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.. SPDX-License-Identifier: BSD-3-Clause
Copyright(c) 2015 Intel Corporation.
Basic Forwarding Sample Application
===================================
The Basic Forwarding sample application is a simple *skeleton* example of a
forwarding application.
Overview
--------
This application demonstrates the basic components of a DPDK forwarding application.
For more detailed implementations, see the L2 and L3 forwarding sample applications.
Compiling the Application
-------------------------
To compile the sample application, see :doc:`compiling`.
The application is located in the ``skeleton`` sub-directory.
Running the Application
-----------------------
To run the example in a ``linux`` environment:
.. code-block:: console
./<build_dir>/examples/dpdk-skeleton -l 1 -n 4
Refer to *DPDK Getting Started Guide* for general information on running
applications and Environment Abstraction Layer (EAL) options.
Explanation
-----------
The following sections provide an explanation of the main components of the
code.
All DPDK library functions used in the sample code are prefixed with ``rte_``
and are explained in detail in the *DPDK API Documentation*.
The Main Function
~~~~~~~~~~~~~~~~~
The ``main()`` function performs the initialization and calls the execution
threads for each lcore.
The first task is to initialize the Environment Abstraction Layer (EAL).
The ``argc`` and ``argv`` arguments are provided to the ``rte_eal_init()``
function. The value returned is the number of parsed arguments:
.. literalinclude:: ../../../examples/skeleton/basicfwd.c
:language: c
:start-after: Initializion the Environment Abstraction Layer (EAL). 8<
:end-before: >8 End of initialization the Environment Abstraction Layer (EAL).
:dedent: 1
The ``main()`` also allocates a mempool to hold the mbufs (Message Buffers)
used by the application:
.. literalinclude:: ../../../examples/skeleton/basicfwd.c
:language: c
:start-after: Allocates mempool to hold the mbufs. 8<
:end-before: >8 End of allocating mempool to hold mbuf.
:dedent: 1
Mbufs are the packet buffer structure used by DPDK. They are explained in
detail in the "Mbuf Library" section of the *DPDK Programmer's Guide*.
The ``main()`` function also initializes all the ports using the user defined
``port_init()`` function which is explained in the next section:
.. literalinclude:: ../../../examples/skeleton/basicfwd.c
:language: c
:start-after: Initializing all ports. 8<
:end-before: >8 End of initializing all ports.
:dedent: 1
Once the initialization is complete, the application is ready to launch a
function on an lcore.
In this example, ``lcore_main()`` is called on a single lcore.
.. literalinclude:: ../../../examples/skeleton/basicfwd.c
:language: c
:start-after: Called on single lcore. 8<
:end-before: >8 End of called on single lcore.
:dedent: 1
The ``lcore_main()`` function is explained below.
The Port Initialization Function
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The main functional part of the port initialization used in the Basic
Forwarding application is shown below:
.. literalinclude:: ../../../examples/skeleton/basicfwd.c
:language: c
:start-after: Main functional part of port initialization. 8<
:end-before: >8 End of main functional part of port initialization.
The Ethernet ports are configured with default settings using the
``rte_eth_dev_configure()`` function.
In this example, the ports are set up with 1 Rx and 1 Tx queue using the
``rte_eth_rx_queue_setup()`` and ``rte_eth_tx_queue_setup()`` functions.
The Ethernet port is then started:
.. literalinclude:: ../../../examples/skeleton/basicfwd.c
:language: c
:start-after: Starting Ethernet port. 8<
:end-before: >8 End of starting of ethernet port.
:dedent: 1
Finally, the Rx port is set in promiscuous mode:
.. literalinclude:: ../../../examples/skeleton/basicfwd.c
:language: c
:start-after: Enable RX in promiscuous mode for the Ethernet device.
:end-before: End of setting RX port in promiscuous mode.
:dedent: 1
The Lcores Main
~~~~~~~~~~~~~~~
As we saw above, the ``main()`` function calls an application function
on the available lcores.
For the basic forwarding application, the lcore function
looks like the following:
.. literalinclude:: ../../../examples/skeleton/basicfwd.c
:language: c
:start-after: Basic forwarding application lcore. 8<
:end-before: >8 End Basic forwarding application lcore.
The main work of the application is done within the loop:
.. literalinclude:: ../../../examples/skeleton/basicfwd.c
:language: c
:start-after: Main work of application loop. 8<
:end-before: >8 End of loop.
:dedent: 1
Packets are received in bursts on the RX ports and transmitted in bursts on
the TX ports. The ports are grouped in pairs with a simple mapping scheme
using the an XOR on the port number::
0 -> 1
1 -> 0
2 -> 3
3 -> 2
etc.
The ``rte_eth_tx_burst()`` function frees the memory buffers of packets that
are transmitted. If packets fail to transmit, ``(nb_tx < nb_rx)``, then they
must be freed explicitly using ``rte_pktmbuf_free()``.
The forwarding loop can be interrupted and the application closed using
``Ctrl-C``.
|
