Register a trace provider

This page describes how to register a new trace provider in a Fuchsia system.

To participate in tracing, new trace providers must be registered with the trace manager in the Fuchsia tracing system. (However, drivers don't have to register as a trace provider since the devhost process does it through libdriver.so.)

To register a trace provider, the steps are:

1. Register a component with the trace manager.
2. Set up capability routing.

Register a component with the trace manager

To register a component as a trace provider, you can use the libtrace-provider library to provide an asynchronous loop in your component's code. (For more information on tracing libraries, see Tracing libraries.)

See the examples below:

#include <lib/async-loop/cpp/loop.h>
#include <lib/async-loop/default.h>
#include <lib/trace-provider/provider.h>
// further includes

int main(int argc, const char** argv) {
  // process argv

  async::Loop loop(&kAsyncLoopConfigAttachToCurrentThread);
  trace::TraceProviderWithFdio trace_provider(
      loop.dispatcher(), "my_trace_provider");

  // further setup

  loop.Run();
  return 0;
}

#include <lib/async-loop/cpp/loop.h>
#include <lib/async-loop/default.h>
#include <lib/trace-provider/provider.h>

int main(int argc, char** argv) {
  zx_status_t status;
  async_loop_t* loop;
  trace_provider_t* trace_provider;

  // Create a message loop.
  status = async_loop_create(&kAsyncLoopConfigNoAttachToCurrentThread, &loop);
  if (status != ZX_OK) exit(1);

  // Start a thread for the loop to run on.
  // Alternatively, use async_loop_run() to run on the current thread.
  status = async_loop_start_thread(loop, "loop", NULL);
  if (status != ZX_OK) exit(1);

  // Create the trace provider.
  async_dispatcher_t* dispatcher = async_loop_get_dispatcher(loop);
  trace_provider = trace_provider_create(dispatcher);
  if (!trace_provider) exit(1);

  // Do something...

  // Tear down.
  trace_provider_destroy(trace_provider);
  async_loop_shutdown(loop);
  return 0;
}

fn main() {
    fuchsia_trace_provider::trace_provider_create_with_fdio();
    // ...
}

Set up capability routing

For your component to request the appropriate tracing capabilities, include the following field in the component manifest (.cml):

{
  include: [
    "trace/client.shard.cml",
  ],
  ...
}

This allows your component to communicate with the trace manager using the fuchsia.tracing.provider.Registry protocol as well as forward the offer to its direct children. If your component is a child of another component, you'll need to include the client.shard.cml in each of the parents' cmls as well.

If your component uses a Chromium-based fuchsia.web service and you want to be able to collect trace data from it, both the fuchsia.tracing.provider.Registry and fuchsia.tracing.perfetto.ProducerConnector capabilities need to be provided to your Context. (To understand how capabilities are passed to the Context, see fuchsia.web/CreateContextParams.service_directory.)

Once you have registered your component as a trace provider, you can enable tracing in your code. For more information, see the next Add tracing in your code page.