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linux-6.19.14/Documentation/dev-tools/checkpatch.rst
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 exist, 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 may be 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 **DEVICE_ATTR_FUNCTIONS** 346 The function names used in DEVICE_ATTR is unusual. 347 Typically, the store and show functions are used with <attr>_store and 348 <attr>_show, where <attr> is a named attribute variable of the device. 349 350 Consider the following examples:: 351 352 static DEVICE_ATTR(type, 0444, type_show, NULL); 353 static DEVICE_ATTR(power, 0644, power_show, power_store); 354 355 The function names should preferably follow the above pattern. 356 357 See: https://www.kernel.org/doc/html/latest/driver-api/driver-model/device.html#attributes 358 359 **DEVICE_ATTR_RO** 360 The DEVICE_ATTR_RO(name) helper macro can be used instead of 361 DEVICE_ATTR(name, 0444, name_show, NULL); 362 363 Note that the macro automatically appends _show to the named 364 attribute variable of the device for the show method. 365 366 See: https://www.kernel.org/doc/html/latest/driver-api/driver-model/device.html#attributes 367 368 **DEVICE_ATTR_RW** 369 The DEVICE_ATTR_RW(name) helper macro can be used instead of 370 DEVICE_ATTR(name, 0644, name_show, name_store); 371 372 Note that the macro automatically appends _show and _store to the 373 named attribute variable of the device for the show and store methods. 374 375 See: https://www.kernel.org/doc/html/latest/driver-api/driver-model/device.html#attributes 376 377 **DEVICE_ATTR_WO** 378 The DEVICE_AATR_WO(name) helper macro can be used instead of 379 DEVICE_ATTR(name, 0200, NULL, name_store); 380 381 Note that the macro automatically appends _store to the 382 named attribute variable of the device for the store method. 383 384 See: https://www.kernel.org/doc/html/latest/driver-api/driver-model/device.html#attributes 385 386 **DUPLICATED_SYSCTL_CONST** 387 Commit d91bff3011cf ("proc/sysctl: add shared variables for range 388 check") added some shared const variables to be used instead of a local 389 copy in each source file. 390 391 Consider replacing the sysctl range checking value with the shared 392 one in include/linux/sysctl.h. The following conversion scheme may 393 be used:: 394 395 &zero -> SYSCTL_ZERO 396 &one -> SYSCTL_ONE 397 &int_max -> SYSCTL_INT_MAX 398 399 See: 400 401 1. https://lore.kernel.org/lkml/20190430180111.10688-1-mcroce@redhat.com/ 402 2. https://lore.kernel.org/lkml/20190531131422.14970-1-mcroce@redhat.com/ 403 404 **ENOSYS** 405 ENOSYS means that a nonexistent system call was called. 406 Earlier, it was wrongly used for things like invalid operations on 407 otherwise valid syscalls. This should be avoided in new code. 408 409 See: https://lore.kernel.org/lkml/5eb299021dec23c1a48fa7d9f2c8b794e967766d.1408730669.git.luto@amacapital.net/ 410 411 **ENOTSUPP** 412 ENOTSUPP is not a standard error code and should be avoided in new patches. 413 EOPNOTSUPP should be used instead. 414 415 See: https://lore.kernel.org/netdev/20200510182252.GA411829@lunn.ch/ 416 417 **EXPORT_SYMBOL** 418 EXPORT_SYMBOL should immediately follow the symbol to be exported. 419 420 **IN_ATOMIC** 421 in_atomic() is not for driver use so any such use is reported as an ERROR. 422 Also in_atomic() is often used to determine if sleeping is permitted, 423 but it is not reliable in this use model. Therefore its use is 424 strongly discouraged. 425 426 However, in_atomic() is ok for core kernel use. 427 428 See: https://lore.kernel.org/lkml/20080320201723.b87b3732.akpm@linux-foundation.org/ 429 430 **LOCKDEP** 431 The lockdep_no_validate class was added as a temporary measure to 432 prevent warnings on conversion of device->sem to device->mutex. 433 It should not be used for any other purpose. 434 435 See: https://lore.kernel.org/lkml/1268959062.9440.467.camel@laptop/ 436 437 **MALFORMED_INCLUDE** 438 The #include statement has a malformed path. This has happened 439 because the author has included a double slash "//" in the pathname 440 accidentally. 