1.. SPDX-License-Identifier: GPL-2.0-only 2 3========== 4Checkpatch 5========== 6 7Checkpatch (scripts/checkpatch.pl) is a perl script which checks for trivial 8style violations in patches and optionally corrects them. Checkpatch can 9also be run on file contexts and without the kernel tree. 10 11Checkpatch is not always right. Your judgement takes precedence over checkpatch 12messages. If your code looks better with the violations, then its probably 13best left alone. 14 15 16Options 17======= 18 19This section will describe the options checkpatch can be run with. 20 21Usage:: 22 23 ./scripts/checkpatch.pl [OPTION]... [FILE]... 24 25Available options: 26 27 - -q, --quiet 28 29 Enable quiet mode. 30 31 - -v, --verbose 32 Enable verbose mode. Additional verbose test descriptions are output 33 so as to provide information on why that particular message is shown. 34 35 - --no-tree 36 37 Run checkpatch without the kernel tree. 38 39 - --no-signoff 40 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. 44 45 Example:: 46 47 Signed-off-by: Random J Developer <random@developer.example.org> 48 49 Setting this flag effectively stops a message for a missing signed-off-by 50 line in a patch context. 51 52 - --patch 53 54 Treat FILE as a patch. This is the default option and need not be 55 explicitly specified. 56 57 - --emacs 58 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 61 patch. 62 63 - --terse 64 65 Output only one line per report. 66 67 - --showfile 68 69 Show the diffed file position instead of the input file position. 70 71 - -g, --git 72 73 Treat FILE as a single commit or a git revision range. 74 75 Single commit with: 76 77 - <rev> 78 - <rev>^ 79 - <rev>~n 80 81 Multiple commits with: 82 83 - <rev1>..<rev2> 84 - <rev1>...<rev2> 85 - <rev>-<count> 86 87 - -f, --file 88 89 Treat FILE as a regular source file. This option must be used when running 90 checkpatch on source files in the kernel. 91 92 - --subjective, --strict 93 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. 96 97 - --list-types 98 99 Every message emitted by checkpatch has an associated TYPE. Add this flag 100 to display all the types in checkpatch. 101 102 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. 104 105 - --types TYPE(,TYPE2...) 106 107 Only display messages with the given types. 108 109 Example:: 110 111 ./scripts/checkpatch.pl mypatch.patch --types EMAIL_SUBJECT,BRACES 112 113 - --ignore TYPE(,TYPE2...) 114 115 Checkpatch will not emit messages for the specified types. 116 117 Example:: 118 119 ./scripts/checkpatch.pl mypatch.patch --ignore EMAIL_SUBJECT,BRACES 120 121 - --show-types 122 123 By default checkpatch doesn't display the type associated with the messages. 124 Set this flag to show the message type in the output. 125 126 - --max-line-length=n 127 128 Set the max line length (default 100). If a line exceeds the specified 129 length, a LONG_LINE message is emitted. 130 131 132 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. 135 136 - --min-conf-desc-length=n 137 138 Set the Kconfig entry minimum description length, if shorter, warn. 139 140 - --tab-size=n 141 142 Set the number of spaces for tab (default 8). 143 144 - --root=PATH 145 146 PATH to the kernel tree root. 147 148 This option must be specified when invoking checkpatch from outside 149 the kernel root. 150 151 - --no-summary 152 153 Suppress the per file summary. 154 155 - --mailback 156 157 Only produce a report in case of Warnings or Errors. Milder Checks are 158 excluded from this. 159 160 - --summary-file 161 162 Include the filename in summary. 163 164 - --debug KEY=[0|1] 165 166 Turn on/off debugging of KEY, where KEY is one of 'values', 'possible', 167 'type', and 'attr' (default is all off). 168 169 - --fix 170 171 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. 174 175 - --fix-inplace 176 177 EXPERIMENTAL - Similar to --fix but input file is overwritten with fixes. 178 179 DO NOT USE this flag unless you are absolutely sure and you have a backup 180 in place. 181 182 - --ignore-perl-version 183 184 Override checking of perl version. Runtime errors maybe encountered after 185 enabling this flag if the perl version does not meet the minimum specified. 186 187 - --codespell 188 189 Use the codespell dictionary for checking spelling errors. 