busybox源代码

Busybox Style Guide =================== This document describes the coding style conventions used in Busybox. If you add a new file to Busybox or are editing an existing file, please format your code according to this style. If you are the maintainer of a file that does not follow these guidelines, please -- at your own convenience -- modify the file(s) you maintain to bring them into conformance with this style guide. Please note that this is a low priority task. To help you format the whitespace of your programs, an ".indent.pro" file is included in the main Busybox source directory that contains option flags to format code as per this style guide. This way you can run GNU indent on your files by typing 'indent myfile.c myfile.h' and it will magically apply all the right formatting rules to your file. Please _do_not_ run this on all the files in the directory, just your own. Declaration Order ----------------- Here is the order in which code should be laid out in a file: - commented program name and one-line description - commented author name and email address(es) - commented GPL boilerplate - commented longer description / notes for the program (if needed) - #includes of .h files with angle brackets (<>) around them - #includes of .h files with quotes ("") around them - #defines (if any, note the section below titled "Avoid the Preprocessor") - const and global variables - function declarations (if necessary) - function implementations Whitespace and Formatting ------------------------- This is everybody's favorite flame topic so let's get it out of the way right up front. Tabs vs. Spaces in Line Indentation ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The preference in Busybox is to indent lines with tabs. Do not indent lines with spaces and do not indents lines using a mixture of tabs and spaces. (The indentation style in the Apache and Postfix source does this sort of thing: \s\s\s\sif (expr) {\n\tstmt; --ick.) The only exception to this rule is multi-line comments that use an asterisk at the beginning of each line, i.e.: \t/* \t * This is a block comment. \t * Note that it has multiple lines \t * and that the beginning of each line has a tab plus a space \t * except for the opening '/*' line where the slash \t * is used instead of a space. \t */ Furthermore, The preference is that tabs be set to display at four spaces wide, but the beauty of using only tabs (and not spaces) at the beginning of lines is that you can set your editor to display tabs at *whatever* number of spaces is desired and the code will still look fine. Operator Spacing ~~~~~~~~~~~~~~~~ Put spaces between terms and operators. Example: Don't do this: for(i=0;i<num_items;i++){ Do this instead: for (i = 0; i < num_items; i++) { While it extends the line a bit longer, the spaced version is more readable. An allowable exception to this rule is the situation where excluding the spacing makes it more obvious that we are dealing with a single term (even if it is a compound term) such as: if (str[idx] == '/' && str[idx-1] != '\\') or if ((argc-1) - (optind+1) > 0) Bracket Spacing ~~~~~~~~~~~~~~~ If an opening bracket starts a function, it should be on the next line with no spacing before it. However, if a bracket follows an opening control block, it should be on the same line with a single space (not a tab) between it and the opening control block statement. Examples: Don't do this: while (!done) { do { Don't do this either: while (!done){ do{ And for heaven's sake, don't do this: while (!done) { do { Do this instead: while (!done) { do { Exceptions: - if you have long logic statements that need to be wrapped, then uncuddling the bracket to improve readability is allowed: if (some_really_long_checks && some_other_really_long_checks \ && some_more_really_long_checks) { do_foo_now; Spacing around Parentheses ~~~~~~~~~~~~~~~~~~~~~~~~~~ Put a space between C keywords and left parens, but not between function names and the left paren that starts it's parameter list (whether it is being declared or called). Examples: Don't do this: while(foo) { for(i = 0; i < n; i++) { Do this instead: while (foo) { for (i = 0; i < n; i++) { But do functions like this: static int my_func(int foo, char bar) ... baz = my_func(1, 2); Also, don't put a space between the left paren and the first term, nor between the last arg and the right paren. Don't do this: if ( x < 1 ) strcmp( thisstr, thatstr ) Do this instead: if (x < 1) strcmp(thisstr, thatstr) Cuddled Elses ~~~~~~~~~~~~~ Also, please "cuddle" your else statements by putting the else keyword on the same line after the right bracket that closes an 'if' statement. Don't do this: if (foo) { stmt; } else { stmt; } Do this instead: if (foo) { stmt; } else { stmt; } The exception to this rule is if you want to include a comment before the else block. Example: if (foo) { stmts... } /* otherwise, we're just kidding ourselves, so re-frob the input */ else { other_stmts... } Variable and Function Names --------------------------- Use the K&R style with names in all lower-case and underscores occasionally used to separate words (e.g., "variable_name" and "numchars" are both acceptable). Using underscores makes variable and function names more readable because it looks like whitespace; using lower-case is easy on the eyes. Frowned upon: hitList TotalChars szFileName pf_Nfol_TriState Preferred: hit_list total_chars file_name sensible_name Exceptions: - Enums, macros, and constant variables are occasionally written in all upper-case with words optionally seperatedy by underscores (i.e. FIFOTYPE, ISBLKDEV()). - Nobody is going to get mad at you for using 'pvar' as the name of a variable that is a pointer to 'var'. Converting to K&R ~~~~~~~~~~~~~~~~~ The Busybox codebase is very much a mixture of code gathered from a variety of sources. This explains why the current codebase contains such a hodge-podge of different naming styles (Java, Pascal, K&R, just-plain-weird, etc.). The K&R guideline explained above should therefore be used on new files that are added to the repository. Furthermore, the maintainer of an existing file that uses alternate naming conventions should, at his own convenience, convert those names over to K&R style. Converting variable names is a very low priority task. If you want to do a search-and-replace of a single variable name in different files, you can do the following in the busybox directory: $ perl -pi -e 's/\bOldVar\b/new_var/g' *.[ch] If you want to convert all the non-K&R vars in your file all at once, follow these steps: - In the busybox directory type 'examples/mk2knr.pl files-to-convert'. This does not do the actual conversion, rather, it generates a script called 'convertme.pl' that shows what will be converted, giving you a chance to review the changes beforehand. - Review the 'convertme.pl' script that gets generated in the busybox directory and remove / edit any of the substitutions in there. Please especially check for false positives (strings that should not be converted). - Type './convertme.pl same-files-as-before' to perform the actual conversion. - Compile and see if everything still works. Please be aware of changes that have cascading effects into other files. For example, if you're changing the name of something in, say utility.c, you should probably run 'examples/mk2knr.pl utility.c' at first, but when you run the 'convertme.pl' script you should run it on _all_ files like so: './convertme.pl *.[ch]'. Avoid The Preprocessor ---------------------- At best, the preprocessor is a necessary evil, helping us account for platform and architecture differences. Using the preprocessor unnecessarily is just plain evil. The Folly of #define ~~~~~~~~~~~~~~~~~~~~