docs/manual: document the br2-external NAME

Update the manual with the new external.desc mandatory file.

Take the opportunity to add a section listing all mandatory files,
Config.in, external.mk and the new external.desc, instead of just
hinting about them in the external package recipes section.

Change the examples to use the NAME-suffixed variable instead of the
raw BR2_EXTERNAL variable.

Change all references to BR2_EXTERNAL elsewhere in the manual to now
use the 'br2-external tree' terminology.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Arnout Vandecappelle <arnout@mind.be>
Cc: Samuel Martin <s.martin49@gmail.com>
Cc: Romain Naour <romain.naour@openwide.fr>
Cc: Julien CORJON <corjon.j@ecagroup.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

6 files changed, 105 insertions, 83 deletions

diff --git a/docs/manual/adding-packages-asciidoc.txt b/docs/manual/adding-packages-asciidoc.txt
index a278d44cc..d870c5108 100644
--- a/docs/manual/adding-packages-asciidoc.txt
+++ b/docs/manual/adding-packages-asciidoc.txt
@@ -19,9 +19,9 @@ Although Buildroot only contains one document written in AsciiDoc, there
 is, as for packages, an infrastructure for rendering documents using the
 AsciiDoc syntax.
 
-Also as for packages, the AsciiDoc infrastructure is available from
-xref:outside-br-custom[BR2_EXTERNAL]. This allows documentation for a
-BR2_EXTERNAL tree to match the Buildroot documentation, as it will be
+Also as for packages, the AsciiDoc infrastructure is available from a
+xref:outside-br-custom[br2-external tree]. This allows documentation for
+a br2-external tree to match the Buildroot documentation, as it will be
 rendered to the same formats and use the same layout and theme.
 
 ==== +asciidoc-document+ tutorial
diff --git a/docs/manual/adding-packages-perl.txt b/docs/manual/adding-packages-perl.txt
index 63fafe655..4f5a6a406 100644
--- a/docs/manual/adding-packages-perl.txt
+++ b/docs/manual/adding-packages-perl.txt
@@ -47,7 +47,7 @@ built.
 Most of these data can be retrieved from https://metacpan.org/.
 So, this file and the Config.in can be generated by running
 the script +supports/scripts/scancpan Foo-Bar+ in the Buildroot directory
-(or in the +BR2_EXTERNAL+ directory).
+(or in a br2-external tree).
 This script creates a Config.in file and foo-bar.mk file for the
 requested package, and also recursively for all dependencies specified by
 CPAN. You should still manually edit the result. In particular, the
diff --git a/docs/manual/adding-packages-python.txt b/docs/manual/adding-packages-python.txt
index 94ac809ff..abcd4ca36 100644
--- a/docs/manual/adding-packages-python.txt
+++ b/docs/manual/adding-packages-python.txt
@@ -195,7 +195,7 @@ license and license files are guessed and must be checked. You also
 need to manually add the package to the +package/Config.in+ file.
 
 If your Buildroot package is not in the official Buildroot tree but in
-a +BR2_EXTERNAL+ tree, use the -o flag as follows:
+a br2-external tree, use the -o flag as follows:
 
 -----------------------
 ./support/script/scanpypi foo bar -o other_package_dir
diff --git a/docs/manual/customize-directory-structure.txt b/docs/manual/customize-directory-structure.txt
index 0be3f77e5..b177319f9 100644
--- a/docs/manual/customize-directory-structure.txt
+++ b/docs/manual/customize-directory-structure.txt
@@ -13,7 +13,8 @@ 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.
+it using a br2-external tree. Both options are valid, the choice is up
+to you.
 
 -----
 +-- board/
@@ -38,8 +39,8 @@ it using +BR2_EXTERNAL+. Both options are valid, the choice is up to you.
 |
 +-- package/
 |   +-- <company>/
-|       +-- Config.in (if not using BR2_EXTERNAL)
-|       +-- <company>.mk (if not using BR2_EXTERNAL)
+|       +-- Config.in (if not using a br2-external tree)
+|       +-- <company>.mk (if not using a br2-external tree)
 |       +-- package1/
 |       |    +-- Config.in
 |       |    +-- package1.mk
@@ -47,14 +48,14 @@ it using +BR2_EXTERNAL+. Both options are valid, the choice is up to you.
 |           +-- Config.in
 |           +-- package2.mk
 |
-+-- Config.in (if using BR2_EXTERNAL)
-+-- external.mk (if using BR2_EXTERNAL)
++-- Config.in (if using a br2-external tree)
++-- external.mk (if using a br2-external tree)
 ------
 
 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>
+tree but in a br2-external tree, the <company> and possibly <boardname>
 components may be superfluous and can be left out.
 
 ==== Implementing layered customizations
diff --git a/docs/manual/customize-outside-br.txt b/docs/manual/customize-outside-br.txt
index 9ad177d00..f2a83a622 100644
--- a/docs/manual/customize-outside-br.txt
+++ b/docs/manual/customize-outside-br.txt
@@ -11,25 +11,27 @@ place project-specific customizations in two locations:
    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:
 
@@ -37,73 +39,107 @@ 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.
diff --git a/docs/manual/customize-packages.txt b/docs/manual/customize-packages.txt
index 9a5e8c5bc..b57280ea1 100644
--- a/docs/manual/customize-packages.txt
+++ b/docs/manual/customize-packages.txt
@@ -14,8 +14,9 @@ packages in a project-specific directory.
 
 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
@@ -37,14 +38,6 @@ have only one extra directory level below +package/<company>/+):
 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.
@@ -59,13 +52,5 @@ Include this new file +package/<company>/Config.in+ from
 +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.