diff --git a/Android.bp b/Android.bp
index 83da02a..79de486 100644
--- a/Android.bp
+++ b/Android.bp
@@ -120,6 +120,7 @@
     "src/tracing/core/trace_stats.cc",
     "src/tracing/core/trace_writer_impl.cc",
     "src/tracing/core/tracing_service_impl.cc",
+    "src/tracing/core/tracing_service_state.cc",
     "src/tracing/core/virtual_destructors.cc",
     "src/tracing/trace_writer_base.cc",
   ],
@@ -333,6 +334,7 @@
     "src/tracing/core/trace_stats.cc",
     "src/tracing/core/trace_writer_impl.cc",
     "src/tracing/core/tracing_service_impl.cc",
+    "src/tracing/core/tracing_service_state.cc",
     "src/tracing/core/virtual_destructors.cc",
     "src/tracing/trace_writer_base.cc",
   ],
@@ -626,6 +628,7 @@
     "src/tracing/core/trace_stats.cc",
     "src/tracing/core/trace_writer_impl.cc",
     "src/tracing/core/tracing_service_impl.cc",
+    "src/tracing/core/tracing_service_state.cc",
     "src/tracing/core/virtual_destructors.cc",
     "src/tracing/trace_writer_base.cc",
   ],
@@ -831,6 +834,7 @@
     "src/tracing/core/trace_stats.cc",
     "src/tracing/core/trace_writer_impl.cc",
     "src/tracing/core/tracing_service_impl.cc",
+    "src/tracing/core/tracing_service_state.cc",
     "src/tracing/core/virtual_destructors.cc",
     "src/tracing/data_source.cc",
     "src/tracing/internal/in_process_tracing_backend.cc",
@@ -911,10 +915,12 @@
   srcs: [
     "protos/perfetto/common/android_log_constants.proto",
     "protos/perfetto/common/commit_data_request.proto",
+    "protos/perfetto/common/data_source_descriptor.proto",
     "protos/perfetto/common/descriptor.proto",
     "protos/perfetto/common/observable_events.proto",
     "protos/perfetto/common/sys_stats_counters.proto",
     "protos/perfetto/common/trace_stats.proto",
+    "protos/perfetto/common/tracing_service_state.proto",
   ],
   tools: [
     "aprotoc",
@@ -923,10 +929,12 @@
   out: [
     "external/perfetto/protos/perfetto/common/android_log_constants.pb.cc",
     "external/perfetto/protos/perfetto/common/commit_data_request.pb.cc",
+    "external/perfetto/protos/perfetto/common/data_source_descriptor.pb.cc",
     "external/perfetto/protos/perfetto/common/descriptor.pb.cc",
     "external/perfetto/protos/perfetto/common/observable_events.pb.cc",
     "external/perfetto/protos/perfetto/common/sys_stats_counters.pb.cc",
     "external/perfetto/protos/perfetto/common/trace_stats.pb.cc",
+    "external/perfetto/protos/perfetto/common/tracing_service_state.pb.cc",
   ],
 }
 
@@ -936,10 +944,12 @@
   srcs: [
     "protos/perfetto/common/android_log_constants.proto",
     "protos/perfetto/common/commit_data_request.proto",
+    "protos/perfetto/common/data_source_descriptor.proto",
     "protos/perfetto/common/descriptor.proto",
     "protos/perfetto/common/observable_events.proto",
     "protos/perfetto/common/sys_stats_counters.proto",
     "protos/perfetto/common/trace_stats.proto",
+    "protos/perfetto/common/tracing_service_state.proto",
   ],
   tools: [
     "aprotoc",
@@ -948,10 +958,12 @@
   out: [
     "external/perfetto/protos/perfetto/common/android_log_constants.pb.h",
     "external/perfetto/protos/perfetto/common/commit_data_request.pb.h",
+    "external/perfetto/protos/perfetto/common/data_source_descriptor.pb.h",
     "external/perfetto/protos/perfetto/common/descriptor.pb.h",
     "external/perfetto/protos/perfetto/common/observable_events.pb.h",
     "external/perfetto/protos/perfetto/common/sys_stats_counters.pb.h",
     "external/perfetto/protos/perfetto/common/trace_stats.pb.h",
+    "external/perfetto/protos/perfetto/common/tracing_service_state.pb.h",
   ],
   export_include_dirs: [
     "protos",
@@ -964,10 +976,12 @@
   srcs: [
     "protos/perfetto/common/android_log_constants.proto",
     "protos/perfetto/common/commit_data_request.proto",
+    "protos/perfetto/common/data_source_descriptor.proto",
     "protos/perfetto/common/descriptor.proto",
     "protos/perfetto/common/observable_events.proto",
     "protos/perfetto/common/sys_stats_counters.proto",
     "protos/perfetto/common/trace_stats.proto",
+    "protos/perfetto/common/tracing_service_state.proto",
   ],
   tools: [
     "aprotoc",
@@ -977,10 +991,12 @@
   out: [
     "external/perfetto/protos/perfetto/common/android_log_constants.pbzero.cc",
     "external/perfetto/protos/perfetto/common/commit_data_request.pbzero.cc",
+    "external/perfetto/protos/perfetto/common/data_source_descriptor.pbzero.cc",
     "external/perfetto/protos/perfetto/common/descriptor.pbzero.cc",
     "external/perfetto/protos/perfetto/common/observable_events.pbzero.cc",
     "external/perfetto/protos/perfetto/common/sys_stats_counters.pbzero.cc",
     "external/perfetto/protos/perfetto/common/trace_stats.pbzero.cc",
+    "external/perfetto/protos/perfetto/common/tracing_service_state.pbzero.cc",
   ],
 }
 
