1.. SPDX-License-Identifier: BSD-3-Clause 2 Copyright 2018 The DPDK contributors 3 4.. _doc_guidelines: 5 6DPDK Documentation Guidelines 7============================= 8 9This document outlines the guidelines for writing the DPDK Guides and API documentation in RST and Doxygen format. 10 11It also explains the structure of the DPDK documentation and how to build it. 12 13 14Structure of the Documentation 15------------------------------ 16 17The DPDK source code repository contains input files to build the API documentation and User Guides. 18 19The main directories that contain files related to documentation are shown below:: 20 21 lib 22 |-- acl 23 |-- cfgfile 24 |-- cmdline 25 |-- eal 26 | |-- ... 27 ... 28 doc 29 |-- api 30 +-- guides 31 |-- freebsd_gsg 32 |-- linux_gsg 33 |-- prog_guide 34 |-- sample_app_ug 35 |-- guidelines 36 |-- testpmd_app_ug 37 |-- rel_notes 38 |-- nics 39 |-- ... 40 41 42The API documentation is built from `Doxygen <http://www.doxygen.nl>`_ comments in the header files. 43These files are mainly in the ``lib/*`` directories although some of the Poll Mode Drivers in ``drivers/net`` 44are also documented with Doxygen. 45 46The configuration files that are used to control the Doxygen output are in the ``doc/api`` directory. 47 48The user guides such as *The Programmers Guide* and the *FreeBSD* and *Linux Getting Started* Guides are generated 49from RST markup text files using the `Sphinx <http://sphinx-doc.org>`_ Documentation Generator. 50 51These files are included in the ``doc/guides/`` directory. 52The output is controlled by the ``doc/guides/conf.py`` file. 53 54 55Role of the Documentation 56------------------------- 57 58The following items outline the roles of the different parts of the documentation and when they need to be updated or 59added to by the developer. 60 61* **Release Notes** 62 63 The Release Notes document which features have been added in the current and previous releases of DPDK and highlight 64 any known issues. 65 The Releases Notes also contain notifications of features that will change ABI compatibility in the next release. 66 67 Developers should include updates to the Release Notes with patch sets that relate to any of the following sections: 68 69 * New Features 70 * Resolved Issues (see below) 71 * Known Issues 72 * API Changes 73 * ABI Changes 74 * Shared Library Versions 75 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. 78 79 Refer to the Release Notes from the previous DPDK release for the correct format of each section. 80 81 82* **API documentation** 83 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. 86 87 The API documentation should be updated via Doxygen comments when new functions are added. 88 89* **Getting Started Guides** 90 91 The Getting Started Guides show how to install and configure DPDK and how to run DPDK based applications on different OSes. 92 93 A Getting Started Guide should be added when DPDK is ported to a new OS. 94 95* **The Programmers Guide** 96 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 describes some of the higher level functionality such as Packet Distributor and Packet Framework. 99 It also shows the build system and explains how to add applications. 100 101 The Programmers Guide should be expanded when new functionality is added to DPDK. 102 103* **App Guides** 104 105 The app guides document the DPDK applications in the ``app`` directory such as ``testpmd``. 106 107 The app guides should be updated if functionality is changed or added. 108 109* **Sample App Guides** 110 111 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 114 major functionality. 115 116 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. 118 119* **Network Interface Controller Drivers** 120 121 The NIC Drivers document explains the features of the individual Poll Mode Drivers, such as software requirements, 122 configuration and initialization. 123 124 New documentation should be added for new Poll Mode Drivers. 125 126* **Guidelines** 127 128 The guideline documents record community process, expectations and design directions. 129 130 They can be extended, amended or discussed by submitting a patch and getting community approval. 