services/tracing/public/mojom/perfetto_service.mojom

// Copyright 2018 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

module tracing.mojom;

const string kTraceEventDataSourceName = "org.chromium.trace_event";
const string kMetaDataSourceName = "org.chromium.trace_metadata";
const string kSystemTraceDataSourceName = "org.chromium.trace_system";
const string kArcTraceDataSourceName = "org.chromium.trace_arc";

// Brief description of the flow: There's a per-process ProducerClient which
// connects to the central PerfettoService and establishes a two-way connection
// with a ProducerHost. The latter will then pass a SharedMemoryBuffer to the
// ProducerClient and tell it to start logging events of a given type into it.
// As chunks of the buffer get filled up, the client will communicate this to
// the ProducerHost, which will tell Perfetto to copy the finished chunks into
// its central storage and pass them on to its consumers.

// For a more complete explanation of a Perfetto tracing session, see
// https://android.googlesource.com/platform/external/perfetto/+/master/docs/life-of-a-tracing-session.md

// See https://android.googlesource.com/platform/external/perfetto/
// for the full documentation of Perfetto concepts and its shared memory ABI.

// Passed by the client process as part of CommitDataRequest() to the central
// Perfetto service. Signals that a chunk (segment/page of the shared memory
// buffer which is owned by a per-thread TraceWriter) is ready for consumption
// (flushed or fully written).
struct ChunksToMove {
  // The page index within the producer:service shared memory buffer.
  uint32 page;
  // The chunk index within the given page.
  uint32 chunk;
  // The target ring-buffer in the service that the chunk should be copied into.
  uint32 target_buffer;
};

// Passed by the client process as part of CommitDataRequest() to the central
// Perfetto service. Used to patch previously written chunks (for example, to
// fill in size fields when protos span multiple chunks).
struct ChunkPatch {
  // Offset relative to the chunk defined in ChunksToPatch.
  uint32 offset;
  string data;
};

struct ChunksToPatch {
  // The triplet {target_buffer, writer_id, chunk_id} uniquely identifies a
  // chunk that has been copied over into the main, non-shared, trace buffer
  // owned by the service.
  uint32 target_buffer;
  uint32 writer_id;
  uint32 chunk_id;
  array<ChunkPatch> patches;
  // If false the chunk should be considered finalized and available to be read.
  bool has_more_patches;
};

struct CommitDataRequest {
  array<ChunksToMove> chunks_to_move;
  array<ChunksToPatch> chunks_to_patch;
  uint64 flush_request_id;
};

struct DataSourceConfig {
  string name;
  string trace_config;
  uint32 target_buffer;
};

struct DataSourceRegistration {
  string name;
  bool will_notify_on_stop;
};

interface ProducerHost {
  // Called by a ProducerClient to ask the service to:
  // 1) Move data from the shared memory buffer into the final tracing buffer
  //    owned by the service (through the |chunks_to_move|).
  // 2) Patch data (i.e. apply diff) that has been previously copied into the
  //    tracing buffer (if it's not been overwritten).
  // The service is robust in terms of tolerating malformed or malicious
  // requests.
  CommitData(CommitDataRequest data_request);

  // Called by a ProducerClient to let the Host know it can provide a specific
  // datasource.
  RegisterDataSource(DataSourceRegistration registration_info);

  // Called to let the Service know that a flush is complete.
  NotifyFlushComplete(uint64 flush_request_id);

  // Called by the ProducerClient to associate a TraceWriter with a target
  // buffer, which is required to support scraping of the SMB by the service.
  RegisterTraceWriter(uint32 writer_id, uint32 target_buffer);
  UnregisterTraceWriter(uint32 writer_id);
};

interface ProducerClient {
    OnTracingStart(handle<shared_buffer> shared_memory);

    // TODO(oysteine): Make a TypeTrait for sending the full DataSourceConfig.
    // Called by Perfetto (via ProducerHost) to request a data source to start
    // logging.
    StartDataSource(uint64 id, DataSourceConfig data_source_config);
    // Requesting a data source to stop logging again, with the id previously
    // sent in the StartDataSource call.
    StopDataSource(uint64 id) => ();
    Flush(uint64 flush_request_id, array<uint64> data_source_ids);
};

interface PerfettoService {
  ConnectToProducerHost(ProducerClient producer_client,
                        ProducerHost& producer_host);
};