From 034dd340b08be1f2f0477ad16131d609f9dbd53c Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Sun, 30 Aug 2026 09:22:00 -0700 Subject: Merge tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace Pull tracing fixes from Steven Rostedt: - Fix error output of boot instance creation failure Currently if a boot instance creation fails, instead of printing out the name of the instance that failed, it prints "(null)". That is because it prints "cur_str" that had already been processed by strsep(). Print the saved name instead. While at it, print the error code of the failure. - Fix use-after-free for same named historgrams Histograms can be named so that they can be used in multiple events. But if the named histogram has a variable attached, the second event that uses the named histogram which duplicates it and needs to free the original after duplication leaves the old variable in place and still visible. If another histogram uses than variable, it will use the stale one which will try to reference the freed duplicate histogram and crash the kernel. Free the duplicate variables along with the duplicated histogram data. - Check return value of kthread_run() in event self test The events self tests uses a kthread for testing but does not check if it succeeded in creating a kthread. If the kthread creation were to fail, the code will still try to call kthread_stop() on the error returned. - Fix race between reading trace_pipe and updating subbuffer size If a user is reading the trace_pipe file at the same time they update the ring buffer sub-buffer size, can cause the trace_pipe read to read stale data. Add trace_access_lock() around updating the ring buffer sub-buffer size. - Fix eventfs_inode on failure path in creation of the events directory In the creation of the "events" directory, if after allocating the eventfs_inode a failure is detected, it calls cleanup_ei() which calls free_ei(). The free_ei() will test if eventfs_inode being freed has no children. It is a bug if it does. But on the failure case of the creation of the "events" directory, the children lists have not yet been initialized and the free will trigger a warning because list_empty() on an uninitialized list returns false. Move the initialization into init_ei() where it makes more sense and makes sure that a created eventfs_inode has its lists initialized upon creation. - Check return value of kthread_run() in ftrace direct sample code The sample code that shows how to use the ftrace direct calls does not test the return of kthread_run() to see if it succeeds. Return a failure if the kthread_run() doesn't succeed. - Clear user events state on fork in case of alloc failure On fork, the child gets a pointer to the parent's user events state. It makes a copy of it then updates the child's pointer to it. But if the allocation fails, the duplication function leaves the child with a pointer to its parent's descriptor. When the child cleans up its data, it will free the parent's descriptor while the parent is still using it. In the duplication function, set the child's user_event_mm to NULL before testing if the allocation succeeded, and when it exits it will not free the parent's descriptor. - Fix retry exhaustion in simple ring buffer reader swap simple_ring_buffer_swap_reader_page() starts with retry set to 8 and post-decrements it only after a failed link replacement. On the final attempt, a successful replacement leaves retry at zero, while a failed replacement leaves it at -1. But the check for success expects the retry value to be non-zero and exits with an error on zero. This is the opposite result. Fix it. - Fail nicely when the remote swap_reader_page() returns an error Currently, if the swap_reader_page() of a remote buffer fails, it triggers a WARN_ON_ONCE() and continues normally. Instead, have it exit with an error and a pr_warn() print instead of a full WARNING. * tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: ring-buffer: Stop remote reader update when page swap fails tracing: Fix retry exhaustion in simple ring buffer reader swap tracing/user_events: Clear copied tracing state before fork duplication samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-multi-modify samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-modify eventfs: Initialize ei->children and ei->list in init_ei() tracing: Fix use-after-free in trace_pipe read on sub-buffer order change tracing: Fix crash passing ERR_PTR to kthread_stop() tracing: Fix use-after-free with same-name named triggers tracing: Fix logged instance name on creation failure --- Documentation/doc-guide/sphinx.rst | 562 +++++++++++++++++++++++++++++++++++++ 1 file changed, 562 insertions(+) create mode 100644 Documentation/doc-guide/sphinx.rst (limited