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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 git HEAD. |
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 and Config.in/Kbuild/usage/applet.h snippets (more on that below |
20 | in this document). Be sure to name the main function <applet>_main instead |
21 | of main. And be sure to put it in <applet>.c. Make sure to #include "libbb.h" |
22 | as the first include file in your applet. |
23 | |
24 | For a new applet mu, here is the code that would go in mu.c: |
25 | |
26 | (libbb.h already includes most usual header files. You do not need |
27 | #include <stdio.h> etc...) |
28 | |
29 | |
30 | ----begin example code------ |
31 | |
32 | /* vi: set sw=4 ts=4: */ |
33 | /* |
34 | * Mini mu implementation for busybox |
35 | * |
36 | * Copyright (C) [YEAR] by [YOUR NAME] <YOUR EMAIL> |
37 | * |
38 | * Licensed under GPLv2, see file LICENSE in this source tree. |
39 | */ |
40 | |
41 | #include "libbb.h" |
42 | #include "other.h" |
43 | |
44 | //config:config MU |
45 | //config: bool "MU" |
46 | //config: default y |
47 | //config: help |
48 | //config: Returns an indeterminate value. |
49 | |
50 | //kbuild:lib-$(CONFIG_MU) += mu.o |
51 | //applet:IF_MU(APPLET(mu, BB_DIR_USR_BIN, BB_SUID_DROP)) |
52 | |
53 | //usage:#define mu_trivial_usage |
54 | //usage: "[-abcde] FILE..." |
55 | //usage:#define mu_full_usage |
56 | //usage: "Returns an indeterminate value\n" |
57 | //usage: "\n -a First function" |
58 | //usage: "\n -b Second function" |
59 | |
60 | int mu_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE; |
61 | int mu_main(int argc, char **argv) |
62 | { |
63 | int fd; |
64 | ssize_t n; |
65 | char mu; |
66 | |
67 | fd = xopen("/dev/random", O_RDONLY); |
68 | |
69 | if ((n = safe_read(fd, &mu, 1)) < 1) |
70 | bb_perror_msg_and_die("/dev/random"); |
71 | |
72 | return mu; |
73 | } |
74 | |
75 | ----end example code------ |
76 | |
77 | |
78 | Coding Style |
79 | ------------ |
80 | |
81 | Before you submit your applet for inclusion in BusyBox, (or better yet, before |
82 | you _write_ your applet) please read through the style guide in the docs |
83 | directory and make your program compliant. |
84 | |
85 | |
86 | Some Words on libbb |
87 | ------------------- |
88 | |
89 | As you are writing your applet, please be aware of the body of pre-existing |
90 | useful functions in libbb. Use these instead of reinventing the wheel. |
91 | |
92 | Additionally, if you have any useful, general-purpose functions in your |
93 | applet that could be useful in other applets, consider putting them in libbb. |
94 | |
95 | And it may be possible that some of the other applets uses functions you |
96 | could use. If so, you have to rip the function out of the applet and make |
97 | a libbb function out of it. |
98 | |
99 | Adding a libbb function: |
100 | ------------------------ |
101 | |
102 | Make a new file named <function_name>.c |
103 | |
104 | ----start example code------ |
105 | |
106 | #include "libbb.h" |
107 | #include "other.h" |
108 | |
109 | //kbuild:lib-y += function.o |
110 | |
111 | int function(char *a) |
112 | { |
113 | return *a; |
114 | } |
115 | |
116 | ----end example code------ |
117 | |
118 | Remember about the kbuild snippet. |
119 | |
120 | You should also try to find a suitable place in include/libbb.h for |
121 | the function declaration. If not, add it somewhere anyway, with or without |
122 | ifdefs to include or not. |
123 | |
124 | You can look at libbb/Config.src and try to find out if the function is |
125 | tunable and add it there if it is. |
126 | |
127 | |
128 | Kbuild/Config.in/usage/applets.h snippets in .c files |
129 | ----------------------------------------------------- |
130 | |
131 | The old way of adding new applets was to put all the information needed by the |
132 | configuration and build system into appropriate files (namely: Kbuild.src and |
133 | Config.src in new applet's directory) and to add the applet declaration and |
134 | usage info text to include/applets.src.h and include/usage.src.h respectively. |
135 | |
136 | Since the scripts/gen_build_files.sh script had been introduced, the preferred |
137 | way is to have all these declarations contained within the applet .c files. |
138 | |
139 | Every line intended to be processed by gen_build_files.sh should start as a |
140 | comment without any preceding whitespaces and be followed by an appropriate |
141 | keyword - kbuild, config, usage or applet - and a colon, just like shown in the |
142 | first example above. |
143 | |
144 | |
145 | Placement / Directory |
146 | --------------------- |
147 | |
148 | Find the appropriate directory for your new applet. |
149 | |
150 | Add the kbuild snippet to the .c file: |
151 | |
152 | //kbuild:lib-$(CONFIG_MU) += mu.o |
153 | |
154 | Add the config snippet to the .c file: |
155 | |
156 | //config:config MU |
157 | //config: bool "MU" |
158 | //config: default y |
159 | //config: help |
160 | //config: Returns an indeterminate value. |
161 | |
162 | |
163 | Usage String(s) |
164 | --------------- |
165 | |
166 | Next, add usage information for your applet to the .c file. |
167 | This should look like the following: |
168 | |
169 | //usage:#define mu_trivial_usage |
170 | //usage: "[-abcde] FILE..." |
171 | //usage:#define mu_full_usage |
172 | //usage: "Returns an indeterminate value\n" |
173 | //usage: "\n -a First function" |
174 | //usage: "\n -b Second function" |
175 | //usage: ... |
176 | |
177 | If your program supports flags, the flags should be mentioned on the first |
178 | line ([-abcde]) and a detailed description of each flag should go in the |
179 | mu_full_usage section, one flag per line. |
180 | |
181 | |
182 | Header Files |
183 | ------------ |
184 | |
185 | Finally add the applet declaration snippet. Be sure to read the top of |
186 | applets.src.h before adding your applet - it contains important info |
187 | on applet macros and conventions. |
188 | |
189 | //applet:IF_MU(APPLET(mu, BB_DIR_USR_BIN, BB_SUID_DROP)) |
190 | |
191 | |
192 | The Grand Announcement |
193 | ---------------------- |
194 | |
195 | Then create a diff by adding the new files to git (remember your libbb files) |
196 | git add <where you put it>/mu.c |
197 | eventually also: |
198 | git add libbb/function.c |
199 | then |
200 | git commit |
201 | git format-patch HEAD^ |
202 | and send it to the mailing list: |
203 | busybox@busybox.net |
204 | http://busybox.net/mailman/listinfo/busybox |
205 | |
206 | Sending patches as attachments is preferred, but not required. |
207 |