131 132 133Building the Documentation 134-------------------------- 135 136Dependencies 137~~~~~~~~~~~~ 138 139The following dependencies must be installed to build the documentation: 140 141* Doxygen. 142* Sphinx (also called python-sphinx). 143 144`Doxygen`_ generates documentation from commented source code. 145It can be installed as follows: 146 147.. code-block:: console 148 149 # Ubuntu/Debian. 150 sudo apt-get -y install doxygen 151 152 # Red Hat/Fedora. 153 sudo dnf -y install doxygen 154 155`Sphinx`_ is a Python documentation tool for converting RST files to HTML. 156For full support with figure and table captioning the latest version of Sphinx can be installed as follows: 157 158.. code-block:: console 159 160 # Ubuntu/Debian. 161 sudo apt-get -y install python3-sphinx python3-sphinx-rtd-theme 162 163 # Red Hat/Fedora. 164 sudo dnf -y install python3-sphinx python3-sphinx_rtd_theme 165 166For further information on getting started with Sphinx see the 167`Sphinx Getting Started <http://www.sphinx-doc.org/en/master/usage/quickstart.html>`_. 168 169.. Note:: 170 171 To get full support for Figure and Table numbering it is best to install Sphinx 1.3.1 or later. 172 173 174Build commands 175~~~~~~~~~~~~~~ 176 177The documentation is built using the standard DPDK build system. 178 179To build the documentation:: 180 181 ninja -C build doc 182 183See :doc:`../linux_gsg/build_dpdk` for more detail on compiling DPDK with meson. 184 185The output is generated in the directory ``build/doc/``, with: 186 187* HTML versions of the guide docs, e.g. Getting Started Guides, Programmers Guide, in ``build/doc/guides/html`` 188* HTML version of the API documentation in ``build/doc/api/html`` 189* Man-page version of the API documentation in ``build/doc/api/man``. 190 If not installing DPDK system-wise, these pages can be accessed by adding this directory to the ``MANPATH`` environment variable. 191 For example: 192 193.. code-block:: console 194 195 export MANPATH=:/path/to/build/doc/api/man 196 197.. Note:: 198 199 Make sure to fix any Sphinx or Doxygen warnings when adding or updating documentation. 200 201 202Document Guidelines 203------------------- 204 205Here are some guidelines in relation to the style of the documentation: 206 207* Document the obvious as well as the obscure since it won't always be obvious to the reader. 208 For example an instruction like "Set up 64 2MB Hugepages" is better when followed by a sample commandline or a link to 209 the appropriate section of the documentation. 210 211* Use American English spellings throughout. 212 This can be checked using the ``aspell`` utility:: 213 214 aspell --lang=en_US --check doc/guides/sample_app_ug/mydoc.rst 215 216 217RST Guidelines 218-------------- 219 220The RST (reStructuredText) format is a plain text markup format 221that can be converted to HTML or other formats. 222It is most closely associated with Python but it can be used to document any language. 223It is used in DPDK to document everything apart from the API. 224 225The Sphinx documentation contains a very useful `RST Primer <http://sphinx-doc.org/rest.html#rst-primer>`_ which is a 226good place to learn the minimal set of syntax required to format a document. 227 228The official `reStructuredText <http://docutils.sourceforge.net/rst.html>`_ website contains the specification for the 229RST format and also examples of how to use it. 230However, for most developers the RST Primer is a better resource. 231 232The most common guidelines for writing RST text are detailed in the 233`Documenting Python <https://docs.python.org/devguide/documenting.html>`_ guidelines. 234The additional guidelines below reiterate or expand upon those guidelines. 235 236 237Line Length and Wrapping 238~~~~~~~~~~~~~~~~~~~~~~~~ 239 240* Documentation lines should be less than 100 characters. 241 242* Each sentence should start on a new line. 243 Multiple sentences, which are not separated by a blank line, 244 are joined automatically into paragraphs. 245 246* Wrap sentences at punctuation points, for example, at a comma. 247 If no punctuation, put the newline at a logical point in the sentence, 248 for example, at the end of a clause before an "and" or "but". 249 250* Lines in literal blocks should be less than 80 characters 251 since they are not wrapped by the document formatters. 