@@ -990,10 +1006,12 @@
   srcs: [
     "protos/perfetto/common/android_log_constants.proto",
     "protos/perfetto/common/commit_data_request.proto",
+    "protos/perfetto/common/data_source_descriptor.proto",
     "protos/perfetto/common/descriptor.proto",
     "protos/perfetto/common/observable_events.proto",
     "protos/perfetto/common/sys_stats_counters.proto",
     "protos/perfetto/common/trace_stats.proto",
+    "protos/perfetto/common/tracing_service_state.proto",
   ],
   tools: [
     "aprotoc",
@@ -1003,10 +1021,12 @@
   out: [
     "external/perfetto/protos/perfetto/common/android_log_constants.pbzero.h",
     "external/perfetto/protos/perfetto/common/commit_data_request.pbzero.h",
+    "external/perfetto/protos/perfetto/common/data_source_descriptor.pbzero.h",
     "external/perfetto/protos/perfetto/common/descriptor.pbzero.h",
     "external/perfetto/protos/perfetto/common/observable_events.pbzero.h",
     "external/perfetto/protos/perfetto/common/sys_stats_counters.pbzero.h",
     "external/perfetto/protos/perfetto/common/trace_stats.pbzero.h",
+    "external/perfetto/protos/perfetto/common/tracing_service_state.pbzero.h",
   ],
   export_include_dirs: [
     "protos",
@@ -1020,7 +1040,6 @@
     "protos/perfetto/config/android/android_log_config.proto",
     "protos/perfetto/config/chrome/chrome_config.proto",
     "protos/perfetto/config/data_source_config.proto",
-    "protos/perfetto/config/data_source_descriptor.proto",
     "protos/perfetto/config/ftrace/ftrace_config.proto",
     "protos/perfetto/config/inode_file/inode_file_config.proto",
     "protos/perfetto/config/power/android_power_config.proto",
@@ -1038,7 +1057,6 @@
     "external/perfetto/protos/perfetto/config/android/android_log_config.pb.cc",
     "external/perfetto/protos/perfetto/config/chrome/chrome_config.pb.cc",
     "external/perfetto/protos/perfetto/config/data_source_config.pb.cc",
-    "external/perfetto/protos/perfetto/config/data_source_descriptor.pb.cc",
     "external/perfetto/protos/perfetto/config/ftrace/ftrace_config.pb.cc",
     "external/perfetto/protos/perfetto/config/inode_file/inode_file_config.pb.cc",
     "external/perfetto/protos/perfetto/config/power/android_power_config.pb.cc",
@@ -1057,7 +1075,6 @@
     "protos/perfetto/config/android/android_log_config.proto",
     "protos/perfetto/config/chrome/chrome_config.proto",
     "protos/perfetto/config/data_source_config.proto",
-    "protos/perfetto/config/data_source_descriptor.proto",
     "protos/perfetto/config/ftrace/ftrace_config.proto",
     "protos/perfetto/config/inode_file/inode_file_config.proto",
     "protos/perfetto/config/power/android_power_config.proto",
@@ -1075,7 +1092,6 @@
     "external/perfetto/protos/perfetto/config/android/android_log_config.pb.h",
     "external/perfetto/protos/perfetto/config/chrome/chrome_config.pb.h",
     "external/perfetto/protos/perfetto/config/data_source_config.pb.h",
-    "external/perfetto/protos/perfetto/config/data_source_descriptor.pb.h",
     "external/perfetto/protos/perfetto/config/ftrace/ftrace_config.pb.h",
     "external/perfetto/protos/perfetto/config/inode_file/inode_file_config.pb.h",
     "external/perfetto/protos/perfetto/config/power/android_power_config.pb.h",
@@ -1097,7 +1113,6 @@
     "protos/perfetto/config/android/android_log_config.proto",
     "protos/perfetto/config/chrome/chrome_config.proto",
     "protos/perfetto/config/data_source_config.proto",
-    "protos/perfetto/config/data_source_descriptor.proto",
     "protos/perfetto/config/ftrace/ftrace_config.proto",
     "protos/perfetto/config/inode_file/inode_file_config.proto",
     "protos/perfetto/config/power/android_power_config.proto",
@@ -1116,7 +1131,6 @@
     "external/perfetto/protos/perfetto/config/android/android_log_config.pbzero.cc",
     "external/perfetto/protos/perfetto/config/chrome/chrome_config.pbzero.cc",
     "external/perfetto/protos/perfetto/config/data_source_config.pbzero.cc",
-    "external/perfetto/protos/perfetto/config/data_source_descriptor.pbzero.cc",
     "external/perfetto/protos/perfetto/config/ftrace/ftrace_config.pbzero.cc",
     "external/perfetto/protos/perfetto/config/inode_file/inode_file_config.pbzero.cc",
     "external/perfetto/protos/perfetto/config/power/android_power_config.pbzero.cc",
@@ -1135,7 +1149,6 @@
     "protos/perfetto/config/android/android_log_config.proto",
     "protos/perfetto/config/chrome/chrome_config.proto",
     "protos/perfetto/config/data_source_config.proto",
-    "protos/perfetto/config/data_source_descriptor.proto",
     "protos/perfetto/config/ftrace/ftrace_config.proto",
     "protos/perfetto/config/inode_file/inode_file_config.proto",
     "protos/perfetto/config/power/android_power_config.proto",
@@ -1154,7 +1167,6 @@
     "external/perfetto/protos/perfetto/config/android/android_log_config.pbzero.h",
     "external/perfetto/protos/perfetto/config/chrome/chrome_config.pbzero.h",
     "external/perfetto/protos/perfetto/config/data_source_config.pbzero.h",
-    "external/perfetto/protos/perfetto/config/data_source_descriptor.pbzero.h",
     "external/perfetto/protos/perfetto/config/ftrace/ftrace_config.pbzero.h",
     "external/perfetto/protos/perfetto/config/inode_file/inode_file_config.pbzero.h",
     "external/perfetto/protos/perfetto/config/power/android_power_config.pbzero.h",
@@ -2906,6 +2918,7 @@
     "src/tracing/core/trace_stats.cc",
     "src/tracing/core/trace_writer_impl.cc",
     "src/tracing/core/tracing_service_impl.cc",
+    "src/tracing/core/tracing_service_state.cc",
     "src/tracing/core/virtual_destructors.cc",
     "src/tracing/ipc/consumer/consumer_ipc_client_impl.cc",
     "src/tracing/ipc/default_socket.cc",
@@ -3262,6 +3275,7 @@
     "src/tracing/core/trace_writer_impl_unittest.cc",
     "src/tracing/core/tracing_service_impl.cc",
     "src/tracing/core/tracing_service_impl_unittest.cc",
+    "src/tracing/core/tracing_service_state.cc",
     "src/tracing/core/virtual_destructors.cc",
     "src/tracing/ipc/posix_shared_memory_unittest.cc",
     "src/tracing/test/aligned_buffer_test.cc",
@@ -3633,6 +3647,7 @@
     "src/tracing/core/trace_stats.cc",
     "src/tracing/core/trace_writer_impl.cc",
     "src/tracing/core/tracing_service_impl.cc",
+    "src/tracing/core/tracing_service_state.cc",
     "src/tracing/core/virtual_destructors.cc",
     "src/tracing/trace_writer_base.cc",
   ],
diff --git a/include/perfetto/ext/tracing/core/BUILD.gn b/include/perfetto/ext/tracing/core/BUILD.gn
index 1812133..78bc8e3 100644
--- a/include/perfetto/ext/tracing/core/BUILD.gn
+++ b/include/perfetto/ext/tracing/core/BUILD.gn
@@ -35,5 +35,6 @@
     "trace_stats.h",
     "trace_writer.h",
     "tracing_service.h",
+    "tracing_service_state.h",
   ]
 }
diff --git a/include/perfetto/ext/tracing/core/consumer.h b/include/perfetto/ext/tracing/core/consumer.h
index b8d722a..ccbd072 100644
--- a/include/perfetto/ext/tracing/core/consumer.h
+++ b/include/perfetto/ext/tracing/core/consumer.h
@@ -28,6 +28,7 @@
 class TraceConfig;
 class TracePacket;
 class TraceStats;
+class TracingServiceState;
 
 class PERFETTO_EXPORT Consumer {
  public:
diff --git a/include/perfetto/ext/tracing/core/data_source_descriptor.h b/include/perfetto/ext/tracing/core/data_source_descriptor.h
index 652261d..ed61e47 100644
--- a/include/perfetto/ext/tracing/core/data_source_descriptor.h
+++ b/include/perfetto/ext/tracing/core/data_source_descriptor.h
@@ -18,7 +18,7 @@
  * AUTOGENERATED - DO NOT EDIT
  *******************************************************************************
  * This file has been generated from the protobuf message
- * perfetto/config/data_source_descriptor.proto
+ * perfetto/common/data_source_descriptor.proto
  * by
  * ../../tools/proto_to_cpp/proto_to_cpp.cc.
  * If you need to make changes here, change the .proto file and then run
diff --git a/include/perfetto/ext/tracing/core/tracing_service.h b/include/perfetto/ext/tracing/core/tracing_service.h
index c24e629..67b5bf3 100644
--- a/include/perfetto/ext/tracing/core/tracing_service.h
+++ b/include/perfetto/ext/tracing/core/tracing_service.h
@@ -39,6 +39,7 @@
 class DataSourceDescriptor;
 class Producer;
 class SharedMemoryArbiter;
+class TracingServiceState;
 class TraceConfig;
 class TraceWriter;
 
@@ -202,6 +203,12 @@
   //
   // TODO(eseckler): Extend this to support producers & data sources.
   virtual void ObserveEvents(uint32_t enabled_event_types) = 0;
+
+  // Used to obtain the list of connected data sources and other info about
+  // the tracing service.
+  using QueryServiceStateCallback =
+      std::function<void(bool success, const TracingServiceState&)>;
+  virtual void QueryServiceState(QueryServiceStateCallback) = 0;
 };  // class ConsumerEndpoint.
 
