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Subject[PATCH RFC v3 2/3] docs: add documentation for checkpatch
Date
Add documentation for kernel script checkpatch.pl.
This documentation is also parsed by checkpatch to
enable a verbose mode.

The message types in checkpatch are documented with rst
field lists. A total of 33 checkpatch type descriptions
are added.

Signed-off-by: Dwaipayan Ray <dwaipayanray1@gmail.com>
---
Documentation/dev-tools/checkpatch.rst | 494 +++++++++++++++++++++++++
1 file changed, 494 insertions(+)
create mode 100644 Documentation/dev-tools/checkpatch.rst

diff --git a/Documentation/dev-tools/checkpatch.rst b/Documentation/dev-tools/checkpatch.rst
new file mode 100644
index 000000000000..8e6ff1e27353
--- /dev/null
+++ b/Documentation/dev-tools/checkpatch.rst
@@ -0,0 +1,494 @@
+.. SPDX-License-Identifier: GPL-2.0-only
+
+==========
+Checkpatch
+==========
+
+This document describes the kernel script checkpatch.pl.
+
+.. Table of Contents
+
+ === 1 Introduction
+ === 2 Options
+ === 3 Message Levels
+ === 4 Type Descriptions
+
+1 Introduction
+--------------
+
+Checkpatch (scripts/checkpatch.pl) is a perl script which checks for trivial style
+violations in patches and optionally corrects them. Checkpatch can also be run on
+file contexts and without the kernel tree.
+
+Checkpatch is not always right. Your judgement takes precedence over checkpatch
+messages. If your code looks better with the violations, then its probably
+best left alone.
+
+
+2 Options
+---------
+
+This section will describe the options checkpatch can be run with.
+
+Usage::
+
+ ./scripts/checkpatch.pl [OPTION]... [FILE]...
+
+Available options:
+
+ - -q, --quiet
+
+ Enable quiet mode.
+
+ - -v, --verbose
+ Enable verbose mode. Additional verbose test descriptions are output
+ so as to provide information on why that particular message is shown.
+
+ - --no-tree
+
+ Run checkpatch without the kernel tree.
+
+ - --no-signoff
+
+ Disable the 'Signed-off-by' line check. The sign-off is a simple line at
+ the end of the explanation for the patch, which certifies that you wrote it
+ or otherwise have the right to pass it on as an open-source patch.
+
+ Example::
+
+ Signed-off-by: Random J Developer <random@developer.example.org>
+
+ Setting this flag effectively stops a message for a missing signed-off-by line
+ in a patch context.
+
+ - --patch
+
+ Treat FILE as a patch. This is the default option and need not be
+ explicitly specified.
+
+ - --emacs
+
+ Set output to emacs compile window format. This allows emacs users to jump
+ from the error in the compile window directly to the offending line in the patch.
+
+ - --terse
+
+ Output only one line per report.
+
+ - --showfile
+
+ Show the diffed file position instead of the input file position.
+
+ - -g, --git
+
+ Treat FILE as a single commit or a git revision range.
+
+ Single commit with:
+
+ - <rev>
+ - <rev>^
+ - <rev>~n
+
+ Multiple commits with:
+
+ - <rev1>..<rev2>
+ - <rev1>...<rev2>
+ - <rev>-<count>
+
+ - -f, --file
+
+ Treat FILE as a regular source file. This option must be used when running
+ checkpatch on source files in the kernel.
+
+ - --subjective, --strict
+
+ Enable stricter tests in checkpatch. By default the tests emitted as CHECK
+ do not activate by default. Use this flag to activate the CHECK tests.
+
+ - --list-types
+
+ Every message emitted by checkpatch has an associated TYPE. Add this flag to
+ display all the types in checkpatch.
+
+ Note that when this flag is active, checkpatch does not read the input FILE, and
+ no message is emitted. Only a list of types in checkpatch is output.
+
+ - --types TYPE(,TYPE2...)
+
+ Only display messages with the given types.
