unit: properly update references to units which are merged

When we merge units that some kind of object points to, those pointers
might become invalidated, and needs to be updated. Introduce a UnitRef
struct which links up all the unit references, to ensure corrected
references.

At the same time, drop configured_sockets in the Service object, and
replace it by proper UNIT_TRIGGERS resp. UNIT_TRIGGERED_BY dependencies,
which allow us to simplify a lot of code.

18 files changed, 268 insertions, 319 deletions

diff --git a/src/automount.c b/src/automount.c
index 6cf3c311b3..b70f8b4684 100644
--- a/src/automount.c
+++ b/src/automount.c
@@ -105,7 +105,7 @@ static void automount_done(Unit *u) {
         assert(a);
 
         unmount_autofs(a);
-        a->mount = NULL;
+        unit_ref_unset(&a->mount);
 
         free(a->where);
         a->where = NULL;
@@ -205,6 +205,7 @@ static int automount_load(Unit *u) {
                 return r;
 
         if (u->meta.load_state == UNIT_LOADED) {
+                Unit *x;
 
                 if (!a->where)
                         if (!(a->where = unit_name_to_path(u->meta.id)))
@@ -215,10 +216,14 @@ static int automount_load(Unit *u) {
                 if ((r = automount_add_mount_links(a)) < 0)
                         return r;
 
-                if ((r = unit_load_related_unit(u, ".mount", (Unit**) &a->mount)) < 0)
+                r = unit_load_related_unit(u, ".mount", &x);
+                if (r < 0)
                         return r;
 
-                if ((r = unit_add_dependency(u, UNIT_BEFORE, UNIT(a->mount), true)) < 0)
+                unit_ref_set(&a->mount, x);
+
+                r = unit_add_two_dependencies(u, UNIT_BEFORE, UNIT_TRIGGERS, UNIT_DEREF(a->mount), true);
+                if (r < 0)
                         return r;
 
                 if (a->meta.default_dependencies)
@@ -569,7 +574,7 @@ static void automount_enter_runnning(Automount *a) {
         DBusError error;
 
         assert(a);
-        assert(a->mount);
+        assert(UNIT_DEREF(a->mount));
 
         dbus_error_init(&error);
 
@@ -591,7 +596,7 @@ static void automount_enter_runnning(Automount *a) {
 
         if (!S_ISDIR(st.st_mode) || st.st_dev != a->dev_id)
                 log_info("%s's automount point already active?", a->meta.id);
-        else if ((r = manager_add_job(a->meta.manager, JOB_START, UNIT(a->mount), JOB_REPLACE, true, &error, NULL)) < 0) {
+        else if ((r = manager_add_job(a->meta.manager, JOB_START, UNIT_DEREF(a->mount), JOB_REPLACE, true, &error, NULL)) < 0) {
                 log_warning("%s failed to queue mount startup job: %s", a->meta.id, bus_error(&error, r));
                 goto fail;
         }
@@ -616,7 +621,7 @@ static int automount_start(Unit *u) {
                 return -EEXIST;
         }
 
-        if (a->mount->meta.load_state != UNIT_LOADED)
+        if (UNIT_DEREF(a->mount)->meta.load_state != UNIT_LOADED)
                 return -ENOENT;
 
         a->failure = false;
@@ -738,10 +743,10 @@ static bool automount_check_gc(Unit *u) {
 
         assert(a);
 
-        if (!a->mount)
+        if (!UNIT_DEREF(a->mount))
                 return false;
 
-        return UNIT_VTABLE(UNIT(a->mount))->check_gc(UNIT(a->mount));
+        return UNIT_VTABLE(UNIT_DEREF(a->mount))->check_gc(UNIT_DEREF(a->mount));
 }
 
 static void automount_fd_event(Unit *u, int fd, uint32_t events, Watch *w) {
diff --git a/src/automount.h b/src/automount.h
index 1a6cc98fd1..c6326ed3c2 100644
--- a/src/automount.h
+++ b/src/automount.h
@@ -42,14 +42,13 @@ struct Automount {
 
         char *where;
 
-        Mount *mount;
+        UnitRef mount;
 
         int pipe_fd;
         mode_t directory_mode;
         Watch pipe_watch;
         dev_t dev_id;
 
-
         Set *tokens;
 
         bool failure:1;
diff --git a/src/dbus-path.c b/src/dbus-path.c
index 15238798ae..f67b5a2b7c 100644
--- a/src/dbus-path.c
+++ b/src/dbus-path.c
@@ -86,7 +86,7 @@ static int bus_path_append_unit(DBusMessageIter *i, const char *property, void *
         assert(property);
         assert(u);
 
-        t = u->path.unit ? u->path.unit->meta.id : "";
+        t = UNIT_DEREF(u->path.unit) ? UNIT_DEREF(u->path.unit)->meta.id : "";
 
         return dbus_message_iter_append_basic(i, DBUS_TYPE_STRING, &t) ? 0 : -ENOMEM;
 }
diff --git a/src/dbus-service.c b/src/dbus-service.c
index 3486623e59..373e3f56b0 100644
--- a/src/dbus-service.c
+++ b/src/dbus-service.c
@@ -59,7 +59,6 @@
         "  <property name=\"BusName\" type=\"s\" access=\"read\"/>\n"   \
         "  <property name=\"StatusText\" type=\"s\" access=\"read\"/>\n" \
         "  <property name=\"FsckPassNo\" type=\"i\" access=\"read\"/>\n" \
-        "  <property name=\"Sockets\" type=\"as\" access=\"read\"/>\n" \
         BUS_SERVICE_SYSV_INTERFACE_FRAGMENT                              \
        " </interface>\n"
 
@@ -120,7 +119,6 @@ DBusHandlerResult bus_service_message_handler(Unit *u, DBusConnection *connectio
                 { "org.freedesktop.systemd1.Service", "ControlPID",             bus_property_append_pid,    "u", &u->service.control_pid               },
                 { "org.freedesktop.systemd1.Service", "BusName",                bus_property_append_string, "s", u->service.bus_name                   },
                 { "org.freedesktop.systemd1.Service", "StatusText",             bus_property_append_string, "s", u->service.status_text                },
-                { "org.freedesktop.systemd1.Service", "Sockets",                bus_unit_append_dependencies, "as", u->service.configured_sockets         },
 #ifdef HAVE_SYSV_COMPAT
                 { "org.freedesktop.systemd1.Service", "SysVRunLevels",          bus_property_append_string, "s", u->service.sysv_runlevels             },
                 { "org.freedesktop.systemd1.Service", "SysVStartPriority",      bus_property_append_int,    "i", &u->service.sysv_start_priority       },
diff --git a/src/dbus-timer.c b/src/dbus-timer.c
index abcbe6f9be..07d425e20e 100644
--- a/src/dbus-timer.c
+++ b/src/dbus-timer.c
@@ -107,7 +107,7 @@ static int bus_timer_append_unit(DBusMessageIter *i, const char *property, void
         assert(property);
         assert(u);
 
