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Contributing To Busybox
This document describes what you need to do to contribute to Busybox, where
you can help, guidelines on testing, and how to submit a well-formed patch
that is more likely to be accepted.
The Busybox home page is at:
Pre-Contribution Checklist
So you want to contribute to Busybox, eh? Great, wonderful, glad you want to
help. However, before you dive in, headlong and hotfoot, there are some things
you need to do:
Checkout the Latest Code
This is a necessary first step. Please do not try to work with the last
released version, as there is a good chance that somebody has already fixed
the bug you found. Somebody might have even added the feature you had in mind.
Don't make your work obsolete before you start!
For information on how to check out Busybox development tree, please look at the
following links:
Read the Mailing List
No one is required to read the entire archives of the mailing list, but you
should at least read up on what people have been talking about lately. If
you've recently discovered a problem, chances are somebody else has too. If
you're the first to discover a problem, post a message and let the rest of us
Archives can be found here:
If you have a serious interest in Busybox, i.e., you are using it day-to-day or
as part of an embedded project, it would be a good idea to join the mailing
A web-based sign-up form can be found here:
Coordinate with the Applet Maintainer
Some (not all) of the applets in Busybox are "owned" by a maintainer who has
put significant effort into it and is probably more familiar with it than
others. To find the maintainer of an applet, look at the top of the .c file
for a name following the word 'Copyright' or 'Written by' or 'Maintainer'.
Before plunging ahead, it's a good idea to send a message to the mailing list
that says: "Hey, I was thinking about adding the 'transmogrify' feature to the
'foo' applet. Would this be useful? Is anyone else working on it?" You might
want to CC the maintainer (if any) with your question.
Areas Where You Can Help
Busybox can always use improvement! If you're looking for ways to help, there
are a variety of areas where you could help.
What Busybox Doesn't Need
Before listing the areas where you _can_ help, it's worthwhile to mention the
areas where you shouldn't bother. While Busybox strives to be the "Swiss Army
Knife" of embedded Linux, there are some applets that will not be accepted:
- Any filesystem manipulation tools: Busybox is filesystem independent and
we do not want to start adding mkfs/fsck tools for every (or any)
filesystem under the sun. (fsck_minix.c and mkfs_minix.c are living on
borrowed time.) There are far too many of these tools out there. Use
the upstream version. Rationale: bugs in these tools can destroy
vast amounts of data. Keeping up with filesystem format development
is impractical (especially in the area of keeping fsck tool safe
and up-to-date).
- Any disk, device, or media-specific tools: Use the -utils or -tools package
that was designed for your device; don't try to shoehorn them into Busybox.
- Any architecture specific tools: Busybox is (or should be) architecture
independent. Do not send us tools that cannot be used across multiple
platforms / arches.
Bug Reporting
If you find bugs, please submit a detailed bug report to the busybox mailing
list at A well-written bug report should include a
transcript of a shell session that demonstrates the bad behavior and enables
anyone else to duplicate the bug on their own machine. The following is such
an example:
Subject: /bin/date doesn't work
Package: busybox
Version: 1.00
When I execute Busybox 'date' it produces unexpected results.
With GNU date I get the following output:
$ date
Wed Mar 21 14:19:41 MST 2001
But when I use BusyBox date I get this instead:
$ date
Illegal instruction
I am using Debian unstable, kernel version 2.4.19-rmk1 on an Netwinder,
and the latest uClibc from CVS.
Note the careful description and use of examples showing not only what BusyBox
does, but also a counter example showing what an equivalent GNU app does. Bug
reports lacking such detail may never be fixed... Thanks for understanding.
Write Documentation
Chances are, documentation in Busybox is either missing or needs improvement.
Either way, help is welcome.
Work is being done to automatically generate documentation from sources,
especially from the usage.h file. If you want to correct the documentation,
please make changes to the pre-generation parts, rather than the generated
documentation. [More to come on this later...]
