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diff --git a/doc/developer/checkpatch.rst b/doc/developer/checkpatch.rst new file mode 100644 index 0000000..d8fe007 --- /dev/null +++ b/doc/developer/checkpatch.rst @@ -0,0 +1,1251 @@ +.. SPDX-License-Identifier: GPL-2.0-only + +.. _checkpatch: + +========== +Checkpatch +========== + +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. + + +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,BRACES + + - --ignore TYPE(,TYPE2...) + + Checkpatch will not emit messages for the specified types. + + Example:: + + ./scripts/checkpatch.pl mypatch.patch --ignore EMAIL_SUBJECT,BRACES + + - --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 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. + +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. + +Type Descriptions +================= + +This section contains a description of all the message types in checkpatch. + +.. Types in this section are also parsed by checkpatch. +.. The types are grouped into subsections based on use. + + +Allocation style +---------------- + + **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. + + See: https://www.kernel.org/doc/html/latest/core-api/memory-allocation.html + + **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), ...) + + See: https://www.kernel.org/doc/html/latest/process/coding-style.html#allocating-memory + + **ALLOC_WITH_MULTIPLY** + Prefer kmalloc_array/kcalloc over kmalloc/kzalloc with a + sizeof multiply. + + See: https://www.kernel.org/doc/html/latest/core-api/memory-allocation.html + + +API usage +--------- + + **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/. + + **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. + + See: https://www.kernel.org/doc/html/latest/process/deprecated.html#bug-and-bug-on + + **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. + + See: https://www.kernel.org/doc/html/latest/process/deprecated.html#simple-strtol-simple-strtoll-simple-strtoul-simple-strtoull + + **CONSTANT_CONVERSION** + Use of __constant_<foo> form is discouraged for the following functions:: + + __constant_cpu_to_be[x] + __constant_cpu_to_le[x] + __constant_be[x]_to_cpu + __constant_le[x]_to_cpu + __constant_htons + __constant_ntohs + + Using any of these outside of include/uapi/ is not preferred as using the + function without __constant_ is identical when the argument is a + constant. + + In big endian systems, the macros like __constant_cpu_to_be32(x) and + cpu_to_be32(x) expand to the same expression:: + + #define __constant_cpu_to_be32(x) ((__force __be32)(__u32)(x)) + #define __cpu_to_be32(x) ((__force __be32)(__u32)(x)) + + In little endian systems, the macros __constant_cpu_to_be32(x) and + cpu_to_be32(x) expand to __constant_swab32 and __swab32. __swab32 + has a __builtin_constant_p check:: + + #define __swab32(x) \ + (__builtin_constant_p((__u32)(x)) ? \ + ___constant_swab32(x) : \ + __fswab32(x)) + + So ultimately they have a special case for constants. + Similar is the case with all of the macros in the list. Thus + using the __constant_... forms are unnecessarily verbose and + not preferred outside of include/uapi. + + See: https://lore.kernel.org/lkml/1400106425.12666.6.camel@joe-AO725/ + + **DEPRECATED_API** + Usage of a deprecated RCU API is detected. It is recommended to replace + old flavourful RCU APIs by their new vanilla-RCU counterparts. + + The full list of available RCU APIs can be viewed from the kernel docs. + + See: https://www.kernel.org/doc/html/latest/RCU/whatisRCU.html#full-list-of-rcu-apis + + **DEPRECATED_VARIABLE** + EXTRA_{A,C,CPP,LD}FLAGS are deprecated and should be replaced by the new + flags added via commit f77bf01425b1 ("kbuild: introduce ccflags-y, + asflags-y and ldflags-y"). + + The following conversion scheme maybe used:: + + EXTRA_AFLAGS -> asflags-y + EXTRA_CFLAGS -> ccflags-y + EXTRA_CPPFLAGS -> cppflags-y + EXTRA_LDFLAGS -> ldflags-y + + See: + + 1. https://lore.kernel.org/lkml/20070930191054.GA15876@uranus.ravnborg.org/ + 2. https://lore.kernel.org/lkml/1313384834-24433-12-git-send-email-lacombar@gmail.com/ + 3. https://www.kernel.org/doc/html/latest/kbuild/makefiles.html#compilation-flags + + **DEVICE_ATTR_FUNCTIONS** + The function names used in DEVICE_ATTR