Refactoring: struct lttng_stack_ctx

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

diff --git a/include/lttng/ust-events.h b/include/lttng/ust-events.h
index 13ecb6d7f05077d4e4bd2ef883b5485630f4f5f4..624af8bb1bc18b37578d9741891ef5bd73a4effd 100644 (file)
--- a/include/lttng/ust-events.h
+++ b/include/lttng/ust-events.h
@@ -566,12 +566,23 @@ struct lttng_channel {
        int tstate:1;                   /* Transient enable state */
 };
 
-#define LTTNG_UST_STACK_CTX_PADDING    32
-struct lttng_stack_ctx {
+/*
+ * 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_stack_ctx {
+       uint32_t struct_size;                   /* Size of this structure */
+
        struct lttng_ust_event_recorder *event_recorder;
        struct lttng_ctx *chan_ctx;     /* RCU dereferenced. */
        struct lttng_ctx *event_ctx;    /* RCU dereferenced. */
-       char padding[LTTNG_UST_STACK_CTX_PADDING];
+
+       /* End of base ABI. Fields below should be used after checking struct_size. */
 };
 
 struct lttng_ust_session_private;