-        t = u->timer.unit ? u->timer.unit->meta.id : "";
+        t = UNIT_DEREF(u->timer.unit) ? UNIT_DEREF(u->timer.unit)->meta.id : "";
 
         return dbus_message_iter_append_basic(i, DBUS_TYPE_STRING, &t) ? 0 : -ENOMEM;
 }
diff --git a/src/dbus-unit.h b/src/dbus-unit.h
index 9fed6d731d..20d5506870 100644
--- a/src/dbus-unit.h
+++ b/src/dbus-unit.h
@@ -141,6 +141,8 @@
         { "org.freedesktop.systemd1.Unit", "Before",               bus_unit_append_dependencies,   "as",   u->meta.dependencies[UNIT_BEFORE] }, \
         { "org.freedesktop.systemd1.Unit", "After",                bus_unit_append_dependencies,   "as",   u->meta.dependencies[UNIT_AFTER]  }, \
         { "org.freedesktop.systemd1.Unit", "OnFailure",            bus_unit_append_dependencies,   "as",   u->meta.dependencies[UNIT_ON_FAILURE] }, \
+        { "org.freedesktop.systemd1.Unit", "Triggers",             bus_unit_append_dependencies,   "as",   u->meta.dependencies[UNIT_TRIGGERS] }, \
+        { "org.freedesktop.systemd1.Unit", "TriggeredBy",          bus_unit_append_dependencies,   "as",   u->meta.dependencies[UNIT_TRIGGERED_BY] }, \
         { "org.freedesktop.systemd1.Unit", "Description",          bus_unit_append_description,    "s",    u                                 }, \
         { "org.freedesktop.systemd1.Unit", "LoadState",            bus_unit_append_load_state,     "s",    &u->meta.load_state               }, \
         { "org.freedesktop.systemd1.Unit", "ActiveState",          bus_unit_append_active_state,   "s",    u                                 }, \
diff --git a/src/load-fragment.c b/src/load-fragment.c
index 12079c640f..19031904f1 100644
--- a/src/load-fragment.c
+++ b/src/load-fragment.c
@@ -84,7 +84,8 @@ int config_parse_unit_deps(
                 char *t, *k;
                 int r;
 
-                if (!(t = strndup(w, l)))
+                t = strndup(w, l);
+                if (!t)
                         return -ENOMEM;
 
                 k = unit_name_printf(u, t);
@@ -94,12 +95,8 @@ int config_parse_unit_deps(
                         return -ENOMEM;
 
                 r = unit_add_dependency_by_name(u, d, k, NULL, true);
-
-                if (r < 0) {
-                        log_error("Failed to add dependency on %s, ignoring: %s", k, strerror(-r));
-                        free(k);
-                        return 0;
-                }
+                if (r < 0)
+                        log_error("[%s:%u] Failed to add dependency on %s, ignoring: %s", filename, line, k, strerror(-r));
 
                 free(k);
         }
@@ -1265,6 +1262,7 @@ int config_parse_timer_unit(
         Timer *t = data;
         int r;
         DBusError error;
+        Unit *u;
 
         assert(filename);
         assert(lvalue);
@@ -1278,12 +1276,15 @@ int config_parse_timer_unit(
                 return 0;
         }
 
-        if ((r = manager_load_unit(t->meta.manager, rvalue, NULL, NULL, &t->unit)) < 0) {
+        r = manager_load_unit(t->meta.manager, rvalue, NULL, NULL, &u);
+        if (r < 0) {
                 log_error("[%s:%u] Failed to load unit %s, ignoring: %s", filename, line, rvalue, bus_error(&error, r));
                 dbus_error_free(&error);
                 return 0;
         }
 
+        unit_ref_set(&t->unit, u);
+
         return 0;
 }
 
@@ -1347,6 +1348,7 @@ int config_parse_path_unit(
         Path *t = data;
         int r;
         DBusError error;
+        Unit *u;
 
         assert(filename);
         assert(lvalue);
@@ -1360,12 +1362,14 @@ int config_parse_path_unit(
                 return 0;
         }
 
-        if ((r = manager_load_unit(t->meta.manager, rvalue, NULL, &error, &t->unit)) < 0) {
+        if ((r = manager_load_unit(t->meta.manager, rvalue, NULL, &error, &u)) < 0) {
                 log_error("[%s:%u] Failed to load unit %s, ignoring: %s", filename, line, rvalue, bus_error(&error, r));
                 dbus_error_free(&error);
                 return 0;
         }
 
+        unit_ref_set(&t->unit, u);
+
         return 0;
 }
 
@@ -1416,7 +1420,6 @@ int config_parse_service_sockets(
 
         Service *s = data;
         int r;
-        DBusError error;
         char *state, *w;
         size_t l;
 
@@ -1425,35 +1428,34 @@ int config_parse_service_sockets(
         assert(rvalue);
         assert(data);
 
-        dbus_error_init(&error);
-
         FOREACH_WORD_QUOTED(w, l, rvalue, state) {
-                char *t;
-                Unit *sock;
+                char *t, *k;
 
-                if (!(t = strndup(w, l)))
+                t = strndup(w, l);
+                if (!t)
                         return -ENOMEM;
 
-                if (!endswith(t, ".socket")) {
-                        log_error("[%s:%u] Unit must be of type socket, ignoring: %s", filename, line, rvalue);
-                        free(t);
-                        continue;
-                }
-
-                r = manager_load_unit(s->meta.manager, t, NULL, &error, &sock);
+                k = unit_name_printf(UNIT(s), t);
                 free(t);
 
-                if (r < 0) {
-                        log_error("[%s:%u] Failed to load unit %s, ignoring: %s", filename, line, rvalue, bus_error(&error, r));
-                        dbus_error_free(&error);
+                if (!k)
+                        return -ENOMEM;
+
+                if (!endswith(k, ".socket")) {
+                        log_error("[%s:%u] Unit must be of type socket, ignoring: %s", filename, line, rvalue);
+                        free(k);
                         continue;
                 }
 
-                if ((r = set_ensure_allocated(&s->configured_sockets, trivial_hash_func, trivial_compare_func)) < 0)
-                        return r;
+                r = unit_add_two_dependencies_by_name(UNIT(s), UNIT_WANTS, UNIT_AFTER, k, NULL, true);
+                if (r < 0)
+                        log_error("[%s:%u] Failed to add dependency on %s, ignoring: %s", filename, line, k, strerror(-r));
 
-                if ((r = set_put(s->configured_sockets, sock)) < 0)
+                r = unit_add_dependency_by_name(UNIT(s), UNIT_TRIGGERED_BY, k, NULL, true);
+                if (r < 0)
                         return r;
+
+                free(k);
         }
 
         return 0;
diff --git a/src/mount.c b/src/mount.c
index 47422ccf8b..f72c50afb7 100644
--- a/src/mount.c
+++ b/src/mount.c
@@ -108,21 +108,12 @@ static void mount_parameters_done(MountParameters *p) {
 
 static void mount_done(Unit *u) {
         Mount *m = MOUNT(u);
-        Meta *other;
 
         assert(m);
 
         free(m->where);
         m->where = NULL;
 
