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 <[email protected]> 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/[email protected]/ 360 2. https://lore.kernel.org/lkml/[email protected]/ 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/[email protected]/ 420 2. https://lore.kernel.org/lkml/[email protected]/ 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/[email protected]/ 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/[email protected]/ 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/[email protected]/ 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. [email protected] 533 2. [email protected] 534 535 For adding version info, the following comment style should be used:: 536 537 [email protected] # 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/[email protected]/ 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 <[email protected]> 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 **TRAILING_STATEMENTS** 720 Trailing statements (for example after any conditional) should be 721 on the next line. 722 Statements, such as:: 723 724 if (x == y) break; 725 726 should be:: 727 728 if (x == y) 729 break; 730 731 732Macros, Attributes and Symbols 733------------------------------ 734 735 **ARRAY_SIZE** 736 The ARRAY_SIZE(foo) macro should be preferred over 737 sizeof(foo)/sizeof(foo[0]) for finding number of elements in an 738 array. 739 740 The macro is defined in include/linux/kernel.h:: 741 742 #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0])) 743 744 **AVOID_EXTERNS** 745 Function prototypes don't need to be declared extern in .h 746 files. It's assumed by the compiler and is unnecessary. 747 748 **AVOID_L_PREFIX** 749 Local symbol names that are prefixed with `.L` should be avoided, 750 as this has special meaning for the assembler; a symbol entry will 751 not be emitted into the symbol table. This can prevent `objtool` 752 from generating correct unwind info. 753 754 Symbols with STB_LOCAL binding may still be used, and `.L` prefixed 755 local symbol names are still generally usable within a function, 756 but `.L` prefixed local symbol names should not be used to denote 757 the beginning or end of code regions via 758 `SYM_CODE_START_LOCAL`/`SYM_CODE_END` 759 760 **BIT_MACRO** 761 Defines like: 1 << <digit> could be BIT(digit). 762 The BIT() macro is defined via include/linux/bits.h:: 763 764 #define BIT(nr) (1UL << (nr)) 765 766 **CONST_READ_MOSTLY** 767 When a variable is tagged with the __read_mostly annotation, it is a 768 signal to the compiler that accesses to the variable will be mostly 769 reads and rarely(but NOT never) a write. 770 771 const __read_mostly does not make any sense as const data is already 772 read-only. The __read_mostly annotation thus should be removed. 773 774 **DATE_TIME** 775 It is generally desirable that building the same source code with 776 the same set of tools is reproducible, i.e. the output is always 777 exactly the same. 778 779 The kernel does *not* use the ``__DATE__`` and ``__TIME__`` macros, 780 and enables warnings if they are used as they can lead to 781 non-deterministic builds. 782 783 See: https://www.kernel.org/doc/html/latest/kbuild/reproducible-builds.html#timestamps 784 785 **DEFINE_ARCH_HAS** 786 The ARCH_HAS_xyz and ARCH_HAVE_xyz patterns are wrong. 787 788 For big conceptual features use Kconfig symbols instead. And for 789 smaller things where we have compatibility fallback functions but 790 want architectures able to override them with optimized ones, we 791 should either use weak functions (appropriate for some cases), or 792 the symbol that protects them should be the same symbol we use. 793 794 See: https://lore.kernel.org/lkml/CA+55aFycQ9XJvEOsiM3txHL5bjUc8CeKWJNR_H+MiicaddB42Q@mail.gmail.com/ 795 796 **DO_WHILE_MACRO_WITH_TRAILING_SEMICOLON** 797 do {} while(0) macros should not have a trailing semicolon. 798 799 **INIT_ATTRIBUTE** 800 Const init definitions should use __initconst instead of 801 __initdata. 802 803 Similarly init definitions without const require a separate 804 use of const. 805 806 **INLINE_LOCATION** 807 The inline keyword should sit between storage class and type. 808 809 For example, the following segment:: 810 811 inline static int example_function(void) 812 { 813 ... 814 } 815 816 should be:: 817 818 static inline int example_function(void) 819 { 820 ... 821 } 822 823 **MISPLACED_INIT** 824 It is possible to use section markers on variables in a way 825 which gcc doesn't understand (or at least not the way the 826 developer intended):: 827 828 static struct __initdata samsung_pll_clock exynos4_plls[nr_plls] = { 829 830 does not put exynos4_plls in the .initdata section. The __initdata 831 marker can be virtually anywhere on the line, except right after 832 "struct". The preferred location is before the "=" sign if there is 833 one, or before the trailing ";" otherwise. 