hush_test: ignore generated files

[oweals/busybox.git] / docs / style-guide.txt

diff --git a/docs/style-guide.txt b/docs/style-guide.txt
index 04fa5ef97a52c6179c3ecdcd121c7d7dee1eb070..7560d698623357a12b3ead68a05eb00ecfbab8bd 100644 (file)
--- a/docs/style-guide.txt
+++ b/docs/style-guide.txt
@@ -20,13 +20,15 @@ in the directory, just your own.
 Declaration Order
 -----------------
 
 Declaration Order
 -----------------
 

-Here is the order in which code should be laid out in a file:
+Here is the preferred 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)
 
  - 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 and #defines
+ - #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
  - const and global variables
  - function declarations (if necessary)
  - function implementations


@@ -49,13 +51,13 @@ 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.:
 
 \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 */
+       \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
 
 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


@@ -124,13 +126,23 @@ between it and the opening control block statement. Examples:
 
                do {
 
 
                do {
 

+If you have long logic statements that need to be wrapped, then uncuddling
+the bracket to improve readability is allowed. Generally, this style makes
+it easier for reader to notice that 2nd and following lines are still
+inside 'if':
+
+               if (some_really_long_checks && some_other_really_long_checks
+                && some_more_really_long_checks
+                && even_more_of_long_checks
+               ) {
+                       do_foo_now;

 
 Spacing around Parentheses
 ~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 
 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:
+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:
 
 
        Don't do this:
 


@@ -197,6 +209,22 @@ block. Example:
        }
 
 
        }
 
 

+Labels
+~~~~~~
+
+Labels should start at the beginning of the line, not indented to the block
+level (because they do not "belong" to block scope, only to whole function).
+
+       if (foo) {
+               stmt;
+ label:
+               stmt2;
+               stmt;
+       }
+
+(Putting label at position 1 prevents diff -p from confusing label for function
+name, but it's not a policy of busybox project to enforce such a minor detail).
+

 
 
 Variable and Function Names
 
 
 Variable and Function Names


@@ -223,28 +251,55 @@ because it looks like whitespace; using lower-case is easy on the eyes.
 
 Exceptions:
 
 
 Exceptions:
 

- - Enums, macros, and constant variables should all be in upper-case with
-   words optionally seperatedy by underscores (i.e. FIFOTYPE, ISBLKDEV()).
+ - Enums, macros, and constant variables are occasionally written in all
+   upper-case with words optionally seperatedy by underscores (i.e. FIFO_TYPE,
+   ISBLKDEV()).

 
  - Nobody is going to get mad at you for using 'pvar' as the name of a
    variable that is a pointer to 'var'.
 
 
  - Nobody is going to get mad at you for using 'pvar' as the name of a
    variable that is a pointer to 'var'.
 

-Note: 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. Perhaps in the future we will include some magical Perl
-script that can go through and convert variable names, left as an exercise for
-the reader for now.

 
 

-For the time being, if you want to do a search-and-replace of a variable name
-in different files, do the following in the busybox directory:
+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]
 
 
        $ 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
 
 
 Avoid The Preprocessor


@@ -262,22 +317,21 @@ Use 'const <type> var' for declaring constants.
 
        Don't do this:
 
 
        Don't do this:
 

-               #define var 80
+               #define CONST 80

 
        Do this instead, when the variable is in a header file and will be used in
 
        Do this instead, when the variable is in a header file and will be used in

-       several source files: 
-
-               const int var = 80; 
+       several source files:

 
 

-       Or do this when the variable is used only in a single source file:
+               enum { CONST = 80 };

 
 

-               static const int var = 80; 
-
-Declaring variables as '[static] const' gives variables an actual type and
-makes the compiler do type checking for you; the preprocessor does _no_ type
-checking whatsoever, making it much more error prone. Declaring variables with
-'[static] const' also makes debugging programs much easier since the value of
-the variable can be easily queried and displayed.
+Although enum may look ugly to some people, it is better for code size.
+With "const int" compiler may fail to optimize it out and will reserve
+a real storage in rodata for it! (Hopefully, newer gcc will get better
+at it...).  With "define", you have slight risk of polluting namespace
+(#define doesn't allow you to redefine the name in the inner scopes),
+and complex "define" are evaluated each time they uesd, not once
+at declarations like enums. Also, the preprocessor does _no_ type checking
+whatsoever, making it much more error prone.

 
 
 The Folly of Macros
 
 
 The Folly of Macros


@@ -297,24 +351,25 @@ Use 'static inline' instead of a macro.
                }
 
 Static inline functions are greatly preferred over macros. They provide type
                }
 
 Static inline functions are greatly preferred over macros. They provide type

-safety, have no length limitations, no formatting limitations, and under gcc
-they are as cheap as macros. Besides, really long macros with backslashes at
-the end of each line are ugly as sin.
+safety, have no length limitations, no formatting limitations, have an actual
+return value, and under gcc they are as cheap as macros. Besides, really long
+macros with backslashes at the end of each line are ugly as sin.

