Coding style is all about readability and maintainability using commonly
available tools.
-The limit on the length of lines is 80 columns and this is a hard limit.
+The limit on the length of lines is 80 columns and this is a strongly
+preferred limit.
Statements longer than 80 columns will be broken into sensible chunks.
Descendants are always substantially shorter than the parent and are placed
substantially to the right. The same applies to function headers with a long
-argument list. Long strings are as well broken into shorter strings.
+argument list. Long strings are as well broken into shorter strings. The
+only exception to this is where exceeding 80 columns significantly increases
+readability and does not hide information.
void fun(int a, int b, int c)
{
25-line terminal screens here), you have more empty lines to put
comments on.
+Do not unnecessarily use braces where a single statement will do.
+
+if (condition)
+ action();
+
+This does not apply if one branch of a conditional statement is a single
+statement. Use braces in both branches.
+
+if (condition) {
+ do_this();
+ do_that();
+} else {
+ otherwise();
+}
+
3.1: Spaces
Linux kernel style for use of spaces depends (mostly) on
and no space around the '.' and "->" structure member operators.
+Do not leave trailing whitespace at the ends of lines. Some editors with
+"smart" indentation will insert whitespace at the beginning of new lines as
+appropriate, so you can start typing the next line of code right away.
+However, some such editors do not remove the whitespace if you end up not
+putting a line of code there, such as if you leave a blank line. As a result,
+you end up with lines containing trailing whitespace.
+
+Git will warn you about patches that introduce trailing whitespace, and can
+optionally strip the trailing whitespace for you; however, if applying a series
+of patches, this may make later patches in the series fail by changing their
+context lines.
+
Chapter 4: Naming
So, you can either get rid of GNU emacs, or change it to use saner
values. To do the latter, you can stick the following in your .emacs file:
-(defun linux-c-mode ()
- "C mode with adjusted defaults for use with the Linux kernel."
- (interactive)
- (c-mode)
- (c-set-style "K&R")
- (setq tab-width 8)
- (setq indent-tabs-mode t)
- (setq c-basic-offset 8))
-
-This will define the M-x linux-c-mode command. When hacking on a
-module, if you put the string -*- linux-c -*- somewhere on the first
-two lines, this mode will be automatically invoked. Also, you may want
-to add
-
-(setq auto-mode-alist (cons '("/usr/src/linux.*/.*\\.[ch]$" . linux-c-mode)
- auto-mode-alist))
-
-to your .emacs file if you want to have linux-c-mode switched on
-automagically when you edit source files under /usr/src/linux.
+(defun c-lineup-arglist-tabs-only (ignored)
+ "Line up argument lists by tabs, not spaces"
+ (let* ((anchor (c-langelem-pos c-syntactic-element))
+ (column (c-langelem-2nd-pos c-syntactic-element))
+ (offset (- (1+ column) anchor))
+ (steps (floor offset c-basic-offset)))
+ (* (max steps 1)
+ c-basic-offset)))
+
+(add-hook 'c-mode-hook
+ (lambda ()
+ (let ((filename (buffer-file-name)))
+ ;; Enable kernel mode for the appropriate files
+ (when (and filename
+ (string-match "~/src/linux-trees" filename))
+ (setq indent-tabs-mode t)
+ (c-set-style "linux")
+ (c-set-offset 'arglist-cont-nonempty
+ '(c-lineup-gcc-asm-reg
+ c-lineup-arglist-tabs-only))))))
+
+This will make emacs go better with the kernel coding style for C
+files below ~/src/linux-trees.
But even if you fail in getting emacs to do sane formatting, not
everything is lost: use "indent".
remember: "indent" is not a fix for bad programming.
- Chapter 10: Configuration-files
+ Chapter 10: Kconfig configuration files
-For configuration options (arch/xxx/Kconfig, and all the Kconfig files),
-somewhat different indentation is used.
+For all of the Kconfig* configuration files throughout the source tree,
+the indentation is somewhat different. Lines under a "config" definition
+are indented with one tab, while help text is indented an additional two
+spaces. Example:
-Help text is indented with 2 spaces.
-
-if CONFIG_EXPERIMENTAL
- tristate CONFIG_BOOM
- default n
- help
- Apply nitroglycerine inside the keyboard (DANGEROUS)
- bool CONFIG_CHEER
- depends on CONFIG_BOOM
- default y
+config AUDIT
+ bool "Auditing support"
+ depends on NET
help
- Output nice messages when you explode
-endif
+ Enable auditing infrastructure that can be used with another
+ kernel subsystem, such as SELinux (which requires this for
+ logging of avc messages output). Does not do system-call
+ auditing without CONFIG_AUDITSYSCALL.
