X-Git-Url: http://git.lttng.org./?a=blobdiff_plain;f=include%2Flttng%2Ftracepoint-types.h;h=5354c3698abc478dd41c6167f5cff07098f7de63;hb=f574bfb4d81b26d3cfc0243868d138e33470a950;hp=ceb476a6f9891d760f0e43e60bda928aed2acae0;hpb=c0c0989ab70574e09b2f7e8b48c2da6af664a849;p=lttng-ust.git

diff --git a/include/lttng/tracepoint-types.h b/include/lttng/tracepoint-types.h
index ceb476a6..5354c369 100644
--- a/include/lttng/tracepoint-types.h
+++ b/include/lttng/tracepoint-types.h
@@ -7,19 +7,44 @@
 #ifndef _LTTNG_TRACEPOINT_TYPES_H
 #define _LTTNG_TRACEPOINT_TYPES_H
 
+#include <stdint.h>
+
+/*
+ * Tracepoint probe definition
+ *
+ * IMPORTANT: this structure is part of the ABI between instrumented
+ * applications and UST. This structure is fixed-size because it is part
+ * of a public array of structures. Rather than extending this
+ * structure, struct lttng_ust_tracepoint should be extended instead.
+ */
+
 struct lttng_ust_tracepoint_probe {
 	void (*func)(void);
 	void *data;
 };
 
-#define LTTNG_UST_TRACEPOINT_PADDING	16
+/*
+ * Tracepoint definition
+ *
+ * IMPORTANT: this structure is part of the ABI between instrumented
+ * applications 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_ust_tracepoint {
+	uint32_t struct_size;
+
 	const char *name;
 	int state;
 	struct lttng_ust_tracepoint_probe *probes;
 	int *tracepoint_provider_ref;
 	const char *signature;
-	char padding[LTTNG_UST_TRACEPOINT_PADDING];
+
+	/* End of base ABI. Fields below should be used after checking struct_size. */
 };
 
 #endif /* _LTTNG_TRACEPOINT_TYPES_H */