checkpatch.rst (40137B)
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 616Comparison style 617---------------- 618 619 **ASSIGN_IN_IF** 620 Do not use assignments in if condition. 621 Example:: 622 623 if ((foo = bar(...)) < BAZ) { 624 625 should be written as:: 626 627 foo = bar(...); 628 if (foo < BAZ) { 629 630 **BOOL_COMPARISON** 631 Comparisons of A to true and false are better written 632 as A and !A. 633 634 See: https://lore.kernel.org/lkml/1365563834.27174.12.camel@joe-AO722/ 635 636 **COMPARISON_TO_NULL** 637 Comparisons to NULL in the form (foo == NULL) or (foo != NULL) 638 are better written as (!foo) and (foo). 639 640 **CONSTANT_COMPARISON** 641 Comparisons with a constant or upper case identifier on the left 642 side of the test should be avoided. 643 644 645Indentation and Line Breaks 646--------------------------- 647 648 **CODE_INDENT** 649 Code indent should use tabs instead of spaces. 650 Outside of comments, documentation and Kconfig, 651 spaces are never used for indentation. 652 653 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#indentation 654 655 **DEEP_INDENTATION** 656 Indentation with 6 or more tabs usually indicate overly indented 657 code. 658 659 It is suggested to refactor excessive indentation of 660 if/else/for/do/while/switch statements. 661 662 See: https://lore.kernel.org/lkml/1328311239.21255.24.camel@joe2Laptop/ 663 664 **SWITCH_CASE_INDENT_LEVEL** 665 switch should be at the same indent as case. 666 Example:: 667 668 switch (suffix) { 669 case 'G': 670 case 'g': 671 mem <<= 30; 672 break; 673 case 'M': 674 case 'm': 675 mem <<= 20; 676 break; 677 case 'K': 678 case 'k': 679 mem <<= 10; 680 fallthrough; 681 default: 682 break; 683 } 684 685 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#indentation 686 687 **LONG_LINE** 688 The line has exceeded the specified maximum length. 689 To use a different maximum line length, the --max-line-length=n option 690 may be added while invoking checkpatch. 691 692 Earlier, the default line length was 80 columns. Commit bdc48fa11e46 693 ("checkpatch/coding-style: deprecate 80-column warning") increased the 694 limit to 100 columns. This is not a hard limit either and it's 695 preferable to stay within 80 columns whenever possible. 696 697 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#breaking-long-lines-and-strings 698 699 **LONG_LINE_STRING** 700 A string starts before but extends beyond the maximum line length. 701 To use a different maximum line length, the --max-line-length=n option 702 may be added while invoking checkpatch. 703 704 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#breaking-long-lines-and-strings 705 706 **LONG_LINE_COMMENT** 707 A comment 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 **SPLIT_STRING** 714 Quoted strings that appear as messages in userspace and can be 715 grepped, should not be split across multiple lines. 716 717 See: https://lore.kernel.org/lkml/20120203052727.GA15035@leaf/ 718 719 **MULTILINE_DEREFERENCE** 720 A single dereferencing identifier spanned on multiple lines like:: 721 722 struct_identifier->member[index]. 723 member = <foo>; 724 725 is generally hard to follow. It can easily lead to typos and so makes 726 the code vulnerable to bugs. 727 728 If fixing the multiple line dereferencing leads to an 80 column 729 violation, then either rewrite the code in a more simple way or if the 730 starting part of the dereferencing identifier is the same and used at 731 multiple places then store it in a temporary variable, and use that 732 temporary variable only at all the places. For example, if there are 733 two dereferencing identifiers:: 734 735 member1->member2->member3.foo1; 736 member1->member2->member3.foo2; 737 738 then store the member1->member2->member3 part in a temporary variable. 739 It not only helps to avoid the 80 column violation but also reduces 740 the program size by removing the unnecessary dereferences. 