timer: implement calendar time events

14 files changed, 1274 insertions, 100 deletions

diff --git a/src/core/dbus-timer.c b/src/core/dbus-timer.c
index 84b823c9a4..11d18cbd83 100644
--- a/src/core/dbus-timer.c
+++ b/src/core/dbus-timer.c
@@ -79,7 +79,8 @@ static int bus_timer_append_timers(DBusMessageIter *i, const char *property, voi
 
                 /* s/Sec/USec/ */
                 l = strlen(t);
-                if (!(buf = new(char, l+2)))
+                buf = new(char, l+2);
+                if (!buf)
                         return -ENOMEM;
 
                 memcpy(buf, t, l-3);
@@ -121,7 +122,8 @@ static DEFINE_BUS_PROPERTY_APPEND_ENUM(bus_timer_append_timer_result, timer_resu
 static const BusProperty bus_timer_properties[] = {
         { "Unit",           bus_timer_append_unit,        "s", 0 },
         { "Timers",         bus_timer_append_timers, "a(stt)", 0 },
-        { "NextElapseUSec", bus_property_append_usec,     "t", offsetof(Timer, next_elapse) },
+        { "NextElapseUSec", bus_property_append_usec,     "t", offsetof(Timer, next_elapse_monotonic) },
+        { "NextElapseUSecRealtime", bus_property_append_usec, "t", offsetof(Timer, next_elapse_realtime) },
         { "Result",         bus_timer_append_timer_result,"s", offsetof(Timer, result)      },
         { NULL, }
 };
diff --git a/src/core/load-fragment-gperf.gperf.m4 b/src/core/load-fragment-gperf.gperf.m4
index be16ba93c8..7212053ca7 100644
--- a/src/core/load-fragment-gperf.gperf.m4
+++ b/src/core/load-fragment-gperf.gperf.m4
@@ -234,6 +234,7 @@ Swap.TimeoutSec,                 config_parse_usec,                  0,
 EXEC_CONTEXT_CONFIG_ITEMS(Swap)m4_dnl
 KILL_CONTEXT_CONFIG_ITEMS(Swap)m4_dnl
 m4_dnl
+Timer.OnCalendar,                config_parse_timer,                 0,                             0
 Timer.OnActiveSec,               config_parse_timer,                 0,                             0
 Timer.OnBootSec,                 config_parse_timer,                 0,                             0
 Timer.OnStartupSec,              config_parse_timer,                 0,                             0
diff --git a/src/core/load-fragment.c b/src/core/load-fragment.c
index 6933e1a21e..e35fdbc5ec 100644
--- a/src/core/load-fragment.c
+++ b/src/core/load-fragment.c
@@ -1136,30 +1136,47 @@ int config_parse_timer(
                 void *userdata) {
 
         Timer *t = data;
-        usec_t u;
+        usec_t u = 0;
         TimerValue *v;
         TimerBase b;
+        CalendarSpec *c = NULL;
+        clockid_t id;
 
         assert(filename);
         assert(lvalue);
         assert(rvalue);
         assert(data);
 
-        if ((b = timer_base_from_string(lvalue)) < 0) {
+        b = timer_base_from_string(lvalue);
+        if (b < 0) {
                 log_error("[%s:%u] Failed to parse timer base, ignoring: %s", filename, line, lvalue);
                 return 0;
         }
 
-        if (parse_usec(rvalue, &u) < 0) {
-                log_error("[%s:%u] Failed to parse timer value, ignoring: %s", filename, line, rvalue);
-                return 0;
+        if (b == TIMER_CALENDAR) {
+                if (calendar_spec_from_string(rvalue, &c) < 0) {
+                        log_error("[%s:%u] Failed to parse calendar specification, ignoring: %s", filename, line, rvalue);
+                        return 0;
+                }
+
+                id = CLOCK_REALTIME;
+        } else {
+                if (parse_usec(rvalue, &u) < 0) {
+                        log_error("[%s:%u] Failed to parse timer value, ignoring: %s", filename, line, rvalue);
+                        return 0;
+                }
+
+                id = CLOCK_MONOTONIC;
         }
 
-        if (!(v = new0(TimerValue, 1)))
+        v = new0(TimerValue, 1);
+        if (!v)
                 return -ENOMEM;
 
         v->base = b;
+        v->clock_id = id;
         v->value = u;
+        v->calendar_spec = c;
 
         LIST_PREPEND(TimerValue, value, t->values, v);
 
diff --git a/src/core/mount.c b/src/core/mount.c
index 14f4863dc6..09a5d286d3 100644
--- a/src/core/mount.c
+++ b/src/core/mount.c
@@ -741,10 +741,12 @@ static int mount_coldplug(Unit *u) {
                         if (m->control_pid <= 0)
                                 return -EBADMSG;
 
-                        if ((r = unit_watch_pid(UNIT(m), m->control_pid)) < 0)
+                        r = unit_watch_pid(UNIT(m), m->control_pid);
+                        if (r < 0)
                                 return r;
 
-                        if ((r = unit_watch_timer(UNIT(m), m->timeout_usec, &m->timer_watch)) < 0)
+                        r = unit_watch_timer(UNIT(m), CLOCK_MONOTONIC, true, m->timeout_usec, &m->timer_watch);
+                        if (r < 0)
                                 return r;
                 }
 
@@ -800,7 +802,8 @@ static int mount_spawn(Mount *m, ExecCommand *c, pid_t *_pid) {
         assert(c);
         assert(_pid);
 
-        if ((r = unit_watch_timer(UNIT(m), m->timeout_usec, &m->timer_watch)) < 0)
+        r = unit_watch_timer(UNIT(m), CLOCK_MONOTONIC, true, m->timeout_usec, &m->timer_watch);
+        if (r < 0)
                 goto fail;
 
         if ((r = exec_spawn(c,
@@ -900,7 +903,8 @@ static void mount_enter_signal(Mount *m, MountState state, MountResult f) {
         }
 
         if (wait_for_exit) {
-                if ((r = unit_watch_timer(UNIT(m), m->timeout_usec, &m->timer_watch)) < 0)
+                r = unit_watch_timer(UNIT(m), CLOCK_MONOTONIC, true, m->timeout_usec, &m->timer_watch);
+                if (r < 0)
                         goto fail;
 
                 mount_set_state(m, state);
diff --git a/src/core/service.c b/src/core/service.c
index 34d24ffa92..25a568f70b 100644
--- a/src/core/service.c
+++ b/src/core/service.c
@@ -249,7 +249,7 @@ static void service_handle_watchdog(Service *s) {
                 return;
         }
 
-        r = unit_watch_timer(UNIT(s), s->watchdog_usec - offset, &s->watchdog_watch);
+        r = unit_watch_timer(UNIT(s), CLOCK_MONOTONIC, true, s->watchdog_usec - offset, &s->watchdog_watch);
         if (r < 0)
                 log_warning("%s failed to install watchdog timer: %s", UNIT(s)->id, strerror(-r));
 }
@@ -1599,7 +1599,8 @@ static int service_coldplug(Unit *u) {
 
                                 k = s->deserialized_state == SERVICE_AUTO_RESTART ? s->restart_usec : s->timeout_start_usec;
 
