Fix: backward compatibility with UST 2.0 app probes

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

diff --git a/include/lttng/ust-events.h b/include/lttng/ust-events.h
index 8a2fa14c04e1c5f2247c6f303d750c7d932e5246..daf589025fd0074031c0290f603ba03538c812e5 100644 (file)
--- a/include/lttng/ust-events.h
+++ b/include/lttng/ust-events.h
@@ -179,13 +179,19 @@ struct lttng_enum {
        char padding[LTTNG_UST_ENUM_TYPE_PADDING];
 };
 
-/* Event field description */
+/*
+ * Event field description
+ *
+ * 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.
+ */
 
 #define LTTNG_UST_EVENT_FIELD_PADDING  28
 struct lttng_event_field {
        const char *name;
        struct lttng_type type;
-       unsigned int written;   /* written into trace */
+       unsigned int nowrite;   /* do not write into trace */
        char padding[LTTNG_UST_EVENT_FIELD_PADDING];
 };
 
@@ -291,14 +297,18 @@ struct lttng_ust_filter_bytecode;
 /*
  * ltt_event structure is referred to by the tracing fast path. It must be
  * kept small.
+ *
+ * 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 ltt_event {
+       /* LTTng-UST 2.0 starts here */
        unsigned int id;
        struct ltt_channel *chan;
        int enabled;
        const struct lttng_event_desc *desc;
        int (*filter)(void *filter_data, const char *filter_stack_data);
-       void *filter_data;
        struct lttng_ctx *ctx;
        enum lttng_ust_instrumentation instrumentation;
        union {
@@ -306,13 +316,20 @@ struct ltt_event {
        struct cds_list_head list;              /* Event list */
        struct cds_list_head wildcard_list;     /* Event list for wildcard */
        struct ust_pending_probe *pending_probe;
-       struct lttng_ust_filter_bytecode *filter_bytecode;
        unsigned int metadata_dumped:1;
+       /* LTTng-UST 2.1 starts here */
+       struct lttng_ust_filter_bytecode *filter_bytecode;
+       void *filter_data;
 };
 
 struct channel;
 struct lttng_ust_shm_handle;
 
+/*
+ * 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 ltt_channel_ops {
        struct ltt_channel *(*channel_create)(const char *name,
                                void *buf_addr,
@@ -348,6 +365,11 @@ struct ltt_channel_ops {
        int (*flush_buffer)(struct channel *chan, struct lttng_ust_shm_handle *handle);
 };
 
+/*
+ * 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 ltt_channel {
        /*
         * The pointers located in this private data are NOT safe to be
@@ -375,6 +397,11 @@ struct ltt_channel {
        unsigned char uuid[LTTNG_UST_UUID_LEN]; /* Trace session unique ID */
 };
 
+/*
+ * 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 ltt_session {
        int active;                     /* Is trace session active ? */
        int been_active;                /* Has trace session been active ? */