-Generally, CONFIG_EXPERIMENTAL should surround all options not considered
-stable. All options that are known to trash data (experimental write-
-support for file-systems, for instance) should be denoted (DANGEROUS), other
-experimental options should be denoted (EXPERIMENTAL).
+Features that might still be considered unstable should be defined as
+dependent on "EXPERIMENTAL":
+
+config SLUB
+ depends on EXPERIMENTAL && !ARCH_USES_SLAB_PAGE_STRUCT
+ bool "SLUB (Unqueued Allocator)"
+ ...
+
+while seriously dangerous features (such as write support for certain
+filesystems) should advertise this prominently in their prompt string:
+
+config ADFS_FS_RW
+ bool "ADFS write support (DANGEROUS)"
+ depends on ADFS_FS
+ ...
+
+For full documentation on the configuration files, see the file
+Documentation/kbuild/kconfig-language.txt.
Chapter 11: Data structures
Kernel developers like to be seen as literate. Do mind the spelling
of kernel messages to make a good impression. Do not use crippled
-words like "dont" and use "do not" or "don't" instead.
+words like "dont"; use "do not" or "don't" instead. Make the messages
+concise, clear, and unambiguous.
Kernel messages do not have to be terminated with a period.
Printing numbers in parentheses (%d) adds no value and should be avoided.
+There are a number of driver model diagnostic macros in <linux/device.h>
+which you should use to make sure messages are matched to the right device
+and driver, and are tagged with the right level: dev_err(), dev_warn(),
+dev_info(), and so forth. For messages that aren't associated with a
+particular device, <linux/kernel.h> defines pr_debug() and pr_info().
+
+Coming up with good debugging messages can be quite a challenge; and once
+you have them, they can be a huge help for remote troubleshooting. Such
+messages should be compiled out when the DEBUG symbol is not defined (that
+is, by default they are not included). When you use dev_dbg() or pr_debug(),
+that's automatic. Many subsystems have Kconfig options to turn on -DDEBUG.
+A related convention uses VERBOSE_DEBUG to add dev_vdbg() messages to the
+ones already enabled by DEBUG.
+
Chapter 14: Allocating memory
There appears to be a common misperception that gcc has a magic "make me
faster" speedup option called "inline". While the use of inlines can be
-appropriate (for example as a means of replacing macros, see Chapter 11), it
+appropriate (for example as a means of replacing macros, see Chapter 12), it
very often is not. Abundant use of the inline keyword leads to a much bigger
kernel, which in turn slows the system as a whole down, due to a bigger
icache footprint for the CPU and simply because there is less memory
NULL or the ERR_PTR mechanism to report failure.
+ Chapter 17: Don't re-invent the kernel macros
+
+The header file include/linux/kernel.h contains a number of macros that
+you should use, rather than explicitly coding some variant of them yourself.
+For example, if you need to calculate the length of an array, take advantage
+of the macro
+
+ #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
+
+Similarly, if you need to calculate the size of some structure member, use
+
+ #define FIELD_SIZEOF(t, f) (sizeof(((t*)0)->f))
+
+There are also min() and max() macros that do strict type checking if you
+need them. Feel free to peruse that header file to see what else is already
+defined that you shouldn't reproduce in your code.
+
+
+ Chapter 18: Editor modelines and other cruft
+
+Some editors can interpret configuration information embedded in source files,
+indicated with special markers. For example, emacs interprets lines marked
+like this:
+
+-*- mode: c -*-
+
+Or like this:
+
+/*
+Local Variables:
+compile-command: "gcc -DMAGIC_DEBUG_FLAG foo.c"
+End:
+*/
+
+Vim interprets markers that look like this:
+
+/* vim:set sw=8 noet */
+
+Do not include any of these in source files. People have their own personal
+editor configurations, and your source files should not override them. This
+includes markers for indentation and mode configuration. People may use their
+own custom mode, or may have some other magic method for making indentation
+work correctly.
+
+
Appendix I: References
http://www.kroah.com/linux/talks/ols_2002_kernel_codingstyle_talk/html/
--
-Last updated on 2006-December-06.
+Last updated on 2007-July-13.
+
git://ftp.safe.ca / safe / jmp / linux-2.6 / blobdiff