-                                if ((r = unit_watch_timer(UNIT(s), k, &s->timer_watch)) < 0)
+                                r = unit_watch_timer(UNIT(s), CLOCK_MONOTONIC, true, k, &s->timer_watch);
+                                if (r < 0)
                                         return r;
                         }
                 }
@@ -1744,7 +1745,7 @@ static int service_spawn(
         }
 
         if (timeout && s->timeout_start_usec) {
-                r = unit_watch_timer(UNIT(s), s->timeout_start_usec, &s->timer_watch);
+                r = unit_watch_timer(UNIT(s), CLOCK_MONOTONIC, true, s->timeout_start_usec, &s->timer_watch);
                 if (r < 0)
                         goto fail;
         } else
@@ -1899,7 +1900,7 @@ static void service_enter_dead(Service *s, ServiceResult f, bool allow_restart)
              !set_contains(s->restart_ignore_status.signal, INT_TO_PTR(s->main_exec_status.status)))
                 ) {
 
-                r = unit_watch_timer(UNIT(s), s->restart_usec, &s->timer_watch);
+                r = unit_watch_timer(UNIT(s), CLOCK_MONOTONIC, true, s->restart_usec, &s->timer_watch);
                 if (r < 0)
                         goto fail;
 
@@ -2012,7 +2013,7 @@ static void service_enter_signal(Service *s, ServiceState state, ServiceResult f
 
         if (wait_for_exit) {
                 if (s->timeout_stop_usec > 0) {
-                        r = unit_watch_timer(UNIT(s), s->timeout_stop_usec, &s->timer_watch);
+                        r = unit_watch_timer(UNIT(s), CLOCK_MONOTONIC, true, s->timeout_stop_usec, &s->timer_watch);
                         if (r < 0)
                                 goto fail;
                 }
@@ -2262,7 +2263,7 @@ static void service_enter_restart(Service *s) {
                 /* Don't restart things if we are going down anyway */
                 log_info("Stop job pending for unit, delaying automatic restart.");
 
-                r = unit_watch_timer(UNIT(s), s->restart_usec, &s->timer_watch);
+                r = unit_watch_timer(UNIT(s), CLOCK_MONOTONIC, true, s->restart_usec, &s->timer_watch);
                 if (r < 0)
                         goto fail;
 
diff --git a/src/core/socket.c b/src/core/socket.c
index 3d5791b114..9b5bcb6e7b 100644
--- a/src/core/socket.c
+++ b/src/core/socket.c
@@ -1146,10 +1146,12 @@ static int socket_coldplug(Unit *u) {
                         if (s->control_pid <= 0)
                                 return -EBADMSG;
 
-                        if ((r = unit_watch_pid(UNIT(s), s->control_pid)) < 0)
+                        r = unit_watch_pid(UNIT(s), s->control_pid);
+                        if (r < 0)
                                 return r;
 
-                        if ((r = unit_watch_timer(UNIT(s), s->timeout_usec, &s->timer_watch)) < 0)
+                        r = unit_watch_timer(UNIT(s), CLOCK_MONOTONIC, true, s->timeout_usec, &s->timer_watch);
+                        if (r < 0)
                                 return r;
                 }
 
@@ -1181,10 +1183,12 @@ static int socket_spawn(Socket *s, ExecCommand *c, pid_t *_pid) {
         assert(c);
         assert(_pid);
 
-        if ((r = unit_watch_timer(UNIT(s), s->timeout_usec, &s->timer_watch)) < 0)
+        r = unit_watch_timer(UNIT(s), CLOCK_MONOTONIC, true, s->timeout_usec, &s->timer_watch);
+        if (r < 0)
                 goto fail;
 
-        if (!(argv = unit_full_printf_strv(UNIT(s), c->argv))) {
+        argv = unit_full_printf_strv(UNIT(s), c->argv);
+        if (!argv) {
                 r = -ENOMEM;
                 goto fail;
         }
@@ -1306,7 +1310,8 @@ static void socket_enter_signal(Socket *s, SocketState state, SocketResult f) {
         }
 
         if (wait_for_exit) {
-                if ((r = unit_watch_timer(UNIT(s), s->timeout_usec, &s->timer_watch)) < 0)
+                r = unit_watch_timer(UNIT(s), CLOCK_MONOTONIC, true, s->timeout_usec, &s->timer_watch);
+                if (r < 0)
                         goto fail;
 
                 socket_set_state(s, state);
diff --git a/src/core/swap.c b/src/core/swap.c
index 97145a9974..bd40516c99 100644
--- a/src/core/swap.c
+++ b/src/core/swap.c
@@ -521,7 +521,7 @@ static int swap_coldplug(Unit *u) {
                         if (r < 0)
                                 return r;
 
-                        r = unit_watch_timer(UNIT(s), s->timeout_usec, &s->timer_watch);
+                        r = unit_watch_timer(UNIT(s), CLOCK_MONOTONIC, true, s->timeout_usec, &s->timer_watch);
                         if (r < 0)
                                 return r;
                 }
@@ -584,7 +584,7 @@ static int swap_spawn(Swap *s, ExecCommand *c, pid_t *_pid) {
         assert(c);
         assert(_pid);
 
-        r = unit_watch_timer(UNIT(s), s->timeout_usec, &s->timer_watch);
+        r = unit_watch_timer(UNIT(s), CLOCK_MONOTONIC, true, s->timeout_usec, &s->timer_watch);
         if (r < 0)
                 goto fail;
 
@@ -689,7 +689,7 @@ static void swap_enter_signal(Swap *s, SwapState state, SwapResult f) {
         }
 
         if (wait_for_exit) {
-                r = unit_watch_timer(UNIT(s), s->timeout_usec, &s->timer_watch);
+                r = unit_watch_timer(UNIT(s), CLOCK_MONOTONIC, true, s->timeout_usec, &s->timer_watch);
                 if (r < 0)
                         goto fail;
 
diff --git a/src/core/timer.c b/src/core/timer.c
index 7080b32c6b..54c0d0b330 100644
--- a/src/core/timer.c
+++ b/src/core/timer.c
@@ -42,7 +42,10 @@ static void timer_init(Unit *u) {
         assert(u);
         assert(u->load_state == UNIT_STUB);
 
-        t->next_elapse = (usec_t) -1;
+        t->next_elapse_monotonic = (usec_t) -1;
+        t->next_elapse_realtime = (usec_t) -1;
+        watch_init(&t->monotonic_watch);
+        watch_init(&t->realtime_watch);
 }
 
 static void timer_done(Unit *u) {
@@ -53,10 +56,15 @@ static void timer_done(Unit *u) {
 
         while ((v = t->values)) {
                 LIST_REMOVE(TimerValue, value, t->values, v);
+
+                if (v->calendar_spec)
+                        calendar_spec_free(v->calendar_spec);
+
                 free(v);
         }
 
-        unit_unwatch_timer(u, &t->timer_watch);
+        unit_unwatch_timer(u, &t->monotonic_watch);
+        unit_unwatch_timer(u, &t->realtime_watch);
 
         unit_ref_unset(&t->unit);
 }
@@ -81,10 +89,12 @@ static int timer_add_default_dependencies(Timer *t) {
         assert(t);
 
         if (UNIT(t)->manager->running_as == SYSTEMD_SYSTEM) {
-                if ((r = unit_add_dependency_by_name(UNIT(t), UNIT_BEFORE, SPECIAL_BASIC_TARGET, NULL, true)) < 0)
+                r = unit_add_dependency_by_name(UNIT(t), UNIT_BEFORE, SPECIAL_BASIC_TARGET, NULL, true);
+                if (r < 0)
                         return r;
 
