sd-bus: add APIs to query the current read and write queue size

src/libsystemd/libsystemd.sym

@@ -549,3 +549,9 @@ global:
         sd_event_source_get_io_fd_own;
         sd_event_source_set_io_fd_own;
 } LIBSYSTEMD_236;
+
+LIBSYSTEMD_238 {
+global:
+        sd_bus_get_n_queued_read;
+        sd_bus_get_n_queued_write;
+} LIBSYSTEMD_237;

src/libsystemd/sd-bus/sd-bus.c

@@ -4091,3 +4091,23 @@ _public_ int sd_bus_get_sender(sd_bus *bus, const char **ret) {
         *ret = bus->patch_sender;
         return 0;
 }
+
+_public_ int sd_bus_get_n_queued_read(sd_bus *bus, uint64_t *ret) {
+        assert_return(bus, -EINVAL);
+        assert_return(bus = bus_resolve(bus), -ENOPKG);
+        assert_return(!bus_pid_changed(bus), -ECHILD);
+        assert_return(ret, -EINVAL);
+
+        *ret = bus->rqueue_size;
+        return 0;
+}
+
+_public_ int sd_bus_get_n_queued_write(sd_bus *bus, uint64_t *ret) {
+        assert_return(bus, -EINVAL);
+        assert_return(bus = bus_resolve(bus), -ENOPKG);
+        assert_return(!bus_pid_changed(bus), -ECHILD);
+        assert_return(ret, -EINVAL);
+
+        *ret = bus->wqueue_size;
+        return 0;
+}