1 .. SPDX-License-Identifier: BSD-3-Clause
2 Copyright 2018 The DPDK contributors
6 DPDK Documentation Guidelines
7 =============================
9 This document outlines the guidelines for writing the DPDK Guides and API documentation in RST and Doxygen format.
11 It also explains the structure of the DPDK documentation and shows how to build the Html and PDF versions of the documents.
14 Structure of the Documentation
15 ------------------------------
17 The DPDK source code repository contains input files to build the API documentation and User Guides.
19 The main directories that contain files related to documentation are shown below::
42 The API documentation is built from `Doxygen <http://www.doxygen.nl>`_ comments in the header files.
43 These files are mainly in the ``lib/librte_*`` directories although some of the Poll Mode Drivers in ``drivers/net``
44 are also documented with Doxygen.
46 The configuration files that are used to control the Doxygen output are in the ``doc/api`` directory.
48 The user guides such as *The Programmers Guide* and the *FreeBSD* and *Linux Getting Started* Guides are generated
49 from RST markup text files using the `Sphinx <http://sphinx-doc.org>`_ Documentation Generator.
51 These files are included in the ``doc/guides/`` directory.
52 The output is controlled by the ``doc/guides/conf.py`` file.
55 Role of the Documentation
56 -------------------------
58 The following items outline the roles of the different parts of the documentation and when they need to be updated or
59 added to by the developer.
63 The Release Notes document which features have been added in the current and previous releases of DPDK and highlight
65 The Releases Notes also contain notifications of features that will change ABI compatibility in the next release.
67 Developers should include updates to the Release Notes with patch sets that relate to any of the following sections:
70 * Resolved Issues (see below)
74 * Shared Library Versions
76 Resolved Issues should only include issues from previous releases that have been resolved in the current release.
77 Issues that are introduced and then fixed within a release cycle do not have to be included here.
79 Refer to the Release Notes from the previous DPDK release for the correct format of each section.
82 * **API documentation**
84 The API documentation explains how to use the public DPDK functions.
85 The `API index page <https://doc.dpdk.org/api/>`_ shows the generated API documentation with related groups of functions.
87 The API documentation should be updated via Doxygen comments when new functions are added.
89 * **Getting Started Guides**
91 The Getting Started Guides show how to install and configure DPDK and how to run DPDK based applications on different OSes.
93 A Getting Started Guide should be added when DPDK is ported to a new OS.
95 * **The Programmers Guide**
97 The Programmers Guide explains how the API components of DPDK such as the EAL, Memzone, Rings and the Hash Library work.
98 It also explains how some higher level functionality such as Packet Distributor, Packet Framework and KNI work.
99 It also shows the build system and explains how to add applications.
101 The Programmers Guide should be expanded when new functionality is added to DPDK.
105 The app guides document the DPDK applications in the ``app`` directory such as ``testpmd``.
107 The app guides should be updated if functionality is changed or added.
109 * **Sample App Guides**
111 The sample app guides document the DPDK example applications in the examples directory.
112 Generally they demonstrate a major feature such as L2 or L3 Forwarding, Multi Process or Power Management.
113 They explain the purpose of the sample application, how to run it and step through some of the code to explain the
116 A new sample application should be accompanied by a new sample app guide.
117 The guide for the Skeleton Forwarding app is a good starting reference.
119 * **Network Interface Controller Drivers**
121 The NIC Drivers document explains the features of the individual Poll Mode Drivers, such as software requirements,
122 configuration and initialization.
124 New documentation should be added for new Poll Mode Drivers.
128 The guideline documents record community process, expectations and design directions.
130 They can be extended, amended or discussed by submitting a patch and getting community approval.
133 Building the Documentation
134 --------------------------
140 The following dependencies must be installed to build the documentation:
144 * Sphinx (also called python-sphinx).
146 * TexLive (at least TexLive-core and the extra Latex support).
150 `Doxygen`_ generates documentation from commented source code.