is unusual. + Typically, the store and show functions are used with <attr>_store and + <attr>_show, where <attr> is a named attribute variable of the device. + + Consider the following examples:: + + static DEVICE_ATTR(type, 0444, type_show, NULL); + static DEVICE_ATTR(power, 0644, power_show, power_store); + + The function names should preferably follow the above pattern. + + See: https://www.kernel.org/doc/html/latest/driver-api/driver-model/device.html#attributes + + **DEVICE_ATTR_RO** + The DEVICE_ATTR_RO(name) helper macro can be used instead of + DEVICE_ATTR(name, 0444, name_show, NULL); + + Note that the macro automatically appends _show to the named + attribute variable of the device for the show method. + + See: https://www.kernel.org/doc/html/latest/driver-api/driver-model/device.html#attributes + + **DEVICE_ATTR_RW** + The DEVICE_ATTR_RW(name) helper macro can be used instead of + DEVICE_ATTR(name, 0644, name_show, name_store); + + Note that the macro automatically appends _show and _store to the + named attribute variable of the device for the show and store methods. + + See: https://www.kernel.org/doc/html/latest/driver-api/driver-model/device.html#attributes + + **DEVICE_ATTR_WO** + The DEVICE_AATR_WO(name) helper macro can be used instead of + DEVICE_ATTR(name, 0200, NULL, name_store); + + Note that the macro automatically appends _store to the + named attribute variable of the device for the store method. + + See: https://www.kernel.org/doc/html/latest/driver-api/driver-model/device.html#attributes + + **DUPLICATED_SYSCTL_CONST** + Commit d91bff3011cf ("proc/sysctl: add shared variables for range + check") added some shared const variables to be used instead of a local + copy in each source file. + + Consider replacing the sysctl range checking value with the shared + one in include/linux/sysctl.h. The following conversion scheme may + be used:: + + &zero -> SYSCTL_ZERO + &one -> SYSCTL_ONE + &int_max -> SYSCTL_INT_MAX + + See: + + 1. https://lore.kernel.org/lkml/20190430180111.10688-1-mcroce@redhat.com/ + 2. https://lore.kernel.org/lkml/20190531131422.14970-1-mcroce@redhat.com/ + + **ENOSYS** + ENOSYS means that a nonexistent system call was called. + Earlier, it was wrongly used for things like invalid operations on + otherwise valid syscalls. This should be avoided in new code. + + See: https://lore.kernel.org/lkml/5eb299021dec23c1a48fa7d9f2c8b794e967766d.1408730669.git.luto@amacapital.net/ + + **ENOTSUPP** + ENOTSUPP is not a standard error code and should be avoided in new patches. + EOPNOTSUPP should be used instead. + + See: https://lore.kernel.org/netdev/20200510182252.GA411829@lunn.ch/ + + **EXPORT_SYMBOL** + EXPORT_SYMBOL should immediately follow the symbol to be exported. + + **IN_ATOMIC** + in_atomic() is not for driver use so any such use is reported as an ERROR. + Also in_atomic() is often used to determine if sleeping is permitted, + but it is not reliable in this use model. Therefore its use is + strongly discouraged. + + However, in_atomic() is ok for core kernel use. + + See: https://lore.kernel.org/lkml/20080320201723.b87b3732.akpm@linux-foundation.org/ + + **LOCKDEP** + The lockdep_no_validate class was added as a temporary measure to + prevent warnings on conversion of device->sem to device->mutex. + It should not be used for any other purpose. + + See: https://lore.kernel.org/lkml/1268959062.9440.467.camel@laptop/ + + **MALFORMED_INCLUDE** + The #include statement has a malformed path. This has happened + because the author has included a double slash "//" in the pathname + accidentally. + + **USE_LOCKDEP** + lockdep_assert_held() annotations should be preferred over + assertions based on spin_is_locked() + + See: https://www.kernel.org/doc/html/latest/locking/lockdep-design.html#annotations + + **UAPI_INCLUDE** + No #include statements in include/uapi should use a uapi/ path. + + **USLEEP_RANGE** + usleep_range() should be preferred over udelay(). The proper way of + using usleep_range() is mentioned in the kernel docs. + + See: https://www.kernel.org/doc/html/latest/timers/timers-howto.html#delays-information-on-the-various-kernel-delay-sleep-mechanisms + + +Comments +-------- + + **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/ + */ + + See: https://www.kernel.org/doc/html/latest/process/coding-style.html#commenting + + **C99_COMMENTS** + C99 style single line comments (//) should not be used. + Prefer the block comment style instead. + + See: https://www.kernel.org/doc/html/latest/process/coding-style.html#commenting + + **DATA_RACE** + Applications of data_race() should have a comment so as to document the + reasoning behind why it was deemed safe. + + See: https://lore.kernel.org/lkml/20200401101714.44781-1-elver@google.com/ + + **FSF_MAILING_ADDRESS** + Kernel maintainers reject new instances of the GPL boilerplate paragraph + directing people to write to the FSF for a copy of the GPL, since the + FSF has moved in the past and may do so again. + So do not write paragraphs about writing to the Free Software Foundation's + mailing address. + + See: https://lore.kernel.org/lkml/20131006222342.GT19510@leaf/ + + +Commit message +-------------- + + **BAD_SIGN_OFF** + The signed-off-by line does not fall in line with the standards + specified by the community. + + See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#developer-s-certificate-of-origin-1-1 + + **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 + + **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. + + See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#describe-your-changes + + **EMAIL_SUBJECT** + Naming the tool that found the issue is not very useful in the + subject line. A good subject line summarizes the change that + the patch brings. + + See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#describe-your-changes + + **FROM_SIGN_OFF_MISMATCH** + The author's email does not match with that in the Signed-off-by: + line(s). This can be sometimes caused due to an improperly configured + email client. + + This message is emitted due to any of the following reasons:: + + - The email names do not match. + - The email addresses do not match. + - The email subaddresses do not match. + - The email comments do not match. + + **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. + + See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#sign-your-work-the-developer-s-certificate-of-origin + + **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. + + See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#sign-your-work-the-developer-s-certificate-of-origin + + **DIFF_IN_COMMIT_MSG** + Avoid having diff content in commit message. + This causes problems when one tries to apply a file containing both + the changelog and the diff because patch(1) tries to apply the diff + which it found in the changelog. + + See: https://lore.kernel.org/lkml/20150611134006.9df79a893e3636019ad2759e@linux-foundation.org/ + + **GERRIT_CHANGE_ID** + To be picked up by gerrit, the footer of the commit message might + have a Change-Id like:: + + Change-Id: Ic8aaa0728a43936cd4c6e1ed590e01ba8f0fbf5b + Signed-off-by: A. U. Thor <author@example.com> + + The Change-Id line must be removed before submitting. + + **GIT_COMMIT_ID** + The proper way to reference a commit id is: + commit <12+ chars of sha1> ("<title line>") + + An example may be:: + + Commit e21d2170f36602ae2708 ("video: remove unnecessary + platform_set_drvdata()") removed the unnecessary + platform_set_drvdata(), but left the variable "dev" unused, + delete it. + + See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#describe-your-changes + + +Comparison style +---------------- + + **ASSIGN_IN_IF** + Do not use assignments in if condition. + Example:: + + if ((foo = bar(...)) < BAZ) { + + should be written as:: + + foo = bar(...); + if (foo < BAZ) { + + **BOOL_COMPARISON** + Comparisons of A to true and false are better written + as A and !A. + + See: https://lore.kernel.org/lkml/1365563834.27174.12.camel@joe-AO722/ + + **COMPARISON_TO_NULL** + Comparisons to NULL in the form (foo == NULL) or (foo != NULL) + are better written as (!foo) and (foo). + + **CONSTANT_COMPARISON** + Comparisons with a constant or upper case identifier on the left + side of the test should be avoided. + + +Indentation and Line Breaks +--------------------------- + + **CODE_INDENT** + Code indent should use tabs instead of spaces. + Outside of comments, documentation and Kconfig, + spaces are never used for