bus: add sd_bus_track object for tracking peers, and port core over to it

This is primarily useful for services that need to track clients which
reference certain objects they maintain, or which explicitly want to
subscribe to certain events. Something like this is done in a large
number of services, and not trivial to do. Hence, let's unify this at
one place.

This also ports over PID 1 to use this to ensure that subscriptions to
job and manager events are correctly tracked. As a side-effect this
makes sure we properly serialize and restore the track list across
daemon reexec/reload, which didn't work correctly before.

This also simplifies how we distribute messages to broadcast to the
direct busses: we only track subscriptions for the API bus and
implicitly assume that all direct busses are subscribed. This should be
a pretty OK simplification since clients connected via direct bus
connections are shortlived anyway.

1 files changed, 22 insertions, 0 deletions

diff --git a/src/libsystemd/sd-bus/sd-bus.c b/src/libsystemd/sd-bus/sd-bus.c
index 636715f759..fbf1a5919f 100644
--- a/src/libsystemd/sd-bus/sd-bus.c
+++ b/src/libsystemd/sd-bus/sd-bus.c
@@ -51,6 +51,7 @@
 #include "bus-util.h"
 #include "bus-container.h"
 #include "bus-protocol.h"
+#include "bus-track.h"
 
 static int bus_poll(sd_bus *bus, bool need_more, uint64_t timeout_usec);
 static int attach_io_events(sd_bus *b);
@@ -131,6 +132,8 @@ static void bus_free(sd_bus *b) {
 
         assert(b);
 
+        assert(!b->track_queue);
+
         sd_bus_detach_event(b);
 
         if (b->default_bus_ptr)
@@ -2000,6 +2003,11 @@ _public_ int sd_bus_get_timeout(sd_bus *bus, uint64_t *timeout_usec) {
         assert_return(BUS_IS_OPEN(bus->state) || bus->state == BUS_CLOSING, -ENOTCONN);
         assert_return(!bus_pid_changed(bus), -ECHILD);
 
+        if (bus->track_queue) {
+                *timeout_usec = 0;
+                return 1;
+        }
+
         if (bus->state == BUS_CLOSING) {
                 *timeout_usec = 0;
                 return 1;
@@ -2282,6 +2290,16 @@ finish:
         return r;
 }
 
+static int dispatch_track(sd_bus *bus) {
+        assert(bus);
+
+        if (!bus->track_queue)
+                return 0;
+
+        bus_track_dispatch(bus->track_queue);
+        return 1;
+}
+
 static int process_running(sd_bus *bus, bool hint_priority, int64_t priority, sd_bus_message **ret) {
         _cleanup_bus_message_unref_ sd_bus_message *m = NULL;
         int r;
@@ -2297,6 +2315,10 @@ static int process_running(sd_bus *bus, bool hint_priority, int64_t priority, sd
         if (r != 0)
                 goto null_message;
 
+        r = dispatch_track(bus);
+        if (r != 0)
+                goto null_message;
+
         r = dispatch_rqueue(bus, hint_priority, priority, &m);
         if (r < 0)
                 return r;