.Dd December 14, 1995
.Dt STYLE 9
.Os FreeBSD 2.2
.Sh NAME
.Nm style
.Nd "Kernel source file style guide"
.Sh DESCRIPTION
This file contains an example of the preferred style for kernel source
files in the FreeBSD source tree.
.in 0
.Bd -literal
/*
 * Style guide for the 4BSD KNF (Kernel Normal Form).
 *
 *	@(#)style	1.14 (Berkeley) 4/28/95
 *
 *	FreeBSD $Id: style.9,v 1.3 1995/12/21 18:35:19 phk Exp $
 *
 */

/*
 * VERY important single-line comments look like this.
 */

/* Most single-line comments look like this. */

/*
 * Multi-line comments look like this.  Make them real sentences.  Fill
 * them so they look like real paragraphs.
 */

/*
 * Kernel include files come first; normally, you'll need <sys/types.h>
 * OR <sys/param.h>, but not both!  <sys/types.h> includes <sys/cdefs.h>,
 * and it's okay to depend on that.
 */
#include <sys/types.h>		/* Non-local includes in brackets. */

/* If it's a network program, put the network include files next. */
#include <net/if.h>
#include <net/if_dl.h>
#include <net/route.h>
#include <netinet/in.h>
#include <protocols/rwhod.h>

/*
 * Then there's a blank line, followed by the /usr include files.
 * The /usr include files should be sorted!
 */
#include <stdio.h>

/*
 * Global pathnames are defined in /usr/include/paths.h.  Pathnames local
 * to the program go in pathnames.h in the local directory.
 */
#include <paths.h>

/* Then, there's a blank line, and the user include files. */
#include "pathnames.h"		/* Local includes in double quotes. */

/*
 * Macros are capitalized, parenthesized, and should avoid side-effects.
 * If they are an inline expansion of a function, the function is defined
 * all in lowercase, the macro has the same name all in uppercase. If the
 * macro needs more than a single line, use braces.  Right-justify the
 * backslashes, it makes it easier to read.
 */
#define	MACRO(x, y) {							\e
	variable = (x) + (y);						\e
	(y) += 2;							\e
}

/* Enum types are capitalized. */
enum enumtype { ONE, TWO } et;

/*
 * When declaring variables in structures, declare them sorted by use, then
 * by size, and then by alphabetical order.  The first category normally
 * doesn't apply, but there are exceptions.  Each one gets its own line.
 * Put a tab after the first word, i.e. use "int^Ix;" and "struct^Ifoo *x;".
 *
 * Major structures should be declared at the top of the file in which they
 * are used, or in separate header files, if they are used in multiple
 * source files.  Use of the structures should be by separate declarations
 * and should be "extern" if they are declared in a header file.
 */
struct foo {
	struct	foo *next;	/* List of active foo */
	struct	mumble amumble;	/* Comment for mumble */
	int	bar;
};
struct foo *foohead;		/* Head of global foo list */

/* Make the structure name match the typedef. */
typedef struct _bar {
	int	level;
} BAR;

/*
 * All functions are prototyped somewhere.
 *
 * Function prototypes for private functions (i.e. functions not used
 * elsewhere) go at the top of the first source module.
 *
 * Functions used from other parts of the kernel are prototyped in the
 * relevant include file.
 *
 * Only use the __P macro from the include file <sys/cdefs.h> if the source
 * file in general is (to be) compilable with a K&R Old testament compiler.
 *
 * Only the kernel has a name associated with the types, i.e. in the kernel
 * use:
 *
 *	void function __P((int fd));
 *
 * in user land use:
 *
 *	void function __P((int));
 */
static char	*function __P((int, const char *));
static void	 usage __P((void));

/*
 * All major routines should have a comment briefly describing what
 * they do.  The comment before the "main" routine should describe
 * what the program does.
 */
int
main(argc, argv)
	int argc;
	char *argv[];
{
	extern char *optarg;
	extern int optind;
	long num;
	int ch;
	char *ep;

	/*
	 * For consistency, getopt should be used to parse options.  Options
	 * should be sorted in the getopt call and the switch statement, unless
	 * parts of the switch cascade.  Elements in a switch statement that
	 * cascade should have a FALLTHROUGH comment.  Numerical arguments
	 * should be checked for accuracy.  Code that cannot be reached should
	 * have a NOTREACHED comment.
	 */
	while ((ch = getopt(argc, argv, "abn")) != EOF)
		switch (ch) {		/* Indent the switch. */
		case 'a':		/* Don't indent the case. */
			aflag = 1;
			/* FALLTHROUGH */
		case 'b':
			bflag = 1;
			break;
		case 'n':
			num = strtol(optarg, &ep, 10);
			if (num <= 0 || *ep != '\e0')
				err("illegal number -- %s", optarg);
			break;
		case '?':
		default:
			usage();
			/* NOTREACHED */
		}
	argc -= optind;
	argv += optind;

	/*
	 * Space after keywords (while, for, return, switch).  No braces are
	 * used for control statements with zero or only a single statement.
	 *
	 * Forever loops are done with for's, not while's.
	 */
	for (p = buf; *p != '\e0'; ++p);
	for (;;)
		stmt;

	/*
	 * Parts of a for loop may be left empty.  Don't put declarations
	 * inside blocks unless the routine is unusually complicated.
	 */
	for (; cnt < 15; cnt++) {
		stmt1;
		stmt2;
	}

	/* Second level indents are four spaces. */
	while (cnt < 20)
		z = a + really + long + statment + that + needs + two lines +
		    gets + indented + four + spaces + on + the + second +
		    and + subsequent + lines.

