Presentation: "Emdedded distro shootout: buildroot vs. Debian" - Mind

Emdebbed distro shootout:
Debian vs Buildroot
© 2013 Essensium N.V.
Parts © Thomas Petazzoni, Free Electrons
This work is licensed under a
Creative Commons Attribution-ShareAlike 3.0
Unported License
http://www.mind.be/content/Presentation_Emdedded-distro-shootout.pdf

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Emdebbed distro shootout:
Debian vs Buildroot
© 2013 Essensium N.V.
Parts © Thomas Petazzoni, Free Electrons
This work is licensed under a
Creative Commons Attribution-ShareAlike 3.0
Unported License
http://www.mind.be/content/Buildroot-vs-Debian.pdf

Debian vs Buildroot
1.Embedded systems are different
2.How to use Debian
for embedded systems
3.How to use buildroot

Why are embedded systems different
●
Controllable
– fine-tune services configuration
– fast boot
– custom kernel
●
Reproducible
– re-create after a year
– different copies as much as possible alike
●
●
Small (128MB Flash, 1GB eMMC)
Non-x86 processor (ARM, PowerPC, MIPS, ARC,
Xtensa, Blackfin, Microblaze)

Why are embedded systems different
●
Controllable
– fine-tune services configuration
– fast boot
– custom kernel
Linux
from
Scratch
●
Reproducible
– re-create after a year
– different copies as much as possible alike
●
●
Small (128MB Flash, 1GB eMMC)
Non-x86 processor (ARM, PowerPC, MIPS, ARC,
Xtensa, Blackfin, Microblaze)

System build infrastructure
is needed for fast deployment
●
●
●
●
●
●
●
Initial default deployment in no time
Fast building
Easy to change configuration
Share with colleagues
Reproducible
Produce a distributable image
(for production and for upgrade)
Easy to add new (custom) packages

Embedded development with Debian
●
●
●
●
Start with installer or minimal tar, play around with it,
see if your application works
Reuse bootloader and kernel from vendor
Install to permanent media, keeping track of all the
modifications you made
Create an image creator script
Write image to target

Creating a Debian image
●
●
●
●
●
pdebuild custom packages
debootstrap target root directory
chroot install required packages
make filesystem modifications
create target image file

Cross-creating a Debian image
●
●
debootstrap cross-build root directory
qemu-boot
●
install build-required packages
●
build custom packages
●
●
●
●
debootstrap target root directory
qemu-boot install required packages
make filesystem modifications
create target image file

Cross-creating a Debian image
● multistrap cross-build root directory
● qemu-boot
Simplified with
●
install build-required packages scratchbox2
●
build custom packages
● multistrap target root directory
● qemu-boot install required packages
● make filesystem modifications
● create target image file

Problems with Debian for embedded
●
●
●
●
●
Cross compilation
No exotic architectures (blackfin, xtensa)
Results in a large system (>100MB)
Not reproducible
Not very controllable

Cross-compilation issues
●
●
Fake native build with qemu
cross-compilation toolchain is hard to use
– Need cross-build-depends installed
– Will be solved with multiarch in Emdebian 3.0
●
some packages need to be patched for crosscompilation

Debian results in a large system
●
●
●
●
Minimal install > 100MB
Remove documentation, translations, …
Remove “essential” packages: perl
Split packages more aggressively
Remove dpkg support files
Still more than 20MB for minimal system

Emdebian: debian for embedded

Emdebian: Debian for embedded
Goals
●
Make smaller Debian
– 100MB → 20MB
●
Support cross-building

Emdebian: Debian for embedded
Tools
●
●
●
●
●
●
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xcontrol files that produce smaller packages
Tools to automatically create xcontrol files
Separate packages for translations
Emdebian-specific 'Required' & 'Essential' packages
Debian packages for cross-compilation toolchains
Tools supporting cross-installation
dpkg-cross, xapt, pdebuild-cross
Many emdebian tools creep into core debian

Debian builds are not reproducible
Packages are removed from debian.org
when updates are available
● Use snapshot.debian.org or
●
Create a local cache (including source & build-deps!)
Create a top-level build script for custom packages

