[Buildroot] [PATCH 01/11] package-infra: add helper to build kernel modules

[Yann E. MORIN]

The Linux kernel offers a nice and easy-to-use infra to build
out-of-tree kernel modules.

Currently, we have quite a few packages that build kernel modules, and
most dupliacte (or rewrite) the same code over-and-over again.

Introduce a new infrastructure that provides helpers to build kernel
modules, so packages do not have to duplicate/rewrite that.

The infrastrucutre, unlike any other package infra, is not standalone.
It needs another package infra to be used. This is so that packages that
provide both userland and kernel modules can be built easily. So, this
infra only defines post-build and post-install hooks, that will build
the kernel modules after the rest of the package.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998 at free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni at free-electrons.com>
---
 package/Makefile.in          |  1 +
 package/pkg-kernel-module.mk | 94 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 95 insertions(+)
 create mode 100644 package/pkg-kernel-module.mk

diff --git a/package/Makefile.in b/package/Makefile.in
index c02d31f..180fd46 100644
--- a/package/Makefile.in
+++ b/package/Makefile.in
@@ -398,3 +398,4 @@ include package/pkg-virtual.mk
 include package/pkg-generic.mk
 include package/pkg-kconfig.mk
 include package/pkg-rebar.mk
+include package/pkg-kernel-module.mk
diff --git a/package/pkg-kernel-module.mk b/package/pkg-kernel-module.mk
new file mode 100644
index 0000000..2a2a2cb
--- /dev/null
+++ b/package/pkg-kernel-module.mk
@@ -0,0 +1,94 @@
+################################################################################
+# kernel module infrastructure for building Linux kernel modules
+#
+# This file implements an frastructure that eases development of package .mk
+# files for out-of-tree Linux kernel modules. It should be used for all
+# packages that build a Linux kernel module.
+#
+# In terms of implementation, this infrastructure requires the .mk file to
+# only specify metadata information about the package: name, version,
+# download URL, etc.
+#
+# It defines post-build and post-install hooks, so that packages can both
+# build user-space (with any of the other *-package infra) and/or build
+# kernel modules.
+#
+# As such, it is to be used in conjunction with another *-package infra,
+# like so:
+#
+#   $(eval $(kernel-module))
+#   $(eval $(generic-package))
+#
+# Note: if the caller needs access to the kernel modules (either after they
+# are built or after they are installed), it will have to define its own
+# post-build/install hooks after calling kernel-module, but before calling
+# the other *-package infra, like so:
+#
+#   $(eval $(kernel-module))
+#   define FOO_MOD_TWEAK
+#   	# do something
+#   endef
+#   FOO_POST_BUILD_HOOKS += FOO_MOD_TWEAK
+#   $(eval $(generic-package))
+#
+# Note: this infra does not check that the kernel is enabled; it is expected
+# to be enforced at the Kconfig level with proper 'depends on'.
+################################################################################
+
+################################################################################
+# inner-kernel-module -- generates the make targets needed to support building
+# a kernel module
+#
+#  argument 1 is the lowercase package name
+#  argument 2 is the uppercase package name, including a HOST_ prefix
+#             for host packages
+#  argument 3 is the uppercase package name, without the HOST_ prefix
+#             for host packages
+#  argument 4 is the type (always 'target')
+################################################################################
+
+define inner-kernel-module
+
+# The kernel must be built first.
+$(2)_DEPENDENCIES += linux
+
+# Duplicate that from pkg-generic because we need it now
+ifndef $(2)_MAKE
+  $(2)_MAKE = $(MAKE)
+endif
+
+ifndef $(2)_MODULE_SUBDIRS
+  $(2)_MODULE_SUBDIRS = .
+endif
+
+# Build the kernel module(s)
+define $(2)_KERNEL_MODULES_BUILD
+	$$(foreach d,$$($(2)_MODULE_SUBDIRS), \
+		@$$(call MESSAGE,"Building kernel module '$$(d)'")$$(sep) \
+		$$($$(PKG)_MAKE) -C $$(LINUX_DIR) \
+			$$(LINUX_MAKE_FLAGS) \
+			$$($(2)_MODULE_MAKE_OPTS) \
+			M=$$($(2)_DIR)/$$(d) \
+			modules$$(sep))
+endef
+$(2)_POST_BUILD_HOOKS += $(2)_KERNEL_MODULES_BUILD
+
+# Install the kernel module(s)
+define $(2)_KERNEL_MODULES_INSTALL
+	$$(foreach d,$$($(2)_MODULE_SUBDIRS), \
+		@$$(call MESSAGE,"Installing kernel module '$$(d)'")$$(sep) \
+		$$($$(PKG)_MAKE) -C $$(LINUX_DIR) \
+			$$(LINUX_MAKE_FLAGS) \
+			$$($(2)_MODULE_MAKE_OPTS) \
+			M=$$($(2)_DIR)/$$(d) \
+			modules_install$$(sep))
+endef
+$(2)_POST_INSTALL_TARGET_HOOKS += $(2)_KERNEL_MODULES_INSTALL
+
+endef
+
+################################################################################
+# kernel-module -- the target generator macro for kernel module packages
+################################################################################
+
+kernel-module = $(call inner-kernel-module,$(pkgname),$(call UPPERCASE,$(pkgname)),$(call UPPERCASE,$(pkgname)),target)
-- 
1.9.1