| <!--#include file="header.html" --> |
| |
| <h3>Frequently Asked Questions</h3> |
| |
| This is a collection of some of the more frequently asked questions |
| about BusyBox. Some of the questions even have answers. If you |
| have additions to this FAQ document, we would love to add them, |
| |
| <h2>General questions</h2> |
| <ol> |
| <li><a href="#getting_started">How can I get started using BusyBox?</a></li> |
| <li><a href="#configure">How do I configure busybox?</a></li> |
| <li><a href="#build">How do I build BusyBox with a cross-compiler?</a></li> |
| <li><a href="#build_system">How do I build a BusyBox-based system?</a></li> |
| <li><a href="#kernel">Which Linux kernel versions are supported?</a></li> |
| <li><a href="#arch">Which architectures does BusyBox run on?</a></li> |
| <li><a href="#libc">Which C libraries are supported?</a></li> |
| <li><a href="#commercial">Can I include BusyBox as part of the software on my device?</a></li> |
| <li><a href="#external">Where can I find other small utilities since busybox does not include the features I want?</a></li> |
| <li><a href="#demanding">I demand that you to add <favorite feature> right now! How come you don't answer all my questions on the mailing list instantly? I demand that you help me with all of my problems <em>Right Now</em>!</a></li> |
| <li><a href="#helpme">I need help with BusyBox! What should I do?</a></li> |
| <li><a href="#contracts">I need you to add <favorite feature>! Are the BusyBox developers willing to be paid in order to fix bugs or add in <favorite feature>? Are you willing to provide support contracts?</a></li> |
| </ol> |
| |
| <h2>Troubleshooting</h2> |
| <ol> |
| <li><a href="#bugs">I think I found a bug in BusyBox! What should I do?!</a></li> |
| <li><a href="#backporting">I'm using an ancient version from the dawn of time and something's broken. Can you backport fixes for free?</a></li> |
| <li><a href="#init">Busybox init isn't working!</a></li> |
| <li><a href="#sed">I can't configure busybox on my system.</a></li> |
| <li><a href="#job_control">Why do I keep getting "sh: can't access tty; job control turned off" errors? Why doesn't Control-C work within my shell?</a></li> |
| </ol> |
| |
| <h2>Misc. questions</h2> |
| <ol> |
| <li><a href="#tz">How do I change the time zone in busybox?</a></li> |
| </ol> |
| |
| <h2>Programming questions</h2> |
| <ol> |
| <li><a href="#goals">What are the goals of busybox?</a></li> |
| <li><a href="#design">What is the design of busybox?</a></li> |
| <li><a href="#source">How is the source code organized?</a> |
| <ul> |
| <li><a href="#source_applets">The applet directories.</a></li> |
| <li><a href="#source_libbb">The busybox shared library (libbb)</a></li> |
| </ul> |
| </li> |
| <li><a href="#optimize">I want to make busybox even smaller, how do I go about it?</a></li> |
| <li><a href="#adding">Adding an applet to busybox</a></li> |
| <li><a href="#standards">What standards does busybox adhere to?</a></li> |
| <li><a href="#portability">Portability.</a></li> |
| <li><a href="#tips">Tips and tricks.</a> |
| <ul> |
| <li><a href="#tips_encrypted_passwords">Encrypted Passwords</a></li> |
| <li><a href="#tips_vfork">Fork and vfork</a></li> |
| <li><a href="#tips_short_read">Short reads and writes</a></li> |
| <li><a href="#tips_memory">Memory used by relocatable code, PIC, and static linking.</a></li> |
| <li><a href="#tips_kernel_headers">Including Linux kernel headers.</a></li> |
| </ul> |
| </li> |
| <li><a href="#who">Who are the BusyBox developers?</a></li> |
| </ul> |
| </ol> |
| |
| |
| <hr /> |
| <h1>General questions</h1> |
| |
| <hr /> |
| <h2><a name="getting_started">How can I get started using BusyBox?</a></h2> |
| |
| <p> If you just want to try out busybox without installing it, download the |
| tarball, extract it, run "make defconfig", and then run "make". |
| </p> |
| <p> |
| This will create a busybox binary with almost all features enabled. To try |
| out a busybox applet, type "./busybox [appletname] [options]", for |
| example "./busybox ls -l" or "./busybox cat LICENSE". Type "./busybox" |
| to see a command list, and "busybox appletname --help" to see a brief |
| usage message for a given applet. |
| </p> |
| <p> |
| BusyBox uses the name it was invoked under to determine which applet is |
| being invoked. (Try "mv busybox ls" and then "./ls -l".) Installing |
| busybox consists of creating symlinks (or hardlinks) to the busybox |
| binary for each applet in busybox, and making sure these links are in |
| the shell's command $PATH. The special applet name "busybox" (or with |
| any optional suffix, such as "busybox-static") uses the first argument |
| to determine which applet to run, as shown above. |
| </p> |
| <p> |
| BusyBox also has a feature called the |
| <a name="standalone_shell">"standalone shell"</a>, where the busybox |
| shell runs any built-in applets before checking the command path. This |
| feature is also enabled by "make allyesconfig", and to try it out run |
| the command line "PATH= ./busybox ash". This will blank your command path |
| and run busybox as your command shell, so the only commands it can find |
| (without an explicit path such as /bin/ls) are the built-in busybox ones. |
| This is another good way to see what's built into busybox. |
| Note that the standalone shell requires CONFIG_BUSYBOX_EXEC_PATH |
| to be set appropriately, depending on whether or not /proc/self/exe is |
| available or not. If you do not have /proc, then point that config option |
| to the location of your busybox binary, usually /bin/busybox. |
| (So if you set it to /proc/self/exe, and happen to be able to chroot into |
| your rootfs, you must mount /proc beforehand.) |
| </p> |
| <p> |
| A typical indication that you set CONFIG_BUSYBOX_EXEC_PATH to proc but |
| forgot to mount proc is: |
| <pre> |
| $ /bin/echo $PATH |
| /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/bin/X11 |
| $ echo $PATH |
| /bin/sh: echo: not found |
| </pre> |
| |
| <hr /> |
| <h2><a name="configure">How do I configure busybox?</a></h2> |
| |
| <p> Busybox is configured similarly to the linux kernel. Create a default |
| configuration and then run "make menuconfig" to modify it. The end |
| result is a .config file that tells the busybox build process what features |
| to include. So instead of "./configure; make; make install" the equivalent |
| busybox build would be "make defconfig; make; make install". |
| </p> |
| |
| <p> Busybox configured with all features enabled is a little under a megabyte |
| dynamically linked on x86. To create a smaller busybox, configure it with |
| fewer features. Individual busybox applets cost anywhere from a few |
| hundred bytes to tens of kilobytes. Disable unneeded applets to save, |
| space, using menuconfig. |
| </p> |
| |
| <p>The most important busybox configurators are:</p> |
| |
| <ul> |
| <li><p>make <b>defconfig</b> - Create the maximum "sane" configuration. This |
| enables almost all features, minus things like debugging options and features |
| that require changes to the rest of the system to work (such as selinux or |
| devfs device names). Use this if you want to start from a full-featured |
| busybox and remove features until it's small enough.</p></li> |
| <li><p>make <b>allnoconfig</b> - Disable everything. This creates a tiny version |
| of busybox that doesn't do anything. Start here if you know exactly what |
| you want and would like to select only those features.</p></li> |
| <li><p>make <b>menuconfig</b> - Interactively modify a .config file through a |
| multi-level menu interface. Use this after one of the previous two.</p></li> |
| </ul> |
| |
| <p>Some other configuration options are:</p> |
| <ul> |
| <li><p>make <b>oldconfig</b> - Update an old .config file for a newer version |
| of busybox.</p></li> |
| <li><p>make <b>allyesconfig</b> - Select absolutely everything. This creates |
| a statically linked version of busybox full of debug code, with dependencies on |
| selinux, using devfs names... This makes sure everything compiles. Whether |
| or not the result would do anything useful is an open question.</p></li> |
| <li><p>make <b>allbareconfig</b> - Select all applets but disable all sub-features |
| within each applet. More build coverage testing.</p></li> |
| <li><p>make <b>randconfig</b> - Create a random configuration for test purposes.</p></li> |
| </ul> |
| |
| <p> Menuconfig modifies your .config file through an interactive menu where you can enable or disable |
| busybox features, and get help about each feature. |
| |
| <p> |
| To build a smaller busybox binary, run "make menuconfig" and disable the |
| features you don't need. (Or run "make allnoconfig" and then use |
| menuconfig to add just the features you need. Don't forget to recompile |
| with "make" once you've finished configuring.) |
| </p> |
| |
| <hr /> |
| <h2><a name="build">How do I build BusyBox with a cross-compiler?</a></h2> |
| |
| <p> |
| To build busybox with a cross-compiler, specify CROSS_COMPILE=<prefix>. |
| </p> |
| <p> |
| CROSS_COMPILE specifies the prefix used for all executables used |
| during compilation. Only gcc and related binutils executables |
| are prefixed with $(CROSS_COMPILE) in the makefiles. |
| CROSS_COMPILE can be set on the command line: |
| <pre> |
| make CROSS_COMPILE=arm-linux-uclibcgnueabi- |
| </pre> |
| Alternatively CROSS_COMPILE can be set in the environment. |
| Default value for CROSS_COMPILE is not to prefix executables. |
| </p> |
| |
| <hr /> |
| <h2><a name="build_system">How do I build a BusyBox-based system?</a></h2> |
| |
| <p> |
| BusyBox is a package that replaces a dozen standard packages, but it is |
| not by itself a complete bootable system. Building an entire Linux |
| distribution from source is a bit beyond the scope of this FAQ, but it |
| understandably keeps cropping up on the mailing list, so here are some |
| pointers. |
| </p> |
| <p> |
| Start by learning how to strip a working system down to the bare essentials |
| needed to run one or two commands, so you know what it is you actually |
| need. An excellent practical place to do |
| this is the <a href="http://www.tldp.org/HOWTO/Bootdisk-HOWTO/">Linux |
| BootDisk Howto</a>, or for a more theoretical approach try |
| <a href="http://www.tldp.org/HOWTO/From-PowerUp-To-Bash-Prompt-HOWTO.html">From |
| PowerUp to Bash Prompt</a>. |
| </p> |
| <p> |
| To learn how to build a working Linux system entirely from source code, |
| the place to go is the <a href="http://www.linuxfromscratch.org/">Linux |
| From Scratch</a> project. They have an entire book of step-by-step |
| instructions you can |
| <a href="http://www.linuxfromscratch.org/lfs/view/stable/">read online</a> |
| or |
| <a href="http://www.linuxfromscratch.org/lfs/downloads/stable/">download</a>. |
| Be sure to check out the other sections of their main page, including |
| Beyond Linux From Scratch, Hardened Linux From Scratch, their Hints |
| directory, and their LiveCD project. (They also have mailing lists which |
| are better sources of answers to Linux-system building questions than |
| the busybox list.) |
| </p> |
| <p> |
| If you want an automated yet customizable system builder which produces |
| a BusyBox and uClibc based system, try |
| <a href="http://buildroot.uclibc.org/">buildroot</a>, which is |
| another project by the maintainer of the uClibc (Erik Andersen). |
| Download the tarball, extract it, unset CC, make. |
| For more instructions, see the website. |
| </p> |
| |
| <hr /> |
| <h2><a name="kernel">Which Linux kernel versions are supported?</a></h2> |
| |
| <p> |
| Full functionality requires Linux 2.4.x or better. (Earlier versions may |
| still work, but are no longer regularly tested.) A large fraction of the |
| code should run on just about anything. While the current code is fairly |
| Linux specific, it should be fairly easy to port the majority of the code |
| to support, say, FreeBSD or Solaris, or Mac OS X, or even Windows (if you |
| are into that sort of thing). |
| </p> |
| |
| <hr /> |
| <h2><a name="arch">Which architectures does BusyBox run on?</a></h2> |
| |
| <p> |
| BusyBox in general will build on any architecture supported by gcc. |
| Kernel module loading for 2.4 Linux kernels is currently |
| limited to ARM, CRIS, H8/300, x86, ia64, x86_64, m68k, MIPS, PowerPC, |
| S390, SH3/4/5, Sparc, v850e, and x86_64 for 2.4.x kernels. |
| </p> |
| <p> |
| With 2.6.x kernels, module loading support should work on all architectures. |
| </p> |
| |
| <hr /> |
| <h2><a name="libc">Which C libraries are supported?</a></h2> |
| |
| <p> |
| On Linux, BusyBox releases are tested against uClibc (0.9.27 or later) and |
| glibc (2.2 or later). Both should provide full functionality with busybox, |
| and if you find a bug we want to hear about it. |
| </p> |
| <p> |
| Linux-libc5 is no longer maintained (and has no known advantages over |
| uClibc), dietlibc is known to have numerous unfixed bugs, and klibc is |
| missing too many features to build BusyBox. If you require a small C |
| library for Linux, the busybox developers recommend uClibc. |
| </p> |
| <p> |
| Some BusyBox applets have been built and run under a combination |
| of newlib and libgloss (see |
| <a href="http://www.busybox.net/lists/busybox/2005-March/013759.html">this thread</a>). |
| This is still experimental, but may be supported in a future release. |
| </p> |
| |
| <hr /> |
| <h2><a name="commercial">Can I include BusyBox as part of the software on my device?</a></h2> |
| |
| <p> |
| Yes. As long as you <a href="http://busybox.net/license.html">fully comply |
| with the generous terms of the GPL BusyBox license</a> you can ship BusyBox |
| as part of the software on your device. |
| </p> |
| |
| <hr /> |
| <h2><a name="external">Where can I find other small utilities since busybox |
| does not include the features i want?</a></h2> |
| |
| <p> |
| we maintain such a <a href="tinyutils.html">list</a> on this site! |
| </p> |
| |
| <hr /> |
| <h2><a name="demanding">I demand that you to add <favorite feature> right now! How come you don't answer all my questions on the mailing list instantly? I demand that you help me with all of my problems <em>Right Now</em>!</a></h2> |
| |
| <p> |
| You have not paid us a single cent and yet you still have the product of |
| many years of our work. We are not your slaves! We work on BusyBox |
| because we find it useful and interesting. If you go off flaming us, we |
