This is a short document describing the preferred coding style for thelinux kernel. Coding style is very personal, and I won't force myviews on anybody, but this is what goes for anything that I have to beable to maintain, and I'd prefer it for most other things too. Pleaseat 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:
1) Indentation¶
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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 tobe 3.
Rationale: The whole idea behind indentation is to clearly define wherea block of control starts and ends. Especially when you've been lookingat your screen for 20 straight hours, you'll find it a lot easier to seehow the indentation works if you have large indentations.
Now, some people will claim that having 8-character indentations makesthe code move too far to the right, and makes it hard to read on a80-character terminal screen. The answer to that is that if you needmore than 3 levels of indentation, you're screwed anyway, and should fixyour program.
In short, 8-char indents make things easier to read, and have the addedbenefit 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 isto align the switch and its subordinate case labels in the same columninstead of double-indenting the case labels. E.g.:
Don't put multiple statements on a single line unless you havesomething to hide:
Don't put multiple assignments on a single line either. Kernel coding styleis super simple. Avoid tricky expressions.
Outside of comments, documentation and except in Kconfig, spaces are neverused for indentation, and the above example is deliberately broken.
Get a decent editor and don't leave whitespace at the end of lines.
2) Breaking long lines and strings¶
Coding style is all about readability and maintainability using commonlyavailable tools.
The limit on the length of lines is 80 columns and this is a stronglypreferred limit.
Statements longer than 80 columns will be broken into sensible chunks, unlessexceeding 80 columns significantly increases readability and does not hideinformation. Descendants are always substantially shorter than the parent andare placed substantially to the right. The same applies to function headerswith a long argument list. However, never break user-visible strings such asprintk messages, because that breaks the ability to grep for them.
3) Placing Braces and Spaces¶
The other issue that always comes up in C styling is the placement ofbraces. Unlike the indent size, there are few technical reasons tochoose one placement strategy over the other, but the preferred way, asshown to us by the prophets Kernighan and Ritchie, is to put the openingbrace last on the line, and put the closing brace first, thusly:
This applies to all non-function statement blocks (if, switch, for,while, do). E.g.:
However, there is one special case, namely functions: they have theopening brace at the beginning of the next line, thus:
Heretic people all over the world have claimed that this inconsistencyis .. well .. inconsistent, but all right-thinking people know that(a) K&R are right and (b) K&R are right. Besides, functions arespecial anyway (you can't nest them in C).
Note that the closing brace is empty on a line of its own, except inthe 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, likethis:
and
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 thesupply of new-lines on your screen is not a renewable resource (think25-line terminal screens here), you have more empty lines to putcomments on.
Do not unnecessarily use braces where a single statement will do.
and
This does not apply if only one branch of a conditional statement is a singlestatement; in the latter case use braces in both branches:
3.1) Spaces¶
Linux kernel style for use of spaces depends (mostly) onfunction-versus-keyword usage. Use a space after (most) keywords. Thenotable exceptions are sizeof, typeof, alignof, and __attribute__, which looksomewhat like functions (and are usually used with parentheses in Linux,although they are not required in the language, as in: sizeofinfo afterstructfileinfoinfo; is declared).
So use a space after these keywords:
but not with sizeof, typeof, alignof, or __attribute__. E.g.,
Do not add spaces around (inside) parenthesized expressions. This example isbad:
When declaring pointer data or a function that returns a pointer type, thepreferred use of * is adjacent to the data name or function name and notadjacent to the type name. Examples:
Use one space around (on each side of) most binary and ternary operators,such as any of these:
but no space after unary operators:
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 withsmart indentation will insert whitespace at the beginning of new lines asappropriate, 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 notputting 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 canoptionally strip the trailing whitespace for you; however, if applying a seriesof patches, this may make later patches in the series fail by changing theircontext lines.
4) Naming¶
C is a Spartan language, and so should your naming be. Unlike Modula-2and Pascal programmers, C programmers do not use cute names likeThisVariableIsATemporaryCounter. A C programmer would call thatvariable tmp, which is much easier to write, and not the least moredifficult to understand.
HOWEVER, while mixed-case names are frowned upon, descriptive names forglobal variables are a must. To call a global function foo is ashooting offense.
GLOBAL variables (to be used only if you really need them) need tohave descriptive names, as do global functions. If you have a functionthat counts the number of active users, you should call thatcount_active_users() or similar, you should not call it cntusr().
Encoding the type of a function into the name (so-called Hungariannotation) is brain damaged - the compiler knows the types anyway and cancheck those, and it only confuses the programmer. No wonder MicroSoftmakes buggy programs.
