Lines Matching +full:use +full:- +full:case
19 --------------
31 Now, some people will claim that having 8-character indentations makes
33 80-character terminal screen. The answer to that is that if you need
37 In short, 8-char indents make things easier to read, and have the added
42 to align the ``switch`` and its subordinate ``case`` labels in the same column
43 instead of ``double-indenting`` the ``case`` labels. E.g.:
45 .. code-block:: c
48 case 'G':
49 case 'g':
52 case 'M':
53 case 'm':
56 case 'K':
57 case 'k':
67 .. code-block:: c
72 Don't use commas to avoid using braces:
74 .. code-block:: c
81 .. code-block:: c
99 ----------------------------------
116 However, never break user-visible strings such as printk messages because
121 ----------------------------
129 .. code-block:: c
135 This applies to all non-function statement blocks (if, switch, for,
138 .. code-block:: c
141 case KOBJ_ADD:
143 case KOBJ_REMOVE:
145 case KOBJ_CHANGE:
151 However, there is one special case, namely functions: they have the
154 .. code-block:: c
162 is ... well ... inconsistent, but all right-thinking people know that
168 ie a ``while`` in a do-statement or an ``else`` in an if-statement, like
171 .. code-block:: c
174 body of do-loop
179 .. code-block:: c
191 Also, note that this brace-placement also minimizes the number of empty
193 supply of new-lines on your screen is not a renewable resource (think
194 25-line terminal screens here), you have more empty lines to put
197 Do not unnecessarily use braces where a single statement will do.
199 .. code-block:: c
206 .. code-block:: none
214 statement; in the latter case use braces in both branches:
216 .. code-block:: c
225 Also, use braces when a loop contains more than a single simple statement:
227 .. code-block:: c
237 Linux kernel style for use of spaces depends (mostly) on
238 function-versus-keyword usage. Use a space after (most) keywords. The
244 So use a space after these keywords::
246 if, switch, case, for, do, while
250 .. code-block:: c
258 .. code-block:: c
264 preferred use of ``*`` is adjacent to the data name or function name and not
267 .. code-block:: c
274 Use one space around (on each side of) most binary and ternary operators,
277 = + - < > * / % | & ^ <= >= == != ? :
281 & * + - ~ ! sizeof typeof alignof __attribute__ defined
285 ++ --
289 ++ --
291 and no space around the ``.`` and ``->`` structure member operators.
307 ---------
310 Unlike Modula-2 and Pascal programmers, C programmers do not use cute
315 HOWEVER, while mixed-case names are frowned upon, descriptive names for
324 Encoding the type of a function into the name (so-called Hungarian
325 notation) is asinine - the compiler knows the types anyway and can check
330 Calling it ``loop_counter`` is non-productive, if there is no chance of it
331 being mis-understood. Similarly, ``tmp`` can be just about any type of
335 problem, which is called the function-growth-hormone-imbalance syndrome.
360 -----------
362 Please don't use things like ``vps_t``.
363 It's a **mistake** to use typedef for structures and pointers. When you see a
365 .. code-block:: c
373 .. code-block:: c
402 Again - there needs to be a **reason** for this. If something is
409 ``unsigned long``, then by all means go ahead and use a typedef.
411 (c) when you use sparse to literally create a **new** type for
412 type-checking.
419 some people object to their use anyway.
421 Therefore, the Linux-specific ``u8/u16/u32/u64`` types and their
423 permitted -- although they are not mandatory in new code of your
429 (e) Types safe for use in userspace.
