2 .\" Copyright (c) 1995-2005 The FreeBSD Project
3 .\" All rights reserved.
5 .\" Redistribution and use in source and binary forms, with or without
6 .\" modification, are permitted provided that the following conditions
8 .\" 1. Redistributions of source code must retain the above copyright
9 .\" notice, this list of conditions and the following disclaimer.
10 .\" 2. Redistributions in binary form must reproduce the above copyright
11 .\" notice, this list of conditions and the following disclaimer in the
12 .\" documentation and/or other materials provided with the distribution.
14 .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 .\" ARE DISCLAIMED. IN NO EVENT SHALL [your name] OR CONTRIBUTORS BE LIABLE
18 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 .\" From: @(#)style 1.14 (Berkeley) 4/28/95
34 .Nd "kernel source file style guide"
36 This file specifies the preferred style for kernel source files in the
39 It is also a guide for the preferred userland code style.
40 Many of the style rules are implicit in the examples.
41 Be careful to check the examples before assuming that
43 is silent on an issue.
46 * Style guide for FreeBSD. Based on the CSRG's KNF (Kernel Normal Form).
48 * @(#)style 1.14 (Berkeley) 4/28/95
53 * VERY important single-line comments look like this.
56 /* Most single-line comments look like this. */
59 * Multi-line comments look like this. Make them real sentences. Fill
60 * them so they look like real paragraphs.
64 The copyright header should be a multi-line comment, with the first
65 line of the comment having a dash after the star like so:
68 * Copyright (c) 1984-2025 John Q. Public
69 * All rights reserved.
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.
86 After any copyright header, there is a blank line, and the
88 for non C/C++ language source files.
89 Version control system ID tags should only exist once in a file
91 Non-C/C++ source files follow the example above, while C/C++ source files
93 All VCS (version control system) revision identification in files obtained
94 from elsewhere should be maintained, including, where applicable, multiple IDs
95 showing a file's history.
96 In general, do not edit foreign IDs or their infrastructure.
97 Unless otherwise wrapped (such as
98 .Dq Li "#if defined(LIBC_SCCS)" ) ,
100 .Dq Li "#if 0 ... #endif"
101 to hide any uncompilable bits
102 and to keep the IDs out of object files.
105 in front of foreign VCS IDs if the file is renamed.
109 static char sccsid[] = "@(#)style 1.14 (Berkeley) 4/28/95";
110 #endif /* not lint */
113 #include <sys/cdefs.h>
114 __FBSDID("$FreeBSD$");
117 Leave another blank line before the header files.
119 Kernel include files (i.e.\&
121 come first; normally, include
129 and it is okay to depend on that.
131 #include <sys/types.h> /* Non-local includes in angle brackets. */
134 For a network program, put the network include files next.
137 #include <net/if_dl.h>
138 #include <net/route.h>
139 #include <netinet/in.h>
140 #include <protocols/rwhod.h>
145 for files in the kernel.
147 Leave a blank line before the next group, the
150 which should be sorted alphabetically by name.
155 Global pathnames are defined in
160 in the local directory.
165 Leave another blank line before the user include files.
167 #include "pathnames.h" /* Local includes in double quotes. */
172 or declare names in the implementation namespace except
173 for implementing application interfaces.
177 macros (ones that have side effects), and the names of macros for
178 manifest constants, are all in uppercase.
179 The expansions of expression-like macros are either a single token
180 or have outer parentheses.
181 Put a single tab character between the
184 If a macro is an inline expansion of a function, the function name is
185 all in lowercase and the macro has the same name all in uppercase.
186 .\" XXX the above conflicts with ANSI style where the names are the
187 .\" same and you #undef the macro (if any) to get the function.
188 .\" It is not followed for MALLOC(), and not very common if inline
189 .\" functions are used.
191 backslashes; it makes it easier to read.
