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Write kernel module for openwrt15.05


1 kernel module code structure

package/hello
├── Makefile
└── src
    ├── hello.c
    ├── Kconfig
    └── Makefile

2 source code

2.1 hello/Makefile

#
# Copyright (C) 2008 OpenWrt.org
#
# This is free software, licensed under the GNU General Public License v2.
# See /LICENSE for more information.
#

include $(TOPDIR)/rules.mk
include $(INCLUDE_DIR)/kernel.mk

PKG_NAME:=hello
PKG_RELEASE:=1

include $(INCLUDE_DIR)/package.mk

define KernelPackage/$(PKG_NAME)
  SUBMENU:=Test Modules
  TITLE:=hello driver
  FILES:=$(PKG_BUILD_DIR)/*.$(LINUX_KMOD_SUFFIX)
  KCONFIG:=
endef

define KernelPackage/$(PKG_NAME)/description
  Kernel module hello
endef

EXTRA_KCONFIG:= \
    CONFIG_HELLO=m

EXTRA_CFLAGS:= \
    $(patsubst CONFIG_%, -DCONFIG_%=1, $(patsubst %=m,%,$(filter %=m,$(EXTRA_KCONFIG)))) \
    $(patsubst CONFIG_%, -DCONFIG_%=1, $(patsubst %=y,%,$(filter %=y,$(EXTRA_KCONFIG)))) \

MAKE_OPTS:= \
    ARCH="$(LINUX_KARCH)" \
    CROSS_COMPILE="$(TARGET_CROSS)" \
    SUBDIRS="$(PKG_BUILD_DIR)" \
    EXTRA_CFLAGS="$(EXTRA_CFLAGS)" \
    $(EXTRA_KCONFIG)

define Build/Prepare
    mkdir -p $(PKG_BUILD_DIR)
    $(CP) ./src/* $(PKG_BUILD_DIR)/
endef

define Build/Compile
    $(MAKE) -C "$(LINUX_DIR)" \
    $(MAKE_OPTS) \
    modules
endef

$(eval $(call KernelPackage,$(PKG_NAME)))

2.2 hello/src/hello.c

#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>

static int __init hello_init(void)
{
  printk("%s\n", __func__);
  return 0;
}

static void __exit hello_exit(void)
{
  printk("%s\n", __func__);
}

module_init(hello_init);
module_exit(hello_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Kevin");

2.3 hello/src/Kconfig

config HELLO
　　tristate "Just a example"
　　help
　　　This is a example, for debugging kernel model.
　　　If unsure, say N.

2.4 hello/src/Makefile

obj-$(CONFIG_HELLO) += hello.o

3 module select and compile

3.1 module select

$ make menuconfig

Kernel modules --->
  Test Modules --->
    <M> kmod-hello

3.2 module compile

make package/hello/{clean,prepare,compile,install} V=s

the compiled module locates in: 

build_dir/target-arm_cortex-a7_uClibc-1.0.14_eabi/linux-ipq806x/hello/

4 download the kernel module

kernel-module-hello.tgz