summaryrefslogtreecommitdiffstats
path: root/Documentation/CodingStyle
diff options
context:
space:
mode:
Diffstat (limited to 'Documentation/CodingStyle')
-rw-r--r--Documentation/CodingStyle860
1 files changed, 0 insertions, 860 deletions
diff --git a/Documentation/CodingStyle b/Documentation/CodingStyle
deleted file mode 100644
index cb9258b..0000000
--- a/Documentation/CodingStyle
+++ /dev/null
@@ -1,860 +0,0 @@
-
- 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.
-
-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;
- }
- ...
-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
-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.
- */
-
-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
- depends on EXPERIMENTAL && !ARCH_USES_SLAB_PAGE_STRUCT
- bool "SLUB (Unqueued Allocator)"
- ...
-
-while seriously dangerous features (such as write support for certain
-filesystems) should advertise this prominently in their prompt string:
-
-config ADFS_FS_RW
- bool "ADFS write support (DANGEROUS)"
- depends on ADFS_FS
- ...
-
-For full documentation on the configuration files, see the file
-Documentation/kbuild/kconfig-language.txt.
-
-
- Chapter 11: Data structures
-
-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/printk.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(), 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 */);
-
-
-
- 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/
-