432 require C99 types and cannot use the ``u32`` form above. Thus, we
433 use __u32 and similar types in all structures which are shared
437 EVER use a typedef unless you can clearly match one of those rules.
444 ------------
453 case-statement, where you have to do lots of small things for a lot of
457 less-than-gifted first-year high-school student might not even
459 maximum limits all the more closely. Use helper functions with
460 descriptive names (you can ask the compiler to in-line them if you think
461 it's performance-critical, and it will probably do a better job of it
465 shouldn't exceed 5-10, or you're doing something wrong. Re-think the
475 .. code-block:: c
487 Do not use the ``extern`` keyword with function prototypes as this makes
492 -----------------------------------
503 Avoid using GW-BASIC names like ``err1:`` and ``err2:``, as you would have to
509 - unconditional statements are easier to understand and follow
510 - nesting is reduced
511 - errors by not updating individual exit points when making
513 - saves the compiler work to optimize redundant code away ;)
515 .. code-block:: c
524 return -ENOMEM;
541 .. code-block:: c
544 kfree(foo->bar);
552 .. code-block:: c
555 kfree(foo->bar);
564 -------------
566 Comments are good, but there is also a danger of over-commenting. NEVER
580 When commenting the kernel API functions, please use the kernel-doc format.
581 See the files at :ref:`Documentation/doc-guide/ <doc_guide>` and
582 ``scripts/kernel-doc`` for details.
584 The preferred style for long (multi-line) comments is:
586 .. code-block:: c
589 * This is the preferred style for multi-line
591 * Please use it consistently.
594 * with beginning and ending almost-blank lines.
597 For files in net/ and drivers/net/ the preferred style for long (multi-line)
600 .. code-block:: c
606 * but there is no initial almost-blank line.
610 types. To this end, use just one data declaration per line (no commas for
612 item, explaining its use.
616 ---------------------------
618 That's OK, we all do. You've probably been told by your long-time Unix
622 typing - an infinite number of monkeys typing into GNU emacs would never
625 So, you can either get rid of GNU emacs, or change it to use saner
628 .. code-block:: none
630 (defun c-lineup-arglist-tabs-only (ignored)
632 (let* ((anchor (c-langelem-pos c-syntactic-element))
633 (column (c-langelem-2nd-pos c-syntactic-element))
634 (offset (- (1+ column) anchor))
635 (steps (floor offset c-basic-offset)))
637 c-basic-offset)))
639 (dir-locals-set-class-variables
640 'linux-kernel
641 '((c-mode . (
642 (c-basic-offset . 8)
643 (c-label-minimum-indentation . 0)
644 (c-offsets-alist . (
645 (arglist-close . c-lineup-arglist-tabs-only)
646 (arglist-cont-nonempty .
647 (c-lineup-gcc-asm-reg c-lineup-arglist-tabs-only))
648 (arglist-intro . +)
649 (brace-list-intro . +)
650 (c . c-lineup-C-comments)
651 (case-label . 0)
652 (comment-intro . c-lineup-comment)
653 (cpp-define-intro . +)
654 (cpp-macro . -1000)
655 (cpp-macro-cont . +)
656 (defun-block-intro . +)
657 (else-clause . 0)
658 (func-decl-cont . +)
660 (inher-cont . c-lineup-multi-inher)
661 (knr-argdecl-intro . 0)
662 (label . -1000)
664 (statement-block-intro . +)
665 (statement-case-intro . +)
666 (statement-cont . +)
669 (indent-tabs-mode . t)
670 (show-trailing-whitespace . t)
673 (dir-locals-set-directory-class
674 (expand-file-name "~/src/linux-trees")
675 'linux-kernel)
678 files below ``~/src/linux-trees``.
681 everything is lost: use ``indent``.
683 Now, again, GNU indent has the same brain-dead settings that GNU emacs
688 options ``-kr -i8`` (stands for ``K&R, 8 character indents``), or use
692 re-formatting you may want to take a look at the man page. But
695 Note that you can also use the ``clang-format`` tool to help you with
696 these rules, to quickly re-format parts of your code automatically,
700 See the file :ref:`Documentation/process/clang-format.rst <clangformat>`
705 -------------------------------
718 logging of avc messages output). Does not do system-call
730 Documentation/kbuild/kconfig-language.rst.
734 -------------------
736 Data structures that have visibility outside the single-threaded
743 users to have access to the data structure in parallel - and not having
757 Examples of this kind of ``multi-level-reference-counting`` can be found in
766 -------------------------
770 .. code-block:: c
777 may be named in lower case.
