[Buildroot] [PATCHv5 4/5] docs/manual: add explanations about BR2_EXTERNAL
Thomas Petazzoni
thomas.petazzoni at free-electrons.com
Wed Dec 4 18:56:12 UTC 2013
This commit updates the manual to add details on how to use the
BR2_EXTERNAL feature.
Signed-off-by: Thomas Petazzoni <thomas.petazzoni at free-electrons.com>
---
docs/manual/customize-outside-br.txt | 136 +++++++++++++++++++++++++++++++++++
docs/manual/customize.txt | 2 +
2 files changed, 138 insertions(+)
create mode 100644 docs/manual/customize-outside-br.txt
diff --git a/docs/manual/customize-outside-br.txt b/docs/manual/customize-outside-br.txt
new file mode 100644
index 0000000..2eb8ff0
--- /dev/null
+++ b/docs/manual/customize-outside-br.txt
@@ -0,0 +1,136 @@
+// -*- mode:doc -*- ;
+
+[[outside-br-custom]]
+Keeping customization outside Buildroot
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The Buildroot community recommends and encourages upstreaming to the
+official Buildroot version the packages and board supports that are
+written by developers. However, it is sometimes not possible or
+desirable because some of these packages or board supports are highly
+specific or proprietary.
+
+In this case, Buildroot users are offered two choices:
+
+ * They can add their packages, board support and configuration files
+ directly within the Buildroot tree, and maintain them by using
+ branches in a version control system.
+
+ * They can use the +BR2_EXTERNAL+ mechanism, which 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. The following paragraphs give details on how to
+ use +BR2_EXTERNAL+.
+
++BR2_EXTERNAL+ is an environment variable that one can use 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, so that it is not
+needed 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.
+
+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 relatively to the main Buildroot source directory, not
+the Buildroot output directory.
+
+Some examples:
+
+-----
+ buildroot/ $ make BR2_EXTERNAL=../foobar menuconfig
+-----
+
+Starting from now on, external definitions from the +../foobar+
+directory will be used:
+
+-----
+ buildroot/ $ make
+ buildroot/ $ make legal-info
+-----
+
+We can switch to another external definitions directory at any time:
+
+-----
+ buildroot/ $ make BR2_EXTERNAL=../barfoo xconfig
+-----
+
+Or disable the usage of external definitions:
+
+-----
+ buildroot/ $ make BR2_EXTERNAL= xconfig
+-----
+
+This +BR2_EXTERNAL+ 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 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
+ +$(BR2_EXTERNAL)/board/<boardname>/kernel.config+ (to specify the
+ location of the kernel configuration file). To achieve this, it is
+ recommended but not mandatory, to store those details in
+ directories called +board/<boardname>/+ under +BR2_EXTERNAL+. This
+ matches the directory structure used within Buildroot.
+
+ * One can store package recipes (i.e +Config.in+ and
+ +<packagename>.mk+), or even custom configuration options and make
+ logic. Buildroot automatically includes +BR2_EXTERNAL/Config.in+ to
+ make it appear in the top-level configuration menu, and includes
+ +BR2_EXTERNAL/external.mk+ with the rest of the makefile logic.
++
+The main usage of this is to store package recipes. The recommended
+ way to do this is to write a +BR2_EXTERNAL/Config.in+ that looks
+ like:
++
+------
+menu "<somecompany> packages"
+
+source "$BR2_EXTERNAL/package/package1/Config.in"
+source "$BR2_EXTERNAL/package/package2/Config.in"
+
+endmenu
+------
++
+Then, have a +BR2_EXTERNAL/external.mk' file that looks like:
++
+------
+include $(sort $(wildcard $(BR2_EXTERNAL)/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[].
+
+ * One can store Buildroot defconfigs in the +configs+ subdirectory of
+ +BR2_EXTERNAL+. Buildroot will automatically show them in the
+ output of +make help+ and allow them to be loaded with the normal
+ +make <name>_defconfig+ command.
+
+In the end, a typical +BR2_EXTERNAL+ directory organization would
+generally be:
+
+-----
++-- Config.in
++-- external.mk
++-- board/
+| +-- <boardname>/
+| +-- linux.config
+| +-- overlay/
+| +-- etc/
+| +-- <some file>
++-- configs/
+| +-- <boardname>_defconfig
++-- package/
+ +-- package1/
+ | +-- Config.in
+ | +-- package1.mk
+ +-- package2/
+ +-- Config.in
+ +-- package2.mk
+------
diff --git a/docs/manual/customize.txt b/docs/manual/customize.txt
index 0456ef1..7e46fd8 100644
--- a/docs/manual/customize.txt
+++ b/docs/manual/customize.txt
@@ -17,3 +17,5 @@ include::customize-toolchain.txt[]
include::customize-store.txt[]
include::customize-packages.txt[]
+
+include::customize-outside-br.txt[]
--
1.8.1.2
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