190 191 - --codespellfile 192 193 Use the specified codespell file. 194 Default is '/usr/share/codespell/dictionary.txt'. 195 196 - --typedefsfile 197 198 Read additional types from this file. 199 200 - --color[=WHEN] 201 202 Use colors 'always', 'never', or only when output is a terminal ('auto'). 203 Default is 'auto'. 204 205 - --kconfig-prefix=WORD 206 207 Use WORD as a prefix for Kconfig symbols (default is `CONFIG_`). 208 209 - -h, --help, --version 210 211 Display the help text. 212 213Message Levels 214============== 215 216Messages in checkpatch are divided into three levels. The levels of messages 217in checkpatch denote the severity of the error. They are: 218 219 - ERROR 220 221 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. 223 224 - WARNING 225 226 This is the next stricter level. Messages of type WARNING requires a 227 more careful review. But it is milder than an ERROR. 228 229 - CHECK 230 231 This is the mildest level. These are things which may require some thought. 232 233Type Descriptions 234================= 235 236This section contains a description of all the message types in checkpatch. 237 238.. Types in this section are also parsed by checkpatch. 239.. The types are grouped into subsections based on use. 240 241 242Allocation style 243---------------- 244 245 **ALLOC_ARRAY_ARGS** 246 The first argument for kcalloc or kmalloc_array should be the 247 number of elements. sizeof() as the first argument is generally 248 wrong. 249 250 See: https://www.kernel.org/doc/html/latest/core-api/memory-allocation.html 251 252 **ALLOC_SIZEOF_STRUCT** 253 The allocation style is bad. In general for family of 254 allocation functions using sizeof() to get memory size, 255 constructs like:: 256 257 p = alloc(sizeof(struct foo), ...) 258 259 should be:: 260 261 p = alloc(sizeof(*p), ...) 262 263 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#allocating-memory 264 265 **ALLOC_WITH_MULTIPLY** 266 Prefer kmalloc_array/kcalloc over kmalloc/kzalloc with a 267 sizeof multiply. 268 269 See: https://www.kernel.org/doc/html/latest/core-api/memory-allocation.html 270 271 272API usage 273--------- 274 275 **ARCH_DEFINES** 276 Architecture specific defines should be avoided wherever 277 possible. 278 279 **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/. 284 285 **AVOID_BUG** 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. 289 290 See: https://www.kernel.org/doc/html/latest/process/deprecated.html#bug-and-bug-on 291 292 **CONSIDER_KSTRTO** 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. 298 299 See: https://www.kernel.org/doc/html/latest/process/deprecated.html#simple-strtol-simple-strtoll-simple-strtoul-simple-strtoull 300 301 **CONSTANT_CONVERSION** 302 Use of __constant_<foo> form is discouraged for the following functions:: 303 304 __constant_cpu_to_be[x] 305 __constant_cpu_to_le[x] 306 __constant_be[x]_to_cpu 307 __constant_le[x]_to_cpu 308 __constant_htons 309 __constant_ntohs 310 311 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 313 constant. 314 315 In big endian systems, the macros like __constant_cpu_to_be32(x) and 316 cpu_to_be32(x) expand to the same expression:: 317 318 #define __constant_cpu_to_be32(x) ((__force __be32)(__u32)(x)) 319 #define __cpu_to_be32(x) ((__force __be32)(__u32)(x)) 320 321 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:: 324 325 #define __swab32(x) \ 326 (__builtin_constant_p((__u32)(x)) ? \ 327 ___constant_swab32(x) : \ 328 __fswab32(x)) 329 330 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. 334 335 See: https://lore.kernel.org/lkml/1400106425.12666.6.camel@joe-AO725/ 336 337 **DEPRECATED_API** 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. 340 341 The full list of available RCU APIs can be viewed from the kernel docs. 342 343 See: https://www.kernel.org/doc/html/latest/RCU/whatisRCU.html#full-list-of-rcu-apis 344 345 **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"). 349 350 The following conversion scheme maybe used:: 351 352 EXTRA_AFLAGS -> asflags-y 353 EXTRA_CFLAGS -> ccflags-y 354 EXTRA_CPPFLAGS -> cppflags-y 355 EXTRA_LDFLAGS -> ldflags-y 356 357 See: 358 359 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 362 363 **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. 