+
+ Example::
+
+ ./scripts/checkpatch.pl mypatch.patch --types EMAIL_SUBJECT,NO_AUTHOR_SIGN_OFF
+
+ - --ignore TYPE(,TYPE2...)
+
+ Checkpatch will not emit messages for the specified types.
+
+ Example::
+
+ ./scripts/checkpatch.pl mypatch.patch --ignore EMAIL_SUBJECT,NO_AUTHOR_SIGN_OFF
+
+ - --show-types
+
+ By default checkpatch doesn't display the type associated with the messages.
+ Set this flag to show the message type in the output.
+
+ - --max-line-length=n
+
+ Set the max line length (default 100). If a line exceeds the specified length,
+ a LONG_LINE message is emitted.
+
+
+ The message level is different for patch and file contexts. For patches, a WARNING is
+ emitted. While a milder CHECK is emitted for files. So for file contexts, the --strict
+ flag must also be enabled.
+
+ - --min-conf-desc-length=n
+
+ Set the Kconfig entry minimum description length, if shorter, warn.
+
+ - --tab-size=n
+
+ Set the number of spaces for tab (default 8).
+
+ - --root=PATH
+
+ PATH to the kernel tree root.
+
+ This option must be specified when invoking checkpatch from outside
+ the kernel root.
+
+ - --no-summary
+
+ Suppress the per file summary.
+
+ - --mailback
+
+ Only produce a report in case of Warnings or Errors. Milder Checks are
+ excluded from this.
+
+ - --summary-file
+
+ Include the filename in summary.
+
+ - --debug KEY=[0|1]
+
+ Turn on/off debugging of KEY, where KEY is one of 'values', 'possible',
+ 'type', and 'attr' (default is all off).
+
+ - --fix
+
+ This is an EXPERIMENTAL feature. If correctable errors exists, a file
+ <inputfile>.EXPERIMENTAL-checkpatch-fixes is created which has the
+ automatically fixable errors corrected.
+
+ - --fix-inplace
+
+ EXPERIMENTAL - Similar to --fix but the input file is overwritten with fixes.
+
+ DO NOT USE this flag unless you are absolutely sure and you have a backup in place.
+
+ - --ignore-perl-version
+
+ Override checking of perl version. Runtime errors maybe encountered after
+ enabling this flag if the perl version does not meet the minimum specified.
+
+ - --codespell
+
+ Use the codespell dictionary for checking spelling errors.
+
+ - --codespellfile
+
+ Use the specified codespell file. Default is '/usr/share/codespell/dictionary.txt'.
+
+ - --typedefsfile
+
+ Read additional types from this file.
+
+ - --color[=WHEN]
+
+ Use colors 'always', 'never', or only when output is a terminal ('auto').
+ Default is 'auto'.
+
+ - --kconfig-prefix=WORD
+
+ Use WORD as a prefix for Kconfig symbols (default is `CONFIG_`).
+
+ - -h, --help, --version
+
+ Display the help text.
+
+3 Message Levels
+----------------
+
+Messages in checkpatch are divided into three levels. The levels of messages in
+checkpatch denote the severity of the error. They are:
+
+ - ERROR
+
+ This is the most strict level. Messages of type ERROR must be taken
+ seriously as they denote things that are very likely to be wrong.
+
+ - WARNING
+
+ This is the next stricter level. Messages of type WARNING requires a
+ more careful review. But it is milder than an ERROR.
+
+ - CHECK
+
+ This is the mildest level. These are things which may require some thought.
+
+4 Type Descriptions
+-------------------
+
+This section contains a description of all the message types in checkpatch.
+
+.. Types in this section are also parsed by checkpatch.
+.. Please keep the types sorted alphabetically.
+
+:ALLOC_ARRAY_ARGS:
+ The first argument for kcalloc or kmalloc_array should be the
+ number of elements. sizeof() as the first argument is generally
+ wrong.
+
+:ALLOC_SIZEOF_STRUCT:
+ The allocation style is bad. In general for family of
+ allocation functions using sizeof() to get memory size,
+ constructs like::
+
+ p = alloc(sizeof(struct foo), ...)
