buildroot/docs/manual/customize-directory-structure.txt

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[[customize-dir-structure]]
=== Recommended directory structure

When customizing Buildroot for your project, you will be creating one or
more project-specific files that need to be stored somewhere. While most
of these files could be placed in _any_ location as their path is to be
specified in the Buildroot configuration, the Buildroot developers
recommend a specific directory structure which is described in this
section.

Orthogonal to this directory structure, you can choose _where_ you place
this structure itself: either inside the Buildroot tree, or outside of
it using +BR2_EXTERNAL+. Both options are valid, the choice is up to you.

-----
+-- board/
|   +-- <company>/
|       +-- <boardname>/
|           +-- linux.config
|           +-- busybox.config
|           +-- <other configuration files>
|           +-- post_build.sh
|           +-- post_image.sh
|           +-- rootfs_overlay/
|           |   +-- etc/
|           |   +-- <some file>
|           +-- patches/
|               +-- foo/
|               |   +-- <some patch>
|               +-- libbar/
|                   +-- <some other patches>
|
+-- configs/
|   +-- <boardname>_defconfig
|
+-- package/
|   +-- <company>/
|       +-- Config.in (if not using BR2_EXTERNAL)
|       +-- <company>.mk (if not using BR2_EXTERNAL)
|       +-- package1/
|       |    +-- Config.in
|       |    +-- package1.mk
|       +-- package2/
|           +-- Config.in
|           +-- package2.mk
|
+-- Config.in (if using BR2_EXTERNAL)
+-- external.mk (if using BR2_EXTERNAL)
------

Details on the files shown above are given further in this chapter.

Note: if you choose to place this structure outside of the Buildroot
tree using +BR2_EXTERNAL+, the <company> and possibly <boardname>
components may be superfluous and can be left out.

==== Implementing layered customizations

It is quite common for a user to have several related projects that partly
need the same customizations. Instead of duplicating these
customizations for each project, it is recommended to use a layered
customization approach, as explained in this section.

Almost all of the customization methods available in Buildroot, like
post-build scripts and root filesystem overlays, accept a
space-separated list of items. The specified items are always treated in
order, from left to right. By creating more than one such item, one for
the common customizations and another one for the really
project-specific customizations, you can avoid unnecessary duplication.
Each layer is typically embodied by a separate directory inside
+board/<company>/+. Depending on your projects, you could even introduce
more than two layers.

An example directory structure for where a user has two customization
layers 'common' and 'fooboard' is:

-----
+-- board/
    +-- <company>/
        +-- common/
        |   +-- post_build.sh
        |   +-- rootfs_overlay/
        |   |   +-- ...
        |   +-- patches/
        |       +-- ...
        |
        +-- fooboard/
            +-- linux.config
            +-- busybox.config
            +-- <other configuration files>
            +-- post_build.sh
            +-- rootfs_overlay/
            |   +-- ...
            +-- patches/
                +-- ...
-----

For example, if the user has the +BR2_GLOBAL_PATCH_DIR+ configuration
option set as:

-----
BR2_GLOBAL_PATCH_DIR="board/<company>/common/patches board/<company>/fooboard/patches"
-----

then first the patches from the 'common' layer would be applied,
followed by the patches from the 'fooboard' layer.