301 lines · plain
1.. SPDX-License-Identifier: GPL-2.02 3How to help improve kernel documentation4========================================5 6Documentation is an important part of any software-development project.7Good documentation helps to bring new developers in and helps established8developers work more effectively. Without top-quality documentation, a lot9of time is wasted in reverse-engineering the code and making avoidable10mistakes.11 12Unfortunately, the kernel's documentation currently falls far short of what13it needs to be to support a project of this size and importance.14 15This guide is for contributors who would like to improve that situation.16Kernel documentation improvements can be made by developers at a variety of17skill levels; they are a relatively easy way to learn the kernel process in18general and find a place in the community. The bulk of what follows is the19documentation maintainer's list of tasks that most urgently need to be20done.21 22The documentation TODO list23---------------------------24 25There is an endless list of tasks that need to be carried out to get our26documentation to where it should be. This list contains a number of27important items, but is far from exhaustive; if you see a different way to28improve the documentation, please do not hold back!29 30Addressing warnings31~~~~~~~~~~~~~~~~~~~32 33The documentation build currently spews out an unbelievable number of34warnings. When you have that many, you might as well have none at all;35people ignore them, and they will never notice when their work adds new36ones. For this reason, eliminating warnings is one of the highest-priority37tasks on the documentation TODO list. The task itself is reasonably38straightforward, but it must be approached in the right way to be39successful.40 41Warnings issued by a compiler for C code can often be dismissed as false42positives, leading to patches aimed at simply shutting the compiler up.43Warnings from the documentation build almost always point at a real44problem; making those warnings go away requires understanding the problem45and fixing it at its source. For this reason, patches fixing documentation46warnings should probably not say "fix a warning" in the changelog title;47they should indicate the real problem that has been fixed.48 49Another important point is that documentation warnings are often created by50problems in kerneldoc comments in C code. While the documentation51maintainer appreciates being copied on fixes for these warnings, the52documentation tree is often not the right one to actually carry those53fixes; they should go to the maintainer of the subsystem in question.54 55For example, in a documentation build I grabbed a pair of warnings nearly56at random::57 58 ./drivers/devfreq/devfreq.c:1818: warning: bad line:59 - Resource-managed devfreq_register_notifier()60 ./drivers/devfreq/devfreq.c:1854: warning: bad line:61 - Resource-managed devfreq_unregister_notifier()62 63(The lines were split for readability).64 65A quick look at the source file named above turned up a couple of kerneldoc66comments that look like this::67 68 /**69 * devm_devfreq_register_notifier()70 - Resource-managed devfreq_register_notifier()71 * @dev: The devfreq user device. (parent of devfreq)72 * @devfreq: The devfreq object.73 * @nb: The notifier block to be unregistered.74 * @list: DEVFREQ_TRANSITION_NOTIFIER.75 */76 77The problem is the missing "*", which confuses the build system's78simplistic idea of what C comment blocks look like. This problem had been79present since that comment was added in 2016 — a full four years. Fixing80it was a matter of adding the missing asterisks. A quick look at the81history for that file showed what the normal format for subject lines is,82and ``scripts/get_maintainer.pl`` told me who should receive it (pass paths to83your patches as arguments to scripts/get_maintainer.pl). The resulting patch84looked like this::85 86 [PATCH] PM / devfreq: Fix two malformed kerneldoc comments87 88 Two kerneldoc comments in devfreq.c fail to adhere to the required format,89 resulting in these doc-build warnings:90 91 ./drivers/devfreq/devfreq.c:1818: warning: bad line:92 - Resource-managed devfreq_register_notifier()93 ./drivers/devfreq/devfreq.c:1854: warning: bad line:94 - Resource-managed devfreq_unregister_notifier()95 96 Add a couple of missing asterisks and make kerneldoc a little happier.97 98 Signed-off-by: Jonathan Corbet <corbet@lwn.net>99 ---100 drivers/devfreq/devfreq.c | 4 ++--101 1 file changed, 2 insertions(+), 2 deletions(-)102 103 diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c104 