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diff --git a/src/core/statistics/census_interface.h b/src/core/statistics/census_interface.h
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+/*
+ *
+ * Copyright 2014, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifndef __GRPC_INTERNAL_STATISTICS_CENSUS_INTERFACE_H__
+#define __GRPC_INTERNAL_STATISTICS_CENSUS_INTERFACE_H__
+
+#include <grpc/support/port_platform.h>
+
+/* Maximum length of an individual census trace annotation. */
+#define CENSUS_MAX_ANNOTATION_LENGTH 200
+
+/* Structure of a census op id. Define as structure because 64bit integer is not
+   available on every platform for C89. */
+typedef struct census_op_id {
+  gpr_uint32 upper;
+  gpr_uint32 lower;
+} census_op_id;
+
+typedef struct census_rpc_stats census_rpc_stats;
+
+/* Initializes Census library. No-op if Census is already initialized. */
+void census_init();
+
+/* Shutdown Census Library. */
+void census_shutdown();
+
+/* Annotates grpc method name on a census_op_id. The method name has the format
+   of <full quantified rpc service name>/<rpc function name>. Returns 0 iff
+   op_id and method_name are all valid. op_id is valid after its creation and
+   before calling census_tracing_end_op().
+
+   TODO(hongyu): Figure out valid characters set for service name and command
+   name and document requirements here.*/
+int census_add_method_tag(census_op_id op_id, const char* method_name);
+
+/* Annotates tracing information to a specific op_id.
+   Up to CENSUS_MAX_ANNOTATION_LENGTH bytes are recorded. */
+void census_tracing_print(census_op_id op_id, const char* annotation);
+
+/* Starts tracing for an RPC. Returns a locally unique census_op_id */
+census_op_id census_tracing_start_op();
+
+/* Ends tracing. Calling this function will invalidate the input op_id. */
+void census_tracing_end_op(census_op_id op_id);
+
+#endif  /* __GRPC_INTERNAL_STATISTICS_CENSUS_INTERFACE_H__ */