252 253 Long literal command lines can be shown wrapped with backslashes. For 254 example:: 255 256 dpdk-testpmd -l 2-3 -n 4 \ 257 --vdev=virtio_user0,path=/dev/vhost-net,queues=2,queue_size=1024 \ 258 -- -i --tx-offloads=0x0000002c --enable-lro --txq=2 --rxq=2 \ 259 --txd=1024 --rxd=1024 260 261 262Whitespace 263~~~~~~~~~~ 264 265* Standard RST indentation is 3 spaces. 266 Code can be indented 4 spaces, especially if it is copied from source files. 267 268* No tabs. 269 Convert tabs in embedded code to 4 or 8 spaces. 270 271* No trailing whitespace. 272 273* Add 2 blank lines before each section header. 274 275* Add 1 blank line after each section header. 276 277* Add 1 blank line between each line of a list. 278 279 280Section Headers 281~~~~~~~~~~~~~~~ 282 283* Section headers should use the following underline formats:: 284 285 Level 1 Heading 286 =============== 287 288 289 Level 2 Heading 290 --------------- 291 292 293 Level 3 Heading 294 ~~~~~~~~~~~~~~~ 295 296 297 Level 4 Heading 298 ^^^^^^^^^^^^^^^ 299 300 301* Level 4 headings should be used sparingly. 302 303* The underlines should match the length of the text. 304 305* In general, the heading should be less than 80 characters, for conciseness. 306 307* As noted above: 308 309 * Add 2 blank lines before each section header. 310 311 * Add 1 blank line after each section header. 312 313 314Lists 315~~~~~ 316 317* Bullet lists should be formatted with a leading ``*`` as follows:: 318 319 * Item one. 320 321 * Item two is a long line that is wrapped and then indented to match 322 the start of the previous line. 323 324 * One space character between the bullet and the text is preferred. 325 326* Numbered lists can be formatted with a leading number but the preference is to use ``#.`` which will give automatic numbering. 327 This is more convenient when adding or removing items:: 328 329 #. Item one. 330 331 #. Item two is a long line that is wrapped and then indented to match 332 the start of the previous line. 333 334 #. Item three. 335 336* Definition lists can be written with or without a bullet:: 337 338 * Item one. 339 340 Some text about item one. 341 342 * Item two. 343 344 Some text about item two. 345 346* All lists, and sub-lists, must be separated from the preceding text by a blank line. 347 This is a syntax requirement. 348 349* All list items should be separated by a blank line for readability. 350 351 352Code and Literal block sections 353~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 354 355* Inline text that is required to be rendered with a fixed width font should be enclosed in backquotes like this: 356 \`\`text\`\`, so that it appears like this: ``text``. 357 358* Fixed width, literal blocks of texts should be indented at least 3 spaces and prefixed with ``::`` like this:: 359 360 Here is some fixed width text:: 361 362 0x0001 0x0001 0x00FF 0x00FF 363 364* It is also possible to specify an encoding for a literal block using the ``.. code-block::`` directive so that syntax 365 highlighting can be applied. 366 Examples of supported highlighting are:: 367 368 .. code-block:: console 369 .. code-block:: c 370 .. code-block:: python 371 .. code-block:: diff 372 .. code-block:: none 373 374 That can be applied as follows:: 375 376 .. code-block:: c 377 378 #include<stdio.h> 379 380 int main() { 381 382 printf("Hello World\n"); 383 384 return 0; 385 } 386 387 Which would be rendered as: 388 389 .. code-block:: c 390 391 #include<stdio.h> 392 393 int main() { 394 395 printf("Hello World\n"); 396 397 return 0; 398 } 399 400* Code snippets can also be included directly from the code using the ``literalinclude`` block. 401 Using this block instead of a code block will ensure that the code snippets 402 shown in the documentation are always up to date with the code. 403 404 The following will include a snippet from the skeleton sample app:: 405 406 .. literalinclude:: ../../../examples/skeleton/basicfwd.c 407 :language: c 408 :start-after: Display the port MAC address. 409 :end-before: Enable RX in promiscuous mode for the Ethernet device. 410 :dedent: 1 411 412 This would be rendered as: 413 414 .. literalinclude:: ../../../examples/skeleton/basicfwd.c 415 :language: c 416 :start-after: Display the port MAC address. 417 :end-before: Enable RX in promiscuous mode for the Ethernet device. 