441 442 **USE_LOCKDEP** 443 lockdep_assert_held() annotations should be preferred over 444 assertions based on spin_is_locked() 445 446 See: https://www.kernel.org/doc/html/latest/locking/lockdep-design.html#annotations 447 448 **UAPI_INCLUDE** 449 No #include statements in include/uapi should use a uapi/ path. 450 451 **USLEEP_RANGE** 452 usleep_range() should be preferred over udelay(). The proper way of 453 using usleep_range() is mentioned in the kernel docs. 454 455 456Comments 457-------- 458 459 **BLOCK_COMMENT_STYLE** 460 The comment style is incorrect. The preferred style for multi- 461 line comments is:: 462 463 /* 464 * This is the preferred style 465 * for multi line comments. 466 */ 467 468 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#commenting 469 470 **C99_COMMENTS** 471 C99 style single line comments (//) should not be used. 472 Prefer the block comment style instead. 473 474 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#commenting 475 476 **DATA_RACE** 477 Applications of data_race() should have a comment so as to document the 478 reasoning behind why it was deemed safe. 479 480 See: https://lore.kernel.org/lkml/20200401101714.44781-1-elver@google.com/ 481 482 **FSF_MAILING_ADDRESS** 483 Kernel maintainers reject new instances of the GPL boilerplate paragraph 484 directing people to write to the FSF for a copy of the GPL, since the 485 FSF has moved in the past and may do so again. 486 So do not write paragraphs about writing to the Free Software Foundation's 487 mailing address. 488 489 See: https://lore.kernel.org/lkml/20131006222342.GT19510@leaf/ 490 491 **UNCOMMENTED_RGMII_MODE** 492 Historically, the RGMII PHY modes specified in Device Trees have been 493 used inconsistently, often referring to the usage of delays on the PHY 494 side rather than describing the board. 495 496 PHY modes "rgmii", "rgmii-rxid" and "rgmii-txid" modes require the clock 497 signal to be delayed on the PCB; this unusual configuration should be 498 described in a comment. If they are not (meaning that the delay is realized 499 internally in the MAC or PHY), "rgmii-id" is the correct PHY mode. 500 501Commit message 502-------------- 503 504 **BAD_SIGN_OFF** 505 The signed-off-by line does not fall in line with the standards 506 specified by the community. 507 508 See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#developer-s-certificate-of-origin-1-1 509 510 **BAD_STABLE_ADDRESS_STYLE** 511 The email format for stable is incorrect. 512 Some valid options for stable address are:: 513 514 1. stable@vger.kernel.org 515 2. stable@kernel.org 516 517 For adding version info, the following comment style should be used:: 518 519 stable@vger.kernel.org # version info 520 521 **COMMIT_COMMENT_SYMBOL** 522 Commit log lines starting with a '#' are ignored by git as 523 comments. To solve this problem addition of a single space 524 infront of the log line is enough. 525 526 **COMMIT_MESSAGE** 527 The patch is missing a commit description. A brief 528 description of the changes made by the patch should be added. 529 530 See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#describe-your-changes 531 532 **EMAIL_SUBJECT** 533 Naming the tool that found the issue is not very useful in the 534 subject line. A good subject line summarizes the change that 535 the patch brings. 536 537 See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#describe-your-changes 538 539 **FROM_SIGN_OFF_MISMATCH** 540 The author's email does not match with that in the Signed-off-by: 541 line(s). This can be sometimes caused due to an improperly configured 542 email client. 543 544 This message is emitted due to any of the following reasons:: 545 546 - The email names do not match. 547 - The email addresses do not match. 548 - The email subaddresses do not match. 549 - The email comments do not match. 550 551 **MISSING_SIGN_OFF** 552 The patch is missing a Signed-off-by line. A signed-off-by 553 line should be added according to Developer's certificate of 554 Origin. 