Merge pull request #4678 from poettering/gc-device

Automatically GC device jobs when there's no need to keep them in the job queue anymore.
Implement systemctl list-jobs --before/--after.
Allow systemd-run -p After/Before/Wants/Requires= ...

19 files changed, 575 insertions, 72 deletions

diff --git a/TODO b/TODO
index baaac9407f..887ddcd081 100644
--- a/TODO
+++ b/TODO
@@ -560,7 +560,6 @@ Features:
   - man: maybe sort directives in man pages, and take sections from --help and apply them to man too
 
 * systemctl:
-  - systemctl list-jobs - show dependencies
   - add systemctl switch to dump transaction without executing it
   - Add a verbose mode to "systemctl start" and friends that explains what is being done or not done
   - "systemctl disable" on a static unit prints no message and does
@@ -735,7 +734,6 @@ Features:
   - maybe introduce WantsMountsFor=? Usecase:
     http://lists.freedesktop.org/archives/systemd-devel/2015-January/027729.html
   - recreate systemd's D-Bus private socket file on SIGUSR2
-  - GC unreferenced jobs (such as .device jobs)
   - move PAM code into its own binary
   - when we automatically restart a service, ensure we restart its rdeps, too.
   - hide PAM options in fragment parser when compile time disabled
diff --git a/man/systemctl.xml b/man/systemctl.xml
index dfa00e0c03..08c3a268bd 100644
--- a/man/systemctl.xml
+++ b/man/systemctl.xml
@@ -209,6 +209,10 @@
           <varname>RequiresMountsFor=</varname>). Both explicitly
           and implicitly introduced dependencies are shown with
           <command>list-dependencies</command>.</para>
+
+          <para>When passed to the <command>list-jobs</command> command, for each printed job show which other jobs are
+          waiting for it. May be combined with <option>--before</option> to show both the jobs waiting for each job as
+          well as all jobs each job is waiting for.</para>
         </listitem>
       </varlistentry>
 
@@ -220,6 +224,10 @@
           units that are ordered after the specified unit. In other
           words, recursively list units following the
           <varname>Before=</varname> dependency.</para>
+
+          <para>When passed to the <command>list-jobs</command> command, for each printed job show which other jobs it
+          is waiting for. May be combined with <option>--after</option> to show both the jobs waiting for each job as
+          well as all jobs each job is waiting for.</para>
         </listitem>
       </varlistentry>
 
@@ -1388,6 +1396,10 @@ kobject-uevent 1 systemd-udevd-kernel.socket systemd-udevd.service
             <para>List jobs that are in progress. If one or more
             <replaceable>PATTERN</replaceable>s are specified, only
             jobs for units matching one of them are shown.</para>
+
+            <para>When combined with <option>--after</option> or <option>--before</option> the list is augmented with
+            information on which other job each job is waiting for, and which other jobs are waiting for it, see
+            above.</para>
           </listitem>
         </varlistentry>
         <varlistentry>
diff --git a/src/core/dbus-job.c b/src/core/dbus-job.c
index ccf7453d47..087a08dc0d 100644
--- a/src/core/dbus-job.c
+++ b/src/core/dbus-job.c
@@ -65,7 +65,7 @@ int bus_job_method_cancel(sd_bus_message *message, void *userdata, sd_bus_error
                 return r;
 
         /* Access is granted to the job owner */
-        if (!sd_bus_track_contains(j->clients, sd_bus_message_get_sender(message))) {
+        if (!sd_bus_track_contains(j->bus_track, sd_bus_message_get_sender(message))) {
 
                 /* And for everybody else consult PolicyKit */
                 r = bus_verify_manage_units_async(j->unit->manager, message, error);
@@ -80,9 +80,61 @@ int bus_job_method_cancel(sd_bus_message *message, void *userdata, sd_bus_error
         return sd_bus_reply_method_return(message, NULL);
 }
 
+int bus_job_method_get_waiting_jobs(sd_bus_message *message, void *userdata, sd_bus_error *error) {
+        _cleanup_(sd_bus_message_unrefp) sd_bus_message *reply = NULL;
+        _cleanup_free_ Job **list = NULL;
+        Job *j = userdata;
+        int r, i, n;
+
+        if (strstr(sd_bus_message_get_member(message), "After"))
+                n = job_get_after(j, &list);
+        else
+                n = job_get_before(j, &list);
+        if (n < 0)
+                return n;
+
+        r = sd_bus_message_new_method_return(message, &reply);
+        if (r < 0)
+                return r;
+
+        r = sd_bus_message_open_container(reply, 'a', "(usssoo)");
+        if (r < 0)
+                return r;
+
+        for (i = 0; i < n; i ++) {
+                _cleanup_free_ char *unit_path = NULL, *job_path = NULL;
+
+                job_path = job_dbus_path(list[i]);
+                if (!job_path)
+                        return -ENOMEM;
+
+                unit_path = unit_dbus_path(list[i]->unit);
+                if (!unit_path)
+                        return -ENOMEM;
+
+                r = sd_bus_message_append(reply, "(usssoo)",
+                                          list[i]->id,
+                                          list[i]->unit->id,
+                                          job_type_to_string(list[i]->type),
+                                          job_state_to_string(list[i]->state),
+                                          job_path,
+                                          unit_path);
+                if (r < 0)
+                        return r;
+        }
+
+        r = sd_bus_message_close_container(reply);
+        if (r < 0)
+                return r;
+
+        return sd_bus_send(NULL, reply, NULL);
+}
+
 const sd_bus_vtable bus_job_vtable[] = {
         SD_BUS_VTABLE_START(0),
         SD_BUS_METHOD("Cancel", NULL, NULL, bus_job_method_cancel, SD_BUS_VTABLE_UNPRIVILEGED),
+        SD_BUS_METHOD("GetAfter", NULL, "a(usssoo)", bus_job_method_get_waiting_jobs, SD_BUS_VTABLE_UNPRIVILEGED),
+        SD_BUS_METHOD("GetBefore", NULL, "a(usssoo)", bus_job_method_get_waiting_jobs, SD_BUS_VTABLE_UNPRIVILEGED),
         SD_BUS_PROPERTY("Id", "u", NULL, offsetof(Job, id), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("Unit", "(so)", property_get_unit, 0, SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("JobType", "s", property_get_type, offsetof(Job, type), SD_BUS_VTABLE_PROPERTY_CONST),
@@ -143,7 +195,7 @@ void bus_job_send_change_signal(Job *j) {
                 j->in_dbus_queue = false;
         }
 
