forked from Minki/linux
docs: add documentation for checkpatch
Add documentation for kernel script checkpatch.pl. This documentation is also parsed by checkpatch to enable a verbose mode. The checkpatch message types are grouped by usage. Under each group the types are described briefly. 34 of such types are documented. Signed-off-by: Dwaipayan Ray <dwaipayanray1@gmail.com> Link: https://lore.kernel.org/r/20210226093827.12700-2-dwaipayanray1@gmail.com Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Dwaipayan Ray
Jonathan Corbet
parent
378261870a
commit
2eecbab864
513
Documentation/dev-tools/checkpatch.rst
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513
Documentation/dev-tools/checkpatch.rst
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@ -0,0 +1,513 @@
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.. SPDX-License-Identifier: GPL-2.0-only
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==========
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Checkpatch
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==========
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Checkpatch (scripts/checkpatch.pl) is a perl script which checks for trivial
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style violations in patches and optionally corrects them. Checkpatch can
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also be run on file contexts and without the kernel tree.
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Checkpatch is not always right. Your judgement takes precedence over checkpatch
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messages. If your code looks better with the violations, then its probably
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best left alone.
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Options
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=======
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This section will describe the options checkpatch can be run with.
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Usage::
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./scripts/checkpatch.pl [OPTION]... [FILE]...
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Available options:
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- -q, --quiet
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Enable quiet mode.
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- -v, --verbose
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Enable verbose mode. Additional verbose test descriptions are output
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so as to provide information on why that particular message is shown.
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- --no-tree
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Run checkpatch without the kernel tree.
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- --no-signoff
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Disable the 'Signed-off-by' line check. The sign-off is a simple line at
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the end of the explanation for the patch, which certifies that you wrote it
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or otherwise have the right to pass it on as an open-source patch.
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Example::
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Signed-off-by: Random J Developer <random@developer.example.org>
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Setting this flag effectively stops a message for a missing signed-off-by
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line in a patch context.
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- --patch
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Treat FILE as a patch. This is the default option and need not be
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explicitly specified.
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- --emacs
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Set output to emacs compile window format. This allows emacs users to jump
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from the error in the compile window directly to the offending line in the
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patch.
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- --terse
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Output only one line per report.
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- --showfile
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Show the diffed file position instead of the input file position.
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- -g, --git
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Treat FILE as a single commit or a git revision range.
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Single commit with:
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- <rev>
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- <rev>^
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- <rev>~n
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Multiple commits with:
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- <rev1>..<rev2>
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- <rev1>...<rev2>
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- <rev>-<count>
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- -f, --file
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Treat FILE as a regular source file. This option must be used when running
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checkpatch on source files in the kernel.
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- --subjective, --strict
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Enable stricter tests in checkpatch. By default the tests emitted as CHECK
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do not activate by default. Use this flag to activate the CHECK tests.
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- --list-types
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Every message emitted by checkpatch has an associated TYPE. Add this flag
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to display all the types in checkpatch.
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Note that when this flag is active, checkpatch does not read the input FILE,
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and no message is emitted. Only a list of types in checkpatch is output.
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- --types TYPE(,TYPE2...)
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Only display messages with the given types.
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Example::
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./scripts/checkpatch.pl mypatch.patch --types EMAIL_SUBJECT,BRACES
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- --ignore TYPE(,TYPE2...)
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Checkpatch will not emit messages for the specified types.
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Example::
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./scripts/checkpatch.pl mypatch.patch --ignore EMAIL_SUBJECT,BRACES
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- --show-types
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By default checkpatch doesn't display the type associated with the messages.
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Set this flag to show the message type in the output.
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- --max-line-length=n
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Set the max line length (default 100). If a line exceeds the specified
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length, a LONG_LINE message is emitted.
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The message level is different for patch and file contexts. For patches,
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a WARNING is emitted. While a milder CHECK is emitted for files. So for
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file contexts, the --strict flag must also be enabled.
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- --min-conf-desc-length=n
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Set the Kconfig entry minimum description length, if shorter, warn.
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- --tab-size=n
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Set the number of spaces for tab (default 8).
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- --root=PATH
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PATH to the kernel tree root.
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This option must be specified when invoking checkpatch from outside
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the kernel root.
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- --no-summary
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Suppress the per file summary.
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- --mailback
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Only produce a report in case of Warnings or Errors. Milder Checks are
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excluded from this.
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- --summary-file
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Include the filename in summary.
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- --debug KEY=[0|1]
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Turn on/off debugging of KEY, where KEY is one of 'values', 'possible',
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'type', and 'attr' (default is all off).
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- --fix
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This is an EXPERIMENTAL feature. If correctable errors exists, a file
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<inputfile>.EXPERIMENTAL-checkpatch-fixes is created which has the
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automatically fixable errors corrected.
