busybox/docs/new-applet-HOWTO.txt

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 - Added stuff for the new directory layout.

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. Be sure to name the main function <applet>_main instead
of main.  And be sure to put it in <applet>.c.  For a new applet mu, here is
the code that would go in mu.c:

----begin example code------

/* vi: set sw=4 ts=4: */
/*
 * Mini mu implementation for busybox
 *
 *
 * Copyright (C) [YEAR] by [YOUR NAME] <YOUR EMAIL>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
 * 02111-1307 USA
 *
 */

#include "busybox.h"

int mu_main(int argc, char **argv)
{
	int fd;
	char mu;

	if ((fd = open("/dev/random", O_RDONLY)) < 0)
		perror_msg_and_die("/dev/random");

	if ((n = safe_read(fd, &mu, 1)) < 1)
		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
program that could be useful in another program, consider putting them in
libbb.


Placement / Directory
---------------------

Find the appropriate directory for your new applet.

Add the applet to the applet directory Makefile:

obj-$(CONFIG_MU)               += mu.o

Add the applet to the applet directory config.in:

bool 'mu'          CONFIG_MU


Usage String(s)
---------------

Next, add usage information for you applet to include/usage.h. 
This should look like the following:

	#define mu_trivial_usage \
		"-[abcde] FILES"
	#define mu_full_usage \
		"Returns an indeterminate value.\n\n" \
		"Options:\n" \
		"\t-a\t\tfirst function\n" \
		"\t-b\t\tsecond function\n" \

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. (Numerous examples of this
currently exist in usage.h.)


Header Files
------------

Next, add an entry to include/applets.h.  Be *sure* to keep the list 
in alphabetical order, or else it will break the binary-search lookup 
algorithm in busybox.c and the Gods of BusyBox smite you. Yea, verily:

	/* all programs above here are alphabetically "less than" 'mu' */
	#ifdef CONFIG_MU
		APPLET("mu", mu_main, _BB_DIR_USR_BIN, mu_usage)
	#endif
	/* all programs below here are alphabetically "greater than" 'mu' */


Finally, add a define for your applet to Config.h:

	#define CONFIG_MU


Documentation
-------------

If you're feeling especially nice, you should also document your applet in the
docs directory (but nobody ever does that).

Adding some text to docs/Configure.help is a nice start.


The Grand Announcement
----------------------

Then create a diff -urN of the files you added (<applet>.c, usage.c,
applets.h, Config.h) and send it to the mailing list:
busybox@busybox.net. Sending patches as attachments is preferred, but
not required.