-        r = bus_foreach_bus(j->manager, j->clients, j->sent_dbus_new_signal ? send_changed_signal : send_new_signal, j);
+        r = bus_foreach_bus(j->manager, j->bus_track, j->sent_dbus_new_signal ? send_changed_signal : send_new_signal, j);
         if (r < 0)
                 log_debug_errno(r, "Failed to send job change signal for %u: %m", j->id);
 
@@ -187,7 +239,75 @@ void bus_job_send_removed_signal(Job *j) {
         if (!j->sent_dbus_new_signal)
                 bus_job_send_change_signal(j);
 
-        r = bus_foreach_bus(j->manager, j->clients, send_removed_signal, j);
+        r = bus_foreach_bus(j->manager, j->bus_track, send_removed_signal, j);
         if (r < 0)
                 log_debug_errno(r, "Failed to send job remove signal for %u: %m", j->id);
 }
+
+static int bus_job_track_handler(sd_bus_track *t, void *userdata) {
+        Job *j = userdata;
+
+        assert(t);
+        assert(j);
+
+        j->bus_track = sd_bus_track_unref(j->bus_track); /* make sure we aren't called again */
+
+        /* Last client dropped off the bus, maybe we should GC this now? */
+        job_add_to_gc_queue(j);
+        return 0;
+}
+
+static int bus_job_allocate_bus_track(Job *j) {
+        int r;
+
+        assert(j);
+
+        if (j->bus_track)
+                return 0;
+
+        r = sd_bus_track_new(j->unit->manager->api_bus, &j->bus_track, bus_job_track_handler, j);
+        if (r < 0)
+                return r;
+
+        return 0;
+}
+
+int bus_job_coldplug_bus_track(Job *j) {
+        int r = 0;
+
+        assert(j);
+
+        if (strv_isempty(j->deserialized_clients))
+                goto finish;
+
+        if (!j->manager->api_bus)
+                goto finish;
+
+        r = bus_job_allocate_bus_track(j);
+        if (r < 0)
+                goto finish;
+
+        r = bus_track_add_name_many(j->bus_track, j->deserialized_clients);
+
+finish:
+        j->deserialized_clients = strv_free(j->deserialized_clients);
+        return r;
+}
+
+int bus_job_track_sender(Job *j, sd_bus_message *m) {
+        int r;
+
+        assert(j);
+        assert(m);
+
+        if (sd_bus_message_get_bus(m) != j->unit->manager->api_bus) {
+                j->ref_by_private_bus = true;
+                return 0;
+        }
+
+        r = bus_job_allocate_bus_track(j);
+        if (r < 0)
+                return r;
+
+        return sd_bus_track_add_sender(j->bus_track, m);
+}
diff --git a/src/core/dbus-job.h b/src/core/dbus-job.h
index 024d06719e..a4366a0720 100644
--- a/src/core/dbus-job.h
+++ b/src/core/dbus-job.h
@@ -26,6 +26,10 @@
 extern const sd_bus_vtable bus_job_vtable[];
 
 int bus_job_method_cancel(sd_bus_message *message, void *job, sd_bus_error *error);
+int bus_job_method_get_waiting_jobs(sd_bus_message *message, void *userdata, sd_bus_error *error);
 
 void bus_job_send_change_signal(Job *j);
 void bus_job_send_removed_signal(Job *j);
+
+int bus_job_coldplug_bus_track(Job *j);
+int bus_job_track_sender(Job *j, sd_bus_message *m);
diff --git a/src/core/dbus-manager.c b/src/core/dbus-manager.c
index 5a7922a249..9af49dd1bc 100644
--- a/src/core/dbus-manager.c
+++ b/src/core/dbus-manager.c
@@ -2285,6 +2285,26 @@ static int method_get_unit_file_links(sd_bus_message *message, void *userdata, s
         return sd_bus_send(NULL, reply, NULL);
 }
 
+static int method_get_job_waiting(sd_bus_message *message, void *userdata, sd_bus_error *error) {
+        Manager *m = userdata;
+        uint32_t id;
+        Job *j;
+        int r;
+
+        assert(message);
+        assert(m);
+
+        r = sd_bus_message_read(message, "u", &id);
+        if (r < 0)
+                return r;
+
+        j = manager_get_job(m, id);
+        if (!j)
+                return sd_bus_error_setf(error, BUS_ERROR_NO_SUCH_JOB, "Job %u does not exist.", (unsigned) id);
+
+        return bus_job_method_get_waiting_jobs(message, j, error);
+}
+
 const sd_bus_vtable bus_manager_vtable[] = {
         SD_BUS_VTABLE_START(0),
 