-        /* Try to detach us from the automount unit if there is any */
-        LIST_FOREACH(units_by_type, other, m->meta.manager->units_by_type[UNIT_AUTOMOUNT]) {
-                Automount *a = (Automount*) other;
-
-                if (a->mount == m)
-                        a->mount = NULL;
-        }
-
         mount_parameters_done(&m->parameters_etc_fstab);
         mount_parameters_done(&m->parameters_proc_self_mountinfo);
         mount_parameters_done(&m->parameters_fragment);
@@ -647,13 +638,18 @@ static int mount_load(Unit *u) {
 static int mount_notify_automount(Mount *m, int status) {
         Unit *p;
         int r;
+        Iterator i;
 
         assert(m);
 
-        if ((r = unit_get_related_unit(UNIT(m), ".automount", &p)) < 0)
-                return r == -ENOENT ? 0 : r;
+        SET_FOREACH(p, m->meta.dependencies[UNIT_TRIGGERED_BY], i)
+                if (p->meta.type == UNIT_AUTOMOUNT) {
+                         r = automount_send_ready(AUTOMOUNT(p), status);
+                         if (r < 0)
+                                 return r;
+                }
 
-        return automount_send_ready(AUTOMOUNT(p), status);
+        return 0;
 }
 
 static void mount_set_state(Mount *m, MountState state) {
diff --git a/src/path.c b/src/path.c
index 3fee24760c..957af05c7e 100644
--- a/src/path.c
+++ b/src/path.c
@@ -39,7 +39,8 @@ static const UnitActiveState state_translation_table[_PATH_STATE_MAX] = {
         [PATH_FAILED] = UNIT_FAILED
 };
 
-int pathspec_watch(PathSpec *s, Unit *u) {
+int path_spec_watch(PathSpec *s, Unit *u) {
+
         static const int flags_table[_PATH_TYPE_MAX] = {
                 [PATH_EXISTS] = IN_DELETE_SELF|IN_MOVE_SELF|IN_ATTRIB,
                 [PATH_EXISTS_GLOB] = IN_DELETE_SELF|IN_MOVE_SELF|IN_ATTRIB,
@@ -55,7 +56,7 @@ int pathspec_watch(PathSpec *s, Unit *u) {
         assert(u);
         assert(s);
 
-        pathspec_unwatch(s, u);
+        path_spec_unwatch(s, u);
 
         if (!(k = strdup(s->path)))
                 return -ENOMEM;
@@ -96,11 +97,11 @@ int pathspec_watch(PathSpec *s, Unit *u) {
 fail:
         free(k);
 
-        pathspec_unwatch(s, u);
+        path_spec_unwatch(s, u);
         return r;
 }
 
-void pathspec_unwatch(PathSpec *s, Unit *u) {
+void path_spec_unwatch(PathSpec *s, Unit *u) {
 
         if (s->inotify_fd < 0)
                 return;
@@ -111,7 +112,7 @@ void pathspec_unwatch(PathSpec *s, Unit *u) {
         s->inotify_fd = -1;
 }
 
-int pathspec_fd_event(PathSpec *s, uint32_t events) {
+int path_spec_fd_event(PathSpec *s, uint32_t events) {
         uint8_t *buf = NULL;
         struct inotify_event *e;
         ssize_t k;
@@ -164,7 +165,7 @@ out:
         return r;
 }
 
-static bool pathspec_check_good(PathSpec *s, bool initial) {
+static bool path_spec_check_good(PathSpec *s, bool initial) {
         bool good = false;
 
         switch (s->type) {
@@ -202,11 +203,11 @@ static bool pathspec_check_good(PathSpec *s, bool initial) {
         return good;
 }
 
-static bool pathspec_startswith(PathSpec *s, const char *what) {
+static bool path_spec_startswith(PathSpec *s, const char *what) {
         return path_startswith(s->path, what);
 }
 
-static void pathspec_mkdir(PathSpec *s, mode_t mode) {
+static void path_spec_mkdir(PathSpec *s, mode_t mode) {
         int r;
 
         if (s->type == PATH_EXISTS || s->type == PATH_EXISTS_GLOB)
@@ -216,7 +217,7 @@ static void pathspec_mkdir(PathSpec *s, mode_t mode) {
                 log_warning("mkdir(%s) failed: %s", s->path, strerror(-r));
 }
 
-static void pathspec_dump(PathSpec *s, FILE *f, const char *prefix) {
+static void path_spec_dump(PathSpec *s, FILE *f, const char *prefix) {
         fprintf(f,
                 "%s%s: %s\n",
                 prefix,
@@ -224,8 +225,10 @@ static void pathspec_dump(PathSpec *s, FILE *f, const char *prefix) {
                 s->path);
 }
 
-void pathspec_done(PathSpec *s) {
+void path_spec_done(PathSpec *s) {
+        assert(s);
         assert(s->inotify_fd == -1);
+
         free(s->path);
 }
 
@@ -244,10 +247,12 @@ static void path_done(Unit *u) {
 
         assert(p);
 
+        unit_ref_unset(&p->unit);
+
         while ((s = p->specs)) {
-                pathspec_unwatch(s, u);
+                path_spec_unwatch(s, u);
                 LIST_REMOVE(PathSpec, spec, p->specs, s);
-                pathspec_done(s);
+                path_spec_done(s);
                 free(s);
         }
 }
@@ -265,7 +270,7 @@ int path_add_one_mount_link(Path *p, Mount *m) {
 
         LIST_FOREACH(spec, s, p->specs) {
 
-                if (!pathspec_startswith(s, m->where))
+                if (!path_spec_startswith(s, m->where))
                         continue;
 
                 if ((r = unit_add_two_dependencies(UNIT(p), UNIT_AFTER, UNIT_REQUIRES, UNIT(m), true)) < 0)
@@ -330,11 +335,18 @@ static int path_load(Unit *u) {
 
         if (u->meta.load_state == UNIT_LOADED) {
 
-                if (!p->unit)
-                        if ((r = unit_load_related_unit(u, ".service", &p->unit)))
+                if (!UNIT_DEREF(p->unit)) {
+                        Unit *x;
+
+                        r = unit_load_related_unit(u, ".service", &x);
+                        if (r < 0)
                                 return r;
 
-                if ((r = unit_add_dependency(u, UNIT_BEFORE, p->unit, true)) < 0)
+                        unit_ref_set(&p->unit, x);
+                }
+
+                r = unit_add_two_dependencies(u, UNIT_BEFORE, UNIT_TRIGGERS, UNIT_DEREF(p->unit), true);
+                if (r < 0)
                         return r;
 
                 if ((r = path_add_mount_links(p)) < 0)
@@ -361,12 +373,12 @@ static void path_dump(Unit *u, FILE *f, const char *prefix) {
                 "%sMakeDirectory: %s\n"
                 "%sDirectoryMode: %04o\n",
                 prefix, path_state_to_string(p->state),
-                prefix, p->unit->meta.id,
+                prefix, UNIT_DEREF(p->unit)->meta.id,
                 prefix, yes_no(p->make_directory),
                 prefix, p->directory_mode);
 
         LIST_FOREACH(spec, s, p->specs)
-                pathspec_dump(s, f, prefix);
+                path_spec_dump(s, f, prefix);
 }
 
 static void path_unwatch(Path *p) {
@@ -375,7 +387,7 @@ static void path_unwatch(Path *p) {
         assert(p);
 
