Adding upstream version 255.4.upstream/255.4

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1773 insertions, 0 deletions

diff --git a/src/basic/time-util.c b/src/basic/time-util.c
new file mode 100644
index 0000000..f9014dc
--- /dev/null
+++ b/src/basic/time-util.c
@@ -0,0 +1,1773 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <ctype.h>
+#include <errno.h>
+#include <limits.h>
+#include <stdlib.h>
+#include <sys/mman.h>
+#include <sys/time.h>
+#include <sys/timerfd.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include "alloc-util.h"
+#include "fd-util.h"
+#include "fileio.h"
+#include "fs-util.h"
+#include "io-util.h"
+#include "log.h"
+#include "macro.h"
+#include "missing_threads.h"
+#include "missing_timerfd.h"
+#include "parse-util.h"
+#include "path-util.h"
+#include "process-util.h"
+#include "stat-util.h"
+#include "string-table.h"
+#include "string-util.h"
+#include "strv.h"
+#include "time-util.h"
+
+static clockid_t map_clock_id(clockid_t c) {
+
+        /* Some more exotic archs (s390, ppc, …) lack the "ALARM" flavour of the clocks. Thus,
+         * clock_gettime() will fail for them. Since they are essentially the same as their non-ALARM
+         * pendants (their only difference is when timers are set on them), let's just map them
+         * accordingly. This way, we can get the correct time even on those archs. */
+
+        switch (c) {
+
+        case CLOCK_BOOTTIME_ALARM:
+                return CLOCK_BOOTTIME;
+
+        case CLOCK_REALTIME_ALARM:
+                return CLOCK_REALTIME;
+
+        default:
+                return c;
+        }
+}
+
+usec_t now(clockid_t clock_id) {
+        struct timespec ts;
+
+        assert_se(clock_gettime(map_clock_id(clock_id), &ts) == 0);
+
+        return timespec_load(&ts);
+}
+
+nsec_t now_nsec(clockid_t clock_id) {
+        struct timespec ts;
+
+        assert_se(clock_gettime(map_clock_id(clock_id), &ts) == 0);
+
+        return timespec_load_nsec(&ts);
+}
+
+dual_timestamp* dual_timestamp_now(dual_timestamp *ts) {
+        assert(ts);
+
+        ts->realtime = now(CLOCK_REALTIME);
+        ts->monotonic = now(CLOCK_MONOTONIC);
+
+        return ts;
+}
+
+triple_timestamp* triple_timestamp_now(triple_timestamp *ts) {
+        assert(ts);
+
+        ts->realtime = now(CLOCK_REALTIME);
+        ts->monotonic = now(CLOCK_MONOTONIC);
+        ts->boottime = now(CLOCK_BOOTTIME);
+
+        return ts;
+}
+
+static usec_t map_clock_usec_internal(usec_t from, usec_t from_base, usec_t to_base) {
+
+        /* Maps the time 'from' between two clocks, based on a common reference point where the first clock
+         * is at 'from_base' and the second clock at 'to_base'. Basically calculates:
+         *
+         *         from - from_base + to_base
+         *
+         * But takes care of overflows/underflows and avoids signed operations. */
+
+        if (from >= from_base) { /* In the future */
+                usec_t delta = from - from_base;
+
+                if (to_base >= USEC_INFINITY - delta) /* overflow? */
+                        return USEC_INFINITY;
+
+                return to_base + delta;
+
+        } else { /* In the past */
+                usec_t delta = from_base - from;
+
+                if (to_base <= delta) /* underflow? */
+                        return 0;
+
+                return to_base - delta;
+        }
+}
+
+usec_t map_clock_usec(usec_t from, clockid_t from_clock, clockid_t to_clock) {
+
+        /* Try to avoid any inaccuracy needlessly added in case we convert from effectively the same clock
+         * onto itself */
+        if (map_clock_id(from_clock) == map_clock_id(to_clock))
+                return from;
+
+        /* Keep infinity as is */
+        if (from == USEC_INFINITY)
+                return from;
+
+        return map_clock_usec_internal(from, now(from_clock), now(to_clock));
+}
+
+dual_timestamp* dual_timestamp_from_realtime(dual_timestamp *ts, usec_t u) {
+        assert(ts);
+
+        if (!timestamp_is_set(u)) {
+                ts->realtime = ts->monotonic = u;
+                return ts;
+        }
+
+        ts->realtime = u;
+        ts->monotonic = map_clock_usec(u, CLOCK_REALTIME, CLOCK_MONOTONIC);
+        return ts;
+}
+
+triple_timestamp* triple_timestamp_from_realtime(triple_timestamp *ts, usec_t u) {
+        usec_t nowr;
+
+        assert(ts);
+
+        if (!timestamp_is_set(u)) {
+                ts->realtime = ts->monotonic = ts->boottime = u;
+                return ts;
+        }
+
+        nowr = now(CLOCK_REALTIME);
+
+        ts->realtime = u;
+        ts->monotonic = map_clock_usec_internal(u, nowr, now(CLOCK_MONOTONIC));
+        ts->boottime = map_clock_usec_internal(u, nowr, now(CLOCK_BOOTTIME));
+
+        return ts;
+}
+
+triple_timestamp* triple_timestamp_from_boottime(triple_timestamp *ts, usec_t u) {
+        usec_t nowb;
+
+        assert(ts);
+
+        if (u == USEC_INFINITY) {
+                ts->realtime = ts->monotonic = ts->boottime = u;
+                return ts;
+        }
+
+        nowb = now(CLOCK_BOOTTIME);
+
+        ts->boottime = u;
+        ts->monotonic = map_clock_usec_internal(u, nowb, now(CLOCK_MONOTONIC));
+        ts->realtime = map_clock_usec_internal(u, nowb, now(CLOCK_REALTIME));
+
+        return ts;
+}
+
+dual_timestamp* dual_timestamp_from_monotonic(dual_timestamp *ts, usec_t u) {
+        assert(ts);
+
+        if (u == USEC_INFINITY) {
+                ts->realtime = ts->monotonic = USEC_INFINITY;
+                return ts;
+        }
+
+        ts->monotonic = u;
+        ts->realtime = map_clock_usec(u, CLOCK_MONOTONIC, CLOCK_REALTIME);
+        return ts;
+}
+
+dual_timestamp* dual_timestamp_from_boottime(dual_timestamp *ts, usec_t u) {
+        usec_t nowm;
+
+        assert(ts);
+
+        if (u == USEC_INFINITY) {
+                ts->realtime = ts->monotonic = USEC_INFINITY;
+                return ts;
+        }
+
+        nowm = now(CLOCK_BOOTTIME);
+        ts->monotonic = map_clock_usec_internal(u, nowm, now(CLOCK_MONOTONIC));
+        ts->realtime = map_clock_usec_internal(u, nowm, now(CLOCK_REALTIME));
+        return ts;
+}
+
+usec_t triple_timestamp_by_clock(triple_timestamp *ts, clockid_t clock) {
+        assert(ts);
+
+        switch (clock) {
+
+        case CLOCK_REALTIME:
+        case CLOCK_REALTIME_ALARM:
+                return ts->realtime;
+
+        case CLOCK_MONOTONIC:
+                return ts->monotonic;
+
+        case CLOCK_BOOTTIME:
+        case CLOCK_BOOTTIME_ALARM:
+                return ts->boottime;
+
+        default:
+                return USEC_INFINITY;
+        }
+}
+
+usec_t timespec_load(const struct timespec *ts) {
+        assert(ts);
+
+        if (ts->tv_sec < 0 || ts->tv_nsec < 0)
+                return USEC_INFINITY;
+
+        if ((usec_t) ts->tv_sec > (UINT64_MAX - (ts->tv_nsec / NSEC_PER_USEC)) / USEC_PER_SEC)
+                return USEC_INFINITY;
+
+        return
+                (usec_t) ts->tv_sec * USEC_PER_SEC +
+                (usec_t) ts->tv_nsec / NSEC_PER_USEC;
+}
+
+nsec_t timespec_load_nsec(const struct timespec *ts) {
+        assert(ts);
+
+        if (ts->tv_sec < 0 || ts->tv_nsec < 0)
+                return NSEC_INFINITY;
+
+        if ((nsec_t) ts->tv_sec >= (UINT64_MAX - ts->tv_nsec) / NSEC_PER_SEC)
+                return NSEC_INFINITY;
+
+        return (nsec_t) ts->tv_sec * NSEC_PER_SEC + (nsec_t) ts->tv_nsec;
+}
+
+struct timespec *timespec_store(struct timespec *ts, usec_t u) {
+        assert(ts);
+
+        if (u == USEC_INFINITY ||
+            u / USEC_PER_SEC >= TIME_T_MAX) {
+                ts->tv_sec = (time_t) -1;
+                ts->tv_nsec = -1L;
+                return ts;
+        }
+
+        ts->tv_sec = (time_t) (u / USEC_PER_SEC);
