[lttng-dev] [babeltrace2]about python self-defined plugin loading

[Simon Marchi]

On 2024-04-26 09:56, Wu, Yannan via lttng-dev wrote:
> Hihi, Kienan,
> 
> I finally find a workaround. I could success with the following code:
> file_name = "bt_plugin_latency_filter.py"
> current_directory=os.getcwd()
> 
> file_path = os.path.join(current_directory, file_name)
> pset=bt2.find_plugins_in_path(file_path)
> 
> forplugininpset:
> if plugin.name=="latency_filter"andhasattr(plugin,"filter_component_classes"):
> 
>     latency_filter_comp_cls=plugin.filter_component_classes['LatencyFilter']
> 
> But loading the whole directory, it just doesnt work from command line.
> Amanda

So, since this works, it confirms that your babeltrace build has support
for Python plugins.  Then there's no reason for your original example
using babeltrace-fun-plugins/my-first-components not to work.

When running the command:

  babeltrace2 --plugin-path . -c source.demo.MyFirstSource -c sink.demo.MyFirstSink

is your working directory babeltrace-fun-plugins/my-first-component?
`--plugin-path .` refers to the current working directory, so it must be
the directory that directly contains the `bt_plugin_*.py` file.

I made an example with docker to show it working, hopefully this can
help you figure out what's wrong on your side.  Put this inside a
`Dockerfile` file:

```
FROM debian:12

RUN apt-get -y update
RUN apt-get -y full-upgrade
RUN apt-get -y install babeltrace2 git
RUN git clone https://github.com/simark/babeltrace-fun-plugins.git
WORKDIR /babeltrace-fun-plugins/my-first-components
ENTRYPOINT babeltrace2 --plugin-path . -c source.demo.MyFirstSource -c sink.demo.MyFirstSink
```

Then, do either (whatever works for you):

  $ docker buildx build -t bt2-example .
  $ docker build -t bt2-example .

And finally:

  $ docker run -it bt2-example
  Stream beginning
  event my-event, timestamp 123
  Stream end

This last command runs babeltrace2, loading the Python plugin from
babeltrace-fun-plugins/my-first-components.

Finally, to investigate more in depth, you can increase the log level of
babeltrace2, like so:

  $ babeltrace2 --log-level DEBUG --plugin-path . -c source.demo.MyFirstSource -c sink.demo.MyFirstSink

This will output all sorts of things about babeltrace looking for
plugins and trying to load them.

Simon