151 It can be installed as follows:
153 .. code-block:: console
156 sudo apt-get -y install doxygen
159 sudo dnf -y install doxygen
161 `Sphinx`_ is a Python documentation tool for converting RST files to Html or to PDF (via LaTeX).
162 For full support with figure and table captioning the latest version of Sphinx can be installed as follows:
164 .. code-block:: console
167 sudo apt-get -y install python3-sphinx python3-sphinx-rtd-theme
170 sudo dnf -y install python3-sphinx python3-sphinx_rtd_theme
172 For further information on getting started with Sphinx see the
173 `Sphinx Getting Started <http://www.sphinx-doc.org/en/master/usage/quickstart.html>`_.
177 To get full support for Figure and Table numbering it is best to install Sphinx 1.3.1 or later.
180 `Inkscape`_ is a vector based graphics program which is used to create SVG images and also to convert SVG images to PDF images.
181 It can be installed as follows:
183 .. code-block:: console
186 sudo apt-get -y install inkscape
189 sudo dnf -y install inkscape
191 `TexLive <http://www.tug.org/texlive/>`_ is an installation package for Tex/LaTeX.
192 It is used to generate the PDF versions of the documentation.
193 The main required packages can be installed as follows:
195 .. code-block:: console
198 sudo apt-get -y install texlive-latex-extra texlive-lang-greek
200 # Red Hat/Fedora, selective install.
201 sudo dnf -y install texlive-collection-latexextra texlive-greek-fontenc
203 `Latexmk <http://personal.psu.edu/jcc8/software/latexmk-jcc/>`_ is a perl script
204 for running LaTeX for resolving cross references,
205 and it also runs auxiliary programs like bibtex, makeindex if necessary, and dvips.
206 It has also a number of other useful capabilities (see man 1 latexmk).
208 .. code-block:: console
211 sudo apt-get -y install latexmk
214 sudo dnf -y install latexmk
220 The documentation is built using the standard DPDK build system.
221 Some examples are shown below:
223 * Generate all the documentation targets::
227 * Generate the Doxygen API documentation in Html::
231 * Generate the guides documentation in Html::
235 * Generate the guides documentation in Pdf::
239 The output of these commands is generated in the ``build`` directory::
252 Make sure to fix any Sphinx or Doxygen warnings when adding or updating documentation.
254 The documentation output files can be removed as follows::
262 Here are some guidelines in relation to the style of the documentation:
264 * Document the obvious as well as the obscure since it won't always be obvious to the reader.
265 For example an instruction like "Set up 64 2MB Hugepages" is better when followed by a sample commandline or a link to
266 the appropriate section of the documentation.
268 * Use American English spellings throughout.
269 This can be checked using the ``aspell`` utility::
271 aspell --lang=en_US --check doc/guides/sample_app_ug/mydoc.rst
277 The RST (reStructuredText) format is a plain text markup format that can be converted to Html, PDF or other formats.
278 It is most closely associated with Python but it can be used to document any language.
279 It is used in DPDK to document everything apart from the API.
281 The Sphinx documentation contains a very useful `RST Primer <http://sphinx-doc.org/rest.html#rst-primer>`_ which is a
282 good place to learn the minimal set of syntax required to format a document.
284 The official `reStructuredText <http://docutils.sourceforge.net/rst.html>`_ website contains the specification for the
285 RST format and also examples of how to use it.
286 However, for most developers the RST Primer is a better resource.
288 The most common guidelines for writing RST text are detailed in the
289 `Documenting Python <https://docs.python.org/devguide/documenting.html>`_ guidelines.
290 The additional guidelines below reiterate or expand upon those guidelines.
296 * Lines in sentences should be less than 80 characters and wrapped at
297 words. Multiple sentences which are not separated by a blank line are joined
298 automatically into paragraphs.
