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diff --git a/doc/guides/contributing/documentation.rst b/doc/guides/contributing/documentation.rst new file mode 100644 index 00000000..ba5c4dec --- /dev/null +++ b/doc/guides/contributing/documentation.rst @@ -0,0 +1,752 @@ +.. _doc_guidelines: + +DPDK Documentation Guidelines +============================= + +This document outlines the guidelines for writing the DPDK Guides and API documentation in RST and Doxygen format. + +It also explains the structure of the DPDK documentation and shows how to build the Html and PDF versions of the documents. + + +Structure of the Documentation +------------------------------ + +The DPDK source code repository contains input files to build the API documentation and User Guides. + +The main directories that contain files related to documentation are shown below:: + + lib + |-- librte_acl + |-- librte_cfgfile + |-- librte_cmdline + |-- librte_compat + |-- librte_eal + | |-- ... + ... + doc + |-- api + +-- guides + |-- freebsd_gsg + |-- linux_gsg + |-- prog_guide + |-- sample_app_ug + |-- guidelines + |-- testpmd_app_ug + |-- rel_notes + |-- nics + |-- xen + |-- ... + + +The API documentation is built from `Doxygen <http://www.stack.nl/~dimitri/doxygen/>`_ comments in the header files. +These files are mainly in the ``lib/librte_*`` directories although some of the Poll Mode Drivers in ``drivers/net`` +are also documented with Doxygen. + +The configuration files that are used to control the Doxygen output are in the ``doc/api`` directory. + +The user guides such as *The Programmers Guide* and the *FreeBSD* and *Linux Getting Started* Guides are generated +from RST markup text files using the `Sphinx <http://sphinx-doc.org/index.html>`_ Documentation Generator. + +These files are included in the ``doc/guides/`` directory. +The output is controlled by the ``doc/guides/conf.py`` file. + + +Role of the Documentation +------------------------- + +The following items outline the roles of the different parts of the documentation and when they need to be updated or +added to by the developer. + +* **Release Notes** + + The Release Notes document which features have been added in the current and previous releases of DPDK and highlight + any known issues. + The Releases Notes also contain notifications of features that will change ABI compatibility in the next major release. + + Developers should include updates to the Release Notes with patch sets that relate to any of the following sections: + + * New Features + * Resolved Issues (see below) + * Known Issues + * API Changes + * ABI Changes + * Shared Library Versions + + Resolved Issues should only include issues from previous releases that have been resolved in the current release. + Issues that are introduced and then fixed within a release cycle do not have to be included here. + + Refer to the Release Notes from the previous DPDK release for the correct format of each section. + + +* **API documentation** + + The API documentation explains how to use the public DPDK functions. + The `API index page <http://dpdk.org/doc/api/>`_ shows the generated API documentation with related groups of functions. + + The API documentation should be updated via Doxygen comments when new functions are added. + +* **Getting Started Guides** + + The Getting Started Guides show how to install and configure DPDK and how to run DPDK based applications on different OSes. + + A Getting Started Guide should be added when DPDK is ported to a new OS. + +* **The Programmers Guide** + + The Programmers Guide explains how the API components of DPDK such as the EAL, Memzone, Rings and the Hash Library work. + It also explains how some higher level functionality such as Packet Distributor, Packet Framework and KNI work. + It also shows the build system and explains how to add applications. + + The Programmers Guide should be expanded when new functionality is added to DPDK. + +* **App Guides** + + The app guides document the DPDK applications in the ``app`` directory such as ``testpmd``. + + The app guides should be updated if functionality is changed or added. + +* **Sample App Guides** + + The sample app guides document the DPDK example applications in the examples directory. + Generally they demonstrate a major feature such as L2 or L3 Forwarding, Multi Process or Power Management. + They explain the purpose of the sample application, how to run it and step through some of the code to explain the + major functionality. + + A new sample application should be accompanied by a new sample app guide. + The guide for the Skeleton Forwarding app is a good starting reference. + +* **Network Interface Controller Drivers** + + The NIC Drivers document explains the features of the individual Poll Mode Drivers, such as software requirements, + configuration and initialization. + + New documentation should be added for new Poll Mode Drivers. + +* **Guidelines** + + The