Debian is not very controllable
●
●
●
Predefined configuration choices
⇒ Build from source, modify debian/rules, …
Difficult to integrate fixes or new features
⇒ Get package from unstable/experimental
⇒ Build from source, with additional patches
System integration (initialization scripts, package dependencies)
⇒ Add/remove files from generated rootfs
But additional complexity to understand them
Various tools: kernel-package, initramfs-tools, fsprotect, …
⇒ Learn to be a system administrator

System build infrastructure
is needed for fast deployment
●
●
●
●
●
●
●
Initial default deployment in no time
Fast building
Easy to change configuration
Share with colleagues
Reproducible
Produce a distributable image
(for production and for upgrade)
Easy to add new (custom) packages

http://buildroot.org
●
●
●
Kconfig-based interactive configuration
Makefile-based build system
Download, patch, build and install
– Toolchain (compiler, library)
– Packages + dependencies
– Boot loader (U-Boot, barebox, grub, ...)
– Linux kernel
– Host tools (openocd, dfu-util, ...)
● Create root filesystem (ext2, jffs2, ubi, ...)

Buildroot has a simple workflow
/etc/init.d/S80startapp
/etc/network/interfaces
Makefiles
Kconfigs
patches make xconfig;
make
libraries
kernel
packages
root
filesystem
Image © Marcello Jo

Buildroot deploys on EVM
in no time

Buildroot makes it easy
to change the configuration

Buildroot makes it easy
to change the configuration
make linux-xconfig

Buildroot makes it easy
to share with colleagues
Set BR2_DEFCONFIG and BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE
make update-all-config

Buildroot is reproducible
●
Configuration files (make update-all-config)
are all that is needed to re-create
exactly the same build
●
Sources can be collected with make source
●
Licenses can be collected with make legal-info

Buildroot makes it easy
to hack a package
LINUX_OVERRIDE_SRCDIR = /home/arnout/src/linux
make linux-rebuild

Buildroot makes it easy
package/foo/foo.mk
to add packages
BR2_PACKAGE_FOO = y
FOO_OVERRIDE_SRCDIR = …/foo
FOO_DEPENDENCIES = opencv libusb
define FOO_BUILD_CMDS
$(TARGET_CONFIGURE_OPTS) $(MAKE) -C $(@D)
endef
define FOO_INSTALL_TARGET_CMDS
$(INSTALL) -D -m 0755 $(@D)/foo \
$(TARGET_DIR)/usr/bin/foo
endef
$(eval $(generic-package))

Buildroot makes it easy
to cross-compile your source
Use /output/host/usr/-gcc
as the cross-compiler
– Automatically uses cross-include and library paths
– Use /output/host/usr/pkg-config
to get package-specific CFLAGS and LDFLAGS
Cross-build environment can be shared
by setting BR2_HOST_DIR

●
Documentation:
– make help
– make manual
Buildroot has good support
– http://buildroot.net/downloads/manual/manual.html
●
Mailing list:
– buildroot@busybox.net
– 40 mails per day (mostly patches)
●
●
●
20 new packages per month
Release every 3 months
buildroot-2013.2-rc1 shortly after FOSDEM
Automatic tests: 100 random builds per day

A range of distro options for embedded
Buildroot
No package management
Upgrades are system-wide
Fixed-functionality systems
PtxDist
OpenWRT
OpenEmbedded
Yocto
Runtime package management
Upgrades are per-package
Functionality is dynamically added
Gentoo
Debian
Root filesystem
generator
Distribution
generator
Distribution

Problems with buildroot
●
●
●
●
●
No live CD
Large number of config options
is a bit overwhelming at first
Only 946 packages, vs. 18773 in Debian sid
No binary packages
⇒ build sometimes takes longer
No package management
⇒ can only remove a package with a clean rebuild

Choosing Debian or Buildroot
●
●
●
●
●
Full distro is nice to get started
if live CD or preinstalled image is available
Reuse vendor-provided bootloader and kernel
Debian is useful to play around with packages
that are not (yet) integrated into buildroot
Emdebian makes good progress for cross-building,
but still a long way to go
In many cases, buildroot is smaller & easier

Bringing up your device is easy
with Buildroot

www.mind.be
www.essensium.com
Essensium NV
Mind - Embedded Software Division
Gaston Geenslaan 9, B-3001 Leuven
Tel : +32 16-28 65 00
Fax : +32 16-28 65 01
email : info@essensium.com