[dpdk-dev] [PATCH v3] doc: add more detail to telemetry guides

[Ciara Power <ciara.power@intel.com>]

This patch adds examples to the Telemetry HowTo guide, to demonstrate
commands that use parameters. The programmer's guide is also modified to
include details on writing a callback function for a new command.

Signed-off-by: Ciara Power <ciara.power@intel.com>

---
v3:
  - Replaced direct code examples with generic examples.
  - Replaced ref label with :doc: syntax to link guides.
  - Replaced console code-block label with :: on previous lines.
  - Added links to API doc.
  - Modified some formatting.
v2:
  - Replaced examples of using commands in the programmer's guide with
    a link to the HowTo guide.
  - Added an example showing the use of a single string value.
  - Replaced inline functions with a synthetic example function below
    the list of parameters.
---
 doc/guides/howto/telemetry.rst          |  67 ++++++----
 doc/guides/prog_guide/telemetry_lib.rst | 160 +++++++++++++++++++-----
 2 files changed, 172 insertions(+), 55 deletions(-)

diff --git a/doc/guides/howto/telemetry.rst b/doc/guides/howto/telemetry.rst
index b4a34ed674..e7b5434152 100644
--- a/doc/guides/howto/telemetry.rst
+++ b/doc/guides/howto/telemetry.rst
@@ -29,17 +29,13 @@ Telemetry Initialization
 
 The library is enabled by default, however an EAL flag to enable the library
 exists, to provide backward compatibility for the previous telemetry library
-interface.
+interface::
 
-.. code-block:: console
+  --telemetry
 
-   --telemetry
+A flag exists to disable Telemetry also::
 
-A flag exists to disable Telemetry also.
-
-.. code-block:: console
-
-   --no-telemetry
+  --no-telemetry
 
 
 Running Telemetry
@@ -48,33 +44,50 @@ Running Telemetry
 The following steps show how to run an application with telemetry support,
 and query information using the telemetry client python script.
 
-#. Launch testpmd as the primary application with telemetry.
-
-   .. code-block:: console
+#. Launch testpmd as the primary application with telemetry::
 
       ./app/dpdk-testpmd
 
-#. Launch the telemetry client script.
-
-   .. code-block:: console
+#. Launch the telemetry client script::
 
       python usertools/dpdk-telemetry.py
 
-#. When connected, the script displays the following, waiting for user input.
+#. When connected, the script displays the following, waiting for user input::
 
-   .. code-block:: console
-
-      Connecting to /var/run/dpdk/rte/dpdk_telemetry.v2
-      {"version": "DPDK 20.05.0-rc0", "pid": 60285, "max_output_len": 16384}
-      -->
+     Connecting to /var/run/dpdk/rte/dpdk_telemetry.v2
+     {"version": "DPDK 20.05.0-rc2", "pid": 60285, "max_output_len": 16384}
+     -->
 
 #. The user can now input commands to send across the socket, and receive the
-   response.
+   response. Some available commands are shown below.
+
+   * List all commands::
+
+       --> /
+       {"/": ["/", "/eal/app_params", "/eal/params", "/ethdev/list",
+       "/ethdev/link_status", "/ethdev/xstats", "/help", "/info"]}
+
+   * Get the list of ethdev ports::
+
+       --> /ethdev/list
+       {"/ethdev/list": [0, 1]}
+
+   .. Note::
+
+      For commands that expect a parameter, use "," to separate the command
+      and parameter. See examples below.
+
+   * Get extended statistics for an ethdev port::
+
+       --> /ethdev/xstats,0
+       {"/ethdev/xstats": {"rx_good_packets": 0, "tx_good_packets": 0,
+       "rx_good_bytes": 0, "tx_good_bytes": 0, "rx_missed_errors": 0,
+       ...
+       "tx_priority7_xon_to_xoff_packets": 0}}
 
-   .. code-block:: console
+   * Get the help text for a command. This will indicate what parameters are
+     required. Pass the command as a parameter::
 
-      --> /
-      {"/": ["/", "/eal/app_params", "/eal/params", "/ethdev/list",
-      "/ethdev/link_status", "/ethdev/xstats", "/help", "/info"]}
-      --> /ethdev/list
-      {"/ethdev/list": [0, 1]}
+       --> /help,/ethdev/xstats
+       {"/help": {"/ethdev/xstats": "Returns the extended stats for a port.
+       Parameters: int port_id"}}
diff --git a/doc/guides/prog_guide/telemetry_lib.rst b/doc/guides/prog_guide/telemetry_lib.rst
index 8563a7200e..c01e2480ce 100644
--- a/doc/guides/prog_guide/telemetry_lib.rst
+++ b/doc/guides/prog_guide/telemetry_lib.rst
@@ -16,47 +16,151 @@ function that will format the library specific stats into the correct data
 format, when requested.
 