555 556 See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#sign-your-work-the-developer-s-certificate-of-origin 557 558 **NO_AUTHOR_SIGN_OFF** 559 The author of the patch has not signed off the patch. It is 560 required that a simple sign off line should be present at the 561 end of explanation of the patch to denote that the author has 562 written it or otherwise has the rights to pass it on as an open 563 source patch. 564 565 See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#sign-your-work-the-developer-s-certificate-of-origin 566 567 **DIFF_IN_COMMIT_MSG** 568 Avoid having diff content in commit message. 569 This causes problems when one tries to apply a file containing both 570 the changelog and the diff because patch(1) tries to apply the diff 571 which it found in the changelog. 572 573 See: https://lore.kernel.org/lkml/20150611134006.9df79a893e3636019ad2759e@linux-foundation.org/ 574 575 **GERRIT_CHANGE_ID** 576 To be picked up by gerrit, the footer of the commit message might 577 have a Change-Id like:: 578 579 Change-Id: Ic8aaa0728a43936cd4c6e1ed590e01ba8f0fbf5b 580 Signed-off-by: A. U. Thor <author@example.com> 581 582 The Change-Id line must be removed before submitting. 583 584 **GIT_COMMIT_ID** 585 The proper way to reference a commit id is: 586 commit <12+ chars of sha1> ("<title line>") 587 588 An example may be:: 589 590 Commit e21d2170f36602ae2708 ("video: remove unnecessary 591 platform_set_drvdata()") removed the unnecessary 592 platform_set_drvdata(), but left the variable "dev" unused, 593 delete it. 594 595 See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#describe-your-changes 596 597 **BAD_FIXES_TAG** 598 The Fixes: tag is malformed or does not follow the community conventions. 599 This can occur if the tag have been split into multiple lines (e.g., when 600 pasted in an email program with word wrapping enabled). 601 602 See: https://www.kernel.org/doc/html/latest/process/submitting-patches.html#describe-your-changes 603 604 605Comparison style 606---------------- 607 608 **ASSIGN_IN_IF** 609 Do not use assignments in if condition. 610 Example:: 611 612 if ((foo = bar(...)) < BAZ) { 613 614 should be written as:: 615 616 foo = bar(...); 617 if (foo < BAZ) { 618 619 **BOOL_COMPARISON** 620 Comparisons of A to true and false are better written 621 as A and !A. 622 623 See: https://lore.kernel.org/lkml/1365563834.27174.12.camel@joe-AO722/ 624 625 **COMPARISON_TO_NULL** 626 Comparisons to NULL in the form (foo == NULL) or (foo != NULL) 627 are better written as (!foo) and (foo). 628 629 **CONSTANT_COMPARISON** 630 Comparisons with a constant or upper case identifier on the left 631 side of the test should be avoided. 632 633 634Indentation and Line Breaks 635--------------------------- 636 637 **CODE_INDENT** 638 Code indent should use tabs instead of spaces. 639 Outside of comments, documentation and Kconfig, 640 spaces are never used for indentation. 641 642 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#indentation 643 644 **DEEP_INDENTATION** 645 Indentation with 6 or more tabs usually indicate overly indented 646 code. 647 648 It is suggested to refactor excessive indentation of 649 if/else/for/do/while/switch statements. 650 651 See: https://lore.kernel.org/lkml/1328311239.21255.24.camel@joe2Laptop/ 652 653 **SWITCH_CASE_INDENT_LEVEL** 654 switch should be at the same indent as case. 655 Example:: 656 657 switch (suffix) { 658 case 'G': 659 case 'g': 660 mem <<= 30; 661 break; 662 case 'M': 663 case 'm': 664 mem <<= 20; 665 break; 666 case 'K': 667 case 'k': 668 mem <<= 10; 669 fallthrough; 670 default: 671 break; 672 } 673 674 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#indentation 675 676 **LONG_LINE** 677 The line has exceeded the specified maximum length. 678 To use a different maximum line length, the --max-line-length=n option 679 may be added while invoking checkpatch. 680 681 Earlier, the default line length was 80 columns. Commit bdc48fa11e46 682 ("checkpatch/coding-style: deprecate 80-column warning") increased the 683 limit to 100 columns. This is not a hard limit either and it's 684 preferable to stay within 80 columns whenever possible. 