781 Macros with multiple statements should be enclosed in a do - while block:
783 .. code-block:: c
795 .. code-block:: c
800 return -EBUGGERED; \
808 .. code-block:: c
815 3) macros with arguments that are used as l-values: FOO(x) = y; will
822 .. code-block:: c
830 .. code-block:: c
839 ret is a common name for a local variable - __foo_ret is less likely
847 ----------------------------
850 of kernel messages to make a good impression. Do not use incorrect
851 contractions like ``dont``; use ``do not`` or ``don't`` instead. Make the
859 which you should use to make sure messages are matched to the right device
867 debug message printing is handled differently than printing other non-debug
874 Many subsystems have Kconfig debug options to turn on -DDEBUG in the
877 already inside a debug-related #ifdef section, printk(KERN_DEBUG ...) can be
882 ---------------------
887 about them. :ref:`Documentation/core-api/memory-allocation.rst
892 .. code-block:: c
906 .. code-block:: c
912 .. code-block:: c
920 without __GFP_NOWARN so there is no use in emitting an additional failure
924 ----------------------
927 faster" speedup option called ``inline``. While the use of inlines can be
929 very often is not. Abundant use of the inline keyword leads to a much bigger
940 function away at compile time. For a good example of this later case, see
952 ------------------------------------
956 failed. Such a value can be represented as an error-code integer
957 (-Exxx = failure, 0 = success) or a ``succeeded`` boolean (0 = failure,
958 non-zero = success).
961 difficult-to-find bugs. If the C language included a strong distinction
967 the function should return an error-code integer. If the name
971 for success or -EBUSY for failure. In the same way, ``PCI device present`` is
981 this rule. Generally they indicate failure by returning some out-of-range
982 result. Typical examples would be functions that return pointers; they use
987 --------------
997 bool function return types and stack variables are always fine to use whenever
998 appropriate. Use of bool is encouraged to improve readability and is often a
1001 Do not use bool if cache line layout or size of the value matters, as its size
1003 optimized for alignment and size should not use bool.
1011 readable alternative if the call-sites have naked true/false constants.
1013 Otherwise limited use of bool in structures and arguments can improve
1016 18) Don't re-invent the kernel macros
1017 -------------------------------------
1020 you should use, rather than explicitly coding some variant of them yourself.
1024 .. code-block:: c
1028 Similarly, if you need to calculate the size of some structure member, use
1030 .. code-block:: c
1032 #define sizeof_field(t, f) (sizeof(((t*)0)->f))
1040 ------------------------------------
1046 .. code-block:: c
1048 -*- mode: c -*-
1052 .. code-block:: c
1056 compile-command: "gcc -DMAGIC_DEBUG_FLAG foo.c"
1062 .. code-block:: c
1068 includes markers for indentation and mode configuration. People may use their
1074 -------------------
1076 In architecture-specific code, you may need to use inline assembly to interface
1078 However, don't use inline assembly gratuitously when C can do the job. You can
1083 that inline assembly can use C parameters.
1085 Large, non-trivial assembly functions should go in .S files, with corresponding
1087 functions should use ``asmlinkage``.
1098 .. code-block:: c
1106 ---------------------------
1108 Wherever possible, don't use preprocessor conditionals (#if, #ifdef) in .c
1110 use such conditionals in a header file defining functions for use in those .c
1111 files, providing no-op stub versions in the #else case, and then call those
1127 Within code, where possible, use the IS_ENABLED macro to convert a Kconfig
1128 symbol into a C boolean expression, and use it in a normal C conditional:
1130 .. code-block:: c
1136 The compiler will constant-fold the conditional away, and include or exclude
1140 references, etc). Thus, you still have to use an #ifdef if the code inside the
1143 At the end of any non-trivial #if or #ifdef block (more than a few lines),
1147 .. code-block:: c
1155 ----------------------
1160 ISBN 0-13-110362-8 (paperback), 0-13-110370-9 (hardback).
1164 Addison-Wesley, Inc., 1999.
1165 ISBN 0-201-61586-X.
1167 GNU manuals - where in compliance with K&R and this text - for cpp, gcc,
1171 language C, URL: http://www.open-std.org/JTC1/SC22/WG14/
1173 Kernel :ref:`process/coding-style.rst <codingstyle>`, by greg@kroah.com at OLS 2002: