2 .\" Copyright (c) 1995-2019 The FreeBSD Project
4 .\" Redistribution and use in source and binary forms, with or without
5 .\" modification, are permitted provided that the following conditions
7 .\" 1. Redistributions of source code must retain the above copyright
8 .\" notice, this list of conditions and the following disclaimer.
9 .\" 2. Redistributions in binary form must reproduce the above copyright
10 .\" notice, this list of conditions and the following disclaimer in the
11 .\" documentation and/or other materials provided with the distribution.
13 .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
14 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
15 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
16 .\" ARE DISCLAIMED. IN NO EVENT SHALL [your name] OR CONTRIBUTORS BE LIABLE
17 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
18 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
19 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
20 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
21 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
22 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
25 .\" From: @(#)style 1.14 (Berkeley) 4/28/95
33 .Nd "kernel source file style guide"
35 This file specifies the preferred style for kernel source files in the
38 It is also a guide for the preferred userland code style.
39 Many of the style rules are implicit in the examples.
40 Be careful to check the examples before assuming that
42 is silent on an issue.
45 * Style guide for FreeBSD. Based on the CSRG's KNF (Kernel Normal Form).
47 * @(#)style 1.14 (Berkeley) 4/28/95
52 * VERY important single-line comments look like this.
55 /* Most single-line comments look like this. */
58 * Multi-line comments look like this. Make them real sentences. Fill
59 * them so they look like real paragraphs.
63 The copyright header should be a multi-line comment, with the first
64 line of the comment having a dash after the star like so:
67 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
69 * Copyright (c) 1984-2025 John Q. Public
71 * Long, boring license goes here, but trimmed for brevity
75 An automatic script collects license information from the tree for
76 all comments that start in the first column with
80 to not reformat a comment that starts in the first column which is not a
81 license or copyright notice, change the dash to a star for those
83 Comments starting in columns other than the first are never
84 considered license statements.
85 Use the appropriate SPDX-License-Identifier line before the copyright.
86 If the copyright assertion contains the phrase
87 .Dq Li "All Rights Reserved"
88 that should be on the same line as the word
90 You should not insert a new copyright line between an old
91 copyright line and this phrase.
92 Instead, you should insert a new copyright phrase after
94 .Dq Li "All Rights Reserved"
96 When making changes, it is acceptable to fold an
97 .Dq Li "All Rights Reserved"
101 For files that have the
102 .Dq Li "All Rights Reserved"
103 line on the same line(s) as the word
105 new copyright assertions should be added last.
108 lines should only be added when making substantial changes to the file,
109 not for trivial changes.
111 After any copyright and license comment, there is a blank line, and the
113 for non C/C++ language source files.
114 Version control system ID tags should only exist once in a file
115 (unlike in this one).
116 Non-C/C++ source files follow the example above, while C/C++ source files
117 follow the one below.
118 All VCS (version control system) revision identification in files obtained
119 from elsewhere should be maintained, including, where applicable, multiple IDs
120 showing a file's history.
121 In general, do not edit foreign IDs or their infrastructure.
122 Unless otherwise wrapped (such as
123 .Dq Li "#if defined(LIBC_SCCS)" ) ,
125 .Dq Li "#if 0 ... #endif"
126 to hide any uncompilable bits
127 and to keep the IDs out of object files.
130 in front of foreign VCS IDs if the file is renamed.
132 /* From: @(#)style 1.14 (Berkeley) 4/28/95 */
134 #include <sys/cdefs.h>
135 __FBSDID("$FreeBSD$");
138 Leave one blank line before the header files.
152 is needed, include it before other include files.
159 The remaining kernel headers should be sorted alphabetically.
161 #include <sys/types.h> /* Non-local includes in angle brackets. */
162 #include <sys/endian.h>
163 #include <sys/lock.h>
164 #include <sys/queue.h>
167 For a network program, put the network include files next.
170 #include <net/if_dl.h>
171 #include <net/route.h>
172 #include <netinet/in.h>
173 #include <protocols/rwhod.h>
176 Do not include files from
180 Leave a blank line before the next group, the
183 which should be sorted alphabetically by name.
188 Global pathnames are defined in
193 in the local directory.
198 Leave another blank line before the local include files.
200 #include "pathnames.h" /* Local includes in double quotes. */
205 or declare names in the implementation namespace except
206 for implementing application interfaces.
