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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>
144 lines
5.0 KiB
Plaintext
144 lines
5.0 KiB
Plaintext
// -*- mode:doc; -*-
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// vim: set syntax=asciidoc:
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=== Infrastructure for packages building kernel modules
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Buildroot offers a helper infrastructure to make it easy to write packages that
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build and install Linux kernel modules. Some packages only contain a kernel
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module, other packages contain programs and libraries in addition to kernel
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modules. Buildroot's helper infrastructure supports either case.
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[[kernel-module-tutorial]]
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==== +kernel-module+ tutorial
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Let's start with an example on how to prepare a simple package that only
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builds a kernel module, and no other component:
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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: FOO_VERSION = 1.2.3
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08: FOO_SOURCE = foo-$(FOO_VERSION).tar.xz
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09: FOO_SITE = http://www.foosoftware.org/download
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10: FOO_LICENSE = GPL-2.0
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11: FOO_LICENSE_FILES = COPYING
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12:
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13: $(eval $(kernel-module))
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14: $(eval $(generic-package))
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----
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Lines 7-11 define the usual meta-data to specify the version, archive name,
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remote URI where to find the package source, licensing information.
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On line 13, we invoke the +kernel-module+ helper infrastructure, that
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generates all the appropriate Makefile rules and variables to build
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that kernel module.
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Finally, on line 14, we invoke the
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xref:generic-package-tutorial[+generic-package+ infrastructure].
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The dependency on +linux+ is automatically added, so it is not needed to
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specify it in +FOO_DEPENDENCIES+.
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What you may have noticed is that, unlike other package infrastructures,
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we explicitly invoke a second infrastructure. This allows a package to
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build a kernel module, but also, if needed, use any one of other package
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infrastructures to build normal userland components (libraries,
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executables...). Using the +kernel-module+ infrastructure on its own is
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not sufficient; another package infrastructure *must* be used.
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Let's look at a more complex example:
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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: FOO_VERSION = 1.2.3
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08: FOO_SOURCE = foo-$(FOO_VERSION).tar.xz
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09: FOO_SITE = http://www.foosoftware.org/download
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10: FOO_LICENSE = GPL-2.0
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11: FOO_LICENSE_FILES = COPYING
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12:
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13: FOO_MODULE_SUBDIRS = driver/base
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14: FOO_MODULE_MAKE_OPTS = KVERSION=$(LINUX_VERSION_PROBED)
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15:
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16: ifeq ($(BR2_PACKAGE_LIBBAR),y)
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17: FOO_DEPENDENCIES += libbar
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18: FOO_CONF_OPTS += --enable-bar
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19: FOO_MODULE_SUBDIRS += driver/bar
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20: else
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21: FOO_CONF_OPTS += --disable-bar
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22: endif
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23:
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24: $(eval $(kernel-module))
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26: $(eval $(autotools-package))
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----
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Here, we see that we have an autotools-based package, that also builds
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the kernel module located in sub-directory +driver/base+ and, if libbar
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is enabled, the kernel module located in sub-directory +driver/bar+, and
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defines the variable +KVERSION+ to be passed to the Linux buildsystem
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when building the module(s).
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[[kernel-module-reference]]
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==== +kernel-module+ reference
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The main macro for the kernel module infrastructure is +kernel-module+.
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Unlike other package infrastructures, it is not stand-alone, and requires
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any of the other +*-package+ macros be called after it.
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The +kernel-module+ macro defines post-build and post-target-install
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hooks to build the kernel modules. If the package's +.mk+ needs access
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to the built kernel modules, it should do so in a post-build hook,
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*registered after* the call to +kernel-module+. Similarly, if the
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package's +.mk+ needs access to the kernel module after it has been
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installed, it should do so in a post-install hook, *registered after*
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the call to +kernel-module+. Here's an example:
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----
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$(eval $(kernel-module))
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define FOO_DO_STUFF_WITH_KERNEL_MODULE
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# Do something with it...
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endef
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FOO_POST_BUILD_HOOKS += FOO_DO_STUFF_WITH_KERNEL_MODULE
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$(eval $(generic-package))
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----
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Finally, unlike the other package infrastructures, there is no
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+host-kernel-module+ variant to build a host kernel module.
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The following additional variables can optionally be defined to further
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configure the build of the kernel module:
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* +FOO_MODULE_SUBDIRS+ may be set to one or more sub-directories (relative
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to the package source top-directory) where the kernel module sources are.
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If empty or not set, the sources for the kernel module(s) are considered
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to be located at the top of the package source tree.
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* +FOO_MODULE_MAKE_OPTS+ may be set to contain extra variable definitions
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to pass to the Linux buildsystem.
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[[kernel-variables]]
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You may also reference (but you may *not* set!) those variables:
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* +LINUX_DIR+ contains the path to where the Linux kernel has been
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extracted and built.
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* +LINUX_VERSION+ contains the version string as configured by the user.
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* +LINUX_VERSION_PROBED+ contains the real version string of the kernel,
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retrieved with running `make -C $(LINUX_DIR) kernelrelease`
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* +KERNEL_ARCH+ contains the name of the current architecture, like `arm`,
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`mips`...
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