branches in a version control system so that upgrading to a newer
Buildroot release is easy.
- * outside of the Buildroot tree, using the +BR2_EXTERNAL+ mechanism.
+ * outside of the Buildroot tree, using the _br2-external_ mechanism.
This mechanism allows to keep package recipes, board support and
configuration files outside of the Buildroot tree, while still
- having them nicely integrated in the build logic. This section
- explains how to use +BR2_EXTERNAL+.
-
-+BR2_EXTERNAL+ is an environment variable that can be used to point to
-a directory that contains Buildroot customizations. It can be passed
-to any Buildroot +make+ invocation. It is automatically saved in the
-hidden +.br-external+ file in the output directory. Thanks to this,
-there is no need to pass +BR2_EXTERNAL+ at every +make+ invocation. It
-can however be changed at any time by passing a new value, and can be
-removed by passing an empty value.
+ having them nicely integrated in the build logic. We call this
+ location a _br2-external tree_. This section explains how to use
+ the br2-external mechanism and what to provide in a br2-external
+ tree.
+
+One can tell Buildroot to use a br2-external tree by setting the
++BR2_EXTERNAL+ make variable set to the path of the br2-external tree
+to use. It can be passed to any Buildroot +make+ invocation. It is
+automatically saved in the hidden +.br-external.mk+ file in the output
+directory. Thanks to this, there is no need to pass +BR2_EXTERNAL+ at
+every +make+ invocation. It can however be changed at any time by
+passing a new value, and can be removed by passing an empty value.
.Note
-The +BR2_EXTERNAL+ path can be either an absolute or a relative path,
-but if it's passed as a relative path, it is important to note that it
-is interpreted relative to the main Buildroot source directory, *not*
-to the Buildroot output directory.
+The path to a br2-external tree can be either absolute or relative.
+If it is passed as a relative path, it is important to note that it is
+interpreted relative to the main Buildroot source directory, *not* to
+the Buildroot output directory.
Some examples:
buildroot/ $ make BR2_EXTERNAL=/path/to/foobar menuconfig
-----
-From now on, external definitions from the +/path/to/foobar+
-directory will be used:
+From now on, definitions from the +/path/to/foobar+ br2-external tree
+will be used:
-----
buildroot/ $ make
buildroot/ $ make legal-info
-----
-We can switch to another external definitions directory at any time:
+We can switch to another br2-external tree at any time:
-----
buildroot/ $ make BR2_EXTERNAL=/where/we/have/barfoo xconfig
-----
-Or disable the usage of external definitions:
+Or disable the usage of any br2-external tree:
-----
buildroot/ $ make BR2_EXTERNAL= xconfig
-----
-+BR2_EXTERNAL+ allows three different things:
-
- * One can store all the board-specific configuration files there,
- such as the kernel configuration, the root filesystem overlay, or
- any other configuration file for which Buildroot allows to set its
- location. The +BR2_EXTERNAL+ value is available within the
- Buildroot configuration using +$(BR2_EXTERNAL)+. As an example, one
- could set the +BR2_ROOTFS_OVERLAY+ Buildroot option to
- +$(BR2_EXTERNAL)/board/<boardname>/overlay/+ (to specify a root
- filesystem overlay), or the +BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE+
- Buildroot option to
- +$(BR2_EXTERNAL)/board/<boardname>/kernel.config+ (to specify the
- location of the kernel configuration file).
-
- * One can store package recipes (i.e. +Config.in+ and
- +<packagename>.mk+), or even custom configuration options and make
- logic. Buildroot automatically includes +$(BR2_EXTERNAL)/Config.in+ to
- make it appear in the top-level configuration menu, and includes
- +$(BR2_EXTERNAL)/external.mk+ with the rest of the makefile logic.
+A br2-external tree must contain at least those three files:
+
++external.desc+::
+ That file shall contain the _name_ for the br2-external tree. That name
+ must only use ASCII characters in the set +[A-Za-z0-9_]+; any other
+ character is forbidden. The format for this file is a single line with
+ the keyword 'name:', followed by one or more spaces, followed by the
+ name.
+
-.Note
-Providing +Config.in+ and +external.mk+ is mandatory, but they can be
- empty.
+Buildroot sets +BR2_EXTERNAL_$(NAME)_PATH+ to the absolute path of the
+ br2-external tree, so that you can use it to refer to your br2-external
+ tree. This variable is available both in Kconfig, so you can use it
+ to source your Kconfig files (see below) and in the Makefile, so that
+ you can use it to include other Makefiles (see below) or refer to other
+ files (like data files) from your br2-external tree.
++
+Example of an +external.desc+ file that declares the name +FOO+:
++
+----
+$ cat external.desc
+name: FOO
+----
++
+Examples of names and the corresponding +BR2_EXTERNAL_$(NAME)_PATH+
+variables:
++
+ * +FOO+ -> +BR2_EXTERNAL_FOO_PATH+
+ * +BAR_42+ -> +BR2_EXTERNAL_BAR_42_PATH+
++
+In the following examples, it is assumed the name to be set to +BAR_42+.