210 macros (ones that have side effects), and the names of macros for
211 manifest constants, are all in uppercase.
212 The expansions of expression-like macros are either a single token
213 or have outer parentheses.
214 Put a single tab character between the
217 If a macro is an inline expansion of a function, the function name is
218 all in lowercase and the macro has the same name all in uppercase.
219 .\" XXX the above conflicts with ANSI style where the names are the
220 .\" same and you #undef the macro (if any) to get the function.
221 .\" It is not followed for MALLOC(), and not very common if inline
222 .\" functions are used.
224 backslashes; it makes it easier to read.
225 If the macro encapsulates a compound statement, enclose it in a
228 so that it can safely be used in
231 Any final statement-terminating semicolon should be
232 supplied by the macro invocation rather than the macro, to make parsing easier
233 for pretty-printers and editors.
235 #define MACRO(x, y) do { \e
236 variable = (x) + (y); \e
241 When code is conditionally compiled using
245 a comment may be added following the matching
249 to permit the reader to easily discern where conditionally compiled code
251 This comment should be used only for (subjectively) long regions, regions
252 greater than 20 lines, or where a series of nested
254 may be confusing to the reader.
255 The comment should be separated from the
260 For short conditionally compiled regions, a closing comment should not be
265 should match the expression used in the corresponding
273 should match the inverse of the expression(s) used in the preceding
278 In the comments, the subexpression
282 For the purposes of comments,
283 .Dq Ic #ifndef Li FOO
285 .Dq Ic #if Li !defined(FOO) .
288 #include <sys/ktrace.h>
292 /* A large region here, or other conditional code. */
293 #else /* !COMPAT_43 */
295 #endif /* COMPAT_43 */
298 /* Yet another large region here, or other conditional code. */
299 #else /* COMPAT_43 */
301 #endif /* !COMPAT_43 */
304 The project prefers the use of
306 unsigned integer identifiers of the form
308 rather than the older
310 integer identifiers of the form
312 New code should use the former, and old code should be converted to
313 the new form if other major work is being done in that area and
314 there is no overriding reason to prefer the older
316 Like white-space commits, care should be taken in making
320 Similarly, the project prefers the use of
323 rather than the older
329 and old code may be converted if it is
331 Literal values are named
335 These are preferred to the old spellings
339 Userspace code should include
341 while kernel code should include
344 Likewise, the project prefers
346 designated initializers when it makes sense to do so.
348 Enumeration values are all uppercase.
350 enum enumtype { ONE, TWO } et;
353 The use of internal_underscores in identifiers is preferred over
354 camelCase or TitleCase.
356 In declarations, do not put any whitespace between asterisks and
357 adjacent tokens, except for tokens that are identifiers related to
359 (These identifiers are the names of basic types, type
361 .Ic typedef Ns -names
362 other than the one being declared.)
363 Separate these identifiers from asterisks using a single space.
365 When declaring variables in structures, declare them sorted by use, then
366 by size (largest to smallest), and then in alphabetical order.
367 The first category normally does not apply, but there are exceptions.
368 Each one gets its own line.
369 Try to make the structure
370 readable by aligning the member names using either one or two tabs
371 depending upon your judgment.
372 You should use one tab only if it suffices to align at least 90% of
374 Names following extremely long types
375 should be separated by a single space.
377 Major structures should be declared at the top of the file in which they
378 are used, or in separate header files if they are used in multiple
380 Use of the structures should be by separate declarations
383 if they are declared in a header file.
386 struct foo *next; /* List of active foo. */
387 struct mumble amumble; /* Comment for mumble. */
388 int bar; /* Try to align the comments. */
389 struct verylongtypename *baz; /* Does not fit in 2 tabs. */
391 struct foo *foohead; /* Head of global foo list. */
396 macros rather than rolling your own lists, whenever possible.
398 the previous example would be better written:
400 #include <sys/queue.h>
403 LIST_ENTRY(foo) link; /* Use queue macros for foo lists. */
404 struct mumble amumble; /* Comment for mumble. */
405 int bar; /* Try to align the comments. */
406 struct verylongtypename *baz; /* Does not fit in 2 tabs. */
408 LIST_HEAD(, foo) foohead; /* Head of global foo list. */
411 Avoid using typedefs for structure types.
412 Typedefs are problematic because they do not properly hide their
413 underlying type; for example you need to know if the typedef is
414 the structure itself or a pointer to the structure.
