[thirdparty/systemd.git] / src / basic / time-util.c

/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/

/***
  This file is part of systemd.

  Copyright 2010 Lennart Poettering

  systemd is free software; you can redistribute it and/or modify it
  under the terms of the GNU Lesser General Public License as published by
  the Free Software Foundation; either version 2.1 of the License, or
  (at your option) any later version.

  systemd is distributed in the hope that it will be useful, but
  WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public License
  along with systemd; If not, see <http://www.gnu.org/licenses/>.
***/

#include <time.h>
#include <string.h>
#include <sys/timex.h>
#include <sys/timerfd.h>

#include "util.h"
#include "time-util.h"
#include "path-util.h"
#include "strv.h"

usec_t now(clockid_t clock_id) {
        struct timespec ts;

        assert_se(clock_gettime(clock_id, &ts) == 0);

        return timespec_load(&ts);
}

nsec_t now_nsec(clockid_t clock_id) {
        struct timespec ts;

        assert_se(clock_gettime(clock_id, &ts) == 0);

        return timespec_load_nsec(&ts);
}

dual_timestamp* dual_timestamp_get(dual_timestamp *ts) {
        assert(ts);

        ts->realtime = now(CLOCK_REALTIME);
        ts->monotonic = now(CLOCK_MONOTONIC);

        return ts;
}

dual_timestamp* dual_timestamp_from_realtime(dual_timestamp *ts, usec_t u) {
        int64_t delta;
        assert(ts);

        if (u == USEC_INFINITY || u <= 0) {
                ts->realtime = ts->monotonic = u;
                return ts;
        }

        ts->realtime = u;

        delta = (int64_t) now(CLOCK_REALTIME) - (int64_t) u;
        ts->monotonic = now(CLOCK_MONOTONIC);

        if ((int64_t) ts->monotonic > delta)
                ts->monotonic -= delta;
        else
                ts->monotonic = 0;

        return ts;
}

dual_timestamp* dual_timestamp_from_monotonic(dual_timestamp *ts, usec_t u) {
        int64_t delta;
        assert(ts);

        if (u == USEC_INFINITY) {
                ts->realtime = ts->monotonic = USEC_INFINITY;
                return ts;
        }

        ts->monotonic = u;
        delta = (int64_t) now(CLOCK_MONOTONIC) - (int64_t) u;

        ts->realtime = now(CLOCK_REALTIME);
        if ((int64_t) ts->realtime > delta)
                ts->realtime -= delta;
        else
                ts->realtime = 0;

        return ts;
}

dual_timestamp* dual_timestamp_from_boottime_or_monotonic(dual_timestamp *ts, usec_t u) {
        int64_t delta;

        if (u == USEC_INFINITY) {
                ts->realtime = ts->monotonic = USEC_INFINITY;
                return ts;
        }
        ts->realtime = now(CLOCK_REALTIME);
        ts->monotonic = now(CLOCK_MONOTONIC);

        delta = (int64_t) now(clock_boottime_or_monotonic()) - (int64_t) u;

        if ((int64_t) ts->realtime > delta)
                ts->realtime -= delta;
        else
                ts->realtime = 0;

        if ((int64_t) ts->monotonic > delta)
                ts->monotonic -= delta;
        else
                ts->monotonic = 0;

        return ts;
}


usec_t timespec_load(const struct timespec *ts) {
        assert(ts);

        if (ts->tv_sec == (time_t) -1 &&
            ts->tv_nsec == (long) -1)
                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 == (time_t) -1 &&
            ts->tv_nsec == (long) -1)
                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) {
                ts->tv_sec = (time_t) -1;
                ts->tv_nsec = (long) -1;
                return ts;
        }

        ts->tv_sec = (time_t) (u / USEC_PER_SEC);
        ts->tv_nsec = (long int) ((u % USEC_PER_SEC) * NSEC_PER_USEC);

        return ts;
}

usec_t timeval_load(const struct timeval *tv) {
        assert(tv);

        if (tv->tv_sec == (time_t) -1 &&
            tv->tv_usec == (suseconds_t) -1)
                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) {
                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;
}

static char *format_timestamp_internal(char *buf, size_t l, usec_t t, bool utc) {
        struct tm tm;
        time_t sec;

        assert(buf);
        assert(l > 0);

