32cec3be97
by using this standard extension `adoc`, these files are rendered on gitlab & github Signed-off-by: Francois Perrad <francois.perrad@gadz.org> Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
153 lines
5.6 KiB
Plaintext
153 lines
5.6 KiB
Plaintext
// -*- mode:doc; -*-
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// vim: set syntax=asciidoc:
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[[linux-kernel-specific-infra]]
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=== Infrastructure specific to the Linux kernel package
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The Linux kernel package can use some specific infrastructures based on package
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hooks for building Linux kernel tools or/and building Linux kernel extensions.
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[[linux-kernel-tools]]
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==== linux-kernel-tools
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Buildroot offers a helper infrastructure to build some userspace tools
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for the target available within the Linux kernel sources. Since their
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source code is part of the kernel source code, a special package,
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+linux-tools+, exists and re-uses the sources of the Linux kernel that
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runs on the target.
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Let's look at an example of a Linux tool. For a new Linux tool named
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+foo+, create a new menu entry in the existing
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+package/linux-tools/Config.in+. This file will contain the option
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descriptions related to each kernel tool that will be used and
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displayed in the configuration tool. It would basically look like:
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------------------------------
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01: config BR2_PACKAGE_LINUX_TOOLS_FOO
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02: bool "foo"
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03: select BR2_PACKAGE_LINUX_TOOLS
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04: help
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05: This is a comment that explains what foo kernel tool is.
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06:
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07: http://foosoftware.org/foo/
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------------------------------
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The name of the option starts with the prefix +BR2_PACKAGE_LINUX_TOOLS_+,
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followed by the uppercase name of the tool (like is done for packages).
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.Note
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Unlike other packages, the +linux-tools+ package options appear in the
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+linux+ kernel menu, under the `Linux Kernel Tools` sub-menu, not under
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the `Target packages` main menu.
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Then for each linux tool, add a new +.mk.in+ file named
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+package/linux-tools/linux-tool-foo.mk.in+. It would basically look like:
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------------------------------
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01: ################################################################################
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02: #
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03: # foo
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04: #
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05: ################################################################################
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06:
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07: LINUX_TOOLS += foo
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08:
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09: FOO_DEPENDENCIES = libbbb
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10:
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11: define FOO_BUILD_CMDS
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12: $(TARGET_MAKE_ENV) $(MAKE) -C $(LINUX_DIR)/tools foo
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13: endef
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14:
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15: define FOO_INSTALL_STAGING_CMDS
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16: $(TARGET_MAKE_ENV) $(MAKE) -C $(LINUX_DIR)/tools \
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17: DESTDIR=$(STAGING_DIR) \
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18: foo_install
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19: endef
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20:
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21: define FOO_INSTALL_TARGET_CMDS
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22: $(TARGET_MAKE_ENV) $(MAKE) -C $(LINUX_DIR)/tools \
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23: DESTDIR=$(TARGET_DIR) \
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24: foo_install
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25: endef
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--------------------------------
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On line 7, we register the Linux tool +foo+ to the list of available
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Linux tools.
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On line 9, we specify the list of dependencies this tool relies on. These
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dependencies are added to the Linux package dependencies list only when the
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+foo+ tool is selected.
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The rest of the Makefile, lines 11-25 defines what should be done at the
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different steps of the Linux tool build process like for a
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xref:generic-package-tutorial[+generic package+]. They will actually be
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used only when the +foo+ tool is selected. The only supported commands are
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+_BUILD_CMDS+, +_INSTALL_STAGING_CMDS+ and +_INSTALL_TARGET_CMDS+.
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.Note
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One *must not* call +$(eval $(generic-package))+ or any other
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package infrastructure! Linux tools are not packages by themselves,
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they are part of the +linux-tools+ package.
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[[linux-kernel-ext]]
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==== linux-kernel-extensions
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Some packages provide new features that require the Linux kernel tree
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to be modified. This can be in the form of patches to be applied on
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the kernel tree, or in the form of new files to be added to the
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tree. The Buildroot's Linux kernel extensions infrastructure provides
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a simple solution to automatically do this, just after the kernel
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sources are extracted and before the kernel patches are
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applied. Examples of extensions packaged using this mechanism are the
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real-time extensions Xenomai and RTAI, as well as the set of
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out-of-tree LCD screens drivers +fbtft+.
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Let's look at an example on how to add a new Linux extension +foo+.
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First, create the package +foo+ that provides the extension: this
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package is a standard package; see the previous chapters on how to
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create such a package. This package is in charge of downloading the
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sources archive, checking the hash, defining the licence informations
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and building user space tools if any.
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Then create the 'Linux extension' proper: create a new menu entry in
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the existing +linux/Config.ext.in+. This file contains the option
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descriptions related to each kernel extension that will be used and
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displayed in the configuration tool. It would basically look like:
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------------------------------
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01: config BR2_LINUX_KERNEL_EXT_FOO
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02: bool "foo"
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03: help
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04: This is a comment that explains what foo kernel extension is.
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05:
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06: http://foosoftware.org/foo/
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------------------------------
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Then for each linux extension, add a new +.mk+ file named
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+linux/linux-ext-foo.mk+. It should basically contain:
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------------------------------
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01: ################################################################################
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02: #
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03: # foo
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04: #
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05: ################################################################################
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06:
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07: LINUX_EXTENSIONS += foo
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08:
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09: define FOO_PREPARE_KERNEL
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10: $(FOO_DIR)/prepare-kernel-tree.sh --linux-dir=$(@D)
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11: endef
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--------------------------------
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On line 7, we add the Linux extension +foo+ to the list of available
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Linux extensions.
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On line 9-11, we define what should be done by the extension to modify
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the Linux kernel tree; this is specific to the linux extension and can
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use the variables defined by the +foo+ package, like: +$(FOO_DIR)+ or
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+$(FOO_VERSION)+... as well as all the Linux variables, like:
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+$(LINUX_VERSION)+ or +$(LINUX_VERSION_PROBED)+, +$(KERNEL_ARCH)+...
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See the xref:kernel-variables[definition of those kernel variables].
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