@@ -2390,6 +2410,8 @@ const sd_bus_vtable bus_manager_vtable[] = {
         SD_BUS_METHOD("StartTransientUnit", "ssa(sv)a(sa(sv))", "o", method_start_transient_unit, SD_BUS_VTABLE_UNPRIVILEGED),
         SD_BUS_METHOD("GetUnitProcesses", "s", "a(sus)", method_get_unit_processes, SD_BUS_VTABLE_UNPRIVILEGED),
         SD_BUS_METHOD("GetJob", "u", "o", method_get_job, SD_BUS_VTABLE_UNPRIVILEGED),
+        SD_BUS_METHOD("GetJobAfter", "u", "a(usssoo)", method_get_job_waiting, SD_BUS_VTABLE_UNPRIVILEGED),
+        SD_BUS_METHOD("GetJobBefore", "u", "a(usssoo)", method_get_job_waiting, SD_BUS_VTABLE_UNPRIVILEGED),
         SD_BUS_METHOD("CancelJob", "u", NULL, method_cancel_job, SD_BUS_VTABLE_UNPRIVILEGED),
         SD_BUS_METHOD("ClearJobs", NULL, NULL, method_clear_jobs, SD_BUS_VTABLE_UNPRIVILEGED),
         SD_BUS_METHOD("ResetFailed", NULL, NULL, method_reset_failed, SD_BUS_VTABLE_UNPRIVILEGED),
diff --git a/src/core/dbus-unit.c b/src/core/dbus-unit.c
index b6cb6e1350..2adc1d9288 100644
--- a/src/core/dbus-unit.c
+++ b/src/core/dbus-unit.c
@@ -22,6 +22,7 @@
 #include "alloc-util.h"
 #include "bus-common-errors.h"
 #include "cgroup-util.h"
+#include "dbus-job.h"
 #include "dbus-unit.h"
 #include "dbus.h"
 #include "fd-util.h"
@@ -1223,17 +1224,9 @@ int bus_unit_queue_job(
         if (r < 0)
                 return r;
 
-        if (sd_bus_message_get_bus(message) == u->manager->api_bus) {
-                if (!j->clients) {
-                        r = sd_bus_track_new(sd_bus_message_get_bus(message), &j->clients, NULL, NULL);
-                        if (r < 0)
-                                return r;
-                }
-
-                r = sd_bus_track_add_sender(j->clients, message);
-                if (r < 0)
-                        return r;
-        }
+        r = bus_job_track_sender(j, message);
+        if (r < 0)
+                return r;
 
         path = job_dbus_path(j);
         if (!path)
@@ -1507,7 +1500,7 @@ int bus_unit_check_load_state(Unit *u, sd_bus_error *error) {
         return sd_bus_error_set_errnof(error, u->load_error, "Unit %s is not loaded properly: %m.", u->id);
 }
 
-static int bus_track_handler(sd_bus_track *t, void *userdata) {
+static int bus_unit_track_handler(sd_bus_track *t, void *userdata) {
         Unit *u = userdata;
 
         assert(t);
@@ -1519,7 +1512,7 @@ static int bus_track_handler(sd_bus_track *t, void *userdata) {
         return 0;
 }
 
-static int allocate_bus_track(Unit *u) {
+static int bus_unit_allocate_bus_track(Unit *u) {
         int r;
 
         assert(u);
@@ -1527,7 +1520,7 @@ static int allocate_bus_track(Unit *u) {
         if (u->bus_track)
                 return 0;
 
-        r = sd_bus_track_new(u->manager->api_bus, &u->bus_track, bus_track_handler, u);
+        r = sd_bus_track_new(u->manager->api_bus, &u->bus_track, bus_unit_track_handler, u);
         if (r < 0)
                 return r;
 
@@ -1545,7 +1538,7 @@ int bus_unit_track_add_name(Unit *u, const char *name) {
 
         assert(u);
 
-        r = allocate_bus_track(u);
+        r = bus_unit_allocate_bus_track(u);
         if (r < 0)
                 return r;
 
@@ -1557,7 +1550,7 @@ int bus_unit_track_add_sender(Unit *u, sd_bus_message *m) {
 
         assert(u);
 
-        r = allocate_bus_track(u);
+        r = bus_unit_allocate_bus_track(u);
         if (r < 0)
                 return r;
 
diff --git a/src/core/dbus.c b/src/core/dbus.c
index 070974fe66..07ab21f199 100644
--- a/src/core/dbus.c
+++ b/src/core/dbus.c
@@ -1054,8 +1054,8 @@ static void destroy_bus(Manager *m, sd_bus **bus) {
                 m->subscribed = sd_bus_track_unref(m->subscribed);
 
         HASHMAP_FOREACH(j, m->jobs, i)
-                if (j->clients && sd_bus_track_get_bus(j->clients) == *bus)
-                        j->clients = sd_bus_track_unref(j->clients);
+                if (j->bus_track && sd_bus_track_get_bus(j->bus_track) == *bus)
+                        j->bus_track = sd_bus_track_unref(j->bus_track);
 
         /* Get rid of queued message on this bus */
         if (m->queued_message && sd_bus_message_get_bus(m->queued_message) == *bus)
@@ -1185,7 +1185,6 @@ void bus_track_serialize(sd_bus_track *t, FILE *f, const char *prefix) {
 }
 
 int bus_track_coldplug(Manager *m, sd_bus_track **t, bool recursive, char **l) {
-        char **i;
         int r = 0;
 
         assert(m);
@@ -1207,16 +1206,7 @@ int bus_track_coldplug(Manager *m, sd_bus_track **t, bool recursive, char **l) {
         if (r < 0)
                 return r;
 
-        r = 0;
-        STRV_FOREACH(i, l) {
-                int k;
-
-                k = sd_bus_track_add_name(*t, *i);
-                if (k < 0)
-                        r = k;
-        }
-
-        return r;
+        return bus_track_add_name_many(*t, l);
 }
 
 int bus_verify_manage_units_async(Manager *m, sd_bus_message *call, sd_bus_error *error) {
diff --git a/src/core/device.c b/src/core/device.c
index c572a6737c..074e93ffe2 100644
--- a/src/core/device.c
+++ b/src/core/device.c
@@ -831,6 +831,8 @@ const UnitVTable device_vtable = {
                 "Device\0"
                 "Install\0",
 
+        .gc_jobs = true,
+
         .init = device_init,
         .done = device_done,
         .load = unit_load_fragment_and_dropin_optional,
diff --git a/src/core/job.c b/src/core/job.c
index ac6910a906..2ba4c78096 100644
--- a/src/core/job.c
+++ b/src/core/job.c
@@ -90,9 +90,12 @@ void job_free(Job *j) {
         if (j->in_dbus_queue)
                 LIST_REMOVE(dbus_queue, j->manager->dbus_job_queue, j);
 
+        if (j->in_gc_queue)
+                LIST_REMOVE(gc_queue, j->manager->gc_job_queue, j);
+
         sd_event_source_unref(j->timer_event_source);
 