+        ts->tv_nsec = (long) ((u % USEC_PER_SEC) * NSEC_PER_USEC);
+
+        return ts;
+}
+
+struct timespec *timespec_store_nsec(struct timespec *ts, nsec_t n) {
+        assert(ts);
+
+        if (n == NSEC_INFINITY ||
+            n / NSEC_PER_SEC >= TIME_T_MAX) {
+                ts->tv_sec = (time_t) -1;
+                ts->tv_nsec = -1L;
+                return ts;
+        }
+
+        ts->tv_sec = (time_t) (n / NSEC_PER_SEC);
+        ts->tv_nsec = (long) (n % NSEC_PER_SEC);
+
+        return ts;
+}
+
+usec_t timeval_load(const struct timeval *tv) {
+        assert(tv);
+
+        if (tv->tv_sec < 0 || tv->tv_usec < 0)
+                return USEC_INFINITY;
+
+        if ((usec_t) tv->tv_sec > (UINT64_MAX - tv->tv_usec) / USEC_PER_SEC)
+                return USEC_INFINITY;
+
+        return
+                (usec_t) tv->tv_sec * USEC_PER_SEC +
+                (usec_t) tv->tv_usec;
+}
+
+struct timeval *timeval_store(struct timeval *tv, usec_t u) {
+        assert(tv);
+
+        if (u == USEC_INFINITY ||
+            u / USEC_PER_SEC > TIME_T_MAX) {
+                tv->tv_sec = (time_t) -1;
+                tv->tv_usec = (suseconds_t) -1;
+        } else {
+                tv->tv_sec = (time_t) (u / USEC_PER_SEC);
+                tv->tv_usec = (suseconds_t) (u % USEC_PER_SEC);
+        }
+
+        return tv;
+}
+
+char *format_timestamp_style(
+                char *buf,
+                size_t l,
+                usec_t t,
+                TimestampStyle style) {
+
+        /* The weekdays in non-localized (English) form. We use this instead of the localized form, so that
+         * our generated timestamps may be parsed with parse_timestamp(), and always read the same. */
+        static const char * const weekdays[] = {
+                [0] = "Sun",
+                [1] = "Mon",
+                [2] = "Tue",
+                [3] = "Wed",
+                [4] = "Thu",
+                [5] = "Fri",
+                [6] = "Sat",
+        };
+
+        struct tm tm;
+        bool utc, us;
+        time_t sec;
+        size_t n;
+
+        assert(buf);
+        assert(style >= 0);
+        assert(style < _TIMESTAMP_STYLE_MAX);
+
+        if (!timestamp_is_set(t))
+                return NULL; /* Timestamp is unset */
+
+        if (style == TIMESTAMP_UNIX) {
+                if (l < (size_t) (1 + 1 + 1))
+                        return NULL; /* not enough space for even the shortest of forms */
+
+                return snprintf_ok(buf, l, "@" USEC_FMT, t / USEC_PER_SEC);  /* round down μs → s */
+        }
+
+        utc = IN_SET(style, TIMESTAMP_UTC, TIMESTAMP_US_UTC, TIMESTAMP_DATE);
+        us = IN_SET(style, TIMESTAMP_US, TIMESTAMP_US_UTC);
+
+        if (l < (size_t) (3 +                   /* week day */
+                          1 + 10 +              /* space and date */
+                          style == TIMESTAMP_DATE ? 0 :
+                          (1 + 8 +              /* space and time */
+                           (us ? 1 + 6 : 0) +   /* "." and microsecond part */
+                           1 + (utc ? 3 : 1)) + /* space and shortest possible zone */
+                          1))
+                return NULL; /* Not enough space even for the shortest form. */
+
+        /* Let's not format times with years > 9999 */
+        if (t > USEC_TIMESTAMP_FORMATTABLE_MAX) {
+                static const char* const xxx[_TIMESTAMP_STYLE_MAX] = {
+                        [TIMESTAMP_PRETTY] = "--- XXXX-XX-XX XX:XX:XX",
+                        [TIMESTAMP_US]     = "--- XXXX-XX-XX XX:XX:XX.XXXXXX",
+                        [TIMESTAMP_UTC]    = "--- XXXX-XX-XX XX:XX:XX UTC",
+                        [TIMESTAMP_US_UTC] = "--- XXXX-XX-XX XX:XX:XX.XXXXXX UTC",
+                        [TIMESTAMP_DATE]   = "--- XXXX-XX-XX",
+                };
+
+                assert(l >= strlen(xxx[style]) + 1);
+                return strcpy(buf, xxx[style]);
+        }
+
+        sec = (time_t) (t / USEC_PER_SEC); /* Round down */
+
+        if (!localtime_or_gmtime_r(&sec, &tm, utc))
+                return NULL;
+
+        /* Start with the week day */
+        assert((size_t) tm.tm_wday < ELEMENTSOF(weekdays));
+        memcpy(buf, weekdays[tm.tm_wday], 4);
+
+        if (style == TIMESTAMP_DATE) {
+                /* Special format string if only date should be shown. */
+                if (strftime(buf + 3, l - 3, " %Y-%m-%d", &tm) <= 0)
+                        return NULL; /* Doesn't fit */
+
+                return buf;
+        }
+
+        /* Add the main components */
+        if (strftime(buf + 3, l - 3, " %Y-%m-%d %H:%M:%S", &tm) <= 0)
+                return NULL; /* Doesn't fit */
+
+        /* Append the microseconds part, if that's requested */
+        if (us) {
+                n = strlen(buf);
+                if (n + 8 > l)
+                        return NULL; /* Microseconds part doesn't fit. */
+
+                sprintf(buf + n, ".%06"PRI_USEC, t % USEC_PER_SEC);
+        }
+
+        /* Append the timezone */
+        n = strlen(buf);
+        if (utc) {
+                /* If this is UTC then let's explicitly use the "UTC" string here, because gmtime_r()
+                 * normally uses the obsolete "GMT" instead. */
+                if (n + 5 > l)
+                        return NULL; /* "UTC" doesn't fit. */
+
+                strcpy(buf + n, " UTC");
+
+        } else if (!isempty(tm.tm_zone)) {
+                size_t tn;
+
+                /* An explicit timezone is specified, let's use it, if it fits */
+                tn = strlen(tm.tm_zone);
+                if (n + 1 + tn + 1 > l) {
+                        /* The full time zone does not fit in. Yuck. */
+
+                        if (n + 1 + _POSIX_TZNAME_MAX + 1 > l)
+                                return NULL; /* Not even enough space for the POSIX minimum (of 6)? In that
+                                              * case, complain that it doesn't fit. */
+
+                        /* So the time zone doesn't fit in fully, but the caller passed enough space for the
+                         * POSIX minimum time zone length. In this case suppress the timezone entirely, in
+                         * order not to dump an overly long, hard to read string on the user. This should be
+                         * safe, because the user will assume the local timezone anyway if none is shown. And
+                         * so does parse_timestamp(). */
+                } else {
+                        buf[n++] = ' ';
+                        strcpy(buf + n, tm.tm_zone);
+                }
+        }
+
+        return buf;
+}
+
+char* format_timestamp_relative_full(char *buf, size_t l, usec_t t, clockid_t clock, bool implicit_left) {
+        const char *s;
+        usec_t n, d;
+
+        assert(buf);
+
+        if (!timestamp_is_set(t))
+                return NULL;
+
+        n = now(clock);
+        if (n > t) {
+                d = n - t;
+                s = " ago";
+        } else {
+                d = t - n;
+                s = implicit_left ? "" : " left";
+        }
+
+        if (d >= USEC_PER_YEAR) {
+                usec_t years = d / USEC_PER_YEAR;
+                usec_t months = (d % USEC_PER_YEAR) / USEC_PER_MONTH;
+
+                (void) snprintf(buf, l, USEC_FMT " %s " USEC_FMT " %s%s",
+                                years,
+                                years == 1 ? "year" : "years",
+                                months,
+                                months == 1 ? "month" : "months",
+                                s);
+        } else if (d >= USEC_PER_MONTH) {
+                usec_t months = d / USEC_PER_MONTH;
+                usec_t days = (d % USEC_PER_MONTH) / USEC_PER_DAY;
+
+                (void) snprintf(buf, l, USEC_FMT " %s " USEC_FMT " %s%s",