+
++Config.in+::
++external.mk+::
+ Those files (which may each be empty) can be used to define package
+ recipes, like for packages bundled in Buildroot itself, or other
+ custom configuration options.
+
+Using a br2-external tree then allows three different things:
+
+ * One can store all the board-specific configuration files there, such
+ as the kernel configuration, the root filesystem overlay, or any other
+ configuration file for which Buildroot allows to set the location (by
+ using the +BR2_EXTERNAL_$(NAME)_PATH+ variable). For example, you
+ could set the paths to a global patch directory, to a rootfs overlay
+ and to the kernel configuration file as follows (e.g. by running
+ `make menuconfig` and filling in these options):
++
+----
+BR2_GLOBAL_PATCH_DIR=$(BR2_EXTERNAL_BAR_42_PATH)/patches/
+BR2_ROOTFS_OVERLAY=$(BR2_EXTERNAL_BAR_42_PATH)/board/<boardname>/overlay/
+BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE=$(BR2_EXTERNAL_BAR_42_FOO)/board/<boardname>/kernel.config
+----
+
+ * One can store package recipes (i.e. +Config.in+ and +<packagename>.mk+),
+ or even custom configuration options and make logic. Buildroot
+ automatically includes +Config.in+ to make it appear in the top-level
+ configuration menu, and includes +external.mk+ with the rest of the
+ makefile logic.
+
-The main usage of this is to store package recipes. The recommended
- way to do this is to write a +$(BR2_EXTERNAL)/Config.in+ file that
- looks like:
+The main usage of this is to store package recipes. The recommended way
+ to do this is to write a +Config.in+ file that looks like:
+
------
-source "$BR2_EXTERNAL/package/package1/Config.in"
-source "$BR2_EXTERNAL/package/package2/Config.in"
+source "$BR2_EXTERNAL_BAR_42_PATH/package/package1/Config.in"
+source "$BR2_EXTERNAL_BAR_42_PATH/package/package2/Config.in"
------
+
-Then, have a +$(BR2_EXTERNAL)/external.mk+ file that looks like:
+Then, have an +external.mk+ file that looks like:
+
------
-include $(sort $(wildcard $(BR2_EXTERNAL)/package/*/*.mk))
+include $(sort $(wildcard $(BR2_EXTERNAL_BAR_42_PATH)/package/*/*.mk))
------
+
-And then in +$(BR2_EXTERNAL)/package/package1+ and
- +$(BR2_EXTERNAL)/package/package2+ create normal Buildroot
- package recipes, as explained in xref:adding-packages[].
+And then in +$(BR2_EXTERNAL_FOO_42_PATH)/package/package1+ and
+ +$(BR2_EXTERNAL_FOO_42_PATH)/package/package2+ create normal
+ Buildroot package recipes, as explained in xref:adding-packages[].
If you prefer, you can also group the packages in subdirectories
called <boardname> and adapt the above paths accordingly.
* One can store Buildroot defconfigs in the +configs+ subdirectory of
- +$(BR2_EXTERNAL)+. Buildroot will automatically show them in the
+ the br2-external tree. Buildroot will automatically show them in the
output of +make list-defconfigs+ and allow them to be loaded with the
normal +make <name>_defconfig+ command. They will be visible under the
+User-provided configs+' label in the 'make list-defconfigs' output.
As shown in xref:customize-dir-structure[], the recommended location for
project-specific packages is +package/<company>/+. If you are using the
-+BR2_EXTERNAL+ feature (see xref:outside-br-custom[]) the recommended
-location is +$(BR2_EXTERNAL)/package/+.
+br2-external tree feature (see xref:outside-br-custom[]) the recommended
+location is to put them in a sub-directory named +package/+ in your
+br2-external tree.
However, Buildroot will not be aware of the packages in this location,
unless we perform some additional steps. As explained in
include $(sort $(wildcard package/<company>/*/*.mk))
-----
-If you are using +BR2_EXTERNAL+, create a file
-+$(BR2_EXTERNAL)/external.mk+ with following contents (again assuming only
-one extra level):
-
------
-include $(sort $(wildcard $(BR2_EXTERNAL)/package/*/*.mk))
------
-
For the +Config.in+ files, create a file +package/<company>/Config.in+
that includes the +Config.in+ files of all your packages. An exhaustive
list has to be provided since wildcards are not supported in the source command of kconfig.
+package/Config.in+, preferably in a company-specific menu to make
merges with future Buildroot versions easier.
-If you are using +BR2_EXTERNAL+, create a file
-+$(BR2_EXTERNAL)/Config.in+ with similar contents:
-
------
-source "$BR2_EXTERNAL/package/package1/Config.in"
-source "$BR2_EXTERNAL/package/package2/Config.in"
------
-
-You do not have to add an include for this +$(BR2_EXTERNAL)/Config.in+
-file as it is included automatically.
+If using a br2-external tree, refer to xref:outside-br-custom[] for how
+to fill in those files.
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