415 In addition they must be declared exactly once, whereas an
416 incomplete structure type can be mentioned as many times as
418 Typedefs are difficult to use in stand-alone header files:
419 the header that defines the typedef must be included
420 before the header that uses it, or by the header that uses
421 it (which causes namespace pollution), or there must be a
422 back-door mechanism for obtaining the typedef.
424 When convention requires a
426 make its name match the struct tag.
427 Avoid typedefs ending in
429 except as specified in Standard C or by POSIX.
431 /* Make the structure name match the typedef. */
435 typedef int foo; /* This is foo. */
436 typedef const long baz; /* This is baz. */
439 All functions are prototyped somewhere.
441 Function prototypes for private functions (i.e., functions not used
442 elsewhere) go at the top of the first source module.
444 local to one source module should be declared
447 Functions used from other parts of the kernel are prototyped in the
448 relevant include file.
449 Function prototypes should be listed in a logical order, preferably
450 alphabetical unless there is a compelling reason to use a different
453 Functions that are used locally in more than one module go into a
454 separate header file, e.g.,
461 In general code can be considered
463 when it makes up about 50% or more of the file(s) involved.
465 to break precedents in the existing code and use the current
469 The kernel has a name associated with parameter types, e.g., in the kernel
472 void function(int fd);
475 In header files visible to userland applications, prototypes that are
476 visible must use either
478 names (ones beginning with an underscore)
479 or no names with the types.
480 It is preferable to use protected names.
488 void function(int _fd);
491 Prototypes may have an extra space after a tab to enable function names
494 static char *function(int _arg, const char *_arg2, struct foo *_arg3,
496 static void usage(void);
499 * All major routines should have a comment briefly describing what
500 * they do. The comment before the "main" routine should describe
501 * what the program does.
504 main(int argc, char *argv[])
513 should be used to parse options.
515 should be sorted in the
525 statement that cascade should have a
528 Numerical arguments should be checked for accuracy.
529 Code which is unreachable for non-obvious reasons may be marked /*
533 while ((ch = getopt(argc, argv, "abNn:")) != -1)
534 switch (ch) { /* Indent the switch. */
535 case 'a': /* Do not indent the case. */
536 aflag = 1; /* Indent case body one tab. */
545 num = strtol(optarg, &ep, 10);
546 if (num <= 0 || *ep != '\e0') {
547 warnx("illegal number, -n argument -- %s",
561 .Pq Ic if , while , for , return , switch .
566 are allowed for single line statements.
567 Either they are used for all single statements, or
568 they are used only where needed for clarity.
569 Usage within a function should be consistent.
570 Forever loops are done with
575 for (p = buf; *p != '\e0'; ++p)
580 z = a + really + long + statement + that + needs +
581 two + lines + gets + indented + four + spaces +
582 on + the + second + and + subsequent + lines;
589 val = realloc(val, newsize);
594 loop may be left empty.
596 for (; cnt < 15; cnt++) {
604 loop may declare and initialize its counting variable.
606 for (int i = 0; i < 15; i++) {
611 Indentation is an 8 character tab.
612 Second level indents are four spaces.
613 If you have to wrap a long statement, put the operator at the end of the
616 while (cnt < 20 && this_variable_name_is_too_long &&
618 z = a + really + long + statement + that + needs +
619 two + lines + gets + indented + four + spaces +
620 on + the + second + and + subsequent + lines;
623 Do not add whitespace at the end of a line, and only use tabs
625 to form the indentation.
626 Do not use more spaces than a tab will produce
627 and do not use spaces in front of tabs.
629 Closing and opening braces go on the same line as the
631 Braces that are not necessary may be left out.
642 No spaces after function names.
643 Commas have a space after them.
655 error = function(a1, a2);
660 Unary operators do not require spaces, binary operators do.
661 Do not use parentheses unless they are required for precedence or unless the
662 statement is confusing without them.
663 Remember that other people may
664 confuse easier than you.
665 Do YOU understand the following?
667 a = b->c[0] + ~d == (e || f) || g && h ? i : j >> 1;
671 Exits should be 0 on success, or 1 on failure.
674 * Avoid obvious comments such as
675 * "Exit 0 on success."
680 The function type should be on a line by itself
681 preceding the function.
682 The opening brace of the function body should be
686 function(int a1, int a2, float fl, int a4, struct bar *bar)
690 When declaring variables in functions declare them sorted by size,
691 then in alphabetical order; multiple ones per line are okay.