418 :dedent: 1 419 420 Specifying ``:language:`` will enable syntax highlighting for the specified language. 421 ``:dedent:`` is used in this example to remove 1 leading tab from each line of the snippet. 422 423* ``start-after`` and ``end-before`` can use any text within a given file, 424 however it may be difficult to find unique text within your code to mark the 425 start and end of your snippets. In these cases, it is recommended to include 426 explicit tags in your code to denote these locations for documentation purposes. 427 The accepted format for these comments is: 428 429 * Before the code snippet, create a new comment which is a sentence explaining 430 what the code snippet contains. The comment is terminated with a scissors ``8<``. 431 * After the code snippet, create another new comment which starts with a 432 scissors ``>8``, then ``End of`` and the first comment repeated. 433 * The scissors should be orientated as shown to make it clear what code is being snipped. 434 435 This can be done as follows: 436 437 .. code-block:: c 438 439 /* Example feature being documented. 8< */ 440 foo(bar); 441 /* >8 End of example feature being documented. */ 442 443 ``foo(bar);`` could then be included in the docs using:: 444 445 .. literalinclude:: ../../../examples/sample_app/main.c 446 :language: c 447 :start-after: Example feature being documented. 8< 448 :end-before: >8 End of example feature being documented. 449 450 If a multiline comment is needed before the snippet, 451 then the last line of the multiline comment should be in the same format as 452 the first comment shown in the example. 453 454* More information about the ``literalinclude`` block can be found within the 455 `Sphinx Documentation <https://www.sphinx-doc.org/en/master/usage/restructuredtext/directives.html?highlight=literalinclude#directive-literalinclude>`_. 456 457* The default encoding for a literal block using the simplified ``::`` 458 directive is ``none``. 459 460* Lines in literal blocks should be less than 80 characters. 461 For long literal lines, try to wrap the text at sensible locations. 462 For example a long command line could be documented like this and still work if copied directly from the docs:: 463 464 ./<build_dir>/app/dpdk-testpmd -l 0-2 -n3 --vdev=net_pcap0,iface=eth0 \ 465 --vdev=net_pcap1,iface=eth1 \ 466 -- -i --nb-cores=2 --nb-ports=2 \ 467 --total-num-mbufs=2048 468 469* Long lines that cannot be wrapped, such as application output, should be truncated to be less than 80 characters. 470 471 472Images 473~~~~~~ 474 475* All images should be in SVG scalar graphics format. 476 They should be true SVG XML files and should not include binary formats embedded in a SVG wrapper. 477 478* The DPDK documentation contains some legacy images in PNG format. 479 These will be converted to SVG in time. 480 481* `Inkscape <http://inkscape.org>`_ is the recommended graphics editor for creating the images. 482 Use some of the older images in ``doc/guides/prog_guide/img/`` as a template, for example ``mbuf1.svg`` 483 or ``ring-enqueue1.svg``. 484 485* The SVG images should include a copyright notice, as an XML comment. 486 487* Images in the documentation should be formatted as follows: 488 489 * The image should be preceded by a label in the format ``.. _figure_XXXX:`` with a leading underscore and 490 where ``XXXX`` is a unique descriptive name. 491 492 * Images should be included using the ``.. figure::`` directive and the file type should be set to ``*`` (not ``.svg``). 493 This allows the format of the image to be changed if required, without updating the documentation. 494 495 * Images must have a caption as part of the ``.. figure::`` directive. 496 497* Here is an example of the previous three guidelines:: 498 499 .. _figure_mempool: 500 501 .. figure:: img/mempool.* 502 503 A mempool in memory with its associated ring. 504 505.. _mock_label: 506 507* Images can then be linked to using the ``:numref:`` directive:: 508 509 The mempool layout is shown in :numref:`figure_mempool`. 510 511 This would be rendered as: *The mempool layout is shown in* :ref:`Fig 6.3 <mock_label>`. 512 513 **Note**: The ``:numref:`` directive requires Sphinx 1.3.1 or later. 514 With earlier versions it will still be rendered as a link but won't have an automatically generated number. 