1 .. SPDX-License-Identifier: GPL-2.0-only
7 Checkpatch (scripts/checkpatch.pl) is a perl script which checks for trivial
8 style violations in patches and optionally corrects them. Checkpatch can
9 also be run on file contexts and without the kernel tree.
11 Checkpatch is not always right. Your judgement takes precedence over checkpatch
12 messages. If your code looks better with the violations, then its probably
19 This section will describe the options checkpatch can be run with.
23 ./scripts/checkpatch.pl [OPTION]... [FILE]...
32 Enable verbose mode. Additional verbose test descriptions are output
33 so as to provide information on why that particular message is shown.
37 Run checkpatch without the kernel tree.
41 Disable the 'Signed-off-by' line check. The sign-off is a simple line at
42 the end of the explanation for the patch, which certifies that you wrote it
43 or otherwise have the right to pass it on as an open-source patch.
47 Signed-off-by: Random J Developer <random@developer.example.org>
49 Setting this flag effectively stops a message for a missing signed-off-by
50 line in a patch context.
54 Treat FILE as a patch. This is the default option and need not be
59 Set output to emacs compile window format. This allows emacs users to jump
60 from the error in the compile window directly to the offending line in the
65 Output only one line per report.
69 Show the diffed file position instead of the input file position.
73 Treat FILE as a single commit or a git revision range.
81 Multiple commits with:
89 Treat FILE as a regular source file. This option must be used when running
90 checkpatch on source files in the kernel.
92 - --subjective, --strict
94 Enable stricter tests in checkpatch. By default the tests emitted as CHECK
95 do not activate by default. Use this flag to activate the CHECK tests.
99 Every message emitted by checkpatch has an associated TYPE. Add this flag
100 to display all the types in checkpatch.
102 Note that when this flag is active, checkpatch does not read the input FILE,
103 and no message is emitted. Only a list of types in checkpatch is output.
105 - --types TYPE(,TYPE2...)
107 Only display messages with the given types.
111 ./scripts/checkpatch.pl mypatch.patch --types EMAIL_SUBJECT,BRACES
113 - --ignore TYPE(,TYPE2...)
115 Checkpatch will not emit messages for the specified types.
119 ./scripts/checkpatch.pl mypatch.patch --ignore EMAIL_SUBJECT,BRACES
123 By default checkpatch doesn't display the type associated with the messages.
124 Set this flag to show the message type in the output.
126 - --max-line-length=n
128 Set the max line length (default 100). If a line exceeds the specified
129 length, a LONG_LINE message is emitted.
132 The message level is different for patch and file contexts. For patches,
133 a WARNING is emitted. While a milder CHECK is emitted for files. So for
134 file contexts, the --strict flag must also be enabled.
136 - --min-conf-desc-length=n
138 Set the Kconfig entry minimum description length, if shorter, warn.
142 Set the number of spaces for tab (default 8).
146 PATH to the kernel tree root.
148 This option must be specified when invoking checkpatch from outside
153 Suppress the per file summary.
157 Only produce a report in case of Warnings or Errors. Milder Checks are
162 Include the filename in summary.
166 Turn on/off debugging of KEY, where KEY is one of 'values', 'possible',
167 'type', and 'attr' (default is all off).
171 This is an EXPERIMENTAL feature. If correctable errors exists, a file
172 <inputfile>.EXPERIMENTAL-checkpatch-fixes is created which has the
173 automatically fixable errors corrected.
177 EXPERIMENTAL - Similar to --fix but input file is overwritten with fixes.
179 DO NOT USE this flag unless you are absolutely sure and you have a backup
182 - --ignore-perl-version
184 Override checking of perl version. Runtime errors maybe encountered after
185 enabling this flag if the perl version does not meet the minimum specified.
189 Use the codespell dictionary for checking spelling errors.
193 Use the specified codespell file.
194 Default is '/usr/share/codespell/dictionary.txt'.
198 Read additional types from this file.
202 Use colors 'always', 'never', or only when output is a terminal ('auto').
205 - --kconfig-prefix=WORD
207 Use WORD as a prefix for Kconfig symbols (default is `CONFIG_`).
209 - -h, --help, --version
211 Display the help text.
216 Messages in checkpatch are divided into three levels. The levels of messages
217 in checkpatch denote the severity of the error. They are:
221 This is the most strict level. Messages of type ERROR must be taken
222 seriously as they denote things that are very likely to be wrong.
