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docs/manual: document providers from br2-external

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Add documentation about how a br2-external tree can provide an external
toolchain or a libjpeg or openssl alternative implementation.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Vadim Kochan <vadim4j@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
This commit is contained in:
Yann E. MORIN 2019-07-29 22:20:03 +02:00 committed by Peter Korsgaard
parent cfb929fbfa
commit 91251cedde
1 changed files with 88 additions and 1 deletions
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89
docs/manual/customize-outside-br.txt
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@ -81,7 +81,8 @@ in the following chapters:
Apart from those mandatory files, there may be additional and optional
content that may be present in a br2-external tree, like the +configs/+
directory. They are described in the following chapters as well.
or +provides/+ directories. They are described in the following chapters
as well.
A complete example br2-external tree layout is also described later.
@ -186,6 +187,22 @@ the one from the last br2-external tree is used. It is thus possible
to override a defconfig bundled in Buildroot or another br2-external
tree.
===== The +provides/+ directory
For some packages, Buildroot provides a choice between two (or more)
implementations of API-compatible such packages. For example, there is
a choice to choose either libjpeg ot jpeg-turbo, and another choice
between openssl or libressl. Finally, there is a choice to select one
of the known, pre-configured toolchains.
It is possible for a br2-external to extend those choices, by providing
a set of files that define those alternatives:
* +provides/toolchains.in+ defines the pre-configured toolchains, which
will then be listed in the toolchain selection;
* +provides/jpeg.in+ defines the alternative libjpeg implementations;
* +provides/openssl.in+ defines the alternative openssl implementations.
===== Free-form content
One can store all the board-specific configuration files there, such
@ -217,8 +234,10 @@ illustration, of course):
| `----
|
|- Config.in
| |source "$BR2_EXTERNAL_BAR_42_PATH/toolchain/toolchain-external-mine/Config.in.options"
| |source "$BR2_EXTERNAL_BAR_42_PATH/package/pkg-1/Config.in"
| |source "$BR2_EXTERNAL_BAR_42_PATH/package/pkg-2/Config.in"
| |source "$BR2_EXTERNAL_BAR_42_PATH/package/my-jpeg/Config.in"
| |
| |config BAR_42_FLASH_ADDR
| | hex "my-board flash address"
@ -259,6 +278,42 @@ illustration, of course):
|- package/pkg-2/pkg-2.hash
|- package/pkg-2/pkg-2.mk
|
|- provides/jpeg.in
| |config BR2_PACKAGE_MY_JPEG
| | bool "my-jpeg"
| `----
|- package/my-jpeg/Config.in
| |config BR2_PACKAGE_PROVIDES_JPEG
| | default "my-jpeg" if BR2_PACKAGE_MY_JPEG
| `----
|- package/my-jpeg/my-jpeg.mk
| |# This is a normal package .mk file
| |MY_JPEG_VERSION = 1.2.3
| |MY_JPEG_SITE = https://example.net/some/place
| |MY_JPEG_PROVIDES = jpeg
| |$(eval $(autotools-package))
| `----
|
|- provides/toolchains.in
| |config BR2_TOOLCHAIN_EXTERNAL_MINE
| | bool "my custom toolchain"
| | depends on BR2_some_arch
| | select BR2_INSTALL_LIBSTDCPP
| `----
|- toolchain/toolchain-external-mine/Config.in.options
| |if BR2_TOOLCHAIN_EXTERNAL_MINE
| |config BR2_TOOLCHAIN_EXTERNAL_PREFIX
| | default "arch-mine-linux-gnu"
| |config BR2_PACKAGE_PROVIDES_TOOLCHAIN_EXTERNAL
| | default "toolchain-external-mine"
| |endif
| `----
|- toolchain/toolchain-external-mine/toolchain-external-mine.mk
| |TOOLCHAIN_EXTERNAL_MINE_SITE = https://example.net/some/place
| |TOOLCHAIN_EXTERNAL_MINE_SOURCE = my-toolchain.tar.gz
| |$(eval $(toolchain-external-package))
| `----
|
|- configs/my-board_defconfig
| |BR2_GLOBAL_PATCH_DIR="$(BR2_EXTERNAL_BAR_42_PATH)/patches/"
| |BR2_ROOTFS_OVERLAY="$(BR2_EXTERNAL_BAR_42_PATH)/board/my-board/overlay/"
@ -311,3 +366,35 @@ External options --->
[ ] foo
[ ] bar
----
Additionally, the jpeg provider will be visible in the jpeg choice:
----
Target packages --->
Libraries --->
Graphics --->
[*] jpeg support
jpeg variant () --->
( ) jpeg
( ) jpeg-turbo
*** jpeg from: Example br2-external tree ***
(X) my-jpeg
*** jpeg from: FOO_27 ***
( ) another-jpeg
----
And similarly for the toolchains:
----
Toolchain --->
Toolchain () --->
( ) Custom toolchain
*** Toolchains from: Example br2-external tree ***
(X) my custom toolchain
----
.Note
The toolchain options in +toolchain/toolchain-external-mine/Config.in.options+
will not appear in the `Toolchain` menu. They must be explicitly included
from within the br2-external's top-level +Config.in+ and will thus appear
in the `External options` menu.