 // The public API of the tracing Service business logic.
diff --git a/include/perfetto/ext/tracing/core/tracing_service_state.h b/include/perfetto/ext/tracing/core/tracing_service_state.h
new file mode 100644
index 0000000..27a5dd6
--- /dev/null
+++ b/include/perfetto/ext/tracing/core/tracing_service_state.h
@@ -0,0 +1,180 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*******************************************************************************
+ * AUTOGENERATED - DO NOT EDIT
+ *******************************************************************************
+ * This file has been generated from the protobuf message
+ * perfetto/common/tracing_service_state.proto
+ * by
+ * ../../tools/proto_to_cpp/proto_to_cpp.cc.
+ * If you need to make changes here, change the .proto file and then run
+ * ./tools/gen_tracing_cpp_headers_from_protos
+ */
+
+#ifndef INCLUDE_PERFETTO_EXT_TRACING_CORE_TRACING_SERVICE_STATE_H_
+#define INCLUDE_PERFETTO_EXT_TRACING_CORE_TRACING_SERVICE_STATE_H_
+
+#include <stdint.h>
+#include <string>
+#include <type_traits>
+#include <vector>
+
+#include "perfetto/base/export.h"
+
+#include "perfetto/ext/tracing/core/data_source_descriptor.h"
+
+// Forward declarations for protobuf types.
+namespace perfetto {
+namespace protos {
+class TracingServiceState;
+class TracingServiceState_Producer;
+class TracingServiceState_DataSource;
+class DataSourceDescriptor;
+}  // namespace protos
+}  // namespace perfetto
+
+namespace perfetto {
+
+class PERFETTO_EXPORT TracingServiceState {
+ public:
+  class PERFETTO_EXPORT Producer {
+   public:
+    Producer();
+    ~Producer();
+    Producer(Producer&&) noexcept;
+    Producer& operator=(Producer&&);
+    Producer(const Producer&);
+    Producer& operator=(const Producer&);
+    bool operator==(const Producer&) const;
+    bool operator!=(const Producer& other) const { return !(*this == other); }
+
+    // Raw proto decoding.
+    void ParseRawProto(const std::string&);
+    // Conversion methods from/to the corresponding protobuf types.
+    void FromProto(const perfetto::protos::TracingServiceState_Producer&);
+    void ToProto(perfetto::protos::TracingServiceState_Producer*) const;
+
+    int32_t id() const { return id_; }
+    void set_id(int32_t value) { id_ = value; }
+
+    const std::string& name() const { return name_; }
+    void set_name(const std::string& value) { name_ = value; }
+
+    int32_t uid() const { return uid_; }
+    void set_uid(int32_t value) { uid_ = value; }
+
+   private:
+    int32_t id_ = {};
+    std::string name_ = {};
+    int32_t uid_ = {};
+
+    // Allows to preserve unknown protobuf fields for compatibility
+    // with future versions of .proto files.
+    std::string unknown_fields_;
+  };
+
+  class PERFETTO_EXPORT DataSource {
+   public:
+    DataSource();
+    ~DataSource();
+    DataSource(DataSource&&) noexcept;
+    DataSource& operator=(DataSource&&);
+    DataSource(const DataSource&);
+    DataSource& operator=(const DataSource&);
+    bool operator==(const DataSource&) const;
+    bool operator!=(const DataSource& other) const { return !(*this == other); }
+
+    // Raw proto decoding.
+    void ParseRawProto(const std::string&);
+    // Conversion methods from/to the corresponding protobuf types.
+    void FromProto(const perfetto::protos::TracingServiceState_DataSource&);
+    void ToProto(perfetto::protos::TracingServiceState_DataSource*) const;
+
+    const DataSourceDescriptor& descriptor() const { return descriptor_; }
+    DataSourceDescriptor* mutable_descriptor() { return &descriptor_; }
+
+    int32_t producer_id() const { return producer_id_; }
+    void set_producer_id(int32_t value) { producer_id_ = value; }
+
+   private:
+    DataSourceDescriptor descriptor_ = {};
+    int32_t producer_id_ = {};
+
+    // Allows to preserve unknown protobuf fields for compatibility
+    // with future versions of .proto files.
+    std::string unknown_fields_;
+  };
+
+  TracingServiceState();
+  ~TracingServiceState();
+  TracingServiceState(TracingServiceState&&) noexcept;
+  TracingServiceState& operator=(TracingServiceState&&);
+  TracingServiceState(const TracingServiceState&);
+  TracingServiceState& operator=(const TracingServiceState&);
+  bool operator==(const TracingServiceState&) const;
+  bool operator!=(const TracingServiceState& other) const {
+    return !(*this == other);
+  }
+
+  // Raw proto decoding.
+  void ParseRawProto(const std::string&);
+  // Conversion methods from/to the corresponding protobuf types.
+  void FromProto(const perfetto::protos::TracingServiceState&);
+  void ToProto(perfetto::protos::TracingServiceState*) const;
+
+  int producers_size() const { return static_cast<int>(producers_.size()); }
+  const std::vector<Producer>& producers() const { return producers_; }
+  std::vector<Producer>* mutable_producers() { return &producers_; }
+  void clear_producers() { producers_.clear(); }
+  Producer* add_producers() {
+    producers_.emplace_back();
+    return &producers_.back();
+  }
+
+  int data_sources_size() const {
+    return static_cast<int>(data_sources_.size());
+  }
+  const std::vector<DataSource>& data_sources() const { return data_sources_; }
+  std::vector<DataSource>* mutable_data_sources() { return &data_sources_; }
+  void clear_data_sources() { data_sources_.clear(); }
+  DataSource* add_data_sources() {
+    data_sources_.emplace_back();
+    return &data_sources_.back();
+  }
+
+  int32_t num_sessions() const { return num_sessions_; }
+  void set_num_sessions(int32_t value) { num_sessions_ = value; }
+
+  int32_t num_sessions_started() const { return num_sessions_started_; }
+  void set_num_sessions_started(int32_t value) {
+    num_sessions_started_ = value;
+  }
+
+ private:
+  std::vector<Producer> producers_;
+  std::vector<DataSource> data_sources_;
+  int32_t num_sessions_ = {};
+  int32_t num_sessions_started_ = {};
+
+  // Allows to preserve unknown protobuf fields for compatibility
+  // with future versions of .proto files.
+  std::string unknown_fields_;
+};
+
+}  // namespace perfetto
+
+#endif  // INCLUDE_PERFETTO_EXT_TRACING_CORE_TRACING_SERVICE_STATE_H_
diff --git a/protos/BUILD b/protos/BUILD
index 4c280e9..bbf632a 100644
--- a/protos/BUILD
+++ b/protos/BUILD
@@ -30,10 +30,12 @@
     srcs = [
         "perfetto/common/android_log_constants.proto",
         "perfetto/common/commit_data_request.proto",
+        "perfetto/common/data_source_descriptor.proto",
         "perfetto/common/descriptor.proto",
         "perfetto/common/observable_events.proto",
         "perfetto/common/sys_stats_counters.proto",
         "perfetto/common/trace_stats.proto",
+        "perfetto/common/tracing_service_state.proto",
     ],
     has_services = 1,
     cc_api_version = 2,
@@ -71,10 +73,12 @@
     srcs = [
         "perfetto/common/android_log_constants.proto",
         "perfetto/common/commit_data_request.proto",
+        "perfetto/common/data_source_descriptor.proto",
         "perfetto/common/descriptor.proto",
         "perfetto/common/observable_events.proto",
         "perfetto/common/sys_stats_counters.proto",
         "perfetto/common/trace_stats.proto",
+        "perfetto/common/tracing_service_state.proto",
     ],
 )
 
@@ -94,7 +98,6 @@
         "perfetto/config/android/android_log_config.proto",
         "perfetto/config/chrome/chrome_config.proto",
         "perfetto/config/data_source_config.proto",
-        "perfetto/config/data_source_descriptor.proto",
         "perfetto/config/ftrace/ftrace_config.proto",
         "perfetto/config/inode_file/inode_file_config.proto",
         "perfetto/config/power/android_power_config.proto",
@@ -180,7 +183,6 @@
         "perfetto/config/android/android_log_config.proto",
         "perfetto/config/chrome/chrome_config.proto",
         "perfetto/config/data_source_config.proto",
-        "perfetto/config/data_source_descriptor.proto",
         "perfetto/config/ftrace/ftrace_config.proto",
         "perfetto/config/inode_file/inode_file_config.proto",
         "perfetto/config/power/android_power_config.proto",
diff --git a/protos/perfetto/common/BUILD.gn b/protos/perfetto/common/BUILD.gn
index 36a9b20..e70b03c 100644
--- a/protos/perfetto/common/BUILD.gn
+++ b/protos/perfetto/common/BUILD.gn
@@ -19,9 +19,11 @@
 common_sources = [
   "android_log_constants.proto",
   "commit_data_request.proto",
+  "data_source_descriptor.proto",
   "descriptor.proto",
   "observable_events.proto",
   "sys_stats_counters.proto",
+  "tracing_service_state.proto",
   "trace_stats.proto",
 ]
 
