Linux 内核编码风格

作者: 川山甲
发布时间:2015-07-01 16:30:09

 
 
  像其他大型软件一样,Linux制订了一套编码风格,对代码的格式、风格和布局做出了规定。我写这篇的目的也就是希望大家能够从中借鉴,有利于大家提高编程效率。
 
  像Linux内核这样大型软件中,涉及许许多多的开发者,故它的编码风格也很有参考价值。
 
 
括号 
 
  1、左括号紧跟在语句的最后,与语句在相同的一行。而右括号要另起一行,作为该行的第一个字符。
 
  
 
  2、如果接下来的部分是相同语句的一部分,那么右括号就不单独占一行。
 
      
 
  3、还有
 
  
 
  4、函数采用以下的书写方式:
  
  
 
  5、最后不需要一定使用括号的语句可以忽略它:
 
  
 
 
 
每行代码的长度
 
  要尽可能地保证代码长度不超过80个字符,如果代码行超过80应该折到下一行。
 
  将参数分行输入,在开头简单地加入两个标准tab:
 
  
 
 
命名规范
 
  名称中不允许使用混合的大小写字符。
局部变量如果能够清楚地表明它的用途,那么选取idx甚至是i这样的名称都是可行的。而像theLoopIndex这样冗长反复的名字不在接受之列。——匈牙利命名法(在变量名称中加入变量的类别)危害极大。
 
 
 
 
函数
 
   根据经验函数的代码长度不应该超过两屏,局部变量不应该超过十个
1、一个函数应该功能单一并且实现精准。
2、将一个函数分解成一些更短小的函数的组合不会带来危害。——如果你担心函数调用导致的开销,可以使用inline关键字
 
 
注释
 
  一般情况下,注释的目的是描述你的代码要做什么和为什么要做,而不是具体通过什么方式实现的。怎么实现应该由代码本身展现。
 
  注释不应该包含谁写了那个函数,修改日期和其他那些琐碎而无实际意义的内容。这些信息应该集中在文件最开头地方。
  内核中一条注释看起来如下:
 
  
  
  重要信息常常以“XXX:”开头,而bug通常以“FIXME"开头,就像:
 
  
 
总结
 
  希望这篇博客对大家有所帮助!
 
更详尽的内容,请看"Linux 内核代码规范原文"
 