        if (t <= 0 || t == USEC_INFINITY)
                return NULL;

        sec = (time_t) (t / USEC_PER_SEC);

        if (utc)
                gmtime_r(&sec, &tm);
        else
                localtime_r(&sec, &tm);
        if (strftime(buf, l, "%a %Y-%m-%d %H:%M:%S %Z", &tm) <= 0)
                return NULL;

        return buf;
}

char *format_timestamp(char *buf, size_t l, usec_t t) {
        return format_timestamp_internal(buf, l, t, false);
}

char *format_timestamp_utc(char *buf, size_t l, usec_t t) {
        return format_timestamp_internal(buf, l, t, true);
}

static char *format_timestamp_internal_us(char *buf, size_t l, usec_t t, bool utc) {
        struct tm tm;
        time_t sec;

        assert(buf);
        assert(l > 0);

        if (t <= 0 || t == USEC_INFINITY)
                return NULL;

        sec = (time_t) (t / USEC_PER_SEC);
        if (utc)
                gmtime_r(&sec, &tm);
        else
                localtime_r(&sec, &tm);

        if (strftime(buf, l, "%a %Y-%m-%d %H:%M:%S", &tm) <= 0)
                return NULL;
        snprintf(buf + strlen(buf), l - strlen(buf), ".%06llu", (unsigned long long) (t % USEC_PER_SEC));
        if (strftime(buf + strlen(buf), l - strlen(buf), " %Z", &tm) <= 0)
                return NULL;

        return buf;
}

char *format_timestamp_us(char *buf, size_t l, usec_t t) {
        return format_timestamp_internal_us(buf, l, t, false);
}

char *format_timestamp_us_utc(char *buf, size_t l, usec_t t) {
        return format_timestamp_internal_us(buf, l, t, true);
}

char *format_timestamp_relative(char *buf, size_t l, usec_t t) {
        const char *s;
        usec_t n, d;

        if (t <= 0 || t == USEC_INFINITY)
                return NULL;

        n = now(CLOCK_REALTIME);
        if (n > t) {
                d = n - t;
                s = "ago";
        } else {
                d = t - n;
                s = "left";
        }

        if (d >= USEC_PER_YEAR)
                snprintf(buf, l, USEC_FMT " years " USEC_FMT " months %s",
                         d / USEC_PER_YEAR,
                         (d % USEC_PER_YEAR) / USEC_PER_MONTH, s);
        else if (d >= USEC_PER_MONTH)
                snprintf(buf, l, USEC_FMT " months " USEC_FMT " days %s",
                         d / USEC_PER_MONTH,
                         (d % USEC_PER_MONTH) / USEC_PER_DAY, s);
        else if (d >= USEC_PER_WEEK)
                snprintf(buf, l, USEC_FMT " weeks " USEC_FMT " days %s",
                         d / USEC_PER_WEEK,
                         (d % USEC_PER_WEEK) / USEC_PER_DAY, s);
        else if (d >= 2*USEC_PER_DAY)
                snprintf(buf, l, USEC_FMT " days %s", d / USEC_PER_DAY, s);
        else if (d >= 25*USEC_PER_HOUR)
                snprintf(buf, l, "1 day " USEC_FMT "h %s",
                         (d - USEC_PER_DAY) / USEC_PER_HOUR, s);
        else if (d >= 6*USEC_PER_HOUR)
                snprintf(buf, l, USEC_FMT "h %s",
                         d / USEC_PER_HOUR, s);
        else if (d >= USEC_PER_HOUR)
                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)
                snprintf(buf, l, USEC_FMT "min %s",
                         d / USEC_PER_MINUTE, s);
        else if (d >= USEC_PER_MINUTE)
                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)
                snprintf(buf, l, USEC_FMT "s %s",
                         d / USEC_PER_SEC, s);
        else if (d >= USEC_PER_MSEC)
                snprintf(buf, l, USEC_FMT "ms %s",
                         d / USEC_PER_MSEC, s);
        else if (d > 0)
                snprintf(buf, l, USEC_FMT"us %s",
                         d, s);
        else
                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 },
        };

        unsigned i;
        char *p = buf;
        bool something = false;

        assert(buf);
        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 (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) {
                        usec_t cc;
                        int j;

                        j = 0;
                        for (cc = table[i].usec; cc > 1; cc /= 10)
                                j++;

                        for (cc = accuracy; cc > 1; cc /= 10) {
                                b /= 10;
                                j--;
                        }

                        if (j > 0) {
                                k = snprintf(p, l,
                                             "%s"USEC_FMT".%0*llu%s",
                                             p > buf ? " " : "",
                                             a,
                                             j,
                                             (unsigned long long) 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);

                l -= n;
                p += n;

                something = true;
        }

        *p = 0;

        return buf;
}

void dual_timestamp_serialize(FILE *f, const char *name, dual_timestamp *t) {

        assert(f);
        assert(name);
        assert(t);

        if (!dual_timestamp_is_set(t))
                return;

        fprintf(f, "%s="USEC_FMT" "USEC_FMT"\n",
                name,
                t->realtime,
                t->monotonic);
}

int dual_timestamp_deserialize(const char *value, dual_timestamp *t) {
        unsigned long long a, b;

        assert(value);
        assert(t);

        if (sscanf(value, "%llu %llu", &a, &b) != 2) {
                log_debug("Failed to parse finish timestamp value %s.", value);
                return -EINVAL;
        }

        t->realtime = a;
        t->monotonic = b;

        return 0;
}

int parse_timestamp(const char *t, usec_t *usec) {
        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 },
        };

        const char *k;
        struct tm tm, copy;
        time_t x;
        usec_t plus = 0, minus = 0, ret;
        int r, weekday = -1;
        unsigned i;

        /*
         * Allowed syntaxes:
         *
         *   2012-09-22 16:34:22
         *   2012-09-22 16:34     (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)
         *
         */

        assert(t);
        assert(usec);

        x = time(NULL);
        assert_se(localtime_r(&x, &tm));
        tm.tm_isdst = -1;

        if (streq(t, "now"))
                goto finish;

        else if (streq(t, "today")) {
                tm.tm_sec = tm.tm_min = tm.tm_hour = 0;
                goto finish;

        } else if (streq(t, "yesterday")) {
                tm.tm_mday --;
                tm.tm_sec = tm.tm_min = tm.tm_hour = 0;
                goto finish;

        } else if (streq(t, "tomorrow")) {
                tm.tm_mday ++;
                tm.tm_sec = tm.tm_min = tm.tm_hour = 0;
                goto finish;

        } else if (t[0] == '+') {
                r = parse_sec(t+1, &plus);
                if (r < 0)
                        return r;

                goto finish;

        } else if (t[0] == '-') {
                r = parse_sec(t+1, &minus);
                if (r < 0)
                        return r;

                goto finish;

        } else if (t[0] == '@')
                return parse_sec(t + 1, usec);

        else if (endswith(t, " ago")) {
                _cleanup_free_ char *z;

                z = strndup(t, strlen(t) - 4);
                if (!z)
                        return -ENOMEM;

                r = parse_sec(z, &minus);
                if (r < 0)
                        return r;

                goto finish;
        } else if (endswith(t, " left")) {
                _cleanup_free_ char *z;

                z = strndup(t, strlen(t) - 4);
                if (!z)
                        return -ENOMEM;

                r = parse_sec(z, &plus);
                if (r < 0)
                        return r;

                goto finish;
        }

        for (i = 0; i < ELEMENTSOF(day_nr); i++) {
                size_t skip;

                if (!startswith_no_case(t, day_nr[i].name))
                        continue;

                skip = strlen(day_nr[i].name);
                if (t[skip] != ' ')
                        continue;

                weekday = day_nr[i].nr;
                t += skip + 1;
                break;
        }

        copy = tm;
        k = strptime(t, "%y-%m-%d %H:%M:%S", &tm);
        if (k && *k == 0)
                goto finish;

        tm = copy;
        k = strptime(t, "%Y-%m-%d %H:%M:%S", &tm);
        if (k && *k == 0)
                goto finish;

        tm = copy;
        k = strptime(t, "%y-%m-%d %H:%M", &tm);
        if (k && *k == 0) {
                tm.tm_sec = 0;
                goto finish;
        }

        tm = copy;
        k = strptime(t, "%Y-%m-%d %H:%M", &tm);
        if (k && *k == 0) {
                tm.tm_sec = 0;
                goto finish;
        }

