style.9 revision 12830
1.Dd December 14, 1995 2.Dt STYLE 9 3.Os FreeBSD 2.2 4.Sh NAME 5.Nm STYLE 6.Nd "Kernel source file style guide" 7.Sh DESCRIPTION 8This file contains an example of the preferred style for kernel source 9files in the FreeBSD source tree. 10.in 0 11.Bd -literal 12/* 13 * Style guide for the 4BSD KNF (Kernel Normal Form). 14 * 15 * @(#)style 1.14 (Berkeley) 4/28/95 16 */ 17 18/* 19 * VERY important single-line comments look like this. 20 */ 21 22/* Most single-line comments look like this. */ 23 24/* 25 * Multi-line comments look like this. Make them real sentences. 26 * Fill them so they look like real paragraphs. 27 */ 28 29/* 30 * Kernel include files come first; normally, you'll need 31 * <sys/types.h> OR <sys/param.h>, but not both! <sys/types.h> 32 * includes <sys/cdefs.h>, and it's okay to depend on that. 33 */ 34#include <sys/types.h> /* Non-local includes in brackets. */ 35 36/* If it's a network program, put the network include files next. */ 37#include <net/if.h> 38#include <net/if_dl.h> 39#include <net/route.h> 40#include <netinet/in.h> 41#include <protocols/rwhod.h> 42 43/* 44 * Then there's a blank line, followed by the /usr include files. 45 * The /usr include files should be sorted! 46 */ 47#include <stdio.h> 48 49/* 50 * Global pathnames are defined in /usr/include/paths.h. Pathnames 51 * local to the program go in pathnames.h in the local directory. 52 */ 53#include <paths.h> 54 55/* Then, there's a blank line, and the user include files. */ 56#include "pathnames.h" /* Local includes in double quotes. */ 57 58/* 59 * Macros are capitalized, parenthesized, and should avoid side- 60 * effects. If they are an inline expansion of a function, the 61 * function is defined all in lowercase, the macro has the same 62 * name all in uppercase. If the macro needs more than a single 63 * line, use braces. Right-justify the backslashes, it makes it 64 * easier to read. 65 */ 66#define MACRO(x, y) { \e 67 variable = (x) + (y); \e 68 (y) += 2; \e 69} 70 71/* Enum types are capitalized. */ 72enum enumtype { ONE, TWO } et; 73 74/* 75 * When declaring variables in structures, declare them sorted by use, 76 * then by size, and then by alphabetical order. The first category 77 * normally doesn't apply, but there are exceptions. Each one gets 78 * its own line. 79 * Put a tab after the first word, i.e. use 80 * "int^Ix;" and "struct^Ifoo *x;". 81 * 82 * Major structures should be declared at the top of the file in which 83 * they are used, or in separate header files, if they are used in 84 * multiple source files. Use of the structures should be by separate 85 * declarations and should be "extern" if they are declared in a header 86 * file. 87 */ 88struct foo { 89 struct foo *next; /* List of active foo */ 90 struct mumble amumble; /* Comment for mumble */ 91 int bar; 92}; 93struct foo *foohead; /* Head of global foo list */ 94 95/* Make the structure name match the typedef. */ 96typedef struct _bar { 97 int level; 98} BAR; 99 100/* 101 * All functions are prototyped somewhere. 102 * 103 * Function prototypes for private functions (i.e. functions 104 * not used elsewhere) go at the top of the first source module. 105 * 106 * Functions used from other parts of the kernel are prototyped 107 * in the relevant include file. 108 * 109 * Only use the __P macro from the include file <sys/cdefs.h> if the 110 * source file in general is compilable with an K&R Old testament 111 * compiler. 112 * 113 * Only the kernel has a name associated with the types, i.e. in the 114 * kernel use: 115 * 116 * void function __P((int fd)); 117 * 118 * in user land use: 119 * 120 * void function __P((int)); 121 */ 122static char *function __P((int, const char *)); 123static void usage __P((void)); 124 125/* 126 * All major routines should have a comment briefly describing what 127 * they do. The comment before the "main" routine should describe 128 * what the program does. 129 */ 130int 131main(argc, argv) 132 int argc; 133 char *argv[]; 134{ 135 extern char *optarg; 136 extern int optind; 137 long num; 138 int ch; 139 char *ep; 140 141 /* 142 * For consistency, getopt should be used to parse options. 143 * Options should be sorted in the getopt call and the switch 144 * statement, unless parts of the switch cascade. Elements 145 * in a switch statement that cascade should have a FALLTHROUGH 146 * comment. Numerical arguments should be checked for accuracy. 147 * Code that cannot be reached should have a NOTREACHED comment. 148 */ 149 while ((ch = getopt(argc, argv, "abn")) != EOF) 150 switch (ch) { /* Indent the switch. */ 151 case 'a': /* Don't indent the case. */ 152 aflag = 1; 153 /* FALLTHROUGH */ 154 case 'b': 155 bflag = 1; 156 break; 157 case 'n': 158 num = strtol(optarg, &ep, 10); 159 if (num <= 0 || *ep != '\e0') 160 err("illegal number -- %s", optarg); 161 break; 162 case '?': 163 default: 164 usage(); 165 /* NOTREACHED */ 166 } 167 argc -= optind; 168 argv += optind; 169 170 /* 171 * Space after keywords (while, for, return, switch). 172 * No braces are used for control statements with zero or only 173 * a single statement. 