 
-Registering Commands
---------------------
+Creating Callback Functions
+---------------------------
 
-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:
+
+Function Type
+~~~~~~~~~~~~~
+
+When creating a callback function in a library/app, it must be of the following type:
 
 .. code-block:: c
 
-    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");
+    typedef int (*telemetry_cb)(const char *cmd, const char *params,
+            struct rte_tel_data *info);
+
+An example callback function is shown below:
+
+.. code-block:: c
 
+    static int
+    handle_example_cmd(const char *cmd __rte_unused, const char *params __rte_unused,
+            struct rte_tel_data *d)
 
-Formatting JSON response
-------------------------
+For more detail on the callback function parameters, please refer to the
+`definition in the API doc
+<https://doc.dpdk.org/api/rte__telemetry_8h.html#a41dc74d561442bb6184ee6dd1f9b5bcc>`_
+
+**Example Callback**
+
+This callback is an example of handling multiple commands in one callback,
+and also shows the use of params which holds a port ID. The params input needs
+to be validated and converted to the required integer type for port ID. The cmd
+parameter is then used in a comparison to decide which command was requested,
+which will decide what port information should fill the rte_tel_data structure.
+
+.. code-block:: c
+
+   int
+   handle_cmd_request(const char *cmd, const char *params,
+         struct rte_tel_data *d)
+   {
+      int port_id, used = 0;
+
+      if (params == NULL || strlen(params) == 0 || !isdigit(*params))
+         return -1;
+
+      port_id = atoi(params);
+      if (!rte_eth_dev_is_valid_port(port_id))
+         return -1;
+
+      if (strcmp(cmd, "/cmd_1") == 0)
+         /* Build up port data requested for command 1 */
+      else
+         /* Build up port data requested for command 2 */
+
+       return used;
+   }
+
+
+Formatting Data
+~~~~~~~~~~~~~~~
 
 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:
+utilities API to build up the data structure with the required information.
+The telemetry library is then responsible for formatting the data structure
+into a JSON response before sending to the client.
 
-.. code-block:: c
 
-    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);
+Array Data
+^^^^^^^^^^
+
+  Some data will need to be formatted in a list structure. For example, if a
+  callback needs to return five integer values in the data response, it can be
+  constructed using the following functions to build up the list:
+
+  .. code-block:: c
+
+      rte_tel_data_start_array(d, RTE_TEL_INT_VAL);
+          for(i = 0; i < 5; i++)
+              rte_tel_data_add_array_int(d, i);
+
+  The resulting response to the client shows the list data provided above
+  by the handler function in the library/app, placed in a JSON reply by
+  telemetry::
 
-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:
+    {"/example_lib/five_ints": [0, 1, 2, 3, 4]}
 
-.. code-block:: console
 
-    {"/ethdev/list": [0, 1]}
+Dictionary Data
+^^^^^^^^^^^^^^^
+
+  For data that needs to be structured in a dictionary with key/value pairs,
+  the data utilities API can also be used. For example, some information about
+  a brownie recipe is constructed in the callback function shown below:
+
+  .. code-block:: c
+
+     rte_tel_data_start_dict(d);
+     rte_tel_data_add_dict_string(d, "Recipe", "Brownies");
+     rte_tel_data_add_dict_int(d, "Prep time (mins)", 25);
+     rte_tel_data_add_dict_int(d, "Cooking time (mins)", 30);
+     rte_tel_data_add_dict_int(d, "Serves", 16);
+
+  The resulting response to the client shows the key/value data provided above
+  by the handler function in telemetry, placed in a JSON reply by telemetry::
+
+    {"/example_lib/brownie_recipe": {"Recipe": "Brownies", "Prep time (mins)": 25,
+      "Cooking time (mins)": 30, "Serves": 16}}
+
+
+String Data
+^^^^^^^^^^^
+
+  Telemetry also supports single string data. The data utilities API can again
+  be used for this, see the example below.
+
+  .. code-block:: c
+
+     rte_tel_data_string(d, "This is an example string");
+
+  Giving the following response to the client::
+
+    {"/example_lib/string_example": "This is an example string"}
 
 For more information on the range of data functions available in the API,
-please refer to the docs.
+please refer to the `API doc <https://doc.dpdk.org/api-20.05/rte__telemetry_8h.html>`_
+
+
+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 command being registered is shown below:
+
+.. code-block:: c
+
+    rte_telemetry_register_cmd("/example_lib/string_example", handle_string,
+            "Returns an example string. Takes no parameters");
+
+
+Using Commands
+--------------
+
+To use commands, with a DPDK app running (e.g. testpmd), use the
+dpdk-telemetry.py script. For details on its use, see the :doc:`../howto/telemetry`.
-- 
2.17.1