| will ignore you. |
| |
| <hr /> |
| <h2><a name="helpme">I need help with BusyBox! What should I do?</a></h2> |
| |
| <p> |
| If you find that you need help with BusyBox, you can ask for help on the |
| BusyBox mailing list at busybox@busybox.net.</p> |
| |
| <p> In addition to the mailing list, Erik Andersen (andersee), Manuel Nova |
| (mjn3), Rob Landley (landley), Mike Frysinger (SpanKY), Bernhard Fischer |
| (blindvt), and other long-time BusyBox developers are known to hang out |
| on the uClibc IRC channel: #uclibc on irc.freenode.net. There is a |
| <a href="http://ibot.Rikers.org/%23uclibc/">web archive of |
| daily logs of the #uclibc IRC channel</a> going back to 2002. |
| </p> |
| |
| <p> |
| <b>Please do not send private email to Rob, Erik, Manuel, or the other |
| BusyBox contributors asking for private help unless you are planning on |
| paying for consulting services.</b> |
| </p> |
| |
| <p> |
| When we answer questions on the BusyBox mailing list, it helps everyone |
| since people with similar problems in the future will be able to get help |
| by searching the mailing list archives. Private help is reserved as a paid |
| service. If you need to use private communication, or if you are serious |
| about getting timely assistance with BusyBox, you should seriously consider |
| paying for consulting services. |
| </p> |
| |
| <hr /> |
| <h2><a name="contracts">I need you to add <favorite feature>! Are the BusyBox developers willing to be paid in order to fix bugs or add in <favorite feature>? Are you willing to provide support contracts?</a></h2> |
| |
| <p> |
| Yes we are. The easy way to sponsor a new feature is to post an offer on |
| the mailing list to see who's interested. You can also email the project's |
| maintainer and ask them to recommend someone. |
| </p> |
| |
| <hr /> |
| <h1>Troubleshooting</h1> |
| |
| <hr /> |
| <h2><a name="bugs">I think I found a bug in BusyBox! What should I do?</a></h2> |
| |
| <p> |
| If you simply need help with using or configuring BusyBox, please submit a |
| detailed description of your problem to the BusyBox mailing list at <a |
| href="mailto:busybox@busybox.net">busybox@busybox.net</a>. |
| Please do not send email to individual developers asking |
| for private help unless you are planning on paying for consulting services. |
| When we answer questions on the BusyBox mailing list, it helps everyone, |
| while private answers help only you... |
| </p> |
| |
| <p> |
| Bug reports and new feature patches sometimes get lost when posted to the |
| mailing list, because the developers of BusyBox are busy people and have |
| only so much they can keep in their brains at a time. You can post a |
| polite reminder after 2-3 days without offending anybody. If that doesn't |
| result in a solution, please use the |
| <a href="http://bugs.busybox.net/">BusyBox Bug |
| and Patch Tracking System</a> to submit a detailed explanation and we'll |
| get to it as soon as we can. |
| </p> |
| |
| <p> |
| Note that bugs entered into the bug system without being mentioned on the |
| mailing list first may languish there for months before anyone even notices |
| them. We generally go through the bug system when preparing for new |
| development releases, to see what fell through the cracks while we were |
| off writing new features. (It's a fast/unreliable vs slow/reliable thing. |
| Saves retransits, but the latency sucks.) |
| </p> |
| |
| <hr /> |
| <h2><a name="backporting">I'm using an ancient version from the dawn of time and something's broken. Can you backport fixes for free?</a></h2> |
| |
| <p>Variants of this one get asked a lot.</p> |
| |
| <p>The purpose of the BusyBox mailing list is to develop and improve BusyBox, |
| and we're happy to respond to our users' needs. But if you're coming to the |
| list for free tech support we're going to ask you to upgrade to a current |
| version before we try to diagnose your problem.</p> |
| |
| <p>If you're building BusyBox 0.50 with uClibc 0.9.19 and gcc 1.27 there's a |
| fairly large chance that whatever problem you're seeing has already been fixed. |
| To get that fix, all you have to do is upgrade to a newer version. If you |
| don't at least _try_ that, you're wasting our time.</p> |
| |
| <p>The volunteers are happy to fix any bugs you point out in the current |
| versions because doing so helps everybody and makes the project better. We |
| want to make the current version work for you. But diagnosing, debugging, and |
| backporting fixes to old versions isn't something we do for free, because it |
| doesn't help anybody but you. The cost of volunteer tech support is using a |
| reasonably current version of the project.</p> |
| |
| <p>If you don't want to upgrade, you have the complete source code and thus |
| the ability to fix it yourself, or hire a consultant to do it for you. If you |
| got your version from a vendor who still supports the older version, they can |
| help you. But there are limits as to what the volunteers will feel obliged to |
| do for you.</p> |
| |
| <p>As a rule of thumb, volunteers will generally answer polite questions about |
| a given version for about three years after its release before it's so old |
| we don't remember the answer off the top of our head. And if you want us to |
| put any _effort_ into tracking it down, we want you to put in a little effort |
| of your own by confirming it's still a problem with the current version. It's |
| also hard for us to fix a problem of yours if we can't reproduce it because |
| we don't have any systems running an environment that old.</p> |
| |
| <p>A consultant will happily set up a special environment just to reproduce |
| your problem, and you can always ask on the list if any of the developers |
| have consulting rates.</p> |
| |
| <hr /> |
| <h2><a name="init">Busybox init isn't working!</a></h2> |
| |
| <p> |
| Init is the first program that runs, so it might be that no programs are |
| working on your new system because of a problem with your cross-compiler, |
| kernel, console settings, shared libraries, root filesystem... To rule all |
| that out, first build a statically linked version of the following "hello |
| world" program with your cross compiler toolchain: |
| </p> |
| <pre> |
| #include <stdio.h> |
| |
| int main(int argc, char *argv) |
| { |
| printf("Hello world!\n"); |
| sleep(999999999); |
| } |
| </pre> |
| |
| <p> |
| Now try to boot your device with an "init=" argument pointing to your |
| hello world program. Did you see the hello world message? Until you |
| do, don't bother messing with busybox init. |
| </p> |
| |
| <p> |
| Once you've got it working statically linked, try getting it to work |
| dynamically linked. Then read the FAQ entry <a href="#build_system">How |
| do I build a BusyBox-based system?</a>, and the |
| <a href="/downloads/BusyBox.html#item_init">documentation for BusyBox |
| init</a>. |
| </p> |
| |
| <hr /> |
| <h2><a name="sed">I can't configure busybox on my system.</a></h2> |
| |
| <p> |
| Configuring Busybox depends on a recent version of sed. Older |
| distributions (Red Hat 7.2, Debian 3.0) may not come with a |