834 835 See: https://lore.kernel.org/lkml/1377655732.3619.19.camel@joe-AO722/ 836 837 **MULTISTATEMENT_MACRO_USE_DO_WHILE** 838 Macros with multiple statements should be enclosed in a 839 do - while block. Same should also be the case for macros 840 starting with `if` to avoid logic defects:: 841 842 #define macrofun(a, b, c) \ 843 do { \ 844 if (a == 5) \ 845 do_this(b, c); \ 846 } while (0) 847 848 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#macros-enums-and-rtl 849 850 **PREFER_FALLTHROUGH** 851 Use the `fallthrough;` pseudo keyword instead of 852 `/* fallthrough */` like comments. 853 854 **WEAK_DECLARATION** 855 Using weak declarations like __attribute__((weak)) or __weak 856 can have unintended link defects. Avoid using them. 857 858 859Functions and Variables 860----------------------- 861 862 **CAMELCASE** 863 Avoid CamelCase Identifiers. 864 865 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#naming 866 867 **CONST_CONST** 868 Using `const <type> const *` is generally meant to be 869 written `const <type> * const`. 870 871 **CONST_STRUCT** 872 Using const is generally a good idea. Checkpatch reads 873 a list of frequently used structs that are always or 874 almost always constant. 875 876 The existing structs list can be viewed from 877 `scripts/const_structs.checkpatch`. 878 879 See: https://lore.kernel.org/lkml/alpine.DEB.2.10.1608281509480.3321@hadrien/ 880 881 **EMBEDDED_FUNCTION_NAME** 882 Embedded function names are less appropriate to use as 883 refactoring can cause function renaming. Prefer the use of 884 "%s", __func__ to embedded function names. 885 886 Note that this does not work with -f (--file) checkpatch option 887 as it depends on patch context providing the function name. 888 889 **FUNCTION_ARGUMENTS** 890 This warning is emitted due to any of the following reasons: 891 892 1. Arguments for the function declaration do not follow 893 the identifier name. Example:: 894 895 void foo 896 (int bar, int baz) 897 898 This should be corrected to:: 899 900 void foo(int bar, int baz) 901 902 2. Some arguments for the function definition do not 903 have an identifier name. Example:: 904 905 void foo(int) 906 907 All arguments should have identifier names. 908 909 **FUNCTION_WITHOUT_ARGS** 910 Function declarations without arguments like:: 911 912 int foo() 913 914 should be:: 915 916 int foo(void) 917 918 **GLOBAL_INITIALISERS** 919 Global variables should not be initialized explicitly to 920 0 (or NULL, false, etc.). Your compiler (or rather your 921 loader, which is responsible for zeroing out the relevant 922 sections) automatically does it for you. 923 924 **INITIALISED_STATIC** 925 Static variables should not be initialized explicitly to zero. 926 Your compiler (or rather your loader) automatically does 927 it for you. 928 929 **RETURN_PARENTHESES** 930 return is not a function and as such doesn't need parentheses:: 931 932 return (bar); 933 934 can simply be:: 935 936 return bar; 937 938 939Permissions 940----------- 941 942 **DEVICE_ATTR_PERMS** 943 The permissions used in DEVICE_ATTR are unusual. 944 Typically only three permissions are used - 0644 (RW), 0444 (RO) 945 and 0200 (WO). 946 947 See: https://www.kernel.org/doc/html/latest/filesystems/sysfs.html#attributes 948 949 **EXECUTE_PERMISSIONS** 950 There is no reason for source files to be executable. The executable 951 bit can be removed safely. 952 953 **EXPORTED_WORLD_WRITABLE** 954 Exporting world writable sysfs/debugfs files is usually a bad thing. 955 When done arbitrarily they can introduce serious security bugs. 956 In the past, some of the debugfs vulnerabilities would seemingly allow 957 any local user to write arbitrary values into device registers - a 958 situation from which little good can be expected to emerge. 959 960 See: https://lore.kernel.org/linux-arm-kernel/[email protected]/ 961 962 **NON_OCTAL_PERMISSIONS** 963 Permission bits should use 4 digit octal permissions (like 0700 or 0444). 964 Avoid using any other base like decimal. 965 966 967Spacing and Brackets 968-------------------- 969 970 **ASSIGNMENT_CONTINUATIONS** 971 Assignment operators should not be written at the start of a 972 line but should follow the operand at the previous line. 973 974 **BRACES** 975 The placement of braces is stylistically incorrect. 976 The preferred way is to put the opening brace last on the line, 977 and put the closing brace first:: 978 979 if (x is true) { 980 we do y 981 } 982 983 This applies for all non-functional blocks. 984 However, there is one special case, namely functions: they have the 985 opening brace at the beginning of the next line, thus:: 986 987 int function(int x) 988 { 989 body of function 990 } 991 992 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces 993 994 **BRACKET_SPACE** 995 Whitespace before opening bracket '[' is prohibited. 996 There are some exceptions: 997 998 1. With a type on the left:: 999 1000 int [] a; 1001 1002 2. At the beginning of a line for slice initialisers:: 1003 1004 [0...10] = 5, 1005 1006 3. Inside a curly brace:: 1007 1008 = { [0...10] = 5 } 1009 1010 **CONCATENATED_STRING** 1011 Concatenated elements should have a space in between. 