diff --git a/protos/perfetto/config/data_source_descriptor.proto b/protos/perfetto/common/data_source_descriptor.proto
similarity index 93%
rename from protos/perfetto/config/data_source_descriptor.proto
rename to protos/perfetto/common/data_source_descriptor.proto
index 28e59d7..08ed058 100644
--- a/protos/perfetto/config/data_source_descriptor.proto
+++ b/protos/perfetto/common/data_source_descriptor.proto
@@ -42,7 +42,4 @@
   // set if the data source writes packets that refer to previous trace
   // contents, and knows how to stop referring to the already-emitted data.
   optional bool handles_incremental_state_clear = 4;
-
-  // TODO: this should have a structure to enable reflection of the proto
-  // fields emitted (see go/perfetto-logging).
 }
diff --git a/protos/perfetto/common/tracing_service_state.proto b/protos/perfetto/common/tracing_service_state.proto
new file mode 100644
index 0000000..dd8572c
--- /dev/null
+++ b/protos/perfetto/common/tracing_service_state.proto
@@ -0,0 +1,59 @@
+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+syntax = "proto2";
+option optimize_for = LITE_RUNTIME;
+
+package perfetto.protos;
+
+import "perfetto/common/data_source_descriptor.proto";
+
+// When editing this file run ./tools/gen_tracing_cpp_headers_from_protos.py
+// to reflect changes in the corresponding C++ headers.
+
+// Reports the state of the tracing service. Used to gather details about the
+// data sources connected.
+// See ConsumerPort::QueryServiceState().
+message TracingServiceState {
+  // Describes a producer process.
+  message Producer {
+    optional int32 id = 1;     // Unique ID of the producer (monotonic counter).
+    optional string name = 2;  // Typically matches the process name.
+    optional int32 uid = 3;    // Unix uid of the remote process.
+  }
+
+  // Describes a data source registered by a producer. Data sources are listed
+  // regardless of the fact that they are being used or not.
+  message DataSource {
+    // Descriptor passed by the data source when calling RegisterDataSource().
+    optional DataSourceDescriptor descriptor = 1;
+
+    // ID of the producer, as per Producer.id.
+    optional int32 producer_id = 2;
+  }
+
+  // Lists all the producers connected.
+  repeated Producer producers = 1;
+
+  // Lists the data sources available.
+  repeated DataSource data_sources = 2;
+
+  // Total number of tracing sessions.
+  optional int32 num_sessions = 3;
+
+  // Number of tracing sessions in the started state. Always <= num_sessions.
+  optional int32 num_sessions_started = 4;
+}
diff --git a/protos/perfetto/config/BUILD.gn b/protos/perfetto/config/BUILD.gn
index 5761fda..966a5c3 100644
--- a/protos/perfetto/config/BUILD.gn
+++ b/protos/perfetto/config/BUILD.gn
@@ -30,7 +30,6 @@
     "android/android_log_config.proto",
     "chrome/chrome_config.proto",
     "data_source_config.proto",
-    "data_source_descriptor.proto",
     "ftrace/ftrace_config.proto",
     "inode_file/inode_file_config.proto",
     "power/android_power_config.proto",
@@ -55,7 +54,6 @@
     "android/android_log_config.proto",
     "chrome/chrome_config.proto",
     "data_source_config.proto",
-    "data_source_descriptor.proto",
     "ftrace/ftrace_config.proto",
     "inode_file/inode_file_config.proto",
     "power/android_power_config.proto",
diff --git a/protos/perfetto/ipc/consumer_port.proto b/protos/perfetto/ipc/consumer_port.proto
index 5c293ab..595c53b 100644
--- a/protos/perfetto/ipc/consumer_port.proto
+++ b/protos/perfetto/ipc/consumer_port.proto
@@ -18,6 +18,7 @@
 option optimize_for = LITE_RUNTIME;
 
 import "perfetto/common/observable_events.proto";
+import "perfetto/common/tracing_service_state.proto";
 import "perfetto/common/trace_stats.proto";
 import "perfetto/config/trace_config.proto";
 
@@ -99,7 +100,13 @@
   rpc ObserveEvents(ObserveEventsRequest)
       returns (stream ObserveEventsResponse) {}
 
-  // TODO rpc ListDataSources(), for the UI.
+  // ----------------------------------------------------
+  // All methods below have been introduced in Android R.
+  // ----------------------------------------------------
+
+  // Allows to obtain the list of data sources connected and their descriptors.
+  rpc QueryServiceState(QueryServiceStateRequest)
+      returns (stream QueryServiceStateResponse) {}
 }
 
 // Arguments for rpc EnableTracing().
@@ -213,3 +220,10 @@
 message ObserveEventsResponse {
   optional ObservableEvents events = 1;
 }
+
+// Arguments for rpc QueryServiceState
+message QueryServiceStateRequest {}
+
+message QueryServiceStateResponse {
+  optional TracingServiceState service_state = 1;
+}
diff --git a/protos/perfetto/ipc/producer_port.proto b/protos/perfetto/ipc/producer_port.proto
index e129afd..465022b 100644
--- a/protos/perfetto/ipc/producer_port.proto
+++ b/protos/perfetto/ipc/producer_port.proto
@@ -19,7 +19,7 @@
 
 import "perfetto/common/commit_data_request.proto";
 import "perfetto/config/data_source_config.proto";
-import "perfetto/config/data_source_descriptor.proto";
+import "perfetto/common/data_source_descriptor.proto";
 
 package perfetto.protos;
 
diff --git a/src/perfetto_cmd/perfetto_cmd.cc b/src/perfetto_cmd/perfetto_cmd.cc
index 823fbdd..9a6d492 100644
--- a/src/perfetto_cmd/perfetto_cmd.cc
+++ b/src/perfetto_cmd/perfetto_cmd.cc
@@ -41,11 +41,13 @@
 #include "perfetto/ext/tracing/core/data_source_descriptor.h"
 #include "perfetto/ext/tracing/core/trace_config.h"
 #include "perfetto/ext/tracing/core/trace_packet.h"
+#include "perfetto/ext/tracing/core/tracing_service_state.h"
 #include "perfetto/protozero/proto_utils.h"
 #include "src/perfetto_cmd/config.h"
 #include "src/perfetto_cmd/pbtxt_to_pb.h"
 #include "src/perfetto_cmd/trigger_producer.h"
 
+#include "perfetto/common/tracing_service_state.pb.h"
 #include "perfetto/config/trace_config.pb.h"
 
 #include "src/tracing/ipc/default_socket.h"
@@ -135,19 +137,27 @@
 // created by the system by setting setprop persist.traced.enable=1.
 const char* kTempDropBoxTraceDir = "/data/misc/perfetto-traces";
 
-using protozero::proto_utils::WriteVarInt;
 using protozero::proto_utils::MakeTagLengthDelimited;
+using protozero::proto_utils::WriteVarInt;
 
 int PerfettoCmd::PrintUsage(const char* argv0) {
   PERFETTO_ELOG(R"(
 Usage: %s
-  --background     -d      : Exits immediately and continues tracing in background
+  --background     -d      : Exits immediately and continues tracing in
+                             background
   --config         -c      : /path/to/trace/config/file or - for stdin
   --out            -o      : /path/to/out/trace/file or - for stdout
   --dropbox           TAG  : Upload trace into DropBox using tag TAG
-  --no-guardrails          : Ignore guardrails triggered when using --dropbox (for testing).
-  --txt                    : Parse config as pbtxt. Not a stable API. Not for production use.
-  --reset-guardrails       : Resets the state of the guardails and exits (for testing).
+  --no-guardrails          : Ignore guardrails triggered when using --dropbox
+                             (for testing).
+  --txt                    : Parse config as pbtxt. Not for production use.
+                             Not a stable API.
+  --reset-guardrails       : Resets the state of the guardails and exits
+                             (for testing).
+  --query                  : Queries the service state and prints it as
+                             human-readable text.
+  --query-raw              : Like --query, but prints raw proto-encoded bytes
+                             of tracing_service_state.proto.
   --help           -h
 
 
@@ -192,6 +202,8 @@
     OPT_ATTACH,
     OPT_IS_DETACHED,
     OPT_STOP,
+    OPT_QUERY,
+    OPT_QUERY_RAW,
   };
   static const struct option long_options[] = {
       {"help", no_argument, nullptr, 'h'},
@@ -214,6 +226,8 @@
       {"is_detached", required_argument, nullptr, OPT_IS_DETACHED},
       {"stop", no_argument, nullptr, OPT_STOP},
       {"app", required_argument, nullptr, OPT_ATRACE_APP},
+      {"query", no_argument, nullptr, OPT_QUERY},
+      {"query-raw", no_argument, nullptr, OPT_QUERY_RAW},
       {nullptr, 0, nullptr, 0}};
 
   int option_index = 0;
@@ -366,6 +380,17 @@
       continue;
     }
 
+    if (option == OPT_QUERY) {
+      query_service_ = true;
+      continue;
+    }
+
+    if (option == OPT_QUERY_RAW) {
+      query_service_ = true;
+      query_service_output_raw_ = true;
+      continue;
+    }
+
     return PrintUsage(argv[0]);
   }
 