+                                months,
+                                months == 1 ? "month" : "months",
+                                days,
+                                days == 1 ? "day" : "days",
+                                s);
+        } else if (d >= USEC_PER_WEEK) {
+                usec_t weeks = d / USEC_PER_WEEK;
+                usec_t days = (d % USEC_PER_WEEK) / USEC_PER_DAY;
+
+                (void) snprintf(buf, l, USEC_FMT " %s " USEC_FMT " %s%s",
+                                weeks,
+                                weeks == 1 ? "week" : "weeks",
+                                days,
+                                days == 1 ? "day" : "days",
+                                s);
+        } else if (d >= 2*USEC_PER_DAY)
+                (void) snprintf(buf, l, USEC_FMT " days%s", d / USEC_PER_DAY,s);
+        else if (d >= 25*USEC_PER_HOUR)
+                (void) snprintf(buf, l, "1 day " USEC_FMT "h%s",
+                                (d - USEC_PER_DAY) / USEC_PER_HOUR, s);
+        else if (d >= 6*USEC_PER_HOUR)
+                (void) snprintf(buf, l, USEC_FMT "h%s",
+                                d / USEC_PER_HOUR, s);
+        else if (d >= USEC_PER_HOUR)
+                (void) snprintf(buf, l, USEC_FMT "h " USEC_FMT "min%s",
+                                d / USEC_PER_HOUR,
+                                (d % USEC_PER_HOUR) / USEC_PER_MINUTE, s);
+        else if (d >= 5*USEC_PER_MINUTE)
+                (void) snprintf(buf, l, USEC_FMT "min%s",
+                                d / USEC_PER_MINUTE, s);
+        else if (d >= USEC_PER_MINUTE)
+                (void) snprintf(buf, l, USEC_FMT "min " USEC_FMT "s%s",
+                                d / USEC_PER_MINUTE,
+                                (d % USEC_PER_MINUTE) / USEC_PER_SEC, s);
+        else if (d >= USEC_PER_SEC)
+                (void) snprintf(buf, l, USEC_FMT "s%s",
+                                d / USEC_PER_SEC, s);
+        else if (d >= USEC_PER_MSEC)
+                (void) snprintf(buf, l, USEC_FMT "ms%s",
+                                d / USEC_PER_MSEC, s);
+        else if (d > 0)
+                (void) snprintf(buf, l, USEC_FMT"us%s",
+                                d, s);
+        else
+                (void) snprintf(buf, l, "now");
+
+        buf[l-1] = 0;
+        return buf;
+}
+
+char* format_timespan(char *buf, size_t l, usec_t t, usec_t accuracy) {
+        static const struct {
+                const char *suffix;
+                usec_t usec;
+        } table[] = {
+                { "y",     USEC_PER_YEAR   },
+                { "month", USEC_PER_MONTH  },
+                { "w",     USEC_PER_WEEK   },
+                { "d",     USEC_PER_DAY    },
+                { "h",     USEC_PER_HOUR   },
+                { "min",   USEC_PER_MINUTE },
+                { "s",     USEC_PER_SEC    },
+                { "ms",    USEC_PER_MSEC   },
+                { "us",    1               },
+        };
+
+        char *p = ASSERT_PTR(buf);
+        bool something = false;
+
+        assert(l > 0);
+
+        if (t == USEC_INFINITY) {
+                strncpy(p, "infinity", l-1);
+                p[l-1] = 0;
+                return p;
+        }
+
+        if (t <= 0) {
+                strncpy(p, "0", l-1);
+                p[l-1] = 0;
+                return p;
+        }
+
+        /* The result of this function can be parsed with parse_sec */
+
+        for (size_t i = 0; i < ELEMENTSOF(table); i++) {
+                int k = 0;
+                size_t n;
+                bool done = false;
+                usec_t a, b;
+
+                if (t <= 0)
+                        break;
+
+                if (t < accuracy && something)
+                        break;
+
+                if (t < table[i].usec)
+                        continue;
+
+                if (l <= 1)
+                        break;
+
+                a = t / table[i].usec;
+                b = t % table[i].usec;
+
+                /* Let's see if we should shows this in dot notation */
+                if (t < USEC_PER_MINUTE && b > 0) {
+                        signed char j = 0;
+
+                        for (usec_t cc = table[i].usec; cc > 1; cc /= 10)
+                                j++;
+
+                        for (usec_t cc = accuracy; cc > 1; cc /= 10) {
+                                b /= 10;
+                                j--;
+                        }
+
+                        if (j > 0) {
+                                k = snprintf(p, l,
+                                             "%s"USEC_FMT".%0*"PRI_USEC"%s",
+                                             p > buf ? " " : "",
+                                             a,
+                                             j,
+                                             b,
+                                             table[i].suffix);
+
+                                t = 0;
+                                done = true;
+                        }
+                }
+
+                /* No? Then let's show it normally */
+                if (!done) {
+                        k = snprintf(p, l,
+                                     "%s"USEC_FMT"%s",
+                                     p > buf ? " " : "",
+                                     a,
+                                     table[i].suffix);
+
+                        t = b;
+                }
+
+                n = MIN((size_t) k, l-1);
+
+                l -= n;
+                p += n;
+
+                something = true;
+        }
+
+        *p = 0;
+
+        return buf;
+}
+
+static int parse_timestamp_impl(
+                const char *t,
+                size_t max_len,
+                bool utc,
+                int isdst,
+                long gmtoff,
+                usec_t *ret) {
+
+        static const struct {
+                const char *name;
+                const int nr;
+        } day_nr[] = {
+                { "Sunday",    0 },
+                { "Sun",       0 },
+                { "Monday",    1 },
+                { "Mon",       1 },
+                { "Tuesday",   2 },
+                { "Tue",       2 },
+                { "Wednesday", 3 },
+                { "Wed",       3 },
+                { "Thursday",  4 },
+                { "Thu",       4 },
+                { "Friday",    5 },
+                { "Fri",       5 },
+                { "Saturday",  6 },
+                { "Sat",       6 },
+        };
+
+        _cleanup_free_ char *t_alloc = NULL;
+        usec_t usec, plus = 0, minus = 0;
+        bool with_tz = false;
+        int r, weekday = -1;
+        unsigned fractional = 0;
+        const char *k;
+        struct tm tm, copy;
+        time_t sec;
+
+        /* Allowed syntaxes:
+         *
+         *   2012-09-22 16:34:22.1[2[3[4[5[6]]]]]
+         *   2012-09-22 16:34:22  (µsec will be set to 0)
+         *   2012-09-22 16:34     (seconds will be set to 0)
+         *   2012-09-22T16:34:22.1[2[3[4[5[6]]]]]
+         *   2012-09-22T16:34:22  (µsec will be set to 0)
+         *   2012-09-22T16:34     (seconds will be set to 0)
+         *   2012-09-22           (time will be set to 00:00:00)
+         *   16:34:22             (date will be set to today)
+         *   16:34                (date will be set to today, seconds to 0)
+         *   now
+         *   yesterday            (time is set to 00:00:00)
+         *   today                (time is set to 00:00:00)
+         *   tomorrow             (time is set to 00:00:00)
+         *   +5min
+         *   -5days
+         *   @2147483647          (seconds since epoch)
+         *
+         * Note, on DST change, 00:00:00 may not exist and in that case the time part may be shifted.
