed and all later calls behave as expected. */
+        return RET_NERRNO(settimeofday(NULL, &tz));
+}
+
+#define EPOCH_FILE "/usr/lib/clock-epoch"
+
+int clock_apply_epoch(ClockChangeDirection *ret_attempted_change) {
+        usec_t epoch_usec, now_usec;
+        struct stat st;
+
+        /* NB: we update *ret_attempted_change in *all* cases, both
+         * on success and failure, to indicate what we intended to do! */
+
+        assert(ret_attempted_change);
+
+        if (stat(EPOCH_FILE, &st) < 0) {
+                if (errno != ENOENT)
+                        log_warning_errno(errno, "Cannot stat " EPOCH_FILE ": %m");
+
+                epoch_usec = (usec_t) TIME_EPOCH * USEC_PER_SEC;
+        } else
+                epoch_usec = timespec_load(&st.st_mtim);
+
+        now_usec = now(CLOCK_REALTIME);
+        if (now_usec < epoch_usec)
+                *ret_attempted_change = CLOCK_CHANGE_FORWARD;
+        else if (CLOCK_VALID_RANGE_USEC_MAX > 0 && now_usec > usec_add(epoch_usec, CLOCK_VALID_RANGE_USEC_MAX))
+                *ret_attempted_change = CLOCK_CHANGE_BACKWARD;
+        else {
+                *ret_attempted_change = CLOCK_CHANGE_NOOP;
+                return 0;
+        }
+
+        if (clock_settime(CLOCK_REALTIME, TIMESPEC_STORE(epoch_usec)) < 0)
+                return -errno;
+
+        return 1;
+}