416 lines
11 KiB
Groff
416 lines
11 KiB
Groff
.Dd December 14, 1995
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.Dt STYLE 9
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.Os FreeBSD 2.2
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.Sh NAME
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.Nm style
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.Nd "Kernel source file style guide"
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.Sh DESCRIPTION
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This file contains an example of the preferred style for kernel source
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files in the FreeBSD source tree.
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.Bd -literal -offset 0i
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/*
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* Style guide for the 4BSD KNF (Kernel Normal Form).
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*
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* @(#)style 1.14 (Berkeley) 4/28/95
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*
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* $Id: style.9,v 1.8 1996/06/13 19:52:42 wollman Exp $
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*
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*/
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/*
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* VERY important single-line comments look like this.
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*/
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/* Most single-line comments look like this. */
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/*
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* Multi-line comments look like this. Make them real sentences. Fill
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* them so they look like real paragraphs.
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*/
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.Ed
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.Pp
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Kernel include files come first; normally, you'll need <sys/types.h>
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OR <sys/param.h>, but not both! <sys/types.h> includes <sys/cdefs.h>,
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and it's okay to depend on that.
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.Bd -literal -offset 0i
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#include <sys/types.h> /* Non-local includes in brackets. */
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.Ed
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.Pp
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If it's a network program, put the network include files next.
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.Bd -literal -offset 0i
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#include <net/if.h>
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#include <net/if_dl.h>
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#include <net/route.h>
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#include <netinet/in.h>
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#include <protocols/rwhod.h>
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.Ed
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.Pp
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Then there's a blank line, followed by the /usr include files.
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The /usr include files should be sorted!
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.Bd -literal -offset 0i
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#include <stdio.h>
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.Ed
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.Pp
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Global pathnames are defined in /usr/include/paths.h. Pathnames local
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to the program go in pathnames.h in the local directory.
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.Bd -literal -offset 0i
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#include <paths.h>
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.Ed
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.Pp
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Then, there's a blank line, and the user include files.
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.Bd -literal -offset 0i
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#include "pathnames.h" /* Local includes in double quotes. */
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.Ed
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.Pp
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Macros are capitalized, parenthesized, and should avoid side-effects.
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If they are an inline expansion of a function, the function is defined
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all in lowercase, the macro has the same name all in uppercase. If the
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macro needs more than a single line, use braces. Right-justify the
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backslashes, it makes it easier to read.
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.Bd -literal -offset 0i
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#define MACRO(x, y) { \e
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variable = (x) + (y); \e
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(y) += 2; \e
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}
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.Ed
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.Pp
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Enum types are capitalized.
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.Bd -literal -offset 0i
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enum enumtype { ONE, TWO } et;
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.Ed
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.Pp
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When declaring variables in structures, declare them sorted by use, then
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by size, and then by alphabetical order. The first category normally
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doesn't apply, but there are exceptions. Each one gets its own line.
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Put a tab after the first word, i.e. use
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.Ql int^Ix;
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and
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.Ql struct^Ifoo *x; .
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.Pp
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Major structures should be declared at the top of the file in which they
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are used, or in separate header files, if they are used in multiple
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source files. Use of the structures should be by separate declarations
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and should be "extern" if they are declared in a header file.
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.Bd -literal -offset 0i
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struct foo {
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struct foo *next; /* List of active foo */
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struct mumble amumble; /* Comment for mumble */
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int bar;
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};
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struct foo *foohead; /* Head of global foo list */
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/* Make the structure name match the typedef. */
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typedef struct _bar {
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int level;
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} BAR;
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.Ed
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.Pp
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All functions are prototyped somewhere.
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.Pp
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Function prototypes for private functions (i.e. functions not used
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elsewhere) go at the top of the first source module. Functions
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local to one source module should be declared
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.Ql static .
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.Pp
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Functions used from other parts of the kernel are prototyped in the
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relevant include file.
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.Pp
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Functions that are used locally in more than one module go into a
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separate header file, e.g.
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.Pa extern.h .
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.Pp
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Only use the __P macro from the include file <sys/cdefs.h> if the source
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file in general is (to be) compilable with a K&R Old testament compiler.
