+/* SPDX-License-Identifier: BSD-3-Clause
+ * Copyright(c) 2020 Intel Corporation
+ */
+
+#ifndef _RTE_TELEMETRY_INTERNAL_H_
+#define _RTE_TELEMETRY_INTERNAL_H_
+
+#include <rte_compat.h>
+#include "rte_telemetry.h"
+
+/**
+ * @internal
+ * @warning
+ * @b EXPERIMENTAL: this API may change without prior notice
+
+ * @file
+ * RTE Telemetry Legacy and internal definitions
+ *
+ ***/
+
+/**
+ * @internal
+ * Value representing if data is required for the command
+ */
+enum rte_telemetry_legacy_data_req {
+ DATA_NOT_REQ = 0,
+ DATA_REQ
+};
+
+/**
+ * This telemetry callback is used when registering a legacy telemetry command.
+ * It handles getting and formatting stats to be returned to telemetry when
+ * requested. Stats up to buf_len in length are put in the buffer.
+ *
+ * @param cmd
+ * The cmd that was requested by the client.
+ * @param params
+ * Contains data required by the callback function.
+ * @param buffer
+ * A buffer to hold the formatted response.
+ * @param buf_len
+ * Length of the buffer.
+ *
+ * @return
+ * Length of buffer used on success.
+ * @return
+ * Negative integer on error.
+ */
+typedef int (*telemetry_legacy_cb)(const char *cmd, const char *params,
+ char *buffer, int buf_len);
+
+/**
+ * @internal
+ * Counter for the number of registered legacy callbacks
+ */
+extern int num_legacy_callbacks;
+
+/**
+ * @internal
+ * Used for handling data received over the legacy telemetry socket.
+ *
+ * @return
+ * Void.
+ */
+void *
+legacy_client_handler(void *sock_id);
+
+/**
+ * @internal
+ *
+ * Used when registering a command and callback function with
+ * telemetry legacy support.
+ *
+ * @return
+ * 0 on success.
+ * @return
+ * -EINVAL for invalid parameters failure.
+ * @return
+ * -ENOENT if max callbacks limit has been reached.
+ */
+__rte_internal
+int
+rte_telemetry_legacy_register(const char *cmd,
+ enum rte_telemetry_legacy_data_req data_req,
+ telemetry_legacy_cb fn);
+
+#endif