It is preferred that modifications to documentation be submitted in patch
format (more on this below), but we're a little more lenient when it comes to
docs. You could, for example, just say "after the listing of the mount
options, the following example would be helpful..."
Consult Existing Sources
For a quick listing of "needs work" spots in the sources, cd into the Busybox
directory and run the following:
for i in TODO FIXME XXX; do find -name '*.[ch]'|xargs grep $i; done
This will show all of the trouble spots or 'questionable' code. Pick a spot,
any spot, these are all invitations for you to contribute.
Add a New Applet
If you want to add a new applet to Busybox, we'd love to see it. However,
before you write any code, please ask beforehand on the mailing list something
like "Do you think applet 'foo' would be useful in Busybox?" or "Would you
guys accept applet 'foo' into Busybox if I were to write it?" If the answer is
"no" by the folks on the mailing list, then you've saved yourself some time.
Conversely, you could get some positive responses from folks who might be
interested in helping you implement it, or can recommend the best approach.
Perhaps most importantly, this is your way of calling "dibs" on something and
avoiding duplication of effort.
Also, before you write a line of code, please read the 'new-applet-HOWTO.txt'
file in the docs/ directory.
Janitorial Work
These are dirty jobs, but somebody's gotta do 'em.
- Security audits:
- Synthetic code removal: - This
is very Perl-specific, but the advice given in here applies equally well to
- C library function use audits: Verifying that functions are being used
properly (called with the right args), replacing unsafe library functions
with safer versions, making sure return codes are being checked, etc.
- Where appropriate, replace preprocessor defined macros and values with
compile-time equivalents.
- Style guide compliance. See: docs/style-guide.txt
- Add testcases to tests/testcases.
- Makefile improvements:
(I think the recursive problems are pretty much taken care of at this point, non?)
- "Ten Commandments" compliance: (this is a "maybe", certainly not as
important as any of the previous items.)
Other useful links:
- the comp.lang.c FAQ:
Submitting Patches To Busybox
Here are some guidelines on how to submit a patch to Busybox.
Making A Patch
If you've got anonymous Git access set up, making a patch is simple. Just make
sure you're in the busybox/ directory and type:
git diff -b -w > mychanges.patch
You can send the resulting .patch file to the mailing list with a description
of what it does. (But not before you test it! See the next section for some
guidelines.) It is preferred that patches be sent as attachments, but it is
not required.
Also, feel free to help test other people's patches and reply to them with
comments. You can apply a patch by saving it into your busybox/ directory and
patch -p1 < mychanges.patch
Then you can recompile, see if it runs, test if it works as advertised, and
post your findings to the mailing list.
NOTE: Please do not include extraneous or irrelevant changes in your patches.
Please do not try to "bundle" two patches together into one. Make single,
discreet changes on a per-patch basis. Sometimes you need to make a patch that
touches code in many places, but these kind of patches are rare and should be
coordinated with a maintainer.
Testing Guidelines
It's considered good form to test your new feature before you submit a patch
to the mailing list, and especially before you push a change to Git. Here
are some guidelines on how to test your changes.
- Always test Busybox applets against GNU counterparts and make sure the
behavior / output is identical between the two.
- Try several different permutations and combinations of the features you're
adding (i.e., different combinations of command-line switches) and make sure
they all work; make sure one feature does not interfere with another.
- 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.
- Run the script in the tests directory and make sure
everything checks out OK. (Do this from within the busybox/ directory by
typing: 'tests/'.)
Making Sure Your Patch Doesn't Get Lost
If you don't want your patch to be lost or forgotten, send it to the busybox
mailing list with a subject line something like this:
[PATCH] - Adds "transmogrify" feature to "foo"
In the body, you should have a pseudo-header that looks like the following:
Package: busybox
Version: v1.01pre (or whatever the current version is)
Severity: wishlist
The remainder of the body should read along these lines:
This patch adds the "transmogrify" feature to the "foo" applet. I have
tested this on [arch] system(s) and it works. I have tested it against the
GNU counterparts and the outputs are identical. I have run the scripts in
the 'tests' directory and nothing breaks.