741 742 But if none of the above methods work then ignore the 80 column 743 violation because it is much easier to read a dereferencing identifier 744 on a single line. 745 746 **TRAILING_STATEMENTS** 747 Trailing statements (for example after any conditional) should be 748 on the next line. 749 Statements, such as:: 750 751 if (x == y) break; 752 753 should be:: 754 755 if (x == y) 756 break; 757 758 759Macros, Attributes and Symbols 760------------------------------ 761 762 **ARRAY_SIZE** 763 The ARRAY_SIZE(foo) macro should be preferred over 764 sizeof(foo)/sizeof(foo[0]) for finding number of elements in an 765 array. 766 767 The macro is defined in include/linux/kernel.h:: 768 769 #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0])) 770 771 **AVOID_EXTERNS** 772 Function prototypes don't need to be declared extern in .h 773 files. It's assumed by the compiler and is unnecessary. 774 775 **AVOID_L_PREFIX** 776 Local symbol names that are prefixed with `.L` should be avoided, 777 as this has special meaning for the assembler; a symbol entry will 778 not be emitted into the symbol table. This can prevent `objtool` 779 from generating correct unwind info. 780 781 Symbols with STB_LOCAL binding may still be used, and `.L` prefixed 782 local symbol names are still generally usable within a function, 783 but `.L` prefixed local symbol names should not be used to denote 784 the beginning or end of code regions via 785 `SYM_CODE_START_LOCAL`/`SYM_CODE_END` 786 787 **BIT_MACRO** 788 Defines like: 1 << <digit> could be BIT(digit). 789 The BIT() macro is defined via include/linux/bits.h:: 790 791 #define BIT(nr) (1UL << (nr)) 792 793 **CONST_READ_MOSTLY** 794 When a variable is tagged with the __read_mostly annotation, it is a 795 signal to the compiler that accesses to the variable will be mostly 796 reads and rarely(but NOT never) a write. 797 798 const __read_mostly does not make any sense as const data is already 799 read-only. The __read_mostly annotation thus should be removed. 800 801 **DATE_TIME** 802 It is generally desirable that building the same source code with 803 the same set of tools is reproducible, i.e. the output is always 804 exactly the same. 805 806 The kernel does *not* use the ``__DATE__`` and ``__TIME__`` macros, 807 and enables warnings if they are used as they can lead to 808 non-deterministic builds. 809 810 See: https://www.kernel.org/doc/html/latest/kbuild/reproducible-builds.html#timestamps 811 812 **DEFINE_ARCH_HAS** 813 The ARCH_HAS_xyz and ARCH_HAVE_xyz patterns are wrong. 814 815 For big conceptual features use Kconfig symbols instead. And for 816 smaller things where we have compatibility fallback functions but 817 want architectures able to override them with optimized ones, we 818 should either use weak functions (appropriate for some cases), or 819 the symbol that protects them should be the same symbol we use. 820 821 See: https://lore.kernel.org/lkml/CA+55aFycQ9XJvEOsiM3txHL5bjUc8CeKWJNR_H+MiicaddB42Q@mail.gmail.com/ 822 823 **DO_WHILE_MACRO_WITH_TRAILING_SEMICOLON** 824 do {} while(0) macros should not have a trailing semicolon. 825 826 **INIT_ATTRIBUTE** 827 Const init definitions should use __initconst instead of 828 __initdata. 829 830 Similarly init definitions without const require a separate 831 use of const. 832 833 **INLINE_LOCATION** 834 The inline keyword should sit between storage class and type. 835 836 For example, the following segment:: 837 838 inline static int example_function(void) 839 { 840 ... 841 } 842 843 should be:: 844 845 static inline int example_function(void) 846 { 847 ... 848 } 849 850 **MISPLACED_INIT** 851 It is possible to use section markers on variables in a way 852 which gcc doesn't understand (or at least not the way the 853 developer intended):: 854 855 static struct __initdata samsung_pll_clock exynos4_plls[nr_plls] = { 856 857 does not put exynos4_plls in the .initdata section. The __initdata 858 marker can be virtually anywhere on the line, except right after 859 "struct". The preferred location is before the "=" sign if there is 860 one, or before the trailing ";" otherwise. 