Videos from FOSDEM 2010

Peter Korsgaard presenting Buildroot in the Cross build systems workshop at FOSDEM 2010

Like every year, the Free and Open Source Developer European Meeting took place early February in Brussels, and Thomas Petazzoni, from Bootlin, attended and recorded a few talks from the embedded session. However, contrary to previous years, I haven’t been able to record all talks from the embedded session, since I attended talks from other sessions which were already being recorded by others.

Gian-Carlo Pascutto presenting Embedded software development best practices at FOSDEM 2010

We also attended talks from the and Coreboot developer roooms : videos for the developer room can be found at and videos for the Coreboot developer room can be found at

Buildroot 2010.08 released!

Buildroot logoOn the last day of August, just in time, the 2010.08 version of Buildroot has been released. For the record, Buildroot is an easy-to-use embedded Linux build system: it can build your toolchain, your root filesystem with all its components (Busybox, libraries, applications, etc.), your kernel and your bootloaders, or any combination of these components.

Amongst the interesting changes in this version :

  • Complete rewrite of the bootloader build code. It contained a lot of legacy, unused and unclear stuff, it is now much easier to use and extend. We’ve removed support for Yaboot and added support for the new Barebox bootloader, and all the code to support AT91Bootstrap, AT91DataFlashBoot, U-Boot, Grub and Grub 2 has been rewritten.
  • Complete rewrite of the Linux kernel build code. It was also complicated to use, with an horribly complicated kernel version selection mechanism, the new code is much easier to configure and use.
  • The configuration file .config is now located in the out-of-tree directory when the O= option is used. So typically, for an out-of-tree build (which are very convenient when using the same Buildroot source tree for different projects/tests), you could do : mkdir ~/myoutput ; make O=~/myoutput menuconfig ; make O=~/myoutput
  • Support for building NPTL toolchains with uClibc, using the latest uClibc snapshots.
  • Support for the gconfig Gtk-based configurator, in addition to the already available menuconfig and xconfig
  • A particular effort has been put on fixing many of the bugs in our Bugzilla, improving robustness thanks to automated random builds, and converting even more packages to the generic and autotools infrastructure
  • Various things have also been deprecated: support for the CRIS, IA64, Sparc64 and Alpha architectures, support for Gtk over DirectFB (which is at the moment not supported upstream), Java support (no maintainer has volunteered to maintain this in Buildroot)
  • Many components have been bumped to newer versions
  • The shared configuration cache, which allowed to speed up the configuration of different packages, has been disabled by default, since it was causing a lot of problems with certain package configurations

I’ve again contributed to a significant portion of this release, being the author of the bootloader build code cleanup, the Linux kernel build code rewrite, leading an effort to reduce the number of outstanding bugs in our Bugzilla and many other little things. The contributors for this release are shown below :

   175  Peter Korsgaard
   168  Thomas Petazzoni
    38  Gustavo Zacarias
    18  cmchao
     8  Luca Ceresoli
     7  Paul Jones
     6  Lionel Landwerlin
     6  Malte Starostik
     5  Yann E. MORIN
     3  Julien Boibessot
     3  Khem Raj
     2  Dmytro Milinevskyy
     2  Francois Perrad
     2  Nick Leverton
     2  Peter Huewe
     2  Stanislav Bogatyrev
     1  Baruch Siach
     1  Bjørn Forsman
     1  Daniel Hobi
     1  Darcy Watkins
     1  Darius Augulis
     1  H Hartley Sweeten
     1  Karl Krach
     1  Kelvin Cheung
     1  Ossy
     1  Sagaert Johan
     1  Simon Pasch
     1  Slava Zanko
     1  Thiago A. Correa
     1  Will Wagner
     1  Yegor Yefremov

For the next release, there are already a few things in the pipeline :