226 This is the next stricter level. Messages of type WARNING requires a
227 more careful review. But it is milder than an ERROR.
231 This is the mildest level. These are things which may require some thought.
236 This section contains a description of all the message types in checkpatch.
238 .. Types in this section are also parsed by checkpatch.
239 .. The types are grouped into subsections based on use.
246 The first argument for kcalloc or kmalloc_array should be the
247 number of elements. sizeof() as the first argument is generally
250 See: https://www.kernel.org/doc/html/latest/core-api/memory-allocation.html
252 **ALLOC_SIZEOF_STRUCT**
253 The allocation style is bad. In general for family of
254 allocation functions using sizeof() to get memory size,
257 p = alloc(sizeof(struct foo), ...)
261 p = alloc(sizeof(*p), ...)
263 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#allocating-memory
265 **ALLOC_WITH_MULTIPLY**
266 Prefer kmalloc_array/kcalloc over kmalloc/kzalloc with a
269 See: https://www.kernel.org/doc/html/latest/core-api/memory-allocation.html
276 Architecture specific defines should be avoided wherever
279 **ARCH_INCLUDE_LINUX**
280 Whenever asm/file.h is included and linux/file.h exists, a
281 conversion can be made when linux/file.h includes asm/file.h.
282 However this is not always the case (See signal.h).
283 This message type is emitted only for includes from arch/.
286 BUG() or BUG_ON() should be avoided totally.
287 Use WARN() and WARN_ON() instead, and handle the "impossible"
288 error condition as gracefully as possible.
290 See: https://www.kernel.org/doc/html/latest/process/deprecated.html#bug-and-bug-on
293 The simple_strtol(), simple_strtoll(), simple_strtoul(), and
294 simple_strtoull() functions explicitly ignore overflows, which
295 may lead to unexpected results in callers. The respective kstrtol(),
296 kstrtoll(), kstrtoul(), and kstrtoull() functions tend to be the
297 correct replacements.
299 See: https://www.kernel.org/doc/html/latest/process/deprecated.html#simple-strtol-simple-strtoll-simple-strtoul-simple-strtoull
301 **CONSTANT_CONVERSION**
302 Use of __constant_<foo> form is discouraged for the following functions::
304 __constant_cpu_to_be[x]
305 __constant_cpu_to_le[x]
306 __constant_be[x]_to_cpu
307 __constant_le[x]_to_cpu
311 Using any of these outside of include/uapi/ is not preferred as using the
312 function without __constant_ is identical when the argument is a
315 In big endian systems, the macros like __constant_cpu_to_be32(x) and
316 cpu_to_be32(x) expand to the same expression::
318 #define __constant_cpu_to_be32(x) ((__force __be32)(__u32)(x))
319 #define __cpu_to_be32(x) ((__force __be32)(__u32)(x))
321 In little endian systems, the macros __constant_cpu_to_be32(x) and
322 cpu_to_be32(x) expand to __constant_swab32 and __swab32. __swab32
323 has a __builtin_constant_p check::
325 #define __swab32(x) \
326 (__builtin_constant_p((__u32)(x)) ? \
327 ___constant_swab32(x) : \
330 So ultimately they have a special case for constants.
331 Similar is the case with all of the macros in the list. Thus
332 using the __constant_... forms are unnecessarily verbose and
333 not preferred outside of include/uapi.
335 See: https://lore.kernel.org/lkml/1400106425.12666.6.camel@joe-AO725/
338 Usage of a deprecated RCU API is detected. It is recommended to replace
339 old flavourful RCU APIs by their new vanilla-RCU counterparts.
341 The full list of available RCU APIs can be viewed from the kernel docs.
343 See: https://www.kernel.org/doc/html/latest/RCU/whatisRCU.html#full-list-of-rcu-apis
345 **DEPRECATED_VARIABLE**
346 EXTRA_{A,C,CPP,LD}FLAGS are deprecated and should be replaced by the new
347 flags added via commit f77bf01425b1 ("kbuild: introduce ccflags-y,
348 asflags-y and ldflags-y").
