Document public event and session structures

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I50cd2a5d122eed9fe5b333919bbba351dd0867d3

diff --git a/include/lttng/ust-events.h b/include/lttng/ust-events.h
index f7915d7d530ae566fc2b7953ebb9c99ddfa5de71..d9e15d34a72f8a0cfedbac33344734dfe4da740b 100644 (file)
--- a/include/lttng/ust-events.h
+++ b/include/lttng/ust-events.h
@@ -355,6 +355,10 @@ enum lttng_ust_event_type {
 };
 
 /*
+ * IMPORTANT: this structure is part of the ABI between the probe and
+ * UST. Fields need to be only added at the end, never reordered, never
+ * removed.
+ *
  * struct lttng_ust_event_common is the common ancestor of the various
  * public event actions. Inheritance is done by composition: The parent
  * has a pointer to its child, and the child has a pointer to its
@@ -383,6 +387,10 @@ struct lttng_ust_event_common {
 struct lttng_ust_event_recorder_private;
 
 /*
+ * IMPORTANT: this structure is part of the ABI between the probe and
+ * UST. Fields need to be only added at the end, never reordered, never
+ * removed.
+ *
  * struct lttng_ust_event_recorder is the action for recording events
  * into a ring buffer. It inherits from struct lttng_ust_event_common
  * by composition to ensure both parent and child structure are
@@ -407,6 +415,10 @@ struct lttng_ust_event_recorder {
 struct lttng_ust_event_notifier_private;
 
 /*
+ * IMPORTANT: this structure is part of the ABI between the probe and
+ * UST. Fields need to be only added at the end, never reordered, never
+ * removed.
+ *
  * struct lttng_ust_event_notifier is the action for sending
  * notifications. It inherits from struct lttng_ust_event_common
  * by composition to ensure both parent and child structure are
@@ -560,12 +572,18 @@ struct lttng_ust_session_private;
  * IMPORTANT: this structure is part of the ABI between the probe and
  * UST. Fields need to be only added at the end, never reordered, never
  * removed.
+ *
+ * The field @struct_size should be used to determine the size of the
+ * structure. It should be queried before using additional fields added
+ * at the end of the structure.
  */
 struct lttng_session {
        uint32_t struct_size;                   /* Size of this structure */
        struct lttng_ust_session_private *priv; /* Private session interface */
 
        int active;                             /* Is trace session active ? */
+
+       /* End of base ABI. Fields below should be used after checking struct_size. */
 };
 
 int lttng_probe_register(struct lttng_probe_desc *desc);