// -*- mode:doc; -*-
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// vim: set syntax=asciidoc:
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== Coding style
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Overall, these coding style rules are here to help you to add new files in
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Buildroot or refactor existing ones.
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If you slightly modify some existing file, the important thing is
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to keep the consistency of the whole file, so you can:
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* either follow the potentially deprecated coding style used in this
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file,
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* or entirely rework it in order to make it comply with these rules.
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[[writing-rules-config-in]]
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=== +Config.in+ file
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+Config.in+ files contain entries for almost anything configurable in
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Buildroot.
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An entry has the following pattern:
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---------------------
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config BR2_PACKAGE_LIBFOO
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bool "libfoo"
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depends on BR2_PACKAGE_LIBBAZ
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select BR2_PACKAGE_LIBBAR
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help
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This is a comment that explains what libfoo is. The help text
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should be wrapped.
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http://foosoftware.org/libfoo/
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---------------------
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* The +bool+, +depends on+, +select+ and +help+ lines are indented
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with one tab.
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* The help text itself should be indented with one tab and two
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spaces.
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* The help text should be wrapped to fit 72 columns, where tab counts
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for 8, so 62 characters in the text itself.
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The +Config.in+ files are the input for the configuration tool
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used in Buildroot, which is the regular _Kconfig_. For further
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details about the _Kconfig_ language, refer to
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http://kernel.org/doc/Documentation/kbuild/kconfig-language.txt[].
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[[writing-rules-mk]]
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=== The +.mk+ file
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* Header: The file starts with a header. It contains the module name,
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preferably in lowercase, enclosed between separators made of 80 hashes. A
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blank line is mandatory after the header:
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+
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---------------------
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################################################################################
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#
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# libfoo
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#
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################################################################################
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---------------------
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+
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* Assignment: use +=+ preceded and followed by one space:
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+
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---------------------
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LIBFOO_VERSION = 1.0
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LIBFOO_CONF_OPTS += --without-python-support
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---------------------
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+
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Do not align the +=+ signs.
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* Indentation: use tab only:
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+
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---------------------
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define LIBFOO_REMOVE_DOC
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$(RM) -fr $(TARGET_DIR)/usr/share/libfoo/doc \
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$(TARGET_DIR)/usr/share/man/man3/libfoo*
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endef
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---------------------
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+
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Note that commands inside a +define+ block should always start with a tab,
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so _make_ recognizes them as commands.
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* Optional dependency:
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** Prefer multi-line syntax.
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+
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YES:
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+
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---------------------
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ifeq ($(BR2_PACKAGE_PYTHON),y)
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LIBFOO_CONF_OPTS += --with-python-support
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LIBFOO_DEPENDENCIES += python
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else
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LIBFOO_CONF_OPTS += --without-python-support
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endif
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---------------------
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+
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NO:
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+
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---------------------
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LIBFOO_CONF_OPTS += --with$(if $(BR2_PACKAGE_PYTHON),,out)-python-support
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LIBFOO_DEPENDENCIES += $(if $(BR2_PACKAGE_PYTHON),python,)
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---------------------
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** Keep configure options and dependencies close together.
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* Optional hooks: keep hook definition and assignment together in one
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if block.
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+
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YES:
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+
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---------------------
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ifneq ($(BR2_LIBFOO_INSTALL_DATA),y)
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define LIBFOO_REMOVE_DATA
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$(RM) -fr $(TARGET_DIR)/usr/share/libfoo/data
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endef
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LIBFOO_POST_INSTALL_TARGET_HOOKS += LIBFOO_REMOVE_DATA
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endif
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---------------------
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+
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NO:
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+
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---------------------
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define LIBFOO_REMOVE_DATA
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$(RM) -fr $(TARGET_DIR)/usr/share/libfoo/data
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endef
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ifneq ($(BR2_LIBFOO_INSTALL_DATA),y)
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LIBFOO_POST_INSTALL_TARGET_HOOKS += LIBFOO_REMOVE_DATA
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endif
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---------------------
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[[writing-genimage-cfg]]
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=== The +genimage.cfg+ file
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+genimage.cfg+ files contain the output image layout that genimage utility
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uses to create final .img file.
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An example follows:
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---------------------
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image efi-part.vfat {
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vfat {
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file EFI {
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image = "efi-part/EFI"
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}
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file Image {
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image = "Image"
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}
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}
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size = 32M
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}
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image sdimage.img {
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hdimage {
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}
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partition u-boot {
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image = "efi-part.vfat"
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offset = 8K
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}
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partition root {
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image = "rootfs.ext2"
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size = 512M
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}
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}
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---------------------
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* Every +section+(i.e. hdimage, vfat etc.), +partition+ must be indented
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with one tab.
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* Every +file+ or other +subnode+ must be indented with two tabs.
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* Every node(+section+, +partition+, +file+, +subnode+) must have an open
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curly bracket on the same line of the node's name, while the closing one
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must be on a newline and after it a newline must be added except for the
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last one node. Same goes for its option, for example option +size = +.
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* Every +option+(i.e. +image+, +offset+, +size+) must have the +=+
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assignment one space from it and one space from the value specified.
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* Filename must at least begin with genimage prefix and have the .cfg
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extension to be easy to recognize.
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The +genimage.cfg+ files are the input for the genimage tool used in
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Buildroot to generate the final image file(i.e. sdcard.img). For further
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details about the _genimage_ language, refer to
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https://github.com/pengutronix/genimage/blob/master/README.rst[].
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=== The documentation
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The documentation uses the
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http://www.methods.co.nz/asciidoc/[asciidoc] format.
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For further details about the asciidoc syntax, refer to
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http://www.methods.co.nz/asciidoc/userguide.html[].
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=== Support scripts
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Some scripts in the +support/+ and +utils/+ directories are written in
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Python and should follow the
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https://www.python.org/dev/peps/pep-0008/[PEP8 Style Guide for Python Code].
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