515 516* The caption of the image can be generated, with a link, using the ``:ref:`` directive:: 517 518 :ref:`figure_mempool` 519 520 This would be rendered as: *A mempool in memory with its associated ring.* 521 522Tables 523~~~~~~ 524 525* RST tables should be used sparingly. 526 They are hard to format and to edit, and the same information 527 can usually be shown just as clearly with a definition or bullet list. 528 529* Tables in the documentation should be formatted as follows: 530 531 * The table should be preceded by a label in the format ``.. _table_XXXX:`` with a leading underscore and where 532 ``XXXX`` is a unique descriptive name. 533 534 * Tables should be included using the ``.. table::`` directive and must have a caption. 535 536* Here is an example of the previous two guidelines:: 537 538 .. _table_qos_pipes: 539 540 .. table:: Sample configuration for QOS pipes. 541 542 +----------+----------+----------+ 543 | Header 1 | Header 2 | Header 3 | 544 | | | | 545 +==========+==========+==========+ 546 | Text | Text | Text | 547 +----------+----------+----------+ 548 | ... | ... | ... | 549 +----------+----------+----------+ 550 551* Tables can be linked to using the ``:numref:`` and ``:ref:`` directives, as shown in the previous section for images. 552 For example:: 553 554 The QOS configuration is shown in :numref:`table_qos_pipes`. 555 556 557.. _links: 558 559Hyperlinks 560~~~~~~~~~~ 561 562* Links to external websites can be plain URLs. 563 The following is rendered as https://dpdk.org:: 564 565 https://dpdk.org 566 567* They can contain alternative text. 568 The following is rendered as `Check out DPDK <https://dpdk.org>`_:: 569 570 `Check out DPDK <https://dpdk.org>`_ 571 572* An internal link can be generated by placing labels in the document with the format ``.. _label_name``. 573 574* The following links to the top of this section: :ref:`links`:: 575 576 .. _links: 577 578 Hyperlinks 579 ~~~~~~~~~~ 580 581 * The following links to the top of this section: :ref:`links`: 582 583.. Note:: 584 585 The label must have a leading underscore but the reference to it must omit it. 586 This is a frequent cause of errors and warnings. 587 588* The use of a label is preferred since it works across files and will still work if the header text changes. 589 590 591.. _doxygen_guidelines: 592 593Doxygen Guidelines 594------------------ 595 596The DPDK API is documented using Doxygen comment annotations in the header files. 597Doxygen is a very powerful tool, it is extremely configurable and with a little effort can be used to create expressive documents. 598See the `Doxygen website <http://www.doxygen.nl>`_ for full details on how to use it. 599 600The following are some guidelines for use of Doxygen in the DPDK API documentation: 601 602* New libraries that are documented with Doxygen should be added to the Doxygen configuration file: ``doc/api/doxy-api.conf``. 603 It is only required to add the directory that contains the files. 604 It isn't necessary to explicitly name each file since the configuration matches all ``rte_*.h`` files in the directory. 605 606* Use proper capitalization and punctuation in the Doxygen comments since they will become sentences in the documentation. 607 This in particular applies to single line comments, which is the case the is most often forgotten. 608 609* Use ``@`` style Doxygen commands instead of ``\`` style commands. 610 611* Add a general description of each library at the head of the main header files: 612 613 .. code-block:: c 614 615 /** 616 * @file 617 * RTE Mempool. 618 * 619 * A memory pool is an allocator of fixed-size object. It is 620 * identified by its name, and uses a ring to store free objects. 621 * ... 622 */ 623 624* Document the purpose of a function, the parameters used and the return 625 value: 626 627 .. code-block:: c 628 629 /** 630 * Try to take the lock. 631 * 632 * @param sl 633 * A pointer to the spinlock. 634 * @return 635 * 1 if the lock is successfully taken; 0 otherwise. 636 */ 637 int rte_spinlock_trylock(rte_spinlock_t *sl); 638 639* Doxygen supports Markdown style syntax such as bold, italics, fixed width text and lists. 