         LIST_FOREACH(spec, s, p->specs)
-                pathspec_unwatch(s, UNIT(p));
+                path_spec_unwatch(s, UNIT(p));
 }
 
 static int path_watch(Path *p) {
@@ -385,7 +397,7 @@ static int path_watch(Path *p) {
         assert(p);
 
         LIST_FOREACH(spec, s, p->specs)
-                if ((r = pathspec_watch(s, UNIT(p))) < 0)
+                if ((r = path_spec_watch(s, UNIT(p))) < 0)
                         return r;
 
         return 0;
@@ -451,7 +463,7 @@ static void path_enter_running(Path *p) {
         if (p->meta.job && p->meta.job->type == JOB_STOP)
                 return;
 
-        if ((r = manager_add_job(p->meta.manager, JOB_START, p->unit, JOB_REPLACE, true, &error, NULL)) < 0)
+        if ((r = manager_add_job(p->meta.manager, JOB_START, UNIT_DEREF(p->unit), JOB_REPLACE, true, &error, NULL)) < 0)
                 goto fail;
 
         p->inotify_triggered = false;
@@ -476,7 +488,7 @@ static bool path_check_good(Path *p, bool initial) {
         assert(p);
 
         LIST_FOREACH(spec, s, p->specs) {
-                good = pathspec_check_good(s, initial);
+                good = path_spec_check_good(s, initial);
 
                 if (good)
                         break;
@@ -526,7 +538,7 @@ static void path_mkdir(Path *p) {
                 return;
 
         LIST_FOREACH(spec, s, p->specs)
-                pathspec_mkdir(s, p->directory_mode);
+                path_spec_mkdir(s, p->directory_mode);
 }
 
 static int path_start(Unit *u) {
@@ -535,7 +547,7 @@ static int path_start(Unit *u) {
         assert(p);
         assert(p->state == PATH_DEAD || p->state == PATH_FAILED);
 
-        if (p->unit->meta.load_state != UNIT_LOADED)
+        if (UNIT_DEREF(p->unit)->meta.load_state != UNIT_LOADED)
                 return -ENOENT;
 
         path_mkdir(p);
@@ -616,7 +628,7 @@ static void path_fd_event(Unit *u, int fd, uint32_t events, Watch *w) {
         /* log_debug("inotify wakeup on %s.", u->meta.id); */
 
         LIST_FOREACH(spec, s, p->specs)
-                if (pathspec_owns_inotify_fd(s, fd))
+                if (path_spec_owns_inotify_fd(s, fd))
                         break;
 
         if (!s) {
@@ -624,7 +636,7 @@ static void path_fd_event(Unit *u, int fd, uint32_t events, Watch *w) {
                 goto fail;
         }
 
-        changed = pathspec_fd_event(s, events);
+        changed = path_spec_fd_event(s, events);
         if (changed < 0)
                 goto fail;
 
@@ -645,36 +657,22 @@ fail:
 }
 
 void path_unit_notify(Unit *u, UnitActiveState new_state) {
-        char *n;
-        int r;
         Iterator i;
+        Unit *k;
 
         if (u->meta.type == UNIT_PATH)
                 return;
 
-        SET_FOREACH(n, u->meta.names, i) {
-                char *k;
-                Unit *t;
+        SET_FOREACH(k, u->meta.dependencies[UNIT_TRIGGERED_BY], i) {
                 Path *p;
 
-                if (!(k = unit_name_change_suffix(n, ".path"))) {
-                        r = -ENOMEM;
-                        goto fail;
-                }
-
-                t = manager_get_unit(u->meta.manager, k);
-                free(k);
-
-                if (!t)
+                if (k->meta.type != UNIT_PATH)
                         continue;
 
-                if (t->meta.load_state != UNIT_LOADED)
+                if (k->meta.load_state != UNIT_LOADED)
                         continue;
 
-                p = PATH(t);
-
-                if (p->unit != u)
-                        continue;
+                p = PATH(k);
 
                 if (p->state == PATH_RUNNING && new_state == UNIT_INACTIVE) {
                         log_debug("%s got notified about unit deactivation.", p->meta.id);
@@ -685,11 +683,6 @@ void path_unit_notify(Unit *u, UnitActiveState new_state) {
                         path_enter_waiting(p, false, p->inotify_triggered);
                 }
         }
-
-        return;
-
-fail:
-        log_error("Failed find path unit: %s", strerror(-r));
 }
 
 static void path_reset_failed(Unit *u) {
diff --git a/src/path.h b/src/path.h
index 1d78fe424a..8b3c0bc119 100644
--- a/src/path.h
+++ b/src/path.h
@@ -58,14 +58,14 @@ typedef struct PathSpec {
         int primary_wd;
 
         bool previous_exists;
-
 } PathSpec;
 
-int  pathspec_watch(PathSpec *s, Unit *u);
-void pathspec_unwatch(PathSpec *s, Unit *u);
-int  pathspec_fd_event(PathSpec *s, uint32_t events);
-void pathspec_done(PathSpec *s);
-static inline bool pathspec_owns_inotify_fd(PathSpec *s, int fd) {
+int path_spec_watch(PathSpec *s, Unit *u);
+void path_spec_unwatch(PathSpec *s, Unit *u);
+int path_spec_fd_event(PathSpec *s, uint32_t events);
+void path_spec_done(PathSpec *s);
+
+static inline bool path_spec_owns_inotify_fd(PathSpec *s, int fd) {
         return s->inotify_fd == fd;
 }
 
@@ -74,7 +74,7 @@ struct Path {
 
         LIST_HEAD(PathSpec, specs);
 
-        Unit *unit;
+        UnitRef unit;
 
         PathState state, deserialized_state;
 
diff --git a/src/service.c b/src/service.c
index c5a796623f..0110c9f12f 100644
--- a/src/service.c
+++ b/src/service.c
@@ -187,11 +187,11 @@ static void service_close_socket_fd(Service *s) {
 static void service_connection_unref(Service *s) {
         assert(s);
 
-        if (!s->accept_socket)
+        if (!UNIT_DEREF(s->accept_socket))
                 return;
 
-        socket_connection_unref(s->accept_socket);
-        s->accept_socket = NULL;
+        socket_connection_unref(SOCKET(UNIT_DEREF(s->accept_socket)));
+        unit_ref_unset(&s->accept_socket);
 }
 
 static void service_done(Unit *u) {
@@ -232,7 +232,7 @@ static void service_done(Unit *u) {
         service_close_socket_fd(s);
         service_connection_unref(s);
 
-        set_free(s->configured_sockets);
+        unit_ref_unset(&s->accept_socket);
 
         unit_unwatch_timer(u, &s->timer_watch);
 }
@@ -1108,22 +1108,6 @@ static int service_add_default_dependencies(Service *s) {
         return unit_add_two_dependencies_by_name(UNIT(s), UNIT_BEFORE, UNIT_CONFLICTS, SPECIAL_SHUTDOWN_TARGET, NULL, true);
 }
 