350 The following conversion scheme maybe used::
352 EXTRA_AFLAGS -> asflags-y
353 EXTRA_CFLAGS -> ccflags-y
354 EXTRA_CPPFLAGS -> cppflags-y
355 EXTRA_LDFLAGS -> ldflags-y
359 1. https://lore.kernel.org/lkml/20070930191054.GA15876@uranus.ravnborg.org/
360 2. https://lore.kernel.org/lkml/1313384834-24433-12-git-send-email-lacombar@gmail.com/
361 3. https://www.kernel.org/doc/html/latest/kbuild/makefiles.html#compilation-flags
363 **DEVICE_ATTR_FUNCTIONS**
364 The function names used in DEVICE_ATTR is unusual.
365 Typically, the store and show functions are used with <attr>_store and
366 <attr>_show, where <attr> is a named attribute variable of the device.
368 Consider the following examples::
370 static DEVICE_ATTR(type, 0444, type_show, NULL);
371 static DEVICE_ATTR(power, 0644, power_show, power_store);
373 The function names should preferably follow the above pattern.
375 See: https://www.kernel.org/doc/html/latest/driver-api/driver-model/device.html#attributes
378 The DEVICE_ATTR_RO(name) helper macro can be used instead of
379 DEVICE_ATTR(name, 0444, name_show, NULL);
381 Note that the macro automatically appends _show to the named
382 attribute variable of the device for the show method.
384 See: https://www.kernel.org/doc/html/latest/driver-api/driver-model/device.html#attributes
387 The DEVICE_ATTR_RW(name) helper macro can be used instead of
388 DEVICE_ATTR(name, 0644, name_show, name_store);
390 Note that the macro automatically appends _show and _store to the
391 named attribute variable of the device for the show and store methods.
393 See: https://www.kernel.org/doc/html/latest/driver-api/driver-model/device.html#attributes
396 The DEVICE_AATR_WO(name) helper macro can be used instead of
397 DEVICE_ATTR(name, 0200, NULL, name_store);
399 Note that the macro automatically appends _store to the
400 named attribute variable of the device for the store method.
402 See: https://www.kernel.org/doc/html/latest/driver-api/driver-model/device.html#attributes
404 **DUPLICATED_SYSCTL_CONST**
405 Commit d91bff3011cf ("proc/sysctl: add shared variables for range
406 check") added some shared const variables to be used instead of a local
407 copy in each source file.
409 Consider replacing the sysctl range checking value with the shared
410 one in include/linux/sysctl.h. The following conversion scheme may
415 &int_max -> SYSCTL_INT_MAX
419 1. https://lore.kernel.org/lkml/20190430180111.10688-1-mcroce@redhat.com/
420 2. https://lore.kernel.org/lkml/20190531131422.14970-1-mcroce@redhat.com/
423 ENOSYS means that a nonexistent system call was called.
424 Earlier, it was wrongly used for things like invalid operations on
425 otherwise valid syscalls. This should be avoided in new code.
427 See: https://lore.kernel.org/lkml/5eb299021dec23c1a48fa7d9f2c8b794e967766d.1408730669.git.luto@amacapital.net/
430 ENOTSUPP is not a standard error code and should be avoided in new patches.
431 EOPNOTSUPP should be used instead.
433 See: https://lore.kernel.org/netdev/20200510182252.GA411829@lunn.ch/
436 EXPORT_SYMBOL should immediately follow the symbol to be exported.
439 in_atomic() is not for driver use so any such use is reported as an ERROR.
440 Also in_atomic() is often used to determine if sleeping is permitted,
441 but it is not reliable in this use model. Therefore its use is
442 strongly discouraged.
444 However, in_atomic() is ok for core kernel use.
446 See: https://lore.kernel.org/lkml/20080320201723.b87b3732.akpm@linux-foundation.org/
449 The lockdep_no_validate class was added as a temporary measure to
450 prevent warnings on conversion of device->sem to device->mutex.