640 For example the second line in the ``devargs`` parameter in the previous example will be rendered as: 641 642 The strings should be a pci address like ``0000:01:00.0`` or **virtual** device name like ``net_pcap0``. 643 644* Use ``-`` instead of ``*`` for lists within the Doxygen comment since the latter can get confused with the comment delimiter. 645 646* Add an empty line between the function description, the ``@params`` and ``@return`` for readability. 647 648* Place the ``@params`` description on separate line and indent it by 2 spaces. 649 (It would be better to use no indentation since this is more common and also because checkpatch complains about leading 650 whitespace in comments. 651 However this is the convention used in the existing DPDK code.) 652 653* Documented functions can be linked to simply by adding ``()`` to the function name: 654 655 .. code-block:: c 656 657 /** 658 * The functions exported by the application Ethernet API to setup 659 * a device designated by its port identifier must be invoked in 660 * the following order: 661 * - rte_eth_dev_configure() 662 * - rte_eth_tx_queue_setup() 663 * - rte_eth_rx_queue_setup() 664 * - rte_eth_dev_start() 665 */ 666 667 In the API documentation the functions will be rendered as links, see the 668 `online section of the rte_ethdev.h docs <https://doc.dpdk.org/api/rte__ethdev_8h.html>`_ that contains the above text. 669 670* The ``@see`` keyword can be used to create a *see also* link to another file or library. 671 This directive should be placed on one line at the bottom of the documentation section. 672 673 .. code-block:: c 674 675 /** 676 * ... 677 * 678 * Some text that references mempools. 679 * 680 * @see eal_memzone.c 681 */ 682 683* Doxygen supports two types of comments for documenting variables, constants and members: prefix and postfix: 684 685 .. code-block:: c 686 687 /** This is a prefix comment. */ 688 #define RTE_FOO_ERROR 0x023. 689 690 #define RTE_BAR_ERROR 0x024. /**< This is a postfix comment. */ 691 692* Postfix comments are preferred for struct members and constants if they can be documented in the same way: 693 694 .. code-block:: c 695 696 struct rte_eth_stats { 697 uint64_t ipackets; /**< Total number of received packets. */ 698 uint64_t opackets; /**< Total number of transmitted packets.*/ 699 uint64_t ibytes; /**< Total number of received bytes. */ 700 uint64_t obytes; /**< Total number of transmitted bytes. */ 701 uint64_t imissed; /**< Total of RX missed packets. */ 702 uint64_t ibadcrc; /**< Total of RX packets with CRC error. */ 703 uint64_t ibadlen; /**< Total of RX packets with bad length. */ 704 } 705 706 Note: postfix comments should be aligned with spaces not tabs in accordance 707 with the :ref:`coding_style`. 708 709* If a single comment type can't be used, due to line length limitations then 710 prefix comments should be preferred. 711 For example this section of the code contains prefix comments, postfix comments on the same line and postfix 712 comments on a separate line: 713 714 .. code-block:: c 715 716 /** Number of elements in the elt_pa array. */ 717 uint32_t pg_num __rte_cache_aligned; 718 uint32_t pg_shift; /**< LOG2 of the physical pages. */ 719 uintptr_t pg_mask; /**< Physical page mask value. */ 720 uintptr_t elt_va_start; 721 /**< Virtual address of the first mempool object. */ 722 uintptr_t elt_va_end; 723 /**< Virtual address of the <size + 1> mempool object. */ 724 phys_addr_t elt_pa[1]; 725 /**< Array of physical page addresses for the mempool buffer. */ 726 727 This doesn't have an effect on the rendered documentation but it is confusing for the developer reading the code. 728 It this case it would be clearer to use prefix comments throughout: 729 730 .. code-block:: c 731 732 /** Number of elements in the elt_pa array. */ 733 uint32_t pg_num __rte_cache_aligned; 734 /** LOG2 of the physical pages. */ 735 uint32_t pg_shift; 736 /** Physical page mask value. */ 737 uintptr_t pg_mask; 738 /** Virtual address of the first mempool object. */ 739 uintptr_t elt_va_start; 740 /** Virtual address of the <size + 1> mempool object. */ 741 uintptr_t elt_va_end; 742 /** Array of physical page addresses for the mempool buffer. */ 743 phys_addr_t elt_pa[1]; 744 745* Read the rendered section of the documentation that you have added for correctness, clarity and consistency 746 with the surrounding text. 747