 
 
 The Folly of #ifdef
 ~~~~~~~~~~~~~~~~~~~
 
 Code cluttered with ifdefs is difficult to read and maintain. Don't do it.
 
 
 The Folly of #ifdef
 ~~~~~~~~~~~~~~~~~~~
 
 Code cluttered with ifdefs is difficult to read and maintain. Don't do it.

-Instead, put your ifdefs in a header, and conditionally define 'static inline'
-functions, (or *maybe* macros), which are used in the code.  
+Instead, put your ifdefs at the top of your .c file (or in a header), and
+conditionally define 'static inline' functions, (or *maybe* macros), which are
+used in the code.

 
        Don't do this:
 
                ret = my_func(bar, baz);
                if (!ret)
                        return -1;
 
        Don't do this:
 
                ret = my_func(bar, baz);
                if (!ret)
                        return -1;

-               #ifdef BB_FEATURE_FUNKY
+               #ifdef CONFIG_FEATURE_FUNKY

                        maybe_do_funky_stuff(bar, baz);
                #endif
 
                        maybe_do_funky_stuff(bar, baz);
                #endif
 


@@ -322,13 +377,13 @@ functions, (or *maybe* macros), which are used in the code.
 
        (in .h header file)
 
 
        (in .h header file)
 

-               #ifdef BB_FEATURE_FUNKY
-               static inline void maybe_do_funky_stuff (int bar, int baz)
+               #if ENABLE_FEATURE_FUNKY
+               static inline void maybe_do_funky_stuff(int bar, int baz)

                {
                        /* lotsa code in here */
                }
                #else
                {
                        /* lotsa code in here */
                }
                #else

-               static inline void maybe_do_funky_stuff (int bar, int baz) {}
+               static inline void maybe_do_funky_stuff(int bar, int baz) {}

                #endif
 
        (in the .c source file)
                #endif
 
        (in the .c source file)


@@ -394,15 +449,16 @@ Unfortunately, the way C handles strings makes them prone to overruns when
 certain library functions are (mis)used. The following table  offers a summary
 of some of the more notorious troublemakers:
 
 certain library functions are (mis)used. The following table  offers a summary
 of some of the more notorious troublemakers:
 

-function     overflows         preferred
-----------------------------------------
-strcpy       dest string       strncpy
-strcat       dest string       strncat
-gets         string it gets    fgets
-getwd        buf string        getcwd
-[v]sprintf   str buffer        [v]snprintf
-realpath     path buffer       use with pathconf
-[vf]scanf    its arguments     just avoid it
+function     overflows                  preferred
+-------------------------------------------------
+strcpy       dest string                safe_strncpy
+strncpy      may fail to 0-terminate dst safe_strncpy
+strcat       dest string                strncat
+gets         string it gets             fgets
+getwd        buf string                 getcwd
+[v]sprintf   str buffer                 [v]snprintf
+realpath     path buffer                use with pathconf
+[vf]scanf    its arguments              just avoid it

 
 
 The above is by no means a complete list. Be careful out there.
 
 
 The above is by no means a complete list. Be careful out there.


@@ -412,11 +468,11 @@ The above is by no means a complete list. Be careful out there.
 Avoid Big Static Buffers
 ------------------------
 
 Avoid Big Static Buffers
 ------------------------
 

-First, some background to put this discussion in context: Static buffers look
+First, some background to put this discussion in context: static buffers look

 like this in code:
 
        /* in a .c file outside any functions */
 like this in code:
 
        /* in a .c file outside any functions */

-       static char *buffer[BUFSIZ]; /* happily used by any function in this file,
+       static char buffer[BUFSIZ]; /* happily used by any function in this file,

                                        but ick! big! */
 
 The problem with these is that any time any busybox app is run, you pay a
                                        but ick! big! */
 
 The problem with these is that any time any busybox app is run, you pay a


@@ -458,10 +514,13 @@ very limited stack space (e.g., uCLinux).
 A macro is declared in busybox.h that implements compile-time selection
 between xmalloc() and stack creation, so you can code the line in question as
 
 A macro is declared in busybox.h that implements compile-time selection
 between xmalloc() and stack creation, so you can code the line in question as
 

-               RESERVE_BB_BUFFER(buffer, BUFSIZ);
+               RESERVE_CONFIG_BUFFER(buffer, BUFSIZ);

 
 and the right thing will happen, based on your configuration.
 
 
 and the right thing will happen, based on your configuration.
 

+Another relatively new trick of similar nature is explained
+in keep_data_small.txt.
+

 
 
 Miscellaneous Coding Guidelines
 
 
 Miscellaneous Coding Guidelines


@@ -478,7 +537,8 @@ When in doubt about the proper behavior of a Busybox program (output,
 formatting, options, etc.), model it after the equivalent GNU program.
 Doesn't matter how that program behaves on some other flavor of *NIX; doesn't
 matter what the POSIX standard says or doesn't say, just model Busybox
 formatting, options, etc.), model it after the equivalent GNU program.
 Doesn't matter how that program behaves on some other flavor of *NIX; doesn't
 matter what the POSIX standard says or doesn't say, just model Busybox

-programs after their GNU counterparts and nobody has to get hurt.
+programs after their GNU counterparts and it will make life easier on (nearly)
+everyone.

 
 The only time we deviate from emulating the GNU behavior is when:
 
 
 The only time we deviate from emulating the GNU behavior is when:
 


@@ -488,7 +548,7 @@ The only time we deviate from emulating the GNU behavior is when:
          would be required, lots more memory would be used, etc.)
        - The difference is minor or cosmetic
 
          would be required, lots more memory would be used, etc.)
        - The difference is minor or cosmetic
 

-A note on the 'cosmetic' case: Output differences might be considered
+A note on the 'cosmetic' case: output differences might be considered

 cosmetic, but if the output is significant enough to break other scripts that
 use the output, it should really be fixed.
 
 cosmetic, but if the output is significant enough to break other scripts that
 use the output, it should really be fixed.
 


@@ -538,7 +598,7 @@ like this:
                if (foo)
                        stmt1;
                        new_line();
                if (foo)
                        stmt1;
                        new_line();

-               stmt2
+               stmt2;

                stmt3;
 
 And the resulting behavior of your program would totally bewilder you. (Don't
                stmt3;
 
 And the resulting behavior of your program would totally bewilder you. (Don't


@@ -580,18 +640,16 @@ begin with a C keyword, but not always.
 
 Furthermore, you should put a single comment (not necessarily one line, just
 one comment) before the block, rather than commenting each and every line.
 
 Furthermore, you should put a single comment (not necessarily one line, just
 one comment) before the block, rather than commenting each and every line.

-There is an optimal ammount of commenting that a program can have; you can
+There is an optimal amount of commenting that a program can have; you can

 comment too much as well as too little.
 
 comment too much as well as too little.
 

-A picture is really worth a thousand words here, so here is an example that
-illustrates emphasizing logical blocks:
+A picture is really worth a thousand words here, the following example
+illustrates how to emphasize logical blocks:

 
 

-       while (line = get_line_from_file(fp)) {
+       while (line = xmalloc_fgets(fp)) {

 
                /* eat the newline, if any */
 
                /* eat the newline, if any */

-               if (line[strlen(line)-1] == '\n') {
-                       line[strlen(line)-1] = '\0';
-               }
+               chomp(line);

 
                /* ignore blank lines */
                if (strlen(file_to_act_on) == 0) {
 
                /* ignore blank lines */
                if (strlen(file_to_act_on) == 0) {


@@ -609,21 +667,48 @@ illustrates emphasizing logical blocks:
        }
 
 
        }
 
 

-Testing Guidelines
-~~~~~~~~~~~~~~~~~~
+Processing Options with getopt
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+If your applet needs to process command-line switches, please use getopt32() to
+do so. Numerous examples can be seen in many of the existing applets, but
+basically it boils down to two things: at the top of the .c file, have this
+line in the midst of your #includes, if you need to parse long options:
+
+       #include <getopt.h>

 
 

-It's considered good form to test your new feature before you submit a patch
-to the mailing list, and especially before you commit a change to CVS. Here
-are some guildlines on testing your changes.
+Then have long options defined:
+
+       static const struct option <applet>_long_options[] = {
+               { "list",    0, NULL, 't' },
+               { "extract", 0, NULL, 'x' },
+               { NULL, 0, NULL, 0 }
+       };
+
+And a code block similar to the following near the top of your applet_main()
+routine:
+
+       char *str_b;
+
+       opt_complementary = "cryptic_string";
+       applet_long_options = <applet>_long_options; /* if you have them */
+       opt = getopt32(argc, argv, "ab:c", &str_b);
+       if (opt & 1) {
+               handle_option_a();
+       }
+       if (opt & 2) {
+               handle_option_b(str_b);
+       }
+       if (opt & 4) {
+               handle_option_c();
+       }

 
 

- - Always test busybox applets against GNU counterparts and make sure the
-   behavior / output is identical between the two.
+If your applet takes no options (such as 'init'), there should be a line
+somewhere in the file reads:

 
 

- - Try several different permutations and combinations of the features you're
-   adding and make sure they all work. (Make sure one feature does not
-   interfere with another, etc.)
+       /* no options, no getopt */

 
 

- - Make sure you test compiling against the source both with the feature
-   turned on and turned off in Config.h and make sure busybox compiles cleanly
-   both ways.
+That way, when people go grepping to see which applets need to be converted to
+use getopt, they won't get false positives.

 
 

+For more info and examples, examine getopt32.c, tar.c, wget.c etc.