300 * Lines in literal blocks **must** be less than 80 characters since
301 they are not wrapped by the document formatters and can exceed the page width
304 Long literal command lines can be shown wrapped with backslashes. For
307 testpmd -l 2-3 -n 4 \
308 --vdev=virtio_user0,path=/dev/vhost-net,queues=2,queue_size=1024 \
309 -- -i --tx-offloads=0x0000002c --enable-lro --txq=2 --rxq=2 \
310 --txd=1024 --rxd=1024
316 * Standard RST indentation is 3 spaces.
317 Code can be indented 4 spaces, especially if it is copied from source files.
320 Convert tabs in embedded code to 4 or 8 spaces.
322 * No trailing whitespace.
324 * Add 2 blank lines before each section header.
326 * Add 1 blank line after each section header.
328 * Add 1 blank line between each line of a list.
334 * Section headers should use the following underline formats::
352 * Level 4 headings should be used sparingly.
354 * The underlines should match the length of the text.
356 * In general, the heading should be less than 80 characters, for conciseness.
360 * Add 2 blank lines before each section header.
362 * Add 1 blank line after each section header.
368 * Bullet lists should be formatted with a leading ``*`` as follows::
372 * Item two is a long line that is wrapped and then indented to match
373 the start of the previous line.
375 * One space character between the bullet and the text is preferred.
377 * Numbered lists can be formatted with a leading number but the preference is to use ``#.`` which will give automatic numbering.
378 This is more convenient when adding or removing items::
382 #. Item two is a long line that is wrapped and then indented to match
383 the start of the previous line.
387 * Definition lists can be written with or without a bullet::
391 Some text about item one.
395 Some text about item two.
397 * All lists, and sub-lists, must be separated from the preceding text by a blank line.
398 This is a syntax requirement.
400 * All list items should be separated by a blank line for readability.
403 Code and Literal block sections
404 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
406 * Inline text that is required to be rendered with a fixed width font should be enclosed in backquotes like this:
407 \`\`text\`\`, so that it appears like this: ``text``.
409 * Fixed width, literal blocks of texts should be indented at least 3 spaces and prefixed with ``::`` like this::
411 Here is some fixed width text::
413 0x0001 0x0001 0x00FF 0x00FF
415 * It is also possible to specify an encoding for a literal block using the ``.. code-block::`` directive so that syntax
416 highlighting can be applied.
417 Examples of supported highlighting are::
419 .. code-block:: console
421 .. code-block:: python
425 That can be applied as follows::
433 printf("Hello World\n");
438 Which would be rendered as:
446 printf("Hello World\n");
452 * The default encoding for a literal block using the simplified ``::``
453 directive is ``none``.
455 * Lines in literal blocks must be less than 80 characters since they can exceed the page width when converted to PDF documentation.
456 For long literal lines that exceed that limit try to wrap the text at sensible locations.
457 For example a long command line could be documented like this and still work if copied directly from the docs::
459 build/app/testpmd -l 0-2 -n3 --vdev=net_pcap0,iface=eth0 \
460 --vdev=net_pcap1,iface=eth1 \
461 -- -i --nb-cores=2 --nb-ports=2 \
462 --total-num-mbufs=2048
464 * Long lines that cannot be wrapped, such as application output, should be truncated to be less than 80 characters.
470 * All images should be in SVG scalar graphics format.
471 They should be true SVG XML files and should not include binary formats embedded in a SVG wrapper.
473 * The DPDK documentation contains some legacy images in PNG format.
474 These will be converted to SVG in time.
476 * `Inkscape <http://inkscape.org>`_ is the recommended graphics editor for creating the images.
477 Use some of the older images in ``doc/guides/prog_guide/img/`` as a template, for example ``mbuf1.svg``
478 or ``ring-enqueue1.svg``.
480 * The SVG images should include a copyright notice, as an XML comment.
482 * Images in the documentation should be formatted as follows:
484 * The image should be preceded by a label in the format ``.. _figure_XXXX:`` with a leading underscore and
485 where ``XXXX`` is a unique descriptive name.
487 * Images should be included using the ``.. figure::`` directive and the file type should be set to ``*`` (not ``.svg``).
488 This allows the format of the image to be changed if required, without updating the documentation.
490 * Images must have a caption as part of the ``.. figure::`` directive.