+         * E.g. "Sun 2023-03-13 America/Havana" is parsed as "Sun 2023-03-13 01:00:00 CDT".
+         *
+         * A simplified strptime-spelled RFC3339 ABNF looks like
+         *   "%Y-%m-%d" "T" "%H" ":" "%M" ":" "%S" [".%N"] ("Z" / (("+" / "-") "%H:%M"))
+         * We additionally allow no seconds and inherited timezone
+         * for symmetry with our other syntaxes and improved interactive usability:
+         *   "%Y-%m-%d" "T" "%H" ":" "%M" ":" ["%S" [".%N"]] ["Z" / (("+" / "-") "%H:%M")]
+         * RFC3339 defines time-secfrac to as "." 1*DIGIT, but we limit to 6 digits,
+         * since we're limited to 1µs resolution.
+         * We also accept "Sat 2012-09-22T16:34:22", RFC3339 warns against it.
+         */
+
+        assert(t);
+
+        if (max_len != SIZE_MAX) {
+                /* If the input string contains timezone, then cut it here. */
+
+                if (max_len == 0) /* Can't be the only field */
+                        return -EINVAL;
+
+                t_alloc = strndup(t, max_len);
+                if (!t_alloc)
+                        return -ENOMEM;
+
+                t = t_alloc;
+                with_tz = true;
+        }
+
+        if (utc) {
+                /* glibc accepts gmtoff more than 24 hours, but we refuse it. */
+                if ((usec_t) labs(gmtoff) * USEC_PER_SEC > USEC_PER_DAY)
+                        return -EINVAL;
+        } else {
+                if (gmtoff != 0)
+                        return -EINVAL;
+        }
+
+        if (t[0] == '@' && !with_tz)
+                return parse_sec(t + 1, ret);
+
+        usec = now(CLOCK_REALTIME);
+
+        if (!with_tz) {
+                if (streq(t, "now"))
+                        goto finish;
+
+                if (t[0] == '+') {
+                        r = parse_sec(t+1, &plus);
+                        if (r < 0)
+                                return r;
+
+                        goto finish;
+                }
+
+                if (t[0] == '-') {
+                        r = parse_sec(t+1, &minus);
+                        if (r < 0)
+                                return r;
+
+                        goto finish;
+                }
+
+                if ((k = endswith(t, " ago"))) {
+                        _cleanup_free_ char *buf = NULL;
+
+                        buf = strndup(t, k - t);
+                        if (!buf)
+                                return -ENOMEM;
+
+                        r = parse_sec(buf, &minus);
+                        if (r < 0)
+                                return r;
+
+                        goto finish;
+                }
+
+                if ((k = endswith(t, " left"))) {
+                        _cleanup_free_ char *buf = NULL;
+
+                        buf = strndup(t, k - t);
+                        if (!buf)
+                                return -ENOMEM;
+
+                        r = parse_sec(buf, &plus);
+                        if (r < 0)
+                                return r;
+
+                        goto finish;
+                }
+        }
+
+        sec = (time_t) (usec / USEC_PER_SEC);
+
+        if (!localtime_or_gmtime_r(&sec, &tm, utc))
+                return -EINVAL;
+
+        tm.tm_isdst = isdst;
+
+        if (streq(t, "today")) {
+                tm.tm_sec = tm.tm_min = tm.tm_hour = 0;
+                goto from_tm;
+
+        } else if (streq(t, "yesterday")) {
+                tm.tm_mday--;
+                tm.tm_sec = tm.tm_min = tm.tm_hour = 0;
+                goto from_tm;
+
+        } else if (streq(t, "tomorrow")) {
+                tm.tm_mday++;
+                tm.tm_sec = tm.tm_min = tm.tm_hour = 0;
+                goto from_tm;
+        }
+
+        for (size_t i = 0; i < ELEMENTSOF(day_nr); i++) {
+                k = startswith_no_case(t, day_nr[i].name);
+                if (!k || *k != ' ')
+                        continue;
+
+                weekday = day_nr[i].nr;
+                t = k + 1;
+                break;
+        }
+
+        copy = tm;
+        k = strptime(t, "%y-%m-%d %H:%M:%S", &tm);
+        if (k) {
+                if (*k == '.')
+                        goto parse_usec;
+                else if (*k == 0)
+                        goto from_tm;
+        }
+
+        /* Our "canonical" RFC3339 syntax variant */
+        tm = copy;
+        k = strptime(t, "%Y-%m-%d %H:%M:%S", &tm);
+        if (k) {
+                if (*k == '.')
+                        goto parse_usec;
+                else if (*k == 0)
+                        goto from_tm;
+        }
+
+        /* RFC3339 syntax */
+        tm = copy;
+        k = strptime(t, "%Y-%m-%dT%H:%M:%S", &tm);
+        if (k) {
+                if (*k == '.')
+                        goto parse_usec;
+                else if (*k == 0)
+                        goto from_tm;
+        }
+
+        /* Support OUTPUT_SHORT and OUTPUT_SHORT_PRECISE formats */
+        tm = copy;
+        k = strptime(t, "%b %d %H:%M:%S", &tm);
+        if (k) {
+                if (*k == '.')
+                        goto parse_usec;
+                else if (*k == 0)
+                        goto from_tm;
+        }
+
+        tm = copy;
+        k = strptime(t, "%y-%m-%d %H:%M", &tm);
+        if (k && *k == 0) {
+                tm.tm_sec = 0;
+                goto from_tm;
+        }
+
+        /* Our "canonical" RFC3339 syntax variant without seconds */
+        tm = copy;
+        k = strptime(t, "%Y-%m-%d %H:%M", &tm);
+        if (k && *k == 0) {
+                tm.tm_sec = 0;
+                goto from_tm;
+        }
+
+        /* RFC3339 syntax without seconds */
+        tm = copy;
+        k = strptime(t, "%Y-%m-%dT%H:%M", &tm);
+        if (k && *k == 0) {
+                tm.tm_sec = 0;
+                goto from_tm;
+        }
+
+        tm = copy;
+        k = strptime(t, "%y-%m-%d", &tm);
+        if (k && *k == 0) {
+                tm.tm_sec = tm.tm_min = tm.tm_hour = 0;
+                goto from_tm;
+        }
+
+        tm = copy;
+        k = strptime(t, "%Y-%m-%d", &tm);
+        if (k && *k == 0) {
+                tm.tm_sec = tm.tm_min = tm.tm_hour = 0;
+                goto from_tm;
+        }
+
+        tm = copy;
+        k = strptime(t, "%H:%M:%S", &tm);
+        if (k) {
+                if (*k == '.')
