bus: rework message handlers to always take an error argument

Message handler callbacks can be simplified drastically if the
dispatcher automatically replies to method calls if errors are returned.

Thus: add an sd_bus_error argument to all message handlers. When we
dispatch a message handler and it returns negative or a set sd_bus_error
we send this as message error back to the client. This means errors
returned by handlers by default are given back to clients instead of
rippling all the way up to the event loop, which is desirable to make
things robust.

As a side-effect we can now easily turn the SELinux checks into normal
function calls, since the method call dispatcher will generate the right
error replies automatically now.

Also, make sure we always pass the error structure to all property and
method handlers as last argument to follow the usual style of passing
variables for return values as last argument.

1 files changed, 4 insertions, 3 deletions

diff --git a/src/core/dbus-client-track.c b/src/core/dbus-client-track.c
index ce514b577c..4a5bdef040 100644
--- a/src/core/dbus-client-track.c
+++ b/src/core/dbus-client-track.c
@@ -19,6 +19,7 @@
   along with systemd; If not, see <http://www.gnu.org/licenses/>.
 ***/
 
+#include "bus-util.h"
 #include "dbus-client-track.h"
 
 static unsigned tracked_client_hash(const void *a) {
@@ -43,7 +44,7 @@ static int tracked_client_compare(const void *a, const void *b) {
         return 0;
 }
 
-static int on_name_owner_changed(sd_bus *bus, sd_bus_message *message, void *userdata) {
+static int on_name_owner_changed(sd_bus *bus, sd_bus_message *message, void *userdata, sd_bus_error *error) {
         BusTrackedClient *c = userdata;
         const char *name, *old, *new;
         int r;
@@ -53,8 +54,8 @@ static int on_name_owner_changed(sd_bus *bus, sd_bus_message *message, void *use
 
         r = sd_bus_message_read(message, "sss", &name, &old, &new);
         if (r < 0) {
-                log_debug("Failed to parse NameOwnerChanged message.");
-                return 0;
+                bus_log_parse_error(r);
+                return r;
         }
 
         bus_client_untrack(c->set, bus, name);