-                if ((r = unit_add_two_dependencies_by_name(UNIT(t), UNIT_AFTER, UNIT_REQUIRES, SPECIAL_SYSINIT_TARGET, NULL, true)) < 0)
+                r = unit_add_two_dependencies_by_name(UNIT(t), UNIT_AFTER, UNIT_REQUIRES, SPECIAL_SYSINIT_TARGET, NULL, true);
+                if (r < 0)
                         return r;
         }
 
@@ -98,7 +108,8 @@ static int timer_load(Unit *u) {
         assert(u);
         assert(u->load_state == UNIT_STUB);
 
-        if ((r = unit_load_fragment_and_dropin(u)) < 0)
+        r = unit_load_fragment_and_dropin(u);
+        if (r < 0)
                 return r;
 
         if (u->load_state == UNIT_LOADED) {
@@ -117,9 +128,11 @@ static int timer_load(Unit *u) {
                 if (r < 0)
                         return r;
 
-                if (UNIT(t)->default_dependencies)
-                        if ((r = timer_add_default_dependencies(t)) < 0)
+                if (UNIT(t)->default_dependencies) {
+                        r = timer_add_default_dependencies(t);
+                        if (r < 0)
                                 return r;
+                }
         }
 
         return timer_verify(t);
@@ -128,8 +141,6 @@ static int timer_load(Unit *u) {
 static void timer_dump(Unit *u, FILE *f, const char *prefix) {
         Timer *t = TIMER(u);
         TimerValue *v;
-        char
-                timespan1[FORMAT_TIMESPAN_MAX];
 
         fprintf(f,
                 "%sTimer State: %s\n"
@@ -139,12 +150,28 @@ static void timer_dump(Unit *u, FILE *f, const char *prefix) {
                 prefix, timer_result_to_string(t->result),
                 prefix, UNIT_DEREF(t->unit)->id);
 
-        LIST_FOREACH(value, v, t->values)
-                fprintf(f,
-                        "%s%s: %s\n",
-                        prefix,
-                        timer_base_to_string(v->base),
-                        strna(format_timespan(timespan1, sizeof(timespan1), v->value)));
+        LIST_FOREACH(value, v, t->values) {
+
+                if (v->base == TIMER_CALENDAR) {
+                        _cleanup_free_ char *p = NULL;
+
+                        calendar_spec_to_string(v->calendar_spec, &p);
+
+                        fprintf(f,
+                                "%s%s: %s\n",
+                                prefix,
+                                timer_base_to_string(v->base),
+                                strna(p));
+                } else  {
+                        char timespan1[FORMAT_TIMESPAN_MAX];
+
+                        fprintf(f,
+                                "%s%s: %s\n",
+                                prefix,
+                                timer_base_to_string(v->base),
+                                strna(format_timespan(timespan1, sizeof(timespan1), v->value)));
+                }
+        }
 }
 
 static void timer_set_state(Timer *t, TimerState state) {
@@ -154,8 +181,10 @@ static void timer_set_state(Timer *t, TimerState state) {
         old_state = t->state;
         t->state = state;
 
-        if (state != TIMER_WAITING)
-                unit_unwatch_timer(UNIT(t), &t->timer_watch);
+        if (state != TIMER_WAITING) {
+                unit_unwatch_timer(UNIT(t), &t->monotonic_watch);
+                unit_unwatch_timer(UNIT(t), &t->realtime_watch);
+        }
 
         if (state != old_state)
                 log_debug("%s changed %s -> %s",
@@ -196,79 +225,117 @@ static void timer_enter_dead(Timer *t, TimerResult f) {
 
 static void timer_enter_waiting(Timer *t, bool initial) {
         TimerValue *v;
-        usec_t base = 0, delay, n;
-        bool found = false;
+        usec_t base = 0;
+        dual_timestamp ts;
+        bool found_monotonic = false, found_realtime = false;
         int r;
 
-        n = now(CLOCK_MONOTONIC);
+        dual_timestamp_get(&ts);
+        t->next_elapse_monotonic = t->next_elapse_realtime = 0;
 
         LIST_FOREACH(value, v, t->values) {
 
                 if (v->disabled)
                         continue;
 
-                switch (v->base) {
+                if (v->base == TIMER_CALENDAR) {
+
+                        r = calendar_spec_next_usec(v->calendar_spec, ts.realtime, &v->next_elapse);
+                        if (r < 0)
+                                continue;
+
+                        if (!initial && v->next_elapse < ts.realtime) {
+                                v->disabled = true;
+                                continue;
+                        }
 
-                case TIMER_ACTIVE:
-                        if (state_translation_table[t->state] == UNIT_ACTIVE)
-                                base = UNIT(t)->inactive_exit_timestamp.monotonic;
+                        if (!found_realtime)
+                                t->next_elapse_realtime = v->next_elapse;
                         else
-                                base = n;
-                        break;
+                                t->next_elapse_realtime = MIN(t->next_elapse_realtime, v->next_elapse);
 
-                case TIMER_BOOT:
-                        /* CLOCK_MONOTONIC equals the uptime on Linux */
-                        base = 0;
-                        break;
+                        found_realtime = true;
 
-                case TIMER_STARTUP:
-                        base = UNIT(t)->manager->userspace_timestamp.monotonic;
-                        break;
+                } else  {
+                        switch (v->base) {
 
-                case TIMER_UNIT_ACTIVE:
+                        case TIMER_ACTIVE:
+                                if (state_translation_table[t->state] == UNIT_ACTIVE)
+                                        base = UNIT(t)->inactive_exit_timestamp.monotonic;
+                                else
+                                        base = ts.monotonic;
+                                break;
 
-                        if (UNIT_DEREF(t->unit)->inactive_exit_timestamp.monotonic <= 0)
-                                continue;
+                        case TIMER_BOOT:
+                                /* CLOCK_MONOTONIC equals the uptime on Linux */
+                                base = 0;
+                                break;
 
-                        base = UNIT_DEREF(t->unit)->inactive_exit_timestamp.monotonic;
-                        break;
+                        case TIMER_STARTUP:
+                                base = UNIT(t)->manager->userspace_timestamp.monotonic;
+                                break;
 
-                case TIMER_UNIT_INACTIVE:
+                        case TIMER_UNIT_ACTIVE:
 
-                        if (UNIT_DEREF(t->unit)->inactive_enter_timestamp.monotonic <= 0)
-                                continue;
+                                if (UNIT_DEREF(t->unit)->inactive_exit_timestamp.monotonic <= 0)
+                                        continue;
 
-                        base = UNIT_DEREF(t->unit)->inactive_enter_timestamp.monotonic;
-                        break;
+                                base = UNIT_DEREF(t->unit)->inactive_exit_timestamp.monotonic;
+                                break;
 
-                default:
-                        assert_not_reached("Unknown timer base");
-                }
+                        case TIMER_UNIT_INACTIVE:
 
-                v->next_elapse = base + v->value;
+                                if (UNIT_DEREF(t->unit)->inactive_enter_timestamp.monotonic <= 0)
+                                        continue;
 
-                if (!initial && v->next_elapse < n) {
-                        v->disabled = true;
-                        continue;
-                }
+                                base = UNIT_DEREF(t->unit)->inactive_enter_timestamp.monotonic;
+                                break;
 