492 * Here is an example of the previous three guidelines::
496 .. figure:: img/mempool.*
498 A mempool in memory with its associated ring.
502 * Images can then be linked to using the ``:numref:`` directive::
504 The mempool layout is shown in :numref:`figure_mempool`.
506 This would be rendered as: *The mempool layout is shown in* :ref:`Fig 6.3 <mock_label>`.
508 **Note**: The ``:numref:`` directive requires Sphinx 1.3.1 or later.
509 With earlier versions it will still be rendered as a link but won't have an automatically generated number.
511 * The caption of the image can be generated, with a link, using the ``:ref:`` directive::
513 :ref:`figure_mempool`
515 This would be rendered as: *A mempool in memory with its associated ring.*
520 * RST tables should be used sparingly.
521 They are hard to format and to edit, they are often rendered incorrectly in PDF format, and the same information
522 can usually be shown just as clearly with a definition or bullet list.
524 * Tables in the documentation should be formatted as follows:
526 * The table should be preceded by a label in the format ``.. _table_XXXX:`` with a leading underscore and where
527 ``XXXX`` is a unique descriptive name.
529 * Tables should be included using the ``.. table::`` directive and must have a caption.
531 * Here is an example of the previous two guidelines::
535 .. table:: Sample configuration for QOS pipes.
537 +----------+----------+----------+
538 | Header 1 | Header 2 | Header 3 |
540 +==========+==========+==========+
541 | Text | Text | Text |
542 +----------+----------+----------+
544 +----------+----------+----------+
546 * Tables can be linked to using the ``:numref:`` and ``:ref:`` directives, as shown in the previous section for images.
549 The QOS configuration is shown in :numref:`table_qos_pipes`.
551 * Tables should not include merged cells since they are not supported by the PDF renderer.
559 * Links to external websites can be plain URLs.
560 The following is rendered as https://dpdk.org::
564 * They can contain alternative text.
565 The following is rendered as `Check out DPDK <https://dpdk.org>`_::
567 `Check out DPDK <https://dpdk.org>`_
569 * An internal link can be generated by placing labels in the document with the format ``.. _label_name``.
571 * The following links to the top of this section: :ref:`links`::
578 * The following links to the top of this section: :ref:`links`:
582 The label must have a leading underscore but the reference to it must omit it.
583 This is a frequent cause of errors and warnings.
585 * The use of a label is preferred since it works across files and will still work if the header text changes.
588 .. _doxygen_guidelines:
593 The DPDK API is documented using Doxygen comment annotations in the header files.
594 Doxygen is a very powerful tool, it is extremely configurable and with a little effort can be used to create expressive documents.
595 See the `Doxygen website <http://www.doxygen.nl>`_ for full details on how to use it.
597 The following are some guidelines for use of Doxygen in the DPDK API documentation:
599 * New libraries that are documented with Doxygen should be added to the Doxygen configuration file: ``doc/api/doxy-api.conf``.
600 It is only required to add the directory that contains the files.
601 It isn't necessary to explicitly name each file since the configuration matches all ``rte_*.h`` files in the directory.
603 * Use proper capitalization and punctuation in the Doxygen comments since they will become sentences in the documentation.
604 This in particular applies to single line comments, which is the case the is most often forgotten.
606 * Use ``@`` style Doxygen commands instead of ``\`` style commands.
608 * Add a general description of each library at the head of the main header files:
616 * A memory pool is an allocator of fixed-size object. It is
617 * identified by its name, and uses a ring to store free objects.
621 * Document the purpose of a function, the parameters used and the return
627 * Try to take the lock.
630 * A pointer to the spinlock.
632 * 1 if the lock is successfully taken; 0 otherwise.
634 int rte_spinlock_trylock(rte_spinlock_t *sl);
636 * Doxygen supports Markdown style syntax such as bold, italics, fixed width text and lists.