Linus 内部代码规范原文
  1         Linux kernel coding style    2     3 This is a short document describing the preferred coding style for the    4 linux kernel.  Coding style is very personal, and I won't _force_ my    5 views on anybody, but this is what goes for anything that I have to be    6 able to maintain, and I'd prefer it for most other things too.  Please    7 at least consider the points made here.    8     9 First off, I'd suggest printing out a copy of the GNU coding standards,   10 and NOT read it.  Burn them, it's a great symbolic gesture.   11    12 Anyway, here goes:   13    14    15          Chapter 1: Indentation   16    17 Tabs are 8 characters, and thus indentations are also 8 characters.   18 There are heretic movements that try to make indentations 4 (or even 2!)   19 characters deep, and that is akin to trying to define the value of PI to   20 be 3.   21    22 Rationale: The whole idea behind indentation is to clearly define where   23 a block of control starts and ends.  Especially when you've been looking   24 at your screen for 20 straight hours, you'll find it a lot easier to see   25 how the indentation works if you have large indentations.   26    27 Now, some people will claim that having 8-character indentations makes   28 the code move too far to the right, and makes it hard to read on a   29 80-character terminal screen.  The answer to that is that if you need   30 more than 3 levels of indentation, you're screwed anyway, and should fix   31 your program.   32    33 In short, 8-char indents make things easier to read, and have the added   34 benefit of warning you when you're nesting your functions too deep.   35 Heed that warning.   36    37 The preferred way to ease multiple indentation levels in a switch statement is   38 to align the "switch" and its subordinate "case" labels in the same column   39 instead of "double-indenting" the "case" labels.  E.g.:   40    41     switch (suffix) {   42     case 'G':   43     case 'g':   44         mem <<= 30;   45         break;   46     case 'M':   47     case 'm':   48         mem <<= 20;   49         break;   50     case 'K':   51     case 'k':   52         mem <<= 10;   53         /* fall through */   54     default:   55         break;   56     }   57    58    59 Don't put multiple statements on a single line unless you have   60 something to hide:   61    62     if (condition) do_this;   63       do_something_everytime;   64    65 Don't put multiple assignments on a single line either.  Kernel coding style   66 is super simple.  Avoid tricky expressions.   67    68 Outside of comments, documentation and except in Kconfig, spaces are never   69 used for indentation, and the above example is deliberately broken.   70    71 Get a decent editor and don't leave whitespace at the end of lines.   72    73    74         Chapter 2: Breaking long lines and strings   75    76 Coding style is all about readability and maintainability using commonly   77 available tools.   78    79 The limit on the length of lines is 80 columns and this is a strongly   80 preferred limit.   81    82 Statements longer than 80 columns will be broken into sensible chunks, unless   83 exceeding 80 columns significantly increases readability and does not hide   84 information. Descendants are always substantially shorter than the parent and   85 are placed substantially to the right. The same applies to function headers   86 with a long argument list. However, never break user-visible strings such as   87 printk messages, because that breaks the ability to grep for them.   88    89    90         Chapter 3: Placing Braces and Spaces   91    92 The other issue that always comes up in C styling is the placement of   93 braces.  Unlike the indent size, there are few technical reasons to   94 choose one placement strategy over the other, but the preferred way, as   95 shown to us by the prophets Kernighan and Ritchie, is to put the opening   96 brace last on the line, and put the closing brace first, thusly:   97    98     if (x is true) {   99         we do y  100     }  101   102 This applies to all non-function statement blocks (if, switch, for,  103 while, do).  E.g.:  104   105     switch (action) {  106     case KOBJ_ADD:  107         return "add";  108     case KOBJ_REMOVE:  109         return "remove";  110     case KOBJ_CHANGE:  111         return "change";  112     default:  113         return NULL;  114     }  115   116 However, there is one special case, namely functions: they have the  117 opening brace at the beginning of the next line, thus:  118   119     int function(int x)  120     {  121         body of function  122     }  123   124 Heretic people all over the world have claimed that this inconsistency  125 is ...  well ...  inconsistent, but all right-thinking people know that  126 (a) K&R are _right_ and (b) K&R are right.  Besides, functions are  127 special anyway (you can't nest them in C).  