-                if (!found)
-                        t->next_elapse = v->next_elapse;
-                else
-                        t->next_elapse = MIN(t->next_elapse, v->next_elapse);
+                        default:
+                                assert_not_reached("Unknown timer base");
+                        }
 
-                found = true;
+                        v->next_elapse = base + v->value;
+
+                        if (!initial && v->next_elapse < ts.monotonic) {
+                                v->disabled = true;
+                                continue;
+                        }
+
+                        if (!found_monotonic)
+                                t->next_elapse_monotonic = v->next_elapse;
+                        else
+                                t->next_elapse_monotonic = MIN(t->next_elapse_monotonic, v->next_elapse);
+
+                        found_monotonic = true;
+                }
         }
 
-        if (!found) {
+        if (!found_monotonic && !found_realtime) {
+                log_debug("%s: Timer is elapsed.", UNIT(t)->id);
                 timer_set_state(t, TIMER_ELAPSED);
                 return;
         }
 
-        delay = n < t->next_elapse ? t->next_elapse - n : 0;
+        if (found_monotonic) {
+                char buf[FORMAT_TIMESPAN_MAX];
+                log_debug("%s: Monotonic timer elapses in %s the next time.", UNIT(t)->id, format_timespan(buf, sizeof(buf), t->next_elapse_monotonic - ts.monotonic));
 
-        if ((r = unit_watch_timer(UNIT(t), delay, &t->timer_watch)) < 0)
-                goto fail;
+                r = unit_watch_timer(UNIT(t), CLOCK_MONOTONIC, false, t->next_elapse_monotonic, &t->monotonic_watch);
+                if (r < 0)
+                        goto fail;
+        } else
+                unit_unwatch_timer(UNIT(t), &t->monotonic_watch);
+
+        if (found_realtime) {
+                char buf[FORMAT_TIMESTAMP_MAX];
+                log_debug("%s: Realtime timer elapses at %s the next time.", UNIT(t)->id, format_timestamp(buf, sizeof(buf), t->next_elapse_realtime));
+
+                r = unit_watch_timer(UNIT(t), CLOCK_REALTIME, false, t->next_elapse_realtime, &t->realtime_watch);
+                if (r < 0)
+                        goto fail;
+        } else
+                unit_unwatch_timer(UNIT(t), &t->realtime_watch);
 
         timer_set_state(t, TIMER_WAITING);
         return;
@@ -289,7 +356,8 @@ static void timer_enter_running(Timer *t) {
         if (UNIT(t)->job && UNIT(t)->job->type == JOB_STOP)
                 return;
 
-        if ((r = manager_add_job(UNIT(t)->manager, JOB_START, UNIT_DEREF(t->unit), JOB_REPLACE, true, &error, NULL)) < 0)
+        r = manager_add_job(UNIT(t)->manager, JOB_START, UNIT_DEREF(t->unit), JOB_REPLACE, true, &error, NULL);
+        if (r < 0)
                 goto fail;
 
         timer_set_state(t, TIMER_RUNNING);
@@ -350,7 +418,8 @@ static int timer_deserialize_item(Unit *u, const char *key, const char *value, F
         if (streq(key, "state")) {
                 TimerState state;
 
-                if ((state = timer_state_from_string(value)) < 0)
+                state = timer_state_from_string(value);
+                if (state < 0)
                         log_debug("Failed to parse state value %s", value);
                 else
                         t->deserialized_state = state;
@@ -473,7 +542,8 @@ static const char* const timer_base_table[_TIMER_BASE_MAX] = {
         [TIMER_BOOT] = "OnBootSec",
         [TIMER_STARTUP] = "OnStartupSec",
         [TIMER_UNIT_ACTIVE] = "OnUnitActiveSec",
-        [TIMER_UNIT_INACTIVE] = "OnUnitInactiveSec"
+        [TIMER_UNIT_INACTIVE] = "OnUnitInactiveSec",
+        [TIMER_CALENDAR] = "OnCalendar"
 };
 
 DEFINE_STRING_TABLE_LOOKUP(timer_base, TimerBase);
diff --git a/src/core/timer.h b/src/core/timer.h
index c6d1d42e44..57a514a68c 100644
--- a/src/core/timer.h
+++ b/src/core/timer.h
@@ -24,6 +24,7 @@
 typedef struct Timer Timer;
 
 #include "unit.h"
+#include "calendarspec.h"
 
 typedef enum TimerState {
         TIMER_DEAD,
@@ -41,18 +42,21 @@ typedef enum TimerBase {
         TIMER_STARTUP,
         TIMER_UNIT_ACTIVE,
         TIMER_UNIT_INACTIVE,
+        TIMER_CALENDAR,
         _TIMER_BASE_MAX,
         _TIMER_BASE_INVALID = -1
 } TimerBase;
 
 typedef struct TimerValue {
+        TimerBase base;
+        bool disabled;
+        clockid_t clock_id;
+
         usec_t value;
+        CalendarSpec *calendar_spec;
         usec_t next_elapse;
 
         LIST_FIELDS(struct TimerValue, value);
-
-        TimerBase base;
-        bool disabled;
 } TimerValue;
 
 typedef enum TimerResult {
@@ -66,12 +70,14 @@ struct Timer {
         Unit meta;
 
         LIST_HEAD(TimerValue, values);
-        usec_t next_elapse;
+        usec_t next_elapse_monotonic;
+        usec_t next_elapse_realtime;
 
         TimerState state, deserialized_state;
         UnitRef unit;
 
-        Watch timer_watch;
+        Watch monotonic_watch;
+        Watch realtime_watch;
 
         TimerResult result;
 };
diff --git a/src/core/unit.c b/src/core/unit.c
index 82dd617e35..45453dce64 100644
--- a/src/core/unit.c
+++ b/src/core/unit.c
@@ -1560,7 +1560,7 @@ void unit_unwatch_pid(Unit *u, pid_t pid) {
         hashmap_remove_value(u->manager->watch_pids, LONG_TO_PTR(pid), u);
 }
 
-int unit_watch_timer(Unit *u, usec_t delay, Watch *w) {
+int unit_watch_timer(Unit *u, clockid_t clock_id, bool relative, usec_t usec, Watch *w) {
         struct itimerspec its;
         int flags, fd;
         bool ours;
@@ -1580,7 +1580,7 @@ int unit_watch_timer(Unit *u, usec_t delay, Watch *w) {
         } else if (w->type == WATCH_INVALID) {
 
                 ours = true;
-                fd = timerfd_create(CLOCK_MONOTONIC, TFD_NONBLOCK|TFD_CLOEXEC);
+                fd = timerfd_create(clock_id, TFD_NONBLOCK|TFD_CLOEXEC);
                 if (fd < 0)
                         return -errno;
         } else
@@ -1588,7 +1588,7 @@ int unit_watch_timer(Unit *u, usec_t delay, Watch *w) {
 
         zero(its);
 
-        if (delay <= 0) {
+        if (usec <= 0) {
                 /* Set absolute time in the past, but not 0, since we
                  * don't want to disarm the timer */
                 its.it_value.tv_sec = 0;
@@ -1596,8 +1596,8 @@ int unit_watch_timer(Unit *u, usec_t delay, Watch *w) {
 
                 flags = TFD_TIMER_ABSTIME;
         } else {
-                timespec_store(&its.it_value, delay);
-                flags = 0;
+                timespec_store(&its.it_value, usec);
+                flags = relative ? 0 : TFD_TIMER_ABSTIME;
         }
 