	/*
	 * Closing and opening braces go on the same line as the else.
	 * Don't add braces that aren't necessary.
	 */
	if (test)
		stmt;
	else if (bar) {
		stmt;
		stmt;
	} else
		stmt;

	/* No spaces after function names. */
	if (error = function(a1, a2))
		exit(error);

	/*
	 * Unary operators don't require spaces, binary operators do. Don't
	 * use parenthesis unless they're required for precedence, or the
	 * statement is really confusing without them.
	 */
	a = b->c[0] + ~d == (e || f) || g && h ? i : j >> 1;
	k = !(l & FLAGS);

	/*
	 * Exits should be 0 on success, and 1 on failure.  Don't denote
	 * all the possible exit points, using the integers 1 through 300.
	 */
	exit(0);    /* Avoid obvious comments such as "Exit 0 on success." */
}

/*
 * If a function type is declared, it should be on a line
 * by itself preceeding the function.
 */
static char *
function(a1, a2, fl, a4)
	int a1, a2, a4;	/* Declare ints, too, don't default them. */
	float fl;	/* List in order declared, as much as possible. */
{
	/*
	 * When declaring variables in functions declare them sorted by size,
	 * then in alphabetical order; multiple ones per line are okay.  Old
	 * style function declarations can go on the same line.  ANSI style
	 * function declarations should go in the include file "extern.h".
	 * If a line overflows reuse the type keyword.
	 *
	 * DO NOT initialize variables in the declarations.
	 */
	extern u_char one;
	extern char two;
	struct foo three, *four;
	double five;
	int *six, seven, eight();
	char *nine, ten, eleven, twelve, thirteen, fourteen, fifteen, sixteen;
	char *overflow __P((void));
	void *mymalloc __P((u_int));

	/*
	 * Casts and sizeof's are not followed by a space.  NULL is any
	 * pointer type, and doesn't need to be cast, so use NULL instead
	 * of (struct foo *)0 or (struct foo *)NULL.  Also, test pointers
	 * against NULL, i.e. use:
	 *
	 * 	(p = f()) == NULL
	 * not:
	 *	!(p = f())
	 *
	 * Don't use '!' for tests unless it's a boolean, e.g. use
	 * "if (*p == '\e0')", not "if (!*p)".
 	 *
	 * Routines returning void * should not have their return values cast
	 * to any pointer type.
	 *
	 * Use err/warn(3), don't roll your own!
	 */
	if ((four = malloc(sizeof(struct foo))) == NULL)
		err(1, NULL);
	if ((six = (int *)overflow()) == NULL)
		errx(1, "Number overflowed.");
	return (eight);
}

/*
 * Don't use ANSI function declarations unless you absolutely have too,
 * i.e. you're declaring functions with variable numbers of arguments.
 *
 * ANSI function return values and braces look like regular functions.
 */
int
function(int a1, int a2)
{
	...
}

/* Variable numbers of arguments should look like this. */
#if __STDC__
#include <stdarg.h>
#else
#include <varargs.h>
#endif

void
#if __STDC__
vaf(const char *fmt, ...)
#else
vaf(fmt, va_alist)
	char *fmt;
	va_dcl
#endif
{
	va_list ap;
#if __STDC__
	va_start(ap, fmt);
#else
	va_start(ap);
#endif
	STUFF;

	va_end(ap);		/* No return needed for void functions. */
}

static void
usage()
{	/* Insert an empty line if the function has no local variables. */

	/*
	 * Use printf(3), not fputs/puts/putchar/whatever, it's faster and
	 * usually cleaner, not to mention avoiding stupid bugs.
	 *
	 * Usage statements should look like the manual pages.  Options w/o
	 * operands come first, in alphabetical order inside a single set of
	 * braces.  Followed by options with operands, in alphabetical order,
	 * each in braces.  Followed by required arguments in the order they
	 * are specified, followed by optional arguments in the order they
	 * are specified.  A bar ('|') separates either/or options/arguments,
	 * and multiple options/arguments which are specified together are
	 * placed in a single set of braces.
	 *
	 * "usage: f [-ade] [-b b_arg] [-m m_arg] req1 req2 [opt1 [opt2]]\en"
	 * "usage: f [-a | -b] [-c [-de] [-n number]]\en"
	 */
	(void)fprintf(stderr, "usage: f [-ab]\en");
	exit(1);
}
.Ed
.Sh HISTORY
This man page is largely based on the src/admin/style/style file from
the BSD 4.4-Lite2 release, with a few updates to reflect the current
practice and desire of the FreeBSD project.