// -*- mode:doc -*-

[[customize-store]]
Storing the configuration
-------------------------

When you have a buildroot configuration that you are satisfied with and
you want to share it with others, put it under revision control or move
on to a different buildroot project, you need to store the configuration
so it can be rebuilt later. The configuration that needs to be stored
consists of the buildroot configuration, the configuration files for
packages that you use (kernel, busybox, uClibc, ...), and your rootfs
modifications.

Basics for storing the configuration
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[[customize-store-basics]]

Buildroot configuration
^^^^^^^^^^^^^^^^^^^^^^^

For storing the buildroot configuration itself, buildroot offers the
following command: +make savedefconfig+

This strips the buildroot configuration down by removing configuration
options that are at their default value. The result is stored in a file
called +defconfig+. Copy this file to +foo_defconfig+ in the +configs+
directory. The configuration can then be rebuilt by running
+make foo_defconfig+

Alternatively, you can copy the file to any other place and rebuild with
+make defconfig BR2_DEFCONFIG=<path-to-defconfig-file>+.


Other package configuration
^^^^^^^^^^^^^^^^^^^^^^^^^^^

The configuration files for busybox, the linux kernel, barebox, uClibc and
crosstool-NG should be stored as well if changed. For each of these, a
buildroot configuration option exists to point to an input configuration
file, e.g. +BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE+.  To save their
configuration, set those configuration options to a path outside
your output directory, e.g. +board/<manufacturer>/<boardname>/linux.config+.
Then, copy the configuration files to that path.

Make sure that you create a configuration file 'before' changing
the +BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE+ etc. options.  Otherwise,
buildroot will try to access this config file, which doesn't exist
yet, and will fail. You can create the configuration file by running
+make linux-menuconfig+ etc.

Buildroot provides a few helper targets to make the saving of
configuration files easier.

* +make linux-update-defconfig+ saves the linux configuration to the
  path specified by +BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE+.  It
  simplifies the config file by removing default values.  However,
  this only works with kernels starting from 2.6.33.  For earlier
  kernels, use +make linux-update-config+.
* +make busybox-update-config+ saves the busybox configuration to the
  path specified by +BR2_PACKAGE_BUSYBOX_CONFIG+.
* +make uclibc-update-config+ saves the uClibc configuration to the
  path specified by +BR2_UCLIBC_CONFIG+.
* +make barebox-update-defconfig+ saves the barebox configuration to the
  path specified by +BR2_TARGET_BAREBOX_CUSTOM_CONFIG_FILE+.
* For crosstool-NG and at91bootstrap3, no helper exists so you
  have to copy the config file manually to +BR2_TOOLCHAIN_CTNG_CONFIG+,
  resp. +BR2_TARGET_AT91BOOTSTRAP3_CUSTOM_CONFIG_FILE+.


Creating your own board support
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Creating your own board support in Buildroot allows users of a
particular hardware platform to easily build a system that is known to
work.

To do so, you need to create a normal Buildroot configuration that
builds a basic system for the hardware: toolchain, kernel, bootloader,
filesystem and a simple Busybox-only userspace. No specific package
should be selected: the configuration should be as minimal as
possible, and should only build a working basic Busybox system for the
target platform. You can of course use more complicated configurations
for your internal projects, but the Buildroot project will only
integrate basic board configurations. This is because package
selections are highly application-specific.

Once you have a known working configuration, run +make
savedefconfig+. This will generate a minimal +defconfig+ file at the
root of the Buildroot source tree. Move this file into the +configs/+
directory, and rename it +<boardname>_defconfig+.

It is recommended to use as much as possible upstream versions of the
Linux kernel and bootloaders, and to use as much as possible default
kernel and bootloader configurations. If they are incorrect for your
board, or no default exists, we encourage you to send fixes to the
corresponding upstream projects.

However, in the mean time, you may want to store kernel or bootloader
configuration or patches specific to your target platform. To do so,
create a directory +board/<manufacturer>+ and a subdirectory
+board/<manufacturer>/<boardname>+. You can then store your patches
and configurations in these directories, and reference them from the main
Buildroot configuration.


Step-by-step instructions for storing configuration
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

To store the configuration for a specific product, device or
application, it is advisable to use the same conventions as for the
board support: put the buildroot defconfig in the +configs+ directory,
and any other files in a subdirectory of the +boards+ directory.  This
section gives step-by-step instructions about how to do that. Of course,
you can skip the steps that are not relevant for your use case.

1. +make menuconfig+ to configure toolchain, packages and kernel.
1. +make linux-menuconfig+ to update the kernel config, similar for
   other configuration.
1. +mkdir -p board/<manufacturer>/<boardname>+
1. Set the following options to +board/<manufacturer>/<boardname>/<package>.config+
   (as far as they are relevant):
   * +BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE+
   * +BR2_PACKAGE_BUSYBOX_CONFIG+
   * +BR2_TOOLCHAIN_CTNG_CONFIG+
   * +BR2_UCLIBC_CONFIG+
   * +BR2_TARGET_AT91BOOTSTRAP3_CUSTOM_CONFIG_FILE+
   * +BR2_TARGET_BAREBOX_CUSTOM_CONFIG_FILE+
1. Write the configuration files:
   * +make linux-update-defconfig+
   * +make busybox-update-config+
   * +cp <output>/build/build-toolchain/.config board/<manufacturer>/<boardname>/ctng.config+
   * +make uclibc-update-config+
   * +cp <output>/build/at91bootstrap3-*/.config board/<manufacturer>/<boardname>/at91bootstrap3.config+
   * +make barebox-update-defconfig+
1. Create +board/<manufacturer>/<boardname>/fs-overlay/+ and fill it
   with additional files you need on your rootfs, e.g.
   +board/<manufacturer>/<boardname>/fs-overlay/etc/inittab+.
   Set +BR2_ROOTFS_OVERLAY+
   to +board/<manufacturer>/<boardname>/fs-overlay+.
1. Create a post-build script
   +board/<manufacturer>/<boardname>/post-build.sh+.  Set
   +BR2_ROOTFS_POST_BUILD_SCRIPT+ to
   +board/<manufacturer>/<boardname>/post-build.sh+
1. If additional setuid permissions have to be set or device nodes have
   to be created, create +board/<manufacturer>/<boardname>/device_table.txt+
   and add that path to +BR2_ROOTFS_DEVICE_TABLE+.
1. +make savedefconfig+ to save the buildroot configuration.
1. +cp defconfig configs/<boardname>_defconfig+
1. To add patches to the linux build, set +BR2_LINUX_KERNEL_PATCH+ to
   +board/<manufacturer>/<boardname>/patches/linux/+ and add your
   patches in that directory. Each patch should be called
   +linux-<num>-<description>.patch+. Similar for U-Boot, barebox,
   at91bootstrap and at91bootstrap3.
1. If you need modifications to other packages, or if you need to add
   packages, do that directly in the +packages/+ directory, following the
   instructions in xref:adding-packages[].