1. Mac OS 内核开发 - 介绍及FreeBSD内核扩展Hello World

在这个专题中，我将和大家一起分享苹果内核开发的常见编程，其中主要包括以下这些内容
1.介绍及FreeBSD驱动开发介绍
2.如何开发内核扩展程序
3.网络内核扩展
4.模块控制器
5.同步原语
6.内核线程
7.中断处理
8.内存管理
9.IO Kit及驱动开发
10.网络重定向实例
11.虚拟网络驱动实例
12.文件系统读写监控实例
13.USB驱动实例
14.串口驱动实例
15.电源管理实例
16.Debug以及开发环境相关内容
You may be think that writing your first kernel module is going to be a long, painful, grueling task, but really it is only slightly harder than writing your first program, Hello World!, in C or C++.

Lets break this into nice easy steps.
Prerequisites

It is assumed you have installed FreeBSD already. If not, follow the instructions below with one change: Install the FreeBSD source during the “Choose Distribution” section.

How do I install FreeBSD?

Step 1 – Create a basic module file

A FreeBSD kernel module is written in C. This is going to be only a slightly harder than writing hello world in C. We are going to create a single text file with a .c extension and put some C code in it.

    1.Create a folder to hold you project. I used this directory:
    /usr/home/jared/code/kernel/hwm
    2.Create the file to hold your code. I named my file this:
    hello_world_kmod.c
    3.Edit the file with you favorite editor, vi, vim, emac, ee. I used easy editor (ee):
    ee hello_world_kmod.c
    4.Add the following code to the file.I have broken the code of the simplest kernel module into four parts or steps:
        Add four required #include statements.
        Create the kernel load/unload event handler.
        Create a struct to name the module and point to the event handler function.
        Call the DECLARE_MODULE macro.

/*
 * Step 1 - Add the four needed libraries to include
 */
#include <sys/param.h>
#include <sys/module.h>
#include <sys/kernel.h>
#include <sys/systm.h>

/*
 * Step 2 - Handle the load/unload event
 */
static int EventHandler(struct module *inModule, int inEvent, void *inArg)
{
        // Set return code to 0
        int returnCode = 0;

        switch (inEvent)
        {
          case MOD_LOAD:
                uprintf("Hello, World! \n");
                break;
          case MOD_UNLOAD:
                uprintf("Bye, World! \n");
                break;
          default:
                returnCode = EOPNOTSUPP;
                break;
        }

        return(returnCode);
}

/*
 * Step 3 - Name the module and the event hander function
 *          This is done using a struct of type moduledata_T
 */
static moduledata_t  moduleData = {
        "hello_world_kmod",     // Module Name
        EventHandler,           // Event handler function name
        NULL                    // Extra data
};

/*
 * Step 4 - Declare the module
 *          This is done with the DECLARE_MODULE macro
 */
DECLARE_MODULE(hello_world_kmod, moduleData, SI_SUB_DRIVERS, SI_ORDER_MIDDLE);

5.Save and close the file.

Step 2 – Create a Makefile

Creating a Makefile to build a kernel module is quite easy because almost all the work is done for you. FreeBSD has a file that you include, /usr/src/share/mk/bsd.kmod.mk, that does most of the work for you and all you have to do is include it.

1. In the same directory where you put your .c file, create a new text file called Makefile.
2. There are three basic parts to the kernel module Makefile:
   1. Module name
   2. Source files
   3. Include of bsd.kmod.mk

# Module Name
KMOD = hello_world_kmod

# Source files

SRCS = hello_world_kmod.c

# Include
.include

3. Save and close the file.

Step 3 – Run make to build the module In the command prompt, in the directory where you have created your code and make file, run make.

> cd /usr/home/jared/code/kernel/hwm
> make
Warning: Object directory not changed from original /usr/home/jared/code/kernel/hwm
@ -> /usr/src/sys
machine -> /usr/src/sys/amd64/include
x86 -> /usr/src/sys/x86/include
cc -O2 -pipe -fno-strict-aliasing -Werror -D_KERNEL -DKLD_MODULE -nostdinc   -I. -I@ -I@/contrib/altq -finline-limit=8000 --param inline-unit-growth=100 --param large-function-growth=1000 -fno-common  -fno-omit-frame-pointer  -mno-sse -mcmodel=kernel -mno-red-zone -mno-mmx -msoft-float  -fno-asynchronous-unwind-tables -ffreestanding -fstack-protector -std=iso9899:1999 -fstack-protector -Wall -Wredundant-decls -Wnested-externs -Wstrict-prototypes  -Wmissing-prototypes -Wpointer-arith -Winline -Wcast-qual  -Wundef -Wno-pointer-sign -fformat-extensions  -Wmissing-include-dirs -fdiagnostics-show-option -c hello_world_kmod.c
ld  -d -warn-common -r -d -o hello_world_kmod.ko hello_world_kmod.o
:> export_syms
awk -f /sys/conf/kmod_syms.awk hello_world_kmod.ko  export_syms | xargs -J% objcopy % hello_world_kmod.ko
objcopy --strip-debug hello_world_kmod.ko
>

Step 4 – Test loading an unloading the module

Loading and unloading kernel modules must be done as root. If you have sudo installed, use it, otherwise install it () or su to root.

Use kldload to load the module and kldunload to unload the module.

> sudo kldload ./hello_world_kmod.ko
Hello, World!
> sudo kldunload ./hello_world_kmod.ko
Bye

You have now performed the Hello World version of a FreeBSD kernel module.