        tm = copy;
        k = strptime(t, "%y-%m-%d", &tm);
        if (k && *k == 0) {
                tm.tm_sec = tm.tm_min = tm.tm_hour = 0;
                goto finish;
        }

        tm = copy;
        k = strptime(t, "%Y-%m-%d", &tm);
        if (k && *k == 0) {
                tm.tm_sec = tm.tm_min = tm.tm_hour = 0;
                goto finish;
        }

        tm = copy;
        k = strptime(t, "%H:%M:%S", &tm);
        if (k && *k == 0)
                goto finish;

        tm = copy;
        k = strptime(t, "%H:%M", &tm);
        if (k && *k == 0) {
                tm.tm_sec = 0;
                goto finish;
        }

        return -EINVAL;

finish:
        x = mktime(&tm);
        if (x == (time_t) -1)
                return -EINVAL;

        if (weekday >= 0 && tm.tm_wday != weekday)
                return -EINVAL;

        ret = (usec_t) x * USEC_PER_SEC;

        ret += plus;
        if (ret > minus)
                ret -= minus;
        else
                ret = 0;

        *usec = ret;

        return 0;
}

int parse_sec(const char *t, usec_t *usec) {
        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 },
                { "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 },
                { "", USEC_PER_SEC }, /* default is sec */
        };

        const char *p, *s;
        usec_t r = 0;
        bool something = false;

        assert(t);
        assert(usec);

        p = t;

        p += strspn(p, WHITESPACE);
        s = startswith(p, "infinity");
        if (s) {
                s += strspn(s, WHITESPACE);
                if (*s != 0)
                        return -EINVAL;

                *usec = USEC_INFINITY;
                return 0;
        }

        for (;;) {
                long long l, z = 0;
                char *e;
                unsigned i, n = 0;

                p += strspn(p, WHITESPACE);

                if (*p == 0) {
                        if (!something)
                                return -EINVAL;

                        break;
                }

                errno = 0;
                l = strtoll(p, &e, 10);

                if (errno > 0)
                        return -errno;

                if (l < 0)
                        return -ERANGE;

                if (*e == '.') {
                        char *b = e + 1;

                        errno = 0;
                        z = strtoll(b, &e, 10);
                        if (errno > 0)
                                return -errno;

                        if (z < 0)
                                return -ERANGE;

                        if (e == b)
                                return -EINVAL;

                        n = e - b;

                } else if (e == p)
                        return -EINVAL;

                e += strspn(e, WHITESPACE);

                for (i = 0; i < ELEMENTSOF(table); i++)
                        if (startswith(e, table[i].suffix)) {
                                usec_t k = (usec_t) z * table[i].usec;

                                for (; n > 0; n--)
                                        k /= 10;

                                r += (usec_t) l * table[i].usec + k;
                                p = e + strlen(table[i].suffix);

                                something = true;
                                break;
                        }

                if (i >= ELEMENTSOF(table))
                        return -EINVAL;

        }

        *usec = r;

        return 0;
}

int parse_nsec(const char *t, nsec_t *nsec) {
        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 },
                { "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 },
                { "nsec", 1ULL },
                { "ns", 1ULL },
                { "", 1ULL }, /* default is nsec */
        };

        const char *p, *s;
        nsec_t r = 0;
        bool something = false;

        assert(t);
        assert(nsec);

        p = t;

        p += strspn(p, WHITESPACE);
        s = startswith(p, "infinity");
        if (s) {
                s += strspn(s, WHITESPACE);
                if (*s != 0)
                        return -EINVAL;

                *nsec = NSEC_INFINITY;
                return 0;
        }

        for (;;) {
                long long l, z = 0;
                char *e;
                unsigned i, n = 0;

                p += strspn(p, WHITESPACE);

                if (*p == 0) {
                        if (!something)
                                return -EINVAL;

                        break;
                }

                errno = 0;
                l = strtoll(p, &e, 10);

                if (errno > 0)
                        return -errno;

                if (l < 0)
                        return -ERANGE;

                if (*e == '.') {
                        char *b = e + 1;

                        errno = 0;
                        z = strtoll(b, &e, 10);
                        if (errno > 0)
                                return -errno;

                        if (z < 0)
                                return -ERANGE;

                        if (e == b)
                                return -EINVAL;

                        n = e - b;