| usable version. Luckily BusyBox can use its own sed to configure itself, |
| although this leads to a bit of a chicken and egg problem. |
| You can work around this by hand-configuring busybox to build with just |
| sed, then putting that sed in your path to configure the rest of busybox |
| with, like so: |
| </p> |
| |
| <pre> |
| tar xvjf sources/busybox-x.x.x.tar.bz2 |
| cd busybox-x.x.x |
| make allnoconfig |
| make include/bb_config.h |
| echo "CONFIG_SED=y" >> .config |
| echo "#undef ENABLE_SED" >> include/bb_config.h |
| echo "#define ENABLE_SED 1" >> include/bb_config.h |
| make |
| mv busybox sed |
| export PATH=`pwd`:"$PATH" |
| </pre> |
| |
| <p>Then you can run "make defconfig" or "make menuconfig" normally.</p> |
| |
| <hr /> |
| <h2><a name="job_control">Why do I keep getting "sh: can't access tty; job control turned off" errors? Why doesn't Control-C work within my shell?</a></h2> |
| |
| <p> |
| Job control will be turned off since your shell can not obtain a controlling |
| terminal. This typically happens when you run your shell on /dev/console. |
| The kernel will not provide a controlling terminal on the /dev/console |
| device. Your should run your shell on a normal tty such as tty1 or ttyS0 |
| and everything will work perfectly. If you <em>REALLY</em> want your shell |
| to run on /dev/console, then you can hack your kernel (if you are into that |
| sortof thing) by changing drivers/char/tty_io.c to change the lines where |
| it sets "noctty = 1;" to instead set it to "0". I recommend you instead |
| run your shell on a real console... |
| </p> |
| |
| <hr /> |
| <h1>Misc. questions</h1> |
| |
| <hr /> |
| <h2><a name="tz">How do I change the time zone in busybox?</a></h2> |
| |
| <p>Busybox has nothing to do with the timezone. Please consult your libc |
| documentation. (<a href="http://google.com/search?q=uclibc+glibc+timezone">http://google.com/search?q=uclibc+glibc+timezone</a>).</p> |
| |
| <hr /> |
| <h1>Development</h1> |
| |
| <hr /> |
| <h2><a name="goals">What are the goals of busybox?</a></h2> |
| |
| <p>Busybox aims to be the smallest and simplest correct implementation of the |
| standard Linux command line tools. First and foremost, this means the |
| smallest executable size we can manage. We also want to have the simplest |
| and cleanest implementation we can manage, be <a href="#standards">standards |
| compliant</a>, minimize run-time memory usage (heap and stack), run fast, and |
| take over the world.</p> |
| |
| <hr /> |
| <h2><a name="design">What is the design of busybox?</a></h2> |
| |
| <p>Busybox is like a swiss army knife: one thing with many functions. |
| The busybox executable can act like many different programs depending on |
| the name used to invoke it. Normal practice is to create a bunch of symlinks |
| pointing to the busybox binary, each of which triggers a different busybox |
| function. (See <a href="FAQ.html#getting_started">getting started</a> in the |
| FAQ for more information on usage, and <a href="BusyBox.html">the |
| busybox documentation</a> for a list of symlink names and what they do.) |
| |
| <p>The "one binary to rule them all" approach is primarily for size reasons: a |
| single multi-purpose executable is smaller then many small files could be. |
| This way busybox only has one set of ELF headers, it can easily share code |
| between different apps even when statically linked, it has better packing |
| efficiency by avoding gaps between files or compression dictionary resets, |
| and so on.</p> |
| |
| <p>Work is underway on new options such as "make standalone" to build separate |
| binaries for each applet, and a "libbb.so" to make the busybox common code |
| available as a shared library. Neither is ready yet at the time of this |
| writing.</p> |
| |
| <a name="source"></a> |
| |
| <hr /> |
| <h2><a name="source_applets">The applet directories</a></h2> |
| |
| <p>The directory "applets" contains the busybox startup code (applets.c and |
| busybox.c), and several subdirectories containing the code for the individual |
| applets.</p> |
| |
| <p>Busybox execution starts with the main() function in applets/busybox.c, |
| which sets the global variable applet_name to argv[0] and calls |
| run_applet_and_exit() in applets/applets.c. That uses the applets[] array |
| (defined in include/busybox.h and filled out in include/applets.h) to |
| transfer control to the appropriate APPLET_main() function (such as |
| cat_main() or sed_main()). The individual applet takes it from there.</p> |
| |
| <p>This is why calling busybox under a different name triggers different |
| functionality: main() looks up argv[0] in applets[] to get a function pointer |
| to APPLET_main().</p> |
| |
| <p>Busybox applets may also be invoked through the multiplexor applet |
| "busybox" (see busybox_main() in libbb/appletlib.c), and through the |
| standalone shell (grep for STANDALONE_SHELL in applets/shell/*.c). |
| See <a href="FAQ.html#getting_started">getting started</a> in the |
| FAQ for more information on these alternate usage mechanisms, which are |
| just different ways to reach the relevant APPLET_main() function.</p> |
| |
| <p>The applet subdirectories (archival, console-tools, coreutils, |
| debianutils, e2fsprogs, editors, findutils, init, loginutils, miscutils, |
| modutils, networking, procps, shell, sysklogd, and util-linux) correspond |
| to the configuration sub-menus in menuconfig. Each subdirectory contains the |
| code to implement the applets in that sub-menu, as well as a Config.in |
| file defining that configuration sub-menu (with dependencies and help text |
| for each applet), and the makefile segment (Makefile.in) for that |
| subdirectory.</p> |
| |
| <p>The run-time --help is stored in usage_messages[], which is initialized at |
| the start of applets/applets.c and gets its help text from usage.h. During the |
| build this help text is also used to generate the BusyBox documentation (in |
| html, txt, and man page formats) in the docs directory. See |
| <a href="#adding">adding an applet to busybox</a> for more |
| information.</p> |
| |
| <hr /> |
| <h2><a name="source_libbb"><b>libbb</b></a></h2> |
| |
| <p>Most non-setup code shared between busybox applets lives in the libbb |
| directory. It's a mess that evolved over the years without much auditing |
| or cleanup. For anybody looking for a great project to break into busybox |
| development with, documenting libbb would be both incredibly useful and good |
| experience.</p> |
| |
| <p>Common themes in libbb include allocation functions that test |
| for failure and abort the program with an error message so the caller doesn't |
| have to test the return value (xmalloc(), xstrdup(), etc), wrapped versions |
| of open(), close(), read(), and write() that test for their own failures |
| and/or retry automatically, linked list management functions (llist.c), |
| command line argument parsing (getopt32.c), and a whole lot more.</p> |
| |
| <hr /> |
| <h2><a name="optimize">I want to make busybox even smaller, how do I go about it?</a></h2> |
| |
| <p> |
| To conserve bytes it's good to know where they're being used, and the |
| size of the final executable isn't always a reliable indicator of |