451 It should not be used for any other purpose.
453 See: https://lore.kernel.org/lkml/1268959062.9440.467.camel@laptop/
455 **MALFORMED_INCLUDE**
456 The #include statement has a malformed path. This has happened
457 because the author has included a double slash "//" in the pathname
461 lockdep_assert_held() annotations should be preferred over
462 assertions based on spin_is_locked()
464 See: https://www.kernel.org/doc/html/latest/locking/lockdep-design.html#annotations
467 No #include statements in include/uapi should use a uapi/ path.
470 usleep_range() should be preferred over udelay(). The proper way of
471 using usleep_range() is mentioned in the kernel docs.
473 See: https://www.kernel.org/doc/html/latest/timers/timers-howto.html#delays-information-on-the-various-kernel-delay-sleep-mechanisms
479 **BLOCK_COMMENT_STYLE**
480 The comment style is incorrect. The preferred style for multi-
484 * This is the preferred style
485 * for multi line comments.
488 The networking comment style is a bit different, with the first line
489 not empty like the former::
491 /* This is the preferred comment style
492 * for files in net/ and drivers/net/
495 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#commenting
498 C99 style single line comments (//) should not be used.
499 Prefer the block comment style instead.
501 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#commenting
504 Applications of data_race() should have a comment so as to document the
505 reasoning behind why it was deemed safe.
507 See: https://lore.kernel.org/lkml/20200401101714.44781-1-elver@google.com/
509 **FSF_MAILING_ADDRESS**
510 Kernel maintainers reject new instances of the GPL boilerplate paragraph
511 directing people to write to the FSF for a copy of the GPL, since the
512 FSF has moved in the past and may do so again.
513 So do not write paragraphs about writing to the Free Software Foundation's
516 See: https://lore.kernel.org/lkml/20131006222342.GT19510@leaf/
523 The signed-off-by line does not fall in line with the standards
524 specified by the community.
526 See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#developer-s-certificate-of-origin-1-1
528 **BAD_STABLE_ADDRESS_STYLE**
529 The email format for stable is incorrect.
530 Some valid options for stable address are::
532 1. stable@vger.kernel.org
535 For adding version info, the following comment style should be used::
537 stable@vger.kernel.org # version info
539 **COMMIT_COMMENT_SYMBOL**
540 Commit log lines starting with a '#' are ignored by git as
541 comments. To solve this problem addition of a single space
542 infront of the log line is enough.
545 The patch is missing a commit description. A brief
546 description of the changes made by the patch should be added.
548 See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#describe-your-changes
551 Naming the tool that found the issue is not very useful in the
552 subject line. A good subject line summarizes the change that
555 See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#describe-your-changes
557 **FROM_SIGN_OFF_MISMATCH**
558 The author's email does not match with that in the Signed-off-by:
559 line(s). This can be sometimes caused due to an improperly configured
562 This message is emitted due to any of the following reasons::
564 - The email names do not match.
565 - The email addresses do not match.
566 - The email subaddresses do not match.
567 - The email comments do not match.
570 The patch is missing a Signed-off-by line. A signed-off-by
571 line should be added according to Developer's certificate of
574 See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#sign-your-work-the-developer-s-certificate-of-origin
576 **NO_AUTHOR_SIGN_OFF**
577 The author of the patch has not signed off the patch. It is
578 required that a simple sign off line should be present at the
579 end of explanation of the patch to denote that the author has
580 written it or otherwise has the rights to pass it on as an open
583 See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#sign-your-work-the-developer-s-certificate-of-origin
585 **DIFF_IN_COMMIT_MSG**
586 Avoid having diff content in commit message.
587 This causes problems when one tries to apply a file containing both
588 the changelog and the diff because patch(1) tries to apply the diff
589 which it found in the changelog.
591 See: https://lore.kernel.org/lkml/20150611134006.9df79a893e3636019ad2759e@linux-foundation.org/
594 To be picked up by gerrit, the footer of the commit message might
595 have a Change-Id like::
597 Change-Id: Ic8aaa0728a43936cd4c6e1ed590e01ba8f0fbf5b
598 Signed-off-by: A. U. Thor <author@example.com>
600 The Change-Id line must be removed before submitting.
603 The proper way to reference a commit id is:
604 commit <12+ chars of sha1> ("<title line>")
608 Commit e21d2170f36602ae2708 ("video: remove unnecessary
609 platform_set_drvdata()") removed the unnecessary
610 platform_set_drvdata(), but left the variable "dev" unused,
613 See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#describe-your-changes
616 The Fixes: tag is malformed or does not follow the community conventions.
617 This can occur if the tag have been split into multiple lines (e.g., when
618 pasted in an email program with word wrapping enabled).