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.Pp
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Only the kernel has a name associated with the types, i.e. in the kernel
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use:
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.Bd -literal -offset 0i
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void function __P((int fd));
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.Ed
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.Pp
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in user land use:
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.Bd -literal -offset 0i
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void function __P((int));
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static char *function __P((int, const char *));
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static void usage __P((void));
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/*
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* All major routines should have a comment briefly describing what
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* they do. The comment before the "main" routine should describe
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* what the program does.
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*/
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int
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main(argc, argv)
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int argc;
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char *argv[];
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{
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extern char *optarg;
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extern int optind;
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long num;
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int ch;
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char *ep;
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.Ed
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.Pp
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For consistency, getopt should be used to parse options. Options
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should be sorted in the getopt call and the switch statement, unless
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parts of the switch cascade. Elements in a switch statement that
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cascade should have a FALLTHROUGH comment. Numerical arguments
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should be checked for accuracy. Code that cannot be reached should
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have a NOTREACHED comment.
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.Bd -literal -offset 0i
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while ((ch = getopt(argc, argv, "abn")) != EOF)
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switch (ch) { /* Indent the switch. */
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case 'a': /* Don't indent the case. */
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aflag = 1;
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/* FALLTHROUGH */
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case 'b':
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bflag = 1;
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break;
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case 'n':
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num = strtol(optarg, &ep, 10);
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if (num <= 0 || *ep != '\e0')
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err("illegal number -- %s", optarg);
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break;
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case '?':
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default:
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usage();
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/* NOTREACHED */
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}
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argc -= optind;
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argv += optind;
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.Ed
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.Pp
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Space after keywords (while, for, return, switch). No braces are
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used for control statements with zero or only a single statement.
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.Pp
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Forever loops are done with for's, not while's.
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.Bd -literal -offset 0i
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for (p = buf; *p != '\e0'; ++p);
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for (;;)
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stmt;
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.Ed
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.Pp
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Parts of a for loop may be left empty. Don't put declarations
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inside blocks unless the routine is unusually complicated.
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.Bd -literal -offset 0i
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for (; cnt < 15; cnt++) {
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stmt1;
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stmt2;
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}
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.Ed
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.Pp
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Second level indents are four spaces.
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.Bd -literal -offset 0i
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while (cnt < 20)
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z = a + really + long + statement + that + needs +
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two lines + gets + indented + four + spaces +
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on + the + second + and + subsequent + lines.
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.Ed
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.Pp
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Closing and opening braces go on the same line as the else.
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Don't add braces that aren't necessary.
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.Bd -literal -offset 0i
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if (test)
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stmt;
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else if (bar) {
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stmt;
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stmt;
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} else
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stmt;
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.Ed
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.Pp
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No spaces after function names.
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.Bd -literal -offset 0i
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if (error = function(a1, a2))
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exit(error);
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.Ed
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.Pp
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Unary operators don't require spaces, binary operators do. Don't
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use parenthesis unless they're required for precedence, or the
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statement is really confusing without them.
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.Bd -literal -offset 0i
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a = b->c[0] + ~d == (e || f) || g && h ? i : j >> 1;
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k = !(l & FLAGS);
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.Ed
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.Pp
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Exits should be 0 on success, or according to the predefined
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values in
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.Xr sysexits 3 .
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.Bd -literal -offset 0i
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exit(EX_OK); /*
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* Avoid obvious comments such as
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* "Exit 0 on success."
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*/
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}
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.Ed
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.Pp
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The function type should be on a line by itself
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preceding the function.
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.Bd -literal -offset 0i
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static char *
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function(a1, a2, fl, a4)
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int a1, a2, a4; /* Declare ints, too, don't default them. */
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float fl; /* List in order declared, as much as possible. */
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{
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.Ed
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.Pp
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When declaring variables in functions declare them sorted by size,
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then in alphabetical order; multiple ones per line are okay.
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Declaring functions inside functions is not recommendable, since their
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linkage scope is always global. If a line overflows reuse the type
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keyword.
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.Pp
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Be careful to not obfuscate the code by initializing variables in
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the declarations. Use this feature only thoughtfully.
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.Bd -literal -offset 0i
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extern u_char one;
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extern char two;
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struct foo three, *four;
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double five;
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int *six, seven, eight();
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char *nine, ten, eleven, twelve, thirteen, fourteen, fifteen;
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char *overflow __P((void));
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void *mymalloc __P((u_int));
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.Ed
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.Pp
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Casts and sizeof's are not followed by a space.