367 368 Consider the following examples:: 369 370 static DEVICE_ATTR(type, 0444, type_show, NULL); 371 static DEVICE_ATTR(power, 0644, power_show, power_store); 372 373 The function names should preferably follow the above pattern. 374 375 See: https://www.kernel.org/doc/html/latest/driver-api/driver-model/device.html#attributes 376 377 **DEVICE_ATTR_RO** 378 The DEVICE_ATTR_RO(name) helper macro can be used instead of 379 DEVICE_ATTR(name, 0444, name_show, NULL); 380 381 Note that the macro automatically appends _show to the named 382 attribute variable of the device for the show method. 383 384 See: https://www.kernel.org/doc/html/latest/driver-api/driver-model/device.html#attributes 385 386 **DEVICE_ATTR_RW** 387 The DEVICE_ATTR_RW(name) helper macro can be used instead of 388 DEVICE_ATTR(name, 0644, name_show, name_store); 389 390 Note that the macro automatically appends _show and _store to the 391 named attribute variable of the device for the show and store methods. 392 393 See: https://www.kernel.org/doc/html/latest/driver-api/driver-model/device.html#attributes 394 395 **DEVICE_ATTR_WO** 396 The DEVICE_AATR_WO(name) helper macro can be used instead of 397 DEVICE_ATTR(name, 0200, NULL, name_store); 398 399 Note that the macro automatically appends _store to the 400 named attribute variable of the device for the store method. 401 402 See: https://www.kernel.org/doc/html/latest/driver-api/driver-model/device.html#attributes 403 404 **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. 408 409 Consider replacing the sysctl range checking value with the shared 410 one in include/linux/sysctl.h. The following conversion scheme may 411 be used:: 412 413 &zero -> SYSCTL_ZERO 414 &one -> SYSCTL_ONE 415 &int_max -> SYSCTL_INT_MAX 416 417 See: 418 419 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/ 421 422 **ENOSYS** 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. 426 427 See: https://lore.kernel.org/lkml/5eb299021dec23c1a48fa7d9f2c8b794e967766d.1408730669.git.luto@amacapital.net/ 428 429 **ENOTSUPP** 430 ENOTSUPP is not a standard error code and should be avoided in new patches. 431 EOPNOTSUPP should be used instead. 432 433 See: https://lore.kernel.org/netdev/20200510182252.GA411829@lunn.ch/ 434 435 **EXPORT_SYMBOL** 436 EXPORT_SYMBOL should immediately follow the symbol to be exported. 437 438 **IN_ATOMIC** 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. 443 444 However, in_atomic() is ok for core kernel use. 445 446 See: https://lore.kernel.org/lkml/20080320201723.b87b3732.akpm@linux-foundation.org/ 447 448 **LOCKDEP** 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. 452 453 See: https://lore.kernel.org/lkml/1268959062.9440.467.camel@laptop/ 454 455 **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 458 accidentally. 459 460 **USE_LOCKDEP** 461 lockdep_assert_held() annotations should be preferred over 462 assertions based on spin_is_locked() 463 464 See: https://www.kernel.org/doc/html/latest/locking/lockdep-design.html#annotations 465 466 **UAPI_INCLUDE** 467 No #include statements in include/uapi should use a uapi/ path. 468 469 **USLEEP_RANGE** 470 usleep_range() should be preferred over udelay(). The proper way of 471 using usleep_range() is mentioned in the kernel docs. 472 473 See: https://www.kernel.org/doc/html/latest/timers/timers-howto.html#delays-information-on-the-various-kernel-delay-sleep-mechanisms 474 475 476Comments 477-------- 478 479 **BLOCK_COMMENT_STYLE** 480 The comment style is incorrect. The preferred style for multi- 481 line comments is:: 482 483 /* 484 * This is the preferred style 485 * for multi line comments. 486 */ 487 488 The networking comment style is a bit different, with the first line 489 not empty like the former:: 490 491 /* This is the preferred comment style 492 * for files in net/ and drivers/net/ 493 */ 494 495 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#commenting 496 497 **C99_COMMENTS** 498 C99 style single line comments (//) should not be used. 499 Prefer the block comment style instead. 500 501 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#commenting 502 503 **DATA_RACE** 504 Applications of data_race() should have a comment so as to document the 505 reasoning behind why it was deemed safe. 506 507 See: https://lore.kernel.org/lkml/20200401101714.44781-1-elver@google.com/ 508 509 **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 514 mailing address. 