+
+ should be::
+
+ p = alloc(sizeof(*p), ...)
+
+:ALLOC_WITH_MULTIPLY:
+ Prefer kmalloc_array/kcalloc over kmalloc/kzalloc with a
+ sizeof multiply.
+ Ref: `Documentation/core-api/memory-allocation.rst`
+
+:ARCH_DEFINES:
+ Architecture specific defines should be avoided wherever
+ possible.
+
+:ARCH_INCLUDE_LINUX:
+ Whenever asm/file.h is included and linux/file.h exists, a
+ conversion can be made when linux/file.h includes asm/file.h.
+ However this is not always the case (See signal.h).
+ This message type is emitted only for includes from arch/.
+
+:ARRAY_SIZE:
+ The ARRAY_SIZE(foo) macro should be preferred over
+ sizeof(foo)/sizeof(foo[0]) for finding number of elements in an
+ array.
+
+ The macro is defined in include/linux/kernel.h::
+
+ #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
+
+:ASSIGNMENT_CONTINUATIONS:
+ Assignment operators should not be written at the start of a
+ line but should follow the operand at the previous line.
+
+:ASSIGN_IN_IF:
+ Do not use assignments in if condition.
+ Example::
+
+ if ((foo = bar(...)) < BAZ) {
+
+ should be written as::
+
+ foo = bar(...);
+ if (foo < BAZ) {
+
+:AVOID_BUG:
+ BUG() or BUG_ON() should be avoided totally.
+ Use WARN() and WARN_ON() instead, and handle the "impossible"
+ error condition as gracefully as possible.
+ Ref: `Documentation/process/deprecated.rst`
+
+:AVOID_EXTERNS:
+ Function prototypes don't need to be declared extern in .h
+ files. It's assumed by the compiler and is unnecessary.
+
+:AVOID_L_PREFIX:
+ Local symbol names that are prefixed with `.L` should be avoided,
+ as this has special meaning for the assembler; a symbol entry will
+ not be emitted into the symbol table. This can prevent `objtool`
+ from generating correct unwind info.
+
+ Symbols with STB_LOCAL binding may still be used, and `.L` prefixed
+ local symbol names are still generally usable within a function,
+ but `.L` prefixed local symbol names should not be used to denote
+ the beginning or end of code regions via
+ `SYM_CODE_START_LOCAL`/`SYM_CODE_END`
+
+:BAD_SIGN_OFF:
+ The signed-off-by line does not fall in line with the standards
+ specified by the community.
+ Ref: `Documentation/process/submitting-patches.rst`
+
+:BAD_STABLE_ADDRESS_STYLE:
+ The email format for stable is incorrect.
+ Some valid options for stable address are::
+
+ 1. stable@vger.kernel.org
+ 2. stable@kernel.org
+
+ For adding version info, the following comment style should be used::
+
+ stable@vger.kernel.org # version info
+
+:BIT_MACRO:
+ Defines like: 1 << <digit> could be BIT(digit).
+ The BIT() macro is defined in include/linux/bitops.h::
+
+ #define BIT(nr) (1UL << (nr))
+
+:BLOCK_COMMENT_STYLE:
+ The comment style is incorrect. The preferred style for multi-
+ line comments is::
+
+ /*
+ * This is the preferred style
+ * for multi line comments.
+ */
+
+ The networking comment style is a bit different, with the first line
+ not empty like the former::
+
+ /* This is the preferred comment style
+ * for files in net/ and drivers/net/
+ */
+
+ Ref: `Documentation/process/coding-style.rst`
+
+:BOOL_COMPARISON:
+ Comparisons of A to true and false are better written
+ as A and !A.
+ Ref: `https://lore.kernel.org/lkml/1365563834.27174.12.camel@joe-AO722/`
+
+:BRACES:
+ The placement of braces is stylistically incorrect.