| the size of the components (since various structures are rounded up, |
| so a small change may not even be visible by itself, but many small |
| savings add up). |
| </p> |
| |
| <p> The busybox Makefile builds two versions of busybox, one of which |
| (busybox_unstripped) has extra information that various analysis tools |
| can use. (This has nothing to do with CONFIG_DEBUG, leave that off |
| when trying to optimize for size.) |
| </p> |
| |
| <p> The <b>"make bloatcheck"</b> option uses Matt Mackall's bloat-o-meter |
| script to compare two versions of busybox (busybox_unstripped vs |
| busybox_old), and report which symbols changed size and by how much. |
| To use it, first build a base version with <b>"make baseline"</b>. |
| (This creates busybox_old, which should have the original sizes for |
| comparison purposes.) Then build the new version with your changes |
| and run "make bloatcheck" to see the size differences from the old |
| version. |
| </p> |
| <p> |
| The first line of output has totals: how many symbols were added or |
| removed, how many symbols grew or shrank, the number of bytes added |
| and number of bytes removed by these changes, and finally the total |
| number of bytes difference between the two files. The remaining |
| lines show each individual symbol, the old and new sizes, and the |
| increase or decrease in size (which results are sorted by). |
| </p> |
| <p> |
| The <b>"make sizes"</b> option produces raw symbol size information for |
| busybox_unstripped. This is the output from the "nm --size-sort" |
| command (see "man nm" for more information), and is the information |
| bloat-o-meter parses to produce the comparison report above. For |
| defconfig, this is a good way to find the largest symbols in the tree |
| (which is a good place to start when trying to shrink the code). To |
| take a closer look at individual applets, configure busybox with just |
| one applet (run "make allnoconfig" and then switch on a single applet |
| with menuconfig), and then use "make sizes" to see the size of that |
| applet's components. |
| </p> |
| <p> |
| The "showasm" command (in the scripts directory) produces an assembly |
| dump of a function, providing a closer look at what changed. Try |
| "scripts/showasm busybox_unstripped" to list available symbols, and |
| "scripts/showasm busybox_unstripped symbolname" to see the assembly |
| for a sepecific symbol. |
| </p> |
| |
| <hr /> |
| <h2><a name="adding">Adding an applet to busybox</a></h2> |
| |
| <p>To add a new applet to busybox, first pick a name for the applet and |
| a corresponding CONFIG_NAME. Then do this:</p> |
| |
| <ul> |
| <li>Figure out where in the busybox source tree your applet best fits, |
| and put your source code there. Be sure to use APPLET_main() instead |
| of main(), where APPLET is the name of your applet.</li> |
| |
| <li>Add your applet to the relevant Config.in file (which file you add |
| it to determines where it shows up in "make menuconfig"). This uses |
| the same general format as the linux kernel's configuration system.</li> |
| |
| <li>Add your applet to the relevant Makefile.in file (in the same |
| directory as the Config.in you chose), using the existing entries as a |
| template and the same CONFIG symbol as you used for Config.in. (Don't |
| forget "needlibm" or "needcrypt" if your applet needs libm or |
| libcrypt.)</li> |
| |
| <li>Add your applet to "include/applets.h", using one of the existing |
| entries as a template. (Note: this is in alphabetical order. Applets |
| are found via binary search, and if you add an applet out of order it |
| won't work.)</li> |
| |
| <li>Add your applet's runtime help text to "include/usage.h". You need |
| at least appname_trivial_usage (the minimal help text, always included |
| in the busybox binary when this applet is enabled) and appname_full_usage |
| (extra help text included in the busybox binary with |
| CONFIG_FEATURE_VERBOSE_USAGE is enabled), or it won't compile. |
| The other two help entry types (appname_example_usage and |
| appname_notes_usage) are optional. They don't take up space in the binary, |
| but instead show up in the generated documentation (BusyBox.html, |
| BusyBox.txt, and the man page BusyBox.1).</li> |
| |
| <li>Run menuconfig, switch your applet on, compile, test, and fix the |
| bugs. Be sure to try both "allyesconfig" and "allnoconfig" (and |
| "allbareconfig" if relevant).</li> |
| |
| </ul> |
| |
| <hr /> |
| <h2><a name="standards">What standards does busybox adhere to?</a></h2> |
| |
| <p>The standard we're paying attention to is the "Shell and Utilities" |
| portion of the <a href="http://www.opengroup.org/onlinepubs/009695399/">Open |
| Group Base Standards</a> (also known as the Single Unix Specification version |
| 3 or SUSv3). Note that paying attention isn't necessarily the same thing as |
| following it.</p> |
| |
| <p>SUSv3 doesn't even mention things like init, mount, tar, or losetup, nor |
| commonly used options like echo's '-e' and '-n', or sed's '-i'. Busybox is |
| driven by what real users actually need, not the fact the standard believes |
| we should implement ed or sccs. For size reasons, we're unlikely to include |
| much internationalization support beyond UTF-8, and on top of all that, our |
| configuration menu lets developers chop out features to produce smaller but |
| very non-standard utilities.</p> |
| |
| <p>Also, Busybox is aimed primarily at Linux. Unix standards are interesting |
| because Linux tries to adhere to them, but portability to dozens of platforms |
| is only interesting in terms of offering a restricted feature set that works |
| everywhere, not growing dozens of platform-specific extensions. Busybox |
| should be portable to all hardware platforms Linux supports, and any other |
| similar operating systems that are easy to do and won't require much |
| maintenance.</p> |
| |
| <p>In practice, standards compliance tends to be a clean-up step once an |
| applet is otherwise finished. When polishing and testing a busybox applet, |
| we ensure we have at least the option of full standards compliance, or else |
| document where we (intentionally) fall short.</p> |
| |
| <hr /> |
| <h2><a name="portability">Portability.</a></h2> |
| |
| <p>Busybox is a Linux project, but that doesn't mean we don't have to worry |
| about portability. First of all, there are different hardware platforms, |
| different C library implementations, different versions of the kernel and |
| build toolchain... The file "include/platform.h" exists to centralize and |
| encapsulate various platform-specific things in one place, so most busybox |
| code doesn't have to care where it's running.</p> |
| |
| <p>To start with, Linux runs on dozens of hardware platforms. We try to test |
| each release on x86, x86-64, arm, power pc, and mips. (Since qemu can handle |
| all of these, this isn't that hard.) This means we have to care about a number |
| of portability issues like endianness, word size, and alignment, all of which |
| belong in platform.h. That header handles conditional #includes and gives |
| us macros we can use in the rest of our code. At some point in the future |