515 516 See: https://lore.kernel.org/lkml/20131006222342.GT19510@leaf/ 517 518 519Commit message 520-------------- 521 522 **BAD_SIGN_OFF** 523 The signed-off-by line does not fall in line with the standards 524 specified by the community. 525 526 See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#developer-s-certificate-of-origin-1-1 527 528 **BAD_STABLE_ADDRESS_STYLE** 529 The email format for stable is incorrect. 530 Some valid options for stable address are:: 531 532 1. stable@vger.kernel.org 533 2. stable@kernel.org 534 535 For adding version info, the following comment style should be used:: 536 537 stable@vger.kernel.org # version info 538 539 **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. 543 544 **COMMIT_MESSAGE** 545 The patch is missing a commit description. A brief 546 description of the changes made by the patch should be added. 547 548 See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#describe-your-changes 549 550 **EMAIL_SUBJECT** 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 553 the patch brings. 554 555 See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#describe-your-changes 556 557 **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 560 email client. 561 562 This message is emitted due to any of the following reasons:: 563 564 - 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. 568 569 **MISSING_SIGN_OFF** 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 572 Origin. 573 574 See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#sign-your-work-the-developer-s-certificate-of-origin 575 576 **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 581 source patch. 582 583 See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#sign-your-work-the-developer-s-certificate-of-origin 584 585 **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. 590 591 See: https://lore.kernel.org/lkml/20150611134006.9df79a893e3636019ad2759e@linux-foundation.org/ 592 593 **GERRIT_CHANGE_ID** 594 To be picked up by gerrit, the footer of the commit message might 595 have a Change-Id like:: 596 597 Change-Id: Ic8aaa0728a43936cd4c6e1ed590e01ba8f0fbf5b 598 Signed-off-by: A. U. Thor <author@example.com> 599 600 The Change-Id line must be removed before submitting. 601 602 **GIT_COMMIT_ID** 603 The proper way to reference a commit id is: 604 commit <12+ chars of sha1> ("<title line>") 605 606 An example may be:: 607 608 Commit e21d2170f36602ae2708 ("video: remove unnecessary 609 platform_set_drvdata()") removed the unnecessary 610 platform_set_drvdata(), but left the variable "dev" unused, 611 delete it. 612 613 See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#describe-your-changes 614 615 **BAD_FIXES_TAG** 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). 619 620 See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#describe-your-changes 621 622 623Comparison style 624---------------- 625 626 **ASSIGN_IN_IF** 627 Do not use assignments in if condition. 628 Example:: 629 630 if ((foo = bar(...)) < BAZ) { 631 632 should be written as:: 633 634 foo = bar(...); 635 if (foo < BAZ) { 636 637 **BOOL_COMPARISON** 638 Comparisons of A to true and false are better written 639 as A and !A. 640 641 See: https://lore.kernel.org/lkml/1365563834.27174.12.camel@joe-AO722/ 642 643 **COMPARISON_TO_NULL** 644 Comparisons to NULL in the form (foo == NULL) or (foo != NULL) 645 are better written as (!foo) and (foo). 646 647 **CONSTANT_COMPARISON** 648 Comparisons with a constant or upper case identifier on the left 649 side of the test should be avoided. 650 651 652Indentation and Line Breaks 653--------------------------- 654 655 **CODE_INDENT** 656 Code indent should use tabs instead of spaces. 657 Outside of comments, documentation and Kconfig, 658 spaces are never used for indentation. 659 660 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#indentation 661 662 **DEEP_INDENTATION** 663 Indentation with 6 or more tabs usually indicate overly indented 664 code. 665 666 It is suggested to refactor excessive indentation of 667 if/else/for/do/while/switch statements. 