to 'Documentation/doc-guide/sphinx.rst') diff --git a/Documentation/doc-guide/sphinx.rst b/Documentation/doc-guide/sphinx.rst new file mode 100644 index 000000000..51c370260 --- /dev/null +++ b/Documentation/doc-guide/sphinx.rst @@ -0,0 +1,562 @@ +.. _sphinxdoc: + +===================================== +Using Sphinx for kernel documentation +===================================== + +The Linux kernel uses `Sphinx`_ to generate pretty documentation from +`reStructuredText`_ files under ``Documentation``. To build the documentation in +HTML or PDF formats, use ``make htmldocs`` or ``make pdfdocs``. The generated +documentation is placed in ``Documentation/output``. + +.. _Sphinx: http://www.sphinx-doc.org/ +.. _reStructuredText: http://docutils.sourceforge.net/rst.html + +The reStructuredText files may contain directives to include structured +documentation comments, or kernel-doc comments, from source files. Usually these +are used to describe the functions and types and design of the code. The +kernel-doc comments have some special structure and formatting, but beyond that +they are also treated as reStructuredText. + +Finally, there are thousands of plain text documentation files scattered around +``Documentation``. Some of these will likely be converted to reStructuredText +over time, but the bulk of them will remain in plain text. + +.. _sphinx_install: + +Sphinx Install +============== + +The ReST markups currently used by the Documentation/ files are meant to be +built with ``Sphinx`` version 3.4.3 or higher. + +There's a script that checks for the Sphinx requirements. Please see +:ref:`sphinx-pre-install` for further details. + +Most distributions are shipped with Sphinx, but its toolchain is fragile, +and it is not uncommon that upgrading it or some other Python packages +on your machine would cause the documentation build to break. + +A way to avoid that is to use a different version than the one shipped +with your distributions. In order to do so, it is recommended to install +Sphinx inside a virtual environment, using ``virtualenv-3`` +or ``virtualenv``, depending on how your distribution packaged Python 3. + +In summary, if you want to install the latest version of Sphinx, you +should do:: + + $ virtualenv sphinx_latest + $ . sphinx_latest/bin/activate + (sphinx_latest) $ pip install -r Documentation/sphinx/requirements.txt + +After running ``. sphinx_latest/bin/activate``, the prompt will change, +in order to indicate that you're using the new environment. If you +open a new shell, you need to rerun this command to enter again at +the virtual environment before building the documentation. + +Image output +------------ + +The kernel documentation build system contains an extension that +handles images in both GraphViz and SVG formats (see :ref:`sphinx_kfigure`). + +For it to work, you need to install both GraphViz and ImageMagick +packages. If those packages are not installed, the build system will +still build the documentation, but won't include any images at the +output. + +PDF and LaTeX builds +-------------------- + +Such builds are currently supported only with Sphinx versions 2.4 and higher. + +For PDF and LaTeX output, you'll also need ``XeLaTeX`` version 3.14159265. + +Depending on the distribution, you may also need to install a series of +``texlive`` packages that provide the minimal set of functionalities +required for ``XeLaTeX`` to work. + +Math Expressions in HTML +------------------------ + +Some ReST pages contain math expressions. Due to the way Sphinx works, +those expressions are written using LaTeX notation. +There are two options for Sphinx to render math expressions in html output. +One is an extension called `imgmath`_ which converts math expressions into +images and embeds them in html pages. +The other is an extension called `mathjax`_ which delegates math rendering +to JavaScript capable web browsers. +The former was the only option for pre-6.1 kernel documentation and it +requires quite a few texlive packages including amsfonts and amsmath among +others. + +Since kernel release 6.1, html pages with math expressions can be built +without installing any texlive packages. See `Choice of Math Renderer`_ for +further info. + +.. _imgmath: https://www.sphinx-doc.org/en/master/usage/extensions/math.html#module-sphinx.ext.imgmath +.. _mathjax: https://www.sphinx-doc.org/en/master/usage/extensions/math.html#module-sphinx.ext.mathjax + +.. _sphinx-pre-install: + +Checking for Sphinx dependencies +-------------------------------- + +There's a script that automatically checks for Sphinx dependencies. If it can +recognize your distribution, it will also give a hint about the install +command line options for your distro:: + + $ ./tools/docs/sphinx-pre-install + Checking