STYLE(9) BSD Kernel Developer's Manual STYLE(9)
NAME
style -- kernel source file style guide
DESCRIPTION
This file specifies the preferred style for kernel source files in the FreeBSD source tree. It is also a guide for preferred userland code
style.
/*
* Style guide for FreeBSD. Based on the CSRG's KNF (Kernel Normal Form).
*
* @(#)style 1.14 (Berkeley) 4/28/95
* $FreeBSD: src/share/man/man9/style.9,v 1.32.2.16 2001/12/17 11:30:19 ru 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.
*/
After any copyright header, there is a blank line, and the rcsid for source files. Version control system ID tags should only exist once in
a file (unlike this one). Non-C/C++ source files follow the example above, while C/C++ source files follow the one below. All VCS (version
control system) revision identification from files obtained from elsewhere should be maintained, including, where applicable, multiple IDs
showing a file's history. In general, keep the IDs intact, including any '$'s. There is no reason to add "From" in front of foreign VCS
IDs. Most non-FreeBSD VCS IDs should be indented by a tab if in a comment.
#include <sys/cdefs.h>
__RCSID("@(#)style 1.14 (Berkeley) 4/28/95");
__FBSDID("$FreeBSD: src/share/man/man9/style.9,v 1.32.2.16 2001/12/17 11:30:19 ru Exp $");
Leave another blank line before the header files.
Kernel include files (i.e. sys/*.h) come first; normally, include <sys/types.h> OR <sys/param.h>, but not both. <sys/types.h> includes
<sys/cdefs.h>, and it is okay to depend on that.
#include <sys/types.h> /* Non-local includes in angle brackets. */
For 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>
Leave a blank line before the next group, the /usr include files, which should be sorted alphabetically by name.
#include <stdio.h>
Global pathnames are defined in <paths.h>. Pathnames local to the program go in "pathnames.h" in the local directory.
#include <paths.h>
Leave another blank line before the user include files.
#include "pathnames.h" /* Local includes in double quotes. */
Do not #define or declare names in the implementation namespace except for implementing application interfaces.
The names of ``unsafe'' macros (ones that have side effects), and the names of macros for manifest constants, are all in uppercase. The
expansions of expression-like macros are either a single token or have outer parentheses. Put a single tab character between the #define and
the macro name. If a macro is an inline expansion of a function, the function name is all in lowercase and the macro has the same name all
in uppercase. If a macro needs more than a single line, use braces ('{' and '}'). Right-justify the backslashes; it makes it easier to
read. If the macro encapsulates a compound statement, enclose it in a do loop, so that it can safely be used in if statements. Any final
statement-terminating semicolon should be supplied by the macro invocation rather than the macro, to make parsing easier for pretty-printers
and editors.
#define MACRO(x, y) do {
variable = (x) + (y);
(y) += 2;
} while(0)
Enumeration values are all uppercase.
enum enumtype { ONE, TWO } et;
When declaring variables in structures, declare them sorted by use, then by size, and then in alphabetical order. The first category nor-
mally does not apply, but there are exceptions. Each one gets its own line. Try to make the structure readable by aligning the member names
using either one or two tabs depending upon your judgment. You should use one tab if it suffices to align most of the member names. Names
following extremely long types should be separated by a single space.
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; /* Try to align the comments. */
struct verylongtypename *baz; /* Won't fit in 2 tabs. */
};
struct foo *foohead; /* Head of global foo list. */
Use queue(3) macros rather than rolling your own lists, whenever possible. Thus, the previous example would be better written:
#include <sys/queue.h>
struct foo {
LIST_ENTRY(foo) link; /* Use queue macros for foo lists. */
struct mumble amumble; /* Comment for mumble. */
int bar; /* Try to align the comments. */
struct verylongtypename *baz; /* Won't fit in 2 tabs. */
};
LIST_HEAD(, foo) foohead; /* Head of global foo list. */
Avoid using typedefs for structure types. This makes it impossible for applications to use pointers to such a structure opaquely, which is
both possible and beneficial when using an ordinary struct tag. When convention requires a typedef, make its name match the struct tag.
Avoid typedefs ending in ``_t'', except as specified in Standard C or by POSIX.
/* 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 local to
one source module should be declared static.
Functions used from other parts of the kernel are prototyped in the relevant include file.
Functions that are used locally in more than one module go into a separate header file, e.g. "extern.h".
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 com-
piler. Use of the __P macro in new code is discouraged, although modifications to existing files should be consistent with that file's con-
ventions.
In general code can be considered ``new code'' when it makes up about 50% or more of the file(s) involved. This is enough to break prece-
dents in the existing code and use the current style guidelines.
The kernel has a name associated with parameter types, e.g., in the kernel use:
void function(int fd);
In header files visible to userland applications, prototypes that are visible must use either ``protected'' names (ones beginning with an
underscore) or no names with the types. It is preferable to use protected names. E.g., use:
void function(int);
or:
void function(int _fd);
Prototypes may have an extra space after a tab to enable function names to line up:
static char *function(int _arg, const char *_arg2, struct foo *_arg3,
struct bar *_arg4);
static void usage(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(int argc, char *argv[])
{
long num;
int ch;
char *ep;
For consistency, getopt(3) should be used to parse options. Options should be sorted in the getopt(3) 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:")) != -1)
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 != '