+                        goto parse_usec;
+                else if (*k == 0)
+                        goto from_tm;
+        }
+
+        tm = copy;
+        k = strptime(t, "%H:%M", &tm);
+        if (k && *k == 0) {
+                tm.tm_sec = 0;
+                goto from_tm;
+        }
+
+        return -EINVAL;
+
+parse_usec:
+        k++;
+        r = parse_fractional_part_u(&k, 6, &fractional);
+        if (r < 0)
+                return -EINVAL;
+        if (*k != '\0')
+                return -EINVAL;
+
+from_tm:
+        assert(plus == 0);
+        assert(minus == 0);
+
+        if (weekday >= 0 && tm.tm_wday != weekday)
+                return -EINVAL;
+
+        if (gmtoff < 0) {
+                plus = -gmtoff * USEC_PER_SEC;
+
+                /* If gmtoff is negative, the string may be too old to be parsed as UTC.
+                 * E.g. 1969-12-31 23:00:00 -06 == 1970-01-01 05:00:00 UTC
+                 * We assumed that gmtoff is in the range of -24:00…+24:00, hence the only date we need to
+                 * handle here is 1969-12-31. So, let's shift the date with one day, then subtract the shift
+                 * later. */
+                if (tm.tm_year == 69 && tm.tm_mon == 11 && tm.tm_mday == 31) {
+                        /* Thu 1970-01-01-00:00:00 */
+                        tm.tm_year = 70;
+                        tm.tm_mon = 0;
+                        tm.tm_mday = 1;
+                        tm.tm_wday = 4;
+                        tm.tm_yday = 0;
+                        minus = USEC_PER_DAY;
+                }
+        } else
+                minus = gmtoff * USEC_PER_SEC;
+
+        sec = mktime_or_timegm(&tm, utc);
+        if (sec < 0)
+                return -EINVAL;
+
+        usec = usec_add(sec * USEC_PER_SEC, fractional);
+
+finish:
+        usec = usec_add(usec, plus);
+
+        if (usec < minus)
+                return -EINVAL;
+
+        usec = usec_sub_unsigned(usec, minus);
+
+        if (usec > USEC_TIMESTAMP_FORMATTABLE_MAX)
+                return -EINVAL;
+
+        if (ret)
+                *ret = usec;
+        return 0;
+}
+
+static int parse_timestamp_maybe_with_tz(const char *t, size_t tz_offset, bool valid_tz, usec_t *ret) {
+        assert(t);
+
+        tzset();
+
+        for (int j = 0; j <= 1; j++) {
+                if (isempty(tzname[j]))
+                        continue;
+
+                if (!streq(t + tz_offset, tzname[j]))
+                        continue;
+
+                /* The specified timezone matches tzname[] of the local timezone. */
+                return parse_timestamp_impl(t, tz_offset - 1, /* utc = */ false, /* isdst = */ j, /* gmtoff = */ 0, ret);
+        }
+
+        /* If we know that the last word is a valid timezone (e.g. Asia/Tokyo), then simply drop the timezone
+         * and parse the remaining string as a local time. If we know that the last word is not a timezone,
+         * then assume that it is a part of the time and try to parse the whole string as a local time. */
+        return parse_timestamp_impl(t, valid_tz ? tz_offset - 1 : SIZE_MAX,
+                                    /* utc = */ false, /* isdst = */ -1, /* gmtoff = */ 0, ret);
+}
+
+typedef struct ParseTimestampResult {
+        usec_t usec;
+        int return_value;
+} ParseTimestampResult;
+
+int parse_timestamp(const char *t, usec_t *ret) {
+        ParseTimestampResult *shared, tmp;
+        const char *k, *tz, *current_tz;
+        size_t max_len, t_len;
+        struct tm tm;
+        int r;
+
+        assert(t);
+
+        t_len = strlen(t);
+        if (t_len > 2 && t[t_len - 1] == 'Z' && t[t_len - 2] != ' ')  /* RFC3339-style welded UTC: "1985-04-12T23:20:50.52Z" */
+                return parse_timestamp_impl(t, t_len - 1, /* utc = */ true, /* isdst = */ -1, /* gmtoff = */ 0, ret);
+
+        if (t_len > 7 && IN_SET(t[t_len - 6], '+', '-') && t[t_len - 7] != ' ') {  /* RFC3339-style welded offset: "1990-12-31T15:59:60-08:00" */
+                k = strptime(&t[t_len - 6], "%z", &tm);
+                if (k && *k == '\0')
+                        return parse_timestamp_impl(t, t_len - 6, /* utc = */ true, /* isdst = */ -1, /* gmtoff = */ tm.tm_gmtoff, ret);
+        }
+
+        tz = strrchr(t, ' ');
+        if (!tz)
+                return parse_timestamp_impl(t, /* max_len = */ SIZE_MAX, /* utc = */ false, /* isdst = */ -1, /* gmtoff = */ 0, ret);
+
+        max_len = tz - t;
+        tz++;
+
+        /* Shortcut, parse the string as UTC. */
+        if (streq(tz, "UTC"))
+                return parse_timestamp_impl(t, max_len, /* utc = */ true, /* isdst = */ -1, /* gmtoff = */ 0, ret);
+
+        /* If the timezone is compatible with RFC-822/ISO 8601 (e.g. +06, or -03:00) then parse the string as
+         * UTC and shift the result. Note, this must be earlier than the timezone check with tzname[], as
+         * tzname[] may be in the same format. */
+        k = strptime(tz, "%z", &tm);
+        if (k && *k == '\0')
+                return parse_timestamp_impl(t, max_len, /* utc = */ true, /* isdst = */ -1, /* gmtoff = */ tm.tm_gmtoff, ret);
+
+        /* If the last word is not a timezone file (e.g. Asia/Tokyo), then let's check if it matches
+         * tzname[] of the local timezone, e.g. JST or CEST. */
+        if (!timezone_is_valid(tz, LOG_DEBUG))
+                return parse_timestamp_maybe_with_tz(t, tz - t, /* valid_tz = */ false, ret);
+
+        /* Shortcut. If the current $TZ is equivalent to the specified timezone, it is not necessary to fork
+         * the process. */
+        current_tz = getenv("TZ");
+        if (current_tz && *current_tz == ':' && streq(current_tz + 1, tz))
+                return parse_timestamp_maybe_with_tz(t, tz - t, /* valid_tz = */ true, ret);
+
+        /* Otherwise, to avoid polluting the current environment variables, let's fork the process and set
+         * the specified timezone in the child process. */
+
+        shared = mmap(NULL, sizeof *shared, PROT_READ|PROT_WRITE, MAP_SHARED|MAP_ANONYMOUS, -1, 0);
+        if (shared == MAP_FAILED)
+                return negative_errno();
+
+        r = safe_fork("(sd-timestamp)", FORK_RESET_SIGNALS|FORK_CLOSE_ALL_FDS|FORK_DEATHSIG_SIGKILL|FORK_WAIT, NULL);
+        if (r < 0) {
+                (void) munmap(shared, sizeof *shared);
+                return r;
+        }
+        if (r == 0) {
+                const char *colon_tz;
+
+                /* tzset(3) says $TZ should be prefixed with ":" if we reference timezone files */
+                colon_tz = strjoina(":", tz);
+
+                if (setenv("TZ", colon_tz, 1) != 0) {
+                        shared->return_value = negative_errno();
+                        _exit(EXIT_FAILURE);
+                }
+
+                shared->return_value = parse_timestamp_maybe_with_tz(t, tz - t, /* valid_tz = */ true, &shared->usec);
+
+                _exit(EXIT_SUCCESS);
+        }
+
+        tmp = *shared;
+        if (munmap(shared, sizeof *shared) != 0)
+                return negative_errno();
+
+        if (tmp.return_value == 0 && ret)
+                *ret = tmp.usec;
+
+        return tmp.return_value;
+}
+
+static const char* extract_multiplier(const char *p, usec_t *ret) {
+        static const struct {
