diff options
authorThomas Petazzoni <>2013-12-05 19:11:13 (GMT)
committer Peter Korsgaard <>2013-12-08 22:01:44 (GMT)
commit2233f5f8fb40527e6d14939bb79ec24ff2325fc1 (patch)
parentff9d6e306032a680e9db43673d9ab57db7d1bf75 (diff)
docs/manual: add explanations about BR2_EXTERNAL
This commit updates the manual to add details on how to use the BR2_EXTERNAL feature. [Peter: minor tweaks, fix asciidoc tag as pointed out by Samuel] Signed-off-by: Thomas Petazzoni <> Reviewed-by: "Yann E. MORIN" <> Acked-by: "Samuel Martin" <> Acked-by: Ryan Barnett <> Signed-off-by: Peter Korsgaard <>
2 files changed, 140 insertions, 0 deletions
diff --git a/docs/manual/customize-outside-br.txt b/docs/manual/customize-outside-br.txt
new file mode 100644
index 0000000..0aabf5a
--- /dev/null
+++ b/docs/manual/customize-outside-br.txt
@@ -0,0 +1,138 @@
+// -*- mode:doc -*- ;
+Keeping customizations outside Buildroot
+The Buildroot community recommends and encourages upstreaming to the
+official Buildroot version the packages and board support that are
+written by developers. However, it is sometimes not possible or
+desirable because some of these packages or board support 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 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 file in the output directory. By doing 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.
+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
++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
+ +$(BR2_EXTERNAL)/board/<boardname>/kernel.config+ (to specify the
+ location of the kernel configuration file). To achieve this, it is
+ recommended but not mandatory, to store those details in
+ directories called +board/<boardname>/+ under +BR2_EXTERNAL+. This
+ matches the directory structure used within Buildroot.
+ * One can store package recipes (i.e and
+ +<packagename>.mk+), or even custom configuration options and make
+ logic. Buildroot automatically includes +BR2_EXTERNAL/ to
+ make it appear in the top-level configuration menu, and includes
+ +BR2_EXTERNAL/ with the rest of the makefile logic.
+The main usage of this is to store package recipes. The recommended
+ way to do this is to write a +BR2_EXTERNAL/ that looks
+ like:
+menu "<somecompany> packages"
+source "$BR2_EXTERNAL/package/package1/"
+source "$BR2_EXTERNAL/package/package2/"
+Then, have a +BR2_EXTERNAL/ 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. They will be visible under the
+ +User-provided configs:+' label in the 'make help' output.
+In the end, a typical +BR2_EXTERNAL+ directory organization would
+generally be:
++-- board/
+| +-- <boardname>/
+| +-- linux.config
+| +-- overlay/
+| +-- etc/
+| +-- <some file>
++-- configs/
+| +-- <boardname>_defconfig
++-- package/
+ +-- package1/
+ | +--
+ | +--
+ +-- package2/
+ +--
+ +--
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[]