bus: when we cannot bus activate a service because we go down, drop one

message from the queue

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

@@ -1476,3 +1476,16 @@ int bus_kernel_try_close(sd_bus *bus) {
 
         return 0;
 }
+
+int bus_kernel_drop_one(int fd) {
+        struct kdbus_cmd_recv recv = {
+                .flags = KDBUS_RECV_DROP
+        };
+
+        assert(fd >= 0);
+
+        if (ioctl(fd, KDBUS_CMD_MSG_RECV, &recv) < 0)
+                return -errno;
+
+        return 0;
+}

src/libsystemd/sd-bus/bus-kernel.h

@@ -79,3 +79,5 @@ int kdbus_translate_request_name_flags(uint64_t sd_bus_flags, uint64_t *kdbus_fl
 int kdbus_translate_attach_flags(uint64_t sd_bus_flags, uint64_t *kdbus_flags);
 
 int bus_kernel_try_close(sd_bus *bus);
+
+int bus_kernel_drop_one(int fd);