685 686 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#breaking-long-lines-and-strings 687 688 **LONG_LINE_STRING** 689 A string starts before but extends beyond the maximum line length. 690 To use a different maximum line length, the --max-line-length=n option 691 may be added while invoking checkpatch. 692 693 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#breaking-long-lines-and-strings 694 695 **LONG_LINE_COMMENT** 696 A comment starts before but extends beyond the maximum line length. 697 To use a different maximum line length, the --max-line-length=n option 698 may be added while invoking checkpatch. 699 700 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#breaking-long-lines-and-strings 701 702 **SPLIT_STRING** 703 Quoted strings that appear as messages in userspace and can be 704 grepped, should not be split across multiple lines. 705 706 See: https://lore.kernel.org/lkml/20120203052727.GA15035@leaf/ 707 708 **MULTILINE_DEREFERENCE** 709 A single dereferencing identifier spanned on multiple lines like:: 710 711 struct_identifier->member[index]. 712 member = <foo>; 713 714 is generally hard to follow. It can easily lead to typos and so makes 715 the code vulnerable to bugs. 716 717 If fixing the multiple line dereferencing leads to an 80 column 718 violation, then either rewrite the code in a more simple way or if the 719 starting part of the dereferencing identifier is the same and used at 720 multiple places then store it in a temporary variable, and use that 721 temporary variable only at all the places. For example, if there are 722 two dereferencing identifiers:: 723 724 member1->member2->member3.foo1; 725 member1->member2->member3.foo2; 726 727 then store the member1->member2->member3 part in a temporary variable. 728 It not only helps to avoid the 80 column violation but also reduces 729 the program size by removing the unnecessary dereferences. 730 731 But if none of the above methods work then ignore the 80 column 732 violation because it is much easier to read a dereferencing identifier 733 on a single line. 734 735 **TRAILING_STATEMENTS** 736 Trailing statements (for example after any conditional) should be 737 on the next line. 738 Statements, such as:: 739 740 if (x == y) break; 741 742 should be:: 743 744 if (x == y) 745 break; 746 747 748Macros, Attributes and Symbols 749------------------------------ 750 751 **ARRAY_SIZE** 752 The ARRAY_SIZE(foo) macro should be preferred over 753 sizeof(foo)/sizeof(foo[0]) for finding number of elements in an 754 array. 755 756 The macro is defined in include/linux/kernel.h:: 757 758 #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0])) 759 760 **AVOID_EXTERNS** 761 Function prototypes don't need to be declared extern in .h 762 files. It's assumed by the compiler and is unnecessary. 763 764 **AVOID_L_PREFIX** 765 Local symbol names that are prefixed with `.L` should be avoided, 766 as this has special meaning for the assembler; a symbol entry will 767 not be emitted into the symbol table. This can prevent `objtool` 768 from generating correct unwind info. 769 770 Symbols with STB_LOCAL binding may still be used, and `.L` prefixed 771 local symbol names are still generally usable within a function, 772 but `.L` prefixed local symbol names should not be used to denote 773 the beginning or end of code regions via 774 `SYM_CODE_START_LOCAL`/`SYM_CODE_END` 775 776 **BIT_MACRO** 777 Defines like: 1 << <digit> could be BIT(digit). 778 The BIT() macro is defined via include/linux/bits.h:: 779 780 #define BIT(nr) (1UL << (nr)) 781 782 **CONST_READ_MOSTLY** 783 When a variable is tagged with the __read_mostly annotation, it is a 784 signal to the compiler that accesses to the variable will be mostly 785 reads and rarely(but NOT never) a write. 786 787 const __read_mostly does not make any sense as const data is already 788 read-only. The __read_mostly annotation thus should be removed. 