if the needed tools for Fedora release 26 (Twenty Six) are available + Warning: better to also install "texlive-luatex85". + You should run: + + sudo dnf install -y texlive-luatex85 + /usr/bin/virtualenv sphinx_2.4.4 + . sphinx_2.4.4/bin/activate + pip install -r Documentation/sphinx/requirements.txt + + Can't build as 1 mandatory dependency is missing at ./tools/docs/sphinx-pre-install line 468. + +By default, it checks all the requirements for both html and PDF, including +the requirements for images, math expressions and LaTeX build, and assumes +that a virtual Python environment will be used. The ones needed for html +builds are assumed to be mandatory; the others to be optional. + +It supports two optional parameters: + +``--no-pdf`` + Disable checks for PDF; + +``--no-virtualenv`` + Use OS packaging for Sphinx instead of Python virtual environment. + +Installing Sphinx Minimal Version +--------------------------------- + +When changing Sphinx build system, it is important to ensure that +the minimal version will still be supported. Nowadays, it is +becoming harder to do that on modern distributions, as it is not +possible to install with Python 3.13 and above. + +Testing with the lowest supported Python version as defined at +Documentation/process/changes.rst can be done by creating +a venv with it with, and install minimal requirements with:: + + /usr/bin/python3.9 -m venv sphinx_min + . sphinx_min/bin/activate + pip install -r Documentation/sphinx/min_requirements.txt + +A more comprehensive test can be done by using: + + tools/docs/test_doc_build.py + +Such script create one Python venv per supported version, +optionally building documentation for a range of Sphinx versions. + + +Sphinx Build +============ + +The usual way to generate the documentation is to run ``make htmldocs`` or +``make pdfdocs``. There are also other formats available: see the documentation +section of ``make help``. The generated documentation is placed in +format-specific subdirectories under ``Documentation/output``. + +To generate documentation, Sphinx (``sphinx-build``) must obviously be +installed. For PDF output you'll also need ``XeLaTeX`` and ``convert(1)`` +from ImageMagick (https://www.imagemagick.org).\ [#ink]_ All of these are +widely available and packaged in distributions. + +To pass extra options to Sphinx, you can use the ``SPHINXOPTS`` make +variable. For example, use ``make SPHINXOPTS=-v htmldocs`` to get more verbose +output. + +It is also possible to pass an extra DOCS_CSS overlay file, in order to customize +the html layout, by using the ``DOCS_CSS`` make variable. + +By default, the "Alabaster" theme is used to build the HTML documentation; +this theme is bundled with Sphinx and need not be installed separately. +The Sphinx theme can be overridden by using the ``DOCS_THEME`` make variable. + +.. note:: + + Some people might prefer to use the RTD theme for html output. + Depending on the Sphinx version, it should be installed separately, + with ``pip install sphinx_rtd_theme``. + +There is another make variable ``SPHINXDIRS``, which is useful when test +building a subset of documentation. For example, you can build documents +under ``Documentation/doc-guide`` by running +``make SPHINXDIRS=doc-guide htmldocs``. +The documentation section of ``make help`` will show you the list of +subdirectories you can specify. + +To remove the generated documentation, run ``make cleandocs``. + +.. [#ink] Having ``inkscape(1)`` from Inkscape (https://inkscape.org) + as well would improve the quality of images embedded in PDF + documents, especially for kernel releases 5.18 and later. + +Choice of Math Renderer +----------------------- + +Since kernel release 6.1, mathjax works as a fallback math renderer for +html output.\ [#sph1_8]_ + +Math renderer is chosen depending on available commands as shown below: + +.. table:: Math Renderer Choices for HTML + + ============= ================= ============ + Math renderer Required commands Image format + ============= ================= ============ + imgmath latex, dvipng PNG (raster) + mathjax + ============= ================= ============ + +The choice can be overridden by setting an environment variable +``SPHINX_IMGMATH`` as shown below: + +.. table:: Effect of Setting ``SPHINX_IMGMATH`` + + ====================== ======== + Setting Renderer + ====================== ======== + ``SPHINX_IMGMATH=yes`` imgmath + ``SPHINX_IMGMATH=no`` mathjax + ====================== ======== + +.. [#sph1_8] Fallback of math renderer requires Sphinx >=1.8. + + +Writing Documentation +===================== + +Adding new documentation can be as simple as: + +1. Add a new ``.rst`` file somewhere under ``Documentation``. +2. Refer to it from the Sphinx main `TOC tree`_ in ``Documentation/index.rst``. + +.. _TOC tree: http://www.sphinx-doc.org/en/stable/markup/toctree.html + +This is usually good enough for simple documentation (like the one you're +reading right now), but for larger documents it may be advisable to create a +subdirectory (or use an existing one). For example, the graphics subsystem +documentation is under ``Documentation/gpu``, split to several ``.rst`` files, +and has a separate ``index.rst`` (with a ``toctree`` of its own) referenced from +the main index. + +See the documentation for `Sphinx`_ and `reStructuredText`_ on what you can do +with them. In particular, the Sphinx `reStructuredText Primer`_ is a good place +to get started with reStructuredText. There are also some `Sphinx specific +markup constructs`_. + +.. _reStructuredText Primer: http://www.sphinx-doc.org/en/stable/rest.html +.. _Sphinx specific markup constructs: http://www.sphinx-doc.org/en/stable/markup/index.html + +Specific guidelines for the kernel documentation +------------------------------------------------ + +Here are some specific guidelines for the kernel documentation: + +* Please don't go overboard with reStructuredText markup. Keep it + simple. For the most part the documentation should be plain text with + just enough consistency in formatting that it can be converted to + other formats. + +* Please keep the formatting changes minimal when converting existing + documentation to reStructuredText. + +* Also update the content, not just the formatting, when converting + documentation. + +* Please stick to this order of heading adornments: + + 1. ``=`` with overline for document title:: + + ============== + Document title + ============== + + 2. ``=`` for chapters:: + + Chapters + ======== + + 3. ``-`` for sections:: + + Section + ------- + + 4. ``~`` for subsections:: + + Subsection + ~~~~~~~~~~ + + Although RST doesn't mandate a specific order ("Rather than imposing a fixed + number and order of section title adornment styles, the order enforced will be + the order as encountered."), having the higher levels the same overall makes + it easier to follow the documents. + +* For inserting fixed width text blocks (for code examples, use case + examples, etc.), use ``::`` for anything that doesn't really benefit + from syntax highlighting, especially short snippets. Use + ``.. code-block:: `` for longer code blocks that benefit + from highlighting. For a short snippet of code embedded in the text, use \`\`. + + +The C domain +------------ + +The **Sphinx C Domain** (name c) is suited for documentation of C API. E.g. a +function prototype: + +.. code-block:: rst + + .. c:function:: int ioctl( int fd, int request ) + +The C domain of the kernel-doc has some additional features. E.g. you can +*rename* the reference name of a function with a common name like ``open`` or +``ioctl``: + +.. code-block:: rst + + .. c:function:: int ioctl( int fd, int request ) + :name: VIDIOC_LOG_STATUS + +The func-name (e.g. ioctl) remains in the output but the ref-name changed from +``ioctl`` to ``VIDIOC_LOG_STATUS``. The index entry for this function is also +changed to ``VIDIOC_LOG_STATUS``. + +Please note that there is no need to use ``c:func:`` to generate cross +references to function documentation. Due to some Sphinx extension magic, +the documentation build system will automatically turn a reference to +``function()`` into a cross reference if an index entry for the given +function name exists. If you see ``c:func:`` use in a kernel document, +please feel free to remove it. + +Tables +------ + +ReStructuredText provides several options for table syntax. Kernel style for +tables is to prefer *simple table* syntax or *grid table* syntax. See the +`reStructuredText user reference for table syntax`_ for more details. + +.. _reStructuredText user reference for table syntax: + https://docutils.sourceforge.io/docs/user/rst/quickref.html#tables + +list tables +~~~~~~~~~~~ + +The list-table formats can be useful for tables that are not easily laid +out in the usual Sphinx ASCII-art formats. These formats are nearly +impossible for readers of the plain-text documents to understand, though, +and should be avoided in the absence of a strong justification for their +use. + +The ``flat-table`` is a double-stage list similar to the ``list-table`` with +some additional features: + +* column-span: with the role ``cspan`` a cell can be extended through + additional columns + +* row-span: with the role ``rspan`` a cell can be extended through + additional rows + +* auto span rightmost cell of a table row over the missing cells on the right + side of that table-row. With Option ``:fill-cells:`` this behavior can + changed from *auto span* to *auto fill*, which automatically inserts (empty) + cells instead of spanning the last cell. + +options: + +* ``:header-rows:`` [int] count of header rows +* ``:stub-columns:`` [int] count of stub columns +* ``:widths:`` [[int] [int] ... ] widths of columns +* ``:fill-cells:`` instead of auto-spanning missing cells, insert missing cells + +roles: + +* ``:cspan:`` [int] additional columns (*morecols*) +* ``:rspan:`` [int] additional rows (*morerows*) + +The example below shows how to use this markup. The first level of the staged +list is the *table-row*. In the *table-row* there is only one markup allowed, +the list of the cells in this *table-row*. Exceptions are *comments* ( ``..