==================================
ϡ
linux-2.6.24/Documentation/CodingStyle 
Ǥ
Ρ JF ץ < http://www.linux.or.jp/JF/ >
  2008/3/26
  Ken Iwamoto <iwamoto dot kn at ncos dot nec dot co dot jp>
	  Toshikazu Nakayama <nakayama dot ts at ncos dot nec dot co dot jp>
	  Nobuo Yoshida <yoshida dot nb at ncos dot nec dot co dot jp>
  Masanori Kobayasi  <zap03216 at nifty dot ne dot jp>
	  Seiji Kaneko   <skaneko at a2 dot mbn dot or dot jp>
	    <m-ikeda at ds dot jp dot nec dot com>
	  軳  <i-kitayama at ap dot jp dot nec dot com>
	  Hiro YAMAZAKI  <hiro dot yamazaki at physics dot ox dot ac dot uk>
==================================


		Linux kernel coding style

		Linux ͥ ǥ󥰵

This is a short document describing the preferred coding style for the
linux kernel.  Coding style is very personal, and I won't _force_ my
views on anybody, but this is what goes for anything that I have to be
able to maintain, and I'd prefer it for most other things too.  Please
at least consider the points made here.

ʸǤϡLinux ͥΥɤιޤñ
Ƥޤǥ󥰤λ˹ߤʬΤ顢ιͤ
ĤϤޤ󡣤Ǥ⡢줫뤳Ȥϻ䤬ʤ
ϤʤʤƤƤϤޤˤǤϼʬʤΤǤ⡢
ˤǽ񤫤ƤɤΤˤȤפäƤޤơʸ
񤫤줿ȤǤäƤ


First off, I'd suggest printing out a copy of the GNU coding standards,
and NOT read it.  Burn them, it's a great symbolic gesture.

ޤǽˡGNU ǥ󥰵(GNU coding standards)ꤷư
ƤߤƤǤ⡢ɤि˰ΤǤϤޤ󡣰ʪ
ǳ䤹ΤǤε줬ޤջɽʤΤǤ


Anyway, here goes:

Ȥˤޤ礦 -


	 	Chapter 1: Indentation

		裱 - ǥ


Tabs are 8 characters, and thus indentations are also 8 characters.
There are heretic movements that try to make indentations 4 (or even 2!)
characters deep, and that is akin to trying to define the value of PI to
be 3.

֤ϣʸǤʤΤǡǥȤ⣸ʸǤǥȤʸˤ
ꡢˤϣʸˤ褦Ȥ褦ʰ۶̤αưޤǤޤɡ
ϦСᣳȷƤޤȤĥƱ褦ʤΤǤ


Rationale: The whole idea behind indentation is to clearly define where
a block of control starts and ends.  Especially when you've been looking
at your screen for 20 straight hours, you'll find it a lot easier to see
how the indentation works if you have large indentations.

 - ⤽⥤ǥȤȤϡ֥åλϤޤȽϤäꤵ뤿
ΤΤǤ礭ʥǥȤβäϡϢ³ƥ˥įƤ
Ȥʤɤä˼´Ǥޤ


Now, some people will claim that having 8-character indentations makes
the code move too far to the right, and makes it hard to read on a
80-character terminal screen.  The answer to that is that if you need
more than 3 levels of indentation, you're screwed anyway, and should fix
your program.

ơͤˤäƤϡ֣ʸñ̤˥ǥȤ򤹤ȡץब˹Ԥ
᤮ơʸβ̤ǤɤߤˤʤäƤޤפȼĥǤ礦
ãˤϡ֣ʳ¿ΥǥȤ򤹤褦ʾϡץ
ऽΤΤɤʤΤ顢ʤפȸޤ礦


In short, 8-char indents make things easier to read, and have the added
benefit of warning you when you're nesting your functions too deep.
Heed that warning.

פˡʸñ̤ΥǥȤ򤹤Хץबɤߤ䤹ʤꡢ
塢ͥȤ᤮ؿ񤤤Ƥޤäηٹˤʤޤٹ
ľʹƤ


The preferred way to ease multiple indentation levels in a switch statement is
to align the "switch" and its subordinate "case" labels in the same column
instead of "double-indenting" the "case" labels.  E.g.:

switch ʸǥǥȤΥ٥Τ˿侩ˡϡcaseץ٥
֥֥륤ǥȡפˤˡswitchפȤ˴ޤޤcaseץ
٥Ʊˤ뤳ȤǤ -

	switch (suffix) {
	case 'G':
	case 'g':
		mem <<= 30;
		break;
	case 'M':
	case 'm':
		mem <<= 20;
		break;
	case 'K':
	case 'k':
		mem <<= 10;
		/* fall through */
	default:
		break;
	}


Don't put multiple statements on a single line unless you have
something to hide:

Ȥʤ¤ꡢԤʣʸ񤫤ʤǤ -

	if (condition) do_this;
	  do_something_everytime;

	if ( ʸ ) Ǥ뤳;
	  ɤʻǤ⤹뤳;


Don't put multiple assignments on a single line either.  Kernel coding style
is super simple.  Avoid tricky expressions.

Ԥʣν񤫤ʤǤͥΥǥ󥰥ϡ
ƤñǤ٤ǤŤäɽ򤱤Ƥ


Outside of comments, documentation and except in Kconfig, spaces are never
used for indentation, and the above example is deliberately broken.

Ȥɥ᡼ƥ󥷥ʳǤϡ褷ƶǥǥȤƤϤ
ޤʤ Kconfig եˡʤߤ˾嵭ϤƤä
ޤ


Get a decent editor and don't leave whitespace at the end of lines.

ޤȤʥǥȤäƤƹԤκǸ˶ʸ֤ʤǤ




		Chapter 2: Breaking long lines and strings

		裲 - ĹԤĹʸʬΥû뤳


Coding style is all about readability and maintainability using commonly
available tools.

ǥ󥰵ŪϡŪʥġѤˡɤߤ䤹
Τ䤹ݤ뤳Ȥˤޤ


The limit on the length of lines is 80 columns and this is a strongly
preferred limit.

ԤĹϣब³ǡ϶侩¤Ǥ


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. The
only exception to this is where exceeding 80 columns significantly increases
readability and does not hide information.

