toybox/www/faq.html

<html><head><title>toybox news</title>
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<ul>
<li><h2><a href="#capitalize">Do you capitalize toybox?</a></h2></li>
<li><h2><a href="#why_toybox">Why toybox? (What was wrong with busybox?)</a></h2></li>
<li><h2><a href="#support_horizon">Why a 7 year support horizon?</a></h2></li>
<li><h2><a href="#code">Where do I start understanding the toybox source code?</a></h2></li>
</ul>

<a name="capitalize" />
<h2>Q: Do you capitalize toybox?</h2>

<p>A: Only at the start of a sentence. The command name is all lower case so
it seems silly to capitalize the project name, but not capitalizing the
start of sentences is awkward, so... compromise. (It is _not_ "ToyBox".)</p>

<a name="why_toybox" />
<h2>Q: "Why is there toybox? What was wrong with busybox?"</h2>

<p>A: Toybox started back in 2006 when I
<a href=https://lwn.net/Articles/202106/>handed off BusyBox maintainership</a>
and <a href=http://landley.net/notes-2006.html#28-09-2006>started over from
scratch</a> on a new codebase after a
<a href=http://lists.busybox.net/pipermail/busybox/2006-September/058617.html>protracted licensing argument</a> took all the fun out of working on BusyBox.</p>

<p>Toybox was just a personal project until it got
<a href=http://landley.net/notes-2011.html#13-11-2011>relaunched
in November 2011</a> with a new goal to
<a href=http://landley.net/aboriginal/about.html#selfhost>make Android
self-hosting</a>. This involved me relicensing my own
code, which <a href=https://lwn.net/Articles/478308/>made people who had
never used or participated in the project loudly angry</a>. The switch came
after a lot of thinking <a href=http://landley.net/talks/ohio-2013.txt>about
licenses</a> and <a href=http://landley.net/notes-2011.html#21-03-2011>the
transition to smartphones</a>, which led to a
<a href=http://landley.net/talks/celf-2013.txt>2013</a>
<a href=https://www.youtube.com/watch?v=SGmtP5Lg_t0>talk</a> laying
out a strategy to make Android self-hosting using toybox. This helped
<a href=https://code.google.com/p/android/issues/detail?id=76861>bring
it to Android's attention</a>, and they
<a href=https://lwn.net/Articles/629362/>merged it</a> into Android M.</p>

<p>The answer to the second question is "licensing". BusyBox predates Android
by almost a decade but Android still doesn't ship with it because GPLv3 came
out around the same time Android did and caused many people to throw
out the GPLv2 baby with the GPLv3 bathwater.
Android <a href=https://source.android.com/source/licenses.html>explicitly
discourages</a> use of GPL and LGPL licenses in its products, and has gradually
reimplemented historical GPL components such as its bluetooth stack under the
Apache license. Similarly, Apple froze xcode at the last GPLv2 releases
(GCC 4.2.1 with binutils 2.17) for over 5 years while it sponsored the
development of new projects (clang/llvm/lld) to replace them,
implemented its SMB server from scratch to replace samba,
<a href=http://meta.ath0.com/2012/02/05/apples-great-gpl-purge/>and so
on</a>. Toybox itself exists because somebody with in a legacy position
just wouldn't shut up about GPLv3, otherwise I would probably
still happily be maintaining BusyBox. (For more on how I wound
up working on busybox in the first place,
<a href=http://landley.net/aboriginal/history.html>see here</a>.)</p>

<h2><a name="support_horizon">Q: Why a 7 year support horizon?</a></h2>

<p>A: Our <a href=http://lists.busybox.net/pipermail/busybox/2006-September/058440.html>longstanding rule of thumb</a> is to try to run and build on
hardware and distributions released up to 7 years ago, and feel ok dropping
support for stuff older than that. (This is a little longer than Ubuntu's
Long Term Support, but not by much.)</p>

<p>If a kernel or libc feature is less than 7 years old, I try to have a
build-time configure test for it and let the functionality cleanly drop out.
I also keep old Ubuntu images around in VMs and perform the occasional
defconfig build there to see what breaks. (I'm not perfect about this,
but I accept bug reports.)</p>

<p>My original theory was "4 to 5 18-month cycles of moore's law should cover
the vast majority of the installed base of PC hardware", loosely based on some
research I did <a href=http://www.catb.org/esr/halloween/halloween9.html#id2867629>back in 2003</a>
and <a href=http://catb.org/esr/writings/world-domination/world-domination-201.html#id248066>updated in 2006</a>
which said that low end systems were 2 iterations of moore's
law below the high end systems, and that another 2-3 iterations should cover
the useful lifetime of most systems no longer being sold but still in use and
potentially being upgraded to new software releases.</p>