`` ) +and *targets* (e.g. a ref to ``:ref:`last row ``` / :ref:`last row +`). + +.. code-block:: rst + + .. flat-table:: table title + :widths: 2 1 1 3 + + * - head col 1 + - head col 2 + - head col 3 + - head col 4 + + * - row 1 + - field 1.1 + - field 1.2 with autospan + + * - row 2 + - field 2.1 + - :rspan:`1` :cspan:`1` field 2.2 - 3.3 + + * .. _`last row`: + + - row 3 + +Rendered as: + + .. flat-table:: table title + :widths: 2 1 1 3 + + * - head col 1 + - head col 2 + - head col 3 + - head col 4 + + * - row 1 + - field 1.1 + - field 1.2 with autospan + + * - row 2 + - field 2.1 + - :rspan:`1` :cspan:`1` field 2.2 - 3.3 + + * .. _`last row`: + + - row 3 + +Cross-referencing +----------------- + +Cross-referencing from one documentation page to another can be done simply by +writing the path to the document file, no special syntax required. The path can +be either absolute or relative. For absolute paths, start it with +"Documentation/". For example, to cross-reference to this page, all the +following are valid options, depending on the current document's directory (note +that the ``.rst`` extension is required):: + + See Documentation/doc-guide/sphinx.rst. This always works. + Take a look at sphinx.rst, which is at this same directory. + Read ../sphinx.rst, which is one directory above. + +If you want the link to have a different rendered text other than the document's +title, you need to use Sphinx's ``doc`` role. For example:: + + See :doc:`my custom link text for document sphinx `. + +For most use cases, the former is preferred, as it is cleaner and more suited +for people reading the source files. If you come across a ``:doc:`` usage that +isn't adding any value, please feel free to convert it to just the document +path. + +For information on cross-referencing to kernel-doc functions or types, see +Documentation/doc-guide/kernel-doc.rst. + +Referencing commits +~~~~~~~~~~~~~~~~~~~ + +References to git commits are automatically hyperlinked given that they are +written in one of these formats:: + + commit 72bf4f1767f0 + commit 72bf4f1767f0 ("net: do not leave an empty skb in write queue") + +.. _sphinx_kfigure: + +Figures & Images +================ + +If you want to add an image, you should use the ``kernel-figure`` and +``kernel-image`` directives. E.g. to insert a figure with a scalable +image format, use SVG (:ref:`svg_image_example`):: + + .. kernel-figure:: svg_image.svg + :alt: simple SVG image + + SVG image example + +.. _svg_image_example: + +.. kernel-figure:: svg_image.svg + :alt: simple SVG image + + SVG image example + +The kernel figure (and image) directive supports **DOT** formatted files, see + +* DOT: http://graphviz.org/pdf/dotguide.pdf +* Graphviz: http://www.graphviz.org/content/dot-language + +A simple example (:ref:`hello_dot_file`):: + + .. kernel-figure:: hello.dot + :alt: hello world + + DOT's hello world example + +.. _hello_dot_file: + +.. kernel-figure:: hello.dot + :alt: hello world + + DOT's hello world example + +Embedded *render* markups (or languages) like Graphviz's **DOT** are provided by the +``kernel-render`` directives.:: + + .. kernel-render:: DOT + :alt: foobar digraph + :caption: Embedded **DOT** (Graphviz) code + + digraph foo { + "bar" -> "baz"; + } + +How this will be rendered depends on the installed tools. If Graphviz is +installed, you will see a vector image. If not, the raw markup is inserted as +*literal-block* (:ref:`hello_dot_render`). + +.. _hello_dot_render: + +.. kernel-render:: DOT + :alt: foobar digraph + :caption: Embedded **DOT** (Graphviz) code + + digraph foo { + "bar" -> "baz"; + } + +The *render* directive has all the options known from the *figure* directive, +plus option ``caption``. If ``caption`` has a value, a *figure* node is +inserted. If not, an *image* node is inserted. A ``caption`` is also needed, if +you want to refer to it (:ref:`hello_svg_render`). + +Embedded **SVG**:: + + .. kernel-render:: SVG + :caption: Embedded **SVG** markup + :alt: so-nw-arrow + + + + ... + + +.. _hello_svg_render: + +.. kernel-render:: SVG + :caption: Embedded **SVG** markup + :alt: so-nw-arrow + + + + + + -- cgit v1.3.1