| How to Add a New Applet to BusyBox |
| ================================== |
| |
| This document details the steps you must take to add a new applet to BusyBox. |
| |
| Credits: |
| Matt Kraai - initial writeup |
| Mark Whitley - the remix |
| Thomas Lundquist - trying to keep it updated |
| |
| When doing this you should consider using the latest git HEAD. |
| This is a good thing if you plan to getting it committed into mainline. |
| |
| Initial Write |
| ------------- |
| |
| First, write your applet. Be sure to include copyright information at the top, |
| such as who you stole the code from and so forth. Also include the mini-GPL |
| boilerplate and Config.in/Kbuild/usage/applet.h snippets (more on that below |
| in this document). Be sure to name the main function <applet>_main instead |
| of main. And be sure to put it in <applet>.c. Make sure to #include "libbb.h" |
| as the first include file in your applet. |
| |
| For a new applet mu, here is the code that would go in mu.c: |
| |
| (libbb.h already includes most usual header files. You do not need |
| #include <stdio.h> etc...) |
| |
| |
| ----begin example code------ |
| |
| /* vi: set sw=4 ts=4: */ |
| /* |
| * Mini mu implementation for busybox |
| * |
| * Copyright (C) [YEAR] by [YOUR NAME] <YOUR EMAIL> |
| * |
| * Licensed under GPLv2, see file LICENSE in this source tree. |
| */ |
| |
| #include "libbb.h" |
| #include "other.h" |
| |
| //config:config MU |
| //config: bool "MU" |
| //config: default y |
| //config: help |
| //config: Returns an indeterminate value. |
| |
| //kbuild:lib-$(CONFIG_MU) += mu.o |
| //applet:IF_MU(APPLET(mu, BB_DIR_USR_BIN, BB_SUID_DROP)) |
| |
| //usage:#define mu_trivial_usage |
| //usage: "[-abcde] FILE..." |
| //usage:#define mu_full_usage |
| //usage: "Returns an indeterminate value\n" |
| //usage: "\n -a First function" |
| //usage: "\n -b Second function" |
| |
| int mu_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE; |
| int mu_main(int argc, char **argv) |
| { |
| int fd; |
| ssize_t n; |
| char mu; |
| |
| fd = xopen("/dev/random", O_RDONLY); |
| |
| if ((n = safe_read(fd, &mu, 1)) < 1) |
| bb_perror_msg_and_die("/dev/random"); |
| |
| return mu; |
| } |
| |
| ----end example code------ |
| |
| |
| Coding Style |
| ------------ |
| |
| Before you submit your applet for inclusion in BusyBox, (or better yet, before |
| you _write_ your applet) please read through the style guide in the docs |
| directory and make your program compliant. |
| |
| |
| Some Words on libbb |
| ------------------- |
| |
| As you are writing your applet, please be aware of the body of pre-existing |
| useful functions in libbb. Use these instead of reinventing the wheel. |
| |
| Additionally, if you have any useful, general-purpose functions in your |
| applet that could be useful in other applets, consider putting them in libbb. |
| |
| And it may be possible that some of the other applets uses functions you |
| could use. If so, you have to rip the function out of the applet and make |
| a libbb function out of it. |
| |
| Adding a libbb function: |
| ------------------------ |
| |
| Make a new file named <function_name>.c |
| |
| ----start example code------ |
| |
| #include "libbb.h" |
| #include "other.h" |
| |
| //kbuild:lib-y += function.o |
| |
| int function(char *a) |
| { |
| return *a; |
| } |
| |
| ----end example code------ |
| |
| Remember about the kbuild snippet. |
| |
| You should also try to find a suitable place in include/libbb.h for |
| the function declaration. If not, add it somewhere anyway, with or without |
| ifdefs to include or not. |
| |
| You can look at libbb/Config.src and try to find out if the function is |
| tunable and add it there if it is. |
| |
| |
| Kbuild/Config.in/usage/applets.h snippets in .c files |
| ----------------------------------------------------- |
| |
| The old way of adding new applets was to put all the information needed by the |
| configuration and build system into appropriate files (namely: Kbuild.src and |
| Config.src in new applet's directory) and to add the applet declaration and |
| usage info text to include/applets.src.h and include/usage.src.h respectively. |
| |
| Since the scripts/gen_build_files.sh script had been introduced, the preferred |
| way is to have all these declarations contained within the applet .c files. |
| |
| Every line intended to be processed by gen_build_files.sh should start as a |
| comment without any preceding whitespaces and be followed by an appropriate |
| keyword - kbuild, config, usage or applet - and a colon, just like shown in the |
| first example above. |
| |
| |
| Placement / Directory |
| --------------------- |
| |
| Find the appropriate directory for your new applet. |
| |
| Add the kbuild snippet to the .c file: |
| |
| //kbuild:lib-$(CONFIG_MU) += mu.o |
| |
| Add the config snippet to the .c file: |
| |
| //config:config MU |
| //config: bool "MU" |
| //config: default y |
| //config: help |
| //config: Returns an indeterminate value. |
| |
| |
| Usage String(s) |
| --------------- |
| |
| Next, add usage information for your applet to the .c file. |
| This should look like the following: |
| |
| //usage:#define mu_trivial_usage |
| //usage: "[-abcde] FILE..." |
| //usage:#define mu_full_usage |
| //usage: "Returns an indeterminate value\n" |
| //usage: "\n -a First function" |
| //usage: "\n -b Second function" |
| //usage: ... |
| |
| If your program supports flags, the flags should be mentioned on the first |
| line ([-abcde]) and a detailed description of each flag should go in the |
| mu_full_usage section, one flag per line. |
| |
| |
| Header Files |
| ------------ |
| |
| Finally add the applet declaration snippet. Be sure to read the top of |
| applets.src.h before adding your applet - it contains important info |
| on applet macros and conventions. |
| |
| //applet:IF_MU(APPLET(mu, BB_DIR_USR_BIN, BB_SUID_DROP)) |
| |
| |
| The Grand Announcement |
| ---------------------- |
| |
| Then create a diff by adding the new files to git (remember your libbb files) |
| git add <where you put it>/mu.c |
| eventually also: |
| git add libbb/function.c |
| then |
| git commit |
| git format-patch HEAD^ |
| and send it to the mailing list: |
| busybox@busybox.net |
| http://busybox.net/mailman/listinfo/busybox |
| |
| Sending patches as attachments is preferred, but not required. |