128   129 Note that the closing brace is empty on a line of its own, _except_ in  130 the cases where it is followed by a continuation of the same statement,  131 ie a "while" in a do-statement or an "else" in an if-statement, like  132 this:  133   134     do {  135         body of do-loop  136     } while (condition);  137   138 and  139   140     if (x == y) {  141         ..  142     } else if (x > y) {  143         ...  144     } else {  145         ....  146     }  147   148 Rationale: K&R.  149   150 Also, note that this brace-placement also minimizes the number of empty  151 (or almost empty) lines, without any loss of readability.  Thus, as the  152 supply of new-lines on your screen is not a renewable resource (think  153 25-line terminal screens here), you have more empty lines to put  154 comments on.  155   156 Do not unnecessarily use braces where a single statement will do.  157   158 if (condition)  159     action();  160   161 and  162   163 if (condition)  164     do_this();  165 else  166     do_that();  167   168 This does not apply if only one branch of a conditional statement is a single  169 statement; in the latter case use braces in both branches:  170   171 if (condition) {  172     do_this();  173     do_that();  174 } else {  175     otherwise();  176 }  177   178         3.1:  Spaces  179   180 Linux kernel style for use of spaces depends (mostly) on  181 function-versus-keyword usage.  Use a space after (most) keywords.  The  182 notable exceptions are sizeof, typeof, alignof, and __attribute__, which look  183 somewhat like functions (and are usually used with parentheses in Linux,  184 although they are not required in the language, as in: "sizeof info" after  185 "struct fileinfo info;" is declared).  186   187 So use a space after these keywords:  188     if, switch, case, for, do, while  189 but not with sizeof, typeof, alignof, or __attribute__.  E.g.,  190     s = sizeof(struct file);  191   192 Do not add spaces around (inside) parenthesized expressions.  This example is  193 *bad*:  194   195     s = sizeof( struct file );  196   197 When declaring pointer data or a function that returns a pointer type, the  198 preferred use of '*' is adjacent to the data name or function name and not  199 adjacent to the type name.  Examples:  200   201     char *linux_banner;  202     unsigned long long memparse(char *ptr, char **retptr);  203     char *match_strdup(substring_t *s);  204   205 Use one space around (on each side of) most binary and ternary operators,  206 such as any of these:  207   208     =  +  -  <  >  *  /  %  |  &  ^  <=  >=  ==  !=  ?  :  209   210 but no space after unary operators:  211     &  *  +  -  ~  !  sizeof  typeof  alignof  __attribute__  defined  212   213 no space before the postfix increment & decrement unary operators:  214     ++  --  215   216 no space after the prefix increment & decrement unary operators:  217     ++  --  218   219 and no space around the '.' and "->" structure member operators.  220   221 Do not leave trailing whitespace at the ends of lines.  Some editors with  222 "smart" indentation will insert whitespace at the beginning of new lines as  223 appropriate, so you can start typing the next line of code right away.  224 However, some such editors do not remove the whitespace if you end up not  225 putting a line of code there, such as if you leave a blank line.  As a result,  226 you end up with lines containing trailing whitespace.  227   228 Git will warn you about patches that introduce trailing whitespace, and can  229 optionally strip the trailing whitespace for you; however, if applying a series  230 of patches, this may make later patches in the series fail by changing their  231 context lines.  232   233   234         Chapter 4: Naming  235   236 C is a Spartan language, and so should your naming be.  Unlike Modula-2  237 and Pascal programmers, C programmers do not use cute names like  238 ThisVariableIsATemporaryCounter.  A C programmer would call that  239 variable "tmp", which is much easier to write, and not the least more  240 difficult to understand.  241   242 HOWEVER, while mixed-case names are frowned upon, descriptive names for  243 global variables are a must.  To call a global function "foo" is a  244 shooting offense.  245   246 GLOBAL variables (to be used only if you _really_ need them) need to  247 have descriptive names, as do global functions.  If you have a function  248 that counts the number of active users, you should call that  249 "count_active_users()" or similar, you should _not_ call it "cntusr()".  250   251 Encoding the type of a function into the name (so-called Hungarian  252 notation) is brain damaged - the compiler knows the types anyway and can  253 check those, and it only confuses the programmer.  No wonder MicroSoft  254 makes buggy programs.  255   256 LOCAL variable names should be short, and to the point.  If you have  257 some random integer loop counter, it should probably be called "i".  258 Calling it "loop_counter" is non-productive, if there is no chance of it  259 being mis-understood.  