789 790 **DATE_TIME** 791 It is generally desirable that building the same source code with 792 the same set of tools is reproducible, i.e. the output is always 793 exactly the same. 794 795 The kernel does *not* use the ``__DATE__`` and ``__TIME__`` macros, 796 and enables warnings if they are used as they can lead to 797 non-deterministic builds. 798 799 See: https://www.kernel.org/doc/html/latest/kbuild/reproducible-builds.html#timestamps 800 801 **DEFINE_ARCH_HAS** 802 The ARCH_HAS_xyz and ARCH_HAVE_xyz patterns are wrong. 803 804 For big conceptual features use Kconfig symbols instead. And for 805 smaller things where we have compatibility fallback functions but 806 want architectures able to override them with optimized ones, we 807 should either use weak functions (appropriate for some cases), or 808 the symbol that protects them should be the same symbol we use. 809 810 See: https://lore.kernel.org/lkml/CA+55aFycQ9XJvEOsiM3txHL5bjUc8CeKWJNR_H+MiicaddB42Q@mail.gmail.com/ 811 812 **DO_WHILE_MACRO_WITH_TRAILING_SEMICOLON** 813 do {} while(0) macros should not have a trailing semicolon. 814 815 **INIT_ATTRIBUTE** 816 Const init definitions should use __initconst instead of 817 __initdata. 818 819 Similarly init definitions without const require a separate 820 use of const. 821 822 **INLINE_LOCATION** 823 The inline keyword should sit between storage class and type. 824 825 For example, the following segment:: 826 827 inline static int example_function(void) 828 { 829 ... 830 } 831 832 should be:: 833 834 static inline int example_function(void) 835 { 836 ... 837 } 838 839 **MISPLACED_INIT** 840 It is possible to use section markers on variables in a way 841 which gcc doesn't understand (or at least not the way the 842 developer intended):: 843 844 static struct __initdata samsung_pll_clock exynos4_plls[nr_plls] = { 845 846 does not put exynos4_plls in the .initdata section. The __initdata 847 marker can be virtually anywhere on the line, except right after 848 "struct". The preferred location is before the "=" sign if there is 849 one, or before the trailing ";" otherwise. 850 851 See: https://lore.kernel.org/lkml/1377655732.3619.19.camel@joe-AO722/ 852 853 **MULTISTATEMENT_MACRO_USE_DO_WHILE** 854 Macros with multiple statements should be enclosed in a 855 do - while block. Same should also be the case for macros 856 starting with `if` to avoid logic defects:: 857 858 #define macrofun(a, b, c) \ 859 do { \ 860 if (a == 5) \ 861 do_this(b, c); \ 862 } while (0) 863 864 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#macros-enums-and-rtl 865 866 **PREFER_FALLTHROUGH** 867 Use the `fallthrough;` pseudo keyword instead of 868 `/* fallthrough */` like comments. 869 870 **TRAILING_SEMICOLON** 871 Macro definition should not end with a semicolon. The macro 872 invocation style should be consistent with function calls. 873 This can prevent any unexpected code paths:: 874 875 #define MAC do_something; 876 877 If this macro is used within a if else statement, like:: 878 879 if (some_condition) 880 MAC; 881 882 else 883 do_something; 884 885 Then there would be a compilation error, because when the macro is 886 expanded there are two trailing semicolons, so the else branch gets 887 orphaned. 888 889 See: https://lore.kernel.org/lkml/1399671106.2912.21.camel@joe-AO725/ 890 891 **MACRO_ARG_UNUSED** 892 If function-like macros do not utilize a parameter, it might result 893 in a build warning. We advocate for utilizing static inline functions 894 to replace such macros. 895 For example, for a macro such as the one below:: 896 897 #define test(a) do { } while (0) 898 899 there would be a warning like below:: 900 901 WARNING: Argument 'a' is not used in function-like macro. 902 903 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#macros-enums-and-rtl 904 905 **SINGLE_STATEMENT_DO_WHILE_MACRO** 906 For the multi-statement macros, it is necessary to use the do-while 907 loop to avoid unpredictable code paths. The do-while loop helps to 908 group the multiple statements into a single one so that a 909 function-like macro can be used as a function only. 910 911 But for the single statement macros, it is unnecessary to use the 912 do-while loop. Although the code is syntactically correct but using 913 the do-while loop is redundant. So remove the do-while loop for single 914 statement macros. 