core: dbus: track bus names per unit

Currently, PID1 installs an unfiltered NameOwnerChanged signal match, and
dispatches the signals itself. This does not scale, as right now, PID1
wakes up every time a bus client connects.

To fix this, install individual matches once they are requested by
unit_watch_bus_name(), and remove the watches again through their slot in
unit_unwatch_bus_name().

If the bus is not available during unit_watch_bus_name(), just store
name in the 'watch_bus' hashmap, and let bus_setup_api() do the installing
later.

1 files changed, 4 insertions, 0 deletions

diff --git a/src/core/unit.h b/src/core/unit.h
index e60168267f..9df5a7e6fb 100644
--- a/src/core/unit.h
+++ b/src/core/unit.h
@@ -115,6 +115,9 @@ struct Unit {
         /* JOB_NOP jobs are special and can be installed without disturbing the real job. */
         Job *nop_job;
 
+        /* The slot used for watching NameOwnerChanged signals */
+        sd_bus_slot *match_bus_slot;
+
         /* Job timeout and action to take */
         usec_t job_timeout;
         FailureAction job_timeout_action;
@@ -522,6 +525,7 @@ void unit_unwatch_all_pids(Unit *u);
 
 void unit_tidy_watch_pids(Unit *u, pid_t except1, pid_t except2);
 
+int unit_install_bus_match(sd_bus *bus, Unit *u, const char *name);
 int unit_watch_bus_name(Unit *u, const char *name);
 void unit_unwatch_bus_name(Unit *u, const char *name);