Similarly, "tmp" can be just about any type of  260 variable that is used to hold a temporary value.  261   262 If you are afraid to mix up your local variable names, you have another  263 problem, which is called the function-growth-hormone-imbalance syndrome.  264 See chapter 6 (Functions).  265   266   267         Chapter 5: Typedefs  268   269 Please don't use things like "vps_t".  270   271 It's a _mistake_ to use typedef for structures and pointers. When you see a  272   273     vps_t a;  274   275 in the source, what does it mean?  276   277 In contrast, if it says  278   279     struct virtual_container *a;  280   281 you can actually tell what "a" is.  282   283 Lots of people think that typedefs "help readability". Not so. They are  284 useful only for:  285   286  (a) totally opaque objects (where the typedef is actively used to _hide_  287      what the object is).  288   289      Example: "pte_t" etc. opaque objects that you can only access using  290      the proper accessor functions.  291   292      NOTE! Opaqueness and "accessor functions" are not good in themselves.  293      The reason we have them for things like pte_t etc. is that there  294      really is absolutely _zero_ portably accessible information there.  295   296  (b) Clear integer types, where the abstraction _helps_ avoid confusion  297      whether it is "int" or "long".  298   299      u8/u16/u32 are perfectly fine typedefs, although they fit into  300      category (d) better than here.  301   302      NOTE! Again - there needs to be a _reason_ for this. If something is  303      "unsigned long", then there's no reason to do  304   305     typedef unsigned long myflags_t;  306   307      but if there is a clear reason for why it under certain circumstances  308      might be an "unsigned int" and under other configurations might be  309      "unsigned long", then by all means go ahead and use a typedef.  310   311  (c) when you use sparse to literally create a _new_ type for  312      type-checking.  313   314  (d) New types which are identical to standard C99 types, in certain  315      exceptional circumstances.  316   317      Although it would only take a short amount of time for the eyes and  318      brain to become accustomed to the standard types like 'uint32_t',  319      some people object to their use anyway.  320   321      Therefore, the Linux-specific 'u8/u16/u32/u64' types and their  322      signed equivalents which are identical to standard types are  323      permitted -- although they are not mandatory in new code of your  324      own.  325   326      When editing existing code which already uses one or the other set  327      of types, you should conform to the existing choices in that code.  328   329  (e) Types safe for use in userspace.  330   331      In certain structures which are visible to userspace, we cannot  332      require C99 types and cannot use the 'u32' form above. Thus, we  333      use __u32 and similar types in all structures which are shared  334      with userspace.  335   336 Maybe there are other cases too, but the rule should basically be to NEVER  337 EVER use a typedef unless you can clearly match one of those rules.  338   339 In general, a pointer, or a struct that has elements that can reasonably  340 be directly accessed should _never_ be a typedef.  341   342   343         Chapter 6: Functions  344   345 Functions should be short and sweet, and do just one thing.  They should  346 fit on one or two screenfuls of text (the ISO/ANSI screen size is 80x24,  347 as we all know), and do one thing and do that well.  348   349 The maximum length of a function is inversely proportional to the  350 complexity and indentation level of that function.  So, if you have a  351 conceptually simple function that is just one long (but simple)  352 case-statement, where you have to do lots of small things for a lot of  353 different cases, it's OK to have a longer function.  354   355 However, if you have a complex function, and you suspect that a  356 less-than-gifted first-year high-school student might not even  357 understand what the function is all about, you should adhere to the  358 maximum limits all the more closely.  Use helper functions with  359 descriptive names (you can ask the compiler to in-line them if you think  360 it's performance-critical, and it will probably do a better job of it  361 than you would have done).  362   363 Another measure of the function is the number of local variables.  They  364 shouldn't exceed 5-10, or you're doing something wrong.  Re-think the  365 function, and split it into smaller pieces.  A human brain can  366 generally easily keep track of about 7 different things, anything more  367 and it gets confused.  You know you're brilliant, but maybe you'd like  368 to understand what you did 2 weeks from now.  369   370 In source files, separate functions with one blank line.  If the function is  371 exported, the EXPORT* macro for it should follow immediately after the closing  372 function brace line.  