49. Telemetry Library

The Telemetry library provides an interface to retrieve information from a variety of DPDK libraries. The library provides this information via socket connection, taking requests from a connected client and replying with the JSON response containing the requested telemetry information.

Telemetry is enabled to run by default when running a DPDK application, and the telemetry information from enabled libraries is made available. Libraries are responsible for registering their own commands, and providing the callback function that will format the library specific stats into the correct data format, when requested.

49.1. Registering Commands

Libraries and applications must register commands to make their information available via the Telemetry library. This involves providing a string command in the required format (“/library/command”), the callback function that will handle formatting the information when required, and help text for the command. An example showing ethdev commands being registered is shown below:

rte_telemetry_register_cmd("/ethdev/list", handle_port_list,
        "Returns list of available ethdev ports. Takes no parameters");
rte_telemetry_register_cmd("/ethdev/xstats", handle_port_xstats,
        "Returns the extended stats for a port. Parameters: int port_id");
rte_telemetry_register_cmd("/ethdev/link_status", handle_port_link_status,
        "Returns the link status for a port. Parameters: int port_id");

49.2. Formatting JSON response

The callback function provided by the library must format its telemetry information in the required data format. The Telemetry library provides a data utilities API to build up the response. For example, the ethdev library provides a list of available ethdev ports in a formatted data response, constructed using the following functions to build up the list:

rte_tel_data_start_array(d, RTE_TEL_INT_VAL);
    RTE_ETH_FOREACH_DEV(port_id)
        rte_tel_data_add_array_int(d, port_id);

The data structure is then formatted into a JSON response before sending. The resulting response shows the port list data provided above by the handler function in ethdev, placed in a JSON reply by telemetry:

{"/ethdev/list": [0, 1]}

For more information on the range of data functions available in the API, please refer to the docs.