-        sd_bus_track_unref(j->clients);
+        sd_bus_track_unref(j->bus_track);
         strv_free(j->deserialized_clients);
 
         free(j);
@@ -226,6 +229,9 @@ Job* job_install(Job *j) {
         log_unit_debug(j->unit,
                        "Installed new job %s/%s as %u",
                        j->unit->id, job_type_to_string(j->type), (unsigned) j->id);
+
+        job_add_to_gc_queue(j);
+
         return j;
 }
 
@@ -267,7 +273,8 @@ JobDependency* job_dependency_new(Job *subject, Job *object, bool matters, bool
          * this means the 'anchor' job (i.e. the one the user
          * explicitly asked for) is the requester. */
 
-        if (!(l = new0(JobDependency, 1)))
+        l = new0(JobDependency, 1);
+        if (!l)
                 return NULL;
 
         l->subject = subject;
@@ -457,9 +464,7 @@ static bool job_is_runnable(Job *j) {
         if (j->type == JOB_NOP)
                 return true;
 
-        if (j->type == JOB_START ||
-            j->type == JOB_VERIFY_ACTIVE ||
-            j->type == JOB_RELOAD) {
+        if (IN_SET(j->type, JOB_START, JOB_VERIFY_ACTIVE, JOB_RELOAD)) {
 
                 /* Immediate result is that the job is or might be
                  * started. In this case let's wait for the
@@ -476,8 +481,7 @@ static bool job_is_runnable(Job *j) {
 
         SET_FOREACH(other, j->unit->dependencies[UNIT_BEFORE], i)
                 if (other->job &&
-                    (other->job->type == JOB_STOP ||
-                     other->job->type == JOB_RESTART))
+                    IN_SET(other->job->type, JOB_STOP, JOB_RESTART))
                         return false;
 
         /* This means that for a service a and a service b where b
@@ -641,6 +645,7 @@ _pure_ static const char *job_get_status_message_format(Unit *u, JobType t, JobR
                 [JOB_DEPENDENCY]  = "Dependency failed for %s.",
                 [JOB_ASSERT]      = "Assertion failed for %s.",
                 [JOB_UNSUPPORTED] = "Starting of %s not supported.",
+                [JOB_COLLECTED]   = "Unecessary job for %s was removed.",
         };
         static const char *const generic_finished_stop_job[_JOB_RESULT_MAX] = {
                 [JOB_DONE]        = "Stopped %s.",
@@ -700,6 +705,7 @@ static void job_print_status_message(Unit *u, JobType t, JobResult result) {
                 [JOB_SKIPPED]     = { ANSI_HIGHLIGHT,        " INFO " },
                 [JOB_ASSERT]      = { ANSI_HIGHLIGHT_YELLOW, "ASSERT" },
                 [JOB_UNSUPPORTED] = { ANSI_HIGHLIGHT_YELLOW, "UNSUPP" },
+                [JOB_COLLECTED]   = { ANSI_HIGHLIGHT,        " INFO " },
         };
 
         const char *format;
@@ -751,6 +757,7 @@ static void job_log_status_message(Unit *u, JobType t, JobResult result) {
                 [JOB_INVALID]     = LOG_INFO,
                 [JOB_ASSERT]      = LOG_WARNING,
                 [JOB_UNSUPPORTED] = LOG_WARNING,
+                [JOB_COLLECTED]   = LOG_INFO,
         };
 
         assert(u);
@@ -862,6 +869,7 @@ int job_finish_and_invalidate(Job *j, JobResult result, bool recursive, bool alr
                 job_set_state(j, JOB_WAITING);
 
                 job_add_to_run_queue(j);
+                job_add_to_gc_queue(j);
 
                 goto finish;
         }
@@ -905,11 +913,15 @@ int job_finish_and_invalidate(Job *j, JobResult result, bool recursive, bool alr
 finish:
         /* Try to start the next jobs that can be started */
         SET_FOREACH(other, u->dependencies[UNIT_AFTER], i)
-                if (other->job)
+                if (other->job) {
                         job_add_to_run_queue(other->job);
+                        job_add_to_gc_queue(other->job);
+                }
         SET_FOREACH(other, u->dependencies[UNIT_BEFORE], i)
-                if (other->job)
+                if (other->job) {
                         job_add_to_run_queue(other->job);
+                        job_add_to_gc_queue(other->job);
+                }
 
         manager_check_finished(u->manager);
 
@@ -1012,7 +1024,7 @@ int job_serialize(Job *j, FILE *f) {
         if (j->begin_usec > 0)
                 fprintf(f, "job-begin="USEC_FMT"\n", j->begin_usec);
 
-        bus_track_serialize(j->clients, f, "subscribed");
+        bus_track_serialize(j->bus_track, f, "subscribed");
 
         /* End marker */
         fputc('\n', f);
@@ -1123,12 +1135,14 @@ int job_coldplug(Job *j) {
 
         /* After deserialization is complete and the bus connection
          * set up again, let's start watching our subscribers again */
-        (void) bus_track_coldplug(j->manager, &j->clients, false, j->deserialized_clients);
-        j->deserialized_clients = strv_free(j->deserialized_clients);
+        (void) bus_job_coldplug_bus_track(j);
 
         if (j->state == JOB_WAITING)
                 job_add_to_run_queue(j);
 
+        /* Maybe due to new dependencies we don't actually need this job anymore? */
+        job_add_to_gc_queue(j);
+
         if (j->begin_usec == 0 || j->unit->job_timeout == USEC_INFINITY)
                 return 0;
 
@@ -1203,9 +1217,225 @@ int job_get_timeout(Job *j, usec_t *timeout) {
         return 1;
 }
 