  • Cleanup of all the board support code in Buildroot, in order to cleanly add support for more boards like BeagleBoard, Qemu boards, Calao boards, etc. We’ll use the new minimal defconfig mechanism used by the kernel. I’ve already started working on this
  • Cleanup of the package download process, to support Git and SVN download. The code has already been written by Maxime Petazzoni, reviewed on the list, so I expect it to be included fairly soon
  • Rewrite of libtool handling code, to remove some of our ugly libtool hacks. The code is currently being worked on by Lionel Landwerlin
  • Support for compiling toolchain using Crosstool-NG as a backend. The code is currently being finalized by Yann E. Morin, the author of Crosstool-NG
  • Further work on package uninstallation, clean partial rebuild. Some work has been started by Lionel Landwerlin, but it needs some discussion
  • Continue the conversion of packages to the generic and autotools infrastructures
  • I have also a ton of other things on my TODO-list : rework gdb/gdbserver support with external toolchains, rework the configuration of IPv6/RPC/locale/etc. with external toolchains, set up a Wiki-based Buildroot website with tutorials and better documentation, clean up the toolchain build process, reduce the number of “enhancement” bugs waiting in our Bugzilla, etc.

As Peter Korsgaard, Buildroot maintainer, said in the 2010.08 announcement: The next release is going to be 2010.11. Expect the first release candidate in late October and the final release at the end of November..

It is worth noting that we will be having a Buildroot Developer Day, on Friday 29th October, right after Embedded Linux Conference Europe. At least Peter Korsgaard, Lionel Landwerlin, Yann E. Morin and myself should be there.

Linux device drivers architecture talk at Libre Software Meeting

recursive device modelThomas Petazzoni gave a talk on the Linux kernel architecture for device drivers at the Libre Software Meeting in Bordeaux, France. While the talk was given in French, the materials are in English and can therefore benefit a larger audience. The talk seems to have been well-received, especially from people already having a basic Linux kernel development experience. The topics covered are part of our Linux Kernel development training, and are also usually very appreciated from the trainees already having Linux kernel experience.

The idea of the talk is to give an overview of how device drivers fit into the kernel, both to expose their functionality to upper layers (such as a network device driver exposes itself to the kernel network infrastructure) and to detect/access the hardware using the device/driver model, which is quite hard to understand from the source code only.

The talk went through the following sections :

  • First a basic introduction to device drivers: how devices are seen from userspace applications, and how a simple, raw, character driver can be implemented. It allowed to expose the principle of operations and their similarity with methods in object-oriented programming, and the principle of registration to an upper-layer infrastructure
  • Then, an introduction to what I call « kernel frameworks », i.e kernel subsystems that specialize a general device type (i.e character device) into a particular device type (i.e serial port device, framebuffer device, etc.). The talk illustrates this with the framebuffer core and the serial port core.
  • Finally, an explanation about the device model: bus drivers, adapter drivers and device drivers. I started with the example of the USB bus: being a dynamically-enumerated bus, it provides a good illustration of the device model principles. At the end, I explained how the device model works for the devices embedded into a SoC using the platform drivers/devices mechanism

The slides for this talk are no longer available, but their updates are now integrated in our Linux kernel and driver development training materials which are freely available.

Buildroot 2010.05 released: again many Bootlin contributions

Buildroot logoJust one day before the end of May, Buildroot 2010.05 has been released by Peter Korsgaard, as predicted by the fixed release schedule used by the project. It can be downloaded at For the record, Buildroot is a simple and efficient tool to build embedded Linux systems: cross-compiling toolchain, root filesystem, kernel image and bootloader.

Major changes

The major user-visible changes are:

  • Re-organization of the menuconfig layout for packages. All packages are now organized in categories, making them easier to find
  • Our package set has been upgraded to 7.5.
  • Several new packages have been added: cdrkit, cramfs, genext2fs, genromfs, libatomic_ops, librsync, libusb-compat, lmbench, netperf, squashfs, squashfs3, squid. Many of them have been added as the result of a filesystem code generation cleanup
  • On the internal toolchain side (i.e toolchains generated by Buildroot), we have added support for uClibc 0.9.31, GCC 4.4.4, GDB 7.x and binutils 2.20.1.
  • On the external toolchain side (i.e. re-using existing toolchains), we have improved support for multilib toolchains (such as CodeSourcery toolchains)

In addition to these changes, 41 bugs of our bug tracker have been fixed, and dozens of packages have been upgraded or fixed.