guideline documents record community process, expectations and design directions. + + They can be extended, amended or discussed by submitting a patch and getting community approval. + + +Building the Documentation +-------------------------- + +Dependencies +~~~~~~~~~~~~ + + +The following dependencies must be installed to build the documentation: + +* Doxygen. + +* Sphinx (also called python-sphinx). + +* TexLive (at least TexLive-core and the extra Latex support). + +* Inkscape. + +`Doxygen`_ generates documentation from commented source code. +It can be installed as follows: + +.. code-block:: console + + # Ubuntu/Debian. + sudo apt-get -y install doxygen + + # Red Hat/Fedora. + sudo yum -y install doxygen + +`Sphinx`_ is a Python documentation tool for converting RST files to Html or to PDF (via LaTeX). +For full support with figure and table captioning the latest version of Sphinx can be installed as follows: + +.. code-block:: console + + # Ubuntu/Debian. + sudo apt-get -y install python-pip + sudo pip install --upgrade sphinx + + # Red Hat/Fedora. + sudo yum -y install python-pip + sudo pip install --upgrade sphinx + +For further information on getting started with Sphinx see the `Sphinx Tutorial <http://sphinx-doc.org/tutorial.html>`_. + +.. Note:: + + To get full support for Figure and Table numbering it is best to install Sphinx 1.3.1 or later. + + +`Inkscape`_ is a vector based graphics program which is used to create SVG images and also to convert SVG images to PDF images. +It can be installed as follows: + +.. code-block:: console + + # Ubuntu/Debian. + sudo apt-get -y install inkscape + + # Red Hat/Fedora. + sudo yum -y install inkscape + +`TexLive <http://www.tug.org/texlive/>`_ is an installation package for Tex/LaTeX. +It is used to generate the PDF versions of the documentation. +The main required packages can be installed as follows: + +.. code-block:: console + + # Ubuntu/Debian. + sudo apt-get -y install texlive-latex-extra + + # Red Hat/Fedora, selective install. + sudo yum -y install texlive-collection-latexextra + + +Build commands +~~~~~~~~~~~~~~ + +The documentation is built using the standard DPDK build system. +Some examples are shown below: + +* Generate all the documentation targets:: + + make doc + +* Generate the Doxygen API documentation in Html:: + + make doc-api-html + +* Generate the guides documentation in Html:: + + make doc-guides-html + +* Generate the guides documentation in Pdf:: + + make doc-guides-pdf + +The output of these commands is generated in the ``build`` directory:: + + build/doc + |-- html + | |-- api + | +-- guides + | + +-- pdf + +-- guides + + +.. Note:: + + Make sure to fix any Sphinx or Doxygen warnings when adding or updating documentation. + +The documentation output files can be removed as follows:: + + make doc-clean + + +Document Guidelines +------------------- + +Here are some guidelines in relation to the style of the documentation: + +* Document the obvious as well as the obscure since it won't always be obvious to the reader. + For example an instruction like "Set up 64 2MB Hugepages" is better when followed by a sample commandline or a link to + the appropriate section of the documentation. + +* Use American English spellings throughout. + This can be checked using the ``aspell`` utility:: + + aspell --lang=en_US --check doc/guides/sample_app_ug/mydoc.rst + + +RST Guidelines +-------------- + +The RST (reStructuredText) format is a plain text markup format that can be converted to Html, PDF or other formats. +It is most closely associated with Python but it can be used to document any language. +It is used in DPDK to document everything apart from the API. + +The Sphinx documentation contains a very useful `RST Primer <http://sphinx-doc.org/rest.html#rst-primer>`_ which is a +good place to learn the minimal set of syntax required to format a document. + +The official `reStructuredText <http://docutils.sourceforge.net/rst.html>`_ website contains the specification for the +RST format and also examples of how to use it. +However, for most developers the RST Primer is a better resource. + +The most common guidelines for writing RST text are detailed in the +`Documenting Python <https://docs.python.org/devguide/documenting.html>`_ guidelines. +The additional guidelines below reiterate or expand upon those guidelines. + + +Line Length +~~~~~~~~~~~ + +* The recommended style for the DPDK documentation is to put sentences on separate lines. + This allows for easier reviewing of patches. + Multiple sentences which are not separated by a blank line are joined automatically into paragraphs, for example:: + + Here is an example sentence. + Long sentences over the limit shown below can be wrapped onto + a new line. + These three sentences will be joined into the same paragraph. + + This is a new paragraph, since it is separated from the + previous paragraph by a blank line. + + This would be rendered as follows: + + *Here is an example sentence. + Long sentences over the limit shown below can be wrapped onto + a new line. + These three sentences will be joined into the same paragraph.