+bool job_check_gc(Job *j) {
+        Unit *other;
+        Iterator i;
+
+        assert(j);
+
+        /* Checks whether this job should be GC'ed away. We only do this for jobs of units that have no effect on their
+         * own and just track external state. For now the only unit type that qualifies for this are .device units. */
+
+        if (!UNIT_VTABLE(j->unit)->gc_jobs)
+                return true;
+
+        if (sd_bus_track_count(j->bus_track) > 0)
+                return true;
+
+        /* FIXME: So this is a bit ugly: for now we don't properly track references made via private bus connections
+         * (because it's nasty, as sd_bus_track doesn't apply to it). We simply remember that the job was once
+         * referenced by one, and reset this whenever we notice that no private bus connections are around. This means
+         * the GC is a bit too conservative when it comes to jobs created by private bus connections. */
+        if (j->ref_by_private_bus) {
+                if (set_isempty(j->unit->manager->private_buses))
+                        j->ref_by_private_bus = false;
+                else
+                        return true;
+        }
+
+        if (j->type == JOB_NOP)
+                return true;
+
+        /* If a job is ordered after ours, and is to be started, then it needs to wait for us, regardless if we stop or
+         * start, hence let's not GC in that case. */
+        SET_FOREACH(other, j->unit->dependencies[UNIT_BEFORE], i) {
+                if (!other->job)
+                        continue;
+
+                if (other->job->ignore_order)
+                        continue;
+
+                if (IN_SET(other->job->type, JOB_START, JOB_VERIFY_ACTIVE, JOB_RELOAD))
+                        return true;
+        }
+
+        /* If we are going down, but something else is orederd After= us, then it needs to wait for us */
+        if (IN_SET(j->type, JOB_STOP, JOB_RESTART)) {
+
+                SET_FOREACH(other, j->unit->dependencies[UNIT_AFTER], i) {
+                        if (!other->job)
+                                continue;
+
+                        if (other->job->ignore_order)
+                                continue;
+
+                        return true;
+                }
+        }
+
+        /* The logic above is kinda the inverse of the job_is_runnable() logic. Specifically, if the job "we" is
+         * ordered before the job "other":
+         *
+         *  we start + other start → stay
+         *  we start + other stop  → gc
+         *  we stop  + other start → stay
+         *  we stop  + other stop  → gc
+         *
+         * "we" are ordered after "other":
+         *
+         *  we start + other start → gc
+         *  we start + other stop  → gc
+         *  we stop  + other start → stay
+         *  we stop  + other stop  → stay
+         *
+         */
+
+        return false;
+}
+
+void job_add_to_gc_queue(Job *j) {
+        assert(j);
+
+        if (j->in_gc_queue)
+                return;
+
+        if (job_check_gc(j))
+                return;
+
+        LIST_PREPEND(gc_queue, j->unit->manager->gc_job_queue, j);
+        j->in_gc_queue = true;
+}
+
+static int job_compare(const void *a, const void *b) {
+        Job *x = *(Job**) a, *y = *(Job**) b;
+
+        if (x->id < y->id)
+                return -1;
+        if (x->id > y->id)
+                return 1;
+
+        return 0;
+}
+
+static size_t sort_job_list(Job **list, size_t n) {
+        Job *previous = NULL;
+        size_t a, b;
+
+        /* Order by numeric IDs */
+        qsort_safe(list, n, sizeof(Job*), job_compare);
+
+        /* Filter out duplicates */
+        for (a = 0, b = 0; a < n; a++) {
+
+                if (previous == list[a])
+                        continue;
+
+                previous = list[b++] = list[a];
+        }
+
+        return b;
+}
+
+int job_get_before(Job *j, Job*** ret) {
+        _cleanup_free_ Job** list = NULL;
+        size_t n = 0, n_allocated = 0;
+        Unit *other = NULL;
+        Iterator i;
+
+        /* Returns a list of all pending jobs that need to finish before this job may be started. */
+
+        assert(j);
+        assert(ret);
+
+        if (j->ignore_order) {
+                *ret = NULL;
+                return 0;
+        }
+
+        if (IN_SET(j->type, JOB_START, JOB_VERIFY_ACTIVE, JOB_RELOAD)) {
+
+                SET_FOREACH(other, j->unit->dependencies[UNIT_AFTER], i) {
+                        if (!other->job)
+                                continue;
+
+                        if (!GREEDY_REALLOC(list, n_allocated, n+1))
+                                return -ENOMEM;
+                        list[n++] = other->job;
+                }
+        }
+
+        SET_FOREACH(other, j->unit->dependencies[UNIT_BEFORE], i) {
+                if (!other->job)
+                        continue;
+
+                if (!IN_SET(other->job->type, JOB_STOP, JOB_RESTART))
+                        continue;
+
+                if (!GREEDY_REALLOC(list, n_allocated, n+1))
+                        return -ENOMEM;
+                list[n++] = other->job;
+        }
+
+        n = sort_job_list(list, n);
+
+        *ret = list;
+        list = NULL;
+
+        return (int) n;
+}
+
+int job_get_after(Job *j, Job*** ret) {
+        _cleanup_free_ Job** list = NULL;
+        size_t n = 0, n_allocated = 0;
+        Unit *other = NULL;
+        Iterator i;
+
+        assert(j);
+        assert(ret);
+
+        /* Returns a list of all pending jobs that are waiting for this job to finish. */
+
+        SET_FOREACH(other, j->unit->dependencies[UNIT_BEFORE], i) {
+                if (!other->job)
+                        continue;
+
+                if (other->job->ignore_order)
+                        continue;
+
+                if (!IN_SET(other->job->type, JOB_START, JOB_VERIFY_ACTIVE, JOB_RELOAD))
+                        continue;
+
+                if (!GREEDY_REALLOC(list, n_allocated, n+1))
+                        return -ENOMEM;
+                list[n++] = other->job;
+        }
+
+        if (IN_SET(j->type, JOB_STOP, JOB_RESTART)) {
+
+                SET_FOREACH(other, j->unit->dependencies[UNIT_AFTER], i) {
+                        if (!other->job)
+                                continue;
+
+                        if (other->job->ignore_order)
+                                continue;
+
+                        if (!GREEDY_REALLOC(list, n_allocated, n+1))
+                                return -ENOMEM;
+                        list[n++] = other->job;
+                }
+        }
+
+        n = sort_job_list(list, n);
+
+        *ret = list;
+        list = NULL;
+
+        return (int) n;
+}
+
 static const char* const job_state_table[_JOB_STATE_MAX] = {
         [JOB_WAITING] = "waiting",
-        [JOB_RUNNING] = "running"
+        [JOB_RUNNING] = "running",
 };
 