620 See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#describe-your-changes
627 Do not use assignments in if condition.
630 if ((foo = bar(...)) < BAZ) {
632 should be written as::
638 Comparisons of A to true and false are better written
641 See: https://lore.kernel.org/lkml/1365563834.27174.12.camel@joe-AO722/
643 **COMPARISON_TO_NULL**
644 Comparisons to NULL in the form (foo == NULL) or (foo != NULL)
645 are better written as (!foo) and (foo).
647 **CONSTANT_COMPARISON**
648 Comparisons with a constant or upper case identifier on the left
649 side of the test should be avoided.
652 Indentation and Line Breaks
653 ---------------------------
656 Code indent should use tabs instead of spaces.
657 Outside of comments, documentation and Kconfig,
658 spaces are never used for indentation.
660 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#indentation
663 Indentation with 6 or more tabs usually indicate overly indented
666 It is suggested to refactor excessive indentation of
667 if/else/for/do/while/switch statements.
669 See: https://lore.kernel.org/lkml/1328311239.21255.24.camel@joe2Laptop/
671 **SWITCH_CASE_INDENT_LEVEL**
672 switch should be at the same indent as case.
692 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#indentation
695 The line has exceeded the specified maximum length.
696 To use a different maximum line length, the --max-line-length=n option
697 may be added while invoking checkpatch.
699 Earlier, the default line length was 80 columns. Commit bdc48fa11e46
700 ("checkpatch/coding-style: deprecate 80-column warning") increased the
701 limit to 100 columns. This is not a hard limit either and it's
702 preferable to stay within 80 columns whenever possible.
704 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#breaking-long-lines-and-strings
707 A string starts before but extends beyond the maximum line length.
708 To use a different maximum line length, the --max-line-length=n option
709 may be added while invoking checkpatch.
711 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#breaking-long-lines-and-strings
713 **LONG_LINE_COMMENT**
714 A comment starts before but extends beyond the maximum line length.
715 To use a different maximum line length, the --max-line-length=n option
716 may be added while invoking checkpatch.
718 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#breaking-long-lines-and-strings
721 Quoted strings that appear as messages in userspace and can be
722 grepped, should not be split across multiple lines.
724 See: https://lore.kernel.org/lkml/20120203052727.GA15035@leaf/
726 **MULTILINE_DEREFERENCE**
727 A single dereferencing identifier spanned on multiple lines like::
729 struct_identifier->member[index].
732 is generally hard to follow. It can easily lead to typos and so makes
733 the code vulnerable to bugs.
735 If fixing the multiple line dereferencing leads to an 80 column
736 violation, then either rewrite the code in a more simple way or if the
737 starting part of the dereferencing identifier is the same and used at
738 multiple places then store it in a temporary variable, and use that
739 temporary variable only at all the places. For example, if there are
740 two dereferencing identifiers::
742 member1->member2->member3.foo1;
743 member1->member2->member3.foo2;
745 then store the member1->member2->member3 part in a temporary variable.
746 It not only helps to avoid the 80 column violation but also reduces
747 the program size by removing the unnecessary dereferences.
749 But if none of the above methods work then ignore the 80 column
750 violation because it is much easier to read a dereferencing identifier
753 **TRAILING_STATEMENTS**
754 Trailing statements (for example after any conditional) should be
756 Statements, such as::
766 Macros, Attributes and Symbols
767 ------------------------------
770 The ARRAY_SIZE(foo) macro should be preferred over
771 sizeof(foo)/sizeof(foo[0]) for finding number of elements in an
774 The macro is defined in include/linux/kernel.h::
776 #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
779 Function prototypes don't need to be declared extern in .h
780 files. It's assumed by the compiler and is unnecessary.
783 Local symbol names that are prefixed with `.L` should be avoided,
784 as this has special meaning for the assembler; a symbol entry will
785 not be emitted into the symbol table. This can prevent `objtool`
786 from generating correct unwind info.