+                const char *suffix;
+                usec_t usec;
+        } table[] = {
+                { "seconds", USEC_PER_SEC    },
+                { "second",  USEC_PER_SEC    },
+                { "sec",     USEC_PER_SEC    },
+                { "s",       USEC_PER_SEC    },
+                { "minutes", USEC_PER_MINUTE },
+                { "minute",  USEC_PER_MINUTE },
+                { "min",     USEC_PER_MINUTE },
+                { "months",  USEC_PER_MONTH  },
+                { "month",   USEC_PER_MONTH  },
+                { "M",       USEC_PER_MONTH  },
+                { "msec",    USEC_PER_MSEC   },
+                { "ms",      USEC_PER_MSEC   },
+                { "m",       USEC_PER_MINUTE },
+                { "hours",   USEC_PER_HOUR   },
+                { "hour",    USEC_PER_HOUR   },
+                { "hr",      USEC_PER_HOUR   },
+                { "h",       USEC_PER_HOUR   },
+                { "days",    USEC_PER_DAY    },
+                { "day",     USEC_PER_DAY    },
+                { "d",       USEC_PER_DAY    },
+                { "weeks",   USEC_PER_WEEK   },
+                { "week",    USEC_PER_WEEK   },
+                { "w",       USEC_PER_WEEK   },
+                { "years",   USEC_PER_YEAR   },
+                { "year",    USEC_PER_YEAR   },
+                { "y",       USEC_PER_YEAR   },
+                { "usec",    1ULL            },
+                { "us",      1ULL            },
+                { "μs",      1ULL            }, /* U+03bc (aka GREEK SMALL LETTER MU) */
+                { "µs",      1ULL            }, /* U+b5 (aka MICRO SIGN) */
+        };
+
+        assert(p);
+        assert(ret);
+
+        for (size_t i = 0; i < ELEMENTSOF(table); i++) {
+                char *e;
+
+                e = startswith(p, table[i].suffix);
+                if (e) {
+                        *ret = table[i].usec;
+                        return e;
+                }
+        }
+
+        return p;
+}
+
+int parse_time(const char *t, usec_t *ret, usec_t default_unit) {
+        const char *p, *s;
+        usec_t usec = 0;
+        bool something = false;
+
+        assert(t);
+        assert(default_unit > 0);
+
+        p = t;
+
+        p += strspn(p, WHITESPACE);
+        s = startswith(p, "infinity");
+        if (s) {
+                s += strspn(s, WHITESPACE);
+                if (*s != 0)
+                        return -EINVAL;
+
+                if (ret)
+                        *ret = USEC_INFINITY;
+                return 0;
+        }
+
+        for (;;) {
+                usec_t multiplier = default_unit, k;
+                long long l;
+                char *e;
+
+                p += strspn(p, WHITESPACE);
+
+                if (*p == 0) {
+                        if (!something)
+                                return -EINVAL;
+
+                        break;
+                }
+
+                if (*p == '-') /* Don't allow "-0" */
+                        return -ERANGE;
+
+                errno = 0;
+                l = strtoll(p, &e, 10);
+                if (errno > 0)
+                        return -errno;
+                if (l < 0)
+                        return -ERANGE;
+
+                if (*e == '.') {
+                        p = e + 1;
+                        p += strspn(p, DIGITS);
+                } else if (e == p)
+                        return -EINVAL;
+                else
+                        p = e;
+
+                s = extract_multiplier(p + strspn(p, WHITESPACE), &multiplier);
+                if (s == p && *s != '\0')
+                        /* Don't allow '12.34.56', but accept '12.34 .56' or '12.34s.56' */
+                        return -EINVAL;
+
+                p = s;
+
+                if ((usec_t) l >= USEC_INFINITY / multiplier)
+                        return -ERANGE;
+
+                k = (usec_t) l * multiplier;
+                if (k >= USEC_INFINITY - usec)
+                        return -ERANGE;
+
+                usec += k;
+
+                something = true;
+
+                if (*e == '.') {
+                        usec_t m = multiplier / 10;
+                        const char *b;
+
+                        for (b = e + 1; *b >= '0' && *b <= '9'; b++, m /= 10) {
+                                k = (usec_t) (*b - '0') * m;
+                                if (k >= USEC_INFINITY - usec)
+                                        return -ERANGE;
+
+                                usec += k;
+                        }
+
+                        /* Don't allow "0.-0", "3.+1", "3. 1", "3.sec" or "3.hoge" */
+                        if (b == e + 1)
+                                return -EINVAL;
+                }
+        }
+
+        if (ret)
+                *ret = usec;
+        return 0;
+}
+
+int parse_sec(const char *t, usec_t *ret) {
+        return parse_time(t, ret, USEC_PER_SEC);
+}
+
+int parse_sec_fix_0(const char *t, usec_t *ret) {
+        usec_t k;
+        int r;
+
+        assert(t);
+        assert(ret);
+
+        r = parse_sec(t, &k);
+        if (r < 0)
+                return r;
+
+        *ret = k == 0 ? USEC_INFINITY : k;
+        return r;
+}
+
+int parse_sec_def_infinity(const char *t, usec_t *ret) {
+        assert(t);
+        assert(ret);
+
+        t += strspn(t, WHITESPACE);
+        if (isempty(t)) {
+                *ret = USEC_INFINITY;
+                return 0;
+        }
+        return parse_sec(t, ret);
+}
+
+static const char* extract_nsec_multiplier(const char *p, nsec_t *ret) {
+        static const struct {
+                const char *suffix;
+                nsec_t nsec;
+        } table[] = {
+                { "seconds", NSEC_PER_SEC    },
+                { "second",  NSEC_PER_SEC    },
+                { "sec",     NSEC_PER_SEC    },
+                { "s",       NSEC_PER_SEC    },
+                { "minutes", NSEC_PER_MINUTE },
+                { "minute",  NSEC_PER_MINUTE },
+                { "min",     NSEC_PER_MINUTE },
+                { "months",  NSEC_PER_MONTH  },
+                { "month",   NSEC_PER_MONTH  },
+                { "M",       NSEC_PER_MONTH  },
+                { "msec",    NSEC_PER_MSEC   },
+                { "ms",      NSEC_PER_MSEC   },
+                { "m",       NSEC_PER_MINUTE },
+                { "hours",   NSEC_PER_HOUR   },
+                { "hour",    NSEC_PER_HOUR   },
+                { "hr",      NSEC_PER_HOUR   },
+                { "h",       NSEC_PER_HOUR   },
+                { "days",    NSEC_PER_DAY    },
+                { "day",     NSEC_PER_DAY    },
+                { "d",       NSEC_PER_DAY    },
+                { "weeks",   NSEC_PER_WEEK   },
+                { "week",    NSEC_PER_WEEK   },
+                { "w",       NSEC_PER_WEEK   },
+                { "years",   NSEC_PER_YEAR   },
+                { "year",    NSEC_PER_YEAR   },
+                { "y",       NSEC_PER_YEAR   },
+                { "usec",    NSEC_PER_USEC   },
+                { "us",      NSEC_PER_USEC   },
+                { "μs",      NSEC_PER_USEC   }, /* U+03bc (aka GREEK LETTER MU) */
+                { "µs",      NSEC_PER_USEC   }, /* U+b5 (aka MICRO SIGN) */
+                { "nsec",    1ULL            },
+                { "ns",      1ULL            },
