..  BSD LICENSE
    Copyright(c) 2015 Intel Corporation. All rights reserved.
    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 Intel Corporation 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.


Basic Forwarding Sample Application
===================================

The Basic Forwarding sample application is a simple *skeleton* example of a
forwarding application.

It is intended as a demonstration of 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 ``linuxapp`` environment:

.. code-block:: console

    ./build/basicfwd -l 1 -n 4

Refer to *DPDK Getting Started Guide* for general information on running
applications and the 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:

.. code-block:: c

    int ret = rte_eal_init(argc, argv);
    if (ret < 0)
        rte_exit(EXIT_FAILURE, "Error with EAL initialization\n");


The ``main()`` also allocates a mempool to hold the mbufs (Message Buffers)
used by the application:

.. code-block:: c

    mbuf_pool = rte_mempool_create("MBUF_POOL",
                                   NUM_MBUFS * nb_ports,
                                   MBUF_SIZE,
                                   MBUF_CACHE_SIZE,
                                   sizeof(struct rte_pktmbuf_pool_private),
                                   rte_pktmbuf_pool_init, NULL,
                                   rte_pktmbuf_init,      NULL,
                                   rte_socket_id(),
                                   0);

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:

.. code-block:: c

    for (portid = 0; portid < nb_ports; portid++) {
        if (port_init(portid, mbuf_pool) != 0) {
            rte_exit(EXIT_FAILURE,
                     "Cannot init port %" PRIu8 "\n", portid);
        }
    }


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.


.. code-block:: c

	lcore_main();

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:

.. code-block:: c

    static inline int
    port_init(uint16_t port, struct rte_mempool *mbuf_pool)
    {
        struct rte_eth_conf port_conf = port_conf_default;
        const uint16_t rx_rings = 1, tx_rings = 1;
        struct ether_addr addr;
        int retval;
        uint16_t q;

        if (port >= rte_eth_dev_count())
            return -1;

        /* Configure the Ethernet device. */
        retval = rte_eth_dev_configure(port, rx_rings, tx_rings, &port_conf);
        if (retval != 0)
            return retval;

        /* Allocate and set up 1 RX queue per Ethernet port. */
        for (q = 0; q < rx_rings; q++) {
            retval = rte_eth_rx_queue_setup(port, q, RX_RING_SIZE,
                    rte_eth_dev_socket_id(port), NULL, mbuf_pool);
            if (retval < 0)
                return retval;
        }

        /* Allocate and set up 1 TX queue per Ethernet port. */
        for (q = 0; q < tx_rings; q++) {
            retval = rte_eth_tx_queue_setup(port, q, TX_RING_SIZE,
                    rte_eth_dev_socket_id(port), NULL);
            if (retval < 0)
                return retval;
        }

        /* Start the Ethernet port. */
        retval = rte_eth_dev_start(port);
        if (retval < 0)
            return retval;

        /* Enable RX in promiscuous mode for the Ethernet device. */
        rte_eth_promiscuous_enable(port);

        return 0;
    }

The Ethernet ports are configured with default settings using the
``rte_eth_dev_configure()`` function and the ``port_conf_default`` struct:

.. code-block:: c

    static const struct rte_eth_conf port_conf_default = {
        .rxmode = { .max_rx_pkt_len = ETHER_MAX_LEN }
    };

For 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:

.. code-block:: c

        retval  = rte_eth_dev_start(port);


Finally the RX port is set in promiscuous mode:

.. code-block:: c

        rte_eth_promiscuous_enable(port);


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:

.. code-block:: c

    static __attribute__((noreturn)) void
    lcore_main(void)
    {
        const uint16_t nb_ports = rte_eth_dev_count();
        uint16_t port;

        /*
         * Check that the port is on the same NUMA node as the polling thread
         * for best performance.
         */
        for (port = 0; port < nb_ports; port++)
            if (rte_eth_dev_socket_id(port) > 0 &&
                    rte_eth_dev_socket_id(port) !=
                            (int)rte_socket_id())
                printf("WARNING, port %u is on remote NUMA node to "
                        "polling thread.\n\tPerformance will "
                        "not be optimal.\n", port);

        printf("\nCore %u forwarding packets. [Ctrl+C to quit]\n",
                rte_lcore_id());

        /* Run until the application is quit or killed. */
        for (;;) {
            /*
             * Receive packets on a port and forward them on the paired
             * port. The mapping is 0 -> 1, 1 -> 0, 2 -> 3, 3 -> 2, etc.
             */
            for (port = 0; port < nb_ports; port++) {

                /* Get burst of RX packets, from first port of pair. */
                struct rte_mbuf *bufs[BURST_SIZE];
                const uint16_t nb_rx = rte_eth_rx_burst(port, 0,
                        bufs, BURST_SIZE);

                if (unlikely(nb_rx == 0))
                    continue;

                /* Send burst of TX packets, to second port of pair. */
                const uint16_t nb_tx = rte_eth_tx_burst(port ^ 1, 0,
                        bufs, nb_rx);

                /* Free any unsent packets. */
                if (unlikely(nb_tx < nb_rx)) {
                    uint16_t buf;
                    for (buf = nb_tx; buf < nb_rx; buf++)
                        rte_pktmbuf_free(bufs[buf]);
                }
            }
        }
    }


The main work of the application is done within the loop:

.. code-block:: c

        for (;;) {
            for (port = 0; port < nb_ports; port++) {

                /* Get burst of RX packets, from first port of pair. */
                struct rte_mbuf *bufs[BURST_SIZE];
                const uint16_t nb_rx = rte_eth_rx_burst(port, 0,
                        bufs, BURST_SIZE);

                if (unlikely(nb_rx == 0))
                    continue;

                /* Send burst of TX packets, to second port of pair. */
                const uint16_t nb_tx = rte_eth_tx_burst(port ^ 1, 0,
                        bufs, nb_rx);

                /* Free any unsent packets. */
                if (unlikely(nb_tx < nb_rx)) {
                    uint16_t buf;
                    for (buf = nb_tx; buf < nb_rx; buf++)
                        rte_pktmbuf_free(bufs[buf]);
                }
            }
        }

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``.
