path: root/doc
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authorH. Peter Anvin <hpa@zytor.com>2009-05-25 21:45:53 -0700
committerH. Peter Anvin <hpa@zytor.com>2009-05-25 21:45:53 -0700
commita90bd72183a56a7312b5b47bff6857c205d98d51 (patch)
treea636dfcc7ccb4cbf9388a43903c309fe6ddd947e /doc
parent9fd03f7c843a9c107bb1a5e65bd9d94f6e48d892 (diff)
doc: add the Linux kernel coding style document
We expect to use Linux kernel coding style, minus the indentation level. Signed-off-by: H. Peter Anvin <hpa@zytor.com>
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diff --git a/doc/CodingStyle.txt b/doc/CodingStyle.txt
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+Syslinux uses Linux kernel coding style, except that we are "heretic"
+in the sense of using 4 spaces instead of 8 for indentation.
+This coding style will be applied after the 3.81 release.
+ -------------------------------------------------
+ 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.
+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.
+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;
+ 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";
+ return "remove";
+ 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
+ do {
+ body of do-loop
+ } while (condition);
+ 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();
+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
+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
+ 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;
+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.
+The rationale 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 = kmalloc(SIZE);
+ if (buffer == NULL)
+ return -ENOMEM;
+ if (condition1) {
+ while (loop1) {
+ ...
+ }
+ result = 1;
+ goto out;
+ }
+ ...
+ kfree(buffer);
+ return result;
+ 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
+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.
+ */
+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)
+ (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.
+Features that might still be considered unstable should be defined as
+dependent on "EXPERIMENTAL":
+config SLUB
+ 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
+ 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)
+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/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
+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.
+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
+ 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 miliseconds. There are a LOT of cpu cycles
+that can go into these 5 miliseconds.
+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
+ 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"
+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
+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:
+Last updated on 2007-July-13.