www/faq.html - third_party/toybox - Git at Google

 <html><head><title>toybox news</title>
 <!--#include file="header.html" -->

 <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>

 <!--#include file="footer.html" -->
	<html><head><title>toybox news</title>
	<!--#include file="header.html" -->

	<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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