692 If a line overflows reuse the type keyword.
693 Variables may be initialized where declared especially when they
694 are constant for the rest of the scope.
695 Declarations may be placed before executable lines at the start
697 Calls to complicated functions should be avoided when initializing variables.
699 struct foo one, *two;
700 struct baz *three = bar_get_baz(bar);
703 char *seven, eight, nine, ten, eleven, twelve;
705 four = my_complicated_function(a1, f1, a4);
708 Do not declare functions inside other functions; ANSI C says that
709 such declarations have file scope regardless of the nesting of the
711 Hiding file declarations in what appears to be a local
712 scope is undesirable and will elicit complaints from a good compiler.
716 are not followed by a space.
719 does not understand this rule.
721 are written with parenthesis always.
722 The redundant parenthesis rules do not apply to
727 is the preferred null pointer constant.
731 .Vt ( "type *" ) Ns 0
733 .Vt ( "type *" ) Ns Dv NULL
734 in contexts where the compiler knows the
735 type, e.g., in assignments.
737 .Vt ( "type *" ) Ns Dv NULL
739 in particular for all function args.
740 (Casting is essential for
741 variadic args and is necessary for other args if the function prototype
742 might not be in scope.)
743 Test pointers against
757 for tests unless it is a boolean, e.g., use:
769 should not have their return values cast
774 statements should be enclosed in parentheses.
780 do not roll your own.
782 if ((four = malloc(sizeof(struct foo))) == NULL)
783 err(1, (char *)NULL);
784 if ((six = (int *)overflow()) == NULL)
785 errx(1, "number overflowed");
790 When converting K&R style declarations to ANSI style, preserve
791 any comments about parameters.
793 Long parameter lists are wrapped with a normal four space indent.
795 Variable numbers of arguments should look like this:
800 vaf(const char *fmt, ...)
807 /* No return needed for void functions. */
813 /* Optional blank line goes here. */
816 Optionally, insert a blank line at the beginning of functions with no local
818 Older versions of this
820 document required the blank line convention, so it is widely used in existing
823 Do not insert a blank line at the beginning of functions with local variables.
824 Instead, these should have local variable declarations first, followed by one
825 blank line, followed by the first statement.
833 whatever; it is faster and usually cleaner, not
834 to mention avoiding stupid bugs.
836 Usage statements should look like the manual pages
838 The usage statement should be structured in the following order:
841 Options without operands come first,
842 in alphabetical order,
843 inside a single set of brackets
848 Options with operands come next,
849 also in alphabetical order,
850 with each option and its argument inside its own pair of brackets.
855 listed in the order they should be specified on the command line.
858 any optional arguments should be listed,
859 listed in the order they should be specified,
860 and all inside brackets.
868 and multiple options/arguments which are specified together are
869 placed in a single set of brackets.
870 .Bd -literal -offset 4n
871 "usage: f [-aDde] [-b b_arg] [-m m_arg] req1 req2 [opt1 [opt2]]\en"
872 "usage: f [-a | -b] [-c [-dEe] [-n number]]\en"
875 (void)fprintf(stderr, "usage: f [-ab]\en");
880 Note that the manual page options description should list the options in
881 pure alphabetical order.
882 That is, without regard to whether an option takes arguments or not.
883 The alphabetical ordering should take into account the case ordering
886 New core kernel code should be reasonably compliant with the
889 The guidelines for third-party maintained modules and device drivers are more
890 relaxed but at a minimum should be internally consistent with their style.
892 Stylistic changes (including whitespace changes) are hard on the source
893 repository and are to be avoided without good reason.
894 Code that is approximately
898 compliant in the repository must not diverge from compliance.
900 Whenever possible, code should be run through a code checker
901 (e.g., various static analyzers or
903 and produce minimal warnings.
910 .Bl -tag -width indent
911 .It Pa /usr/src/tools/tools/editing/freebsd.el
912 An Emacs plugin to follow the
916 .It Pa /usr/src/tools/tools/editing/freebsd.vim
917 A Vim plugin to follow the
926 .Xr style.Makefile 5 ,
930 This manual page is largely based on the
931 .Pa src/admin/style/style
934 release, with occasional updates to reflect the current practice and
938 .Pa src/admin/style/style
939 is a codification by the CSRG of the programming style of Ken Thompson and