915 916 **WEAK_DECLARATION** 917 Using weak declarations like __attribute__((weak)) or __weak 918 can have unintended link defects. Avoid using them. 919 920 921Functions and Variables 922----------------------- 923 924 **CAMELCASE** 925 Avoid CamelCase Identifiers. 926 927 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#naming 928 929 **CONST_CONST** 930 Using `const <type> const *` is generally meant to be 931 written `const <type> * const`. 932 933 **CONST_STRUCT** 934 Using const is generally a good idea. Checkpatch reads 935 a list of frequently used structs that are always or 936 almost always constant. 937 938 The existing structs list can be viewed from 939 `scripts/const_structs.checkpatch`. 940 941 See: https://lore.kernel.org/lkml/alpine.DEB.2.10.1608281509480.3321@hadrien/ 942 943 **EMBEDDED_FUNCTION_NAME** 944 Embedded function names are less appropriate to use as 945 refactoring can cause function renaming. Prefer the use of 946 "%s", __func__ to embedded function names. 947 948 Note that this does not work with -f (--file) checkpatch option 949 as it depends on patch context providing the function name. 950 951 **FUNCTION_ARGUMENTS** 952 This warning is emitted due to any of the following reasons: 953 954 1. Arguments for the function declaration do not follow 955 the identifier name. Example:: 956 957 void foo 958 (int bar, int baz) 959 960 This should be corrected to:: 961 962 void foo(int bar, int baz) 963 964 2. Some arguments for the function definition do not 965 have an identifier name. Example:: 966 967 void foo(int) 968 969 All arguments should have identifier names. 970 971 **FUNCTION_WITHOUT_ARGS** 972 Function declarations without arguments like:: 973 974 int foo() 975 976 should be:: 977 978 int foo(void) 979 980 **GLOBAL_INITIALISERS** 981 Global variables should not be initialized explicitly to 982 0 (or NULL, false, etc.). Your compiler (or rather your 983 loader, which is responsible for zeroing out the relevant 984 sections) automatically does it for you. 985 986 **INITIALISED_STATIC** 987 Static variables should not be initialized explicitly to zero. 988 Your compiler (or rather your loader) automatically does 989 it for you. 990 991 **MULTIPLE_ASSIGNMENTS** 992 Multiple assignments on a single line makes the code unnecessarily 993 complicated. So on a single line assign value to a single variable 994 only, this makes the code more readable and helps avoid typos. 995 996 **RETURN_PARENTHESES** 997 return is not a function and as such doesn't need parentheses:: 998 999 return (bar); 1000 1001 can simply be:: 1002 1003 return bar; 1004 1005 **UNINITIALIZED_PTR_WITH_FREE** 1006 Pointers with __free attribute should be declared at the place of use 1007 and initialized (see include/linux/cleanup.h). In this case 1008 declarations at the top of the function rule can be relaxed. Not doing 1009 so may lead to undefined behavior as the memory assigned (garbage, 1010 in case not initialized) to the pointer is freed automatically when 1011 the pointer goes out of scope. 1012 1013 Also see: https://lore.kernel.org/lkml/58fd478f408a34b578ee8d949c5c4b4da4d4f41d.camel@HansenPartnership.com/ 1014 1015 Example:: 1016 1017 type var __free(free_func); 1018 ... // var not used, but, in future someone might add a return here 1019 var = malloc(var_size); 1020 ... 1021 1022 should be initialized as:: 1023 1024 ... 1025 type var __free(free_func) = malloc(var_size); 1026 ... 1027 1028 1029Permissions 1030----------- 1031 1032 **DEVICE_ATTR_PERMS** 1033 The permissions used in DEVICE_ATTR are unusual. 1034 Typically only three permissions are used - 0644 (RW), 0444 (RO) 1035 and 0200 (WO). 1036 1037 See: https://www.kernel.org/doc/html/latest/filesystems/sysfs.html#attributes 1038 1039 **EXECUTE_PERMISSIONS** 1040 There is no reason for source files to be executable. The executable 1041 bit can be removed safely. 