668 669 See: https://lore.kernel.org/lkml/1328311239.21255.24.camel@joe2Laptop/ 670 671 **SWITCH_CASE_INDENT_LEVEL** 672 switch should be at the same indent as case. 673 Example:: 674 675 switch (suffix) { 676 case 'G': 677 case 'g': 678 mem <<= 30; 679 break; 680 case 'M': 681 case 'm': 682 mem <<= 20; 683 break; 684 case 'K': 685 case 'k': 686 mem <<= 10; 687 fallthrough; 688 default: 689 break; 690 } 691 692 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#indentation 693 694 **LONG_LINE** 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. 698 699 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. 703 704 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#breaking-long-lines-and-strings 705 706 **LONG_LINE_STRING** 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. 710 711 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#breaking-long-lines-and-strings 712 713 **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. 717 718 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#breaking-long-lines-and-strings 719 720 **SPLIT_STRING** 721 Quoted strings that appear as messages in userspace and can be 722 grepped, should not be split across multiple lines. 723 724 See: https://lore.kernel.org/lkml/20120203052727.GA15035@leaf/ 725 726 **MULTILINE_DEREFERENCE** 727 A single dereferencing identifier spanned on multiple lines like:: 728 729 struct_identifier->member[index]. 730 member = <foo>; 731 732 is generally hard to follow. It can easily lead to typos and so makes 733 the code vulnerable to bugs. 734 735 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:: 741 742 member1->member2->member3.foo1; 743 member1->member2->member3.foo2; 744 745 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. 748 749 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 751 on a single line. 752 753 **TRAILING_STATEMENTS** 754 Trailing statements (for example after any conditional) should be 755 on the next line. 756 Statements, such as:: 757 758 if (x == y) break; 759 760 should be:: 761 762 if (x == y) 763 break; 764 765 766Macros, Attributes and Symbols 767------------------------------ 768 769 **ARRAY_SIZE** 770 The ARRAY_SIZE(foo) macro should be preferred over 771 sizeof(foo)/sizeof(foo[0]) for finding number of elements in an 772 array. 773 774 The macro is defined in include/linux/kernel.h:: 775 776 #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0])) 777 778 **AVOID_EXTERNS** 779 Function prototypes don't need to be declared extern in .h 780 files. It's assumed by the compiler and is unnecessary. 781 782 **AVOID_L_PREFIX** 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. 787 788 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` 793 794 **BIT_MACRO** 795 Defines like: 1 << <digit> could be BIT(digit). 796 The BIT() macro is defined via include/linux/bits.h:: 797 798 #define BIT(nr) (1UL << (nr)) 799 800 **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. 804 805 const __read_mostly does not make any sense as const data is already 806 read-only. The __read_mostly annotation thus should be removed. 807 808 **DATE_TIME** 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 811 exactly the same. 812 813 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. 816 817 See: https://www.kernel.org/doc/html/latest/kbuild/reproducible-builds.html#timestamps 818 819 **DEFINE_ARCH_HAS** 820 The ARCH_HAS_xyz and ARCH_HAVE_xyz patterns are wrong. 821 822 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. 827 828 See: https://lore.kernel.org/lkml/CA+55aFycQ9XJvEOsiM3txHL5bjUc8CeKWJNR_H+MiicaddB42Q@mail.gmail.com/ 829 830 **DO_WHILE_MACRO_WITH_TRAILING_SEMICOLON** 831 do {} while(0) macros should not have a trailing semicolon. 832 833 **INIT_ATTRIBUTE** 834 Const init definitions should use __initconst instead of 835 __initdata. 836 837 Similarly init definitions without const require a separate 838 use of const. 839 840 **INLINE_LOCATION** 841 The inline keyword should sit between storage class and type. 842 843 For example, the following segment:: 844 845 inline static int example_function(void) 846 { 847 ... 848 } 849 850 should be:: 851 852 static inline int example_function(void) 853 { 854 ... 855 } 856 857 **MISPLACED_INIT** 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):: 861 862 static struct __initdata samsung_pll_clock exynos4_plls[nr_plls] = { 863 864 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. 