E.g.:  373   374 int system_is_up(void)  375 {  376     return system_state == SYSTEM_RUNNING;  377 }  378 EXPORT_SYMBOL(system_is_up);  379   380 In function prototypes, include parameter names with their data types.  381 Although this is not required by the C language, it is preferred in Linux  382 because it is a simple way to add valuable information for the reader.  383   384   385         Chapter 7: Centralized exiting of functions  386   387 Albeit deprecated by some people, the equivalent of the goto statement is  388 used frequently by compilers in form of the unconditional jump instruction.  389   390 The goto statement comes in handy when a function exits from multiple  391 locations and some common work such as cleanup has to be done.  392   393 The rationale is:  394   395 - unconditional statements are easier to understand and follow  396 - nesting is reduced  397 - errors by not updating individual exit points when making  398     modifications are prevented  399 - saves the compiler work to optimize redundant code away ;)  400   401 int fun(int a)  402 {  403     int result = 0;  404     char *buffer = kmalloc(SIZE);  405   406     if (buffer == NULL)  407         return -ENOMEM;  408   409     if (condition1) {  410         while (loop1) {  411             ...  412         }  413         result = 1;  414         goto out;  415     }  416     ...  417 out:  418     kfree(buffer);  419     return result;  420 }  421   422         Chapter 8: Commenting  423   424 Comments are good, but there is also a danger of over-commenting.  NEVER  425 try to explain HOW your code works in a comment: it's much better to  426 write the code so that the _working_ is obvious, and it's a waste of  427 time to explain badly written code.  428   429 Generally, you want your comments to tell WHAT your code does, not HOW.  430 Also, try to avoid putting comments inside a function body: if the  431 function is so complex that you need to separately comment parts of it,  432 you should probably go back to chapter 6 for a while.  You can make  433 small comments to note or warn about something particularly clever (or  434 ugly), but try to avoid excess.  Instead, put the comments at the head  435 of the function, telling people what it does, and possibly WHY it does  436 it.  437   438 When commenting the kernel API functions, please use the kernel-doc format.  439 See the files Documentation/kernel-doc-nano-HOWTO.txt and scripts/kernel-doc  440 for details.  441   442 Linux style for comments is the C89 "/* ... */" style.  443 Don't use C99-style "// ..." comments.  444   445 The preferred style for long (multi-line) comments is:  446   447     /*  448      * This is the preferred style for multi-line  449      * comments in the Linux kernel source code.  450      * Please use it consistently.  451      *  452      * Description:  A column of asterisks on the left side,  453      * with beginning and ending almost-blank lines.  454      */  455   456 For files in net/ and drivers/net/ the preferred style for long (multi-line)  457 comments is a little different.  458   459     /* The preferred comment style for files in net/ and drivers/net  460      * looks like this.  461      *  462      * It is nearly the same as the generally preferred comment style,  463      * but there is no initial almost-blank line.  464      */  465   466 It's also important to comment data, whether they are basic types or derived  467 types.  To this end, use just one data declaration per line (no commas for  468 multiple data declarations).  This leaves you room for a small comment on each  469 item, explaining its use.  470   471   472         Chapter 9: You've made a mess of it  473   474 That's OK, we all do.  You've probably been told by your long-time Unix  475 user helper that "GNU emacs" automatically formats the C sources for  476 you, and you've noticed that yes, it does do that, but the defaults it  477 uses are less than desirable (in fact, they are worse than random  478 typing - an infinite number of monkeys typing into GNU emacs would never  479 make a good program).  480   481 So, you can either get rid of GNU emacs, or change it to use saner  482 values.  To do the latter, you can stick the following in your .emacs file:  483   484 (defun c-lineup-arglist-tabs-only (ignored)  485   "Line up argument lists by tabs, not spaces"  486   (let* ((anchor (c-langelem-pos c-syntactic-element))  487      (column (c-langelem-2nd-pos c-syntactic-element))  488      (offset (- (1+ column) anchor))  489      (steps (floor offset c-basic-offset)))  490     (* (max steps 1)  491        c-basic-offset)))  492   493 (add-hook 'c-mode-common-hook  494           (lambda ()  495             ;; Add kernel style  496             (c-add-style  497              "linux-tabs-only"  498              '("linux" (c-offsets-alist  499                         (arglist-cont-nonempty  500                          c-lineup-gcc-asm-reg  501                          c-lineup-arglist-tabs-only))))))  502   503 (add-hook 'c-mode-hook  504           (lambda ()  505             (let ((filename (buffer-file-name)))  506               ;; Enable kernel mode for the appropriate files  507               (when (and filename  508                          (string-match (expand-file-name "~/src/linux-trees")  509                                        filename))  510                 (setq indent-tabs-mode t)  511                 (c-set-style "linux-tabs-only")))))  512   513 This will make emacs go better with the kernel coding style for C  514 files below ~/src/linux-trees.  