-static int service_add_socket_dependencies(Service *s) {
-        Iterator i;
-        Unit *u;
-        int r;
-
-        /* Make sure we pull in all explicitly configured sockets */
-
-        SET_FOREACH(u, s->configured_sockets, i) {
-                r = unit_add_two_dependencies(UNIT(s), UNIT_AFTER, UNIT_REQUIRES, u, true);
-                if (r < 0)
-                        return r;
-        }
-
-        return 0;
-}
-
 static void service_fix_output(Service *s) {
         assert(s);
 
@@ -1197,12 +1181,6 @@ static int service_load(Unit *u) {
                         if ((r = unit_add_two_dependencies_by_name(u, UNIT_AFTER, UNIT_REQUIRES, SPECIAL_DBUS_SOCKET, NULL, true)) < 0)
                                 return r;
 
-                if (!set_isempty(s->configured_sockets)) {
-                        r = service_add_socket_dependencies(s);
-                        if (r < 0)
-                                return r;
-                }
-
                 if (s->meta.default_dependencies)
                         if ((r = service_add_default_dependencies(s)) < 0)
                                 return r;
@@ -1393,86 +1371,22 @@ static int service_search_main_pid(Service *s) {
         return 0;
 }
 
-static int service_get_sockets(Service *s, Set **_set) {
-        Set *set;
+static void service_notify_sockets_dead(Service *s) {
         Iterator i;
-        char *t;
-        int r;
-
-        assert(s);
-        assert(_set);
-
-        if (s->socket_fd >= 0)
-                return 0;
-
-        if (!set_isempty(s->configured_sockets))
-                return 0;
-
-        /* Collects all Socket objects that belong to this
-         * service. Note that a service might have multiple sockets
-         * via multiple names. */
-
-        if (!(set = set_new(NULL, NULL)))
-                return -ENOMEM;
-
-        SET_FOREACH(t, s->meta.names, i) {
-                char *k;
-                Unit *p;
-
-                /* Look for all socket objects that go by any of our
-                 * units and collect their fds */
-
-                if (!(k = unit_name_change_suffix(t, ".socket"))) {
-                        r = -ENOMEM;
-                        goto fail;
-                }
-
-                p = manager_get_unit(s->meta.manager, k);
-                free(k);
-
-                if (!p)
-                        continue;
-
-                if ((r = set_put(set, p)) < 0)
-                        goto fail;
-        }
-
-        *_set = set;
-        return 0;
-
-fail:
-        set_free(set);
-        return r;
-}
-
-static int service_notify_sockets_dead(Service *s) {
-        Iterator i;
-        Set *set, *free_set = NULL;
-        Socket *sock;
-        int r;
+        Unit *u;
 
         assert(s);
 
         /* Notifies all our sockets when we die */
 
         if (s->socket_fd >= 0)
-                return 0;
-
-        if (!set_isempty(s->configured_sockets))
-                set = s->configured_sockets;
-        else {
-                if ((r = service_get_sockets(s, &free_set)) < 0)
-                        return r;
-
-                set = free_set;
-        }
-
-        SET_FOREACH(sock, set, i)
-                socket_notify_service_dead(sock);
+                return;
 
-        set_free(free_set);
+        SET_FOREACH(u, s->meta.dependencies[UNIT_TRIGGERED_BY], i)
+                if (u->meta.type == UNIT_SOCKET)
+                        socket_notify_service_dead(SOCKET(u));
 
-        return 0;
+        return;
 }
 
 static void service_unwatch_pid_file(Service *s) {
@@ -1480,8 +1394,8 @@ static void service_unwatch_pid_file(Service *s) {
                 return;
 
         log_debug("Stopping watch for %s's PID file %s", s->meta.id, s->pid_file_pathspec->path);
-        pathspec_unwatch(s->pid_file_pathspec, UNIT(s));
-        pathspec_done(s->pid_file_pathspec);
+        path_spec_unwatch(s->pid_file_pathspec, UNIT(s));
+        path_spec_done(s->pid_file_pathspec);
         free(s->pid_file_pathspec);
         s->pid_file_pathspec = NULL;
 }
@@ -1644,8 +1558,7 @@ static int service_collect_fds(Service *s, int **fds, unsigned *n_fds) {
         int r;
         int *rfds = NULL;
         unsigned rn_fds = 0;
-        Set *set, *free_set = NULL;
-        Socket *sock;
+        Unit *u;
 
         assert(s);
         assert(fds);
@@ -1654,18 +1567,15 @@ static int service_collect_fds(Service *s, int **fds, unsigned *n_fds) {
         if (s->socket_fd >= 0)
                 return 0;
 
-        if (!set_isempty(s->configured_sockets))
-                set = s->configured_sockets;
-        else {
-                if ((r = service_get_sockets(s, &free_set)) < 0)
-                        return r;
-
-                set = free_set;
-        }
-
-        SET_FOREACH(sock, set, i) {
+        SET_FOREACH(u, s->meta.dependencies[UNIT_TRIGGERED_BY], i) {
                 int *cfds;
                 unsigned cn_fds;
+                Socket *sock;
+
+                if (u->meta.type != UNIT_SOCKET)
+                        continue;
+
+                sock = SOCKET(u);
 
                 if ((r = socket_collect_fds(sock, &cfds, &cn_fds)) < 0)
                         goto fail;
@@ -1698,12 +1608,9 @@ static int service_collect_fds(Service *s, int **fds, unsigned *n_fds) {
         *fds = rfds;
         *n_fds = rn_fds;
 
-        set_free(free_set);
-
         return 0;
 
 fail:
-        set_free(set);
         free(rfds);
 
         return r;
@@ -2659,7 +2566,7 @@ static int service_watch_pid_file(Service *s) {
         int r;
 
         log_debug("Setting watch for %s's PID file %s", s->meta.id, s->pid_file_pathspec->path);
-        r = pathspec_watch(s->pid_file_pathspec, UNIT(s));
+        r = path_spec_watch(s->pid_file_pathspec, UNIT(s));
         if (r < 0)
                 goto fail;
 
@@ -2709,11 +2616,11 @@ static void service_fd_event(Unit *u, int fd, uint32_t events, Watch *w) {
         assert(fd >= 0);
         assert(s->state == SERVICE_START || s->state == SERVICE_START_POST);
         assert(s->pid_file_pathspec);
-        assert(pathspec_owns_inotify_fd(s->pid_file_pathspec, fd));
+        assert(path_spec_owns_inotify_fd(s->pid_file_pathspec, fd));
 
         log_debug("inotify event for %s", u->meta.id);
 
-        if (pathspec_fd_event(s->pid_file_pathspec, events) < 0)
+        if (path_spec_fd_event(s->pid_file_pathspec, events) < 0)
                 goto fail;
 
         if (service_retry_pid_file(s) == 0)
@@ -3458,6 +3365,7 @@ static void service_bus_query_pid_done(
 }
 
 int service_set_socket_fd(Service *s, int fd, Socket *sock) {
+
         assert(s);
         assert(fd >= 0);
 
@@ -3476,9 +3384,10 @@ int service_set_socket_fd(Service *s, int fd, Socket *sock) {
 
         s->socket_fd = fd;
         s->got_socket_fd = true;
-        s->accept_socket = sock;
 
-        return 0;
+        unit_ref_set(&s->accept_socket, UNIT(sock));
+
+        return unit_add_two_dependencies(UNIT(sock), UNIT_BEFORE, UNIT_TRIGGERS, UNIT(s), false);
 }
 
 static void service_reset_failed(Unit *u) {
diff --git a/src/service.h b/src/service.h
index 2102826723..8f67ad50a8 100644
--- a/src/service.h
+++ b/src/service.h
@@ -27,6 +27,7 @@ typedef struct Service Service;
 #include "unit.h"
 #include "path.h"
 #include "ratelimit.h"
+#include "service.h"
 
 typedef enum ServiceState {
         SERVICE_DEAD,
@@ -154,8 +155,7 @@ struct Service {
 
         RateLimit ratelimit;
 
-        struct Socket *accept_socket;
-        Set *configured_sockets;
+        UnitRef accept_socket;
 
         Watch timer_watch;
         PathSpec *pid_file_pathspec;
@@ -165,6 +165,8 @@ struct Service {
 
 extern const UnitVTable service_vtable;
 
+struct Socket;
+
 int service_set_socket_fd(Service *s, int fd, struct Socket *socket);
 
 const char* service_state_to_string(ServiceState i);
diff --git a/src/socket.c b/src/socket.c
index 1f5e067337..7034436be0 100644
--- a/src/socket.c
+++ b/src/socket.c
@@ -98,7 +98,6 @@ static void socket_unwatch_control_pid(Socket *s) {
 static void socket_done(Unit *u) {
         Socket *s = SOCKET(u);
         SocketPort *p;
-        Meta *i;
 
         assert(s);
 
@@ -120,7 +119,7 @@ static void socket_done(Unit *u) {
 
         socket_unwatch_control_pid(s);
 
-        s->service = NULL;
+        unit_ref_unset(&s->service);
 
         free(s->tcp_congestion);
         s->tcp_congestion = NULL;
@@ -129,16 +128,6 @@ static void socket_done(Unit *u) {
         s->bind_to_device = NULL;
 
         unit_unwatch_timer(u, &s->timer_watch);
-
-        /* Make sure no service instance refers to us anymore. */
-        LIST_FOREACH(units_by_type, i, u->meta.manager->units_by_type[UNIT_SERVICE]) {
-                Service *service = (Service *) i;
-
-                if (service->accept_socket == s)
-                        service->accept_socket = NULL;
-
-                set_remove(service->configured_sockets, s);
-        }
 }
 
 static int socket_instantiate_service(Socket *s) {
@@ -153,7 +142,7 @@ static int socket_instantiate_service(Socket *s) {
          * here. For Accept=no this is mostly a NOP since the service
          * is figured out at load time anyway. */
 
-        if (s->service)
+        if (UNIT_DEREF(s->service))
                 return 0;
 
         assert(s->accept);
@@ -181,8 +170,9 @@ static int socket_instantiate_service(Socket *s) {
 #endif
 
         u->meta.no_gc = true;
-        s->service = SERVICE(u);
-        return 0;
+        unit_ref_set(&s->service, u);
+
+        return unit_add_two_dependencies(UNIT(s), UNIT_BEFORE, UNIT_TRIGGERS, u, false);
 }
 
 static bool have_non_accept_socket(Socket *s) {
@@ -226,7 +216,7 @@ static int socket_verify(Socket *s) {
                 return -EINVAL;
         }
 
-        if (s->accept && s->service) {
+        if (s->accept && UNIT_DEREF(s->service)) {
                 log_error("Explicit service configuration for accepting sockets not supported on %s. Refusing.", s->meta.id);
                 return -EINVAL;
         }
@@ -349,11 +339,18 @@ static int socket_load(Unit *u) {
 
                 if (have_non_accept_socket(s)) {
 
-                        if (!s->service)
-                                if ((r = unit_load_related_unit(u, ".service", (Unit**) &s->service)) < 0)
+                        if (!UNIT_DEREF(s->service)) {
+                                Unit *x;
+
+                                r = unit_load_related_unit(u, ".service", &x);
+                                if (r < 0)
                                         return r;
 
-                        if ((r = unit_add_dependency(u, UNIT_BEFORE, UNIT(s->service), true)) < 0)
+                                unit_ref_set(&s->service, x);
+                        }
+
+                        r = unit_add_two_dependencies(u, UNIT_BEFORE, UNIT_TRIGGERS, UNIT_DEREF(s->service), true);
+                        if (r < 0)
                                 return r;
                 }
 
@@ -912,8 +909,9 @@ static int socket_open_fds(Socket *s) {
                                 if ((r = socket_instantiate_service(s)) < 0)
                                         return r;
 
-                                if (s->service && s->service->exec_command[SERVICE_EXEC_START]) {
-                                        r = label_get_create_label_from_exe(s->service->exec_command[SERVICE_EXEC_START]->path, &label);
+                                if (UNIT_DEREF(s->service) &&
+                                    SERVICE(UNIT_DEREF(s->service))->exec_command[SERVICE_EXEC_START]) {
+                                        r = label_get_create_label_from_exe(SERVICE(UNIT_DEREF(s->service))->exec_command[SERVICE_EXEC_START]->path, &label);
 
                                         if (r < 0) {
                                                 if (r != -EPERM)
@@ -1380,26 +1378,20 @@ static void socket_enter_running(Socket *s, int cfd) {
         }
 
         if (cfd < 0) {
+                Iterator i;
+                Unit *u;
                 bool pending = false;
-                Meta *i;
 
                 /* If there's already a start pending don't bother to
                  * do anything */
-                LIST_FOREACH(units_by_type, i, s->meta.manager->units_by_type[UNIT_SERVICE]) {
-                        Service *service = (Service *) i;
-
-                        if (!set_get(service->configured_sockets, s))
-                                continue;
-
-                        if (!unit_pending_active(UNIT(service)))
-                                continue;
-
-                        pending = true;
-                        break;
-                }
+                SET_FOREACH(u, s->meta.dependencies[UNIT_TRIGGERS], i)
+                        if (unit_pending_active(u)) {
+                                pending = true;
+                                break;
+                        }
 
                 if (!pending)
-                        if ((r = manager_add_job(s->meta.manager, JOB_START, UNIT(s->service), JOB_REPLACE, true, &error, NULL)) < 0)
+                        if ((r = manager_add_job(s->meta.manager, JOB_START, UNIT_DEREF(s->service), JOB_REPLACE, true, &error, NULL)) < 0)
                                 goto fail;
 
                 socket_set_state(s, SOCKET_RUNNING);
@@ -1434,13 +1426,13 @@ static void socket_enter_running(Socket *s, int cfd) {
                         goto fail;
                 }
 
-                if ((r = unit_add_name(UNIT(s->service), name)) < 0) {
+                if ((r = unit_add_name(UNIT_DEREF(s->service), name)) < 0) {
                         free(name);
                         goto fail;
                 }
 
-                service = s->service;
-                s->service = NULL;
+                service = SERVICE(UNIT_DEREF(s->service));
+                unit_ref_unset(&s->service);
                 s->n_accepted ++;
 
                 service->meta.no_gc = false;
@@ -1523,23 +1515,27 @@ static int socket_start(Unit *u) {
                 return 0;
 
         /* Cannot run this without the service being around */
-        if (s->service) {
-                if (s->service->meta.load_state != UNIT_LOADED) {
-                        log_error("Socket service %s not loaded, refusing.", s->service->meta.id);
+        if (UNIT_DEREF(s->service)) {
+                Service *service;
+
+                service = SERVICE(UNIT_DEREF(s->service));
+
+                if (service->meta.load_state != UNIT_LOADED) {
+                        log_error("Socket service %s not loaded, refusing.", service->meta.id);
                         return -ENOENT;
                 }
 
                 /* If the service is already active we cannot start the
                  * socket */
-                if (s->service->state != SERVICE_DEAD &&
-                    s->service->state != SERVICE_FAILED &&
-                    s->service->state != SERVICE_AUTO_RESTART) {
-                        log_error("Socket service %s already active, refusing.", s->service->meta.id);
+                if (service->state != SERVICE_DEAD &&
+                    service->state != SERVICE_FAILED &&
+                    service->state != SERVICE_AUTO_RESTART) {
+                        log_error("Socket service %s already active, refusing.", service->meta.id);
                         return -EBUSY;
                 }
 
 #ifdef HAVE_SYSV_COMPAT
-                if (s->service->sysv_path) {
+                if (service->sysv_path) {
                         log_error("Using SysV services for socket activation is not supported. Refusing.");
                         return -ENOENT;
                 }
diff --git a/src/socket.h b/src/socket.h
index fbd29dad72..4fc2cbe690 100644
--- a/src/socket.h
+++ b/src/socket.h
@@ -28,6 +28,7 @@ typedef struct Socket Socket;
 #include "unit.h"
 #include "socket-util.h"
 #include "mount.h"
+#include "service.h"
 
 typedef enum SocketState {
         SOCKET_DEAD,
@@ -93,7 +94,7 @@ struct Socket {
         /* For Accept=no sockets refers to the one service we'll
         activate. For Accept=yes sockets is either NULL, or filled
         when the next service we spawn. */
-        Service *service;
+        UnitRef service;
 
         SocketState state, deserialized_state;
 
@@ -103,9 +104,6 @@ struct Socket {
         SocketExecCommand control_command_id;
         pid_t control_pid;
 
-        /* Only for INET6 sockets: issue IPV6_V6ONLY sockopt */
-        SocketAddressBindIPv6Only bind_ipv6_only;
-
         mode_t directory_mode;
         mode_t socket_mode;
 
@@ -130,6 +128,9 @@ struct Socket {
         char *tcp_congestion;
         long mq_maxmsg;
         long mq_msgsize;
+
+        /* Only for INET6 sockets: issue IPV6_V6ONLY sockopt */
+        SocketAddressBindIPv6Only bind_ipv6_only;
 };
 
 /* Called from the service code when collecting fds */
diff --git a/src/timer.c b/src/timer.c
index e6f207fbb6..c732076105 100644
--- a/src/timer.c
+++ b/src/timer.c
@@ -57,6 +57,8 @@ static void timer_done(Unit *u) {
         }
 
         unit_unwatch_timer(u, &t->timer_watch);
+
+        unit_ref_unset(&t->unit);
 }
 
 static int timer_verify(Timer *t) {
@@ -101,11 +103,18 @@ static int timer_load(Unit *u) {
 
         if (u->meta.load_state == UNIT_LOADED) {
 
-                if (!t->unit)
-                        if ((r = unit_load_related_unit(u, ".service", &t->unit)))
+                if (!UNIT_DEREF(t->unit)) {
+                        Unit *x;
+
+                        r = unit_load_related_unit(u, ".service", &x);
+                        if (r < 0)
                                 return r;
 
-                if ((r = unit_add_dependency(u, UNIT_BEFORE, t->unit, true)) < 0)
+                        unit_ref_set(&t->unit, x);
+                }
+
+                r = unit_add_two_dependencies(u, UNIT_BEFORE, UNIT_TRIGGERS, UNIT_DEREF(t->unit), true);
+                if (r < 0)
                         return r;
 
                 if (t->meta.default_dependencies)
@@ -126,7 +135,7 @@ static void timer_dump(Unit *u, FILE *f, const char *prefix) {
                 "%sTimer State: %s\n"
                 "%sUnit: %s\n",
                 prefix, timer_state_to_string(t->state),
-                prefix, t->unit->meta.id);
+                prefix, UNIT_DEREF(t->unit)->meta.id);
 
         LIST_FOREACH(value, v, t->values)
                 fprintf(f,
@@ -216,18 +225,18 @@ static void timer_enter_waiting(Timer *t, bool initial) {
 
                 case TIMER_UNIT_ACTIVE:
 
-                        if (t->unit->meta.inactive_exit_timestamp.monotonic <= 0)
+                        if (UNIT_DEREF(t->unit)->meta.inactive_exit_timestamp.monotonic <= 0)
                                 continue;
 
-                        base = t->unit->meta.inactive_exit_timestamp.monotonic;
+                        base = UNIT_DEREF(t->unit)->meta.inactive_exit_timestamp.monotonic;
                         break;
 
                 case TIMER_UNIT_INACTIVE:
 
-                        if (t->unit->meta.inactive_enter_timestamp.monotonic <= 0)
+                        if (UNIT_DEREF(t->unit)->meta.inactive_enter_timestamp.monotonic <= 0)
                                 continue;
 
-                        base = t->unit->meta.inactive_enter_timestamp.monotonic;
+                        base = UNIT_DEREF(t->unit)->meta.inactive_enter_timestamp.monotonic;
                         break;
 
                 default:
@@ -278,7 +287,7 @@ static void timer_enter_running(Timer *t) {
         if (t->meta.job && t->meta.job->type == JOB_STOP)
                 return;
 
-        if ((r = manager_add_job(t->meta.manager, JOB_START, t->unit, JOB_REPLACE, true, &error, NULL)) < 0)
+        if ((r = manager_add_job(t->meta.manager, JOB_START, UNIT_DEREF(t->unit), JOB_REPLACE, true, &error, NULL)) < 0)
                 goto fail;
 
         timer_set_state(t, TIMER_RUNNING);
@@ -297,7 +306,7 @@ static int timer_start(Unit *u) {
         assert(t);
         assert(t->state == TIMER_DEAD || t->state == TIMER_FAILED);
 
-        if (t->unit->meta.load_state != UNIT_LOADED)
+        if (UNIT_DEREF(t->unit)->meta.load_state != UNIT_LOADED)
                 return -ENOENT;
 
         t->failure = false;
@@ -374,37 +383,24 @@ static void timer_timer_event(Unit *u, uint64_t elapsed, Watch *w) {
 }
 
 void timer_unit_notify(Unit *u, UnitActiveState new_state) {
-        char *n;
         int r;
         Iterator i;
+        Unit *k;
 
         if (u->meta.type == UNIT_TIMER)
                 return;
 
