Refactoring: struct lttng_event_desc and lttng_probe_desc

[lttng-ust.git] / include / lttng / ust-events.h

diff --git a/include/lttng/ust-events.h b/include/lttng/ust-events.h
index d9e15d34a72f8a0cfedbac33344734dfe4da740b..b43b49e1a9f7ce7389f1f29aa6c28f8ab3e99db7 100644 (file)
--- a/include/lttng/ust-events.h
+++ b/include/lttng/ust-events.h
@@ -274,34 +274,51 @@ struct lttng_ctx {
        char padding[LTTNG_UST_CTX_PADDING];
 };
 
-#define LTTNG_UST_EVENT_DESC_PADDING   40
-struct lttng_event_desc {
+/*
+ * 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_ust_event_desc {
+       uint32_t struct_size;                   /* Size of this structure. */
        const char *name;
        void (*probe_callback)(void);
        const struct lttng_event_ctx *ctx;      /* context */
        const struct lttng_event_field *fields; /* event payload */
        unsigned int nr_fields;
        const int **loglevel;
-       const char *signature;  /* Argument types/names received */
-       union {
-               struct {
-                       const char **model_emf_uri;
-               } ext;
-               char padding[LTTNG_UST_EVENT_DESC_PADDING];
-       } u;
+       const char *signature;                  /* Argument types/names received */
+       const char **model_emf_uri;
+
+       /* End of base ABI. Fields below should be used after checking struct_size. */
 };
 
-#define LTTNG_UST_PROBE_DESC_PADDING   12
-struct lttng_probe_desc {
+/*
+ * 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_ust_probe_desc {
+       uint32_t struct_size;                   /* Size of this structure. */
+
        const char *provider;
-       const struct lttng_event_desc **event_desc;
+       const struct lttng_ust_event_desc **event_desc;
        unsigned int nr_events;
        struct cds_list_head head;              /* chain registered probes */
        struct cds_list_head lazy_init_head;
        int lazy;                               /* lazy registration */
        uint32_t major;
        uint32_t minor;
-       char padding[LTTNG_UST_PROBE_DESC_PADDING];
+
+       /* End of base ABI. Fields below should be used after checking struct_size. */
 };
 
 /* Data structures used by the tracer. */
@@ -586,8 +603,8 @@ struct lttng_session {
        /* End of base ABI. Fields below should be used after checking struct_size. */
 };
 
-int lttng_probe_register(struct lttng_probe_desc *desc);
-void lttng_probe_unregister(struct lttng_probe_desc *desc);
+int lttng_ust_probe_register(struct lttng_ust_probe_desc *desc);
+void lttng_ust_probe_unregister(struct lttng_ust_probe_desc *desc);
 
 /*
  * Can be used by applications that change their procname to clear the ust cached value.