515   516 But even if you fail in getting emacs to do sane formatting, not  517 everything is lost: use "indent".  518   519 Now, again, GNU indent has the same brain-dead settings that GNU emacs  520 has, which is why you need to give it a few command line options.  521 However, that's not too bad, because even the makers of GNU indent  522 recognize the authority of K&R (the GNU people aren't evil, they are  523 just severely misguided in this matter), so you just give indent the  524 options "-kr -i8" (stands for "K&R, 8 character indents"), or use  525 "scripts/Lindent", which indents in the latest style.  526   527 "indent" has a lot of options, and especially when it comes to comment  528 re-formatting you may want to take a look at the man page.  But  529 remember: "indent" is not a fix for bad programming.  530   531   532         Chapter 10: Kconfig configuration files  533   534 For all of the Kconfig* configuration files throughout the source tree,  535 the indentation is somewhat different.  Lines under a "config" definition  536 are indented with one tab, while help text is indented an additional two  537 spaces.  Example:  538   539 config AUDIT  540     bool "Auditing support"  541     depends on NET  542     help  543       Enable auditing infrastructure that can be used with another  544       kernel subsystem, such as SELinux (which requires this for  545       logging of avc messages output).  Does not do system-call  546       auditing without CONFIG_AUDITSYSCALL.  547   548 Features that might still be considered unstable should be defined as  549 dependent on "EXPERIMENTAL":  550   551 config SLUB  552     depends on EXPERIMENTAL && !ARCH_USES_SLAB_PAGE_STRUCT  553     bool "SLUB (Unqueued Allocator)"  554     ...  555   556 while seriously dangerous features (such as write support for certain  557 filesystems) should advertise this prominently in their prompt string:  558   559 config ADFS_FS_RW  560     bool "ADFS write support (DANGEROUS)"  561     depends on ADFS_FS  562     ...  563   564 For full documentation on the configuration files, see the file  565 Documentation/kbuild/kconfig-language.txt.  566   567   568         Chapter 11: Data structures  569   570 Data structures that have visibility outside the single-threaded  571 environment they are created and destroyed in should always have  572 reference counts.  In the kernel, garbage collection doesn't exist (and  573 outside the kernel garbage collection is slow and inefficient), which  574 means that you absolutely _have_ to reference count all your uses.  575   576 Reference counting means that you can avoid locking, and allows multiple  577 users to have access to the data structure in parallel - and not having  578 to worry about the structure suddenly going away from under them just  579 because they slept or did something else for a while.  580   581 Note that locking is _not_ a replacement for reference counting.  582 Locking is used to keep data structures coherent, while reference  583 counting is a memory management technique.  Usually both are needed, and  584 they are not to be confused with each other.  585   586 Many data structures can indeed have two levels of reference counting,  587 when there are users of different "classes".  The subclass count counts  588 the number of subclass users, and decrements the global count just once  589 when the subclass count goes to zero.  590   591 Examples of this kind of "multi-level-reference-counting" can be found in  592 memory management ("struct mm_struct": mm_users and mm_count), and in  593 filesystem code ("struct super_block": s_count and s_active).  594   595 Remember: if another thread can find your data structure, and you don't  596 have a reference count on it, you almost certainly have a bug.  597   598   599         Chapter 12: Macros, Enums and RTL  600   601 Names of macros defining constants and labels in enums are capitalized.  602   603 #define CONSTANT 0x12345  604   605 Enums are preferred when defining several related constants.  606   607 CAPITALIZED macro names are appreciated but macros resembling functions  608 may be named in lower case.  609   610 Generally, inline functions are preferable to macros resembling functions.  