| we might grow a platform.c, possibly even a platform subdirectory. As long |
| as the applets themselves don't have to care.</p> |
| |
| <p>On a related note, we made the "default signedness of char varies" problem |
| go away by feeding the compiler -funsigned-char. This gives us consistent |
| behavior on all platforms, and defaults to 8-bit clean text processing (which |
| gets us halfway to UTF-8 support). NOMMU support is less easily separated |
| (see the tips section later in this document), but we're working on it.</p> |
| |
| <p>Another type of portability is build environments: we unapologetically use |
| a number of gcc and glibc extensions (as does the Linux kernel), but these have |
| been picked up by packages like uClibc, TCC, and Intel's C Compiler. As for |
| gcc, we take advantage of newer compiler optimizations to get the smallest |
| possible size, but we also regression test against an older build environment |
| using the Red Hat 9 image at "http://busybox.net/downloads/qemu". This has a |
| 2.4 kernel, gcc 3.2, make 3.79.1, and glibc 2.3, and is the oldest |
| build/deployment environment we still put any effort into maintaining. (If |
| anyone takes an interest in older kernels you're welcome to submit patches, |
| but the effort would probably be better spent |
| <a href="http://www.selenic.com/linux-tiny/">trimming |
| down the 2.6 kernel</a>.) Older gcc versions than that are uninteresting since |
| we now use c99 features, although |
| <a href="http://fabrice.bellard.free.fr/tcc/">tcc</a> might be worth a |
| look.</p> |
| |
| <p>We also test busybox against the current release of uClibc. Older versions |
| of uClibc aren't very interesting (they were buggy, and uClibc wasn't really |
| usable as a general-purpose C library before version 0.9.26 anyway).</p> |
| |
| <p>Other unix implementations are mostly uninteresting, since Linux binaries |
| have become the new standard for portable Unix programs. Specifically, |
| the ubiquity of Linux was cited as the main reason the Intel Binary |
| Compatability Standard 2 died, by the standards group organized to name a |
| successor to ibcs2: <a href="http://www.telly.org/86open/">the 86open |
| project</a>. That project disbanded in 1999 with the endorsement of an |
| existing standard: Linux ELF binaries. Since then, the major players at the |
| time (such as <a |
| href="http://www-03.ibm.com/servers/aix/products/aixos/linux/index.html">AIX</a>, <a |
| href="http://www.sun.com/software/solaris/ds/linux_interop.jsp#3">Solaris</a>, and |
| <a href="http://www.onlamp.com/pub/a/bsd/2000/03/17/linuxapps.html">FreeBSD</a>) |
| have all either grown Linux support or folded.</p> |
| |
| <p>The major exceptions are newcomer MacOS X, some embedded environments |
| (such as newlib+libgloss) which provide a posix environment but not a full |
| Linux environment, and environments like Cygwin that provide only partial Linux |
| emulation. Also, some embedded Linux systems run a Linux kernel but amputate |
| things like the /proc directory to save space.</p> |
| |
| <p>Supporting these systems is largely a question of providing a clean subset |
| of BusyBox's functionality -- whichever applets can easily be made to |
| work in that environment. Annotating the configuration system to |
| indicate which applets require which prerequisites (such as procfs) is |
| also welcome. Other efforts to support these systems (swapping #include |
| files to build in different environments, adding adapter code to platform.h, |
| adding more extensive special-case supporting infrastructure such as mount's |
| legacy mtab support) are handled on a case-by-case basis. Support that can be |
| cleanly hidden in platform.h is reasonably attractive, and failing that |
| support that can be cleanly separated into a separate conditionally compiled |
| file is at least worth a look. Special-case code in the body of an applet is |
| something we're trying to avoid.</p> |
| |
| <hr /> |
| <h2><a name="tips">Programming tips and tricks.</a></h2> |
| |
| <p>Various things busybox uses that aren't particularly well documented |
| elsewhere.</p> |
| |
| <hr /> |
| <h2><a name="tips_encrypted_passwords">Encrypted Passwords</a></h2> |
| |
| <p>Password fields in /etc/passwd and /etc/shadow are in a special format. |
| If the first character isn't '$', then it's an old DES style password. If |
| the first character is '$' then the password is actually three fields |
| separated by '$' characters:</p> |
| <pre> |
| <b>$type$salt$encrypted_password</b> |
| </pre> |
| |
| <p>The "type" indicates which encryption algorithm to use: 1 for MD5 and 2 for SHA1.</p> |
| |
| <p>The "salt" is a bunch of ramdom characters (generally 8) the encryption |
| algorithm uses to perturb the password in a known and reproducible way (such |
| as by appending the random data to the unencrypted password, or combining |
| them with exclusive or). Salt is randomly generated when setting a password, |
| and then the same salt value is re-used when checking the password. (Salt is |
| thus stored unencrypted.)</p> |
| |
| <p>The advantage of using salt is that the same cleartext password encrypted |
| with a different salt value produces a different encrypted value. |
| If each encrypted password uses a different salt value, an attacker is forced |
| to do the cryptographic math all over again for each password they want to |
| check. Without salt, they could simply produce a big dictionary of commonly |
| used passwords ahead of time, and look up each password in a stolen password |
| file to see if it's a known value. (Even if there are billions of possible |
| passwords in the dictionary, checking each one is just a binary search against |
| a file only a few gigabytes long.) With salt they can't even tell if two |
| different users share the same password without guessing what that password |
| is and decrypting it. They also can't precompute the attack dictionary for |
| a specific password until they know what the salt value is.</p> |
| |
| <p>The third field is the encrypted password (plus the salt). For md5 this |
| is 22 bytes.</p> |
| |
| <p>The busybox function to handle all this is pw_encrypt(clear, salt) in |
| "libbb/pw_encrypt.c". The first argument is the clear text password to be |
| encrypted, and the second is a string in "$type$salt$password" format, from |
| which the "type" and "salt" fields will be extracted to produce an encrypted |
| value. (Only the first two fields are needed, the third $ is equivalent to |
| the end of the string.) The return value is an encrypted password in |
| /etc/passwd format, with all three $ separated fields. It's stored in |
| a static buffer, 128 bytes long.</p> |
| |
| <p>So when checking an existing password, if pw_encrypt(text, |
| old_encrypted_password) returns a string that compares identical to |
| old_encrypted_password, you've got the right password. When setting a new |
| password, generate a random 8 character salt string, put it in the right |
| format with sprintf(buffer, "$%c$%s", type, salt), and feed buffer as the |
| second argument to pw_encrypt(text,buffer).</p> |
| |
| <hr /> |
| <h2><a name="tips_vfork">Fork and vfork</a></h2> |
| |