1012 Example:: 1013 1014 printk(KERN_INFO"bar"); 1015 1016 should be:: 1017 1018 printk(KERN_INFO "bar"); 1019 1020 **ELSE_AFTER_BRACE** 1021 `else {` should follow the closing block `}` on the same line. 1022 1023 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces 1024 1025 **LINE_SPACING** 1026 Vertical space is wasted given the limited number of lines an 1027 editor window can display when multiple blank lines are used. 1028 1029 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces 1030 1031 **OPEN_BRACE** 1032 The opening brace should be following the function definitions on the 1033 next line. For any non-functional block it should be on the same line 1034 as the last construct. 1035 1036 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces 1037 1038 **POINTER_LOCATION** 1039 When using pointer data or a function that returns a pointer type, 1040 the preferred use of * is adjacent to the data name or function name 1041 and not adjacent to the type name. 1042 Examples:: 1043 1044 char *linux_banner; 1045 unsigned long long memparse(char *ptr, char **retptr); 1046 char *match_strdup(substring_t *s); 1047 1048 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces 1049 1050 **SPACING** 1051 Whitespace style used in the kernel sources is described in kernel docs. 1052 1053 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces 1054 1055 **TRAILING_WHITESPACE** 1056 Trailing whitespace should always be removed. 1057 Some editors highlight the trailing whitespace and cause visual 1058 distractions when editing files. 1059 1060 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces 1061 1062 **UNNECESSARY_PARENTHESES** 1063 Parentheses are not required in the following cases: 1064 1065 1. Function pointer uses:: 1066 1067 (foo->bar)(); 1068 1069 could be:: 1070 1071 foo->bar(); 1072 1073 2. Comparisons in if:: 1074 1075 if ((foo->bar) && (foo->baz)) 1076 if ((foo == bar)) 1077 1078 could be:: 1079 1080 if (foo->bar && foo->baz) 1081 if (foo == bar) 1082 1083 3. addressof/dereference single Lvalues:: 1084 1085 &(foo->bar) 1086 *(foo->bar) 1087 1088 could be:: 1089 1090 &foo->bar 1091 *foo->bar 1092 1093 **WHILE_AFTER_BRACE** 1094 while should follow the closing bracket on the same line:: 1095 1096 do { 1097 ... 1098 } while(something); 1099 1100 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces 1101 1102 1103Others 1104------ 1105 1106 **CONFIG_DESCRIPTION** 1107 Kconfig symbols should have a help text which fully describes 1108 it. 1109 1110 **CORRUPTED_PATCH** 1111 The patch seems to be corrupted or lines are wrapped. 1112 Please regenerate the patch file before sending it to the maintainer. 1113 1114 **CVS_KEYWORD** 1115 Since linux moved to git, the CVS markers are no longer used. 1116 So, CVS style keywords ($Id$, $Revision$, $Log$) should not be 1117 added. 1118 1119 **DEFAULT_NO_BREAK** 1120 switch default case is sometimes written as "default:;". This can 1121 cause new cases added below default to be defective. 1122 1123 A "break;" should be added after empty default statement to avoid 1124 unwanted fallthrough. 1125 1126 **DOS_LINE_ENDINGS** 1127 For DOS-formatted patches, there are extra ^M symbols at the end of 1128 the line. These should be removed. 1129 1130 **DT_SCHEMA_BINDING_PATCH** 1131 DT bindings moved to a json-schema based format instead of 1132 freeform text. 1133 1134 See: https://www.kernel.org/doc/html/latest/devicetree/bindings/writing-schema.html 1135 1136 **DT_SPLIT_BINDING_PATCH** 1137 Devicetree bindings should be their own patch. This is because 1138 bindings are logically independent from a driver implementation, 1139 they have a different maintainer (even though they often 1140 are applied via the same tree), and it makes for a cleaner history in the 1141 DT only tree created with git-filter-branch. 1142 1143 See: https://www.kernel.org/doc/html/latest/devicetree/bindings/submitting-patches.html#i-for-patch-submitters 1144 1145 **EMBEDDED_FILENAME** 1146 Embedding the complete filename path inside the file isn't particularly 1147 useful as often the path is moved around and becomes incorrect. 1148 1149 **FILE_PATH_CHANGES** 1150 Whenever files are added, moved, or deleted, the MAINTAINERS file 1151 patterns can be out of sync or outdated. 1152 1153 So MAINTAINERS might need updating in these cases. 1154 1155 **MEMSET** 1156 The memset use appears to be incorrect. This may be caused due to 1157 badly ordered parameters. Please recheck the usage. 1158 1159 **NOT_UNIFIED_DIFF** 1160 The patch file does not appear to be in unified-diff format. Please 1161 regenerate the patch file before sending it to the maintainer. 1162 1163 **PRINTF_0XDECIMAL** 1164 Prefixing 0x with decimal output is defective and should be corrected. 1165 1166 **SPDX_LICENSE_TAG** 1167 The source file is missing or has an improper SPDX identifier tag. 1168 The Linux kernel requires the precise SPDX identifier in all source files, 1169 and it is thoroughly documented in the kernel docs. 1170 1171 See: https://www.kernel.org/doc/html/latest/process/license-rules.html 1172 1173 **TYPO_SPELLING** 1174 Some words may have been misspelled. Consider reviewing them. 1175