Ĺʸϡʬ䤹褦ʬ䤷ޤ礦ʬΣܰ
ߤϣܤˤʤûʤ걦֤ޤƱȤĹ
ꥹȤĴؿˤŬѤǤޤƱͤˡĹʸûʸ
ʬǤޤФͣ㳰ϡۤ뤳Ȥǡɤ
䤹ʤ˸夹ˡ󤬱ʤǤ


void fun(int a, int b, int c)
{
	if (condition)
		printk(KERN_WARNING "Warning this is a long printk with "
						"3 parameters a: %u b: %u "
						"c: %u \n", a, b, c);
	else
		next_statement;
}

void fun(int a, int b, int c)
{
	if ( ʸ )
		printk(KERN_WARNING "Warning this is a long printk with "
						"3 parameters a: %u b: %u "
						"c: %u \n", a, b, c);
	else
		ʸ ;
}



		Chapter 3: Placing Braces and Spaces

		裳 - ̤ΰ֤ȶ

The other issue that always comes up in C styling is the placement of
braces.  Unlike the indent size, there are few technical reasons to
choose one placement strategy over the other, but the preferred way, as
shown to us by the prophets Kernighan and Ritchie, is to put the opening
brace last on the line, and put the closing brace first, thusly:

øΥǥ󥰵ǡ⤦ġ褯ˤʤΤ̤ΰ֤Ǥ
ǥȤξȤϰ㤤ɤ˳̤֤ΤͥƤ뤫Ȥ褦
ŪʺϤۤȤɤޤ󡣤Ǥ⹥ޤ̤ΰ֤ȤΤ
äơKernighan  Ritchie ξˤøŵ̾ K&R ȸƤФ
֥ץߥ󥰸áסˤ˼ƤΤǤ֥åγϹԤι
˳ϳ̤֤ơ֥åκǽԤλϤޤ˽λ̤֤Ȥ
ΤǡΤ褦ˤʤޤ -


	if (x is true) {
		we do y
	}

	if ( x ) {
		y¹;
	}


This applies to all non-function statement blocks (if, switch, for,
while, do).  E.g.:

ϡؿʳΥ֥åơifswitchforwhiledoˤˤƤϤޤ
ޤ -

	switch (action) {
	case KOBJ_ADD:
		return "add";
	case KOBJ_REMOVE:
		return "remove";
	case KOBJ_CHANGE:
		return "change";
	default:
		return NULL;
	}


However, there is one special case, namely functions: they have the
opening brace at the beginning of the next line, thus:

ؿγ̤㳰ǡϳ̤ϼιԤλϤޤ֤ޤ -


	int function(int x)
	{
		body of function
	}

	int ؿ̾(int x)
	{
		ؿ
	}


Heretic people all over the world have claimed that this inconsistency
is ...  well ...  inconsistent, but all right-thinking people know that
(a) K&R are _right_ and (b) K&R are right.  Besides, functions are
special anyway (you can't nest them in C).

Ȥΰ۶̤ϡΰ̵...Ǥ...
̵ʸäƤޤۤä͡ (a)
K&R (b) K&R ΤȤ狼äƤޤˡȤ
ؿȤΤ̤ʤΤʤΤǤʣøǴؿΥͥ
ϤǤޤˡ


Note that the closing brace is empty on a line of its own, _except_ in
the cases where it is followed by a continuation of the same statement,
ie a "while" in a do-statement or an "else" in an if-statement, like
this:

ǰդƤޤλ̡̤λ̤ιԤˤʤޤ
λ̤ʸʤˤϤιԤ³Ȥˤʤޤʤ
 do ʸǤ "while"  if ʸǤ "else" 뤳Ȥޤ -


	do {
		body of do-loop
	} while (condition);

and

	if (x == y) {
		..
	} else if (x > y) {
		...
	} else {
		....
	}


	do {
		do롼פ
	} while ( ʸ );

䡢

	if (x == y) {
		..
	} else if (x > y) {
		...
	} else {
		....
	}



Rationale: K&R.

 - ŵK&R


Also, note that this brace-placement also minimizes the number of empty
(or almost empty) lines, without any loss of readability.  Thus, as the
supply of new-lines on your screen is not a renewable resource (think
25-line terminal screens here), you have more empty lines to put
comments on.

ˡ褦˳̤֤Сɤߤ䤹ˤʤǡ
ԡʤȤۤȤɶԡˤǾ¤ˤȤɤ뤳ȤǤǤ礦
̤ɽǤԤϸ¤ƤޤʤǤϣԤṳ̈ǰƬ֤
ä򤷤ƤޤˡΤ褦ˤƶԤ򸺤餷ʬȤ뤳
Ǥޤ


Do not unnecessarily use braces where a single statement will do.

Ĥʸ¹ԤʤȤˡɬפΤʤ̤ȤʤǤ


if (condition)
	action();

if ( ʸ )
	action();



This does not apply if one branch of a conditional statement is a single
statement. Use braces in both branches.

ϡʸʬĤʸǤ硢ƤϤޤޤξʬ
˳̤ѤƤ


if (condition) {
	do_this();
	do_that();
} else {
	otherwise();
}

if ( ʸ ) {
	do_this();
	do_that();
} else {
	otherwise();
}



		3.1:  Spaces

		 - 


Linux kernel style for use of spaces depends (mostly) on
function-versus-keyword usage.  Use a space after (most) keywords.  The
notable exceptions are sizeof, typeof, alignof, and __attribute__, which look
somewhat like functions (and are usually used with parentheses in Linux,
although they are not required in the language, as in: "sizeof info" after
"struct fileinfo info;" is declared).

Linux ͥ륹ˤλˡϡʼˡ˴ؿɤ
ˤäѤޤʬΡ˥ɤθˤϡȤäƤ
դ٤㳰ϡؿΤ褦˸ sizeoftypeofalignof__attribute__
Ǥʤϡ"struct fileinfo info;"  "sizeof info" Ȥ
褦ˡ;塢ɬ̤ɬפǤϤʤɤ⡢Linux Ǥ̾
̤Ȥޤˡ


So use a space after these keywords:

ʲΥɤθˤϡȤäƤ -

	if, switch, case, for, do, while

but not with sizeof, typeof, alignof, or __attribute__.  E.g.,

sizeoftypeofalignof__attribute__ θˤ϶ȤʤǤ
 -

	s = sizeof(struct file);


Do not add spaces around (inside) parenthesized expressions.  This example is
*bad*:

μˡȤʤǤʲϰǤ -

	s = sizeof( struct file );


When declaring pointer data or a function that returns a pointer type, the
preferred use of '*' is adjacent to the data name or function name and not
adjacent to the type name.  Examples:

ݥ󥿥ǡޤϥݥ󥿷֤ؿȤ*פɤȤ
ϥǡ̾ޤϴؿ̾ˤϤĤơ̾ˤĤޤ -

	char *linux_banner;
	unsigned long long memparse(char *ptr, char **retptr);
	char *match_strdup(substring_t *s);


Use one space around (on each side of) most binary and ternary operators,
such as any of these:

ʲΤ褦ˡƤ黻Ҥ仰黻Ҥα黻Ҥβˡˡˡ
ʸȤäƤ -

	=  +  -  <  >  *  /  %  |  &  ^  <=  >=  ==  !=  ?  :


but no space after unary operators:

ñ黻ҤθˤϡȤʤǤ -

	&  *  +  -  ~  !  sizeof  typeof  alignof  __attribute__  defined


no space before the postfix increment & decrement unary operators:

֥󥯥ñ黻Ҥ֥ǥñ黻Ҥˤϡ
ʤǤ -

	++  --


no space after the prefix increment & decrement unary operators:

֥󥯥ñ黻Ҥ֥ǥñ黻Ҥθ˶Ȥ
Ǥ -

	++  --


and no space around the '.' and "->" structure member operators.

ơ¤α黻ҡ.פȡ->פˡȤʤǤ


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.

̵̤ʶĤʤǤǥȵǽĥǥ
ϡԤƬŬڤʶƤΤǡιԤ顢˥
ɤ񤭻Ϥ뤳ȤǤޤʤ顢Τ褦ʥǥˤϡ
ʤԤĤȤơɤɲäʤäƤ
ʤΤޤη̵̡̤ʶ򤬻Ĥޤ


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.

git Ϲ̵̤ʶΤѥåФơٹ𤷤ƤǤ礦
̵̤ʶǤդ˼ȤǤޤ - ʤ顢ʣΥѥåŬ
硢git ̵̤ʶ뤳ȤǡƱԤѹ롢
ŬѤѥåԤ뤫줷ޤ



		Chapter 4: Naming

		裴 - ̾


C is a Spartan language, and so should your naming be.  Unlike Modula-2
and Pascal programmers, C programmers do not use cute names like
ThisVariableIsATemporaryCounter.  A C programmer would call that
variable "tmp", which is much easier to write, and not the least more
difficult to understand.

øϥѥ륿ʤΤǤ顢ˤդ路ѿؿ̿̾ޤ
礦Modula-2  Pascal ΥץޤȤϰäơøץޤ ֤
ѿϰŪ˻Ȥ륫󥿡Ǥ(ThisVariableIsATemporaryCounter)
ʤɤȤ褦ʵΤ̾ϻȤޤ󡣣øץޤϡ"tmp" 
ɤνʬ˽񤭤䤹ǤƾʤȤʬˤϤʤʤѿ̾
֤ΤǤ


HOWEVER, while mixed-case names are frowned upon, descriptive names for
global variables are a must.  To call a global function "foo" is a
shooting offense.

ʸʸ򺮤褦̾ϷޤХѿˤϡ̣
Τ狼̾ɬפǤХؿ "foo" ʤɤȤ̵̣̾
դ뤳ȤԲͿƤޤޤ


GLOBAL variables (to be used only if you _really_ need them) need to
have descriptive names, as do global functions.  If you have a function
that counts the number of active users, you should call that
"count_active_users()" or similar, you should _not_ call it "cntusr()".

ХѿɬפʻˤȤȡˤˤϰ̣褯ʬ̾
դƤХؿƱǡƥ֤ʥ桼
Хؿˤ "count_active_users()" 䤽̾Ȥ
Ǥꡢ"cntusr()" Ȥ٤ǤϤޤ


Encoding the type of a function into the name (so-called Hungarian
notation) is brain damaged - the compiler knows the types anyway and can
check those, and it only confuses the programmer.  No wonder MicroSoft
makes buggy programs.

ؿηؿ̾˴ޤʤϥ󥬥꡼ˡˤϡ餫˴ְ
ƤޤʤȤ򤷤ʤƤ⡢ȤˤѥϷΤäƤޤ
ΥåǤޤɤϥץ޼Ȥ𤵤Ǥ
Microsoft Х¿ץäƤΤԻ׵ĤǤϤޤ


LOCAL variable names should be short, and to the point.  If you have
some random integer loop counter, it should probably be called "i".
Calling it "loop_counter" is non-productive, if there is no chance of it
being mis-understood.  Similarly, "tmp" can be just about any type of
variable that is used to hold a temporary value.

ѿ̾ûơѿħɽΤˤޤ롼פμ
ԲŬ󥿤֤ʤС餯 "i" ̾դ
Ǥ򤵤뤳ȤʤΤˡloop_counter ȸƤ֤Ȥϼ¤꤬
ƱͤˡŪͤݻƥݥѿϷ˷餺ñ
tmp Ȥޤ礦


If you are afraid to mix up your local variable names, you have another
problem, which is called the function-growth-hormone-imbalance syndrome.
See chapter 6 (Functions).

⤷ѿ̾դ¤äƤ褦ʤ顢̤Ƥ
ǤִؿĹۥԶѹվɸפȸƤФƤޤܤ裶ϡ
ؿˤ򸫤Ƥ



		Chapter 5: Typedefs

		裵 - Typedef


Please don't use things like "vps_t".

"vps_t" Τ褦ϻȤʤǤ


It's a _mistake_ to use typedef for structures and pointers. When you see a

	vps_t a;

in the source, what does it mean?

¤Τݥ󥿤 typedef ȤȤְäƤޤǡ
vps_t a;פȤʸ򸫤Ȥɤʰ̣ȹͤޤ


In contrast, if it says

	struct virtual_container *a;

you can actually tell what "a" is.

оŪˡstruct virtual_container *a;פʤ顢"a" Ǥ뤫º
˸Ƥ뤳ȤǤޤ


Lots of people think that typedefs "help readability". Not so. They are
useful only for:

typedef ϡɤߤ䤹μפˤʤȡ¿ο͡ϹͤƤޤ
ǤϤޤtypedef ϼξˤΩޤ


 (a) totally opaque objects (where the typedef is actively used to _hide_
     what the object is).

 (a) Τɬפʤ֥ȡʤΥ֥ȤǤ뤫ä
     뤿ᡢѶŪ typedef Ѥ


     Example: "pte_t" etc. opaque objects that you can only access using
     the proper accessor functions.

     㤨 - "pte_t" ʤɤΡŬڤؿȤäƤΤߥ
     ȤǤ롢ΤɬפΤʤ֥ȡ


     NOTE! Opaqueness and "accessor functions" are not good in themselves.
     The reason we have them for things like pte_t etc. is that there
     really is absolutely _zero_ portably accessible information there.

     դǤΤɬפʤǡ¤ȡؿפϡ
     ɤޤpte_t ʤɤʤäƤͳϡܿΤ
     ǽʾ󤬴ˡ֤ʤˤʤפǤ


 (b) Clear integer types, where the abstraction _helps_ avoid confusion
     whether it is "int" or "long".

 (b) int  long θɬפʤݲˤäȤ
     Ϥäꤵ硣


     u8/u16/u32 are perfectly fine typedefs, although they fit into
     category (d) better than here.

     Υƥꡢƥ(d) ˴Ϣޤu8/u16/u32 ϲ
     ʤ typedef Ǥ


     NOTE! Again - there needs to be a _reason_ for this. If something is
     "unsigned long", then there's no reason to do

	typedef unsigned long myflags_t;

     դǤˤͳɬפǤunsined long Ȥư
     ηʲΤ褦˺ͳϲ⤢ޤ

	typedef unsigned long myflags_t;


     but if there is a clear reason for why it under certain circumstances
     might be an "unsigned int" and under other configurations might be
     "unsigned long", then by all means go ahead and use a typedef.

     ĶǤ unsigned int Ǥꡢ¾δĶǤ unsigned long 
     褦ʤϤäȤͳˤϡҤȤ typedef Ȥ
     Ƥ


 (c) when you use sparse to literally create a _new_ type for
     type-checking.

 (c) sparse ġȤäåѤˡʸֿ̤פ
     硣


 (d) New types which are identical to standard C99 types, in certain
     exceptional circumstances.

 (d) ȤơC99 Ƴ줿ɸ෿Ʊ硣


     Although it would only take a short amount of time for the eyes and
     brain to become accustomed to the standard types like 'uint32_t',
     some people object to their use anyway.

     ܤǾϡuint32_tפΤ褦ɸ෿ˤޤǤ⤳Τ褦
     ʷȤȤȿФͤޤ


     Therefore, the Linux-specific 'u8/u16/u32/u64' types and their
     signed equivalents which are identical to standard types are
     permitted -- although they are not mandatory in new code of your
     own.

     ΤᡢC99ɸ෿ƱǤLinux ͭ u8/u16/u32/u64
     ȤȡդηƤޤ - ȤäƤ⡢
     ʤɤ񤯤ȤˡɬȤʤƤϤʤʤ
     櫓ǤϤޤ


     When editing existing code which already uses one or the other set
     of types, you should conform to the existing choices in that code.

     ΤĤηѤƤ¸ΥɤԽˤϡ
     Υɤ˽äƤ


 (e) Types safe for use in userspace.

 (e) 桼֤ǰ˻Ѥ뤿η


     In certain structures which are visible to userspace, we cannot
     require C99 types and cannot use the 'u32' form above. Thus, we
     use __u32 and similar types in all structures which are shared
     with userspace.

     Ĥι¤Τϡ桼֤ǤѤޤΤ褦ʹ¤
     ǤϡC99 줿ǽҤ٤u32 Τ褦ʷϻѤǤ
     󡣤Τ桼֤ͭ뤹٤Ƥι¤ΤǤϡ
     __u32פΤ褦ʷѤޤ


Maybe there are other cases too, but the rule should basically be to NEVER
EVER use a typedef unless you can clearly match one of those rules.

¾Υ뤫⤷ޤ󤬡˵󤲤롼ƤϤޤʤϡ
Ū typedef ȤäƤϤޤ


In general, a pointer, or a struct that has elements that can reasonably
be directly accessed should _never_ be a typedef.

Ūˡݥ󥿤䡢ľܥФĹ¤Τϡ褷
typedef ƤϤޤ



		Chapter 6: Functions

		裶 - ؿ


Functions should be short and sweet, and do just one thing.  They should
fit on one or two screenfuls of text (the ISO/ANSI screen size is 80x24,
as we all know), and do one thing and do that well.

ؿûƿڡñ˰ĤΤȤԤޤ礦ƴؿϡʳΤ
Ƥ ISO/ANSI 80ʸx24Ԥǡˣ̤̤˼ޤ礦Ĥ
ؿϰĤνǰơ򥭥åȹԤޤ礦


The maximum length of a function is inversely proportional to the
complexity and indentation level of that function.  So, if you have a
conceptually simple function that is just one long (but simple)
case-statement, where you have to do lots of small things for a lot of
different cases, it's OK to have a longer function.

ؿĹϡδؿʣȴؿΥǥȤοȿ
ޤܼŪˤñʴؿǤĹʤñʡswitch case ʸ
ޤؿäȤޤ case 줾ǰۤʤä
ԤΤǤСؿΤĹʤäƤɤǤ礦


However, if you have a complex function, and you suspect that a
less-than-gifted first-year high-school student might not even
understand what the function is all about, you should adhere to the
maximum limits all the more closely.  Use helper functions with
descriptive names (you can ask the compiler to in-line them if you think
it's performance-critical, and it will probably do a better job of it
than you would have done).

ʤʣʴؿƤޤʿޤʹ⹻ǯǤϷ褷ơδ
ƤǤʤʡפȴ顢פ̣Ǥκ
кܤƤκݤˤϡ狼פ̾ؿѤƤ
ʴؿƤӽФȼǽ㲼ǰΤǤСѥإ
饤Ÿ׵ᤷޤ礦ʬǤꤺäȾн褷Ƥ뤳
Ǥ礦ˡ


Another measure of the function is the number of local variables.  They
shouldn't exceed 5-10, or you're doing something wrong.  Re-think the
function, and split it into smaller pieces.  A human brain can
generally easily keep track of about 7 different things, anything more
and it gets confused.  You know you're brilliant, but maybe you'd like
to understand what you did 2 weeks from now.

ؿΥѿοܰ¤ȤʤޤѿϣĤˤȤ
٤ΤǡĶƤ褦ʤ鲿Ȥ򤷤ƤΤǤ
ϴؿľ٤ʬ䤷ƤŪˡʹ֤Ǿ
;͵äƱɤ뤳ȤϣĤ餤³ǡʾ夢Ⱥ
Ƥޤޤʬ餷ϼʬΤäƤ뤳ȤǤ礦
˽񤤤Τʬȴ򤷤Ȥϻפޤ󤫡


In source files, separate functions with one blank line.  If the function is
exported, the EXPORT* macro for it should follow immediately after the closing
function brace line.  E.g.:

եǤϡԣԤǴؿڤäƤؿݡ
Ƥ硢ؿνλ̤ΤԤΤ EXPORT* ޥ֤٤
 -


int system_is_up(void)
{
	return system_state == SYSTEM_RUNNING;
}
EXPORT_SYMBOL(system_is_up);


In function prototypes, include parameter names with their data types.
Although this is not required by the C language, it is preferred in Linux
because it is a simple way to add valuable information for the reader.

ؿץȥˤϡǡηȰˡѥ᡼̾ޤƤ
ϣøˤȤäơ;塢ɬפǤϤޤ󤬡ɤ߼ˤȤäƲͤΤ
äñˡʤΤǡLinux ǤϿ侩ޤ



		Chapter 7: Centralized exiting of functions

		裷 - ؿλɤζ̲(goto out)


Albeit deprecated by some people, the equivalent of the goto statement is
used frequently by compilers in form of the unconditional jump instruction.

goto ʸѤŪʿͤ⤤ޤѥ goto ʸ̵
 jump ̿ˤ˽ϤƤΤǤ


The goto statement comes in handy when a function exits from multiple
locations and some common work such as cleanup has to be done.

goto ʸϡؿĤξǽλƤ鶦Ūư㤨
Х꡼󥢥åưˤԤ˽ޤ


The rationale is:

ȤưʲΤ褦ʤȤޤ


- unconditional statements are easier to understand and follow
- nesting is reduced
- errors by not updating individual exit points when making
    modifications are prevented
- saves the compiler work to optimize redundant code away ;)

- ̵ʸ򤷤䤹ήɤΤư
- ͥȤ
- κݡ̤˼λΰ򹹿˺롢Ȥͽ
   Ǥ
- ĹʥɤŬǤ褦ѥ


int fun(int a)
{
	int result = 0;
	char *buffer = kmalloc(SIZE);

	if (buffer == NULL)
		return -ENOMEM;

	if (condition1) {
		while (loop1) {
			...
		}
		result = 1;
		goto out;
	}
	...
out:
	kfree(buffer);
	return result;
}

int fun(int a)
{
	int result = 0;
	char *buffer = kmalloc(SIZE);

	if (buffer == NULL)
		return -ENOMEM;

	if ( ʸ1 ) {
		while ( 롼׾1 ) {
			...
		}
		result = 1;
		goto out;
	}
	...
out:
	kfree(buffer);
	return result;
}



		Chapter 8: Commenting

		裸 - 


Comments are good, but there is also a danger of over-commenting.  NEVER
try to explain HOW your code works in a comment: it's much better to
write the code so that the _working_ is obvious, and it's a waste of
time to explain badly written code.

ȤΩĤΤǤȤդʤȤռƤ
褷ơȤǥץλȤߤ褦ȤƤϤޤ
 - ɤưƤʥɤڤˤ褤ȤǤ
   Ỵʥɤ˻֤ݤ뤳Ȥ̵̤Ǥ


Generally, you want your comments to tell WHAT your code does, not HOW.
Also, try to avoid putting comments inside a function body: if the
function is so complex that you need to separately comment parts of it,
you should probably go back to chapter 6 for a while.  You can make
small comments to note or warn about something particularly clever (or
ugly), but try to avoid excess.  Instead, put the comments at the head
of the function, telling people what it does, and possibly WHY it does
it.

ŪˡȤǥɤ򤷤ƤΤ(WHAT)򼨤ȤϤޤ
ɤäƤΤHOWˤϼʤǤ礦ޤؿ˥Ȥ
ܤ뤳Ȥ򤱤ޤ礦 - ؿʣʤΤǡӤ˴ؿȤɬ
פȹͤΤǤС裶ϤɤľƤֶˤƹ̯ʥ略ʱ
Ȥ⤤ˤȤäפդˤϤäȤȤդƤ
ǤꤹʤǤ⡢ؿƬ˥ȤͿ
򤹤ؿʤΤ˲ǽǤСΤ򤹤ΤޤǼޤ礦


When commenting the kernel API functions, please use the kernel-doc format.
See the files Documentation/kernel-doc-nano-HOWTO.txt and scripts/kernel-doc
for details.

ͥ API ؿإȤդϡkernel-doc ѤƤ
ܺ٤ Documentation/kernel-doc-nano-HOWTO.txtscripts/kernel-doc 
ޤ


Linux style for comments is the C89 "/* ... */" style.
Don't use C99-style "// ..." comments.

Linux ͥˤ륳ȥϡC89  "/* ... */" Ǥ
C99  "// ..." ΥȤϻѤƤϤޤ

The preferred style for long (multi-line) comments is:

ĹʣԤˤ錄˥ȤˤȤäƿ侩륹򼡤˼ޤ

	/*
	 * This is the preferred style for multi-line
	 * comments in the Linux kernel source code.
	 * Please use it consistently.
	 *
	 * Description:  A column of asterisks on the left side,
	 * with beginning and ending almost-blank lines.
	 */

	/*
	 * ηLinux ͥ륽ʣԤΥȤˤ
	 * ƿ侩륹Ǥ
	 * ӤơѤƤ
	 *
	 *  - ¦˥ꥹ֤ϹԤȽλԤˤϡۤȤ
	 * ɤʤˤʤԤ֤Ƥ
	 */

It's also important to comment data, whether they are basic types or derived
types.  To this end, use just one data declaration per line (no commas for
multiple data declarations).  This leaves you room for a small comment on each
item, explaining its use.

ܷޤǤ뤫ɤ˴ؤ餺ǡ˥Ȥ뤳Ȥ⡢
פǤΤˡʥޤѤơʣΥǡ򤻤ˡԤˤĤ
ĤΥǡƤ뤳Ȥǡǡˡˡ
٤ûȤ򵭽Ҥ;ϤǤޤ



		Chapter 9: You've made a mess of it

		裹 - Ƥޤä


That's OK, we all do.  You've probably been told by your long-time Unix
user helper that "GNU emacs" automatically formats the C sources for
you, and you've noticed that yes, it does do that, but the defaults it
uses are less than desirable (in fact, they are worse than random
typing - an infinite number of monkeys typing into GNU emacs would never
make a good program).

פǤԤïǤ⤹ΤǤ֤󤢤ʤĹǯ UNIX λȤ
ɥХƤ褦ڤ顢GNU emacsפΣåɼư
򶵤äƤơȻפǤΤǤ礦ΤˤʤΤ
emacs ΥǥեǤ˾̤ˤϤʤʤΤǤʼºݡŬ
˥ץǤۤޤȤˤʤޤ - ̵Υ뤬䡹 GNU
emacs إץǤǤ⡢褷餷ץϴޤ



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:

ʤΤǡGNU emacs Ѥ뤫ޤȤˤ뤫Τɤ餫Ǥ
θľˤĤƤϡۡǥ쥯ȥΡ.emacsץե˼Τ褦
ɵԤäƤ -


(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.

 M-x linux-c-mode ޥɤޤեƬ
Τɤˡ-*- linux-c -*-פȤʸ֤ƤСϥå󥰤
ݤˡưŪ linux-c-mode ˤʤޤޤ/usr/src/linux ˤ륽
եԽϼưŪ linux-c-mode ڤؤȤΤǤ
С.emacsץե

(setq auto-mode-alist (cons '("/usr/src/linux.*/.*\\.[ch]$" . linux-c-mode)
                       auto-mode-alist))

äƤ


But even if you fail in getting emacs to do sane formatting, not
everything is lost: use "indent".

emacs ǤޤȤ»ͤƤ⡢ޤפǤ - indent ޥɤȤ
ߤޤ


Now, again, GNU indent has the same brain-dead settings that GNU emacs
has, which is why you need to give it a few command line options.
However, that's not too bad, because even the makers of GNU indent
recognize the authority of K&R (the GNU people aren't evil, they are
just severely misguided in this matter), so you just give indent the
options "-kr -i8" (stands for "K&R, 8 character indents"), or use
"scripts/Lindent", which indents in the latest style.

GNU  indent ޥɤ GNU emacs ƱΩʥǥեˤʤä
ơĤΥޥɥ饤󥪥ץɬפˤʤޤGNU indent
κԤ K&R θҤǧƤϤΤǡޤǤҤɤϤޤ
GNU οٰͤȤäƤΤǤϤʤøץν񼰤˴ؤ
ɼƻ򳰤ƤޤäȤȤǤˡindent ޥɤΥץ
"-kr -i8" ꤹʤϡK&RʸǥȡפάˤǤ褤
ǿΥǥȤˤС"scripts/Lindent" Ѥ
⤢ޤ


"indent" has a lot of options, and especially when it comes to comment
re-formatting you may want to take a look at the man page.  But
remember: "indent" is not a fix for bad programming.

indent ޥɤ¿Υץ󤬤Τǡä˥Ȥˡ
˴ؤƤϥޥ˥奢ڡ򸫤ΤɤȻפޤindent ޥ
ɤϰץΤǤϤʤȤȤФƤƤ



		Chapter 10: Kconfig configuration files

		裱 - Kconfig ե


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:

ĥ꡼ Kconfig* եˤϡۤʤ륤ǥȥ롼뤬
ޤ"config" ιԤ˴ؤƤϡĤΥ֤ǥǥȤ졢
 help ƥȤ˴ؤƤϡĤζɲäƥǥȤޤ -


config AUDIT
	bool "Auditing support"
	depends on NET
	help
	  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.


Features that might still be considered unstable should be defined as
dependent on "EXPERIMENTAL":

ޤ԰꤫⤷ʤȤܤϡ"EXPERIMENTALʼ¸" ʳ
ƤʤФʤޤ -


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:

ơΥե륷ƥФ write ݡȤΤ褦ˡˡѴ
ʹܤϡץץʸˡϤäȤΤȤΤʤФʤޤ
 -


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.

ե˴ؤ봰ʥɥȤȤơʲΥե򻲾ȤƤ

Documentation/kbuild/kconfig-language.txt



		Chapter 11: Data structures

		裱 - ǡ¤


Data structures that have visibility outside the single-threaded
environment they are created and destroyed in should always have
reference counts.  In the kernel, garbage collection doesn't exist (and
outside the kernel garbage collection is slow and inefficient), which
means that you absolutely _have_ to reference count all your uses.

ǡ¤Υåɡʥƥȡˤ˴ǡ
åɤγ¦⻲ȤǤ硢äǡ¤ˤϾ˻ȥ
ɬפǤͥˤϥ٥å쥯¸ߤޤʤ
ơͥ볰Υ٥å쥯®ΨǤˡäơ
ѤƤΥǡɬȥȤʤФʤޤ


Reference counting means that you can avoid locking, and allows multiple
users to have access to the data structure in parallel - and not having
to worry about the structure suddenly going away from under them just
because they slept or did something else for a while.

ȥȤˤäơǡ¤ؤΥå򤱤졢ʣ桼
ʥåɤʤɤΥƥȡˤ¹ԤƱǡ¤إǤ
 -  sleep ̤νԤäȤäơȤƤǡ
¤԰դ˥Ǥʤʤ뿴ۤפǤ


Note that locking is _not_ a replacement for reference counting.
Locking is used to keep data structures coherent, while reference
counting is a memory management technique.  Usually both are needed, and
they are not to be confused with each other.

ǰդƤޤåϡȥ󥿤ˤϤʤޤ
åϡǡΰݤĤΤ˻Ȥޤȥ󥿤ϡ
ˤѤޤ̾ξȤɬפǤꡢߤ˺ƱƤϤޤ


Many data structures can indeed have two levels of reference counting,
when there are users of different "classes".  The subclass count counts
the number of subclass users, and decrements the global count just once
when the subclass count goes to zero.

¤¿Υǡ¤ϡۤʤ "class" Υ桼ľˤơ
λȥ󥿤äƤޤsubclass 󥿤 subclass 桼
Ȥ󥿤ˤʤä˸¤äƥХ륫󥿤ǥ
Ȥޤ


Examples of this kind of "multi-level-reference-counting" can be found in
memory management ("struct mm_struct": mm_users and mm_count), and in
filesystem code ("struct super_block": s_count and s_active).

¿ʳλȥ󥿤㤬˸ޤmm_struct
¤Τ mm_users  mm_count Ǥˡե륷ƥΥɤˤ⸫
ޤsuper_block ¤Τ s_count  s_active Ǥˡ


Remember: if another thread can find your data structure, and you don't
have a reference count on it, you almost certainly have a bug.

ФƤƤ - ̤ΥåɤʤΥǡ¤õȤǤ
ΤˡʤϤΥǡ¤˻ȥ󥿤äƤʤȤȡۤܳ
¤˥Хޤ



		Chapter 12: Macros, Enums and RTL

		裱 - ޥ󷿤 RTL


Names of macros defining constants and labels in enums are capitalized.

ޥ̾ʸǵҤޤ


#define CONSTANT 0x12345


Enums are preferred when defining several related constants.

󷿤ʣδϢȤ˹Ѥޤ


CAPITALIZED macro names are appreciated but macros resembling functions
may be named in lower case.

ޥʸޤǤؿޥϾʸǤ⹽ޤ


Generally, inline functions are preferable to macros resembling functions.

Ūˡؿޥ⥤饤ؿ˾ޤǤ礦


Macros with multiple statements should be enclosed in a do - while block:

ʣʸ鹽ޥ do - while ֥åǰϤ٤Ǥ


#define macrofun(a, b, c) 			\
	do {					\
		if (a == 5)			\
			do_this(b, c);		\
	} while (0)


Things to avoid when using macros:

ޥѻ򤱤٤ -


1) macros that affect control flow:

1) ή˱ƶͿޥ -


#define FOO(x)					\
	do {					\
		if (blah(x) < 0)		\
			return -EBUGGERED;	\
	} while(0)


is a _very_ bad idea.  It looks like a function call but exits the "calling"
function; don't break the internal parsers of those who will read the code.

Υޥ˰ǥǤؿƤӽФΤ褦˸ʤ顢ָ
״ؿȴƤޤޤ - ɤɤ͡ƬΥѡ
Ϥޤ


2) macros that depend on having a local variable with a magic name:

2) ̾Υѿ˰¸Ƥޥ


#define FOO(val) bar(index, val)

might look like a good thing, but it's confusing as hell when one reads the
code and it's prone to breakage from seemingly innocent changes.

ΥޥɤȤΤ褦˸뤫⤷ޤ󤬡ïɤɤ
ϹΤ褦˺𤵤뤷ɽ̾塢̵ѹˤ
ޤ


3) macros with arguments that are used as l-values: FOO(x) = y; will
bite you if somebody e.g. turns FOO into an inline function.

3) ͤȤƻȤեޥ - FOO(x) = y - 㤨С⤷ï
   ޥ򥤥饤ؿѹ褦ȤʸǤ礦


4) forgetting about precedence: macros defining constants using expressions
must enclose the expression in parentheses. Beware of similar issues with
macros using parameters.

4) 黻Ҥͥ٤ˤĤ˺뤳 - ޥϼ̤
   ϤޤʤФʤޤ󡣰ѤޥƱ褦ѿޤ
   礦


#define CONSTANT 0x4000
#define CONSTEXP (CONSTANT | 3)


The cpp manual deals with macros exhaustively. The gcc internals manual also
covers RTL which is used frequently with assembly language in the kernel.

ޥξܺ٤ˤĤƤ cpp ޥ˥奢򻲾ȤƤͥǥ
֥ȶˤ褯Ѥ RTL ˤĤƤ gcc 󥿡ʥޥ˥奢
򻲾Ȥޤ礦



		Chapter 13: Printing kernel messages

		裱 - ͥåɽ


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"; use "do not" or "don't" instead.  Make the messages
concise, clear, and unambiguous.

ͥ볫ȯԤ϶ܿͤΤ褦˸줿ΤǤɤݤͿ륫ͥ
å֤˵ȤäƤ"dont" Τ褦ʲ줿դϻȤä
Ϥޤ"do not"  "don't" ˻Ȥޤ礦åϴʷ
ΤʤΤˤޤ礦


Kernel messages do not have to be terminated with a period.

ͥåϥԥꥪɤǽɬפϤޤ


Printing numbers in parentheses (%d) adds no value and should be avoided.

̤Ĥο (%d) ɽ뤳Ȥϲ̵ͤ򤱤٤Ǥ礦


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().

<linux/device.h> ˤϡåŬڤʥǥХȥɥ饤Ф˹פŬ
ʥ٥: dev_err(), dev_warn(), dev_info(), ¾˥դƤ
ȤǧΤ˻Ȥ¿Υɥ饤ХǥǥޥޤΥ
Х˴Ϣʤåΰ٤ˡ<linux/kernel.h> Ǥϡpr_debug() 
pr_info() Ƥޤ


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.

ɤǥХåѥåͤФȤϡ񤷤 - ơä
줬ǤС⡼ȥȥ֥륷塼ƥ󥰤ˤ礭ʽˤ
Ǥ礦Τ褦ʥå DEBUG ܥ뤬Ƥʤˤ
٤ǤʥǥեȤ DEBUG ܥϴޤޤƤޤˡ
ʤdev_dbg()  pr_debug() ѤȤϼưŪ˹Ԥޤ¿
Υ֥ƥǤ -DDEBUG ͭˤ Kconfig ץäƤޤ
Ϣ뤷ȤƤϡDEBUG ͭˤʤäΤ˲ädev_vdbg() 
ɲä VERBOSE_DEBUG Ȥޤ



		Chapter 14: Allocating memory

		裱 - 


The kernel provides the following general purpose memory allocators:
kmalloc(), kzalloc(), kcalloc(), and vmalloc().  Please refer to the API
documentation for further information about them.

ͥϼѥꥢ󶡤ޤ - kmalloc(), kzalloc(),
kcalloc(),  vmalloc()ˤĤƤι˾ܤܺ٤ˤĤƤ API
ɥȤ򻲾ȤƤ


The preferred form for passing a size of a struct is the following:

ޤ¤ΥϤϼΤΤǤ

	p = kmalloc(sizeof(*p), ...);


The alternative form where struct name is spelled out hurts readability and
introduces an opportunity for a bug when the pointer variable type is changed
but the corresponding sizeof that is passed to a memory allocator is not.

˹¤η̾򵭽ҤϤ򤹤ȡɤߤˤ
äݥѿηѹ硢ꥢϤб
ʤХβˤʤޤ


Casting the return value which is a void pointer is redundant. The conversion
from void pointer to any other pointer type is guaranteed by the C programming
language.

void ݥ󥿤֤줿ֵͤ򥭥㥹Ȥ뤳ȤϾĹǤvoid ݥ
¾Υݥ󥿷ؤѴϣøˤäݾڤƤޤ



		Chapter 15: The inline disease

		裱 - 饤


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 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
available for the pagecache. Just think about it; a pagecache miss causes a
disk seek, which easily takes 5 miliseconds. There are a LOT of cpu cycles
that can go into these 5 miliseconds.

gcc ϡֻ®ơפȤˡ"inline" ȸƤФ®ץ
äƤȤ̤θǧޤinline λѤŬڤǤ⤢
ޤ(㤨Сޥ֤硢ϻ)ˤˤϤޤ
inline ɤˤѤȥͥ礭ʤޤˤ
 CPU ̿ᥭåΥҥåΨ㲼åեåȥץȤ
ޤޤñ˥ڡåȤƻѤǤ꤬ޤ
װˤäơƥΤ٤ʤޤˤĤƹͻƤߤޤ
 - ڡåߥưפˣߥäǥΥȯ
ޤΣߥäˤϡ͡ʽԤȤǤ¿ CPU 
뤳ȤǤΤǤ


A reasonable rule of thumb is to not put inline at functions that have more
than 3 lines of code in them. An exception to this rule are the cases where
a parameter is known to be a compiletime constant, and as a result of this
constantness you *know* the compiler will be able to optimize most of your
function away at compile time. For a good example of this later case, see
the kmalloc() inline function.

ηи§Ǥϣ԰ʾδؿϥ饤ؿˤʤȤǤ
§㳰ϡѥǤ뤳Ȥ狼äƤȡ
ȼѥκŬˤäƴؿʬʬäƤ
Ǥ㤨СԤɤ㤬 kmalloc() 饤ؿǤ礦


Often people argue that adding inline to functions that are static and used
only once is always a win since there is no space tradeoff. While this is
technically correct, gcc is capable of inlining these automatically without
help, and the maintenance issue of removing the inline when a second user
appears outweighs the potential value of the hint that tells gcc to do
something it would have done anyway.

͡Ϥ褯static ǰ󤷤Ѥʤؿ򥤥饤ؿˤΤϾ
ˤޤȼĥޤʤʤ饵ˤʤǤϵ
ŪˤΤǤgcc Ͻ̵˼ưŪ˥饤ؿˤ뤳Ȥ
ǽǤѤ褦ˤʤä inline 򳰤ʤФʤʤ
ͤȡgcc ɤ¹Ԥ뤳ȤФƥҥȤͿΤϡۤ
ŪͤΤʤȤǤ礦



		Chapter 16: Function return values and names

		裱 - ؿֵͤ̾


Functions can return values of many different kinds, and one of the
most common is a value indicating whether the function succeeded or
failed.  Such a value can be represented as an error-code integer
(-Exxx = failure, 0 = success) or a "succeeded" boolean (0 = failure,
non-zero = success).

ؿ¿ΰۤʤ֤ͤȤǤǤ⤢դ줿ͤΰĤϴ
Ԥ򼨤ͤǤΤ褦ͤϥ顼ɤ
(-Exxx = ԡ0 = )ɤפɽ boolean0 = 
ԡ0 ʳ = )ɽޤ


Mixing up these two sorts of representations is a fertile source of
difficult-to-find bugs.  If the C language included a strong distinction
between integers and booleans then the compiler would find these mistakes
for us... but it doesn't.  To help prevent such bugs, always follow this
convention:

ĤɽߤˤϡĤ뤳Ȥ񤷤Х˭˼¤
ޤ⤷ø줬 boolean Τ˶̤Ƥʤ顢ѥ
ϻãΤˤΥߥ򸫤ĤƤǤ礦...̤Ƥ
ޤ󡣤Τ褦ʥХɤˤϡ˼Τ˽ȤǤ -


	If the name of a function is an action or an imperative command,
	the function should return an error-code integer.  If the name
	is a predicate, the function should return a "succeeded" boolean.

	⤷ؿ̾ư̿Ūʻؼä餽δؿϥ顼
	Ȥ֤٤Ǥ⤷̾(οȽꤹ褦
	ʤ)ǤФδؿɤפɽ boolean ֤
	٤Ǥ


For example, "add work" is a command, and the add_work() function returns 0
for success or -EBUSY for failure.  In the same way, "PCI device present" is
a predicate, and the pci_dev_present() function returns 1 if it succeeds in
finding a matching device or 0 if it doesn't.

㤨С"add work" ϻؼǤꡢ add_work() ؿˣ֤
Ի -EBUSY ֤ޤƱ褦ˡ"PCI device present" Ͻ
ꡢ pci_dev_present() ؿϡбǥХ򸫤Ĥ줿顢
֤Ĥʤä飰֤ޤ


All EXPORTed functions must respect this convention, and so should all
public functions.  Private (static) functions need not, but it is
recommended that they do.

ƤΥݡȤ줿ؿϤε˽äƤꡢƤθ줿ؿ
Ϥ٤Ǥץ饤١(static)ؿϤɬפ̵뤳
Ȥ侩ޤ


Functions whose return value is the actual result of a computation, rather
than an indication of whether the computation succeeded, are not subject to
this rule.  Generally they indicate failure by returning some out-of-range
result.  Typical examples would be functions that return pointers; they use
NULL or the ERR_PTR mechanism to report failure.

ɤǤϤʤơ׻μ·̤ͤȤ֤ؿϡ
оݤǤϤޤ󡣰Ūˡδؿϰϳη̤֤
ǼԤ򼨤ޤŵŪϡݥ󥿤֤ؿǤ -  NULL
 ERR_PTR ˤäơԤ𤷤ޤ



		Chapter 17:  Don't re-invent the kernel macros

		裱 - ͥޥȯʤǤ


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

include/linux/kernel.h إåեˤϡ餫ˤʤȤѼ
ǥ󥰤⡢ʤȤ٤¿ΥޥޤǤޤ㤨
ʤĹ׻ɬפʤ顢ʲΥޥ꤯ѤƤ



  #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))


Similarly, if you need to calculate the size of some structure member, use

Ʊͤˡ⤷ʤ¤ΥФΥ׻ɬפʤ顢Υޥ
ѤƤ


  #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.

¾ˤ⡢ɬפʤ鸷̩ʷåԤ min()  max() ޥ⤢ޤ
ƤΤ򤴼ȤΥɤǺƺʤ褦ˡإåե
ɤƤ



		Chapter 18:  Editor modelines and other cruft

		裱 - ǥΥ⡼ɥ饤䤽¾ν񤭴


Some editors can interpret configuration information embedded in source files,
indicated with special markers.  For example, emacs interprets lines marked
like this:

ǥˤϡեޤ줿ǤΤ
ޤ㤨СEmacs ϤΤ褦˥ޡ줿Ԥᤷޤ


-*- mode: c -*-

Or like this:

⤷ϡΤ褦ʡ


/*
Local Variables:
compile-command: "gcc -DMAGIC_DEBUG_FLAG foo.c"
End:
*/

Vim interprets markers that look like this:

Vim ϼΤ褦ʥޡᤷޤ


/* 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.

򥽡ե˴ޤʤǤ͡ϼʬθĿŪʥǥ
äƤꡢʤΥեϤ񤭤٤ǤϤޤ
ϥǥȤ⡼ΰ٤ΥޡޤǤޤ͡ϼʬ
⡼ɤȤǥȤ褦ʾʼʤäƤǤ礦



		Appendix I: References

		Ͽ I - ʸ


The C Programming Language, Second Edition
by Brian W. Kernighan and Dennis M. Ritchie.
Prentice Hall, Inc., 1988.
ISBN 0-13-110362-8 (paperback), 0-13-110370-9 (hardback).
URL: http://cm.bell-labs.com/cm/cs/cbook/

ץߥ󥰸 裲 ANSI ʽ
Brian W. Kernighan, Dennis M. Ritchie  / 
Ω 1989
ISBN 4-320-02692-6
URL: http://cm.bell-labs.com/cm/cs/cbook/


The Practice of Programming
by Brian W. Kernighan and Rob Pike.
Addison-Wesley, Inc., 1999.
ISBN 0-201-61586-X.
URL: http://cm.bell-labs.com/cm/cs/tpop/

ץߥ󥰺ˡ
Brian W. Kernighan, Rob Pike  / ʡ
 2000
ISBN 4-7561-3649-4
URL: http://cm.bell-labs.com/cm/cs/tpop/


GNU manuals - where in compliance with K&R and this text - for cpp, gcc,
gcc internals and indent, all available from http://www.gnu.org/manual/

GNU ޥ˥奢 - K&R ȤΥƥȤ˽ä - cpp, gcc, gcc internals 
indent ޥ, Ƥ http://www.gnu.org/manual/ ˤޤ


WG14 is the international standardization working group for the programming
language C, URL: http://www.open-std.org/JTC1/SC22/WG14/

WG14 ϥץߥ󥰸äΤιɸಽĤǤ
URL: http://www.open-std.org/JTC1/SC22/WG14/


Kernel CodingStyle, by greg@kroah.com at OLS 2002:
http://www.kroah.com/linux/talks/ols_2002_kernel_codingstyle_talk/html/

--
Last updated on 2007-July-13.