192 If the macro encapsulates a compound statement, enclose it in a
195 so that it can safely be used in
198 Any final statement-terminating semicolon should be
199 supplied by the macro invocation rather than the macro, to make parsing easier
200 for pretty-printers and editors.
202 #define MACRO(x, y) do { \e
203 variable = (x) + (y); \e
208 When code is conditionally compiled using
212 a comment may be added following the matching
216 to permit the reader to easily discern where conditionally compiled code
218 This comment should be used only for (subjectively) long regions, regions
219 greater than 20 lines, or where a series of nested
221 may be confusing to the reader.
222 Exceptions may be made for cases where code is conditionally not compiled for
225 even though the uncompiled region may be small.
226 The comment should be separated from the
231 For short conditionally compiled regions, a closing comment should not be
236 should match the expression used in the corresponding
244 should match the inverse of the expression(s) used in the preceding
249 In the comments, the subexpression
253 For the purposes of comments,
254 .Dq Ic #ifndef Li FOO
256 .Dq Ic #if Li !defined(FOO) .
259 #include <sys/ktrace.h>
263 /* A large region here, or other conditional code. */
264 #else /* !COMPAT_43 */
266 #endif /* COMPAT_43 */
269 /* Yet another large region here, or other conditional code. */
270 #else /* COMPAT_43 */
272 #endif /* !COMPAT_43 */
275 The project is slowly moving to use the
277 unsigned integer identifiers of the form
279 in preference to the older
281 integer identifiers of the form
283 New code should use the former, and old code should be converted to
284 the new form if other major work is being done in that area and
285 there is no overriding reason to prefer the older
287 Like white-space commits, care should be taken in making
291 Enumeration values are all uppercase.
293 enum enumtype { ONE, TWO } et;
296 The use of internal_underscores in identifiers is preferred over
297 camelCase or TitleCase.
299 In declarations, do not put any whitespace between asterisks and
300 adjacent tokens, except for tokens that are identifiers related to
302 (These identifiers are the names of basic types, type
304 .Ic typedef Ns -names
305 other than the one being declared.)
306 Separate these identifiers from asterisks using a single space.
308 When declaring variables in structures, declare them sorted by use, then
309 by size (largest to smallest), and then in alphabetical order.
310 The first category normally does not apply, but there are exceptions.
311 Each one gets its own line.
312 Try to make the structure
313 readable by aligning the member names using either one or two tabs
314 depending upon your judgment.
315 You should use one tab only if it suffices to align at least 90% of
317 Names following extremely long types
318 should be separated by a single space.
320 Major structures should be declared at the top of the file in which they
321 are used, or in separate header files if they are used in multiple
323 Use of the structures should be by separate declarations
326 if they are declared in a header file.
329 struct foo *next; /* List of active foo. */
330 struct mumble amumble; /* Comment for mumble. */
331 int bar; /* Try to align the comments. */
332 struct verylongtypename *baz; /* Won't fit in 2 tabs. */
334 struct foo *foohead; /* Head of global foo list. */
339 macros rather than rolling your own lists, whenever possible.
341 the previous example would be better written:
343 #include <sys/queue.h>
346 LIST_ENTRY(foo) link; /* Use queue macros for foo lists. */
347 struct mumble amumble; /* Comment for mumble. */
348 int bar; /* Try to align the comments. */
349 struct verylongtypename *baz; /* Won't fit in 2 tabs. */
351 LIST_HEAD(, foo) foohead; /* Head of global foo list. */
354 Avoid using typedefs for structure types.
355 Typedefs are problematic because they do not properly hide their
356 underlying type; for example you need to know if the typedef is
357 the structure itself or a pointer to the structure.
358 In addition they must be declared exactly once, whereas an
359 incomplete structure type can be mentioned as many times as
361 Typedefs are difficult to use in stand-alone header files:
362 the header that defines the typedef must be included
363 before the header that uses it, or by the header that uses
364 it (which causes namespace pollution), or there must be a
365 back-door mechanism for obtaining the typedef.