868 869 See: https://lore.kernel.org/lkml/1377655732.3619.19.camel@joe-AO722/ 870 871 **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:: 875 876 #define macrofun(a, b, c) \ 877 do { \ 878 if (a == 5) \ 879 do_this(b, c); \ 880 } while (0) 881 882 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#macros-enums-and-rtl 883 884 **PREFER_FALLTHROUGH** 885 Use the `fallthrough;` pseudo keyword instead of 886 `/* fallthrough */` like comments. 887 888 **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:: 892 893 #define MAC do_something; 894 895 If this macro is used within a if else statement, like:: 896 897 if (some_condition) 898 MAC; 899 900 else 901 do_something; 902 903 Then there would be a compilation error, because when the macro is 904 expanded there are two trailing semicolons, so the else branch gets 905 orphaned. 906 907 See: https://lore.kernel.org/lkml/1399671106.2912.21.camel@joe-AO725/ 908 909 **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. 914 915 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 918 statement macros. 919 920 **WEAK_DECLARATION** 921 Using weak declarations like __attribute__((weak)) or __weak 922 can have unintended link defects. Avoid using them. 923 924 925Functions and Variables 926----------------------- 927 928 **CAMELCASE** 929 Avoid CamelCase Identifiers. 930 931 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#naming 932 933 **CONST_CONST** 934 Using `const <type> const *` is generally meant to be 935 written `const <type> * const`. 936 937 **CONST_STRUCT** 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. 941 942 The existing structs list can be viewed from 943 `scripts/const_structs.checkpatch`. 944 945 See: https://lore.kernel.org/lkml/alpine.DEB.2.10.1608281509480.3321@hadrien/ 946 947 **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. 951 952 Note that this does not work with -f (--file) checkpatch option 953 as it depends on patch context providing the function name. 954 955 **FUNCTION_ARGUMENTS** 956 This warning is emitted due to any of the following reasons: 957 958 1. Arguments for the function declaration do not follow 959 the identifier name. Example:: 960 961 void foo 962 (int bar, int baz) 963 964 This should be corrected to:: 965 966 void foo(int bar, int baz) 967 968 2. Some arguments for the function definition do not 969 have an identifier name. Example:: 970 971 void foo(int) 972 973 All arguments should have identifier names. 974 975 **FUNCTION_WITHOUT_ARGS** 976 Function declarations without arguments like:: 977 978 int foo() 979 980 should be:: 981 982 int foo(void) 983 984 **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. 989 990 **INITIALISED_STATIC** 991 Static variables should not be initialized explicitly to zero. 992 Your compiler (or rather your loader) automatically does 993 it for you. 994 995 **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. 999 1000 **RETURN_PARENTHESES** 1001 return is not a function and as such doesn't need parentheses:: 1002 1003 return (bar); 1004 1005 can simply be:: 1006 1007 return bar; 1008 1009 1010Permissions 1011----------- 1012 1013 **DEVICE_ATTR_PERMS** 1014 The permissions used in DEVICE_ATTR are unusual. 1015 Typically only three permissions are used - 0644 (RW), 0444 (RO) 1016 and 0200 (WO). 1017 1018 See: https://www.kernel.org/doc/html/latest/filesystems/sysfs.html#attributes 1019 1020 **EXECUTE_PERMISSIONS** 1021 There is no reason for source files to be executable. The executable 1022 bit can be removed safely. 1023 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. 1030 1031 See: https://lore.kernel.org/linux-arm-kernel/cover.1296818921.git.segoon@openwall.com/ 1032 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. 1036 1037 **SYMBOLIC_PERMS** 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. 1045 1046 See: https://lore.kernel.org/lkml/CA+55aFw5v23T-zvDZp-MmD_EYxF8WbafwwB59934FV7g21uMGQ@mail.gmail.com/ 1047 1048 1049Spacing and Brackets 1050-------------------- 1051 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. 1055 1056 **BRACES** 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:: 1060 1061 if (x is true) { 1062 we do y 1063 } 1064 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:: 1068 1069 int function(int x) 1070 { 1071 body of function 1072 } 1073 1074 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces 1075 1076 **BRACKET_SPACE** 1077 Whitespace before opening bracket '[' is prohibited. 