1042 1043 **EXPORTED_WORLD_WRITABLE** 1044 Exporting world writable sysfs/debugfs files is usually a bad thing. 1045 When done arbitrarily they can introduce serious security bugs. 1046 In the past, some of the debugfs vulnerabilities would seemingly allow 1047 any local user to write arbitrary values into device registers - a 1048 situation from which little good can be expected to emerge. 1049 1050 See: https://lore.kernel.org/linux-arm-kernel/cover.1296818921.git.segoon@openwall.com/ 1051 1052 **NON_OCTAL_PERMISSIONS** 1053 Permission bits should use 4 digit octal permissions (like 0700 or 0444). 1054 Avoid using any other base like decimal. 1055 1056 **SYMBOLIC_PERMS** 1057 Permission bits in the octal form are more readable and easier to 1058 understand than their symbolic counterparts because many command-line 1059 tools use this notation. Experienced kernel developers have been using 1060 these traditional Unix permission bits for decades and so they find it 1061 easier to understand the octal notation than the symbolic macros. 1062 For example, it is harder to read S_IWUSR|S_IRUGO than 0644, which 1063 obscures the developer's intent rather than clarifying it. 1064 1065 See: https://lore.kernel.org/lkml/CA+55aFw5v23T-zvDZp-MmD_EYxF8WbafwwB59934FV7g21uMGQ@mail.gmail.com/ 1066 1067 1068Spacing and Brackets 1069-------------------- 1070 1071 **ASSIGNMENT_CONTINUATIONS** 1072 Assignment operators should not be written at the start of a 1073 line but should follow the operand at the previous line. 1074 1075 **BRACES** 1076 The placement of braces is stylistically incorrect. 1077 The preferred way is to put the opening brace last on the line, 1078 and put the closing brace first:: 1079 1080 if (x is true) { 1081 we do y 1082 } 1083 1084 This applies for all non-functional blocks. 1085 However, there is one special case, namely functions: they have the 1086 opening brace at the beginning of the next line, thus:: 1087 1088 int function(int x) 1089 { 1090 body of function 1091 } 1092 1093 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces 1094 1095 **BRACKET_SPACE** 1096 Whitespace before opening bracket '[' is prohibited. 1097 There are some exceptions: 1098 1099 1. With a type on the left:: 1100 1101 int [] a; 1102 1103 2. At the beginning of a line for slice initialisers:: 1104 1105 [0...10] = 5, 1106 1107 3. Inside a curly brace:: 1108 1109 = { [0...10] = 5 } 1110 1111 **CONCATENATED_STRING** 1112 Concatenated elements should have a space in between. 1113 Example:: 1114 1115 printk(KERN_INFO"bar"); 1116 1117 should be:: 1118 1119 printk(KERN_INFO "bar"); 1120 1121 **ELSE_AFTER_BRACE** 1122 `else {` should follow the closing block `}` on the same line. 1123 1124 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces 1125 1126 **LINE_SPACING** 1127 Vertical space is wasted given the limited number of lines an 1128 editor window can display when multiple blank lines are used. 1129 1130 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces 1131 1132 **OPEN_BRACE** 1133 The opening brace should be following the function definitions on the 1134 next line. For any non-functional block it should be on the same line 1135 as the last construct. 1136 1137 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces 1138 1139 **POINTER_LOCATION** 1140 When using pointer data or a function that returns a pointer type, 1141 the preferred use of * is adjacent to the data name or function name 1142 and not adjacent to the type name. 1143 Examples:: 1144 1145 char *linux_banner; 1146 unsigned long long memparse(char *ptr, char **retptr); 1147 char *match_strdup(substring_t *s); 1148 1149 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces 1150 1151 **SPACING** 1152 Whitespace style used in the kernel sources is described in kernel docs. 1153 1154 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces 1155 1156 **TRAILING_WHITESPACE** 1157 Trailing whitespace should always be removed. 1158 Some editors highlight the trailing whitespace and cause visual 1159 distractions when editing files. 