-        SET_FOREACH(n, u->meta.names, i) {
-                char *k;
-                Unit *p;
+        SET_FOREACH(k, u->meta.dependencies[UNIT_TRIGGERED_BY], i) {
                 Timer *t;
                 TimerValue *v;
 
-                if (!(k = unit_name_change_suffix(n, ".timer"))) {
-                        r = -ENOMEM;
-                        goto fail;
-                }
-
-                p = manager_get_unit(u->meta.manager, k);
-                free(k);
-
-                if (!p)
+                if (k->meta.type != UNIT_TIMER)
                         continue;
 
-                if (p->meta.load_state != UNIT_LOADED)
+                if (k->meta.load_state != UNIT_LOADED)
                         continue;
 
-                t = TIMER(p);
-
-                if (t->unit != u)
-                        continue;
+                t = TIMER(k);
 
                 /* Reenable all timers that depend on unit state */
                 LIST_FOREACH(value, v, t->values)
@@ -438,11 +434,6 @@ void timer_unit_notify(Unit *u, UnitActiveState new_state) {
                         assert_not_reached("Unknown timer state");
                 }
         }
-
-        return;
-
-fail:
-        log_error("Failed find timer unit: %s", strerror(-r));
 }
 
 static void timer_reset_failed(Unit *u) {
diff --git a/src/timer.h b/src/timer.h
index 6295605510..ad55cf7c87 100644
--- a/src/timer.h
+++ b/src/timer.h
@@ -63,7 +63,7 @@ struct Timer {
         usec_t next_elapse;
 
         TimerState state, deserialized_state;
-        Unit *unit;
+        UnitRef unit;
 
         Watch timer_watch;
 
diff --git a/src/unit.c b/src/unit.c
index 8630c3c59d..3b476a8e02 100644
--- a/src/unit.c
+++ b/src/unit.c
@@ -377,12 +377,15 @@ void unit_free(Unit *u) {
 
         free(u->meta.description);
         free(u->meta.fragment_path);
+        free(u->meta.instance);
 
         set_free_free(u->meta.names);
 
         condition_free_list(u->meta.conditions);
 
-        free(u->meta.instance);
+        while (u->meta.refs)
+                unit_ref_unset(u->meta.refs);
+
         free(u);
 }
 
@@ -498,6 +501,10 @@ int unit_merge(Unit *u, Unit *other) {
         /* Merge names */
         merge_names(u, other);
 
+        /* Redirect all references */
+        while (other->meta.refs)
+                unit_ref_set(other->meta.refs, u);
+
         /* Merge dependencies */
         for (d = 0; d < _UNIT_DEPENDENCY_MAX; d++)
                 merge_dependencies(u, other, d);
@@ -1530,7 +1537,9 @@ int unit_add_dependency(Unit *u, UnitDependency d, Unit *other, bool add_referen
                 [UNIT_AFTER] = UNIT_BEFORE,
                 [UNIT_ON_FAILURE] = _UNIT_DEPENDENCY_INVALID,
                 [UNIT_REFERENCES] = UNIT_REFERENCED_BY,
-                [UNIT_REFERENCED_BY] = UNIT_REFERENCES
+                [UNIT_REFERENCED_BY] = UNIT_REFERENCES,
+                [UNIT_TRIGGERS] = UNIT_TRIGGERED_BY,
+                [UNIT_TRIGGERED_BY] = UNIT_TRIGGERS
         };
         int r, q = 0, v = 0, w = 0;
 
@@ -2592,6 +2601,28 @@ UnitFileState unit_get_unit_file_state(Unit *u) {
         return u->meta.unit_file_state;
 }
 
+Unit* unit_ref_set(UnitRef *ref, Unit *u) {
+        assert(ref);
+        assert(u);
+
+        if (ref->unit)
+                unit_ref_unset(ref);
+
+        ref->unit = u;
+        LIST_PREPEND(UnitRef, refs, u->meta.refs, ref);
+        return u;
+}
+
+void unit_ref_unset(UnitRef *ref) {
+        assert(ref);
+
+        if (!ref->unit)
+                return;
+
+        LIST_REMOVE(UnitRef, refs, ref->unit->meta.refs, ref);
+        ref->unit = NULL;
+}
+
 static const char* const unit_load_state_table[_UNIT_LOAD_STATE_MAX] = {
         [UNIT_STUB] = "stub",
         [UNIT_LOADED] = "loaded",
@@ -2630,7 +2661,9 @@ static const char* const unit_dependency_table[_UNIT_DEPENDENCY_MAX] = {
         [UNIT_AFTER] = "After",
         [UNIT_REFERENCES] = "References",
         [UNIT_REFERENCED_BY] = "ReferencedBy",
-        [UNIT_ON_FAILURE] = "OnFailure"
+        [UNIT_ON_FAILURE] = "OnFailure",
+        [UNIT_TRIGGERS] = "Triggers",
+        [UNIT_TRIGGERED_BY] = "TriggeredBy"
 };
 
 DEFINE_STRING_TABLE_LOOKUP(unit_dependency, UnitDependency);
diff --git a/src/unit.h b/src/unit.h
index b32c1a702e..4d83309591 100644
--- a/src/unit.h
+++ b/src/unit.h
@@ -32,6 +32,7 @@ typedef enum UnitType UnitType;
 typedef enum UnitLoadState UnitLoadState;
 typedef enum UnitActiveState UnitActiveState;
 typedef enum UnitDependency UnitDependency;
+typedef struct UnitRef UnitRef;
 
 #include "set.h"
 #include "util.h"
@@ -119,6 +120,10 @@ enum UnitDependency {
         /* On Failure */
         UNIT_ON_FAILURE,
 
+        /* Triggers (i.e. a socket triggers a service) */
+        UNIT_TRIGGERS,
+        UNIT_TRIGGERED_BY,
+
         /* Reference information for GC logic */
         UNIT_REFERENCES,              /* Inverse of 'references' is 'referenced_by' */
         UNIT_REFERENCED_BY,
@@ -156,6 +161,9 @@ struct Meta {
 
         usec_t job_timeout;
 
+        /* References to this */
+        LIST_HEAD(UnitRef, refs);
+
         /* Conditions to check */
         LIST_HEAD(Condition, conditions);
 
@@ -237,6 +245,15 @@ struct Meta {
         bool in_audit:1;
 };
 
+struct UnitRef {
+        /* Keeps tracks of references to a unit. This is useful so
+         * that we can merge two units if necessary and correct all
+         * references to them */
+
+        Unit* unit;
+        LIST_FIELDS(UnitRef, refs);
+};
+
 #include "service.h"
 #include "timer.h"
 #include "socket.h"
@@ -536,6 +553,11 @@ bool unit_condition_test(Unit *u);
 
 UnitFileState unit_get_unit_file_state(Unit *u);
 
+Unit* unit_ref_set(UnitRef *ref, Unit *u);
+void unit_ref_unset(UnitRef *ref);
+
+#define UNIT_DEREF(ref) ((ref).unit)
+
 const char *unit_load_state_to_string(UnitLoadState i);
 UnitLoadState unit_load_state_from_string(const char *s);