index 57f6944d65a6..00c9b80b3d33 100644105 --- a/drivers/devfreq/devfreq.c106 +++ b/drivers/devfreq/devfreq.c107 @@ -1814,7 +1814,7 @@ static void devm_devfreq_notifier_release(struct device *dev, void *res)108 109 /**110 * devm_devfreq_register_notifier()111 - - Resource-managed devfreq_register_notifier()112 + * - Resource-managed devfreq_register_notifier()113 * @dev: The devfreq user device. (parent of devfreq)114 * @devfreq: The devfreq object.115 * @nb: The notifier block to be unregistered.116 @@ -1850,7 +1850,7 @@ EXPORT_SYMBOL(devm_devfreq_register_notifier);117 118 /**119 * devm_devfreq_unregister_notifier()120 - - Resource-managed devfreq_unregister_notifier()121 + * - Resource-managed devfreq_unregister_notifier()122 * @dev: The devfreq user device. (parent of devfreq)123 * @devfreq: The devfreq object.124 * @nb: The notifier block to be unregistered.125 --126 2.24.1127 128The entire process only took a few minutes. Of course, I then found that129somebody else had fixed it in a separate tree, highlighting another lesson:130always check linux-next to see if a problem has been fixed before you dig131into it.132 133Other fixes will take longer, especially those relating to structure134members or function parameters that lack documentation. In such cases, it135is necessary to work out what the role of those members or parameters is136and describe them correctly. Overall, this task gets a little tedious at137times, but it's highly important. If we can actually eliminate warnings138from the documentation build, then we can start expecting developers to139avoid adding new ones.140 141In addition to warnings from the regular documentation build, you can also142run ``make refcheckdocs`` to find references to nonexistent documentation143files.144 145Languishing kerneldoc comments146~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~147 148Developers are encouraged to write kerneldoc comments for their code, but149many of those comments are never pulled into the docs build. That makes150this information harder to find and, for example, makes Sphinx unable to151generate links to that documentation. Adding ``kernel-doc`` directives to152the documentation to bring those comments in can help the community derive153the full value of the work that has gone into creating them.154 155The ``scripts/find-unused-docs.sh`` tool can be used to find these156overlooked comments.157 158Note that the most value comes from pulling in the documentation for159exported functions and data structures. Many subsystems also have160kerneldoc comments for internal use; those should not be pulled into the161documentation build unless they are placed in a document that is162specifically aimed at developers working within the relevant subsystem.163 164 165Typo fixes166~~~~~~~~~~167 168Fixing typographical or formatting errors in the documentation is a quick169way to figure out how to create and send patches, and it is a useful170service. I am always willing to accept such patches. That said, once you171have fixed a few, please consider moving on to more advanced tasks, leaving172some typos for the next beginner to address.173 174Please note that some things are *not* typos and should not be "fixed":175 176 - Both American and British English spellings are allowed within the177 kernel documentation. There is no need to fix one by replacing it with178 the other.179 180 - The question of whether a period should be followed by one or two spaces181 is not to be debated in the context of kernel documentation. Other182 areas of rational disagreement, such as the "Oxford comma", are also183 off-topic here.184 185As with any patch to any project, please consider whether your change is186really making things better.187 188Ancient documentation189~~~~~~~~~~~~~~~~~~~~~190 191Some kernel documentation is current, maintained, and useful. Some192documentation is ... not. Dusty, old, and inaccurate documentation can193mislead readers and casts doubt on our documentation as a whole. Anything194that can be done to address such problems is more than welcome.195 196Whenever you are working with a document, please consider whether it is197current, whether it needs updating, or whether it should perhaps be removed198altogether. There are a number of warning signs that you can pay attention199to here:200 201 - References to 2.x kernels202 - Pointers to SourceForge repositories203 - Nothing but typo fixes in the history for several years204 - Discussion of pre-Git workflows205 206The best thing to do, of course, would be to bring the documentation207current, adding whatever information is needed. Such