367 When convention requires a
369 make its name match the struct tag.
370 Avoid typedefs ending in
372 except as specified in Standard C or by
375 /* Make the structure name match the typedef. */
379 typedef int foo; /* This is foo. */
380 typedef const long baz; /* This is baz. */
383 All functions are prototyped somewhere.
385 Function prototypes for private functions (i.e., functions not used
386 elsewhere) go at the top of the first source module.
388 local to one source module should be declared
391 Functions used from other parts of the kernel are prototyped in the
392 relevant include file.
393 Function prototypes should be listed in a logical order, preferably
394 alphabetical unless there is a compelling reason to use a different
397 Functions that are used locally in more than one module go into a
398 separate header file, e.g.\&
405 In general code can be considered
407 when it makes up about 50% or more of the file(s) involved.
409 to break precedents in the existing code and use the current
413 The kernel has a name associated with parameter types, e.g., in the kernel
416 void function(int fd);
419 In header files visible to userland applications, prototypes that are
420 visible must use either
422 names (ones beginning with an underscore)
423 or no names with the types.
424 It is preferable to use protected names.
432 void function(int _fd);
435 Prototypes may have an extra space after a tab to enable function names
438 static char *function(int _arg, const char *_arg2, struct foo *_arg3,
440 static void usage(void);
443 * All major routines should have a comment briefly describing what
444 * they do. The comment before the "main" routine should describe
445 * what the program does.
448 main(int argc, char *argv[])
457 should be used to parse options.
459 should be sorted in the
469 statement that cascade should have a
472 Numerical arguments should be checked for accuracy.
473 Code which is unreachable for non-obvious reasons may be marked /*
477 while ((ch = getopt(argc, argv, "abNn:")) != -1)
478 switch (ch) { /* Indent the switch. */
479 case 'a': /* Don't indent the case. */
480 aflag = 1; /* Indent case body one tab. */
489 num = strtol(optarg, &ep, 10);
490 if (num <= 0 || *ep != '\e0') {
491 warnx("illegal number, -n argument -- %s",
505 .Pq Ic if , while , for , return , switch .
511 used for control statements with zero or only a single statement unless that
512 statement is more than a single line in which case they are permitted.
513 Forever loops are done with
518 for (p = buf; *p != '\e0'; ++p)
523 z = a + really + long + statement + that + needs +
524 two + lines + gets + indented + four + spaces +
525 on + the + second + and + subsequent + lines;
532 val = realloc(val, newsize);
537 loop may be left empty.
538 Do not put declarations
539 inside blocks unless the routine is unusually complicated.
541 for (; cnt < 15; cnt++) {
547 Indentation is an 8 character tab.
548 Second level indents are four spaces.
549 If you have to wrap a long statement, put the operator at the end of the
552 while (cnt < 20 && this_variable_name_is_too_long &&
554 z = a + really + long + statement + that + needs +
555 two + lines + gets + indented + four + spaces +
556 on + the + second + and + subsequent + lines;
559 Do not add whitespace at the end of a line, and only use tabs
561 to form the indentation.
562 Do not use more spaces than a tab will produce
563 and do not use spaces in front of tabs.
565 Closing and opening braces go on the same line as the
567 Braces that are not necessary may be left out.
578 No spaces after function names.
579 Commas have a space after them.
591 error = function(a1, a2);
596 Unary operators do not require spaces, binary operators do.
597 Do not use parentheses unless they are required for precedence or unless the
598 statement is confusing without them.
599 Remember that other people may
600 confuse easier than you.
601 Do YOU understand the following?
603 a = b->c[0] + ~d == (e || f) || g && h ? i : j >> 1;
607 Exits should be 0 on success, or 1 on failure.
610 * Avoid obvious comments such as
611 * "Exit 0 on success."
616 The function type should be on a line by itself
617 preceding the function.