@@ -374,6 +399,11 @@
     config_options.categories.push_back(argv[i]);
   }
 
+  if (query_service_ && (is_detach() || is_attach() || background)) {
+    PERFETTO_ELOG("--query cannot be combined with any other argument");
+    return 1;
+  }
+
   if (is_detach() && is_attach()) {
     PERFETTO_ELOG("--attach and --detach are mutually exclusive");
     return 1;
@@ -398,9 +428,10 @@
   perfetto::protos::TraceConfig trace_config_proto;
   std::vector<std::string> triggers_to_activate;
   bool parsed = false;
-  if (is_attach()) {
+  const bool will_trace = !is_attach() && !query_service_;
+  if (!will_trace) {
     if ((!trace_config_raw.empty() || has_config_options)) {
-      PERFETTO_ELOG("Cannot specify a trace config with --attach");
+      PERFETTO_ELOG("Cannot specify a trace config with this option");
       return 1;
     }
   } else if (has_config_options) {
@@ -430,7 +461,7 @@
     *trace_config_proto.mutable_statsd_metadata() = std::move(statsd_metadata);
     trace_config_->FromProto(trace_config_proto);
     trace_config_raw.clear();
-  } else if (!is_attach()) {
+  } else if (will_trace) {
     PERFETTO_ELOG("The trace config is invalid, bailing out.");
     return 1;
   }
@@ -457,10 +488,10 @@
   }
 
   bool open_out_file = true;
-  if (is_attach()) {
+  if (!will_trace) {
     open_out_file = false;
     if (!trace_out_path_.empty() || !dropbox_tag_.empty()) {
-      PERFETTO_ELOG("Can't pass an --out file (or --dropbox) to --attach");
+      PERFETTO_ELOG("Can't pass an --out file (or --dropbox) with this option");
       return 1;
     }
   } else if (!triggers_to_activate.empty()) {
@@ -508,16 +539,24 @@
   // the options.
   if (!triggers_to_activate.empty()) {
     bool finished_with_success = false;
-    TriggerProducer producer(&task_runner_,
-                             [this, &finished_with_success](bool success) {
-                               finished_with_success = success;
-                               task_runner_.Quit();
-                             },
-                             &triggers_to_activate);
+    TriggerProducer producer(
+        &task_runner_,
+        [this, &finished_with_success](bool success) {
+          finished_with_success = success;
+          task_runner_.Quit();
+        },
+        &triggers_to_activate);
     task_runner_.Run();
     return finished_with_success ? 0 : 1;
   }
 
+  if (query_service_) {
+    consumer_endpoint_ =
+        ConsumerIPCClient::Connect(GetConsumerSocket(), this, &task_runner_);
+    task_runner_.Run();
+    return 1;  // We can legitimately get here if the service disconnects.
+  }
+
   RateLimiter::Args args{};
   args.is_dropbox = !dropbox_tag_.empty();
   args.current_time = base::GetWallTimeS();
@@ -549,6 +588,16 @@
 }
 
 void PerfettoCmd::OnConnect() {
+  if (query_service_) {
+    consumer_endpoint_->QueryServiceState(
+        [this](bool success, const TracingServiceState& svc_state) {
+          PrintServiceState(success, svc_state);
+          fflush(stdout);
+          exit(success ? 0 : 1);
+        });
+    return;
+  }
+
   if (is_attach()) {
     consumer_endpoint_->Attach(attach_key_);
     return;
@@ -774,6 +823,43 @@
   // TODO(eseckler): Support GetTraceStats().
 }
 
+void PerfettoCmd::PrintServiceState(bool success,
+                                    const TracingServiceState& svc_state) {
+  if (!success) {
+    PERFETTO_ELOG("Failed to query the service state");
+    return;
+  }
+
+  if (query_service_output_raw_) {
+    protos::TracingServiceState proto;
+    svc_state.ToProto(&proto);
+    std::string str = proto.SerializeAsString();
+    fwrite(str.data(), 1, str.size(), stdout);
+    return;
+  }
+
+  printf("Not meant for machine consumption. Use --query-raw for scripts.\n");
+
+  for (const auto& producer : svc_state.producers()) {
+    printf("producers: {\n");
+    printf("  id: %d\n", producer.id());
+    printf("  name: \"%s\" \n", producer.name().c_str());
+    printf("  uid: %d \n", producer.uid());
+    printf("}\n");
+  }
+
+  for (const auto& ds : svc_state.data_sources()) {
+    printf("data_sources: {\n");
+    printf("  producer_id: %d\n", ds.producer_id());
+    printf("  descriptor: {\n");
+    printf("    name: \"%s\"\n", ds.descriptor().name().c_str());
+    printf("  }\n");
+    printf("}\n");
+  }
+  printf("num_sessions: %d\n", svc_state.num_sessions());
+  printf("num_sessions_started: %d\n", svc_state.num_sessions_started());
+}
+
 void PerfettoCmd::OnObservableEvents(
     const ObservableEvents& /*observable_events*/) {}
 
diff --git a/src/perfetto_cmd/perfetto_cmd.h b/src/perfetto_cmd/perfetto_cmd.h
index 0461ab8..959b669 100644
--- a/src/perfetto_cmd/perfetto_cmd.h
+++ b/src/perfetto_cmd/perfetto_cmd.h
@@ -70,6 +70,7 @@
   void SetupCtrlCSignalHandler();
   void FinalizeTraceAndExit();
   int PrintUsage(const char* argv0);
+  void PrintServiceState(bool success, const TracingServiceState&);
   void OnTimeout();
   bool is_detach() const { return !detach_key_.empty(); }
   bool is_attach() const { return !attach_key_.empty(); }
@@ -88,6 +89,8 @@
   std::string attach_key_;
   bool stop_trace_once_attached_ = false;
   bool redetach_once_attached_ = false;
+  bool query_service_ = false;
+  bool query_service_output_raw_ = false;
 };
 
 }  // namespace perfetto
diff --git a/src/tracing/BUILD.gn b/src/tracing/BUILD.gn
index 0ac05d4..39fbf25 100644
--- a/src/tracing/BUILD.gn
+++ b/src/tracing/BUILD.gn
@@ -62,6 +62,7 @@
     "core/trace_writer_impl.h",
     "core/tracing_service_impl.cc",
     "core/tracing_service_impl.h",
+    "core/tracing_service_state.cc",
     "core/virtual_destructors.cc",
   ]
 }
diff --git a/src/tracing/core/data_source_descriptor.cc b/src/tracing/core/data_source_descriptor.cc
index 9c2ccb2..650ce42 100644
--- a/src/tracing/core/data_source_descriptor.cc
+++ b/src/tracing/core/data_source_descriptor.cc
@@ -18,7 +18,7 @@
  * AUTOGENERATED - DO NOT EDIT
  *******************************************************************************
  * This file has been generated from the protobuf message
- * perfetto/config/data_source_descriptor.proto
+ * perfetto/common/data_source_descriptor.proto
  * by
  * ../../tools/proto_to_cpp/proto_to_cpp.cc.
  * If you need to make changes here, change the .proto file and then run
@@ -27,7 +27,7 @@
 
 #include "perfetto/ext/tracing/core/data_source_descriptor.h"
 
-#include "perfetto/config/data_source_descriptor.pb.h"
+#include "perfetto/common/data_source_descriptor.pb.h"
 
 namespace perfetto {
 
diff --git a/src/tracing/core/tracing_service_impl.cc b/src/tracing/core/tracing_service_impl.cc
index 083e759..c0908d1 100644
--- a/src/tracing/core/tracing_service_impl.cc
+++ b/src/tracing/core/tracing_service_impl.cc
@@ -44,11 +44,13 @@
 #include "perfetto/ext/base/watchdog.h"
 #include "perfetto/ext/tracing/core/consumer.h"
 #include "perfetto/ext/tracing/core/data_source_config.h"
+#include "perfetto/ext/tracing/core/data_source_descriptor.h"
 #include "perfetto/ext/tracing/core/producer.h"
 #include "perfetto/ext/tracing/core/shared_memory.h"
 #include "perfetto/ext/tracing/core/shared_memory_abi.h"
 #include "perfetto/ext/tracing/core/trace_packet.h"
 #include "perfetto/ext/tracing/core/trace_writer.h"
+#include "perfetto/ext/tracing/core/tracing_service_state.h"
 #include "src/tracing/core/packet_stream_validator.h"
 #include "src/tracing/core/shared_memory_arbiter_impl.h"
 #include "src/tracing/core/trace_buffer.h"
@@ -2484,6 +2486,36 @@
   return observable_events_.get();
 }
 
+void TracingServiceImpl::ConsumerEndpointImpl::QueryServiceState(
+    QueryServiceStateCallback callback) {
+  PERFETTO_DCHECK_THREAD(thread_checker_);
+  TracingServiceState svc_state;
+
+  const auto& sessions = service_->tracing_sessions_;
+  svc_state.set_num_sessions(static_cast<int>(sessions.size()));
+
+  int num_started = 0;
+  for (const auto& kv : sessions)
+    num_started += kv.second.state == TracingSession::State::STARTED ? 1 : 0;
+  svc_state.set_num_sessions_started(static_cast<int>(num_started));
+
+  for (const auto& kv : service_->producers_) {
+    auto* producer = svc_state.add_producers();
+    producer->set_id(static_cast<int>(kv.first));
+    producer->set_name(kv.second->name_);
+    producer->set_uid(static_cast<int32_t>(producer->uid()));
+  }
+
+  for (const auto& kv : service_->data_sources_) {
+    const auto& registered_data_source = kv.second;
+    auto* data_source = svc_state.add_data_sources();
+    *data_source->mutable_descriptor() = registered_data_source.descriptor;
+    data_source->set_producer_id(
+        static_cast<int>(registered_data_source.producer_id));
+  }
+  callback(/*success=*/true, svc_state);
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // TracingServiceImpl::ProducerEndpointImpl implementation
 ////////////////////////////////////////////////////////////////////////////////
diff --git a/src/tracing/core/tracing_service_impl.h b/src/tracing/core/tracing_service_impl.h
index 3d734cd..bcd4d90 100644
--- a/src/tracing/core/tracing_service_impl.h
+++ b/src/tracing/core/tracing_service_impl.h
@@ -115,6 +115,8 @@
       return base::nullopt;
     }
 