637 For example the second line in the ``devargs`` parameter in the previous example will be rendered as:
639 The strings should be a pci address like ``0000:01:00.0`` or **virtual** device name like ``net_pcap0``.
641 * Use ``-`` instead of ``*`` for lists within the Doxygen comment since the latter can get confused with the comment delimiter.
643 * Add an empty line between the function description, the ``@params`` and ``@return`` for readability.
645 * Place the ``@params`` description on separate line and indent it by 2 spaces.
646 (It would be better to use no indentation since this is more common and also because checkpatch complains about leading
647 whitespace in comments.
648 However this is the convention used in the existing DPDK code.)
650 * Documented functions can be linked to simply by adding ``()`` to the function name:
655 * The functions exported by the application Ethernet API to setup
656 * a device designated by its port identifier must be invoked in
657 * the following order:
658 * - rte_eth_dev_configure()
659 * - rte_eth_tx_queue_setup()
660 * - rte_eth_rx_queue_setup()
661 * - rte_eth_dev_start()
664 In the API documentation the functions will be rendered as links, see the
665 `online section of the rte_ethdev.h docs <https://doc.dpdk.org/api/rte__ethdev_8h.html>`_ that contains the above text.
667 * The ``@see`` keyword can be used to create a *see also* link to another file or library.
668 This directive should be placed on one line at the bottom of the documentation section.
675 * Some text that references mempools.
680 * Doxygen supports two types of comments for documenting variables, constants and members: prefix and postfix:
684 /** This is a prefix comment. */
685 #define RTE_FOO_ERROR 0x023.
687 #define RTE_BAR_ERROR 0x024. /**< This is a postfix comment. */
689 * Postfix comments are preferred for struct members and constants if they can be documented in the same way:
693 struct rte_eth_stats {
694 uint64_t ipackets; /**< Total number of received packets. */
695 uint64_t opackets; /**< Total number of transmitted packets.*/
696 uint64_t ibytes; /**< Total number of received bytes. */
697 uint64_t obytes; /**< Total number of transmitted bytes. */
698 uint64_t imissed; /**< Total of RX missed packets. */
699 uint64_t ibadcrc; /**< Total of RX packets with CRC error. */
700 uint64_t ibadlen; /**< Total of RX packets with bad length. */
703 Note: postfix comments should be aligned with spaces not tabs in accordance
704 with the :ref:`coding_style`.
706 * If a single comment type can't be used, due to line length limitations then
707 prefix comments should be preferred.
708 For example this section of the code contains prefix comments, postfix comments on the same line and postfix
709 comments on a separate line:
713 /** Number of elements in the elt_pa array. */
714 uint32_t pg_num __rte_cache_aligned;
715 uint32_t pg_shift; /**< LOG2 of the physical pages. */
716 uintptr_t pg_mask; /**< Physical page mask value. */
717 uintptr_t elt_va_start;
718 /**< Virtual address of the first mempool object. */
719 uintptr_t elt_va_end;
720 /**< Virtual address of the <size + 1> mempool object. */
721 phys_addr_t elt_pa[MEMPOOL_PG_NUM_DEFAULT];
722 /**< Array of physical page addresses for the mempool buffer. */
724 This doesn't have an effect on the rendered documentation but it is confusing for the developer reading the code.
725 It this case it would be clearer to use prefix comments throughout:
729 /** Number of elements in the elt_pa array. */
730 uint32_t pg_num __rte_cache_aligned;
731 /** LOG2 of the physical pages. */
733 /** Physical page mask value. */
735 /** Virtual address of the first mempool object. */
736 uintptr_t elt_va_start;
737 /** Virtual address of the <size + 1> mempool object. */
738 uintptr_t elt_va_end;
739 /** Array of physical page addresses for the mempool buffer. */
740 phys_addr_t elt_pa[MEMPOOL_PG_NUM_DEFAULT];
742 * Check for Doxygen warnings in new code by checking the API documentation build::
744 make doc-api-html >/dev/null
746 * Read the rendered section of the documentation that you have added for correctness, clarity and consistency
747 with the surrounding text.