788 Symbols with STB_LOCAL binding may still be used, and `.L` prefixed
789 local symbol names are still generally usable within a function,
790 but `.L` prefixed local symbol names should not be used to denote
791 the beginning or end of code regions via
792 `SYM_CODE_START_LOCAL`/`SYM_CODE_END`
795 Defines like: 1 << <digit> could be BIT(digit).
796 The BIT() macro is defined via include/linux/bits.h::
798 #define BIT(nr) (1UL << (nr))
800 **CONST_READ_MOSTLY**
801 When a variable is tagged with the __read_mostly annotation, it is a
802 signal to the compiler that accesses to the variable will be mostly
803 reads and rarely(but NOT never) a write.
805 const __read_mostly does not make any sense as const data is already
806 read-only. The __read_mostly annotation thus should be removed.
809 It is generally desirable that building the same source code with
810 the same set of tools is reproducible, i.e. the output is always
813 The kernel does *not* use the ``__DATE__`` and ``__TIME__`` macros,
814 and enables warnings if they are used as they can lead to
815 non-deterministic builds.
817 See: https://www.kernel.org/doc/html/latest/kbuild/reproducible-builds.html#timestamps
820 The ARCH_HAS_xyz and ARCH_HAVE_xyz patterns are wrong.
822 For big conceptual features use Kconfig symbols instead. And for
823 smaller things where we have compatibility fallback functions but
824 want architectures able to override them with optimized ones, we
825 should either use weak functions (appropriate for some cases), or
826 the symbol that protects them should be the same symbol we use.
828 See: https://lore.kernel.org/lkml/CA+55aFycQ9XJvEOsiM3txHL5bjUc8CeKWJNR_H+MiicaddB42Q@mail.gmail.com/
830 **DO_WHILE_MACRO_WITH_TRAILING_SEMICOLON**
831 do {} while(0) macros should not have a trailing semicolon.
834 Const init definitions should use __initconst instead of
837 Similarly init definitions without const require a separate
841 The inline keyword should sit between storage class and type.
843 For example, the following segment::
845 inline static int example_function(void)
852 static inline int example_function(void)
858 It is possible to use section markers on variables in a way
859 which gcc doesn't understand (or at least not the way the
860 developer intended)::
862 static struct __initdata samsung_pll_clock exynos4_plls[nr_plls] = {
864 does not put exynos4_plls in the .initdata section. The __initdata
865 marker can be virtually anywhere on the line, except right after
866 "struct". The preferred location is before the "=" sign if there is
867 one, or before the trailing ";" otherwise.
869 See: https://lore.kernel.org/lkml/1377655732.3619.19.camel@joe-AO722/
871 **MULTISTATEMENT_MACRO_USE_DO_WHILE**
872 Macros with multiple statements should be enclosed in a
873 do - while block. Same should also be the case for macros
874 starting with `if` to avoid logic defects::
876 #define macrofun(a, b, c) \
882 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#macros-enums-and-rtl
884 **PREFER_FALLTHROUGH**
885 Use the `fallthrough;` pseudo keyword instead of
886 `/* fallthrough */` like comments.
888 **TRAILING_SEMICOLON**
889 Macro definition should not end with a semicolon. The macro
890 invocation style should be consistent with function calls.
891 This can prevent any unexpected code paths::
893 #define MAC do_something;
895 If this macro is used within a if else statement, like::
903 Then there would be a compilation error, because when the macro is
904 expanded there are two trailing semicolons, so the else branch gets
907 See: https://lore.kernel.org/lkml/1399671106.2912.21.camel@joe-AO725/
909 **SINGLE_STATEMENT_DO_WHILE_MACRO**
910 For the multi-statement macros, it is necessary to use the do-while
911 loop to avoid unpredictable code paths. The do-while loop helps to
912 group the multiple statements into a single one so that a
913 function-like macro can be used as a function only.
915 But for the single statement macros, it is unnecessary to use the
916 do-while loop. Although the code is syntactically correct but using
917 the do-while loop is redundant. So remove the do-while loop for single
921 Using weak declarations like __attribute__((weak)) or __weak
922 can have unintended link defects. Avoid using them.
925 Functions and Variables
926 -----------------------
929 Avoid CamelCase Identifiers.
931 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#naming
934 Using `const <type> const *` is generally meant to be
935 written `const <type> * const`.