+ The preferred way is to put the opening brace last on the line,
+ and put the closing brace first::
+
+ if (x is true) {
+ we do y
+ }
+
+ This applies for all non-functional blocks.
+ However, there is one special case, namely functions: they have the
+ opening brace at the beginning of the next line, thus::
+
+ int function(int x)
+ {
+ body of function
+ }
+
+ Ref: `Documentation/process/coding-style.rst Section 3`
+
+:BRACKET_SPACE:
+ Whitespace before opening bracket '[' is prohibited.
+ There are some exceptions:
+
+ 1. With a type on the left::
+
+ ;int [] a;
+
+ 2. At the beginning of a line for slice initialisers::
+
+ [0...10] = 5,
+
+ 3. Inside a curly brace::
+
+ = { [0...10] = 5 }
+
+:C99_COMMENTS:
+ C99 style single line comments (//) should not be used.
+ Prefer the block comment style instead.
+ Ref: `Documentation/process/coding-style.rst Section 8`
+
+:CAMELCASE:
+ Avoid CamelCase Identifiers. snake_case can be an
+ alternative.
+
+:CODE_INDENT:
+ Code indent should use tabs instead of spaces.
+ Outside of comments, documentation and Kconfig,
+ spaces are never used for indentation.
+ Ref: `Documentation/process/coding-style.rst Section 1`
+
+:COMMIT_COMMENT_SYMBOL:
+ Commit log lines starting with a '#' are ignored by git as
+ comments. To solve this problem addition of a single space
+ infront of the log line is enough.
+
+:COMMIT_MESSAGE:
+ The patch is missing a commit description. A brief
+ description of the changes made by the patch should be added.
+ Ref: `Documentation/process/submitting-patches.rst`
+
+:COMPARISON_TO_NULL:
+ Comparisons to NULL in the form (foo == NULL) or (foo != NULL)
+ are better written as (!foo) and (foo).
+
+:COMPLEX_MACRO:
+ Macros with complex values should be enclosed within parentheses.
+ Consider::
+
+ #define SOME_MACRO IS_ENABLED(CONFIG_XX) ? 1 : 0
+
+ This can be better written as::
+
+ #define SOME_MACRO (IS_ENABLED(CONFIG_XX) ? 1 : 0)
+
+:CONCATENATED_STRING:
+ Concatenated elements should have a space in between.
+ Example::
+
+ printk(KERN_INFO"bar");
+
+ should be::
+
+ printk(KERN_INFO "bar");
+
+:CONFIG_DESCRIPTION:
+ Kconfig symbols should have a help text which fully describes
+ it.
+
+:CONSIDER_KSTRTO:
+ The simple_strtol(), simple_strtoll(), simple_strtoul(), and
+ simple_strtoull() functions explicitly ignore overflows, which
+ may lead to unexpected results in callers. The respective kstrtol(),
+ kstrtoll(), kstrtoul(), and kstrtoull() functions tend to be the
+ correct replacements.
+ Ref: `Documentation/process/deprecated.rst`
+
+:CONSTANT_COMPARISON:
+ Comparisons with a constant or upper case identifier on the left
+ side of the test should be avoided.
+
+:LINE_SPACING:
+ Vertical space is wasted given the limited number of lines an
+ editor window can display when multiple blank lines are used.
+ Ref: `Documentation/process/coding-style.rst Section 3.1`
+
+:MISSING_SIGN_OFF:
+ The patch is missing a Signed-off-by line. A signed-off-by
+ line should be added according to Developer's certificate of
+ Origin.
+ ref: `Documentation/process/submitting-patches.rst`
+
+:NO_AUTHOR_SIGN_OFF:
+ The author of the patch has not signed off the patch. It is
+ required that a simple sign off line should be present at the
+ end of explanation of the patch to denote that the author has
+ written it or otherwise has the rights to pass it on as an open
+ source patch.
+
+:TRAILING_WHITESPACE:
+ Trailing whitespace should always be removed.
+ Some editors highlight the trailing whitespace and cause visual
+ distractions when editing files.
--
2.30.0
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