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- --fix-inplace
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EXPERIMENTAL - Similar to --fix but input file is overwritten with fixes.
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DO NOT USE this flag unless you are absolutely sure and you have a backup
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in place.
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- --ignore-perl-version
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Override checking of perl version. Runtime errors maybe encountered after
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enabling this flag if the perl version does not meet the minimum specified.
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- --codespell
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Use the codespell dictionary for checking spelling errors.
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- --codespellfile
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Use the specified codespell file.
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Default is '/usr/share/codespell/dictionary.txt'.
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- --typedefsfile
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Read additional types from this file.
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- --color[=WHEN]
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Use colors 'always', 'never', or only when output is a terminal ('auto').
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Default is 'auto'.
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- --kconfig-prefix=WORD
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Use WORD as a prefix for Kconfig symbols (default is `CONFIG_`).
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- -h, --help, --version
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Display the help text.
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Message Levels
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==============
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Messages in checkpatch are divided into three levels. The levels of messages
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in checkpatch denote the severity of the error. They are:
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- ERROR
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This is the most strict level. Messages of type ERROR must be taken
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seriously as they denote things that are very likely to be wrong.
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- WARNING
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This is the next stricter level. Messages of type WARNING requires a
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more careful review. But it is milder than an ERROR.
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- CHECK
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This is the mildest level. These are things which may require some thought.
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Type Descriptions
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=================
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This section contains a description of all the message types in checkpatch.
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.. Types in this section are also parsed by checkpatch.
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.. The types are grouped into subsections based on use.
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Allocation style
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----------------
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**ALLOC_ARRAY_ARGS**
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The first argument for kcalloc or kmalloc_array should be the
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number of elements. sizeof() as the first argument is generally
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wrong.
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See: https://www.kernel.org/doc/html/latest/core-api/memory-allocation.html
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**ALLOC_SIZEOF_STRUCT**
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The allocation style is bad. In general for family of
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allocation functions using sizeof() to get memory size,
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constructs like::
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p = alloc(sizeof(struct foo), ...)
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should be::
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p = alloc(sizeof(*p), ...)
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See: https://www.kernel.org/doc/html/latest/process/coding-style.html#allocating-memory
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**ALLOC_WITH_MULTIPLY**
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Prefer kmalloc_array/kcalloc over kmalloc/kzalloc with a
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sizeof multiply.
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See: https://www.kernel.org/doc/html/latest/core-api/memory-allocation.html
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API usage
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---------
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**ARCH_DEFINES**
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Architecture specific defines should be avoided wherever
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possible.
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**ARCH_INCLUDE_LINUX**
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Whenever asm/file.h is included and linux/file.h exists, a
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conversion can be made when linux/file.h includes asm/file.h.
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However this is not always the case (See signal.h).
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This message type is emitted only for includes from arch/.
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**ARRAY_SIZE**
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The ARRAY_SIZE(foo) macro should be preferred over
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sizeof(foo)/sizeof(foo[0]) for finding number of elements in an
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array.
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The macro is defined in include/linux/kernel.h::
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#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
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**AVOID_BUG**
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BUG() or BUG_ON() should be avoided totally.
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Use WARN() and WARN_ON() instead, and handle the "impossible"
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error condition as gracefully as possible.
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See: https://www.kernel.org/doc/html/latest/process/deprecated.html#bug-and-bug-on
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**AVOID_EXTERNS**
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Function prototypes don't need to be declared extern in .h
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files. It's assumed by the compiler and is unnecessary.
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**AVOID_L_PREFIX**
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Local symbol names that are prefixed with `.L` should be avoided,
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as this has special meaning for the assembler; a symbol entry will
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not be emitted into the symbol table. This can prevent `objtool`
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from generating correct unwind info.
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Symbols with STB_LOCAL binding may still be used, and `.L` prefixed
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local symbol names are still generally usable within a function,
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but `.L` prefixed local symbol names should not be used to denote
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the beginning or end of code regions via
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`SYM_CODE_START_LOCAL`/`SYM_CODE_END`
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**BIT_MACRO**
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Defines like: 1 << <digit> could be BIT(digit).
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The BIT() macro is defined in include/linux/bitops.h::
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#define BIT(nr) (1UL << (nr))
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**CONSIDER_KSTRTO**
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The simple_strtol(), simple_strtoll(), simple_strtoul(), and
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simple_strtoull() functions explicitly ignore overflows, which
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may lead to unexpected results in callers. The respective kstrtol(),
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kstrtoll(), kstrtoul(), and kstrtoull() functions tend to be the
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correct replacements.
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See: https://www.kernel.org/doc/html/latest/process/deprecated.html#simple-strtol-simple-strtoll-simple-strtoul-simple-strtoull
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Comment style
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-------------
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**BLOCK_COMMENT_STYLE**
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The comment style is incorrect. The preferred style for multi-
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line comments is::
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/*
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* This is the preferred style
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* for multi line comments.