LOCAL variable names should be short, and to the point. If you havesome random integer loop counter, it should probably be called i.Calling it loop_counter is non-productive, if there is no chance of itbeing mis-understood. Similarly, tmp can be just about any type ofvariable that is used to hold a temporary value.
If you are afraid to mix up your local variable names, you have anotherproblem, which is called the function-growth-hormone-imbalance syndrome.See chapter 6 (Functions).
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
in the source, what does it mean?In contrast, if it says
you can actually tell what a is.
Lots of people think that typedefs helpreadability. Not so. They areuseful only for:
totally opaque objects (where the typedef is actively used to hidewhat the object is).
Example:
pte_tetc. opaque objects that you can only access usingthe proper accessor functions.Note
Opaqueness and
accessorfunctionsare not good in themselves.The reason we have them for things like pte_t etc. is that therereally is absolutely zero portably accessible information there.Clear integer types, where the abstraction helps avoid confusionwhether it is
intorlong.u8/u16/u32 are perfectly fine typedefs, although they fit intocategory (d) better than here.
Note
Again - there needs to be a reason for this. If something is
unsignedlong, then there's no reason to dobut if there is a clear reason for why it under certain circumstancesmight be an
unsignedintand under other configurations might beunsignedlong, then by all means go ahead and use a typedef.when you use sparse to literally create a new type fortype-checking.
New types which are identical to standard C99 types, in certainexceptional circumstances.
Although it would only take a short amount of time for the eyes andbrain to become accustomed to the standard types like
uint32_t,some people object to their use anyway.Therefore, the Linux-specific
u8/u16/u32/u64types and theirsigned equivalents which are identical to standard types arepermitted – although they are not mandatory in new code of yourown.When editing existing code which already uses one or the other setof types, you should conform to the existing choices in that code.
Types safe for use in userspace.
In certain structures which are visible to userspace, we cannotrequire C99 types and cannot use the
u32form above. Thus, weuse __u32 and similar types in all structures which are sharedwith userspace.
Maybe there are other cases too, but the rule should basically be to NEVEREVER use a typedef unless you can clearly match one of those rules.
In general, a pointer, or a struct that has elements that can reasonablybe directly accessed should never be a typedef.
6) Functions¶
Functions should be short and sweet, and do just one thing. They shouldfit 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 thecomplexity and indentation level of that function. So, if you have aconceptually simple function that is just one long (but simple)case-statement, where you have to do lots of small things for a lot ofdifferent cases, it's OK to have a longer function.
However, if you have a complex function, and you suspect that aless-than-gifted first-year high-school student might not evenunderstand what the function is all about, you should adhere to themaximum limits all the more closely. Use helper functions withdescriptive names (you can ask the compiler to in-line them if you thinkit's performance-critical, and it will probably do a better job of itthan you would have done).
Another measure of the function is the number of local variables. Theyshouldn't exceed 5-10, or you're doing something wrong. Re-think thefunction, and split it into smaller pieces. A human brain cangenerally easily keep track of about 7 different things, anything moreand it gets confused. You know you're brilliant, but maybe you'd liketo understand what you did 2 weeks from now.
In source files, separate functions with one blank line. If the function isexported, the EXPORT macro for it should follow immediately after theclosing function brace line. E.g.:
In function prototypes, include parameter names with their data types.Although this is not required by the C language, it is preferred in Linuxbecause it is a simple way to add valuable information for the reader.
7) Centralized exiting of functions¶
Albeit deprecated by some people, the equivalent of the goto statement isused frequently by compilers in form of the unconditional jump instruction.
The goto statement comes in handy when a function exits from multiplelocations and some common work such as cleanup has to be done. If there is nocleanup needed then just return directly.
Choose label names which say what the goto does or why the goto exists. Anexample of a good name could be out_free_buffer: if the goto frees buffer.Avoid using GW-BASIC names like err1: and err2:, as you would have torenumber them if you ever add or remove exit paths, and they make correctnessdifficult to verify anyway.
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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 makingmodifications are prevented
- saves the compiler work to optimize redundant code away ;)
Best sound editing software. A common type of bug to be aware of is oneerrbugs which look like this:
The bug in this code is that on some exit paths foo is NULL. Normally thefix for this is to split it up into two error labels err_free_bar: anderr_free_foo::
Ideally you should simulate errors to test all exit paths.
8) Commenting¶
Comments are good, but there is also a danger of over-commenting. NEVERtry to explain HOW your code works in a comment: it's much better towrite the code so that the working is obvious, and it's a waste oftime 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 thefunction 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 makesmall comments to note or warn about something particularly clever (orugly), but try to avoid excess. Instead, put the comments at the headof the function, telling people what it does, and possibly WHY it doesit.