938 Using const is generally a good idea. Checkpatch reads
939 a list of frequently used structs that are always or
940 almost always constant.
942 The existing structs list can be viewed from
943 `scripts/const_structs.checkpatch`.
945 See: https://lore.kernel.org/lkml/alpine.DEB.2.10.1608281509480.3321@hadrien/
947 **EMBEDDED_FUNCTION_NAME**
948 Embedded function names are less appropriate to use as
949 refactoring can cause function renaming. Prefer the use of
950 "%s", __func__ to embedded function names.
952 Note that this does not work with -f (--file) checkpatch option
953 as it depends on patch context providing the function name.
955 **FUNCTION_ARGUMENTS**
956 This warning is emitted due to any of the following reasons:
958 1. Arguments for the function declaration do not follow
959 the identifier name. Example::
964 This should be corrected to::
966 void foo(int bar, int baz)
968 2. Some arguments for the function definition do not
969 have an identifier name. Example::
973 All arguments should have identifier names.
975 **FUNCTION_WITHOUT_ARGS**
976 Function declarations without arguments like::
984 **GLOBAL_INITIALISERS**
985 Global variables should not be initialized explicitly to
986 0 (or NULL, false, etc.). Your compiler (or rather your
987 loader, which is responsible for zeroing out the relevant
988 sections) automatically does it for you.
990 **INITIALISED_STATIC**
991 Static variables should not be initialized explicitly to zero.
992 Your compiler (or rather your loader) automatically does
995 **MULTIPLE_ASSIGNMENTS**
996 Multiple assignments on a single line makes the code unnecessarily
997 complicated. So on a single line assign value to a single variable
998 only, this makes the code more readable and helps avoid typos.
1000 **RETURN_PARENTHESES**
1001 return is not a function and as such doesn't need parentheses::
1013 **DEVICE_ATTR_PERMS**
1014 The permissions used in DEVICE_ATTR are unusual.
1015 Typically only three permissions are used - 0644 (RW), 0444 (RO)
1018 See: https://www.kernel.org/doc/html/latest/filesystems/sysfs.html#attributes
1020 **EXECUTE_PERMISSIONS**
1021 There is no reason for source files to be executable. The executable
1022 bit can be removed safely.
1024 **EXPORTED_WORLD_WRITABLE**
1025 Exporting world writable sysfs/debugfs files is usually a bad thing.
1026 When done arbitrarily they can introduce serious security bugs.
1027 In the past, some of the debugfs vulnerabilities would seemingly allow
1028 any local user to write arbitrary values into device registers - a
1029 situation from which little good can be expected to emerge.
1031 See: https://lore.kernel.org/linux-arm-kernel/cover.1296818921.git.segoon@openwall.com/
1033 **NON_OCTAL_PERMISSIONS**
1034 Permission bits should use 4 digit octal permissions (like 0700 or 0444).
1035 Avoid using any other base like decimal.
1038 Permission bits in the octal form are more readable and easier to
1039 understand than their symbolic counterparts because many command-line
1040 tools use this notation. Experienced kernel developers have been using
1041 these traditional Unix permission bits for decades and so they find it
1042 easier to understand the octal notation than the symbolic macros.
1043 For example, it is harder to read S_IWUSR|S_IRUGO than 0644, which
1044 obscures the developer's intent rather than clarifying it.
1046 See: https://lore.kernel.org/lkml/CA+55aFw5v23T-zvDZp-MmD_EYxF8WbafwwB59934FV7g21uMGQ@mail.gmail.com/
1049 Spacing and Brackets
1050 --------------------
1052 **ASSIGNMENT_CONTINUATIONS**
1053 Assignment operators should not be written at the start of a
1054 line but should follow the operand at the previous line.
1057 The placement of braces is stylistically incorrect.
1058 The preferred way is to put the opening brace last on the line,
1059 and put the closing brace first::
1065 This applies for all non-functional blocks.
1066 However, there is one special case, namely functions: they have the
1067 opening brace at the beginning of the next line, thus::
1074 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces
1077 Whitespace before opening bracket '[' is prohibited.
1078 There are some exceptions:
1080 1. With a type on the left::
1084 2. At the beginning of a line for slice initialisers::
1088 3. Inside a curly brace::
1092 **CONCATENATED_STRING**
1093 Concatenated elements should have a space in between.
1096 printk(KERN_INFO"bar");
1100 printk(KERN_INFO "bar");
1102 **ELSE_AFTER_BRACE**
1103 `else {` should follow the closing block `}` on the same line.
