9a212dc06c
Currently the sample app user guides use hard coded code snippets,
this patch changes these to use literalinclude which will dynamically
update the snippets as changes are made to the code.
This was introduced in commit 413c75c33c40 ("doc: show how to include
code in guides"). Comments within the sample apps were updated to
accommodate this as part of this patch. This will help to ensure that
the code within the sample app user guides is up to date and not out
of sync with the actual code.
Signed-off-by: Conor Fogarty <conor.fogarty@intel.com>
Signed-off-by: Conor Walsh <conor.walsh@intel.com>
Acked-by: John McNamara <john.mcnamara@intel.com>
175 lines
5.5 KiB
ReStructuredText
175 lines
5.5 KiB
ReStructuredText
.. SPDX-License-Identifier: BSD-3-Clause
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Copyright(c) 2015 Intel Corporation.
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Basic Forwarding Sample Application
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===================================
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The Basic Forwarding sample application is a simple *skeleton* example of a
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forwarding application.
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It is intended as a demonstration of the basic components of a DPDK forwarding
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application. For more detailed implementations see the L2 and L3 forwarding
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sample applications.
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Compiling the Application
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-------------------------
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To compile the sample application see :doc:`compiling`.
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The application is located in the ``skeleton`` sub-directory.
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Running the Application
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-----------------------
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To run the example in a ``linux`` environment:
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.. code-block:: console
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./<build_dir>/examples/dpdk-skeleton -l 1 -n 4
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Refer to *DPDK Getting Started Guide* for general information on running
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applications and the Environment Abstraction Layer (EAL) options.
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Explanation
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-----------
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The following sections provide an explanation of the main components of the
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code.
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All DPDK library functions used in the sample code are prefixed with ``rte_``
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and are explained in detail in the *DPDK API Documentation*.
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The Main Function
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~~~~~~~~~~~~~~~~~
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The ``main()`` function performs the initialization and calls the execution
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threads for each lcore.
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The first task is to initialize the Environment Abstraction Layer (EAL). The
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``argc`` and ``argv`` arguments are provided to the ``rte_eal_init()``
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function. The value returned is the number of parsed arguments:
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.. literalinclude:: ../../../examples/skeleton/basicfwd.c
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:language: c
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:start-after: Initializion the Environment Abstraction Layer (EAL). 8<
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:end-before: >8 End of initializion the Environment Abstraction Layer (EAL).
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:dedent: 1
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The ``main()`` also allocates a mempool to hold the mbufs (Message Buffers)
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used by the application:
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.. literalinclude:: ../../../examples/skeleton/basicfwd.c
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:language: c
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:start-after: Allocates mempool to hold the mbufs. 8<
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:end-before: >8 End of allocating mempool to hold mbuf.
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:dedent: 1
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Mbufs are the packet buffer structure used by DPDK. They are explained in
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detail in the "Mbuf Library" section of the *DPDK Programmer's Guide*.
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The ``main()`` function also initializes all the ports using the user defined
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``port_init()`` function which is explained in the next section:
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.. literalinclude:: ../../../examples/skeleton/basicfwd.c
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:language: c
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:start-after: Initializing all ports. 8<
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:end-before: >8 End of initializing all ports.
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:dedent: 1
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Once the initialization is complete, the application is ready to launch a
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function on an lcore. In this example ``lcore_main()`` is called on a single
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lcore.
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.. literalinclude:: ../../../examples/skeleton/basicfwd.c
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:language: c
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:start-after: Called on single lcore. 8<
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:end-before: >8 End of called on single lcore.
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:dedent: 1
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The ``lcore_main()`` function is explained below.
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The Port Initialization Function
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The main functional part of the port initialization used in the Basic
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Forwarding application is shown below:
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.. literalinclude:: ../../../examples/skeleton/basicfwd.c
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:language: c
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:start-after: Main functional part of port initialization. 8<
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:end-before: >8 End of main functional part of port initialization.
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The Ethernet ports are configured with default settings using the
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``rte_eth_dev_configure()`` function and the ``port_conf_default`` struct:
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.. literalinclude:: ../../../examples/skeleton/basicfwd.c
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:language: c
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:start-after: Configuration of ethernet ports. 8<
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:end-before: >8 End of configuration of ethernet ports.
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For this example the ports are set up with 1 RX and 1 TX queue using the
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``rte_eth_rx_queue_setup()`` and ``rte_eth_tx_queue_setup()`` functions.
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The Ethernet port is then started:
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.. literalinclude:: ../../../examples/skeleton/basicfwd.c
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:language: c
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:start-after: Starting Ethernet port. 8<
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:end-before: >8 End of starting of ethernet port.
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:dedent: 1
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Finally the RX port is set in promiscuous mode:
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.. literalinclude:: ../../../examples/skeleton/basicfwd.c
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:language: c
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:start-after: Enable RX in promiscuous mode for the Ethernet device.
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:end-before: End of setting RX port in promiscuous mode.
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:dedent: 1
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The Lcores Main
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~~~~~~~~~~~~~~~
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As we saw above the ``main()`` function calls an application function on the
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available lcores. For the Basic Forwarding application the lcore function
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looks like the following:
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.. literalinclude:: ../../../examples/skeleton/basicfwd.c
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:language: c
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:start-after: Basic forwarding application lcore. 8<
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:end-before: >8 End Basic forwarding application lcore.
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The main work of the application is done within the loop:
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.. literalinclude:: ../../../examples/skeleton/basicfwd.c
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:language: c
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:start-after: Main work of application loop. 8<
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:end-before: >8 End of loop.
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:dedent: 1
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Packets are received in bursts on the RX ports and transmitted in bursts on
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the TX ports. The ports are grouped in pairs with a simple mapping scheme
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using the an XOR on the port number::
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0 -> 1
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1 -> 0
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2 -> 3
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3 -> 2
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etc.
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The ``rte_eth_tx_burst()`` function frees the memory buffers of packets that
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are transmitted. If packets fail to transmit, ``(nb_tx < nb_rx)``, then they
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must be freed explicitly using ``rte_pktmbuf_free()``.
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The forwarding loop can be interrupted and the application closed using
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``Ctrl-C``.
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