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Although it is possible to use relative paths, there are a few pitfalls when doing so. To avoid confusion for a (newcoming) user, use absolute paths in the manual (as is done in examples for $(O)), since it is guaranteed to be working without corner cases. [Peter: s/relatively/relative/ as suggested by Thomas] Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr> Cc: Samuel Martin <s.martin49@gmail.com> Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
136 lines
4.7 KiB
Plaintext
136 lines
4.7 KiB
Plaintext
// -*- mode:doc -*- ;
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[[outside-br-custom]]
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Keeping customizations outside Buildroot
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The Buildroot community recommends and encourages upstreaming to the
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official Buildroot version the packages and board support that are
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written by developers. However, it is sometimes not possible or
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desirable because some of these packages or board support are highly
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specific or proprietary.
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In this case, Buildroot users are offered two choices:
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* They can add their packages, board support and configuration files
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directly within the Buildroot tree, and maintain them by using
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branches in a version control system.
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* They can use the +BR2_EXTERNAL+ mechanism, which allows to keep
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package recipes, board support and configuration files outside of
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the Buildroot tree, while still having them nicely integrated in
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the build logic. The following paragraphs give details on how to
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use +BR2_EXTERNAL+.
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+BR2_EXTERNAL+ is an environment variable that can be used to point to
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a directory that contains Buildroot customizations. It can be passed
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to any Buildroot +make+ invocation. It is automatically saved in the
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hidden +.br-external+ file in the output directory. By doing this,
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there is no need to pass +BR2_EXTERNAL+ at every +make+ invocation. It
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can however be changed at any time by passing a new value, and can be
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removed by passing an empty value.
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*Note:* the +BR2_EXTERNAL+ path can be either an absolute or a relative path,
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but if it's passed as a relative path, it is important to note that it
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is interpreted relative to the main Buildroot source directory, *not*
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the Buildroot output directory.
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Some examples:
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-----
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buildroot/ $ make BR2_EXTERNAL=/path/to/foobar menuconfig
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-----
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Starting from now on, external definitions from the +/path/to/foobar+
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directory will be used:
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-----
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buildroot/ $ make
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buildroot/ $ make legal-info
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-----
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We can switch to another external definitions directory at any time:
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-----
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buildroot/ $ make BR2_EXTERNAL=/where/we/have/barfoo xconfig
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-----
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Or disable the usage of external definitions:
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-----
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buildroot/ $ make BR2_EXTERNAL= xconfig
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-----
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+BR2_EXTERNAL+ then allows three different things:
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* One can store all the board-specific configuration files there,
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such as the kernel configuration, the root filesystem overlay, or
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any other configuration file for which Buildroot allows to set its
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location. The +BR2_EXTERNAL+ value is available within the
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Buildroot configuration using +$(BR2_EXTERNAL)+. As an example, one
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could set the +BR2_ROOTFS_OVERLAY+ Buildroot option to
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+$(BR2_EXTERNAL)/board/<boardname>/overlay/+ (to specify a root
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filesystem overlay), or the +BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE+
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Buildroot option to
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+$(BR2_EXTERNAL)/board/<boardname>/kernel.config+ (to specify the
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location of the kernel configuration file). To achieve this, it is
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recommended but not mandatory, to store those details in
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directories called +board/<boardname>/+ under +BR2_EXTERNAL+. This
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matches the directory structure used within Buildroot.
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* One can store package recipes (i.e +Config.in+ and
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+<packagename>.mk+), or even custom configuration options and make
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logic. Buildroot automatically includes +BR2_EXTERNAL/Config.in+ to
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make it appear in the top-level configuration menu, and includes
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+BR2_EXTERNAL/external.mk+ with the rest of the makefile logic.
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Providing those two files is mandatory, but they can be empty.
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+
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The main usage of this is to store package recipes. The recommended
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way to do this is to write a +BR2_EXTERNAL/Config.in+ that looks
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like:
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+
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------
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source "$BR2_EXTERNAL/package/package1/Config.in"
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source "$BR2_EXTERNAL/package/package2/Config.in"
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------
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+
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Then, have a +BR2_EXTERNAL/external.mk+ file that looks like:
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+
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------
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include $(sort $(wildcard $(BR2_EXTERNAL)/package/*/*.mk))
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------
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+
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And then in +BR2_EXTERNAL/package/package1+ and
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+BR2_EXTERNAL/package/package2+ create normal Buildroot package
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recipes, as explained in xref:adding-packages[].
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* One can store Buildroot defconfigs in the +configs+ subdirectory of
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+BR2_EXTERNAL+. Buildroot will automatically show them in the
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output of +make help+ and allow them to be loaded with the normal
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+make <name>_defconfig+ command. They will be visible under the
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+User-provided configs:+' label in the 'make help' output.
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In the end, a typical +BR2_EXTERNAL+ directory organization would
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generally be:
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-----
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$(BR2_EXTERNAL)/
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+-- Config.in
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+-- external.mk
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+-- board/
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| +-- <boardname>/
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| +-- linux.config
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| +-- overlay/
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| +-- etc/
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| +-- <some file>
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+-- configs/
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| +-- <boardname>_defconfig
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+-- package/
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+-- package1/
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| +-- Config.in
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| +-- package1.mk
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+-- package2/
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+-- Config.in
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+-- package2.mk
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------
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