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.Pp
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NULL is the preferred null pointer constant. Use NULL instead of
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(type *)0 or (type *)NULL in contexts where the compiler knows the
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type, e.g., in assignments. Use (type *)NULL in other contexts,
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in particular for all function args. (Casting is essential for
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varadic args and is necessary for other args if the function prototype
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might not be in scope; since we pretend to support K&R compilers,
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most prototypes might not be in scope.)
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Test pointers
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against NULL, e.g., use:
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.Bd -literal -offset 0i
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(p = f()) == NULL
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.Ed
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.Pp
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not:
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.Bd -literal -offset 0i
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!(p = f())
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.Ed
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.Pp
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Don't use '!' for tests unless it's a boolean, e.g. use
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.Bd -literal -offset 0i
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if (*p == '\e0')
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.Ed
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.Pp
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not
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.Bd -literal -offset 0i
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if (!*p)
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.Ed
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.Pp
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Routines returning void * should not have their return values cast
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to any pointer type.
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.Pp
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Use
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.Xr err 3
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or
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.Xr warn 3 ,
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don't roll your own!
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.Bd -literal -offset 0i
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if ((four = malloc(sizeof(struct foo))) == NULL)
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err(1, (char *)NULL);
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if ((six = (int *)overflow()) == NULL)
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errx(1, "Number overflowed.");
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return (eight);
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}
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.Ed
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.Pp
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Don't use ANSI function declarations unless you absolutely have too,
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i.e. you're declaring functions with variable numbers of arguments.
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.Pp
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ANSI function return values and braces look like regular functions.
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.Bd -literal -offset 0i
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int
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function(int a1, int a2)
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{
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...
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}
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.Ed
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.Pp
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Variable numbers of arguments should look like this.
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.Bd -literal -offset 0i
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#if __STDC__
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#include <stdarg.h>
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#else
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#include <varargs.h>
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#endif
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void
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#if __STDC__
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vaf(const char *fmt, ...)
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#else
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vaf(fmt, va_alist)
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char *fmt;
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va_dcl
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#endif
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{
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va_list ap;
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#if __STDC__
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va_start(ap, fmt);
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#else
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va_start(ap);
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#endif
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STUFF;
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va_end(ap); /* No return needed for void functions. */
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}
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static void
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usage()
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{
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/* Insert an empty line if the function has no local variables. */
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.Ed
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.Pp
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Use
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.Xr printf 3 ,
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not fputs/puts/putchar/whatever, it's faster and usually cleaner, not
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to mention avoiding stupid bugs.
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.Pp
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Usage statements should look like the manual pages. Options w/o
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operands come first, in alphabetical order inside a single set of
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braces. Followed by options with operands, in alphabetical order,
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each in braces. Followed by required arguments in the order they
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are specified, followed by optional arguments in the order they
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are specified. A bar
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.Pq Sq \&|
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separates either/or options/arguments,
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and multiple options/arguments which are specified together are
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placed in a single set of braces.
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.Pp
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.Bd -ragged -offset 0.3i
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"usage: f [-ade] [-b b_arg] [-m m_arg] req1 req2 [opt1 [opt2]]\en"
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"usage: f [-a | -b] [-c [-de] [-n number]]\en"
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.Ed
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.Bd -literal -offset 0i
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(void)fprintf(stderr, "usage: f [-ab]\en");
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exit(1);
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}
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.Ed
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.Pp
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Note that the policy regarding the usage of K&R versus ANSI function
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definitions could not be commonly agreed to. While keeping the old
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form is more consistent with the existing code base, sticking to it
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defeats the migration to the more modern ANSI style. For new code,
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chose what you feel is more important. However, when modifying
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existing subsystems or files, stick with the style that is already
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there.
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.Sh SEE ALSO
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.Xr err 3 ,
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.Xr warn 3 ,
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.Xr sysexits 3
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.Sh HISTORY
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This man page is largely based on the src/admin/style/style file from
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the BSD 4.4-Lite2 release, with a few updates to reflect the current
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practice and desire of the FreeBSD project.
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