<p>It turns out <a href=http://landley.net/notes-2011.html#26-06-2011>I missed
industry changes</a> in the 1990's that stretched the gap
from low end to high end from 2 cycles to 4 cycles, and _that_ analysis
ignored the switch from PC to smartphone cutting off the R&D air supply of the
laptop market.  Meanwhile the Moore's Law s-curve started bending
down in 2000 and these days is pretty flat because the drive for faster clock
speeds <a href=http://www.anandtech.com/show/613>stumbled</a>
then <a href=http://www.pcworld.com/article/118603/article.html>died</a>, and
the subsequent drive to go wide maxed out around 4x SMP with ~2 megabyte
caches for most applications. These days the switch from exponential to
linear growth in hardware capabilities is
<a href=https://www.cnet.com/news/end-of-moores-law-its-not-just-about-physics/>common</a>
<a href=http://www.acm.org/articles/people-of-acm/2016/david-patterson>knowledge</a>.</p>

<p>But the 7 year rule of thumb stuck around anyway: if a kernel or libc
feature is less than 7 years old, I try to have a build-time configure test
for it and let the functionality cleanly drop out. I also keep old Ubuntu
images around in VMs and perform the occasional defconfig build there to
see what breaks.</p>

<h2><a name="code" />Where do I start understanding the source code?</h2>

<p>Toybox is written in C. There are longer writeups of the
<a href=design.html>design ideas</a> and a <a href=code.html>code walkthrough</a>,
and the <a href=about.html>about page</a> summarizes what we're trying to
accomplish, but here's a quick start:</p>

<p>Toybox uses the standard three stage configure/make/install
<a href=code.html#building>build</a>, in this case "<b>make defconfig;
make; make install</b>". Type "<b>make help</b>" to
see available make targets.</p>

<p><b>The configure stage is copied from the Linux kernel</b> (in the "kconfig"
directory), and saves your selections in the file ".config" at the top
level. The "defconfig" target selects the
maximum sane configuration (enabling all the commands and features that
aren't unfinished, only intended as examples, debug code, etc) and is
probably what you want. You can use "make menuconfig" to manually select
specific commands to include, through an interactive menu (cursor up and
down, enter to descend into a sub-menu, space to select an entry, ? to see
an entry's help text, esc to exit). The menuconfig help text is the
same as the command's --help output.</p>

<p><b>The "make" stage creates a toybox binary</b> (which is stripped, look in
generated/unstripped for the debug versions), and "install" adds a bunch of
symlinks to toybox under the various command names. Toybox determines which
command to run based on the filename, or you can use the "toybox" name in which case the first
argument is the command to run (ala "toybox ls -l"). <b>You can also build
individual commands as standalone executables</b>, ala "make sed cat ls".</p>

<p><b>The main() function is in main.c at the top level</b>,
along with setup plumbing and selecting which command to run this time.
The function toybox_main() implements the "toybox" multiplexer command.</p>

<p><b>The individual command implementations are under "toys"</b>, and are grouped
into categories (mostly based on which standard they come from, posix, lsb,
android...) The "pending" directory contains unfinished commands, and the
"examples" directory contains examples. Commands in those two directories
are _not_ selected by defconfig. (These days pending directory is mostly
third party submissions that have not yet undergone proper code review.)</p>

<p><b>Common infrastructure shared between commands is under "lib"</b>. Most
commands call lib/args.c to parse their command line arguments before calling
the command's own main() function, which uses the option string in
the command's NEWTOY() macro. This is similar to the libc function getopt(),
but more powerful, and is documented at the top of lib/args.c.</p>

<p>Most of the actual <b>build/install infrastructure is shell scripts under
"scripts"</b>. <b>These populate the "generated" directory</b> with headers
created from other files, which are <a href=code.html#generated>described</a>
in the code walkthrough. All the
build's temporary files live under generated, including the .o files built
from the .c files (in generated/obj). The "make clean" target deletes that
directory. ("make distclean" also deletes your .config and deletes the
kconfig binaries that process .config.)</p>

<p>Each command's file contains all the information for that command, so
<b>adding a command to toybox means adding a single file under "toys"</b>.
Usually you <a href=code.html#adding>start a new command</a> by copying an
existing command file to a new filename
(toys/examples/hello.c, toys/examples/skeleton.c, toys/posix/cat.c,
and toys/posix/true.c have all been used for this purpose) and then replacing
all instances of its old name with the new name (which should match the
new filename), and modifying the help text, argument string, and what the
code does. You might have to "make distclean" before you new command
shows up in defconfig or menuconfig.</p>

<p><b>The toybox test suite lives in the "tests" directory</b>. From the top
level you can "make tests" to test everything, or "make test_sed" test a
single command's standalone version (which should behave identically)
but that's why we test.</p>

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