                } else if (e == p)
                        return -EINVAL;

                e += strspn(e, WHITESPACE);

                for (i = 0; i < ELEMENTSOF(table); i++)
                        if (startswith(e, table[i].suffix)) {
                                nsec_t k = (nsec_t) z * table[i].nsec;

                                for (; n > 0; n--)
                                        k /= 10;

                                r += (nsec_t) l * table[i].nsec + k;
                                p = e + strlen(table[i].suffix);

                                something = true;
                                break;
                        }

                if (i >= ELEMENTSOF(table))
                        return -EINVAL;

        }

        *nsec = r;

        return 0;
}

bool ntp_synced(void) {
        struct timex txc = {};

        if (adjtimex(&txc) < 0)
                return false;

        if (txc.status & STA_UNSYNC)
                return false;

        return true;
}

int get_timezones(char ***ret) {
        _cleanup_fclose_ FILE *f = NULL;
        _cleanup_strv_free_ char **zones = NULL;
        size_t n_zones = 0, n_allocated = 0;

        assert(ret);

        zones = strv_new("UTC", NULL);
        if (!zones)
                return -ENOMEM;

        n_allocated = 2;
        n_zones = 1;

        f = fopen("/usr/share/zoneinfo/zone.tab", "re");
        if (f) {
                char l[LINE_MAX];

                FOREACH_LINE(l, f, return -errno) {
                        char *p, *w;
                        size_t k;

                        p = strstrip(l);

                        if (isempty(p) || *p == '#')
                                continue;

                        /* Skip over country code */
                        p += strcspn(p, WHITESPACE);
                        p += strspn(p, WHITESPACE);

                        /* Skip over coordinates */
                        p += strcspn(p, WHITESPACE);
                        p += strspn(p, WHITESPACE);

                        /* Found timezone name */
                        k = strcspn(p, WHITESPACE);
                        if (k <= 0)
                                continue;

                        w = strndup(p, k);
                        if (!w)
                                return -ENOMEM;

                        if (!GREEDY_REALLOC(zones, n_allocated, n_zones + 2)) {
                                free(w);
                                return -ENOMEM;
                        }

                        zones[n_zones++] = w;
                        zones[n_zones] = NULL;
                }

                strv_sort(zones);

        } else if (errno != ENOENT)
                return -errno;

        *ret = zones;
        zones = NULL;

        return 0;
}

bool timezone_is_valid(const char *name) {
        bool slash = false;
        const char *p, *t;
        struct stat st;

        if (isempty(name))
                return false;

        if (name[0] == '/')
                return false;

        for (p = name; *p; p++) {
                if (!(*p >= '0' && *p <= '9') &&
                    !(*p >= 'a' && *p <= 'z') &&
                    !(*p >= 'A' && *p <= 'Z') &&
                    !(*p == '-' || *p == '_' || *p == '+' || *p == '/'))
                        return false;

                if (*p == '/') {

                        if (slash)
                                return false;

                        slash = true;
                } else
                        slash = false;
        }

        if (slash)
                return false;

        t = strjoina("/usr/share/zoneinfo/", name);
        if (stat(t, &st) < 0)
                return false;

        if (!S_ISREG(st.st_mode))
                return false;

        return true;
}

clockid_t clock_boottime_or_monotonic(void) {
        static clockid_t clock = -1;
        int fd;

        if (clock != -1)
                return clock;

        fd = timerfd_create(CLOCK_BOOTTIME, TFD_NONBLOCK|TFD_CLOEXEC);
        if (fd < 0)
                clock = CLOCK_MONOTONIC;
        else {
                safe_close(fd);
                clock = CLOCK_BOOTTIME;
        }

        return clock;
}

int get_timezone(char **tz) {
        _cleanup_free_ char *t = NULL;
        const char *e;
        char *z;
        int r;

        r = readlink_malloc("/etc/localtime", &t);
        if (r < 0)
                return r; /* returns EINVAL if not a symlink */

        e = path_startswith(t, "/usr/share/zoneinfo/");
        if (!e)
                e = path_startswith(t, "../usr/share/zoneinfo/");
        if (!e)
                return -EINVAL;

        if (!timezone_is_valid(e))
                return -EINVAL;

        z = strdup(e);
        if (!z)
                return -ENOMEM;

        *tz = z;
        return 0;
}