+    uid_t uid() const { return uid_; }
+
    private:
     friend class TracingServiceImpl;
     friend class TracingServiceImplTest;
@@ -181,6 +183,7 @@
     void Attach(const std::string& key) override;
     void GetTraceStats() override;
     void ObserveEvents(uint32_t enabled_event_types) override;
+    void QueryServiceState(QueryServiceStateCallback) override;
 
     // If |observe_data_source_instances == true|, will queue a task to notify
     // the consumer about the state change.
diff --git a/src/tracing/core/tracing_service_impl_unittest.cc b/src/tracing/core/tracing_service_impl_unittest.cc
index c96d097..0067384 100644
--- a/src/tracing/core/tracing_service_impl_unittest.cc
+++ b/src/tracing/core/tracing_service_impl_unittest.cc
@@ -2758,4 +2758,55 @@
   consumer->WaitForTracingDisabled();
 }
 
+TEST_F(TracingServiceImplTest, QueryServiceState) {
+  std::unique_ptr<MockConsumer> consumer = CreateMockConsumer();
+  consumer->Connect(svc.get());
+
+  std::unique_ptr<MockProducer> producer1 = CreateMockProducer();
+  producer1->Connect(svc.get(), "producer1");
+
+  std::unique_ptr<MockProducer> producer2 = CreateMockProducer();
+  producer2->Connect(svc.get(), "producer2");
+
+  producer1->RegisterDataSource("common_ds");
+  producer2->RegisterDataSource("common_ds");
+
+  producer1->RegisterDataSource("p1_ds");
+  producer2->RegisterDataSource("p2_ds");
+
+  TracingServiceState svc_state = consumer->QueryServiceState();
+
+  EXPECT_EQ(svc_state.producers_size(), 2u);
+  EXPECT_EQ(svc_state.producers().at(0).id(), 1);
+  EXPECT_EQ(svc_state.producers().at(0).name(), "producer1");
+  EXPECT_EQ(svc_state.producers().at(1).id(), 2);
+  EXPECT_EQ(svc_state.producers().at(1).name(), "producer2");
+
+  EXPECT_EQ(svc_state.data_sources_size(), 4u);
+
+  EXPECT_EQ(svc_state.data_sources().at(0).producer_id(), 1);
+  EXPECT_EQ(svc_state.data_sources().at(0).descriptor().name(), "common_ds");
+
+  EXPECT_EQ(svc_state.data_sources().at(1).producer_id(), 2);
+  EXPECT_EQ(svc_state.data_sources().at(1).descriptor().name(), "common_ds");
+
+  EXPECT_EQ(svc_state.data_sources().at(2).producer_id(), 1);
+  EXPECT_EQ(svc_state.data_sources().at(2).descriptor().name(), "p1_ds");
+
+  EXPECT_EQ(svc_state.data_sources().at(3).producer_id(), 2);
+  EXPECT_EQ(svc_state.data_sources().at(3).descriptor().name(), "p2_ds");
+
+  // Test that descriptors are cleared when a producer disconnects.
+  producer1.reset();
+  svc_state = consumer->QueryServiceState();
+
+  EXPECT_EQ(svc_state.producers_size(), 1u);
+  EXPECT_EQ(svc_state.data_sources_size(), 2u);
+
+  EXPECT_EQ(svc_state.data_sources().at(0).producer_id(), 2);
+  EXPECT_EQ(svc_state.data_sources().at(0).descriptor().name(), "common_ds");
+  EXPECT_EQ(svc_state.data_sources().at(1).producer_id(), 2);
+  EXPECT_EQ(svc_state.data_sources().at(1).descriptor().name(), "p2_ds");
+}
+
 }  // namespace perfetto
diff --git a/src/tracing/core/tracing_service_state.cc b/src/tracing/core/tracing_service_state.cc
new file mode 100644
index 0000000..f6f4c1e
--- /dev/null
+++ b/src/tracing/core/tracing_service_state.cc
@@ -0,0 +1,217 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*******************************************************************************
+ * AUTOGENERATED - DO NOT EDIT
+ *******************************************************************************
+ * This file has been generated from the protobuf message
+ * perfetto/common/tracing_service_state.proto
+ * by
+ * ../../tools/proto_to_cpp/proto_to_cpp.cc.
+ * If you need to make changes here, change the .proto file and then run
+ * ./tools/gen_tracing_cpp_headers_from_protos
+ */
+
+#include "perfetto/ext/tracing/core/tracing_service_state.h"
+
+#include "perfetto/common/data_source_descriptor.pb.h"
+#include "perfetto/common/tracing_service_state.pb.h"
+
+namespace perfetto {
+
+TracingServiceState::TracingServiceState() = default;
+TracingServiceState::~TracingServiceState() = default;
+TracingServiceState::TracingServiceState(const TracingServiceState&) = default;
+TracingServiceState& TracingServiceState::operator=(
+    const TracingServiceState&) = default;
+TracingServiceState::TracingServiceState(TracingServiceState&&) noexcept =
+    default;
+TracingServiceState& TracingServiceState::operator=(TracingServiceState&&) =
+    default;
+
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wfloat-equal"
+bool TracingServiceState::operator==(const TracingServiceState& other) const {
+  return (producers_ == other.producers_) &&
+         (data_sources_ == other.data_sources_) &&
+         (num_sessions_ == other.num_sessions_) &&
+         (num_sessions_started_ == other.num_sessions_started_);
+}
+#pragma GCC diagnostic pop
+
+void TracingServiceState::ParseRawProto(const std::string& raw) {
+  perfetto::protos::TracingServiceState proto;
+  proto.ParseFromString(raw);
+  FromProto(proto);
+}
+
+void TracingServiceState::FromProto(
+    const perfetto::protos::TracingServiceState& proto) {
+  producers_.clear();
+  for (const auto& field : proto.producers()) {
+    producers_.emplace_back();
+    producers_.back().FromProto(field);
+  }
+
+  data_sources_.clear();
+  for (const auto& field : proto.data_sources()) {
+    data_sources_.emplace_back();
+    data_sources_.back().FromProto(field);
+  }
+
+  static_assert(sizeof(num_sessions_) == sizeof(proto.num_sessions()),
+                "size mismatch");
+  num_sessions_ = static_cast<decltype(num_sessions_)>(proto.num_sessions());
+
+  static_assert(
+      sizeof(num_sessions_started_) == sizeof(proto.num_sessions_started()),
+      "size mismatch");
+  num_sessions_started_ = static_cast<decltype(num_sessions_started_)>(
+      proto.num_sessions_started());
+  unknown_fields_ = proto.unknown_fields();
+}
+
+void TracingServiceState::ToProto(
+    perfetto::protos::TracingServiceState* proto) const {
+  proto->Clear();
+
+  for (const auto& it : producers_) {
+    auto* entry = proto->add_producers();
+    it.ToProto(entry);
+  }
+
+  for (const auto& it : data_sources_) {
+    auto* entry = proto->add_data_sources();
+    it.ToProto(entry);
+  }
+
+  static_assert(sizeof(num_sessions_) == sizeof(proto->num_sessions()),
+                "size mismatch");
+  proto->set_num_sessions(
+      static_cast<decltype(proto->num_sessions())>(num_sessions_));
+
+  static_assert(
+      sizeof(num_sessions_started_) == sizeof(proto->num_sessions_started()),
+      "size mismatch");
+  proto->set_num_sessions_started(
+      static_cast<decltype(proto->num_sessions_started())>(
+          num_sessions_started_));
+  *(proto->mutable_unknown_fields()) = unknown_fields_;
+}
+
+TracingServiceState::Producer::Producer() = default;
+TracingServiceState::Producer::~Producer() = default;
+TracingServiceState::Producer::Producer(const TracingServiceState::Producer&) =
+    default;
+TracingServiceState::Producer& TracingServiceState::Producer::operator=(
+    const TracingServiceState::Producer&) = default;
+TracingServiceState::Producer::Producer(
+    TracingServiceState::Producer&&) noexcept = default;
+TracingServiceState::Producer& TracingServiceState::Producer::operator=(
+    TracingServiceState::Producer&&) = default;
+
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wfloat-equal"
+bool TracingServiceState::Producer::operator==(
+    const TracingServiceState::Producer& other) const {
+  return (id_ == other.id_) && (name_ == other.name_) && (uid_ == other.uid_);
+}
+#pragma GCC diagnostic pop
+
+void TracingServiceState::Producer::ParseRawProto(const std::string& raw) {
+  perfetto::protos::TracingServiceState_Producer proto;
+  proto.ParseFromString(raw);
+  FromProto(proto);
+}
+
+void TracingServiceState::Producer::FromProto(
+    const perfetto::protos::TracingServiceState_Producer& proto) {
+  static_assert(sizeof(id_) == sizeof(proto.id()), "size mismatch");
+  id_ = static_cast<decltype(id_)>(proto.id());
+
+  static_assert(sizeof(name_) == sizeof(proto.name()), "size mismatch");
+  name_ = static_cast<decltype(name_)>(proto.name());
+
+  static_assert(sizeof(uid_) == sizeof(proto.uid()), "size mismatch");
+  uid_ = static_cast<decltype(uid_)>(proto.uid());
+  unknown_fields_ = proto.unknown_fields();
+}
+
+void TracingServiceState::Producer::ToProto(
+    perfetto::protos::TracingServiceState_Producer* proto) const {
+  proto->Clear();
+
+  static_assert(sizeof(id_) == sizeof(proto->id()), "size mismatch");
+  proto->set_id(static_cast<decltype(proto->id())>(id_));
+
+  static_assert(sizeof(name_) == sizeof(proto->name()), "size mismatch");
+  proto->set_name(static_cast<decltype(proto->name())>(name_));
+
+  static_assert(sizeof(uid_) == sizeof(proto->uid()), "size mismatch");
+  proto->set_uid(static_cast<decltype(proto->uid())>(uid_));
+  *(proto->mutable_unknown_fields()) = unknown_fields_;
+}
+
+TracingServiceState::DataSource::DataSource() = default;
+TracingServiceState::DataSource::~DataSource() = default;
+TracingServiceState::DataSource::DataSource(
+    const TracingServiceState::DataSource&) = default;
+TracingServiceState::DataSource& TracingServiceState::DataSource::operator=(
+    const TracingServiceState::DataSource&) = default;
+TracingServiceState::DataSource::DataSource(
+    TracingServiceState::DataSource&&) noexcept = default;
+TracingServiceState::DataSource& TracingServiceState::DataSource::operator=(
+    TracingServiceState::DataSource&&) = default;
+
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wfloat-equal"
+bool TracingServiceState::DataSource::operator==(
+    const TracingServiceState::DataSource& other) const {
+  return (descriptor_ == other.descriptor_) &&
+         (producer_id_ == other.producer_id_);
+}
+#pragma GCC diagnostic pop
+
+void TracingServiceState::DataSource::ParseRawProto(const std::string& raw) {
+  perfetto::protos::TracingServiceState_DataSource proto;
+  proto.ParseFromString(raw);
+  FromProto(proto);
+}
+
+void TracingServiceState::DataSource::FromProto(
+    const perfetto::protos::TracingServiceState_DataSource& proto) {
+  descriptor_.FromProto(proto.descriptor());
+
+  static_assert(sizeof(producer_id_) == sizeof(proto.producer_id()),
+                "size mismatch");
+  producer_id_ = static_cast<decltype(producer_id_)>(proto.producer_id());
+  unknown_fields_ = proto.unknown_fields();
+}
+
+void TracingServiceState::DataSource::ToProto(
+    perfetto::protos::TracingServiceState_DataSource* proto) const {
+  proto->Clear();
+
+  descriptor_.ToProto(proto->mutable_descriptor());
+
+  static_assert(sizeof(producer_id_) == sizeof(proto->producer_id()),
+                "size mismatch");
+  proto->set_producer_id(
+      static_cast<decltype(proto->producer_id())>(producer_id_));
+  *(proto->mutable_unknown_fields()) = unknown_fields_;
+}
+
+}  // namespace perfetto
diff --git a/src/tracing/ipc/consumer/consumer_ipc_client_impl.cc b/src/tracing/ipc/consumer/consumer_ipc_client_impl.cc
index b38e2ba..ee87cd3 100644
--- a/src/tracing/ipc/consumer/consumer_ipc_client_impl.cc
+++ b/src/tracing/ipc/consumer/consumer_ipc_client_impl.cc
@@ -25,6 +25,7 @@
 #include "perfetto/ext/tracing/core/observable_events.h"
 #include "perfetto/ext/tracing/core/trace_config.h"
 #include "perfetto/ext/tracing/core/trace_stats.h"
+#include "perfetto/ext/tracing/core/tracing_service_state.h"
 