When commenting the kernel API functions, please use the kernel-doc format.See the files at Documentation/doc-guide/ andscripts/kernel-doc for details.
The preferred style for long (multi-line) comments is:
For files in net/ and drivers/net/ the preferred style for long (multi-line)comments is a little different.
It's also important to comment data, whether they are basic types or derivedtypes. To this end, use just one data declaration per line (no commas formultiple data declarations). This leaves you room for a small comment on eachitem, explaining its use.
9) You've made a mess of it¶
That's OK, we all do. You've probably been told by your long-time Unixuser helper that GNUemacs automatically formats the C sources foryou, and you've noticed that yes, it does do that, but the defaults ituses are less than desirable (in fact, they are worse than randomtyping - an infinite number of monkeys typing into GNU emacs would nevermake a good program).
So, you can either get rid of GNU emacs, or change it to use sanervalues. To do the latter, you can stick the following in your .emacs file:
This will make emacs go better with the kernel coding style for Cfiles below ~/src/linux-trees.
But even if you fail in getting emacs to do sane formatting, noteverything is lost: use indent.
Now, again, GNU indent has the same brain-dead settings that GNU emacshas, 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 indentrecognize the authority of K&R (the GNU people aren't evil, they arejust severely misguided in this matter), so you just give indent theoptions -kr-i8 (stands for K&R,8characterindents), or usescripts/Lindent, which indents in the latest style.
indent has a lot of options, and especially when it comes to commentre-formatting you may want to take a look at the man page. Butremember: indent is not a fix for bad programming.
10) Kconfig configuration files¶
For all of the Kconfig* configuration files throughout the source tree,the indentation is somewhat different. Lines under a config definitionare indented with one tab, while help text is indented an additional twospaces. Example:
Seriously dangerous features (such as write support for certainfilesystems) should advertise this prominently in their prompt string:
For full documentation on the configuration files, see the fileDocumentation/kbuild/kconfig-language.txt.
11) Data structures¶
Data structures that have visibility outside the single-threadedenvironment they are created and destroyed in should always havereference counts. In the kernel, garbage collection doesn't exist (andoutside the kernel garbage collection is slow and inefficient), whichmeans that you absolutely have to reference count all your uses.
Reference counting means that you can avoid locking, and allows multipleusers to have access to the data structure in parallel - and not havingto worry about the structure suddenly going away from under them justbecause 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 referencecounting is a memory management technique. Usually both are needed, andthey 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 countsthe number of subclass users, and decrements the global count just oncewhen the subclass count goes to zero.
Examples of this kind of multi-level-reference-counting can be found inmemory management (structmm_struct: mm_users and mm_count), and infilesystem code (structsuper_block: s_count and s_active).
Remember: if another thread can find your data structure, and you don'thave a reference count on it, you almost certainly have a bug.
12) Macros, Enums and RTL¶
Names of macros defining constants and labels in enums are capitalized.
Enums are preferred when defining several related constants.
CAPITALIZED macro names are appreciated but macros resembling functionsmay 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:
Things to avoid when using macros:
- macros that affect control flow:
is a very bad idea. It looks like a function call but exits the callingfunction; don't break the internal parsers of those who will read the code.
- macros that depend on having a local variable with a magic name:
might look like a good thing, but it's confusing as hell when one reads thecode and it's prone to breakage from seemingly innocent changes.
3) macros with arguments that are used as l-values: FOO(x) = y; willbite you if somebody e.g. turns FOO into an inline function.
4) forgetting about precedence: macros defining constants using expressionsmust enclose the expression in parentheses. Beware of similar issues withmacros using parameters.
5) namespace collisions when defining local variables in macros resemblingfunctions:
ret is a common name for a local variable - __foo_ret is less likelyto collide with an existing variable.
The cpp manual deals with macros exhaustively. The gcc internals manual alsocovers RTL which is used frequently with assembly language in the kernel.
13) Printing kernel messages¶
Kernel developers like to be seen as literate. Do mind the spellingof kernel messages to make a good impression. Do not use crippledwords like dont; use donot or don't instead. Make the messagesconcise, 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 which you should use to make sure messages are matched to the right deviceand driver, and are tagged with the right level: dev_err(), dev_warn(),dev_info(), and so forth. For messages that aren't associated with aparticular device, defines pr_notice(), pr_info(),pr_warn(), pr_err(), etc.