work often requires208the cooperation of developers familiar with the subsystem in question, of209course. Developers are often more than willing to cooperate with people210working to improve the documentation when asked nicely, and when their211answers are listened to and acted upon.212 213Some documentation is beyond hope; we occasionally find documents that214refer to code that was removed from the kernel long ago, for example.215There is surprising resistance to removing obsolete documentation, but we216should do that anyway. Extra cruft in our documentation helps nobody.217 218In cases where there is perhaps some useful information in a badly outdated219document, and you are unable to update it, the best thing to do may be to220add a warning at the beginning. The following text is recommended::221 222 .. warning ::223 This document is outdated and in need of attention. Please use224 this information with caution, and please consider sending patches225 to update it.226 227That way, at least our long-suffering readers have been warned that the228document may lead them astray.229 230Documentation coherency231~~~~~~~~~~~~~~~~~~~~~~~232 233The old-timers around here will remember the Linux books that showed up on234the shelves in the 1990s. They were simply collections of documentation235files scrounged from various locations on the net. The books have (mostly)236improved since then, but the kernel's documentation is still mostly built237on that model. It is thousands of files, almost each of which was written238in isolation from all of the others. We don't have a coherent body of239kernel documentation; we have thousands of individual documents.240 241We have been trying to improve the situation through the creation of242a set of "books" that group documentation for specific readers. These243include:244 245 - Documentation/admin-guide/index.rst246 - Documentation/core-api/index.rst247 - Documentation/driver-api/index.rst248 - Documentation/userspace-api/index.rst249 250As well as this book on documentation itself.251 252Moving documents into the appropriate books is an important task and needs253to continue. There are a couple of challenges associated with this work,254though. Moving documentation files creates short-term pain for the people255who work with those files; they are understandably unenthusiastic about256such changes. Usually the case can be made to move a document once; we257really don't want to keep shifting them around, though.258 259Even when all documents are in the right place, though, we have only260managed to turn a big pile into a group of smaller piles. The work of261trying to knit all of those documents together into a single whole has not262yet begun. If you have bright ideas on how we could proceed on that front,263we would be more than happy to hear them.264 265Stylesheet improvements266~~~~~~~~~~~~~~~~~~~~~~~267 268With the adoption of Sphinx we have much nicer-looking HTML output than we269once did. But it could still use a lot of improvement; Donald Knuth and270Edward Tufte would be unimpressed. That requires tweaking our stylesheets271to create more typographically sound, accessible, and readable output.272 273Be warned: if you take on this task you are heading into classic bikeshed274territory. Expect a lot of opinions and discussion for even relatively275obvious changes. That is, alas, the nature of the world we live in.276 277Non-LaTeX PDF build278~~~~~~~~~~~~~~~~~~~279 280This is a decidedly nontrivial task for somebody with a lot of time and281Python skills. The Sphinx toolchain is relatively small and well282contained; it is easy to add to a development system. But building PDF or283EPUB output requires installing LaTeX, which is anything but small or well284contained. That would be a nice thing to eliminate.285 286The original hope had been to use the rst2pdf tool (https://rst2pdf.org/)287for PDF generation, but it turned out to not be up to the task.288Development work on rst2pdf seems to have picked up again in recent times,289though, which is a hopeful sign. If a suitably motivated developer were to290work with that project to make rst2pdf work with the kernel documentation291build, the world would be eternally grateful.292 293Write more documentation294~~~~~~~~~~~~~~~~~~~~~~~~295 296Naturally, there are massive parts of the kernel that are severely297underdocumented. If you have the knowledge to document a specific kernel298subsystem and the desire to do so, please do not hesitate to do some299writing and contribute the result to the kernel. Untold numbers of kernel300developers and users will thank you.301