Improving Your Chances of Patch Acceptance
Even after you send a brilliant patch to the mailing list, sometimes it can go
unnoticed, un-replied-to, and sometimes (sigh) even lost. This is an
unfortunate fact of life, but there are steps you can take to help your patch
get noticed and convince a maintainer that it should be added:
Be Succinct
A patch that includes small, isolated, obvious changes is more likely to be
accepted than a patch that touches code in lots of different places or makes
sweeping, dubious changes.
Back It Up
Hard facts on why your patch is better than the existing code will go a long
way toward convincing maintainers that your patch should be included.
Specifically, patches are more likely to be accepted if they are provably more
correct, smaller, faster, simpler, or more maintainable than the existing
Conversely, any patch that is supported with nothing more than "I think this
would be cool" or "this patch is good because I say it is and I've got a Phd
in Computer Science" will likely be ignored.
Follow The Style Guide
It's considered good form to abide by the established coding style used in a
project; Busybox is no exception. We have gone so far as to delineate the
"elements of Busybox style" in the file docs/style-guide.txt. Please follow
Work With Someone Else
Working on a patch in isolation is less effective than working with someone
else for a variety of reasons. If another Busybox user is interested in what
you're doing, then it's two (or more) voices instead of one that can petition
for inclusion of the patch. You'll also have more people that can test your
changes, or even offer suggestions on better approaches you could take.
Getting other folks interested follows as a natural course if you've received
responses from queries to applet maintainer or positive responses from folks
on the mailing list.
We've made strident efforts to put a useful "collaboration" infrastructure in
place in the form of mailing lists, the bug tracking system, and Git. Please
use these resources.
Send Patches to the Bug Tracking System
This was mentioned above in the "Making Sure Your Patch Doesn't Get Lost"
section, but it is worth mentioning again. A patch sent to the mailing list
might be unnoticed and forgotten. A patch sent to the bug tracking system will
be stored and closely connected to the bug it fixes.
Be Polite
The old saying "You'll catch more flies with honey than you will with vinegar"
applies when submitting patches to the mailing list for approval. The way you
present your patch is sometimes just as important as the actual patch itself
(if not more so). Being rude to the maintainers is not an effective way to
convince them that your patch should be included; it will likely have the
opposite effect.
Pushing Changes to Git
If you submit several patches that demonstrate that you are a skilled and wise
coder, you may be invited to become a committer, thus enabling you to push
changes directly to Git. This is nice because you don't have to wait for
someone else to push your change for you, you can just do it yourself.
But note that this is a privilege that comes with some responsibilities. You
should test your changes before you push them. You should also talk to an
applet maintainer before you make any kind of sweeping changes to somebody
else's code. Big changes should still go to the mailing list first. Remember,
being wise, polite, and discreet is more important than being clever.
For more information on Git push access, see:
When To Push
Generally, you should feel free to push a change if:
- Your changes are small and don't touch many files
- You are fixing a bug
- Somebody has told you that it's okay
- It's obviously the Right Thing
The more of the above are true, the better it is to just push a change
directly to Git.
When Not To Push
Even if you have push access, you should probably still post a patch to the
mailing list if:
- Your changes are broad and touch many different files
- You are adding a feature
- Your changes are speculative or experimental (i.e., trying a new algorithm)
- You are not the maintainer and your changes make the maintainer cringe
The more of the above are true, the better it is to post a patch to the
mailing list instead of pushing.
Final Words
If all of this seems complicated, don't panic, it's really not that tough. If
you're having difficulty following some of the steps outlined in this
document don't worry, the folks on the Busybox mailing list are a fairly
good-natured bunch and will work with you to help get your patches into shape
or help you make contributions.