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*/
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The networking comment style is a bit different, with the first line
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not empty like the former::
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/* This is the preferred comment style
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* for files in net/ and drivers/net/
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*/
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See: https://www.kernel.org/doc/html/latest/process/coding-style.html#commenting
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**C99_COMMENTS**
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C99 style single line comments (//) should not be used.
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Prefer the block comment style instead.
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See: https://www.kernel.org/doc/html/latest/process/coding-style.html#commenting
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Commit message
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--------------
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**BAD_SIGN_OFF**
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The signed-off-by line does not fall in line with the standards
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specified by the community.
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See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#developer-s-certificate-of-origin-1-1
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**BAD_STABLE_ADDRESS_STYLE**
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The email format for stable is incorrect.
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Some valid options for stable address are::
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1. stable@vger.kernel.org
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2. stable@kernel.org
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For adding version info, the following comment style should be used::
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stable@vger.kernel.org # version info
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**COMMIT_COMMENT_SYMBOL**
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Commit log lines starting with a '#' are ignored by git as
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comments. To solve this problem addition of a single space
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infront of the log line is enough.
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**COMMIT_MESSAGE**
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The patch is missing a commit description. A brief
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description of the changes made by the patch should be added.
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See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#describe-your-changes
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**MISSING_SIGN_OFF**
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The patch is missing a Signed-off-by line. A signed-off-by
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line should be added according to Developer's certificate of
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Origin.
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See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#sign-your-work-the-developer-s-certificate-of-origin
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**NO_AUTHOR_SIGN_OFF**
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The author of the patch has not signed off the patch. It is
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required that a simple sign off line should be present at the
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end of explanation of the patch to denote that the author has
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written it or otherwise has the rights to pass it on as an open
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source patch.
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See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#sign-your-work-the-developer-s-certificate-of-origin
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Comparison style
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----------------
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**ASSIGN_IN_IF**
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Do not use assignments in if condition.
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Example::
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if ((foo = bar(...)) < BAZ) {
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should be written as::
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foo = bar(...);
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if (foo < BAZ) {
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**BOOL_COMPARISON**
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Comparisons of A to true and false are better written
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as A and !A.
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See: https://lore.kernel.org/lkml/1365563834.27174.12.camel@joe-AO722/
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**COMPARISON_TO_NULL**
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Comparisons to NULL in the form (foo == NULL) or (foo != NULL)
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are better written as (!foo) and (foo).
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**CONSTANT_COMPARISON**
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Comparisons with a constant or upper case identifier on the left
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side of the test should be avoided.
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Spacing and Brackets
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--------------------
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**ASSIGNMENT_CONTINUATIONS**
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Assignment operators should not be written at the start of a
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line but should follow the operand at the previous line.
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**BRACES**
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The placement of braces is stylistically incorrect.
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The preferred way is to put the opening brace last on the line,
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and put the closing brace first::
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if (x is true) {
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we do y
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}
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This applies for all non-functional blocks.
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However, there is one special case, namely functions: they have the
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opening brace at the beginning of the next line, thus::
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int function(int x)
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{
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body of function
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}
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See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces
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**BRACKET_SPACE**
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Whitespace before opening bracket '[' is prohibited.
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There are some exceptions:
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1. With a type on the left::
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;int [] a;
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2. At the beginning of a line for slice initialisers::
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[0...10] = 5,
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3. Inside a curly brace::
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= { [0...10] = 5 }
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**CODE_INDENT**
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Code indent should use tabs instead of spaces.
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Outside of comments, documentation and Kconfig,
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spaces are never used for indentation.
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See: https://www.kernel.org/doc/html/latest/process/coding-style.html#indentation
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**CONCATENATED_STRING**
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Concatenated elements should have a space in between.
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Example::
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printk(KERN_INFO"bar");
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should be::
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printk(KERN_INFO "bar");
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**LINE_SPACING**
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Vertical space is wasted given the limited number of lines an
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editor window can display when multiple blank lines are used.
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See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces
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**SPACING**
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Whitespace style used in the kernel sources is described in kernel docs.
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See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces
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**TRAILING_WHITESPACE**
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Trailing whitespace should always be removed.
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Some editors highlight the trailing whitespace and cause visual
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distractions when editing files.
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See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces
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Others
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------
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**CAMELCASE**
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Avoid CamelCase Identifiers.
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See: https://www.kernel.org/doc/html/latest/process/coding-style.html#naming
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**CONFIG_DESCRIPTION**
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Kconfig symbols should have a help text which fully describes
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it.
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@ -14,6 +14,7 @@ whole; patches welcome!
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.. toctree::
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:maxdepth: 2
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checkpatch
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coccinelle
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sparse
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kcov
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