 DEFINE_STRING_TABLE_LOOKUP(job_state, JobState);
@@ -1246,6 +1476,7 @@ static const char* const job_result_table[_JOB_RESULT_MAX] = {
         [JOB_INVALID] = "invalid",
         [JOB_ASSERT] = "assert",
         [JOB_UNSUPPORTED] = "unsupported",
+        [JOB_COLLECTED] = "collected",
 };
 
 DEFINE_STRING_TABLE_LOOKUP(job_result, JobResult);
diff --git a/src/core/job.h b/src/core/job.h
index 85368f0d30..bea743f462 100644
--- a/src/core/job.h
+++ b/src/core/job.h
@@ -107,6 +107,7 @@ enum JobResult {
         JOB_INVALID,             /* JOB_RELOAD of inactive unit */
         JOB_ASSERT,              /* Couldn't start a unit, because an assert didn't hold */
         JOB_UNSUPPORTED,         /* Couldn't start a unit, because the unit type is not supported on the system */
+        JOB_COLLECTED,           /* Job was garbage collected, since nothing needed it anymore */
         _JOB_RESULT_MAX,
         _JOB_RESULT_INVALID = -1
 };
@@ -122,8 +123,8 @@ struct JobDependency {
         LIST_FIELDS(JobDependency, subject);
         LIST_FIELDS(JobDependency, object);
 
-        bool matters;
-        bool conflicts;
+        bool matters:1;
+        bool conflicts:1;
 };
 
 struct Job {
@@ -133,6 +134,7 @@ struct Job {
         LIST_FIELDS(Job, transaction);
         LIST_FIELDS(Job, run_queue);
         LIST_FIELDS(Job, dbus_queue);
+        LIST_FIELDS(Job, gc_queue);
 
         LIST_HEAD(JobDependency, subject_list);
         LIST_HEAD(JobDependency, object_list);
@@ -156,7 +158,7 @@ struct Job {
          *
          * There can be more than one client, because of job merging.
          */
-        sd_bus_track *clients;
+        sd_bus_track *bus_track;
         char **deserialized_clients;
 
         JobResult result;
@@ -168,6 +170,8 @@ struct Job {
         bool sent_dbus_new_signal:1;
         bool ignore_order:1;
         bool irreversible:1;
+        bool in_gc_queue:1;
+        bool ref_by_private_bus:1;
 };
 
 Job* job_new(Unit *unit, JobType type);
@@ -227,6 +231,12 @@ void job_shutdown_magic(Job *j);
 
 int job_get_timeout(Job *j, usec_t *timeout) _pure_;
 
+bool job_check_gc(Job *j);
+void job_add_to_gc_queue(Job *j);
+
+int job_get_before(Job *j, Job*** ret);
+int job_get_after(Job *j, Job*** ret);
+
 const char* job_type_to_string(JobType t) _const_;
 JobType job_type_from_string(const char *s) _pure_;
 
diff --git a/src/core/manager.c b/src/core/manager.c
index 52174eac07..31770eef3a 100644
--- a/src/core/manager.c
+++ b/src/core/manager.c
@@ -981,10 +981,9 @@ good:
         unit_gc_mark_good(u, gc_marker);
 }
 
-static unsigned manager_dispatch_gc_queue(Manager *m) {
+static unsigned manager_dispatch_gc_unit_queue(Manager *m) {
+        unsigned n = 0, gc_marker;
         Unit *u;
-        unsigned n = 0;
-        unsigned gc_marker;
 
         assert(m);
 
@@ -996,12 +995,12 @@ static unsigned manager_dispatch_gc_queue(Manager *m) {
 
         gc_marker = m->gc_marker;
 
-        while ((u = m->gc_queue)) {
+        while ((u = m->gc_unit_queue)) {
                 assert(u->in_gc_queue);
 
                 unit_gc_sweep(u, gc_marker);
 
-                LIST_REMOVE(gc_queue, m->gc_queue, u);
+                LIST_REMOVE(gc_queue, m->gc_unit_queue, u);
                 u->in_gc_queue = false;
 
                 n++;
@@ -1015,7 +1014,29 @@ static unsigned manager_dispatch_gc_queue(Manager *m) {
                 }
         }
 
-        m->n_in_gc_queue = 0;
+        return n;
+}
+
+static unsigned manager_dispatch_gc_job_queue(Manager *m) {
+        unsigned n = 0;
+        Job *j;
+
+        assert(m);
+
+        while ((j = m->gc_job_queue)) {
+                assert(j->in_gc_queue);
+
+                LIST_REMOVE(gc_queue, m->gc_job_queue, j);
+                j->in_gc_queue = false;
+
+                n++;
+
+                if (job_check_gc(j))
+                        continue;
+
+                log_unit_debug(j->unit, "Collecting job.");
+                (void) job_finish_and_invalidate(j, JOB_COLLECTED, false, false);
+        }
 
         return n;
 }
@@ -1035,7 +1056,8 @@ static void manager_clear_jobs_and_units(Manager *m) {
         assert(!m->dbus_unit_queue);
         assert(!m->dbus_job_queue);
         assert(!m->cleanup_queue);
-        assert(!m->gc_queue);
+        assert(!m->gc_unit_queue);
+        assert(!m->gc_job_queue);
 
         assert(hashmap_isempty(m->jobs));
         assert(hashmap_isempty(m->units));
@@ -2228,7 +2250,10 @@ int manager_loop(Manager *m) {
                 if (manager_dispatch_load_queue(m) > 0)
                         continue;
 