| <p>On systems that haven't got a Memory Management Unit, fork() is unreasonably |
| expensive to implement (and sometimes even impossible), so a less capable |
| function called vfork() is used instead. (Using vfork() on a system with an |
| MMU is like pounding a nail with a wrench. Not the best tool for the job, but |
| it works.)</p> |
| |
| <p>Busybox hides the difference between fork() and vfork() in |
| libbb/bb_fork_exec.c. If you ever want to fork and exec, use bb_fork_exec() |
| (which returns a pid and takes the same arguments as execve(), although in |
| this case envp can be NULL) and don't worry about it. This description is |
| here in case you want to know why that does what it does.</p> |
| |
| <p>Implementing fork() depends on having a Memory Management Unit. With an |
| MMU then you can simply set up a second set of page tables and share the |
| physical memory via copy-on-write. So a fork() followed quickly by exec() |
| only copies a few pages of the parent's memory, just the ones it changes |
| before freeing them.</p> |
| |
| <p>With a very primitive MMU (using a base pointer plus length instead of page |
| tables, which can provide virtual addresses and protect processes from each |
| other, but no copy on write) you can still implement fork. But it's |
| unreasonably expensive, because you have to copy all the parent process' |
| memory into the new process (which could easily be several megabytes per fork). |
| And you have to do this even though that memory gets freed again as soon as the |
| exec happens. (This is not just slow and a waste of space but causes memory |
| usage spikes that can easily cause the system to run out of memory.)</p> |
| |
| <p>Without even a primitive MMU, you have no virtual addresses. Every process |
| can reach out and touch any other process' memory, because all pointers are to |
| physical addresses with no protection. Even if you copy a process' memory to |
| new physical addresses, all of its pointers point to the old objects in the |
| old process. (Searching through the new copy's memory for pointers and |
| redirect them to the new locations is not an easy problem.)</p> |
| |
| <p>So with a primitive or missing MMU, fork() is just not a good idea.</p> |
| |
| <p>In theory, vfork() is just a fork() that writeably shares the heap and stack |
| rather than copying it (so what one process writes the other one sees). In |
| practice, vfork() has to suspend the parent process until the child does exec, |
| at which point the parent wakes up and resumes by returning from the call to |
| vfork(). All modern kernel/libc combinations implement vfork() to put the |
| parent to sleep until the child does its exec. There's just no other way to |
| make it work: the parent has to know the child has done its exec() or exit() |
| before it's safe to return from the function it's in, so it has to block |
| until that happens. In fact without suspending the parent there's no way to |
| even store separate copies of the return value (the pid) from the vfork() call |
| itself: both assignments write into the same memory location.</p> |
| |
| <p>One way to understand (and in fact implement) vfork() is this: imagine |
| the parent does a setjmp and then continues on (pretending to be the child) |
| until the exec() comes around, then the _exec_ does the actual fork, and the |
| parent does a longjmp back to the original vfork call and continues on from |
| there. (It thus becomes obvious why the child can't return, or modify |
| local variables it doesn't want the parent to see changed when it resumes.) |
| |
| <p>Note a common mistake: the need for vfork doesn't mean you can't have two |
| processes running at the same time. It means you can't have two processes |
| sharing the same memory without stomping all over each other. As soon as |
| the child calls exec(), the parent resumes.</p> |
| |
| <p>If the child's attempt to call exec() fails, the child should call _exit() |
| rather than a normal exit(). This avoids any atexit() code that might confuse |
| the parent. (The parent should never call _exit(), only a vforked child that |
| failed to exec.)</p> |
| |
| <p>(Now in theory, a nommu system could just copy the _stack_ when it forks |
| (which presumably is much shorter than the heap), and leave the heap shared. |
| Even with no MMU at all |
| In practice, you've just wound up in a multi-threaded situation and you can't |
| do a malloc() or free() on your heap without freeing the other process' memory |
| (and if you don't have the proper locking for being threaded, corrupting the |
| heap if both of you try to do it at the same time and wind up stomping on |
| each other while traversing the free memory lists). The thing about vfork is |
| that it's a big red flag warning "there be dragons here" rather than |
| something subtle and thus even more dangerous.)</p> |
| |
| <hr /> |
| <h2><a name="tips_sort_read">Short reads and writes</a></h2> |
| |
| <p>Busybox has special functions, bb_full_read() and bb_full_write(), to |
| check that all the data we asked for got read or written. Is this a real |
| world consideration? Try the following:</p> |
| |
| <pre>while true; do echo hello; sleep 1; done | tee out.txt</pre> |
| |
| <p>If tee is implemented with bb_full_read(), tee doesn't display output |
| in real time but blocks until its entire input buffer (generally a couple |
| kilobytes) is read, then displays it all at once. In that case, we _want_ |
| the short read, for user interface reasons. (Note that read() should never |
| return 0 unless it has hit the end of input, and an attempt to write 0 |
| bytes should be ignored by the OS.)</p> |
| |
| <p>As for short writes, play around with two processes piping data to each |
| other on the command line (cat bigfile | gzip > out.gz) and suspend and |
| resume a few times (ctrl-z to suspend, "fg" to resume). The writer can |
| experience short writes, which are especially dangerous because if you don't |
| notice them you'll discard data. They can also happen when a system is under |
| load and a fast process is piping to a slower one. (Such as an xterm waiting |
| on x11 when the scheduler decides X is being a CPU hog with all that |
| text console scrolling...)</p> |
| |
| <p>So will data always be read from the far end of a pipe at the |
| same chunk sizes it was written in? Nope. Don't rely on that. For one |
| counterexample, see <a href="http://www.faqs.org/rfcs/rfc896.html">rfc 896 |
| for Nagle's algorithm</a>, which waits a fraction of a second or so before |
| sending out small amounts of data through a TCP/IP connection in case more |
| data comes in that can be merged into the same packet. (In case you were |
| wondering why action games that use TCP/IP set TCP_NODELAY to lower the latency |
| on their their sockets, now you know.)</p> |
| |
| <hr /> |
| <h2><a name="tips_memory">Memory used by relocatable code, PIC, and static linking.</a></h2> |
| |
| <p>The downside of standard dynamic linking is that it results in self-modifying |
| code. Although each executable's pages are mmaped() into a process' address |
| space from the executable file and are thus naturally shared between processes |
