Commit timestamp guarantees

[lttng-modules.git] / ltt-ring-buffer-client.h

diff --git a/ltt-ring-buffer-client.h b/ltt-ring-buffer-client.h
index 5173b23b1a53bc3e2c904ed70babe544f1141153..904c42eb466b68e8745f1108ad50922460ba4980 100644 (file)
--- a/ltt-ring-buffer-client.h
+++ b/ltt-ring-buffer-client.h
@@ -22,6 +22,14 @@
  * you ever add/remove a field from this header. Packed attribute is not used
  * because gcc generates poor code on at least powerpc and mips. Don't ever
  * let gcc add padding between the structure elements.
+ *
+ * The guarantee we have with timestamps is that all the events in a
+ * packet are included (inclusive) within the begin/end timestamps of
+ * the packet. Another guarantee we have is that the "timestamp begin",
+ * as well as the event timestamps, are monotonically increasing (never
+ * decrease) when moving forward in a stream (physically). But this
+ * guarantee does not apply to "timestamp end", because it is sampled at
+ * commit time, which is not ordered with respect to space reservation.
  */
 
 struct packet_header {
@@ -149,7 +157,7 @@ unsigned char record_header_size(const struct lib_ring_buffer_config *config,
 
 #include "wrapper/ringbuffer/api.h"
 
-extern
+static
 void ltt_write_event_header_slow(const struct lib_ring_buffer_config *config,
                                 struct lib_ring_buffer_ctx *ctx,
                                 uint32_t event_id);
@@ -198,8 +206,8 @@ void ltt_write_event_header(const struct lib_ring_buffer_config *config,
                WARN_ON_ONCE(1);
        }
 
-       ctx_record(ctx, ltt_chan, event->ctx);
        ctx_record(ctx, ltt_chan, ltt_chan->ctx);
+       ctx_record(ctx, ltt_chan, event->ctx);
 
        return;
 
@@ -207,6 +215,7 @@ slow_path:
        ltt_write_event_header_slow(config, ctx, event_id);
 }
 
+static
 void ltt_write_event_header_slow(const struct lib_ring_buffer_config *config,
                                 struct lib_ring_buffer_ctx *ctx,
                                 uint32_t event_id)
@@ -260,8 +269,8 @@ void ltt_write_event_header_slow(const struct lib_ring_buffer_config *config,
        default:
                WARN_ON_ONCE(1);
        }
-       ctx_record(ctx, ltt_chan, event->ctx);
        ctx_record(ctx, ltt_chan, ltt_chan->ctx);
+       ctx_record(ctx, ltt_chan, event->ctx);
 }
 
 static const struct lib_ring_buffer_config client_config;