-                if (manager_dispatch_gc_queue(m) > 0)
+                if (manager_dispatch_gc_job_queue(m) > 0)
+                        continue;
+
+                if (manager_dispatch_gc_unit_queue(m) > 0)
                         continue;
 
                 if (manager_dispatch_cleanup_queue(m) > 0)
diff --git a/src/core/manager.h b/src/core/manager.h
index 35172fdba9..d54ca54107 100644
--- a/src/core/manager.h
+++ b/src/core/manager.h
@@ -104,8 +104,9 @@ struct Manager {
         /* Units to remove */
         LIST_HEAD(Unit, cleanup_queue);
 
-        /* Units to check when doing GC */
-        LIST_HEAD(Unit, gc_queue);
+        /* Units and jobs to check when doing GC */
+        LIST_HEAD(Unit, gc_unit_queue);
+        LIST_HEAD(Job, gc_job_queue);
 
         /* Units that should be realized */
         LIST_HEAD(Unit, cgroup_queue);
@@ -229,7 +230,6 @@ struct Manager {
         int pin_cgroupfs_fd;
 
         int gc_marker;
-        unsigned n_in_gc_queue;
 
         /* Flags */
         ManagerExitCode exit_code:5;
diff --git a/src/core/org.freedesktop.systemd1.conf b/src/core/org.freedesktop.systemd1.conf
index a61677e645..e824a2233c 100644
--- a/src/core/org.freedesktop.systemd1.conf
+++ b/src/core/org.freedesktop.systemd1.conf
@@ -66,6 +66,14 @@
 
                 <allow send_destination="org.freedesktop.systemd1"
                        send_interface="org.freedesktop.systemd1.Manager"
+                       send_member="GetJobAfter"/>
+
+                <allow send_destination="org.freedesktop.systemd1"
+                       send_interface="org.freedesktop.systemd1.Manager"
+                       send_member="GetJobBefore"/>
+
+                <allow send_destination="org.freedesktop.systemd1"
+                       send_interface="org.freedesktop.systemd1.Manager"
                        send_member="ListUnits"/>
 
                 <allow send_destination="org.freedesktop.systemd1"
@@ -250,6 +258,14 @@
                        send_interface="org.freedesktop.systemd1.Job"
                        send_member="Cancel"/>
 
+                <allow send_destination="org.freedesktop.systemd1"
+                       send_interface="org.freedesktop.systemd1.Job"
+                       send_member="GetAfter"/>
+
+                <allow send_destination="org.freedesktop.systemd1"
+                       send_interface="org.freedesktop.systemd1.Job"
+                       send_member="GetBefore"/>
+
                 <allow receive_sender="org.freedesktop.systemd1"/>
         </policy>
 
diff --git a/src/core/unit.c b/src/core/unit.c
index da9bb58a52..fbb21e4985 100644
--- a/src/core/unit.c
+++ b/src/core/unit.c
@@ -389,10 +389,8 @@ void unit_add_to_gc_queue(Unit *u) {
         if (unit_check_gc(u))
                 return;
 
-        LIST_PREPEND(gc_queue, u->manager->gc_queue, u);
+        LIST_PREPEND(gc_queue, u->manager->gc_unit_queue, u);
         u->in_gc_queue = true;
-
-        u->manager->n_in_gc_queue++;
 }
 
 void unit_add_to_dbus_queue(Unit *u) {
@@ -570,10 +568,8 @@ void unit_free(Unit *u) {
         if (u->in_cleanup_queue)
                 LIST_REMOVE(cleanup_queue, u->manager->cleanup_queue, u);
 
-        if (u->in_gc_queue) {
-                LIST_REMOVE(gc_queue, u->manager->gc_queue, u);
-                u->manager->n_in_gc_queue--;
-        }
+        if (u->in_gc_queue)
+                LIST_REMOVE(gc_queue, u->manager->gc_unit_queue, u);
 
         if (u->in_cgroup_queue)
                 LIST_REMOVE(cgroup_queue, u->manager->cgroup_queue, u);
diff --git a/src/core/unit.h b/src/core/unit.h
index 991543664b..6d6885b487 100644
--- a/src/core/unit.h
+++ b/src/core/unit.h
@@ -441,6 +441,9 @@ struct UnitVTable {
 
         /* True if transient units of this type are OK */
         bool can_transient:1;
+
+        /* True if queued jobs of this type should be GC'ed if no other job needs them anymore */
+        bool gc_jobs:1;
 };
 
 extern const UnitVTable * const unit_vtable[_UNIT_TYPE_MAX];
diff --git a/src/shared/bus-unit-util.c b/src/shared/bus-unit-util.c
index 4f66497f3a..388b391342 100644
--- a/src/shared/bus-unit-util.c
+++ b/src/shared/bus-unit-util.c
@@ -62,6 +62,7 @@ int bus_parse_unit_info(sd_bus_message *message, UnitInfo *u) {
 
 int bus_append_unit_property_assignment(sd_bus_message *m, const char *assignment) {
         const char *eq, *field;
+        UnitDependency dep;
         int r, rl;
 
         assert(m);
@@ -572,7 +573,9 @@ int bus_append_unit_property_assignment(sd_bus_message *m, const char *assignmen
                         flags = (~flags) & NAMESPACE_FLAGS_ALL;
 
                 r = sd_bus_message_append(m, "v", "t", flags);
-        } else {
+        } else if ((dep = unit_dependency_from_string(field)) >= 0)
+                r = sd_bus_message_append(m, "v", "as", 1, eq);
+        else {
                 log_error("Unknown assignment %s.", assignment);
                 return -EINVAL;
         }
@@ -838,6 +841,8 @@ static int check_wait_response(BusWaitForJobs *d, bool quiet, const char* const*
                         log_error("Assertion failed on job for %s.", strna(d->name));
                 else if (streq(d->result, "unsupported"))
                         log_error("Operation on or unit type of %s not supported on this system.", strna(d->name));
+                else if (streq(d->result, "collected"))
+                        log_error("Queued job for %s was garbage collected.", strna(d->name));
                 else if (!streq(d->result, "done") && !streq(d->result, "skipped")) {
                         if (d->name) {
                                 int q;
@@ -853,7 +858,7 @@ static int check_wait_response(BusWaitForJobs *d, bool quiet, const char* const*
                 }
         }
 