861 862 See: https://lore.kernel.org/lkml/1377655732.3619.19.camel@joe-AO722/ 863 864 **MULTISTATEMENT_MACRO_USE_DO_WHILE** 865 Macros with multiple statements should be enclosed in a 866 do - while block. Same should also be the case for macros 867 starting with `if` to avoid logic defects:: 868 869 #define macrofun(a, b, c) \ 870 do { \ 871 if (a == 5) \ 872 do_this(b, c); \ 873 } while (0) 874 875 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#macros-enums-and-rtl 876 877 **PREFER_FALLTHROUGH** 878 Use the `fallthrough;` pseudo keyword instead of 879 `/* fallthrough */` like comments. 880 881 **TRAILING_SEMICOLON** 882 Macro definition should not end with a semicolon. The macro 883 invocation style should be consistent with function calls. 884 This can prevent any unexpected code paths:: 885 886 #define MAC do_something; 887 888 If this macro is used within a if else statement, like:: 889 890 if (some_condition) 891 MAC; 892 893 else 894 do_something; 895 896 Then there would be a compilation error, because when the macro is 897 expanded there are two trailing semicolons, so the else branch gets 898 orphaned. 899 900 See: https://lore.kernel.org/lkml/1399671106.2912.21.camel@joe-AO725/ 901 902 **SINGLE_STATEMENT_DO_WHILE_MACRO** 903 For the multi-statement macros, it is necessary to use the do-while 904 loop to avoid unpredictable code paths. The do-while loop helps to 905 group the multiple statements into a single one so that a 906 function-like macro can be used as a function only. 907 908 But for the single statement macros, it is unnecessary to use the 909 do-while loop. Although the code is syntactically correct but using 910 the do-while loop is redundant. So remove the do-while loop for single 911 statement macros. 912 913 **WEAK_DECLARATION** 914 Using weak declarations like __attribute__((weak)) or __weak 915 can have unintended link defects. Avoid using them. 916 917 918Functions and Variables 919----------------------- 920 921 **CAMELCASE** 922 Avoid CamelCase Identifiers. 923 924 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#naming 925 926 **CONST_CONST** 927 Using `const <type> const *` is generally meant to be 928 written `const <type> * const`. 929 930 **CONST_STRUCT** 931 Using const is generally a good idea. Checkpatch reads 932 a list of frequently used structs that are always or 933 almost always constant. 934 935 The existing structs list can be viewed from 936 `scripts/const_structs.checkpatch`. 937 938 See: https://lore.kernel.org/lkml/alpine.DEB.2.10.1608281509480.3321@hadrien/ 939 940 **EMBEDDED_FUNCTION_NAME** 941 Embedded function names are less appropriate to use as 942 refactoring can cause function renaming. Prefer the use of 943 "%s", __func__ to embedded function names. 944 945 Note that this does not work with -f (--file) checkpatch option 946 as it depends on patch context providing the function name. 947 948 **FUNCTION_ARGUMENTS** 949 This warning is emitted due to any of the following reasons: 950 951 1. Arguments for the function declaration do not follow 952 the identifier name. Example:: 953 954 void foo 955 (int bar, int baz) 956 957 This should be corrected to:: 958 959 void foo(int bar, int baz) 960 961 2. Some arguments for the function definition do not 962 have an identifier name. Example:: 963 964 void foo(int) 965 966 All arguments should have identifier names. 967 968 **FUNCTION_WITHOUT_ARGS** 969 Function declarations without arguments like:: 970 971 int foo() 972 973 should be:: 974 975 int foo(void) 976 977 **GLOBAL_INITIALISERS** 978 Global variables should not be initialized explicitly to 979 0 (or NULL, false, etc.). Your compiler (or rather your 980 loader, which is responsible for zeroing out the relevant 981 sections) automatically does it for you. 982 983 **INITIALISED_STATIC** 984 Static variables should not be initialized explicitly to zero. 985 Your compiler (or rather your loader) automatically does 986 it for you. 987 988 **MULTIPLE_ASSIGNMENTS** 989 Multiple assignments on a single line makes the code unnecessarily 990 complicated. So on a single line assign value to a single variable 991 only, this makes the code more readable and helps avoid typos. 