indentation. + + See: https://www.kernel.org/doc/html/latest/process/coding-style.html#indentation + + **DEEP_INDENTATION** + Indentation with 6 or more tabs usually indicate overly indented + code. + + It is suggested to refactor excessive indentation of + if/else/for/do/while/switch statements. + + See: https://lore.kernel.org/lkml/1328311239.21255.24.camel@joe2Laptop/ + + **SWITCH_CASE_INDENT_LEVEL** + switch should be at the same indent as case. + Example:: + + switch (suffix) { + case 'G': + case 'g': + mem <<= 30; + break; + case 'M': + case 'm': + mem <<= 20; + break; + case 'K': + case 'k': + mem <<= 10; + fallthrough; + default: + break; + } + + See: https://www.kernel.org/doc/html/latest/process/coding-style.html#indentation + + **LONG_LINE** + The line has exceeded the specified maximum length. + To use a different maximum line length, the --max-line-length=n option + may be added while invoking checkpatch. + + Earlier, the default line length was 80 columns. Commit bdc48fa11e46 + ("checkpatch/coding-style: deprecate 80-column warning") increased the + limit to 100 columns. This is not a hard limit either and it's + preferable to stay within 80 columns whenever possible. + + See: https://www.kernel.org/doc/html/latest/process/coding-style.html#breaking-long-lines-and-strings + + **LONG_LINE_STRING** + A string starts before but extends beyond the maximum line length. + To use a different maximum line length, the --max-line-length=n option + may be added while invoking checkpatch. + + See: https://www.kernel.org/doc/html/latest/process/coding-style.html#breaking-long-lines-and-strings + + **LONG_LINE_COMMENT** + A comment starts before but extends beyond the maximum line length. + To use a different maximum line length, the --max-line-length=n option + may be added while invoking checkpatch. + + See: https://www.kernel.org/doc/html/latest/process/coding-style.html#breaking-long-lines-and-strings + + **SPLIT_STRING** + Quoted strings that appear as messages in userspace and can be + grepped, should not be split across multiple lines. + + See: https://lore.kernel.org/lkml/20120203052727.GA15035@leaf/ + + **MULTILINE_DEREFERENCE** + A single dereferencing identifier spanned on multiple lines like:: + + struct_identifier->member[index]. + member = <foo>; + + is generally hard to follow. It can easily lead to typos and so makes + the code vulnerable to bugs. + + If fixing the multiple line dereferencing leads to an 80 column + violation, then either rewrite the code in a more simple way or if the + starting part of the dereferencing identifier is the same and used at + multiple places then store it in a temporary variable, and use that + temporary variable only at all the places. For example, if there are + two dereferencing identifiers:: + + member1->member2->member3.foo1; + member1->member2->member3.foo2; + + then store the member1->member2->member3 part in a temporary variable. + It not only helps to avoid the 80 column violation but also reduces + the program size by removing the unnecessary dereferences. + + But if none of the above methods work then ignore the 80 column + violation because it is much easier to read a dereferencing identifier + on a single line. + + **TRAILING_STATEMENTS** + Trailing statements (for example after any conditional) should be + on the next line. + Statements, such as:: + + if (x == y) break; + + should be:: + + if (x == y) + break; + + +Macros, Attributes and Symbols +------------------------------ + + **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])) + + **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` + + **BIT_MACRO** + Defines like: 1 << <digit> could be BIT(digit). + The BIT() macro is defined via include/linux/bits.h:: + + #define BIT(nr) (1UL << (nr)) + + **CONST_READ_MOSTLY** + When a variable is tagged with the __read_mostly annotation, it is a + signal to the compiler that accesses to the variable will be mostly + reads and rarely(but NOT never) a write. + + const __read_mostly does not make any sense as const data is already + read-only. The __read_mostly annotation thus should be removed. + + **DATE_TIME** + It is generally desirable that building the same source code with + the same set of tools is reproducible, i.e. the output