+                { "",        1ULL            }, /* default is nsec */
+        };
+        size_t i;
+
+        assert(p);
+        assert(ret);
+
+        for (i = 0; i < ELEMENTSOF(table); i++) {
+                char *e;
+
+                e = startswith(p, table[i].suffix);
+                if (e) {
+                        *ret = table[i].nsec;
+                        return e;
+                }
+        }
+
+        return p;
+}
+
+int parse_nsec(const char *t, nsec_t *ret) {
+        const char *p, *s;
+        nsec_t nsec = 0;
+        bool something = false;
+
+        assert(t);
+        assert(ret);
+
+        p = t;
+
+        p += strspn(p, WHITESPACE);
+        s = startswith(p, "infinity");
+        if (s) {
+                s += strspn(s, WHITESPACE);
+                if (*s != 0)
+                        return -EINVAL;
+
+                *ret = NSEC_INFINITY;
+                return 0;
+        }
+
+        for (;;) {
+                nsec_t multiplier = 1, k;
+                long long l;
+                char *e;
+
+                p += strspn(p, WHITESPACE);
+
+                if (*p == 0) {
+                        if (!something)
+                                return -EINVAL;
+
+                        break;
+                }
+
+                if (*p == '-') /* Don't allow "-0" */
+                        return -ERANGE;
+
+                errno = 0;
+                l = strtoll(p, &e, 10);
+                if (errno > 0)
+                        return -errno;
+                if (l < 0)
+                        return -ERANGE;
+
+                if (*e == '.') {
+                        p = e + 1;
+                        p += strspn(p, DIGITS);
+                } else if (e == p)
+                        return -EINVAL;
+                else
+                        p = e;
+
+                s = extract_nsec_multiplier(p + strspn(p, WHITESPACE), &multiplier);
+                if (s == p && *s != '\0')
+                        /* Don't allow '12.34.56', but accept '12.34 .56' or '12.34s.56' */
+                        return -EINVAL;
+
+                p = s;
+
+                if ((nsec_t) l >= NSEC_INFINITY / multiplier)
+                        return -ERANGE;
+
+                k = (nsec_t) l * multiplier;
+                if (k >= NSEC_INFINITY - nsec)
+                        return -ERANGE;
+
+                nsec += k;
+
+                something = true;
+
+                if (*e == '.') {
+                        nsec_t m = multiplier / 10;
+                        const char *b;
+
+                        for (b = e + 1; *b >= '0' && *b <= '9'; b++, m /= 10) {
+                                k = (nsec_t) (*b - '0') * m;
+                                if (k >= NSEC_INFINITY - nsec)
+                                        return -ERANGE;
+
+                                nsec += k;
+                        }
+
+                        /* Don't allow "0.-0", "3.+1", "3. 1", "3.sec" or "3.hoge" */
+                        if (b == e + 1)
+                                return -EINVAL;
+                }
+        }
+
+        *ret = nsec;
+
+        return 0;
+}
+
+static int get_timezones_from_zone1970_tab(char ***ret) {
+        _cleanup_fclose_ FILE *f = NULL;
+        _cleanup_strv_free_ char **zones = NULL;
+        int r;
+
+        assert(ret);
+
+        f = fopen("/usr/share/zoneinfo/zone1970.tab", "re");
+        if (!f)
+                return -errno;
+
+        for (;;) {
+                _cleanup_free_ char *line = NULL, *cc = NULL, *co = NULL, *tz = NULL;
+
+                r = read_line(f, LONG_LINE_MAX, &line);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        break;
+
+                const char *p = line;
+
+                /* Line format is:
+                 * 'country codes' 'coordinates' 'timezone' 'comments' */
+                r = extract_many_words(&p, NULL, 0, &cc, &co, &tz, NULL);
+                if (r < 0)
+                        continue;
+
+                /* Lines that start with # are comments. */
+                if (*cc == '#')
+                        continue;
+
+                r = strv_extend(&zones, tz);
+                if (r < 0)
+                        return r;
+        }
+
+        *ret = TAKE_PTR(zones);
+        return 0;
+}
+
+static int get_timezones_from_tzdata_zi(char ***ret) {
+        _cleanup_fclose_ FILE *f = NULL;
+        _cleanup_strv_free_ char **zones = NULL;
+        int r;
+
+        assert(ret);
+
+        f = fopen("/usr/share/zoneinfo/tzdata.zi", "re");
+        if (!f)
+                return -errno;
+
+        for (;;) {
+                _cleanup_free_ char *line = NULL, *type = NULL, *f1 = NULL, *f2 = NULL;
+
+                r = read_line(f, LONG_LINE_MAX, &line);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        break;
+
+                const char *p = line;
+
+                /* The only lines we care about are Zone and Link lines.
+                 * Zone line format is:
+                 * 'Zone' 'timezone' ...
+                 * Link line format is:
+                 * 'Link' 'target' 'alias'
+                 * See 'man zic' for more detail. */
+                r = extract_many_words(&p, NULL, 0, &type, &f1, &f2, NULL);
+                if (r < 0)
+                        continue;
+
+                char *tz;
+                if (IN_SET(*type, 'Z', 'z'))
+                        /* Zone lines have timezone in field 1. */
+                        tz = f1;
+                else if (IN_SET(*type, 'L', 'l'))
+                        /* Link lines have timezone in field 2. */
+                        tz = f2;
+                else
+                        /* Not a line we care about. */
+                        continue;
+
+                r = strv_extend(&zones, tz);
+                if (r < 0)
+                        return r;
+        }
+
+        *ret = TAKE_PTR(zones);
+        return 0;
+}
+
+int get_timezones(char ***ret) {
+        _cleanup_strv_free_ char **zones = NULL;
+        int r;
+
+        assert(ret);
+
+        r = get_timezones_from_tzdata_zi(&zones);
+        if (r == -ENOENT) {
+                log_debug_errno(r, "Could not get timezone data from tzdata.zi, using zone1970.tab: %m");
+                r = get_timezones_from_zone1970_tab(&zones);
+                if (r == -ENOENT)
+                        log_debug_errno(r, "Could not get timezone data from zone1970.tab, using UTC: %m");
+        }
+        if (r < 0 && r != -ENOENT)
+                return r;
+
+        /* Always include UTC */
+        r = strv_extend(&zones, "UTC");
+        if (r < 0)
+                return -ENOMEM;
+
+        strv_sort(zones);
+        strv_uniq(zones);
+
+        *ret = TAKE_PTR(zones);
+        return 0;
+}
+
+int verify_timezone(const char *name, int log_level) {
+        bool slash = false;
+        const char *p, *t;
+        _cleanup_close_ int fd = -EBADF;
+        char buf[4];
+        int r;
+
+        if (isempty(name))
+                return -EINVAL;
+
+        /* Always accept "UTC" as valid timezone, since it's the fallback, even if user has no timezones installed. */
+        if (streq(name, "UTC"))
+                return 0;
+
+        if (name[0] == '/')
+                return -EINVAL;