992 993 **RETURN_PARENTHESES** 994 return is not a function and as such doesn't need parentheses:: 995 996 return (bar); 997 998 can simply be:: 999 1000 return bar; 1001 1002 1003Permissions 1004----------- 1005 1006 **DEVICE_ATTR_PERMS** 1007 The permissions used in DEVICE_ATTR are unusual. 1008 Typically only three permissions are used - 0644 (RW), 0444 (RO) 1009 and 0200 (WO). 1010 1011 See: https://www.kernel.org/doc/html/latest/filesystems/sysfs.html#attributes 1012 1013 **EXECUTE_PERMISSIONS** 1014 There is no reason for source files to be executable. The executable 1015 bit can be removed safely. 1016 1017 **EXPORTED_WORLD_WRITABLE** 1018 Exporting world writable sysfs/debugfs files is usually a bad thing. 1019 When done arbitrarily they can introduce serious security bugs. 1020 In the past, some of the debugfs vulnerabilities would seemingly allow 1021 any local user to write arbitrary values into device registers - a 1022 situation from which little good can be expected to emerge. 1023 1024 See: https://lore.kernel.org/linux-arm-kernel/cover.1296818921.git.segoon@openwall.com/ 1025 1026 **NON_OCTAL_PERMISSIONS** 1027 Permission bits should use 4 digit octal permissions (like 0700 or 0444). 1028 Avoid using any other base like decimal. 1029 1030 **SYMBOLIC_PERMS** 1031 Permission bits in the octal form are more readable and easier to 1032 understand than their symbolic counterparts because many command-line 1033 tools use this notation. Experienced kernel developers have been using 1034 these traditional Unix permission bits for decades and so they find it 1035 easier to understand the octal notation than the symbolic macros. 1036 For example, it is harder to read S_IWUSR|S_IRUGO than 0644, which 1037 obscures the developer's intent rather than clarifying it. 1038 1039 See: https://lore.kernel.org/lkml/CA+55aFw5v23T-zvDZp-MmD_EYxF8WbafwwB59934FV7g21uMGQ@mail.gmail.com/ 1040 1041 1042Spacing and Brackets 1043-------------------- 1044 1045 **ASSIGNMENT_CONTINUATIONS** 1046 Assignment operators should not be written at the start of a 1047 line but should follow the operand at the previous line. 1048 1049 **BRACES** 1050 The placement of braces is stylistically incorrect. 1051 The preferred way is to put the opening brace last on the line, 1052 and put the closing brace first:: 1053 1054 if (x is true) { 1055 we do y 1056 } 1057 1058 This applies for all non-functional blocks. 1059 However, there is one special case, namely functions: they have the 1060 opening brace at the beginning of the next line, thus:: 1061 1062 int function(int x) 1063 { 1064 body of function 1065 } 1066 1067 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces 1068 1069 **BRACKET_SPACE** 1070 Whitespace before opening bracket '[' is prohibited. 1071 There are some exceptions: 1072 1073 1. With a type on the left:: 1074 1075 int [] a; 1076 1077 2. At the beginning of a line for slice initialisers:: 1078 1079 [0...10] = 5, 1080 1081 3. Inside a curly brace:: 1082 1083 = { [0...10] = 5 } 1084 1085 **CONCATENATED_STRING** 1086 Concatenated elements should have a space in between. 1087 Example:: 1088 1089 printk(KERN_INFO"bar"); 1090 1091 should be:: 1092 1093 printk(KERN_INFO "bar"); 1094 1095 **ELSE_AFTER_BRACE** 1096 `else {` should follow the closing block `}` on the same line. 1097 1098 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces 1099 1100 **LINE_SPACING** 1101 Vertical space is wasted given the limited number of lines an 1102 editor window can display when multiple blank lines are used. 1103 1104 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces 1105 1106 **OPEN_BRACE** 1107 The opening brace should be following the function definitions on the 1108 next line. For any non-functional block it should be on the same line 1109 as the last construct. 