 // TODO(fmayer): Add a test to check to what happens when ConsumerIPCClientImpl
 // gets destroyed w.r.t. the Consumer pointer. Also think to lifetime of the
@@ -328,4 +329,25 @@
   consumer_port_.ObserveEvents(req, std::move(async_response));
 }
 
+void ConsumerIPCClientImpl::QueryServiceState(
+    QueryServiceStateCallback callback) {
+  if (!connected_) {
+    PERFETTO_DLOG(
+        "Cannot QueryServiceState(), not connected to tracing service");
+    return;
+  }
+
+  protos::QueryServiceStateRequest req;
+  ipc::Deferred<protos::QueryServiceStateResponse> async_response;
+  async_response.Bind(
+      [callback](ipc::AsyncResult<protos::QueryServiceStateResponse> response) {
+        if (!response)
+          callback(false, TracingServiceState());
+        TracingServiceState svc_state;
+        svc_state.FromProto(response->service_state());
+        callback(true, svc_state);
+      });
+  consumer_port_.QueryServiceState(req, std::move(async_response));
+}
+
 }  // namespace perfetto
diff --git a/src/tracing/ipc/consumer/consumer_ipc_client_impl.h b/src/tracing/ipc/consumer/consumer_ipc_client_impl.h
index 320e5c0..12670b1 100644
--- a/src/tracing/ipc/consumer/consumer_ipc_client_impl.h
+++ b/src/tracing/ipc/consumer/consumer_ipc_client_impl.h
@@ -70,6 +70,7 @@
   void Attach(const std::string& key) override;
   void GetTraceStats() override;
   void ObserveEvents(uint32_t enabled_event_types) override;
+  void QueryServiceState(QueryServiceStateCallback) override;
 
   // ipc::ServiceProxy::EventListener implementation.
   // These methods are invoked by the IPC layer, which knows nothing about
diff --git a/src/tracing/ipc/service/consumer_ipc_service.cc b/src/tracing/ipc/service/consumer_ipc_service.cc
index 0d10c3e..fc1c564 100644
--- a/src/tracing/ipc/service/consumer_ipc_service.cc
+++ b/src/tracing/ipc/service/consumer_ipc_service.cc
@@ -29,6 +29,7 @@
 #include "perfetto/ext/tracing/core/trace_packet.h"
 #include "perfetto/ext/tracing/core/trace_stats.h"
 #include "perfetto/ext/tracing/core/tracing_service.h"
+#include "perfetto/ext/tracing/core/tracing_service_state.h"
 
 namespace perfetto {
 
@@ -187,6 +188,22 @@
     remote_consumer->CloseObserveEventsResponseStream();
 }
 
+// Called by the IPC layer.
+void ConsumerIPCService::QueryServiceState(
+    const protos::QueryServiceStateRequest&,
+    DeferredQueryServiceStateResponse resp) {
+  RemoteConsumer* remote_consumer = GetConsumerForCurrentRequest();
+  auto it = pending_query_service_responses_.insert(
+      pending_query_service_responses_.end(), std::move(resp));
+  auto weak_this = weak_ptr_factory_.GetWeakPtr();
+  auto callback = [weak_this, it](bool success,
+                                  const TracingServiceState& svc_state) {
+    if (weak_this)
+      weak_this->OnQueryServiceCallback(success, svc_state, std::move(it));
+  };
+  remote_consumer->service_endpoint->QueryServiceState(callback);
+}
+
 // Called by the service in response to a service_endpoint->Flush() request.
 void ConsumerIPCService::OnFlushCallback(
     bool success,
@@ -200,6 +217,22 @@
   }
 }
 