is always + exactly the same. + + The kernel does *not* use the ``__DATE__`` and ``__TIME__`` macros, + and enables warnings if they are used as they can lead to + non-deterministic builds. + + See: https://www.kernel.org/doc/html/latest/kbuild/reproducible-builds.html#timestamps + + **DEFINE_ARCH_HAS** + The ARCH_HAS_xyz and ARCH_HAVE_xyz patterns are wrong. + + For big conceptual features use Kconfig symbols instead. And for + smaller things where we have compatibility fallback functions but + want architectures able to override them with optimized ones, we + should either use weak functions (appropriate for some cases), or + the symbol that protects them should be the same symbol we use. + + See: https://lore.kernel.org/lkml/CA+55aFycQ9XJvEOsiM3txHL5bjUc8CeKWJNR_H+MiicaddB42Q@mail.gmail.com/ + + **DO_WHILE_MACRO_WITH_TRAILING_SEMICOLON** + do {} while(0) macros should not have a trailing semicolon. + + **INIT_ATTRIBUTE** + Const init definitions should use __initconst instead of + __initdata. + + Similarly init definitions without const require a separate + use of const. + + **INLINE_LOCATION** + The inline keyword should sit between storage class and type. + + For example, the following segment:: + + inline static int example_function(void) + { + ... + } + + should be:: + + static inline int example_function(void) + { + ... + } + + **MISPLACED_INIT** + It is possible to use section markers on variables in a way + which gcc doesn't understand (or at least not the way the + developer intended):: + + static struct __initdata samsung_pll_clock exynos4_plls[nr_plls] = { + + does not put exynos4_plls in the .initdata section. The __initdata + marker can be virtually anywhere on the line, except right after + "struct". The preferred location is before the "=" sign if there is + one, or before the trailing ";" otherwise. + + See: https://lore.kernel.org/lkml/1377655732.3619.19.camel@joe-AO722/ + + **MULTISTATEMENT_MACRO_USE_DO_WHILE** + Macros with multiple statements should be enclosed in a + do - while block. Same should also be the case for macros + starting with `if` to avoid logic defects:: + + #define macrofun(a, b, c) \ + do { \ + if (a == 5) \ + do_this(b, c); \ + } while (0) + + See: https://www.kernel.org/doc/html/latest/process/coding-style.html#macros-enums-and-rtl + + **PREFER_FALLTHROUGH** + Use the `fallthrough;` pseudo keyword instead of + `/* fallthrough */` like comments. + + **TRAILING_SEMICOLON** + Macro definition should not end with a semicolon. The macro + invocation style should be consistent with function calls. + This can prevent any unexpected code paths:: + + #define MAC do_something; + + If this macro is used within a if else statement, like:: + + if (some_condition) + MAC; + + else + do_something; + + Then there would be a compilation error, because when the macro is + expanded there are two trailing semicolons, so the else branch gets + orphaned. + + See: https://lore.kernel.org/lkml/1399671106.2912.21.camel@joe-AO725/ + + **SINGLE_STATEMENT_DO_WHILE_MACRO** + For the multi-statement macros, it is necessary to use the do-while + loop to avoid unpredictable code paths. The do-while loop helps to + group the multiple statements into a single one so that a + function-like macro can be used as a function only. + + But for the single statement macros, it is unnecessary to use the + do-while loop. Although the code is syntactically correct but using + the do-while loop is redundant. So remove the do-while loop for single + statement macros. + + **WEAK_DECLARATION** + Using weak declarations like __attribute__((weak)) or __weak + can have unintended link defects. Avoid using them. + + +Functions and Variables +----------------------- + + **CAMELCASE** + Avoid CamelCase Identifiers. + + See: https://www.kernel.org/doc/html/latest/process/coding-style.html#naming + + **CONST_CONST** + Using `const <type> const *` is generally meant to be + written `const <type> * const`. + + **CONST_STRUCT** + Using const is generally a good idea. Checkpatch reads + a list of frequently used structs that are always or + almost always constant. + + The existing structs list can be viewed from + `scripts/const_structs.checkpatch`. + + See: https://lore.kernel.org/lkml/alpine.DEB.2.10.1608281509480.3321@hadrien/ + + **EMBEDDED_FUNCTION_NAME** + Embedded function names are less appropriate to use as + refactoring can cause function renaming. Prefer the use of + "%s", __func__ to embedded function names. + + Note that this does not work with -f (--file) checkpatch option + as it depends on patch context providing the function name. + + **FUNCTION_ARGUMENTS** + This warning is emitted due to any of the following reasons: + + 1. Arguments for the function declaration do not follow + the identifier name. Example:: + + void foo + (int bar, int baz) + + This should be corrected to:: + + void foo(int bar, int baz) + + 2. Some arguments for the function definition do not + have an identifier name. Example:: + + void foo(int) + + All arguments should have identifier names. + + **FUNCTION_WITHOUT_ARGS** + Function declarations without arguments like:: + + int foo() + + should be:: + + int foo(void) + + **GLOBAL_INITIALISERS** + Global variables should not be initialized explicitly to + 0 (or NULL, false, etc.). Your compiler (or rather your + loader, which is responsible for zeroing out the relevant + sections) automatically does it for you. + + **INITIALISED_STATIC** + Static variables should not be initialized explicitly to zero. + Your compiler (or rather your loader) automatically does + it for you. + + **MULTIPLE_ASSIGNMENTS** + Multiple assignments on a single line makes the code unnecessarily + complicated. So on a single line assign value to a single variable + only, this makes the code more readable and helps avoid typos. + + **RETURN_PARENTHESES** + return is not a function and as such doesn't need parentheses:: + + return (bar); + + can simply be:: + + return bar; + + +Permissions +----------- + + **DEVICE_ATTR_PERMS** + The permissions used in DEVICE_ATTR are unusual. + Typically only three permissions are used - 0644 (RW), 0444 (RO) + and 0200 (WO). + + See: https://www.kernel.org/doc/html/latest/filesystems/sysfs.html#attributes + + **EXECUTE_PERMISSIONS** + There is no reason for source files to be executable. The executable + bit can be removed safely. + + **EXPORTED_WORLD_WRITABLE** + Exporting world writable sysfs/debugfs files is usually a bad thing. + When done arbitrarily they can introduce serious security bugs. + In the past, some of the debugfs vulnerabilities would seemingly allow + any local user to write arbitrary values into device registers - a + situation from which little good can be expected to emerge. + + See: https://lore.kernel.org/linux-arm-kernel/cover.1296818921.git.segoon@openwall.com/ + + **NON_OCTAL_PERMISSIONS** + Permission bits should use 4 digit octal permissions (like 0700 or 0444). + Avoid using any other base like decimal. + + **SYMBOLIC_PERMS** + Permission bits in the octal form are more readable and easier to + understand than their symbolic counterparts because many command-line + tools use this notation. Experienced kernel developers have been using + these traditional Unix permission bits for decades and so they find it + easier to understand the octal notation than the symbolic macros. + For example, it is harder to read S_IWUSR|S_IRUGO than 0644, which + obscures the developer's intent rather than clarifying it. + + See: https://lore.kernel.org/lkml/CA+55aFw5v23T-zvDZp-MmD_EYxF8WbafwwB59934FV7g21uMGQ@mail.gmail.com/ + + +Spacing and Brackets +-------------------- + + **ASSIGNMENT_CONTINUATIONS** + Assignment operators should not be written at the start of a + line but should follow the operand at the previous line. + + **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 + } + + See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces + + **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 } + + **CONCATENATED_STRING** + Concatenated elements should have a space in between. + Example:: + + printk(KERN_INFO"bar"); + + should be:: + + printk(KERN_INFO "bar"); + + **ELSE_AFTER_BRACE** + `else {` should follow the closing block `}` on the same line. + + See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces + + **LINE_SPACING** + Vertical space is wasted given the limited number of lines an + editor window can display when multiple blank lines are used. + + See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces + + **OPEN_BRACE** + The opening brace should be following the function definitions on the + next line. For any non-functional block it should be on the same line + as the last construct. + + See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces + + **POINTER_LOCATION** + When using pointer data or a function that returns a pointer type, + the preferred use of * is adjacent to the data name or function name + and not adjacent to the type name. + Examples:: + + char *linux_banner; + unsigned long long memparse(char *ptr, char **retptr); + char *match_strdup(substring_t *s); + + See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces + + **SPACING** + Whitespace style used in the kernel sources is described in kernel docs. + + See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces + + **TRAILING_WHITESPACE** + Trailing whitespace should always be removed. + Some editors highlight the trailing whitespace and cause visual + distractions when editing files. + + See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces + + **UNNECESSARY_PARENTHESES** + Parentheses are not required in the following cases: + + 1. Function pointer uses:: + + (foo->bar)(); + + could be:: + + foo->bar(); + + 2. Comparisons in if:: + + if ((foo->bar) && (foo->baz)) + if ((foo == bar)) + + could be:: + + if (foo->bar && foo->baz) + if (foo == bar) + + 3. addressof/dereference single Lvalues:: + + &(foo->bar) + *(foo->bar) + + could be:: + + &foo->bar + *foo->bar + + **WHILE_AFTER_BRACE** + while should follow the closing bracket on the same line:: + + do { + ... + } while(something); + + See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces + + +Others +------ + + **CONFIG_DESCRIPTION** + Kconfig symbols should have a help text which fully describes + it. + + **CORRUPTED_PATCH** + The patch seems to be corrupted or lines are wrapped. + Please regenerate the patch file before sending it to the maintainer. + + **CVS_KEYWORD** + Since linux moved to git, the CVS markers are no longer used. + So, CVS style keywords ($Id$, $Revision$, $Log$) should not be + added. + + **DEFAULT_NO_BREAK** + switch default case is sometimes written as "default:;". This can + cause new cases added below default to be defective. + + A "break;" should be added after empty default statement to avoid + unwanted fallthrough. + + **DOS_LINE_ENDINGS** + For DOS-formatted patches, there are extra ^M symbols at the end of + the line. These should be removed. + + **DT_SCHEMA_BINDING_PATCH** + DT bindings moved to a json-schema based format instead of + freeform text. + + See: https://www.kernel.org/doc/html/latest/devicetree/bindings/writing-schema.html + + **DT_SPLIT_BINDING_PATCH** + Devicetree bindings should be their own patch. This is because + bindings are logically independent from a driver implementation, + they have a different maintainer (even though they often + are applied via the same tree), and it makes for a cleaner history in the + DT only tree created with git-filter-branch. + + See: https://www.kernel.org/doc/html/latest/devicetree/bindings/submitting-patches.html#i-for-patch-submitters + + **EMBEDDED_FILENAME** + Embedding the complete filename path inside the file isn't particularly + useful as often the path is moved around and becomes incorrect. + + **FILE_PATH_CHANGES** + Whenever files are added, moved, or deleted, the MAINTAINERS file + patterns can be out of sync or outdated. + + So MAINTAINERS might need updating in these cases. + + **MEMSET** + The memset use appears to be incorrect. This may be caused due to + badly ordered parameters. Please recheck the usage. + + **NOT_UNIFIED_DIFF** + The patch file does not appear to be in unified-diff format. Please + regenerate the patch file before sending it to the maintainer. + + **PRINTF_0XDECIMAL** + Prefixing 0x with decimal output is defective and should be corrected. + + **SPDX_LICENSE_TAG** + The source file is missing or has an improper SPDX identifier tag. + The Linux kernel requires the precise SPDX identifier in all source files, + and it is thoroughly documented in the kernel docs. + + See: https://www.kernel.org/doc/html/latest/process/license-rules.html + + **TYPO_SPELLING** + Some words may have been misspelled. Consider reviewing them. |