+
+        for (p = name; *p; p++) {
+                if (!ascii_isdigit(*p) &&
+                    !ascii_isalpha(*p) &&
+                    !IN_SET(*p, '-', '_', '+', '/'))
+                        return -EINVAL;
+
+                if (*p == '/') {
+
+                        if (slash)
+                                return -EINVAL;
+
+                        slash = true;
+                } else
+                        slash = false;
+        }
+
+        if (slash)
+                return -EINVAL;
+
+        if (p - name >= PATH_MAX)
+                return -ENAMETOOLONG;
+
+        t = strjoina("/usr/share/zoneinfo/", name);
+
+        fd = open(t, O_RDONLY|O_CLOEXEC);
+        if (fd < 0)
+                return log_full_errno(log_level, errno, "Failed to open timezone file '%s': %m", t);
+
+        r = fd_verify_regular(fd);
+        if (r < 0)
+                return log_full_errno(log_level, r, "Timezone file '%s' is not  a regular file: %m", t);
+
+        r = loop_read_exact(fd, buf, 4, false);
+        if (r < 0)
+                return log_full_errno(log_level, r, "Failed to read from timezone file '%s': %m", t);
+
+        /* Magic from tzfile(5) */
+        if (memcmp(buf, "TZif", 4) != 0)
+                return log_full_errno(log_level, SYNTHETIC_ERRNO(EBADMSG),
+                                      "Timezone file '%s' has wrong magic bytes", t);
+
+        return 0;
+}
+
+bool clock_supported(clockid_t clock) {
+        struct timespec ts;
+
+        switch (clock) {
+
+        case CLOCK_MONOTONIC:
+        case CLOCK_REALTIME:
+        case CLOCK_BOOTTIME:
+                /* These three are always available in our baseline, and work in timerfd, as of kernel 3.15 */
+                return true;
+
+        default:
+                /* For everything else, check properly */
+                return clock_gettime(clock, &ts) >= 0;
+        }
+}
+
+int get_timezone(char **ret) {
+        _cleanup_free_ char *t = NULL;
+        const char *e;
+        char *z;
+        int r;
+
+        assert(ret);
+
+        r = readlink_malloc("/etc/localtime", &t);
+        if (r == -ENOENT) {
+                /* If the symlink does not exist, assume "UTC", like glibc does */
+                z = strdup("UTC");
+                if (!z)
+                        return -ENOMEM;
+
+                *ret = z;
+                return 0;
+        }
+        if (r < 0)
+                return r; /* returns EINVAL if not a symlink */
+
+        e = PATH_STARTSWITH_SET(t, "/usr/share/zoneinfo/", "../usr/share/zoneinfo/");
+        if (!e)
+                return -EINVAL;
+
+        if (!timezone_is_valid(e, LOG_DEBUG))
+                return -EINVAL;
+
+        z = strdup(e);
+        if (!z)
+                return -ENOMEM;
+
+        *ret = z;
+        return 0;
+}
+
+time_t mktime_or_timegm(struct tm *tm, bool utc) {
+        assert(tm);
+
+        return utc ? timegm(tm) : mktime(tm);
+}
+
+struct tm *localtime_or_gmtime_r(const time_t *t, struct tm *tm, bool utc) {
+        assert(t);
+        assert(tm);
+
+        return utc ? gmtime_r(t, tm) : localtime_r(t, tm);
+}
+
+static uint32_t sysconf_clock_ticks_cached(void) {
+        static thread_local uint32_t hz = 0;
+        long r;
+
+        if (hz == 0) {
+                r = sysconf(_SC_CLK_TCK);
+
+                assert(r > 0);
+                hz = r;
+        }
+
+        return hz;
+}
+
+uint32_t usec_to_jiffies(usec_t u) {
+        uint32_t hz = sysconf_clock_ticks_cached();
+        return DIV_ROUND_UP(u, USEC_PER_SEC / hz);
+}
+
+usec_t jiffies_to_usec(uint32_t j) {
+        uint32_t hz = sysconf_clock_ticks_cached();
+        return DIV_ROUND_UP(j * USEC_PER_SEC, hz);
+}
+
+usec_t usec_shift_clock(usec_t x, clockid_t from, clockid_t to) {
+        usec_t a, b;
+
+        if (x == USEC_INFINITY)
+                return USEC_INFINITY;
+        if (map_clock_id(from) == map_clock_id(to))
+                return x;
+
+        a = now(from);
+        b = now(to);
+
+        if (x > a)
+                /* x lies in the future */
+                return usec_add(b, usec_sub_unsigned(x, a));
+        else
+                /* x lies in the past */
+                return usec_sub_unsigned(b, usec_sub_unsigned(a, x));
+}
+
+bool in_utc_timezone(void) {
+        tzset();
+
+        return timezone == 0 && daylight == 0;
+}
+
+int time_change_fd(void) {
+
+        /* We only care for the cancellation event, hence we set the timeout to the latest possible value. */
+        static const struct itimerspec its = {
+                .it_value.tv_sec = TIME_T_MAX,
+        };
+
+        _cleanup_close_ int fd = -EBADF;
+
+        assert_cc(sizeof(time_t) == sizeof(TIME_T_MAX));
+
+        /* Uses TFD_TIMER_CANCEL_ON_SET to get notifications whenever CLOCK_REALTIME makes a jump relative to
+         * CLOCK_MONOTONIC. */
+
+        fd = timerfd_create(CLOCK_REALTIME, TFD_NONBLOCK|TFD_CLOEXEC);
+        if (fd < 0)
+                return -errno;
+
+        if (timerfd_settime(fd, TFD_TIMER_ABSTIME|TFD_TIMER_CANCEL_ON_SET, &its, NULL) >= 0)
+                return TAKE_FD(fd);
+
+        /* So apparently there are systems where time_t is 64-bit, but the kernel actually doesn't support
+         * 64-bit time_t. In that case configuring a timer to TIME_T_MAX will fail with EOPNOTSUPP or a
+         * similar error. If that's the case let's try with INT32_MAX instead, maybe that works. It's a bit
+         * of a black magic thing though, but what can we do?
+         *
+         * We don't want this code on x86-64, hence let's conditionalize this for systems with 64-bit time_t
+         * but where "long" is shorter than 64-bit, i.e. 32-bit archs.
+         *
+         * See: https://github.com/systemd/systemd/issues/14362 */
+
+#if SIZEOF_TIME_T == 8 && ULONG_MAX < UINT64_MAX
+        if (ERRNO_IS_NOT_SUPPORTED(errno) || errno == EOVERFLOW) {
+                static const struct itimerspec its32 = {
+                        .it_value.tv_sec = INT32_MAX,
+                };
+
+                if (timerfd_settime(fd, TFD_TIMER_ABSTIME|TFD_TIMER_CANCEL_ON_SET, &its32, NULL) >= 0)
+                        return TAKE_FD(fd);
+        }
+#endif
+
+        return -errno;
+}
+
+static const char* const timestamp_style_table[_TIMESTAMP_STYLE_MAX] = {
+        [TIMESTAMP_PRETTY] = "pretty",
+        [TIMESTAMP_US]     = "us",
+        [TIMESTAMP_UTC]    = "utc",
+        [TIMESTAMP_US_UTC] = "us+utc",
+        [TIMESTAMP_UNIX]   = "unix",
+};
+
+/* Use the macro for enum → string to allow for aliases */
+DEFINE_STRING_TABLE_LOOKUP_TO_STRING(timestamp_style, TimestampStyle);
+
+/* For the string → enum mapping we use the generic implementation, but also support two aliases */
+TimestampStyle timestamp_style_from_string(const char *s) {
+        TimestampStyle t;
+
+        t = (TimestampStyle) string_table_lookup(timestamp_style_table, ELEMENTSOF(timestamp_style_table), s);
+        if (t >= 0)
+                return t;
+        if (STRPTR_IN_SET(s, "µs", "μs")) /* accept both µ symbols in unicode, i.e. micro symbol + Greek small letter mu. */
+                return TIMESTAMP_US;
+        if (STRPTR_IN_SET(s, "µs+utc", "μs+utc"))
+                return TIMESTAMP_US_UTC;
+        return t;
+}