+// Called by the service in response to service_endpoint->QueryServiceState().
+void ConsumerIPCService::OnQueryServiceCallback(
+    bool success,
+    const TracingServiceState& svc_state,
+    PendingQuerySvcResponses::iterator pending_response_it) {
+  DeferredQueryServiceStateResponse response(std::move(*pending_response_it));
+  pending_query_service_responses_.erase(pending_response_it);
+  if (success) {
+    auto resp = ipc::AsyncResult<protos::QueryServiceStateResponse>::Create();
+    svc_state.ToProto(resp->mutable_service_state());
+    response.Resolve(std::move(resp));
+  } else {
+    response.Reject();
+  }
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // RemoteConsumer methods
 ////////////////////////////////////////////////////////////////////////////////
diff --git a/src/tracing/ipc/service/consumer_ipc_service.h b/src/tracing/ipc/service/consumer_ipc_service.h
index 22957a9..c4aa012 100644
--- a/src/tracing/ipc/service/consumer_ipc_service.h
+++ b/src/tracing/ipc/service/consumer_ipc_service.h
@@ -31,6 +31,8 @@
 
 namespace perfetto {
 
+class TracingServiceState;
+
 namespace ipc {
 class Host;
 }  // namespace ipc
@@ -63,6 +65,8 @@
                      DeferredGetTraceStatsResponse) override;
   void ObserveEvents(const protos::ObserveEventsRequest&,
                      DeferredObserveEventsResponse) override;
+  void QueryServiceState(const protos::QueryServiceStateRequest&,
+                         DeferredQueryServiceStateResponse) override;
   void OnClientDisconnected() override;
 
  private:
@@ -117,6 +121,7 @@
 
   // This has to be a container that doesn't invalidate iterators.
   using PendingFlushResponses = std::list<DeferredFlushResponse>;
+  using PendingQuerySvcResponses = std::list<DeferredQueryServiceStateResponse>;
 
   ConsumerIPCService(const ConsumerIPCService&) = delete;
   ConsumerIPCService& operator=(const ConsumerIPCService&) = delete;
@@ -126,6 +131,9 @@
   RemoteConsumer* GetConsumerForCurrentRequest();
 
   void OnFlushCallback(bool success, PendingFlushResponses::iterator);
+  void OnQueryServiceCallback(bool success,
+                              const TracingServiceState&,
+                              PendingQuerySvcResponses::iterator);
 
   TracingService* const core_service_;
 
@@ -134,6 +142,7 @@
   std::map<ipc::ClientID, std::unique_ptr<RemoteConsumer>> consumers_;
 
   PendingFlushResponses pending_flush_responses_;
+  PendingQuerySvcResponses pending_query_service_responses_;
 
   base::WeakPtrFactory<ConsumerIPCService> weak_ptr_factory_;  // Keep last.
 };
diff --git a/src/tracing/test/mock_consumer.cc b/src/tracing/test/mock_consumer.cc
index 137ef4e..34facdc 100644
--- a/src/tracing/test/mock_consumer.cc
+++ b/src/tracing/test/mock_consumer.cc
@@ -161,4 +161,20 @@
   return events;
 }
 
+TracingServiceState MockConsumer::QueryServiceState() {
+  static int i = 0;
+  TracingServiceState res;
+  std::string checkpoint_name = "query_service_state_" + std::to_string(i++);
+  auto checkpoint = task_runner_->CreateCheckpoint(checkpoint_name);
+  auto callback = [checkpoint, &res](bool success,
+                                     const TracingServiceState& svc_state) {
+    EXPECT_TRUE(success);
+    res = svc_state;
+    checkpoint();
+  };
+  service_endpoint_->QueryServiceState(callback);
+  task_runner_->RunUntilCheckpoint(checkpoint_name);
+  return res;
+}
+
 }  // namespace perfetto
diff --git a/src/tracing/test/mock_consumer.h b/src/tracing/test/mock_consumer.h
index 53b789f..83f258e 100644
--- a/src/tracing/test/mock_consumer.h
+++ b/src/tracing/test/mock_consumer.h
@@ -23,6 +23,7 @@
 #include "perfetto/ext/tracing/core/consumer.h"
 #include "perfetto/ext/tracing/core/trace_packet.h"
 #include "perfetto/ext/tracing/core/tracing_service.h"
+#include "perfetto/ext/tracing/core/tracing_service_state.h"
 
 #include "perfetto/trace/trace_packet.pb.h"
 
@@ -57,6 +58,7 @@
   std::vector<protos::TracePacket> ReadBuffers();
   void GetTraceStats();
   void WaitForTraceStats(bool success);
+  TracingServiceState QueryServiceState();
   void ObserveEvents(uint32_t enabled_event_types);
   ObservableEvents WaitForObservableEvents();
 
diff --git a/test/end_to_end_integrationtest.cc b/test/end_to_end_integrationtest.cc
index 7d77e58..9953047 100644
--- a/test/end_to_end_integrationtest.cc
+++ b/test/end_to_end_integrationtest.cc
@@ -606,10 +606,10 @@
 
   EXPECT_EQ(1,
             ExecPerfetto({"-c", "-", "--txt", "-o", "-", "--attach=foo"}, cfg));
-  EXPECT_THAT(stderr_, HasSubstr("trace config with --attach"));
+  EXPECT_THAT(stderr_, HasSubstr("Cannot specify a trace config"));
 
   EXPECT_EQ(1, ExecPerfetto({"-t", "2s", "-o", "-", "--attach=foo"}, cfg));
-  EXPECT_THAT(stderr_, HasSubstr("trace config with --attach"));
+  EXPECT_THAT(stderr_, HasSubstr("Cannot specify a trace config"));
 
   EXPECT_EQ(1, ExecPerfetto({"--attach"}, cfg));
   EXPECT_THAT(stderr_, ContainsRegex("option.*--attach.*requires an argument"));
@@ -619,6 +619,12 @@
 
   EXPECT_EQ(1, ExecPerfetto({"-t", "2s", "--detach=foo"}, cfg));
   EXPECT_THAT(stderr_, HasSubstr("--out or --dropbox is required"));
+
+  EXPECT_EQ(1, ExecPerfetto({"-t", "2s", "--query"}, cfg));
+  EXPECT_THAT(stderr_, HasSubstr("Cannot specify a trace config"));
+
+  EXPECT_EQ(1, ExecPerfetto({"-c", "-", "--query"}, cfg));
+  EXPECT_THAT(stderr_, HasSubstr("Cannot specify a trace config"));
 }
 
 TEST_F(PerfettoCmdlineTest, NoSanitizers(TxtConfig)) {
@@ -1003,4 +1009,9 @@
   EXPECT_FALSE(base::ReadFile(path, &trace_str));
 }
 
+TEST_F(PerfettoCmdlineTest, NoSanitizers(Query)) {
+  EXPECT_EQ(0, ExecPerfetto({"--query"})) << stderr_;
+  EXPECT_EQ(0, ExecPerfetto({"--query-raw"})) << stderr_;
+}
+
 }  // namespace perfetto
diff --git a/tools/gen_all b/tools/gen_all
index 7a22c22..dc5021c 100755
--- a/tools/gen_all
+++ b/tools/gen_all
@@ -29,8 +29,9 @@
 def call(cmd, *args):
   path = os.path.join('tools', cmd)
   command = [path] + list(args)
+  print 'Running ', ' '.join(command)
   try:
-    subprocess.check_call([path] + list(args), cwd=ROOT_DIR)
+    subprocess.check_call(command, cwd=ROOT_DIR)
   except subprocess.CalledProcessError as e:
     assert False, 'Command: {} failed'.format(' '.join(command))
 
@@ -46,11 +47,11 @@
         'Output directory "{}" is not a directory'.format(out)
     call('fix_include_guards')
     call('gen_bazel')
-    call('gen_amalgamated', '--check', '--quiet')
     call('gen_android_bp')
     call('gen_merged_protos')
     call('gen_binary_descriptors', '--protoc', protoc_path(out))
     call('gen_tracing_cpp_headers_from_protos', out)
+    call('gen_amalgamated', '--check', '--quiet')  # Keep last
 
   except AssertionError as e:
     if not str(e):
diff --git a/tools/gen_tracing_cpp_headers_from_protos b/tools/gen_tracing_cpp_headers_from_protos
index e02c539..1c0b0ae 100755
--- a/tools/gen_tracing_cpp_headers_from_protos
+++ b/tools/gen_tracing_cpp_headers_from_protos
@@ -22,11 +22,12 @@
 
 PROTOS = (
     ('perfetto/common/commit_data_request.proto', CORE_H, CORE_CPP),
+    ('perfetto/common/data_source_descriptor.proto', CORE_H, CORE_CPP),
     ('perfetto/common/observable_events.proto', CORE_H, CORE_CPP),
+    ('perfetto/common/tracing_service_state.proto', CORE_H, CORE_CPP),
     ('perfetto/common/trace_stats.proto', CORE_H, CORE_CPP),
     ('perfetto/config/chrome/chrome_config.proto', CORE_H, CORE_CPP),
     ('perfetto/config/data_source_config.proto', CORE_H, CORE_CPP),
-    ('perfetto/config/data_source_descriptor.proto', CORE_H, CORE_CPP),
     ('perfetto/config/test_config.proto', CORE_H, CORE_CPP),
     ('perfetto/config/trace_config.proto', CORE_H, CORE_CPP),