-        if (streq(d->result, "canceled"))
+        if (STR_IN_SET(d->result, "canceled", "collected"))
                 r = -ECANCELED;
         else if (streq(d->result, "timeout"))
                 r = -ETIME;
diff --git a/src/shared/bus-util.c b/src/shared/bus-util.c
index e7b1b1cb20..6aebe18fc0 100644
--- a/src/shared/bus-util.c
+++ b/src/shared/bus-util.c
@@ -1583,3 +1583,22 @@ int bus_property_get_rlimit(
 
         return sd_bus_message_append(reply, "t", u);
 }
+
+int bus_track_add_name_many(sd_bus_track *t, char **l) {
+        int r = 0;
+        char **i;
+
+        assert(t);
+
+        /* Continues adding after failure, and returns the first failure. */
+
+        STRV_FOREACH(i, l) {
+                int k;
+
+                k = sd_bus_track_add_name(t, *i);
+                if (k < 0 && r >= 0)
+                        r = k;
+        }
+
+        return r;
+}
diff --git a/src/shared/bus-util.h b/src/shared/bus-util.h
index 934e0b5b77..af5f133912 100644
--- a/src/shared/bus-util.h
+++ b/src/shared/bus-util.h
@@ -159,3 +159,5 @@ int bus_path_encode_unique(sd_bus *b, const char *prefix, const char *sender_id,
 int bus_path_decode_unique(const char *path, const char *prefix, char **ret_sender, char **ret_external);
 
 int bus_property_get_rlimit(sd_bus *bus, const char *path, const char *interface, const char *property, sd_bus_message *reply, void *userdata, sd_bus_error *error);
+
+int bus_track_add_name_many(sd_bus_track *t, char **l);
diff --git a/src/systemctl/systemctl.c b/src/systemctl/systemctl.c
index 49a97ff268..db836639b5 100644
--- a/src/systemctl/systemctl.c
+++ b/src/systemctl/systemctl.c
@@ -173,6 +173,8 @@ static OutputMode arg_output = OUTPUT_SHORT;
 static bool arg_plain = false;
 static bool arg_firmware_setup = false;
 static bool arg_now = false;
+static bool arg_jobs_before = false;
+static bool arg_jobs_after = false;
 
 static int daemon_reload(int argc, char *argv[], void* userdata);
 static int trivial_method(int argc, char *argv[], void *userdata);
@@ -204,6 +206,9 @@ static int acquire_bus(BusFocus focus, sd_bus **ret) {
         if (arg_transport != BUS_TRANSPORT_LOCAL)
                 focus = BUS_FULL;
 
+        if (getenv_bool("SYSTEMCTL_FORCE_BUS") > 0)
+                focus = BUS_FULL;
+
         if (!busses[focus]) {
                 bool user;
 
@@ -2192,12 +2197,55 @@ finish:
         return r;
 }
 
+static void output_waiting_jobs(sd_bus *bus, uint32_t id, const char *method, const char *prefix) {
+        _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
+        _cleanup_(sd_bus_message_unrefp) sd_bus_message *reply = NULL;
+        const char *name, *type, *state, *job_path, *unit_path;
+        uint32_t other_id;
+        int r;
+
+        assert(bus);
+
+        r = sd_bus_call_method(
+                        bus,
+                        "org.freedesktop.systemd1",
+                        "/org/freedesktop/systemd1",
+                        "org.freedesktop.systemd1.Manager",
+                        method,
+                        &error,
+                        &reply,
+                        "u", id);
+        if (r < 0) {
+                log_debug_errno(r, "Failed to get waiting jobs for job %" PRIu32, id);
+                return;
+        }
+
+        r = sd_bus_message_enter_container(reply, 'a', "(usssoo)");
+        if (r < 0) {
+                bus_log_parse_error(r);
+                return;
+        }
+
+        while ((r = sd_bus_message_read(reply, "(usssoo)", &other_id, &name, &type, &state, &job_path, &unit_path)) > 0)
+                printf("%s%u (%s/%s)\n", prefix, other_id, name, type);
+        if (r < 0) {
+                bus_log_parse_error(r);
+                return;
+        }
+
+        r = sd_bus_message_exit_container(reply);
+        if (r < 0) {
+                bus_log_parse_error(r);
+                return;
+        }
+}
+
 struct job_info {
         uint32_t id;
         const char *name, *type, *state;
 };
 
-static void output_jobs_list(const struct job_info* jobs, unsigned n, bool skipped) {
+static void output_jobs_list(sd_bus *bus, const struct job_info* jobs, unsigned n, bool skipped) {
         unsigned id_len, unit_len, type_len, state_len;
         const struct job_info *j;
         const char *on, *off;
@@ -2259,6 +2307,11 @@ static void output_jobs_list(const struct job_info* jobs, unsigned n, bool skipp
                        on, unit_len, e ? e : j->name, off,
                        type_len, j->type,
                        on, state_len, j->state, off);
+
+                if (arg_jobs_after)
+                        output_waiting_jobs(bus, j->id, "GetJobAfter", "\tA job waits for this job: ");
+                if (arg_jobs_before)
+                        output_waiting_jobs(bus, j->id, "GetJobBefore", "\tThis job waits for a job: ");
         }
 
         if (!arg_no_legend) {
@@ -2327,7 +2380,7 @@ static int list_jobs(int argc, char *argv[], void *userdata) {
 
         pager_open(arg_no_pager, false);
 
-        output_jobs_list(jobs, c, skipped);
+        output_jobs_list(bus, jobs, c, skipped);
         return 0;
 }
 
@@ -7302,10 +7355,12 @@ static int systemctl_parse_argv(int argc, char *argv[]) {
 
                 case ARG_AFTER:
                         arg_dependency = DEPENDENCY_AFTER;
+                        arg_jobs_after = true;
                         break;
 
                 case ARG_BEFORE:
                         arg_dependency = DEPENDENCY_BEFORE;
+                        arg_jobs_before = true;
                         break;
 
                 case ARG_SHOW_TYPES: