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+
+		Linux kernel coding style
+
+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.
+
+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.
+
+Anyway, here goes:
+
+
+		Chapter 1: Indentation
+
+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.
+
+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.
+
+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.
+
+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.
+
+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 (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:
+
+	if (condition) do_this;
+	  do_something_everytime;
+
+Don't put multiple assignments on a single line either.  Kernel coding style
+is super simple.  Avoid tricky expressions.
+
+Outside of comments, documentation and except in Kconfig, spaces are never
+used for indentation, and the above example is deliberately broken.
+
+Get a decent editor and don't leave whitespace at the end of lines.
+
+
+		Chapter 2: Breaking long lines and strings
+
+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 strongly
+preferred limit.
+
+Statements longer than 80 columns will be broken into sensible chunks, unless
+exceeding 80 columns significantly increases readability and does not hide
+information. 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. However, never break user-visible strings such as
+printk messages, because that breaks the ability to grep for them.
+
+
+		Chapter 3: Placing Braces and Spaces
+
+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:
+
+	if (x is true) {
+		we do y
+	}
+
+This applies to all non-function statement blocks (if, switch, for,
+while, do).  E.g.:
+
+	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:
+
+	int function(int x)
+	{
+		body of function
+	}
+
+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).
+
+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:
+
+	do {
+		body of do-loop
+	} while (condition);
+
+and
+
+	if (x == y) {
+		..
+	} else if (x > y) {
+		...
+	} else {
+		....
+	}
+
+Rationale: K&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.
+
+Do not unnecessarily use braces where a single statement will do.
+
+	if (condition)
+		action();
+
+and
+
+	if (condition)
+		do_this();
+	else
+		do_that();
+
+This does not apply if only one branch of a conditional statement is a single
+statement; in the latter case 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
+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).
+
+So use a space after these keywords:
+
+	if, switch, case, for, do, while
+
+but not with sizeof, typeof, alignof, or __attribute__.  E.g.,
+
+	s = sizeof(struct file);
+
+Do not add spaces around (inside) parenthesized expressions.  This example is
+*bad*:
+
+	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:
+
+	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:
+
+	=  +  -  <  >  *  /  %  |  &  ^  <=  >=  ==  !=  ?  :
+
+but no space after unary operators:
+
+	&  *  +  -  ~  !  sizeof  typeof  alignof  __attribute__  defined
+
+no space before the postfix increment & decrement unary operators:
+
+	++  --
+
+no space after the prefix increment & decrement unary operators:
+
+	++  --
+
+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
+
+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.
+
+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.
+
+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()".
+
+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.
+
+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.
+
+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).
+
+
+		Chapter 5: Typedefs
+
+Please don't use things like "vps_t".
+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?
+In contrast, if it says
+
+	struct virtual_container *a;
+
+you can actually tell what "a" is.
+
+Lots of people think that typedefs "help readability". Not so. They are
+useful only for:
+
+ (a) totally opaque objects (where the typedef is actively used to _hide_
+     what the object is).
+
+     Example: "pte_t" etc. opaque objects that you can only access using
+     the proper accessor functions.
+
+     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.
+
+ (b) Clear integer types, where the abstraction _helps_ avoid confusion
+     whether it is "int" or "long".
+
+     u8/u16/u32 are perfectly fine typedefs, although they fit into
+     category (d) better than here.
+
+     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;
+
+     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.
+
+ (c) when you use sparse to literally create a _new_ type for
+     type-checking.
+
+ (d) New types which are identical to standard C99 types, in certain
+     exceptional circumstances.
+
+     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.
+
+     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.
+
+     When editing existing code which already uses one or the other set
+     of types, you should conform to the existing choices in that code.
+
+ (e) Types safe for use in userspace.
+
+     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.
+
+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.
+
+In general, a pointer, or a struct that has elements that can reasonably
+be directly accessed should _never_ be a typedef.
+
+
+		Chapter 6: Functions
+
+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.
+
+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.
+
+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).
+
+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.
+
+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.:
+
+	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.
+
+
+		Chapter 7: Centralized exiting of functions
+
+Albeit deprecated by some people, the equivalent of the goto statement is
+used frequently by compilers in form of the unconditional jump instruction.
+
+The goto statement comes in handy when a function exits from multiple
+locations and some common work such as cleanup has to be done.  If there is no
+cleanup needed then just return directly.
+
+Choose label names which say what the goto does or why the goto exists.  An
+example of a good name could be "out_buffer:" if the goto frees "buffer".  Avoid
+using GW-BASIC names like "err1:" and "err2:".  Also don't name them after the
+goto location like "err_kmalloc_failed:"
+
+The rationale for using gotos is:
+
+- 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 ;)
+
+	int fun(int a)
+	{
+		int result = 0;
+		char *buffer;
+
+		buffer = kmalloc(SIZE, GFP_KERNEL);
+		if (!buffer)
+			return -ENOMEM;
+
+		if (condition1) {
+			while (loop1) {
+				...
+			}
+			result = 1;
+			goto out_buffer;
+		}
+		...
+	out_buffer:
+		kfree(buffer);
+		return result;
+	}
+
+A common type of bug to be aware of it "one err bugs" which look like this:
+
+	err:
+		kfree(foo->bar);
+		kfree(foo);
+		return ret;
+
+The bug in this code is that on some exit paths "foo" is NULL.  Normally the
+fix for this is to split it up into two error labels "err_bar:" and "err_foo:".
+
+
+		Chapter 8: Commenting
+
+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.
+
+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.
+
+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.
+
+Linux style for comments is the C89 "/* ... */" style.
+Don't use C99-style "// ..." comments.
+
+The preferred style for long (multi-line) comments is:
+
+	/*
+	 * 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.
+	 */
+
+For files in net/ and drivers/net/ the preferred style for long (multi-line)
+comments is a little different.
+
+	/* The preferred comment style for files in net/ and drivers/net
+	 * looks like this.
+	 *
+	 * It is nearly the same as the generally preferred comment style,
+	 * but there is no initial almost-blank line.
+	 */
+
+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.
+
+
+		Chapter 9: You've made a mess of it
+
+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).
+
+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 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-common-hook
+          (lambda ()
+            ;; Add kernel style
+            (c-add-style
+             "linux-tabs-only"
+             '("linux" (c-offsets-alist
+                        (arglist-cont-nonempty
+                         c-lineup-gcc-asm-reg
+                         c-lineup-arglist-tabs-only))))))
+
+(add-hook 'c-mode-hook
+          (lambda ()
+            (let ((filename (buffer-file-name)))
+              ;; Enable kernel mode for the appropriate files
+              (when (and filename
+                         (string-match (expand-file-name "~/src/linux-trees")
+                                       filename))
+                (setq indent-tabs-mode t)
+                (setq show-trailing-whitespace t)
+                (c-set-style "linux-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".
+
+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.
+
+"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.
+
+
+		Chapter 10: Kconfig configuration files
+
+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:
+
+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.
+
+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
+
+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.
+
+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.
+
+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.
+
+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.
+
+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).
+
+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.
+
+
+		Chapter 12: Macros, Enums and RTL
+
+Names of macros defining constants and labels in enums are capitalized.
+
+	#define CONSTANT 0x12345
+
+Enums are preferred when defining several related constants.
+
+CAPITALIZED macro names are appreciated but macros resembling functions
+may be named in lower case.
+
+Generally, inline functions are preferable to macros resembling functions.
+
+Macros with multiple statements should be enclosed in a do - while block:
+
+	#define macrofun(a, b, c) 			\
+		do {					\
+			if (a == 5)			\
+				do_this(b, c);		\
+		} while (0)
+
+Things to avoid when using macros:
+
+1) macros that affect control flow:
+
+	#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.
+
+2) macros that depend on having a local variable with a magic name:
+
+	#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.
+
+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.
+
+4) forgetting about precedence: macros defining constants using expressions
+must enclose the expression in parentheses. Beware of similar issues with
+macros using parameters.
+
+	#define CONSTANT 0x4000
+	#define CONSTEXP (CONSTANT | 3)
+
+5) namespace collisions when defining local variables in macros resembling
+functions:
+
+#define FOO(x)				\
+({					\
+	typeof(x) ret;			\
+	ret = calc_ret(x);		\
+	(ret);				\
+)}
+
+ret is a common name for a local variable - __foo_ret is less likely
+to collide with an existing variable.
+
+The cpp manual deals with macros exhaustively. The gcc internals manual also
+covers RTL which is used frequently with assembly language in the kernel.
+
+
+		Chapter 13: Printing kernel messages
+
+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.
+
+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/printk.h> defines pr_notice(), pr_info(),
+pr_warn(), pr_err(), etc.
+
+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.  However
+debug message printing is handled differently than printing other non-debug
+messages.  While the other pr_XXX() functions print unconditionally,
+pr_debug() does not; it is compiled out by default, unless either DEBUG is
+defined or CONFIG_DYNAMIC_DEBUG is set.  That is true for dev_dbg() also,
+and a related convention uses VERBOSE_DEBUG to add dev_vdbg() messages to
+the ones already enabled by DEBUG.
+
+Many subsystems have Kconfig debug options to turn on -DDEBUG in the
+corresponding Makefile; in other cases specific files #define DEBUG.  And
+when a debug message should be unconditionally printed, such as if it is
+already inside a debug-related #ifdef section, printk(KERN_DEBUG ...) can be
+used.
+
+
+		Chapter 14: Allocating memory
+
+The kernel provides the following general purpose memory allocators:
+kmalloc(), kzalloc(), kmalloc_array(), kcalloc(), vmalloc(), and
+vzalloc().  Please refer to the API documentation for further information
+about them.
+
+The preferred form for passing a size of a struct is the following:
+
+	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.
+
+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.
+
+The preferred form for allocating an array is the following:
+
+	p = kmalloc_array(n, sizeof(...), ...);
+
+The preferred form for allocating a zeroed array is the following:
+
+	p = kcalloc(n, sizeof(...), ...);
+
+Both forms check for overflow on the allocation size n * sizeof(...),
+and return NULL if that occurred.
+
+
+		Chapter 15: The inline disease
+
+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 milliseconds. There are a LOT of cpu cycles
+that can go into these 5 milliseconds.
+
+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.
+
+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.
+
+
+		Chapter 16: Function return values and names
+
+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).
+
+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:
+
+	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.
+
+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.
+
+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.
+
+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.
+
+
+		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.
+
+
+		Chapter 19:  Inline assembly
+
+In architecture-specific code, you may need to use inline assembly to interface
+with CPU or platform functionality.  Don't hesitate to do so when necessary.
+However, don't use inline assembly gratuitously when C can do the job.  You can
+and should poke hardware from C when possible.
+
+Consider writing simple helper functions that wrap common bits of inline
+assembly, rather than repeatedly writing them with slight variations.  Remember
+that inline assembly can use C parameters.
+
+Large, non-trivial assembly functions should go in .S files, with corresponding
+C prototypes defined in C header files.  The C prototypes for assembly
+functions should use "asmlinkage".
+
+You may need to mark your asm statement as volatile, to prevent GCC from
+removing it if GCC doesn't notice any side effects.  You don't always need to
+do so, though, and doing so unnecessarily can limit optimization.
+
+When writing a single inline assembly statement containing multiple
+instructions, put each instruction on a separate line in a separate quoted
+string, and end each string except the last with \n\t to properly indent the
+next instruction in the assembly output:
+
+	asm ("magic %reg1, #42\n\t"
+	     "more_magic %reg2, %reg3"
+	     : /* outputs */ : /* inputs */ : /* clobbers */);
+
+
+		Chapter 20: Conditional Compilation
+
+Wherever possible, don't use preprocessor conditionals (#if, #ifdef) in .c
+files; doing so makes code harder to read and logic harder to follow.  Instead,
+use such conditionals in a header file defining functions for use in those .c
+files, providing no-op stub versions in the #else case, and then call those
+functions unconditionally from .c files.  The compiler will avoid generating
+any code for the stub calls, producing identical results, but the logic will
+remain easy to follow.
+
+Prefer to compile out entire functions, rather than portions of functions or
+portions of expressions.  Rather than putting an ifdef in an expression, factor
+out part or all of the expression into a separate helper function and apply the
+conditional to that function.
+
+If you have a function or variable which may potentially go unused in a
+particular configuration, and the compiler would warn about its definition
+going unused, mark the definition as __maybe_unused rather than wrapping it in
+a preprocessor conditional.  (However, if a function or variable *always* goes
+unused, delete it.)
+
+Within code, where possible, use the IS_ENABLED macro to convert a Kconfig
+symbol into a C boolean expression, and use it in a normal C conditional:
+
+	if (IS_ENABLED(CONFIG_SOMETHING)) {
+		...
+	}
+
+The compiler will constant-fold the conditional away, and include or exclude
+the block of code just as with an #ifdef, so this will not add any runtime
+overhead.  However, this approach still allows the C compiler to see the code
+inside the block, and check it for correctness (syntax, types, symbol
+references, etc).  Thus, you still have to use an #ifdef if the code inside the
+block references symbols that will not exist if the condition is not met.
+
+At the end of any non-trivial #if or #ifdef block (more than a few lines),
+place a comment after the #endif on the same line, noting the conditional
+expression used.  For instance:
+
+	#ifdef CONFIG_SOMETHING
+	...
+	#endif /* CONFIG_SOMETHING */
+
+
+		Appendix I: References
+
+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/
+
+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/
+
+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/
+
+WG14 is the international standardization working group for the programming
+language C, 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/
+