         /* This will also flush the elapse counter */
diff --git a/src/core/unit.h b/src/core/unit.h
index bf961c2aac..11804d8bcf 100644
--- a/src/core/unit.h
+++ b/src/core/unit.h
@@ -484,7 +484,7 @@ void unit_unwatch_fd(Unit *u, Watch *w);
 int unit_watch_pid(Unit *u, pid_t pid);
 void unit_unwatch_pid(Unit *u, pid_t pid);
 
-int unit_watch_timer(Unit *u, usec_t delay, Watch *w);
+int unit_watch_timer(Unit *u, clockid_t, bool relative, usec_t usec, Watch *w);
 void unit_unwatch_timer(Unit *u, Watch *w);
 
 int unit_watch_bus_name(Unit *u, const char *name);
diff --git a/src/shared/calendarspec.c b/src/shared/calendarspec.c
new file mode 100644
index 0000000000..3cddb0eed0
--- /dev/null
+++ b/src/shared/calendarspec.c
@@ -0,0 +1,927 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+/***
+  This file is part of systemd.
+
+  Copyright 2012 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 <stdlib.h>
+#include <string.h>
+
+#include "calendarspec.h"
+
+static void free_chain(CalendarComponent *c) {
+        CalendarComponent *n;
+
+        while (c) {
+                n = c->next;
+                free(c);
+                c = n;
+        }
+}
+
+void calendar_spec_free(CalendarSpec *c) {
+        assert(c);
+
+        free_chain(c->year);
+        free_chain(c->month);
+        free_chain(c->day);
+        free_chain(c->hour);
+        free_chain(c->minute);
+        free_chain(c->second);
+
+        free(c);
+}
+
+static int component_compare(const void *_a, const void *_b) {
+        CalendarComponent * const *a = _a, * const *b = _b;
+
+        if ((*a)->value < (*b)->value)
+                return -1;
+        if ((*a)->value > (*b)->value)
+                return 1;
+
+        if ((*a)->repeat < (*b)->repeat)
+                return -1;
+        if ((*a)->repeat > (*b)->repeat)
+                return 1;
+
+        return 0;
+}
+
+static void sort_chain(CalendarComponent **c) {
+        unsigned n = 0, k;
+        CalendarComponent **b, *i, **j, *next;
+
+        assert(c);
+
+        for (i = *c; i; i = i->next)
+                n++;
+
+        if (n <= 1)
+                return;
+
+        j = b = alloca(sizeof(CalendarComponent*) * n);
+        for (i = *c; i; i = i->next)
+                *(j++) = i;
+
+        qsort(b, n, sizeof(CalendarComponent*), component_compare);
+
+        b[n-1]->next = NULL;
+        next = b[n-1];
+
+        /* Drop non-unique entries */
+        for (k = n-1; k > 0; k--) {
+                if (b[k-1]->value == next->value &&
+                    b[k-1]->repeat == next->repeat) {
+                        free(b[k-1]);
+                        continue;
+                }
+
+                b[k-1]->next = next;
+                next = b[k-1];
+        }
+
+        *c = next;
+}
+
+static void fix_year(CalendarComponent *c) {
+        /* Turns 12 → 2012, 89 → 1989 */
+
+        while(c) {
+                CalendarComponent *n = c->next;
+
+                if (c->value >= 0 && c->value < 70)
+                        c->value += 2000;
+
+                if (c->value >= 70 && c->value < 100)
+                        c->value += 1900;
+
+                c = n;
+        }
+}
+
+int calendar_spec_normalize(CalendarSpec *c) {
+        assert(c);
+
+        if (c->weekdays_bits <= 0 || c->weekdays_bits >= 127)
+                c->weekdays_bits = -1;
+
+        fix_year(c->year);
+
+        sort_chain(&c->year);
+        sort_chain(&c->month);
+        sort_chain(&c->day);
+        sort_chain(&c->hour);
+        sort_chain(&c->minute);
+        sort_chain(&c->second);
+
+        return 0;
+}
+
+static bool chain_valid(CalendarComponent *c, int from, int to) {
+        if (!c)
+                return true;
+
+        if (c->value < from || c->value > to)
+                return false;
+
+        if (c->value + c->repeat > to)
+                return false;
+
+        if (c->next)
+                return chain_valid(c->next, from, to);
+
+        return true;
+}
+
+bool calendar_spec_valid(CalendarSpec *c) {
+        assert(c);
+
+        if (c->weekdays_bits > 127)
+                return false;
+
+        if (!chain_valid(c->year, 1970, 2199))
+                return false;
+
+        if (!chain_valid(c->month, 1, 12))
+                return false;
+
+        if (!chain_valid(c->day, 1, 31))
+                return false;
+
+        if (!chain_valid(c->hour, 0, 23))
+                return false;
+
+        if (!chain_valid(c->minute, 0, 59))
+                return false;
+
+        if (!chain_valid(c->second, 0, 59))
+                return false;
+
+        return true;
+}
+
+static void format_weekdays(FILE *f, const CalendarSpec *c) {
+        static const char *const days[] = {
+                "Mon",
+                "Tue",
+                "Wed",
+                "Thu",
+                "Fri",
+                "Sat",
+                "Sun"
+        };
+
+        int l, x;
+        bool need_colon = false;
+
+        assert(f);
+        assert(c);
+        assert(c->weekdays_bits > 0 && c->weekdays_bits <= 127);
+
+        for (x = 0, l = -1; x < (int) ELEMENTSOF(days); x++) {
+
+                if (c->weekdays_bits & (1 << x)) {
+
+                        if (l < 0) {
+                                if (need_colon)
+                                        fputc(',', f);
+                                else
+                                        need_colon = true;
+
+                                fputs(days[x], f);
+                                l = x;
+                        }
+
+                } else if (l >= 0) {
+
+                        if (x > l + 1) {
+                                fputc(x > l + 2 ? '-' : ',', f);
+                                fputs(days[x-1], f);
+                        }
+
+                        l = -1;
+                }
+        }
+
+        if (l >= 0 && x > l + 1) {
+                fputc(x > l + 2 ? '-' : ',', f);
+                fputs(days[x-1], f);
+        }
+}
+
+static void format_chain(FILE *f, int space, const CalendarComponent *c) {
+        assert(f);
+
+        if (!c) {
+                fputc('*', f);
+                return;
+        }
+
+        assert(c->value >= 0);
+        fprintf(f, "%0*i", space, c->value);
+
+        if (c->repeat > 0)
+                fprintf(f, "/%i", c->repeat);
+
+        if (c->next) {
+                fputc(',', f);
+                format_chain(f, space, c->next);
+        }
+}
+
+int calendar_spec_to_string(const CalendarSpec *c, char **p) {
+        char *buf = NULL;
+        size_t sz = 0;
+        FILE *f;
+
+        assert(c);
+        assert(p);
+
+        f = open_memstream(&buf, &sz);
+        if (!f)
+                return -ENOMEM;
+
+        if (c->weekdays_bits > 0 && c->weekdays_bits <= 127) {
+                format_weekdays(f, c);
+                fputc(' ', f);
+        }
+
+        format_chain(f, 4, c->year);
+        fputc('-', f);
+        format_chain(f, 2, c->month);
+        fputc('-', f);
+        format_chain(f, 2, c->day);
+        fputc(' ', f);
+        format_chain(f, 2, c->hour);
+        fputc(':', f);
+        format_chain(f, 2, c->minute);
+        fputc(':', f);
+        format_chain(f, 2, c->second);
+
+        fflush(f);
+
+        if (ferror(f)) {
+                free(buf);
+                fclose(f);
+                return -ENOMEM;
+        }
+
+        fclose(f);
+
+        *p = buf;
+        return 0;
+}
+
+static int parse_weekdays(const char **p, CalendarSpec *c) {
+        static const struct {
+                const char *name;
+                const int nr;
+        } day_nr[] = {
+                { "Monday",    0 },
+                { "Mon",       0 },
+                { "Tuesday",   1 },
+                { "Tue",       1 },
+                { "Wednesday", 2 },
+                { "Wed",       2 },
+                { "Thursday",  3 },
+                { "Thu",       3 },
+                { "Friday",    4 },
+                { "Fri",       4 },
+                { "Saturday",  5 },
+                { "Sat",       5 },
+                { "Sunday",    6 },
+                { "Sun",       6 }
+        };
+
+        int l = -1;
+        bool first = true;
+
+        assert(p);
+        assert(*p);
+        assert(c);
+
+        for (;;) {
+                unsigned i;
+
+                if (!first && **p == ' ')
+                        return 0;
+
+                for (i = 0; i < ELEMENTSOF(day_nr); i++) {
+                        size_t skip;
+
+                        if (!startswith_no_case(*p, day_nr[i].name))
+                                continue;
+
+                        skip = strlen(day_nr[i].name);
+
+                        if ((*p)[skip] != '-' &&
+                            (*p)[skip] != ',' &&
+                            (*p)[skip] != ' ' &&
+                            (*p)[skip] != 0)
+                                return -EINVAL;
+
+                        c->weekdays_bits |= 1 << day_nr[i].nr;
+
+                        if (l >= 0) {
+                                int j;
+
+                                if (l > day_nr[i].nr)
+                                        return -EINVAL;
+
+                                for (j = l + 1; j < day_nr[i].nr; j++)
+                                        c->weekdays_bits |= 1 << j;
+                        }
+
+                        *p += skip;
+                        break;
+                }
+
+                /* Couldn't find this prefix, so let's assume the
+                   weekday was not specified and let's continue with
+                   the date */
+                if (i >= ELEMENTSOF(day_nr))
+                        return first ? 0 : -EINVAL;
+
+                /* We reached the end of the string */
+                if (**p == 0)
+                        return 0;
+
+                /* We reached the end of the weekday spec part */
+                if (**p == ' ') {
+                        *p += strspn(*p, " ");
+                        return 0;
+                }
+
+                if (**p == '-') {
+                        if (l >= 0)
+                                return -EINVAL;
+
+                        l = day_nr[i].nr;
+                } else
+                        l = -1;
+
+                *p += 1;
+                first = false;
+        }
+}
+
+static int prepend_component(const char **p, CalendarComponent **c) {
+        unsigned long value, repeat = 0;
+        char *e = NULL, *ee = NULL;
+        CalendarComponent *cc;
+
+        assert(p);
+        assert(c);
+
+        errno = 0;
+        value = strtoul(*p, &e, 10);
+        if (errno != 0)
+                return -errno;
+        if (e == *p)
+                return -EINVAL;
+        if ((unsigned long) (int) value != value)
+                return -ERANGE;
+
+        if (*e == '/') {
+                repeat = strtoul(e+1, &ee, 10);
+                if (errno != 0)
+                        return -errno;
+                if (ee == e+1)
+                        return -EINVAL;
+                if ((unsigned long) (int) repeat != repeat)
+                        return -ERANGE;
+                if (repeat <= 0)
+                        return -ERANGE;
+
+                e = ee;
+        }
+
+        if (*e != 0 && *e != ' ' && *e != ',' && *e != '-' && *e != ':')
+                return -EINVAL;
+
+        cc = new0(CalendarComponent, 1);
+        if (!cc)
+                return -ENOMEM;
+
+        cc->value = value;
+        cc->repeat = repeat;
+        cc->next = *c;
+
+        *p = e;
+        *c = cc;
+
+        if (*e ==',') {
+                *p += 1;
+                return prepend_component(p, c);
+        }
+
+        return 0;
+}
+
+static int parse_chain(const char **p, CalendarComponent **c) {
+        const char *t;
+        CalendarComponent *cc = NULL;
+        int r;
+
+        assert(p);
+        assert(c);
+
+        t = *p;
+
+        if (t[0] == '*') {
+                *p = t + 1;
+                *c = NULL;
+                return 0;
+        }
+
+        r = prepend_component(&t, &cc);
+        if (r < 0) {
+                free_chain(cc);
+                return r;
+        }
+
+        *p = t;
+        *c = cc;
+        return 0;
+}
+
+static int const_chain(int value, CalendarComponent **c) {
+        CalendarComponent *cc = NULL;
+
+        assert(c);
+
+        cc = new0(CalendarComponent, 1);
+        if (!cc)
+                return -ENOMEM;
+
+        cc->value = value;
+        cc->repeat = 0;
+        cc->next = NULL;
+
+        *c = cc;
+
+        return 0;
+}
+
+static int parse_date(const char **p, CalendarSpec *c) {
+        const char *t;
+        int r;
+        CalendarComponent *first, *second, *third;
+
+        assert(p);
+        assert(*p);
+        assert(c);
+
+        t = *p;
+
+        if (*t == 0)
+                return 0;
+
+        r = parse_chain(&t, &first);
+        if (r < 0)
+                return r;
+
+        /* Already the end? A ':' as separator? In that case this was a time, not a date */
+        if (*t == 0 || *t == ':') {
+                free_chain(first);
+                return 0;
+        }
+
+        if (*t != '-') {
+                free_chain(first);
+                return -EINVAL;
+        }
+
+        t++;
+        r = parse_chain(&t, &second);
+        if (r < 0) {
+                free_chain(first);
+                return r;
+        }
+
+        /* Got two parts, hence it's month and day */
+        if (*t == ' ' || *t == 0) {
+                *p = t + strspn(t, " ");
+                c->month = first;
+                c->day = second;
+                return 0;
+        }
+
+        if (*t != '-') {
+                free_chain(first);
+                free_chain(second);
+                return -EINVAL;
+        }
+
+        t++;
+        r = parse_chain(&t, &third);
+        if (r < 0) {
+                free_chain(first);
+                free_chain(second);
+                return r;
+        }
+
+        /* Got tree parts, hence it is year, month and day */
+        if (*t == ' ' || *t == 0) {
+                *p = t + strspn(t, " ");
+                c->year = first;
+                c->month = second;
+                c->day = third;
+                return 0;
+        }
+
+        free_chain(first);
+        free_chain(second);