* + + *This is a new paragraph, since it is separated from the + previous paragraph by a blank line.* + + +* Long sentences should be wrapped at 120 characters +/- 10 characters. They should be wrapped at words. + +* Lines in literal blocks must by less than 80 characters since they aren't wrapped by the document formatters + and can exceed the page width in PDF documents. + + +Whitespace +~~~~~~~~~~ + +* Standard RST indentation is 3 spaces. + Code can be indented 4 spaces, especially if it is copied from source files. + +* No tabs. + Convert tabs in embedded code to 4 or 8 spaces. + +* No trailing whitespace. + +* Add 2 blank lines before each section header. + +* Add 1 blank line after each section header. + +* Add 1 blank line between each line of a list. + + +Section Headers +~~~~~~~~~~~~~~~ + +* Section headers should use the use the following underline formats:: + + Level 1 Heading + =============== + + + Level 2 Heading + --------------- + + + Level 3 Heading + ~~~~~~~~~~~~~~~ + + + Level 4 Heading + ^^^^^^^^^^^^^^^ + + +* Level 4 headings should be used sparingly. + +* The underlines should match the length of the text. + +* In general, the heading should be less than 80 characters, for conciseness. + +* As noted above: + + * Add 2 blank lines before each section header. + + * Add 1 blank line after each section header. + + +Lists +~~~~~ + +* Bullet lists should be formatted with a leading ``*`` as follows:: + + * Item one. + + * Item two is a long line that is wrapped and then indented to match + the start of the previous line. + + * One space character between the bullet and the text is preferred. + +* Numbered lists can be formatted with a leading number but the preference is to use ``#.`` which will give automatic numbering. + This is more convenient when adding or removing items:: + + #. Item one. + + #. Item two is a long line that is wrapped and then indented + to match the start of the e first line. + + #. Item two is a long line that is wrapped and then indented to match + the start of the previous line. + +* Definition lists can be written with or without a bullet:: + + * Item one. + + Some text about item one. + + * Item two. + + Some text about item two. + +* All lists, and sub-lists, must be separated from the preceding text by a blank line. + This is a syntax requirement. + +* All list items should be separated by a blank line for readability. + + +Code and Literal block sections +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +* Inline text that is required to be rendered with a fixed width font should be enclosed in backquotes like this: + \`\`text\`\`, so that it appears like this: ``text``. + +* Fixed width, literal blocks of texts should be indented at least 3 spaces and prefixed with ``::`` like this:: + + Here is some fixed width text:: + + 0x0001 0x0001 0x00FF 0x00FF + +* It is also possible to specify an encoding for a literal block using the ``.. code-block::`` directive so that syntax + highlighting can be applied. + Examples of supported highlighting are:: + + .. code-block:: console + .. code-block:: c + .. code-block:: python + .. code-block:: diff + .. code-block:: none + + That can be applied as follows:: + + .. code-block:: c + + #include<stdio.h> + + int main() { + + printf("Hello World\n"); + + return 0; + } + + Which would be rendered as: + + .. code-block:: c + + #include<stdio.h> + + int main() { + + printf("Hello World\n"); + + return 0; + } + + +* The default encoding for a literal block using the simplified ``::`` + directive is ``none``. + +* Lines in literal blocks must be less than 80 characters since they can exceed the page width when converted to PDF documentation. + For long literal lines that exceed that limit try to wrap the text at sensible locations. + For example a long command line could be documented like this and still work if copied directly from the docs:: + + build/app/testpmd -c7 -n3 --vdev=eth_pcap0,iface=eth0 \ + --vdev=eth_pcap1,iface=eth1 \ + -- -i --nb-cores=2 --nb-ports=2 \ + --total-num-mbufs=2048 + +* Long lines that cannot be wrapped, such as application output, should be truncated to be less than 80 characters. + + +Images +~~~~~~ + +* All images should be in SVG scalar graphics format. + They should be true SVG XML files and should not include binary formats embedded in a SVG wrapper. + +* The DPDK documentation contains some legacy images in PNG format. + These will be converted to SVG in time. + +* `Inkscape <http://inkscape.org>`_ is the recommended graphics editor for creating the images. + Use some of the older images in ``doc/guides/prog_guide/img/`` as a template, for example ``mbuf1.svg`` + or ``ring-enqueue.svg``. + +* The SVG images should include a copyright notice, as an XML comment. + +* Images in the documentation should be formatted as follows: + + * The image should be preceded by a label in the format ``.. _figure_XXXX:`` with a leading underscore and + where ``XXXX`` is a unique descriptive name. + + * Images should be included using the ``.. figure::`` directive and the file type should be set to ``*`` (not ``.svg``). + This allows the format of the image to be changed if required, without updating the documentation. + + * Images must have a caption as part of the ``.. figure::`` directive. + +* Here is an example of the previous three guidelines:: + + .. _figure_mempool: + + .. figure:: img/mempool.