| out of the page cache, the library loader (ld-linux.so.2 or ld-uClibc.so.0) |
| writes to these pages to supply addresses for relocatable symbols. This |
| dirties the pages, triggering copy-on-write allocation of new memory for each |
| processes' dirtied pages.</p> |
| |
| <p>One solution to this is Position Independent Code (PIC), a way of linking |
| a file so all the relocations are grouped together. This dirties fewer |
| pages (often just a single page) for each process' relocations. The down |
| side is this results in larger executables, which take up more space on disk |
| (and a correspondingly larger space in memory). But when many copies of the |
| same program are running, PIC dynamic linking trades a larger disk footprint |
| for a smaller memory footprint, by sharing more pages.</p> |
| |
| <p>A third solution is static linking. A statically linked program has no |
| relocations, and thus the entire executable is shared between all running |
| instances. This tends to have a significantly larger disk footprint, but |
| on a system with only one or two executables, shared libraries aren't much |
| of a win anyway.</p> |
| |
| <p>You can tell the glibc linker to display debugging information about its |
| relocations with the environment variable "LD_DEBUG". Try |
| "LD_DEBUG=help /bin/true" for a list of commands. Learning to interpret |
| "LD_DEBUG=statistics cat /proc/self/statm" could be interesting.</p> |
| |
| <p>For more on this topic, here's Rich Felker:</p> |
| <blockquote> |
| <p>Dynamic linking (without fixed load addresses) fundamentally requires |
| at least one dirty page per dso that uses symbols. Making calls (but |
| never taking the address explicitly) to functions within the same dso |
| does not require a dirty page by itself, but will with ELF unless you |
| use -Bsymbolic or hidden symbols when linking.</p> |
| |
| <p>ELF uses significant additional stack space for the kernel to pass all |
| the ELF data structures to the newly created process image. These are |
| located above the argument list and environment. This normally adds 1 |
| dirty page to the process size.</p> |
| |
| <p>The ELF dynamic linker has its own data segment, adding one or more |
| dirty pages. I believe it also performs relocations on itself.</p> |
| |
| <p>The ELF dynamic linker makes significant dynamic allocations to manage |
| the global symbol table and the loaded dso's. This data is never |
| freed. It will be needed again if libdl is used, so unconditionally |
| freeing it is not possible, but normal programs do not use libdl. Of |
| course with glibc all programs use libdl (due to nsswitch) so the |
| issue was never addressed.</p> |
| |
| <p>ELF also has the issue that segments are not page-aligned on disk. |
| This saves up to 4k on disk, but at the expense of using an additional |
| dirty page in most cases, due to a large portion of the first data |
| page being filled with a duplicate copy of the last text page.</p> |
| |
| <p>The above is just a partial list of the tiny memory penalties of ELF |
| dynamic linking, which eventually add up to quite a bit. The smallest |
| I've been able to get a process down to is 8 dirty pages, and the |
| above factors seem to mostly account for it (but some were difficult |
| to measure).</p> |
| </blockquote> |
| |
| <hr /> |
| <h2><a name="tips_kernel_headers"></a>Including kernel headers</h2> |
| |
| <p>The "linux" or "asm" directories of /usr/include |
| contain Linux kernel |
| headers, so that the C library can talk directly to the Linux kernel. In |
| a perfect world, applications shouldn't include these headers directly, but |
| we don't live in a perfect world.</p> |
| |
| <p>For example, Busybox's losetup code wants linux/loop.c because nothing else |
| #defines the structures to call the kernel's loopback device setup ioctls. |
| Attempts to cut and paste the information into a local busybox header file |
| proved incredibly painful, because portions of the loop_info structure vary by |
| architecture, namely the type __kernel_dev_t has different sizes on alpha, |
| arm, x86, and so on. Meaning we either #include <linux/posix_types.h> or |
| we hardwire #ifdefs to check what platform we're building on and define this |
| type appropriately for every single hardware architecture supported by |
| Linux, which is simply unworkable.</p> |
| |
| <p>This is aside from the fact that the relevant type defined in |
| posix_types.h was renamed to __kernel_old_dev_t during the 2.5 series, so |
| to cut and paste the structure into our header we have to #include |
| <linux/version.h> to figure out which name to use. (What we actually |
| do is |
| check if we're building on 2.6, and if so just use the new 64 bit structure |
| instead to avoid the rename entirely.) But we still need the version |
| check, since 2.4 didn't have the 64 bit structure.</p> |
| |
| <p>The BusyBox developers spent <u>two years</u> trying to figure |
| out a clean way to do all this. There isn't one. The losetup in the |
| util-linux package from kernel.org isn't doing it cleanly either, they just |
| hide the ugliness by nesting #include files. Their mount/loop.h |
| #includes "my_dev_t.h", which #includes <linux/posix_types.h> |
| and <linux/version.h> just like we do. There simply is no alternative. |
| </p> |
| |
| <p>Just because directly #including kernel headers is sometimes |
| unavoidable doesn't me we should include them when there's a better |
| way to do it. However, block copying information out of the kernel headers |
| is not a better way.</p> |
| |
| <hr /> |
| <h2><a name="who">Who are the BusyBox developers?</a></h2> |
| |
| <p>The following login accounts currently exist on busybox.net. (I.E. these |
| people can commit <a href="http://busybox.net/downloads/patches/">patches</a> |
| into subversion for the BusyBox, uClibc, and buildroot projects.)</p> |
| |
| <pre> |
| aldot :Bernhard Reutner-Fischer |
| andersen :Erik Andersen - uClibc and BuildRoot maintainer. |
| bug1 :Glenn McGrath |
| davidm :David McCullough |
| gkajmowi :Garrett Kajmowicz - uClibc++ maintainer |
| jbglaw :Jan-Benedict Glaw |
| jocke :Joakim Tjernlund |
| landley :Rob Landley |
| lethal :Paul Mundt |
| mjn3 :Manuel Novoa III |
| osuadmin :osuadmin |
| pgf :Paul Fox |
| pkj :Peter Kjellerstedt |
| prpplague :David Anders |
| psm :Peter S. Mazinger |
| russ :Russ Dill |
| sandman :Robert Griebl |
| sjhill :Steven J. Hill |
| solar :Ned Ludd |
| timr :Tim Riker |
| tobiasa :Tobias Anderberg |
| vapier :Mike Frysinger |
| vda :Denys Vlasenko - BusyBox maintainer |
| </pre> |
| |
| <p>The following accounts used to exist on busybox.net, but don't anymore so |
| I can't ask /etc/passwd for their names. Rob Wentworth |
| <robwen at gmail.com> asked Google and recovered the names:</p> |
| |
| <pre> |
| aaronl :Aaron Lehmann |
| beppu :John Beppu |
| dwhedon :David Whedon |
| erik :Erik Andersen |
| gfeldman :Gennady Feldman |
| jimg :Jim Gleason |
| kraai :Matt Kraai |
| markw :Mark Whitley |
| miles :Miles Bader |
| proski :Pavel Roskin |
| rjune :Richard June |
| tausq :Randolph Chung |
| vodz :Vladimir N. Oleynik |
| </pre> |
| |
| |
| <br> |
| <br> |
| <br> |
| |
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