1105 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces
1108 Vertical space is wasted given the limited number of lines an
1109 editor window can display when multiple blank lines are used.
1111 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces
1114 The opening brace should be following the function definitions on the
1115 next line. For any non-functional block it should be on the same line
1116 as the last construct.
1118 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces
1120 **POINTER_LOCATION**
1121 When using pointer data or a function that returns a pointer type,
1122 the preferred use of * is adjacent to the data name or function name
1123 and not adjacent to the type name.
1127 unsigned long long memparse(char *ptr, char **retptr);
1128 char *match_strdup(substring_t *s);
1130 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces
1133 Whitespace style used in the kernel sources is described in kernel docs.
1135 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces
1137 **TRAILING_WHITESPACE**
1138 Trailing whitespace should always be removed.
1139 Some editors highlight the trailing whitespace and cause visual
1140 distractions when editing files.
1142 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces
1144 **UNNECESSARY_PARENTHESES**
1145 Parentheses are not required in the following cases:
1147 1. Function pointer uses::
1155 2. Comparisons in if::
1157 if ((foo->bar) && (foo->baz))
1162 if (foo->bar && foo->baz)
1165 3. addressof/dereference single Lvalues::
1175 **WHILE_AFTER_BRACE**
1176 while should follow the closing bracket on the same line::
1182 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces
1188 **CONFIG_DESCRIPTION**
1189 Kconfig symbols should have a help text which fully describes
1193 The patch seems to be corrupted or lines are wrapped.
1194 Please regenerate the patch file before sending it to the maintainer.
1197 Since linux moved to git, the CVS markers are no longer used.
1198 So, CVS style keywords ($Id$, $Revision$, $Log$) should not be
1201 **DEFAULT_NO_BREAK**
1202 switch default case is sometimes written as "default:;". This can
1203 cause new cases added below default to be defective.
1205 A "break;" should be added after empty default statement to avoid
1206 unwanted fallthrough.
1208 **DOS_LINE_ENDINGS**
1209 For DOS-formatted patches, there are extra ^M symbols at the end of
1210 the line. These should be removed.
1212 **DT_SCHEMA_BINDING_PATCH**
1213 DT bindings moved to a json-schema based format instead of
1216 See: https://www.kernel.org/doc/html/latest/devicetree/bindings/writing-schema.html
1218 **DT_SPLIT_BINDING_PATCH**
1219 Devicetree bindings should be their own patch. This is because
1220 bindings are logically independent from a driver implementation,
1221 they have a different maintainer (even though they often
1222 are applied via the same tree), and it makes for a cleaner history in the
1223 DT only tree created with git-filter-branch.
1225 See: https://www.kernel.org/doc/html/latest/devicetree/bindings/submitting-patches.html#i-for-patch-submitters
1227 **EMBEDDED_FILENAME**
1228 Embedding the complete filename path inside the file isn't particularly
1229 useful as often the path is moved around and becomes incorrect.
1231 **FILE_PATH_CHANGES**
1232 Whenever files are added, moved, or deleted, the MAINTAINERS file
1233 patterns can be out of sync or outdated.
1235 So MAINTAINERS might need updating in these cases.
1238 The memset use appears to be incorrect. This may be caused due to
1239 badly ordered parameters. Please recheck the usage.
1241 **NOT_UNIFIED_DIFF**
1242 The patch file does not appear to be in unified-diff format. Please
1243 regenerate the patch file before sending it to the maintainer.
1245 **PRINTF_0XDECIMAL**
1246 Prefixing 0x with decimal output is defective and should be corrected.
1248 **SPDX_LICENSE_TAG**
1249 The source file is missing or has an improper SPDX identifier tag.
1250 The Linux kernel requires the precise SPDX identifier in all source files,
1251 and it is thoroughly documented in the kernel docs.
1253 See: https://www.kernel.org/doc/html/latest/process/license-rules.html
1256 Some words may have been misspelled. Consider reviewing them.