* + + A mempool in memory with its associated ring. + +.. _mock_label: + +* Images can then be linked to using the ``:numref:`` directive:: + + The mempool layout is shown in :numref:`figure_mempool`. + + This would be rendered as: *The mempool layout is shown in* :ref:`Fig 6.3 <mock_label>`. + + **Note**: The ``:numref:`` directive requires Sphinx 1.3.1 or later. + With earlier versions it will still be rendered as a link but won't have an automatically generated number. + +* The caption of the image can be generated, with a link, using the ``:ref:`` directive:: + + :ref:`figure_mempool` + + This would be rendered as: *A mempool in memory with its associated ring.* + +Tables +~~~~~~ + +* RST tables should be used sparingly. + They are hard to format and to edit, they are often rendered incorrectly in PDF format, and the same information + can usually be shown just as clearly with a definition or bullet list. + +* Tables in the documentation should be formatted as follows: + + * The table should be preceded by a label in the format ``.. _table_XXXX:`` with a leading underscore and where + ``XXXX`` is a unique descriptive name. + + * Tables should be included using the ``.. table::`` directive and must have a caption. + +* Here is an example of the previous two guidelines:: + + .. _table_qos_pipes: + + .. table:: Sample configuration for QOS pipes. + + +----------+----------+----------+ + | Header 1 | Header 2 | Header 3 | + | | | | + +==========+==========+==========+ + | Text | Text | Text | + +----------+----------+----------+ + | ... | ... | ... | + +----------+----------+----------+ + +* Tables can be linked to using the ``:numref:`` and ``:ref:`` directives, as shown in the previous section for images. + For example:: + + The QOS configuration is shown in :numref:`table_qos_pipes`. + +* Tables should not include merged cells since they are not supported by the PDF renderer. + + +.. _links: + +Hyperlinks +~~~~~~~~~~ + +* Links to external websites can be plain URLs. + The following is rendered as http://dpdk.org:: + + http://dpdk.org + +* They can contain alternative text. + The following is rendered as `Check out DPDK <http://dpdk.org>`_:: + + `Check out DPDK <http://dpdk.org>`_ + +* An internal link can be generated by placing labels in the document with the format ``.. _label_name``. + +* The following links to the top of this section: :ref:`links`:: + + .. _links: + + Hyperlinks + ~~~~~~~~~~ + + * The following links to the top of this section: :ref:`links`: + +.. Note:: + + The label must have a leading underscore but the reference to it must omit it. + This is a frequent cause of errors and warnings. + +* The use of a label is preferred since it works across files and will still work if the header text changes. + + +.. _doxygen_guidelines: + +Doxygen Guidelines +------------------ + +The DPDK API is documented using Doxygen comment annotations in the header files. +Doxygen is a very powerful tool, it is extremely configurable and with a little effort can be used to create expressive documents. +See the `Doxygen website <http://www.stack.nl/~dimitri/doxygen/>`_ for full details on how to use it. + +The following are some guidelines for use of Doxygen in the DPDK API documentation: + +* New libraries that are documented with Doxygen should be added to the Doxygen configuration file: ``doc/api/doxy-api.conf``. + It is only required to add the directory that contains the files. + It isn't necessary to explicitly name each file since the configuration matches all ``rte_*.h`` files in the directory. + +* Use proper capitalization and punctuation in the Doxygen comments since they will become sentences in the documentation. + This in particular applies to single line comments, which is the case the is most often forgotten. + +* Use ``@`` style Doxygen commands instead of ``\`` style commands. + +* Add a general description of each library at the head of the main header files: + + .. code-block:: c + + /** + * @file + * RTE Mempool. + * + * A memory pool is an allocator of fixed-size object. It is + * identified by its name, and uses a ring to store free objects. + * ... + */ + +* Document the purpose of a function, the parameters used and the return + value: + + .. code-block:: c + + /** + * Attach a new Ethernet device specified by arguments. + * + * @param devargs + * A pointer to a strings array describing the new device + * to be attached. The strings should be a pci address like + * `0000:01:00.0` or **virtual** device name like `eth_pcap0`. + * @param port_id + * A pointer to a port identifier actually attached. + * + * @return + * 0 on success and port_id is filled, negative on error. + */ + int rte_eth_dev_attach(const char *devargs, uint8_t *port_id); + +* Doxygen supports Markdown style syntax such as bold, italics, fixed width text and lists. + For example the second line in the ``devargs`` parameter in the previous example will be rendered as: + + The strings should be a pci address like ``0000:01:00.0`` or **virtual** device name like ``eth_pcap0``. + +* Use ``-`` instead of ``*`` for lists within the Doxygen comment since the latter can get confused with the comment delimiter. + +* Add an empty line between the function description, the ``@params`` and ``@return`` for readability. + +* Place the ``@params`` description on separate line and indent it by 2 spaces. + (It would be better to use no indentation since this is more common and also because checkpatch complains about leading + whitespace in comments. + However this is the convention used in the existing DPDK code.) + +* Documented functions can be linked to simply by adding ``()`` to the function name: + + .. code-block:: c + + /** + * The functions exported by the application Ethernet API to setup + * a device designated by its port identifier must be invoked in + * the following order: + * - rte_eth_dev_configure() + * - rte_eth_tx_queue_setup() + * - rte_eth_rx_queue_setup() + * - rte_eth_dev_start() + */ + + In the API documentation the functions will be rendered as links, see the + `online section of the rte_ethdev.h docs <http://dpdk.org/doc/api/rte__ethdev_8h.html>`_ that contains the above text. + +* The ``@see`` keyword can be used to create a *see also* link to another file or library. + This directive should be placed on one line at the bottom of the documentation section. + + .. code-block:: c + + /** + * ... + * + * Some text that references mempools. + * + * @see eal_memzone.c + */ + +* Doxygen supports two types of comments for documenting variables, constants and members: prefix and postfix: + + .. code-block:: c + + /** This is a prefix comment. */ + #define RTE_FOO_ERROR 0x023. + + #define RTE_BAR_ERROR 0x024. /**< This is a postfix comment. */ + +* Postfix comments are preferred for struct members and constants if they can be documented in the same way: + + .. code-block:: c + + struct rte_eth_stats { + uint64_t ipackets; /**< Total number of received packets. */ + uint64_t opackets; /**< Total number of transmitted packets.*/ + uint64_t ibytes; /**< Total number of received bytes. */ + uint64_t obytes; /**< Total number of transmitted bytes. */ + uint64_t imissed; /**< Total of RX missed packets. */ + uint64_t ibadcrc; /**< Total of RX packets with CRC error. */ + uint64_t ibadlen; /**< Total of RX packets with bad length. */ + } + + Note: postfix comments should be aligned with spaces not tabs in accordance + with the :ref:`coding_style`. + +* If a single comment type can't be used, due to line length limitations then + prefix comments should be preferred. + For example this section of the code contains prefix comments, postfix comments on the same line and postfix + comments on a separate line: + + .. code-block:: c + + /** Number of elements in the elt_pa array. */ + uint32_t pg_num __rte_cache_aligned; + uint32_t pg_shift; /**< LOG2 of the physical pages. */ + uintptr_t pg_mask; /**< Physical page mask value. */ + uintptr_t elt_va_start; + /**< Virtual address of the first mempool object. */ + uintptr_t elt_va_end; + /**< Virtual address of the <size + 1> mempool object. */ + phys_addr_t elt_pa[MEMPOOL_PG_NUM_DEFAULT]; + /**< Array of physical page addresses for the mempool buffer. */ + + This doesn't have an effect on the rendered documentation but it is confusing for the developer reading the code. + It this case it would be clearer to use prefix comments throughout: + + .. code-block:: c + + /** Number of elements in the elt_pa array. */ + uint32_t pg_num __rte_cache_aligned; + /** LOG2 of the physical pages. */ + uint32_t pg_shift; + /** Physical page mask value. */ + uintptr_t pg_mask; + /** Virtual address of the first mempool object. */ + uintptr_t elt_va_start; + /** Virtual address of the <size + 1> mempool object. */ + uintptr_t elt_va_end; + /** Array of physical page addresses for the mempool buffer. */ + phys_addr_t elt_pa[MEMPOOL_PG_NUM_DEFAULT]; + +* Check for Doxygen warnings in new code by checking the API documentation build:: + + make doc-api-html >/dev/null + +* Read the rendered section of the documentation that you have added for correctness, clarity and consistency + with the surrounding text. |