611   612 Macros with multiple statements should be enclosed in a do - while block:  613   614 #define macrofun(a, b, c)             \  615     do {                    \  616         if (a == 5)            \  617             do_this(b, c);        \  618     } while (0)  619   620 Things to avoid when using macros:  621   622 1) macros that affect control flow:  623   624 #define FOO(x)                    \  625     do {                    \  626         if (blah(x) < 0)        \  627             return -EBUGGERED;    \  628     } while(0)  629   630 is a _very_ bad idea.  It looks like a function call but exits the "calling"  631 function; don't break the internal parsers of those who will read the code.  632   633 2) macros that depend on having a local variable with a magic name:  634   635 #define FOO(val) bar(index, val)  636   637 might look like a good thing, but it's confusing as hell when one reads the  638 code and it's prone to breakage from seemingly innocent changes.  639   640 3) macros with arguments that are used as l-values: FOO(x) = y; will  641 bite you if somebody e.g. turns FOO into an inline function.  642   643 4) forgetting about precedence: macros defining constants using expressions  644 must enclose the expression in parentheses. Beware of similar issues with  645 macros using parameters.  646   647 #define CONSTANT 0x4000  648 #define CONSTEXP (CONSTANT | 3)  649   650 The cpp manual deals with macros exhaustively. The gcc internals manual also  651 covers RTL which is used frequently with assembly language in the kernel.  652   653   654         Chapter 13: Printing kernel messages  655   656 Kernel developers like to be seen as literate. Do mind the spelling  657 of kernel messages to make a good impression. Do not use crippled  658 words like "dont"; use "do not" or "don't" instead.  Make the messages  659 concise, clear, and unambiguous.  660   661 Kernel messages do not have to be terminated with a period.  662   663 Printing numbers in parentheses (%d) adds no value and should be avoided.  664   665 There are a number of driver model diagnostic macros in <linux/device.h>  666 which you should use to make sure messages are matched to the right device  667 and driver, and are tagged with the right level:  dev_err(), dev_warn(),  668 dev_info(), and so forth.  For messages that aren't associated with a  669 particular device, <linux/printk.h> defines pr_debug() and pr_info().  670   671 Coming up with good debugging messages can be quite a challenge; and once  672 you have them, they can be a huge help for remote troubleshooting.  Such  673 messages should be compiled out when the DEBUG symbol is not defined (that  674 is, by default they are not included).  When you use dev_dbg() or pr_debug(),  675 that's automatic.  Many subsystems have Kconfig options to turn on -DDEBUG.  676 A related convention uses VERBOSE_DEBUG to add dev_vdbg() messages to the  677 ones already enabled by DEBUG.  678   679   680         Chapter 14: Allocating memory  681   682 The kernel provides the following general purpose memory allocators:  683 kmalloc(), kzalloc(), kmalloc_array(), kcalloc(), vmalloc(), and  684 vzalloc().  Please refer to the API documentation for further information  685 about them.  686   687 The preferred form for passing a size of a struct is the following:  688   689     p = kmalloc(sizeof(*p), ...);  690   691 The alternative form where struct name is spelled out hurts readability and  692 introduces an opportunity for a bug when the pointer variable type is changed  693 but the corresponding sizeof that is passed to a memory allocator is not.  694   695 Casting the return value which is a void pointer is redundant. The conversion  696 from void pointer to any other pointer type is guaranteed by the C programming  697 language.  698   699 The preferred form for allocating an array is the following:  700   701     p = kmalloc_array(n, sizeof(...), ...);  702   703 The preferred form for allocating a zeroed array is the following:  704   705     p = kcalloc(n, sizeof(...), ...);  706   707 Both forms check for overflow on the allocation size n * sizeof(...),  708 and return NULL if that occurred.  709   710   711         Chapter 15: The inline disease  712   713 There appears to be a common misperception that gcc has a magic "make me  714 faster" speedup option called "inline". While the use of inlines can be  715 appropriate (for example as a means of replacing macros, see Chapter 12), it  716 very often is not. Abundant use of the inline keyword leads to a much bigger  717 kernel, which in turn slows the system as a whole down, due to a bigger  718 icache footprint for the CPU and simply because there is less memory  719 available for the pagecache. Just think about it; a pagecache miss causes a  720 disk seek, which easily takes 5 milliseconds. There are a LOT of cpu cycles  721 that can go into these 5 milliseconds.  722   723 A reasonable rule of thumb is to not put inline at functions that have more  724 than 3 lines of code in them
                    

标签: Linux 编码
来源:http://www.cnblogs.com/baochuan/archive/2013/04/08/3006615.h

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