timer: implement calendar time events

11 files changed, 206 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);