1078 There are some exceptions: 1079 1080 1. With a type on the left:: 1081 1082 int [] a; 1083 1084 2. At the beginning of a line for slice initialisers:: 1085 1086 [0...10] = 5, 1087 1088 3. Inside a curly brace:: 1089 1090 = { [0...10] = 5 } 1091 1092 **CONCATENATED_STRING** 1093 Concatenated elements should have a space in between. 1094 Example:: 1095 1096 printk(KERN_INFO"bar"); 1097 1098 should be:: 1099 1100 printk(KERN_INFO "bar"); 1101 1102 **ELSE_AFTER_BRACE** 1103 `else {` should follow the closing block `}` on the same line. 1104 1105 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces 1106 1107 **LINE_SPACING** 1108 Vertical space is wasted given the limited number of lines an 1109 editor window can display when multiple blank lines are used. 1110 1111 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces 1112 1113 **OPEN_BRACE** 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. 1117 1118 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces 1119 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. 1124 Examples:: 1125 1126 char *linux_banner; 1127 unsigned long long memparse(char *ptr, char **retptr); 1128 char *match_strdup(substring_t *s); 1129 1130 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces 1131 1132 **SPACING** 1133 Whitespace style used in the kernel sources is described in kernel docs. 1134 1135 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces 1136 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. 1141 1142 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces 1143 1144 **UNNECESSARY_PARENTHESES** 1145 Parentheses are not required in the following cases: 1146 1147 1. Function pointer uses:: 1148 1149 (foo->bar)(); 1150 1151 could be:: 1152 1153 foo->bar(); 1154 1155 2. Comparisons in if:: 1156 1157 if ((foo->bar) && (foo->baz)) 1158 if ((foo == bar)) 1159 1160 could be:: 1161 1162 if (foo->bar && foo->baz) 1163 if (foo == bar) 1164 1165 3. addressof/dereference single Lvalues:: 1166 1167 &(foo->bar) 1168 *(foo->bar) 1169 1170 could be:: 1171 1172 &foo->bar 1173 *foo->bar 1174 1175 **WHILE_AFTER_BRACE** 1176 while should follow the closing bracket on the same line:: 1177 1178 do { 1179 ... 1180 } while(something); 1181 1182 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces 1183 1184 1185Others 1186------ 1187 1188 **CONFIG_DESCRIPTION** 1189 Kconfig symbols should have a help text which fully describes 1190 it. 1191 1192 **CORRUPTED_PATCH** 1193 The patch seems to be corrupted or lines are wrapped. 1194 Please regenerate the patch file before sending it to the maintainer. 1195 1196 **CVS_KEYWORD** 1197 Since linux moved to git, the CVS markers are no longer used. 1198 So, CVS style keywords ($Id$, $Revision$, $Log$) should not be 1199 added. 1200 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. 1204 1205 A "break;" should be added after empty default statement to avoid 1206 unwanted fallthrough. 1207 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. 1211 1212 **DT_SCHEMA_BINDING_PATCH** 1213 DT bindings moved to a json-schema based format instead of 1214 freeform text. 1215 1216 See: https://www.kernel.org/doc/html/latest/devicetree/bindings/writing-schema.html 1217 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. 1224 1225 See: https://www.kernel.org/doc/html/latest/devicetree/bindings/submitting-patches.html#i-for-patch-submitters 1226 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. 1230 1231 **FILE_PATH_CHANGES** 1232 Whenever files are added, moved, or deleted, the MAINTAINERS file 1233 patterns can be out of sync or outdated. 1234 1235 So MAINTAINERS might need updating in these cases. 1236 1237 **MEMSET** 1238 The memset use appears to be incorrect. This may be caused due to 1239 badly ordered parameters. Please recheck the usage. 1240 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. 1244 1245 **PRINTF_0XDECIMAL** 1246 Prefixing 0x with decimal output is defective and should be corrected. 1247 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. 1252 1253 See: https://www.kernel.org/doc/html/latest/process/license-rules.html 1254 1255 **TYPO_SPELLING** 1256 Some words may have been misspelled. Consider reviewing them. 1257