174 * 175 * Forever loops are done with for's, not while's. 176 */ 177 for (p = buf; *p != '\e0'; ++p); 178 for (;;) 179 stmt; 180 181 /* 182 * Parts of a for loop may be left empty. Don't put 183 * declarations inside blocks unless the routine is unusually 184 * complicated. 185 */ 186 for (; cnt < 15; cnt++) { 187 stmt1; 188 stmt2; 189 } 190 191 /* Second level indents are four spaces. */ 192 while (cnt < 20) 193 z = a + really + long + statment + that + needs + 194 two lines + gets + indented + four + spaces + on + 195 the + second + and + subsequent + lines. 196 197 /* 198 * Closing and opening braces go on the same line as the else. 199 * Don't add braces that aren't necessary. 200 */ 201 if (test) 202 stmt; 203 else if (bar) { 204 stmt; 205 stmt; 206 } else 207 stmt; 208 209 /* No spaces after function names. */ 210 if (error = function(a1, a2)) 211 exit(error); 212 213 /* 214 * Unary operators don't require spaces, binary operators do. 215 * Don't use parenthesis unless they're required for precedence, 216 * or the statement is really confusing without them. 217 */ 218 a = b->c[0] + ~d == (e || f) || g && h ? i : j >> 1; 219 k = !(l & FLAGS); 220 221 /* 222 * Exits should be 0 on success, and 1 on failure. Don't 223 * denote all the possible exit points, using the integers 224 * 1 through 300. 225 */ 226 exit(0); /* Avoid obvious comments such as "Exit 0 on success." */ 227} 228 229/* 230 * If a function type is declared, it should be on a line 231 * by itself preceeding the function. 232 */ 233static char * 234function(a1, a2, fl, a4) 235 int a1, a2, a4; /* Declare ints, too, don't default them. */ 236 float fl; /* List in order declared, as much as possible. */ 237{ 238 /* 239 * When declaring variables in functions declare them sorted 240 * by size, then in alphabetical order; multiple ones per line 241 * are okay. Old style function declarations can go on the same 242 * line. ANSI style function declarations should go in the 243 * include file "extern.h". If a line overflows reuse the type 244 * keyword. 245 * 246 * DO NOT initialize variables in the declarations. 247 */ 248 extern u_char one; 249 extern char two; 250 struct foo three, *four; 251 double five; 252 int *six, seven, eight(); 253 char *nine, ten, eleven, twelve, thirteen, fourteen, fifteen; 254 char *overflow __P((void)); 255 void *mymalloc __P((u_int)); 256 257 /* 258 * Casts and sizeof's are not followed by a space. NULL is any 259 * pointer type, and doesn't need to be cast, so use NULL instead 260 * of (struct foo *)0 or (struct foo *)NULL. Also, test pointers 261 * against NULL, i.e. use: 262 * 263 * (p = f()) == NULL 264 * not: 265 * !(p = f()) 266 * 267 * Don't use '!' for tests unless it's a boolean, e.g. use 268 * "if (*p == '\e0')", not "if (!*p)". 269 * 270 * Routines returning void * should not have their return 271 * values cast to any pointer type. 272 * 273 * Use err/warn(3), don't roll your own! 274 */ 275 if ((four = malloc(sizeof(struct foo))) == NULL) 276 err(1, NULL); 277 if ((six = (int *)overflow()) == NULL) 278 errx(1, "Number overflowed."); 279 return (eight); 280} 281 282/* 283 * Don't use ANSI function declarations unless you absolutely have too, 284 * i.e. you're declaring functions with variable numbers of arguments. 285 * 286 * ANSI function return values and braces look like regular functions. 287 */ 288int 289function(int a1, int a2) 290{ 291 ... 292} 293 294/* Variable numbers of arguments should look like this. */ 295#if __STDC__ 296#include <stdarg.h> 297#else 298#include <varargs.h> 299#endif 300 301void 302#if __STDC__ 303vaf(const char *fmt, ...) 304#else 305vaf(fmt, va_alist) 306 char *fmt; 307 va_dcl 308#endif 309{ 310 va_list ap; 311#if __STDC__ 312 va_start(ap, fmt); 313#else 314 va_start(ap); 315#endif 316 STUFF; 317 318 va_end(ap); /* No return needed for void functions. */ 319} 320 321static void 322usage() 323{ /* Insert an empty line if the function has no local variables. */ 324 325 /* 326 * Use printf(3), not fputs/puts/putchar/whatever, it's faster 327 * and usually cleaner, not to mention avoiding stupid bugs. 328 * 329 * Usage statements should look like the manual pages. Options 330 * w/o operands come first, in alphabetical order inside a single 331 * set of braces. Followed by options with operands, in 332 * alphabetical order, each in braces. Followed by required 333 * arguments in the order they are specified, followed by optional 334 * arguments in the order they are specified. A bar ('|') 335 * separates either/or options/arguments, and multiple options/ 336 * arguments which are specified together are placed in a single 337 * set of braces. 338 * 339 * "usage: f [-ade] [-b b_arg] [-m m_arg] req1 req2 [opt1 [opt2]]\en" 340 * "usage: f [-a | -b] [-c [-de] [-n number]]\en" 341 */ 342 (void)fprintf(stderr, "usage: f [-ab]\en"); 343 exit(1); 344} 345.Ed 346.Sh HISTORY 347This man page is largely based on the src/admin/style/style file from 348the BSD 4.4-Lite2 release, with a few updates to reflect the current 349practice and desire of the FreeBSD project. 350 351 352