1110 1111 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces 1112 1113 **POINTER_LOCATION** 1114 When using pointer data or a function that returns a pointer type, 1115 the preferred use of * is adjacent to the data name or function name 1116 and not adjacent to the type name. 1117 Examples:: 1118 1119 char *linux_banner; 1120 unsigned long long memparse(char *ptr, char **retptr); 1121 char *match_strdup(substring_t *s); 1122 1123 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces 1124 1125 **SPACING** 1126 Whitespace style used in the kernel sources is described in kernel docs. 1127 1128 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces 1129 1130 **TRAILING_WHITESPACE** 1131 Trailing whitespace should always be removed. 1132 Some editors highlight the trailing whitespace and cause visual 1133 distractions when editing files. 1134 1135 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces 1136 1137 **UNNECESSARY_PARENTHESES** 1138 Parentheses are not required in the following cases: 1139 1140 1. Function pointer uses:: 1141 1142 (foo->bar)(); 1143 1144 could be:: 1145 1146 foo->bar(); 1147 1148 2. Comparisons in if:: 1149 1150 if ((foo->bar) && (foo->baz)) 1151 if ((foo == bar)) 1152 1153 could be:: 1154 1155 if (foo->bar && foo->baz) 1156 if (foo == bar) 1157 1158 3. addressof/dereference single Lvalues:: 1159 1160 &(foo->bar) 1161 *(foo->bar) 1162 1163 could be:: 1164 1165 &foo->bar 1166 *foo->bar 1167 1168 **WHILE_AFTER_BRACE** 1169 while should follow the closing bracket on the same line:: 1170 1171 do { 1172 ... 1173 } while(something); 1174 1175 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces 1176 1177 1178Others 1179------ 1180 1181 **CONFIG_DESCRIPTION** 1182 Kconfig symbols should have a help text which fully describes 1183 it. 1184 1185 **CORRUPTED_PATCH** 1186 The patch seems to be corrupted or lines are wrapped. 1187 Please regenerate the patch file before sending it to the maintainer. 1188 1189 **CVS_KEYWORD** 1190 Since linux moved to git, the CVS markers are no longer used. 1191 So, CVS style keywords ($Id$, $Revision$, $Log$) should not be 1192 added. 1193 1194 **DEFAULT_NO_BREAK** 1195 switch default case is sometimes written as "default:;". This can 1196 cause new cases added below default to be defective. 1197 1198 A "break;" should be added after empty default statement to avoid 1199 unwanted fallthrough. 1200 1201 **DOS_LINE_ENDINGS** 1202 For DOS-formatted patches, there are extra ^M symbols at the end of 1203 the line. These should be removed. 1204 1205 **DT_SCHEMA_BINDING_PATCH** 1206 DT bindings moved to a json-schema based format instead of 1207 freeform text. 1208 1209 See: https://www.kernel.org/doc/html/latest/devicetree/bindings/writing-schema.html 1210 1211 **DT_SPLIT_BINDING_PATCH** 1212 Devicetree bindings should be their own patch. This is because 1213 bindings are logically independent from a driver implementation, 1214 they have a different maintainer (even though they often 1215 are applied via the same tree), and it makes for a cleaner history in the 1216 DT only tree created with git-filter-branch. 1217 1218 See: https://www.kernel.org/doc/html/latest/devicetree/bindings/submitting-patches.html#i-for-patch-submitters 1219 1220 **EMBEDDED_FILENAME** 1221 Embedding the complete filename path inside the file isn't particularly 1222 useful as often the path is moved around and becomes incorrect. 1223 1224 **FILE_PATH_CHANGES** 1225 Whenever files are added, moved, or deleted, the MAINTAINERS file 1226 patterns can be out of sync or outdated. 1227 1228 So MAINTAINERS might need updating in these cases. 1229 1230 **MEMSET** 1231 The memset use appears to be incorrect. This may be caused due to 1232 badly ordered parameters. Please recheck the usage. 1233 1234 **NOT_UNIFIED_DIFF** 1235 The patch file does not appear to be in unified-diff format. Please 1236 regenerate the patch file before sending it to the maintainer. 1237 1238 **PRINTF_0XDECIMAL** 1239 Prefixing 0x with decimal output is defective and should be corrected. 1240 1241 **SPDX_LICENSE_TAG** 1242 The source file is missing or has an improper SPDX identifier tag. 1243 The Linux kernel requires the precise SPDX identifier in all source files, 1244 and it is thoroughly documented in the kernel docs. 1245 1246 See: https://www.kernel.org/doc/html/latest/process/license-rules.html 1247 1248 **TYPO_SPELLING** 1249 Some words may have been misspelled. Consider reviewing them.