From f7821e37bf57965ff4f6c4f86d4a2d6f86b34a50 Mon Sep 17 00:00:00 2001
From: Christophe Bedard <fixed-term.christophe.bourquebedard@de.bosch.com>
Date: Wed, 26 Jun 2019 15:00:56 +0200
Subject: [PATCH] Add building and tracing instructions

---
 README.md | 27 +++++++++++++++++++++++----
 1 file changed, 23 insertions(+), 4 deletions(-)

diff --git a/README.md b/README.md
index 684b35d..4dd130e 100644
--- a/README.md
+++ b/README.md
@@ -8,21 +8,40 @@ If tracing is not enabled when building, or if LTTng is not found, then this pac
 
 To enable tracing:
 
-1. Install [LTTng](https://lttng.org/docs/v2.10/#doc-ubuntu):
+1. Install [LTTng](https://lttng.org/docs/#doc-ubuntu) with the Python interfaces to control tracing and read trace:
     ```
+    $ sudo apt-add-repository ppa:lttng/stable-2.10
+    $ sudo apt-get update
     $ sudo apt-get install lttng-tools lttng-modules-dkms liblttng-ust-dev
+    $ sudo apt-get install python3-babeltrace python3-lttng
     ```
+    Note: the LTTng stable 2.10 PPA is used to get more recent versions.
 2. Build with the `WITH_LTTNG` flag:
     ```
     $ colcon build --cmake-args " -DWITH_LTTNG=ON"
     ```
-3. Check if tracing is enabled (after sourcing):
+3. Source and check that tracing is enabled:
     ```
+    $ source ./install/local_setup.bash
     $ ros2 run tracetools tracetools_status
     ```
 
 ## Tracing
 
-By default, the steps above will not lead to trace data being generated, and thus they will have no impact on execution.
+The steps above will not lead to trace data being generated, and thus they will have no impact on execution. LTTng has to be enabled. The packages in this repo provide two options.
 
-LTTng has to be enabled: TODO mention scripts
+### Trace command
+
+The first option is to use the `ros2 trace` command.
+
+```
+$ ros2 trace
+```
+
+By default, it will enable all ROS tracepoints and a few kernel tracepoints. The trace will be written to `/tmp/session-YYYYMMDDHHMMSS`. Run the command with `-h` for more information.
+
+### Launch file trace action
+
+Another option is to use the `Trace` action in a launch file along with your `Node` action(s).
+
+See [this example launch file](./tracetools_launch/launch/example.launch.py) for more information.