Bootlin contributions

Bootlin has again made significant contributions to this release:

git shortlog -s -n 2010.02..
   224  Paulius Zaleckas
   182  Thomas Petazzoni, from Bootlin
   148  Peter Korsgaard
    28  Gustavo Zacarias
    26  Will Wagner
    14  Lionel Landwerlin
     6  Yann E. MORIN

The things we have contributed include:

  • A big cleanup in the Buildroot code that generates the root filesystem images. It has been moved from various directories in target/ to a single, central location: fs/. The code that handled the compilation of host utilities to generate the filesystem images (genext2fs, cdrkit, mtd-utils, cramfs, squashfs, etc.) has been moved to normal packages, and an infrastructure has been added to factorize the common code of the various filesystem generation makefiles.
  • Better support for multilib external toolchains
  • A new script that generates nice dependency graph (see below)
  • A clarification of the gettext integration, to make it work properly with glibc toolchains.
  • Fixes to bug #75, bug #1789.
  • Dozens of build fixes found by testing random configurations.
  • Various code cleanups, that lead to the removal of several configuration options, which makes the usage of Buildroot a little bit easier.

Dependency graph generation

Thanks to the new package infrastructure that we have included in Buildroot a few releases ago, it is now easier to retrieve the list of dependencies of each package in a generic way. Using this, I recently implemented a dependency graph generation tool. It allows to generate nice graphs of the dependencies for a given package, like libgtk2 in the following example (click for the full sized version):

Note that packages in red are packages that do not use the generic or autotools infrastructure, so we couldn’t determine what their dependencies are.

We can also generate the dependency graph for a complete Buildroot configuration, with all packages:

Using this tool is fairly easy. You must first install the graphviz package on your distribution. For a single package dependency graph:

./scripts/graph-depends libgtk2 >
dot -Tpdf -o libgtk2.pdf

For a full dependency graph:

./scripts/graph-depends >
dot -Tpdf -o full.pdf

Note that the dependency graph always depends on the selected set of packages. It is not the absolute dependency graph, which would contain all existing dependencies. It only show the dependencies as they are in your current configuration.

Plans for the next release

The next release is scheduled for August (2010.08). I have in mind various things:

  • Cleanup of the bootloader compilation code and integration of support for Barebox. This is already implemented in one of my branch, so I should be able to push this fairly soon to Buildroot
  • Cleanup of the Linux kernel compilation code, with a much-wanted simplification of this. Again, this is already implemented on my side, but requires a little bit more work before being able to push this
  • Continue the effort to convert packages to the generic or autotools infrastructure. I have already sent a status update on this topic to the project mailing-list. We have 56 packages to convert to the generic infrastructure and 77 to convert to the autotools infrastructure.
  • Integration with Crosstool-NG, which is a job that Yann Morin, developer of Crosstool-NG has already started.
  • More improvements of the external toolchain integration
  • If some time is left, a cleanup and reorganization of the board support mechanism, so that we can add more boards in a sane way

Location of Embedded Linux Conference Europe 2010 announced

Cambridge, UKWhile the American Embedded Linux Conference always takes place in the San Francisco area in California, the European Embedded Linux Conference Europe travels each year in a different country across Europe: it took place in Austria in 2007, in the Netherlands in 2008 and in France in 2009. The location for the 2010 edition of ELCE has been announced recently: it will take place on October 27th and 28th in Cambridge, United Kingdom. As usual there will be many talks, Bird-of-a-Feather sessions, technical demonstrations and more. If you’re an embedded Linux developer in Europe, you should definitely ask your employer to send you to this conference!

Presentations on the following topics are encouraged: audio, video, and graphics systems for embedded products, security, system size, boot-up time, meeting real-time constraints, power management, streaming media, flash memory devices and filesystems, technologies related to cell phones, digital set top boxes, handheld devices, or other CE products, development tools for embedded users, use of Linux in actual products, practical experience and war stories, standards for CE products. The proposal must be received by June, 30th. My colleague Michael Opdenacker, founder of Bootlin, is a member of the program committee.

On the day before, note that there will also be an interesting event: GStreamer Conference 2010. As GStreamer is a key component of today’s multimedia systems based on embedded Linux. Staying in Cambridge for three days instead of two could then make a lot of sense.