Coming up with good debugging messages can be quite a challenge; and onceyou have them, they can be a huge help for remote troubleshooting. Howeverdebug message printing is handled differently than printing other non-debugmessages. While the other pr_XXX() functions print unconditionally,pr_debug() does not; it is compiled out by default, unless either DEBUG isdefined 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 tothe ones already enabled by DEBUG.
Many subsystems have Kconfig debug options to turn on -DDEBUG in thecorresponding Makefile; in other cases specific files #define DEBUG. Andwhen a debug message should be unconditionally printed, such as if it isalready inside a debug-related #ifdef section, printk(KERN_DEBUG ..) can beused.
14) Allocating memory¶
The kernel provides the following general purpose memory allocators:kmalloc(), kzalloc(), kmalloc_array(), kcalloc(), vmalloc(), andvzalloc(). Please refer to the API documentation for further informationabout them.
The preferred form for passing a size of a struct is the following:
The alternative form where struct name is spelled out hurts readability andintroduces an opportunity for a bug when the pointer variable type is changedbut the corresponding sizeof that is passed to a memory allocator is not.
Casting the return value which is a void pointer is redundant. The conversionfrom void pointer to any other pointer type is guaranteed by the C programminglanguage.
The preferred form for allocating an array is the following:
The preferred form for allocating a zeroed array is the following:
Both forms check for overflow on the allocation size n * sizeof(..),and return NULL if that occurred.
15) The inline disease¶
There appears to be a common misperception that gcc has a magic 'make mefaster' speedup option called inline. While the use of inlines can beappropriate (for example as a means of replacing macros, see Chapter 12), itvery often is not. Abundant use of the inline keyword leads to a much biggerkernel, which in turn slows the system as a whole down, due to a biggericache footprint for the CPU and simply because there is less memoryavailable for the pagecache. Just think about it; a pagecache miss causes adisk seek, which easily takes 5 milliseconds. There are a LOT of cpu cyclesthat can go into these 5 milliseconds. How to open zip file macbook.
A reasonable rule of thumb is to not put inline at functions that have morethan 3 lines of code in them. An exception to this rule are the cases wherea parameter is known to be a compiletime constant, and as a result of thisconstantness you know the compiler will be able to optimize most of yourfunction away at compile time. For a good example of this later case, seethe kmalloc() inline function.
Often people argue that adding inline to functions that are static and usedonly once is always a win since there is no space tradeoff. While this istechnically correct, gcc is capable of inlining these automatically withouthelp, and the maintenance issue of removing the inline when a second userappears outweighs the potential value of the hint that tells gcc to dosomething it would have done anyway.
16) Function return values and names¶
Functions can return values of many different kinds, and one of themost common is a value indicating whether the function succeeded orfailed. 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 ofdifficult-to-find bugs. If the C language included a strong distinctionbetween integers and booleans then the compiler would find these mistakesfor us.. but it doesn't. To help prevent such bugs, always follow thisconvention:
For example, addwork is a command, and the add_work() function returns 0for success or -EBUSY for failure. In the same way, PCIdevicepresent isa predicate, and the pci_dev_present() function returns 1 if it succeeds infinding a matching device or 0 if it doesn't.
All EXPORTed functions must respect this convention, and so should allpublic functions. Private (static) functions need not, but it isrecommended that they do.
Functions whose return value is the actual result of a computation, ratherthan an indication of whether the computation succeeded, are not subject tothis rule. Generally they indicate failure by returning some out-of-rangeresult. Typical examples would be functions that return pointers; they useNULL or the ERR_PTR mechanism to report failure.
17) Don't re-invent the kernel macros¶
The header file include/linux/kernel.h contains a number of macros thatyou should use, rather than explicitly coding some variant of them yourself.For example, if you need to calculate the length of an array, take advantageof the macro
15) The inline disease¶
There appears to be a common misperception that gcc has a magic 'make mefaster' speedup option called inline. While the use of inlines can beappropriate (for example as a means of replacing macros, see Chapter 12), itvery often is not. Abundant use of the inline keyword leads to a much biggerkernel, which in turn slows the system as a whole down, due to a biggericache footprint for the CPU and simply because there is less memoryavailable for the pagecache. Just think about it; a pagecache miss causes adisk seek, which easily takes 5 milliseconds. There are a LOT of cpu cyclesthat can go into these 5 milliseconds. How to open zip file macbook.
A reasonable rule of thumb is to not put inline at functions that have morethan 3 lines of code in them. An exception to this rule are the cases wherea parameter is known to be a compiletime constant, and as a result of thisconstantness you know the compiler will be able to optimize most of yourfunction away at compile time. For a good example of this later case, seethe kmalloc() inline function.
