+ uint32_t tracker_type; /* enum lttng_tracker_type */
+ uint32_t id_type; /* enum lttng_tracker_id_type */
+ union {
+ int32_t value;
+ uint32_t var_len;
+ } u;
+ /*
+ * for LTTNG_ID_STRING, followed by a variable length
+ * zero-terminated string of length "var_len", which
+ * includes the final \0.
+ */
+ } LTTNG_PACKED id_tracker;
+ struct {
+ uint32_t tracker_type; /* enum lttng_tracker_type */
+ } LTTNG_PACKED id_tracker_list;