1160 1161 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#spaces 1162 1163 **UNNECESSARY_PARENTHESES** 1164 Parentheses are not required in the following cases: 1165 1166 1. Function pointer uses:: 1167 1168 (foo->bar)(); 1169 1170 could be:: 1171 1172 foo->bar(); 1173 1174 2. Comparisons in if:: 1175 1176 if ((foo->bar) && (foo->baz)) 1177 if ((foo == bar)) 1178 1179 could be:: 1180 1181 if (foo->bar && foo->baz) 1182 if (foo == bar) 1183 1184 3. addressof/dereference single Lvalues:: 1185 1186 &(foo->bar) 1187 *(foo->bar) 1188 1189 could be:: 1190 1191 &foo->bar 1192 *foo->bar 1193 1194 **WHILE_AFTER_BRACE** 1195 while should follow the closing bracket on the same line:: 1196 1197 do { 1198 ... 1199 } while(something); 1200 1201 See: https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces 1202 1203 1204Others 1205------ 1206 1207 **CONFIG_DESCRIPTION** 1208 Kconfig symbols should have a help text which fully describes 1209 it. 1210 1211 **CORRUPTED_PATCH** 1212 The patch seems to be corrupted or lines are wrapped. 1213 Please regenerate the patch file before sending it to the maintainer. 1214 1215 **CVS_KEYWORD** 1216 Since linux moved to git, the CVS markers are no longer used. 1217 So, CVS style keywords ($Id$, $Revision$, $Log$) should not be 1218 added. 1219 1220 **DEFAULT_NO_BREAK** 1221 switch default case is sometimes written as "default:;". This can 1222 cause new cases added below default to be defective. 1223 1224 A "break;" should be added after empty default statement to avoid 1225 unwanted fallthrough. 1226 1227 **DOS_LINE_ENDINGS** 1228 For DOS-formatted patches, there are extra ^M symbols at the end of 1229 the line. These should be removed. 1230 1231 **DT_SCHEMA_BINDING_PATCH** 1232 DT bindings moved to a json-schema based format instead of 1233 freeform text. 1234 1235 See: https://www.kernel.org/doc/html/latest/devicetree/bindings/writing-schema.html 1236 1237 **DT_SPLIT_BINDING_PATCH** 1238 Devicetree bindings should be their own patch. This is because 1239 bindings are logically independent from a driver implementation, 1240 they have a different maintainer (even though they often 1241 are applied via the same tree), and it makes for a cleaner history in the 1242 DT only tree created with git-filter-branch. 1243 1244 See: https://www.kernel.org/doc/html/latest/devicetree/bindings/submitting-patches.html#i-for-patch-submitters 1245 1246 **EMBEDDED_FILENAME** 1247 Embedding the complete filename path inside the file isn't particularly 1248 useful as often the path is moved around and becomes incorrect. 1249 1250 **FILE_PATH_CHANGES** 1251 Whenever files are added, moved, or deleted, the MAINTAINERS file 1252 patterns can be out of sync or outdated. 1253 1254 So MAINTAINERS might need updating in these cases. 1255 1256 **MEMSET** 1257 The memset use appears to be incorrect. This may be caused due to 1258 badly ordered parameters. Please recheck the usage. 1259 1260 **NOT_UNIFIED_DIFF** 1261 The patch file does not appear to be in unified-diff format. Please 1262 regenerate the patch file before sending it to the maintainer. 1263 1264 **PLACEHOLDER_USE** 1265 Detects unhandled placeholder text left in cover letters or commit headers/logs. 1266 Common placeholders include lines like:: 1267 1268 *** SUBJECT HERE *** 1269 *** BLURB HERE *** 1270 1271 These typically come from autogenerated templates. Replace them with a proper 1272 subject and description before sending. 1273 1274 **PRINTF_0XDECIMAL** 1275 Prefixing 0x with decimal output is defective and should be corrected. 1276 1277 **SPDX_LICENSE_TAG** 1278 The source file is missing or has an improper SPDX identifier tag. 1279 The Linux kernel requires the precise SPDX identifier in all source files, 1280 and it is thoroughly documented in the kernel docs. 1281 1282 See: https://www.kernel.org/doc/html/latest/process/license-rules.html 1283 1284 **TYPO_SPELLING** 1285 Some words may have been misspelled. Consider reviewing them.
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