Often people argue that adding inline to functions that are static and usedonly once is always a win since there is no space tradeoff. While this istechnically correct, gcc is capable of inlining these automatically withouthelp, and the maintenance issue of removing the inline when a second userappears outweighs the potential value of the hint that tells gcc to dosomething it would have done anyway.
16) Function return values and names¶
Functions can return values of many different kinds, and one of themost common is a value indicating whether the function succeeded orfailed. 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 ofdifficult-to-find bugs. If the C language included a strong distinctionbetween integers and booleans then the compiler would find these mistakesfor us.. but it doesn't. To help prevent such bugs, always follow thisconvention:
For example, addwork is a command, and the add_work() function returns 0for success or -EBUSY for failure. In the same way, PCIdevicepresent isa predicate, and the pci_dev_present() function returns 1 if it succeeds infinding a matching device or 0 if it doesn't.
All EXPORTed functions must respect this convention, and so should allpublic functions. Private (static) functions need not, but it isrecommended that they do.
Functions whose return value is the actual result of a computation, ratherthan an indication of whether the computation succeeded, are not subject tothis rule. Generally they indicate failure by returning some out-of-rangeresult. Typical examples would be functions that return pointers; they useNULL or the ERR_PTR mechanism to report failure.
17) Don't re-invent the kernel macros¶
The header file include/linux/kernel.h contains a number of macros thatyou should use, rather than explicitly coding some variant of them yourself.For example, if you need to calculate the length of an array, take advantageof the macro
Similarly, if you need to calculate the size of some structure member, use
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There are also min() and max() macros that do strict type checking if youneed them. Feel free to peruse that header file to see what else is alreadydefined that you shouldn't reproduce in your code.
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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 markedlike this:
Or like this:
Vim interprets markers that look like this:
Do not include any of these in source files. People have their own personaleditor configurations, and your source files should not override them. Thisincludes markers for indentation and mode configuration. People may use theirown custom mode, or may have some other magic method for making indentationwork correctly.
19) Inline assembly¶
In architecture-specific code, you may need to use inline assembly to interfacewith 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 canand should poke hardware from C when possible.
Consider writing simple helper functions that wrap common bits of inlineassembly, rather than repeatedly writing them with slight variations. Rememberthat inline assembly can use C parameters.
Large, non-trivial assembly functions should go in .S files, with correspondingC prototypes defined in C header files. The C prototypes for assemblyfunctions should use asmlinkage.
You may need to mark your asm statement as volatile, to prevent GCC fromremoving it if GCC doesn't notice any side effects. You don't always need todo so, though, and doing so unnecessarily can limit optimization.
When writing a single inline assembly statement containing multipleinstructions, put each instruction on a separate line in a separate quotedstring, and end each string except the last with nt to properly indent thenext instruction in the assembly output:
20) Conditional Compilation¶
Wherever possible, don't use preprocessor conditionals (#if, #ifdef) in .cfiles; 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 .cfiles, providing no-op stub versions in the #else case, and then call thosefunctions unconditionally from .c files. The compiler will avoid generatingany code for the stub calls, producing identical results, but the logic willremain easy to follow.
Prefer to compile out entire functions, rather than portions of functions orportions of expressions. Rather than putting an ifdef in an expression, factorout part or all of the expression into a separate helper function and apply theconditional to that function.
If you have a function or variable which may potentially go unused in aparticular configuration, and the compiler would warn about its definitiongoing unused, mark the definition as __maybe_unused rather than wrapping it ina preprocessor conditional. (However, if a function or variable always goesunused, delete it.)
Within code, where possible, use the IS_ENABLED macro to convert a Kconfigsymbol into a C boolean expression, and use it in a normal C conditional:
The compiler will constant-fold the conditional away, and include or excludethe block of code just as with an #ifdef, so this will not add any runtimeoverhead. However, this approach still allows the C compiler to see the codeinside the block, and check it for correctness (syntax, types, symbolreferences, etc). Thus, you still have to use an #ifdef if the code inside theblock 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 conditionalexpression used. For instance:
Appendix I) References¶
The C Programming Language, Second Editionby Brian W. Kernighan and Dennis M. Ritchie.Prentice Hall, Inc., 1988.ISBN 0-13-110362-8 (paperback), 0-13-110370-9 (hardback).
The Practice of Programmingby Brian W. Kernighan and Rob Pike.Addison-Wesley, Inc., 1999.ISBN 0-201-61586-X.
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 programminglanguage C, URL: http://www.open-std.org/JTC1/SC22/WG14/
Kernel process/coding-style.rst, by greg@kroah.com at OLS 2002:http://www.kroah.com/linux/talks/ols_2002_kernel_codingstyle_talk/html/
