编译OpenWrt内核驱动

  编译OpenWrt内核驱动可以参考OpenWrt内部其它驱动的编写例程，来修改成自己需要的驱动

一、OpenWrt源代码获取与编译

1.1、搭建环境

  下载OpenWrt的官方源码：

git clone https://github.com/openwrt/openwrt.git

1.2、安装编译依赖项

sudo apt update -y
sudo apt full-upgrade -y
sudo apt install -y ack antlr3 asciidoc autoconf automake autopoint binutils bison build-essential \
bzip2 ccache cmake cpio curl device-tree-compiler fastjar flex gawk gettext gcc-multilib g++-multilib \
git gperf haveged help2man intltool libc6-dev-i386 libelf-dev libglib2.0-dev libgmp3-dev libltdl-dev \
libmpc-dev libmpfr-dev libncurses5-dev libncursesw5-dev libreadline-dev libssl-dev libtool lrzsz \
mkisofs msmtp nano ninja-build p7zip p7zip-full patch pkgconf python2.7 python3 python3-pyelftools \
libpython3-dev qemu-utils rsync scons squashfs-tools subversion swig texinfo uglifyjs upx-ucl unzip \
vim wget xmlto xxd zlib1g-dev python3-setuptools

1.3、更新 feeds

  进入openwrt目录后执行以下指令

./scripts/feeds update -a
./scripts/feeds install -a

1.4、配置编译选项

  根据自己的平台来选择编译选项

make menuconfig

1.5、下载 dl 库

  进入openwrt目录后执行以下指令

make download -j8

1.6、编译

make V=s -j1

二、OpenWrt驱动源代码分析

  OpenWrt驱动存放目录为openwrt\package\kernel

  以gpio-button-hotplug驱动为例，进行分析。在gpio-button-hotplug文件夹下面有一个Makefile文件和src文件夹，而src文件夹下有模块源码gpio-button-hotplug.c和源码编译Makefile

2.1、顶层makefile分析

  顶层makefile如下：

#
# Copyright (C) 2008-2012 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:=gpio-button-hotplug
PKG_RELEASE:=3
PKG_LICENSE:=GPL-2.0

include $(INCLUDE_DIR)/package.mk

define KernelPackage/gpio-button-hotplug
  SUBMENU:=Other modules
  TITLE:=Simple GPIO Button Hotplug driver
  FILES:=$(PKG_BUILD_DIR)/gpio-button-hotplug.ko
  AUTOLOAD:=$(call AutoLoad,30,gpio-button-hotplug,1)
  KCONFIG:=
endef

define KernelPackage/gpio-button-hotplug/description
 This is a replacement for the following in-kernel drivers:
 1) gpio_keys (KEYBOARD_GPIO)
 2) gpio_keys_polled (KEYBOARD_GPIO_POLLED)

 Instead of generating input events (like in-kernel drivers do) it generates
 uevent-s and broadcasts them. This allows disabling input subsystem which is
 an overkill for OpenWrt simple needs.
endef

define Build/Compile
	$(KERNEL_MAKE) M="$(PKG_BUILD_DIR)" modules
endef

$(eval $(call KernelPackage,gpio-button-hotplug))

2.1.1、第一步

  首先包含rules.mk、kernel.mk和package.mk文件。接着将驱动模块的名称定义为“gpio-button-hotplug”，并设置版本编号为“3”。

2.1.2、第二步

  在软件包定义中的一些变量赋值：
  SUBMENU：我们内核模块放置于“Other modules”。我们在make menuconfig时，可以在Kernel modules/other modules菜单下找到这个模块。
  TITLE：标题，驱动模块的简短描述。
  FILES：生成的驱动模块的存放位置。此处为设置为在编译目录下（就是编译过程中的临时目录build_dir）。
  AUTOLOAD：代表是否在系统启动时自动装载到内核中，后面括号内有3个参数（参数1不变，参数2为驱动模块的装载顺序(可以省略这个参数，省略后系统自动分配状态顺序)，参数3代表驱动模块名称）。
  DEPENDS：如果驱动模块还需要依赖，则此变量设置为依赖文件名（此处没有依赖所以就未设置）。

2.1.3、第三步

  配置menuconfig时的描述信息

2.1.4、第四步

  编译源代码选项，在大多数情况下应该不用定义而使用默认值

2.1.5、第五步

  最后KernelPackage，将驱动模块的名称作为参数传递给KernelPackage

2.2、源码makefile

obj-m += gpio-button-hotplug.o

2.3、源码gpio-button-hotplug.c

  gpio-button-hotplug.c就是驱动的实际代码

三、编写自己的OpenWrt驱动代码

  将gpio-button-hotplug文件夹复制为mykernel_test，放置到gpio-button-hotplug相同的目录下

3.1、顶层makefile

  修改顶层makefile如下：

#
# Copyright (C) 2008-2012 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:=mykernel_test
PKG_RELEASE:=3
PKG_LICENSE:=GPL-2.0

include $(INCLUDE_DIR)/package.mk

define KernelPackage/mykernel_test
  SUBMENU:=Other modules
  TITLE:=Simple GPIO Button Hotplug driver
  FILES:=$(PKG_BUILD_DIR)/mykernel_test.ko
  AUTOLOAD:=$(call AutoLoad,30,mykernel_test,1)
  KCONFIG:=
endef

define KernelPackage/mykernel_test/description
 This is a replacement for the following in-kernel drivers:
 1) gpio_keys (KEYBOARD_GPIO)
 2) gpio_keys_polled (KEYBOARD_GPIO_POLLED)

 Instead of generating input events (like in-kernel drivers do) it generates
 uevent-s and broadcasts them. This allows disabling input subsystem which is
 an overkill for OpenWrt simple needs.
endef

define Build/Compile
	$(KERNEL_MAKE) M="$(PKG_BUILD_DIR)" modules
endef

$(eval $(call KernelPackage,mykernel_test))

3.2、源码makefile

obj-m += mykernel_test.o

3.3、源码mykernel_test.c.c

#include 
#include 
 
static int __init mykernel_test_init(void)
{
	printk(KERN_INFO "mykernel_test enter\n");
	return 0;
}

 
static void __exit mykernel_test_exit(void)
{
	printk(KERN_INFO "mykernel_test  exit\n ");
}
module_init(mykernel_test_init);
module_exit(mykernel_test_exit);
MODULE_LICENSE("GPL v2");

四、编译自己的OpenWrt驱动代码

4.1、配置

  在OpenWrt源码顶级目录下输入下面的命令配置内核

make menuconfig

  依次按照如下顺序选择：

4.2、编译

  在OpenWrt源码顶级目录下输入下面的命令编译驱动模块

make package/kernel/mykernel_test/compile V=s

  编译完成之后会在下面的目录中看到我们的内核模块

  此ko模块和普通的linux内核的驱动模块的装载方法一样，不再赘述。