Contents of /tags/mkinitrd-6_3_4/busybox/docs/new-applet-HOWTO.txt
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Thu Dec 16 01:27:43 2010 UTC (13 years, 9 months ago) by niro
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tagged 'mkinitrd-6_3_4'
1 | How to Add a New Applet to BusyBox |
2 | ================================== |
3 | |
4 | This document details the steps you must take to add a new applet to BusyBox. |
5 | |
6 | Credits: |
7 | Matt Kraai - initial writeup |
8 | Mark Whitley - the remix |
9 | Thomas Lundquist - Trying to keep it updated. |
10 | |
11 | When doing this you should consider using the latest svn trunk. |
12 | This is a good thing if you plan to getting it committed into mainline. |
13 | |
14 | Initial Write |
15 | ------------- |
16 | |
17 | First, write your applet. Be sure to include copyright information at the top, |
18 | such as who you stole the code from and so forth. Also include the mini-GPL |
19 | boilerplate. Be sure to name the main function <applet>_main instead of main. |
20 | And be sure to put it in <applet>.c. Usage does not have to be taken care of by |
21 | your applet. |
22 | Make sure to #include "libbb.h" as the first include file in your applet so |
23 | the bb_config.h and appropriate platform specific files are included properly. |
24 | |
25 | For a new applet mu, here is the code that would go in mu.c: |
26 | |
27 | (busybox.h already includes most usual header files. You do not need |
28 | #include <stdio.h> etc...) |
29 | |
30 | |
31 | ----begin example code------ |
32 | |
33 | /* vi: set sw=4 ts=4: */ |
34 | /* |
35 | * Mini mu implementation for busybox |
36 | * |
37 | * Copyright (C) [YEAR] by [YOUR NAME] <YOUR EMAIL> |
38 | * |
39 | * Licensed under GPLv2 or later, see file LICENSE in this tarball for details. |
40 | */ |
41 | |
42 | #include "libbb.h" |
43 | #include "other.h" |
44 | |
45 | int mu_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE; |
46 | int mu_main(int argc, char **argv) |
47 | { |
48 | int fd; |
49 | ssize_t n; |
50 | char mu; |
51 | |
52 | fd = xopen("/dev/random", O_RDONLY); |
53 | |
54 | if ((n = safe_read(fd, &mu, 1)) < 1) |
55 | bb_perror_msg_and_die("/dev/random"); |
56 | |
57 | return mu; |
58 | } |
59 | |
60 | ----end example code------ |
61 | |
62 | |
63 | Coding Style |
64 | ------------ |
65 | |
66 | Before you submit your applet for inclusion in BusyBox, (or better yet, before |
67 | you _write_ your applet) please read through the style guide in the docs |
68 | directory and make your program compliant. |
69 | |
70 | |
71 | Some Words on libbb |
72 | ------------------- |
73 | |
74 | As you are writing your applet, please be aware of the body of pre-existing |
75 | useful functions in libbb. Use these instead of reinventing the wheel. |
76 | |
77 | Additionally, if you have any useful, general-purpose functions in your |
78 | applet that could be useful in other applets, consider putting them in libbb. |
79 | |
80 | And it may be possible that some of the other applets uses functions you |
81 | could use. If so, you have to rip the function out of the applet and make |
82 | a libbb function out of it. |
83 | |
84 | Adding a libbb function: |
85 | ------------------------ |
86 | |
87 | Make a new file named <function_name>.c |
88 | |
89 | ----start example code------ |
90 | |
91 | #include "libbb.h" |
92 | #include "other.h" |
93 | |
94 | int function(char *a) |
95 | { |
96 | return *a; |
97 | } |
98 | |
99 | ----end example code------ |
100 | |
101 | Add <function_name>.o in the right alphabetically sorted place |
102 | in libbb/Kbuild. You should look at the conditional part of |
103 | libbb/Kbuild aswell. |
104 | |
105 | You should also try to find a suitable place in include/libbb.h for |
106 | the function declaration. If not, add it somewhere anyway, with or without |
107 | ifdefs to include or not. |
108 | |
109 | You can look at libbb/Config.in and try to find out if the function is |
110 | tunable and add it there if it is. |
111 | |
112 | |
113 | Placement / Directory |
114 | --------------------- |
115 | |
116 | Find the appropriate directory for your new applet. |
117 | |
118 | Make sure you find the appropriate places in the files, the applets are |
119 | sorted alphabetically. |
120 | |
121 | Add the applet to Kbuild in the chosen directory: |
122 | |
123 | lib-$(CONFIG_MU) += mu.o |
124 | |
125 | Add the applet to Config.in in the chosen directory: |
126 | |
127 | config MU |
128 | bool "MU" |
129 | default n |
130 | help |
131 | Returns an indeterminate value. |
132 | |
133 | |
134 | Usage String(s) |
135 | --------------- |
136 | |
137 | Next, add usage information for you applet to include/usage.h. |
138 | This should look like the following: |
139 | |
140 | #define mu_trivial_usage \ |
141 | "-[abcde] FILES" |
142 | #define mu_full_usage \ |
143 | "Returns an indeterminate value.\n\n" \ |
144 | "Options:\n" \ |
145 | "\t-a\t\tfirst function\n" \ |
146 | "\t-b\t\tsecond function\n" \ |
147 | ... |
148 | |
149 | If your program supports flags, the flags should be mentioned on the first |
150 | line (-[abcde]) and a detailed description of each flag should go in the |
151 | mu_full_usage section, one flag per line. (Numerous examples of this |
152 | currently exist in usage.h.) |
153 | |
154 | |
155 | Header Files |
156 | ------------ |
157 | |
158 | Next, add an entry to include/applets.h. Be *sure* to keep the list |
159 | in alphabetical order, or else it will break the binary-search lookup |
160 | algorithm in busybox.c and the Gods of BusyBox smite you. Yea, verily: |
161 | |
162 | Be sure to read the top of applets.h before adding your applet. |
163 | |
164 | /* all programs above here are alphabetically "less than" 'mu' */ |
165 | IF_MU(APPLET(mu, _BB_DIR_USR_BIN, _BB_SUID_DROP)) |
166 | /* all programs below here are alphabetically "greater than" 'mu' */ |
167 | |
168 | |
169 | The Grand Announcement |
170 | ---------------------- |
171 | |
172 | Then create a diff by adding the new files with svn (remember your libbb files) |
173 | svn add <where you put it>/mu.c |
174 | eventually also: |
175 | svn add libbb/function.c |
176 | then |
177 | svn diff |
178 | and send it to the mailing list: |
179 | busybox@busybox.net |
180 | http://busybox.net/mailman/listinfo/busybox |
181 | |
182 | Sending patches as attachments is preferred, but not required. |