+        free_chain(third);
+        return -EINVAL;
+}
+
+static int parse_time(const char **p, CalendarSpec *c) {
+        CalendarComponent *h = NULL, *m = NULL, *s = NULL;
+        const char *t;
+        int r;
+
+        assert(p);
+        assert(*p);
+        assert(c);
+
+        t = *p;
+
+        if (*t == 0) {
+                /* If no time is specified at all, but a date of some
+                 * kind, then this means 00:00:00 */
+                if (c->day || c->weekdays_bits > 0)
+                        goto null_hour;
+
+                goto finish;
+        }
+
+        r = parse_chain(&t, &h);
+        if (r < 0)
+                goto fail;
+
+        if (*t != ':') {
+                r = -EINVAL;
+                goto fail;
+        }
+
+        t++;
+        r = parse_chain(&t, &m);
+        if (r < 0)
+                goto fail;
+
+        /* Already at the end? Then it's hours and minutes, and seconds are 0 */
+        if (*t == 0) {
+                if (m != NULL)
+                        goto null_second;
+
+                goto finish;
+        }
+
+        if (*t != ':') {
+                r = -EINVAL;
+                goto fail;
+        }
+
+        t++;
+        r = parse_chain(&t, &s);
+        if (r < 0)
+                goto fail;
+
+        /* At the end? Then it's hours, minutes and seconds */
+        if (*t == 0)
+                goto finish;
+
+        r = -EINVAL;
+        goto fail;
+
+null_hour:
+        r = const_chain(0, &h);
+        if (r < 0)
+                goto fail;
+
+        r = const_chain(0, &m);
+        if (r < 0)
+                goto fail;
+
+null_second:
+        r = const_chain(0, &s);
+        if (r < 0)
+                goto fail;
+
+finish:
+        *p = t;
+        c->hour = h;
+        c->minute = m;
+        c->second = s;
+        return 0;
+
+fail:
+        free_chain(h);
+        free_chain(m);
+        free_chain(s);
+        return r;
+}
+
+int calendar_spec_from_string(const char *p, CalendarSpec **spec) {
+        CalendarSpec *c;
+        int r;
+
+        assert(p);
+        assert(spec);
+
+        if (isempty(p))
+                return -EINVAL;
+
+        c = new0(CalendarSpec, 1);
+        if (!c)
+                return -ENOMEM;
+
+        if (strcasecmp(p, "hourly") == 0) {
+                r = const_chain(0, &c->minute);
+                if (r < 0)
+                        goto fail;
+                r = const_chain(0, &c->second);
+                if (r < 0)
+                        goto fail;
+
+        } else if (strcasecmp(p, "daily") == 0) {
+                r = const_chain(0, &c->hour);
+                if (r < 0)
+                        goto fail;
+                r = const_chain(0, &c->minute);
+                if (r < 0)
+                        goto fail;
+                r = const_chain(0, &c->second);
+                if (r < 0)
+                        goto fail;
+
+        } else if (strcasecmp(p, "monthly") == 0) {
+                r = const_chain(1, &c->day);
+                if (r < 0)
+                        goto fail;
+                r = const_chain(0, &c->hour);
+                if (r < 0)
+                        goto fail;
+                r = const_chain(0, &c->minute);
+                if (r < 0)
+                        goto fail;
+                r = const_chain(0, &c->second);
+                if (r < 0)
+                        goto fail;
+
+        } else if (strcasecmp(p, "weekly") == 0) {
+
+                c->weekdays_bits = 1;
+
+                r = const_chain(0, &c->hour);
+                if (r < 0)
+                        goto fail;
+                r = const_chain(0, &c->minute);
+                if (r < 0)
+                        goto fail;
+                r = const_chain(0, &c->second);
+                if (r < 0)
+                        goto fail;
+
+        } else {
+                r = parse_weekdays(&p, c);
+                if (r < 0)
+                        goto fail;
+
+                r = parse_date(&p, c);
+                if (r < 0)
+                        goto fail;
+
+                r = parse_time(&p, c);
+                if (r < 0)
+                        goto fail;
+
+                if (*p != 0) {
+                        r = -EINVAL;
+                        goto fail;
+                }
+        }
+
+        r = calendar_spec_normalize(c);
+        if (r < 0)
+                goto fail;
+
+        if (!calendar_spec_valid(c)) {
+                r = -EINVAL;
+                goto fail;
+        }
+
+        *spec = c;
+        return 0;
+
+fail:
+        calendar_spec_free(c);
+        return r;
+}
+
+static int find_matching_component(const CalendarComponent *c, int *val) {
+        const CalendarComponent *n;
+        int d;
+        bool d_set = false;
+        int r;
+
+        assert(val);
+
+        if (!c)
+                return 0;
+
+        while (c) {
+                n = c->next;
+
+                if (c->value >= *val) {
+
+                        if (!d_set || c->value < d) {
+                                d = c->value;
+                                d_set = true;
+                        }
+
+                } else if (c->repeat > 0) {
+                        int k;
+
+                        k = c->value + c->repeat * ((*val - c->value + c->repeat -1) / c->repeat);
+
+                        if (!d_set || k < d) {
+                                d = k;
+                                d_set = true;
+                        }
+                }
+
+                c = n;
+        }
+
+        if (!d_set)
+                return -ENOENT;
+
+        r = *val != d;
+        *val = d;
+        return r;
+}
+
+static bool tm_out_of_bounds(const struct tm *tm) {
+        struct tm t;
+        assert(tm);
+
+        t = *tm;
+
+        if (mktime(&t) == (time_t) -1)
+                return true;
+
+        /* Did any normalization take place? If so, it was out of bounds before */
+        return
+                t.tm_year != tm->tm_year ||
+                t.tm_mon != tm->tm_mon ||
+                t.tm_mday != tm->tm_mday ||
+                t.tm_hour != tm->tm_hour ||
+                t.tm_min != tm->tm_min ||
+                t.tm_sec != tm->tm_sec;
+}
+
+static bool matches_weekday(int weekdays_bits, const struct tm *tm) {
+        struct tm t;
+        int k;
+
+        if (weekdays_bits < 0 || weekdays_bits >= 127)
+                return true;
+
+        t = *tm;
+        if (mktime(&t) == (time_t) -1)
+                return false;
+
+        k = t.tm_wday == 0 ? 6 : t.tm_wday - 1;
+        return (weekdays_bits & (1 << k));
+}
+
+static int find_next(const CalendarSpec *spec, struct tm *tm) {
+        struct tm c;
+        int r;
+
+        assert(spec);
+        assert(tm);
+
+        c = *tm;
+
+        for (;;) {
+                /* Normalize the current date */
+                mktime(&c);
+                c.tm_isdst = -1;
+
+                c.tm_year += 1900;
+                r = find_matching_component(spec->year, &c.tm_year);
+                c.tm_year -= 1900;
+
+                if (r > 0) {
+                        c.tm_mon = 0;
+                        c.tm_mday = 1;
+                        c.tm_hour = c.tm_min = c.tm_sec = 0;
+                }
+                if (r < 0 || tm_out_of_bounds(&c))
+                        return r;
+
+                c.tm_mon += 1;
+                r = find_matching_component(spec->month, &c.tm_mon);
+                c.tm_mon -= 1;
+
+                if (r > 0) {
+                        c.tm_mday = 1;
+                        c.tm_hour = c.tm_min = c.tm_sec = 0;
+                }
+                if (r < 0 || tm_out_of_bounds(&c)) {
+                        c.tm_year ++;
+                        c.tm_mon = 0;
+                        c.tm_mday = 1;
+                        c.tm_hour = c.tm_min = c.tm_sec = 0;
+                        continue;
+                }
+
+                r = find_matching_component(spec->day, &c.tm_mday);
+                if (r > 0)
+                        c.tm_hour = c.tm_min = c.tm_sec = 0;
+                if (r < 0 || tm_out_of_bounds(&c)) {
+                        c.tm_mon ++;
+                        c.tm_mday = 1;
+                        c.tm_hour = c.tm_min = c.tm_sec = 0;
+                        continue;
+                }
+
+                if (!matches_weekday(spec->weekdays_bits, &c)) {
+                        c.tm_mday++;
+                        c.tm_hour = c.tm_min = c.tm_sec = 0;
+                        continue;
+                }
+
+                r = find_matching_component(spec->hour, &c.tm_hour);
+                if (r > 0)
+                        c.tm_min = c.tm_sec = 0;
+                if (r < 0 || tm_out_of_bounds(&c)) {
+                        c.tm_mday ++;
+                        c.tm_hour = c.tm_min = c.tm_sec = 0;
+                        continue;
+                }
+
+                r = find_matching_component(spec->minute, &c.tm_min);
+                if (r > 0)
+                        c.tm_sec = 0;
+                if (r < 0 || tm_out_of_bounds(&c)) {
+                        c.tm_hour ++;
+                        c.tm_min = c.tm_sec = 0;
+                        continue;
+                }
+
+                r = find_matching_component(spec->second, &c.tm_sec);
+                if (r < 0 || tm_out_of_bounds(&c)) {
+                        c.tm_min ++;
+                        c.tm_sec = 0;
+                        continue;
+                }
+
+
+                *tm = c;
+                return 0;
+        }
+}
+
+int calendar_spec_next_usec(const CalendarSpec *spec, usec_t usec, usec_t *next) {
+        struct tm tm;
+        time_t t;
+        int r;
+
+        assert(spec);
+        assert(next);
+
+        t = (time_t) (usec / USEC_PER_SEC) + 1;
+        assert_se(localtime_r(&t, &tm));
+
+        r = find_next(spec, &tm);
+        if (r < 0)
+                return r;
+
+        t = mktime(&tm);
+        if (t == (time_t) -1)
+                return -EINVAL;
+
+
+        *next = (usec_t) t * USEC_PER_SEC;
+        return 0;
+}
diff --git a/src/shared/calendarspec.h b/src/shared/calendarspec.h
new file mode 100644
index 0000000000..7baf318249
--- /dev/null
+++ b/src/shared/calendarspec.h
@@ -0,0 +1,57 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+#pragma once
+
+/***
+  This file is part of systemd.
+
+  Copyright 2012 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/>.
+***/
+
+/* A structure for specifying (possibly repetitive) points in calendar
+ * time, a la cron */
+
+#include <stdbool.h>
+#include "util.h"
+
+typedef struct CalendarComponent {
+        int value;
+        int repeat;
+
+        struct CalendarComponent *next;
+} CalendarComponent;
+
+typedef struct CalendarSpec {
+        int weekdays_bits;
+
+        CalendarComponent *year;
+        CalendarComponent *month;
+        CalendarComponent *day;
+
+        CalendarComponent *hour;
+        CalendarComponent *minute;
+        CalendarComponent *second;
+} CalendarSpec;
+
+void calendar_spec_free(CalendarSpec *c);
+
+int calendar_spec_normalize(CalendarSpec *spec);
+bool calendar_spec_valid(CalendarSpec *spec);
+
+int calendar_spec_to_string(const CalendarSpec *spec, char **p);
+int calendar_spec_from_string(const char *p, CalendarSpec **spec);
+
+int calendar_spec_next_usec(const CalendarSpec *spec, usec_t usec, usec_t *next);
diff --git a/src/test/test-calendarspec.c b/src/test/test-calendarspec.c
new file mode 100644
index 0000000000..b0fec8b28a
--- /dev/null
+++ b/src/test/test-calendarspec.c
@@ -0,0 +1,84 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+/***
+  This file is part of systemd.
+
+  Copyright 2012 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 <string.h>
+
+#include "calendarspec.h"
+#include "util.h"
+
+static void test_one(const char *input, const char *output) {
+        CalendarSpec *c;
+        char *p;
+        usec_t u;
+        char buf[FORMAT_TIMESTAMP_MAX];
+        int r;
+
+        assert_se(calendar_spec_from_string(input, &c) >= 0);
+
+        assert_se(calendar_spec_to_string(c, &p) >= 0);
+        printf("\"%s\" → \"%s\"\n", input, p);
+
+        assert_se(streq(p, output));
+        free(p);
+
+        u = now(CLOCK_REALTIME);
+        r = calendar_spec_next_usec(c, u, &u);
+        printf("Next: %s\n", r < 0 ? strerror(-r) : format_timestamp(buf, sizeof(buf), u));
+
+        calendar_spec_free(c);
+}
+
+int main(int argc, char* argv[]) {
+        CalendarSpec *c;
+
+        test_one("Sat,Thu,Mon-Wed,Sat-Sun", "Mon-Thu,Sat,Sun *-*-* 00:00:00");
+        test_one("Mon,Sun 12-*-* 2,1:23", "Mon,Sun 2012-*-* 01,02:23:00");
+        test_one("Wed *-1", "Wed *-*-01 00:00:00");
+        test_one("Wed-Wed,Wed *-1", "Wed *-*-01 00:00:00");
+        test_one("Wed, 17:48", "Wed *-*-* 17:48:00");
+        test_one("Wed-Sat,Tue 12-10-15 1:2:3", "Tue-Sat 2012-10-15 01:02:03");
+        test_one("*-*-7 0:0:0", "*-*-07 00:00:00");
+        test_one("10-15", "*-10-15 00:00:00");
+        test_one("monday *-12-* 17:00", "Mon *-12-* 17:00:00");
+        test_one("Mon,Fri *-*-3,1,2 *:30:45", "Mon,Fri *-*-01,02,03 *:30:45");
+        test_one("12,14,13,12:20,10,30", "*-*-* 12,13,14:10,20,30:00");
+        test_one("mon,fri *-1/2-1,3 *:30:45", "Mon,Fri *-01/2-01,03 *:30:45");
+        test_one("03-05 08:05:40", "*-03-05 08:05:40");
+        test_one("08:05:40", "*-*-* 08:05:40");
+        test_one("05:40", "*-*-* 05:40:00");
+        test_one("Sat,Sun 12-05 08:05:40", "Sat,Sun *-12-05 08:05:40");
+        test_one("Sat,Sun 08:05:40", "Sat,Sun *-*-* 08:05:40");
+        test_one("2003-03-05 05:40", "2003-03-05 05:40:00");
+        test_one("2003-03-05", "2003-03-05 00:00:00");
+        test_one("03-05", "*-03-05 00:00:00");
+        test_one("hourly", "*-*-* *:00:00");
+        test_one("daily", "*-*-* 00:00:00");
+        test_one("monthly", "*-*-01 00:00:00");
+        test_one("weekly", "Mon *-*-* 00:00:00");
+        test_one("*:2/3", "*-*-* *:02/3:00");
+
+        assert_se(calendar_spec_from_string("test", &c) < 0);
+        assert_se(calendar_spec_from_string("", &c) < 0);
+        assert_se(calendar_spec_from_string("7", &c) < 0);
+        assert_se(calendar_spec_from_string("121212:1:2", &c) < 0);
+
+        return 0;
+}