README.md: Document LTTNG_TRACEPOINT_EVENT

Suggested-by: David Boles <blioboles@gmail.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/README.md b/README.md
index 17553e63346d96dbbaef254eb3de3b13ebf5e509..450f3630d582ebf63f47161e93c23cacb59fd544 100644 (file)
--- a/README.md
+++ b/README.md
@@ -94,6 +94,19 @@ available from LTTng:
   - `CONFIG_KALLSYMS_ALL`: state dump of mapping between block device
     number and name
 
+Customization/Extension
+-----------------------
+
+The lttng-modules source includes definitions for the actual callback
+functions that will be attached to the kernel tracepoints by lttng.
+The lttng-modules project implements its own macros generating these
+callbacks: the LTTNG_TRACEPOINT_EVENT macro family found in
+instrumentation/events/lttng-module/. In order to show up in a
+lttng-modules trace, a kernel tracepoint must be defined within the
+kernel tree, and also defined within lttng-modules with the
+LTTNG_TRACEPOINT_EVENT macro family. Customizations or extensions must
+be done by modifying instances of these macros within the lttng-modules
+source.
 
 Usage
 -----