618 The opening brace of the function body should be
622 function(int a1, int a2, float fl, int a4)
626 When declaring variables in functions declare them sorted by size,
627 then in alphabetical order; multiple ones per line are okay.
628 If a line overflows reuse the type keyword.
630 Be careful to not obfuscate the code by initializing variables in
632 Use this feature only thoughtfully.
633 DO NOT use function calls in initializers.
635 struct foo one, *two;
638 char *six, seven, eight, nine, ten, eleven, twelve;
643 Do not declare functions inside other functions; ANSI C says that
644 such declarations have file scope regardless of the nesting of the
646 Hiding file declarations in what appears to be a local
647 scope is undesirable and will elicit complaints from a good compiler.
651 are not followed by a space.
654 does not understand this rule.
656 are written with parenthesis always.
657 The redundant parenthesis rules do not apply to
662 is the preferred null pointer constant.
666 .Vt ( "type *" ) Ns 0
668 .Vt ( "type *" ) Ns Dv NULL
669 in contexts where the compiler knows the
670 type, e.g., in assignments.
672 .Vt ( "type *" ) Ns Dv NULL
674 in particular for all function args.
675 (Casting is essential for
676 variadic args and is necessary for other args if the function prototype
677 might not be in scope.)
678 Test pointers against
692 for tests unless it is a boolean, e.g.\& use:
704 should not have their return values cast
709 statements should be enclosed in parentheses.
715 do not roll your own.
717 if ((four = malloc(sizeof(struct foo))) == NULL)
718 err(1, (char *)NULL);
719 if ((six = (int *)overflow()) == NULL)
720 errx(1, "number overflowed");
725 Old-style function declarations look like this:
728 function(a1, a2, fl, a4)
729 int a1, a2; /* Declare ints, too, don't default them. */
730 float fl; /* Beware double vs. float prototype differences. */
731 int a4; /* List in order declared. */
735 Use ANSI function declarations unless you explicitly need K&R compatibility.
736 Long parameter lists are wrapped with a normal four space indent.
738 Variable numbers of arguments should look like this:
743 vaf(const char *fmt, ...)
750 /* No return needed for void functions. */
756 /* Insert an empty line if the function has no local variables. */
765 whatever; it is faster and usually cleaner, not
766 to mention avoiding stupid bugs.
768 Usage statements should look like the manual pages
770 The usage statement should be structured in the following order:
773 Options without operands come first,
774 in alphabetical order,
775 inside a single set of brackets
780 Options with operands come next,
781 also in alphabetical order,
782 with each option and its argument inside its own pair of brackets.
787 listed in the order they should be specified on the command line.
790 any optional arguments should be listed,
791 listed in the order they should be specified,
792 and all inside brackets.
800 and multiple options/arguments which are specified together are
801 placed in a single set of brackets.
802 .Bd -literal -offset 4n
803 "usage: f [-aDde] [-b b_arg] [-m m_arg] req1 req2 [opt1 [opt2]]\en"
804 "usage: f [-a | -b] [-c [-dEe] [-n number]]\en"
807 (void)fprintf(stderr, "usage: f [-ab]\en");
812 Note that the manual page options description should list the options in
813 pure alphabetical order.
814 That is, without regard to whether an option takes arguments or not.
815 The alphabetical ordering should take into account the case ordering
818 New core kernel code should be reasonably compliant with the
821 The guidelines for third-party maintained modules and device drivers are more
822 relaxed but at a minimum should be internally consistent with their style.
824 Stylistic changes (including whitespace changes) are hard on the source
825 repository and are to be avoided without good reason.
826 Code that is approximately
830 compliant in the repository must not diverge from compliance.
832 Whenever possible, code should be run through a code checker
837 and produce minimal warnings.
845 This manual page is largely based on the
846 .Pa src/admin/style/style
849 release, with occasional updates to reflect the current practice and
853 .Pa src/admin/style/style
854 is a codification by the CSRG of the programming style of Ken Thompson and