学号后三位：446 原创作品转载请注明出处
https://github.com/mengning/linuxkernel/。
1.环境配置
由于自己机器下载linux内核太慢，于是便决定在实验楼上进行操作。
环境：实验楼+linuxkernel3.94+qemu虚拟机
实验楼地址：https://www.shiyanlou.com/courses/195
github地址：https://github.com/mengning/linuxkernel/
若在自己的linux上做实验，请看：https://github.com/mengning/mykernel/
2.实验准备
打开shell，依次输入命令。
cd LinuxKernel/linux-3.9.4
rm -rf mykernel
patch -p1 < ../mykernel_for_linux3.9.4sc.patch
make allnoconfig
make ＃编译内核，第一次较缓慢
qemu -kernel arch/x86/boot/bzImage #开启虚拟机
3.mykernel分析。
3.1mykernel运行结果分析
可以从上图中看到启动后会循环运行my_start_kernel，并周期运行my_timer_heandler时钟程中断程序。
3.2 mykernel代码分析
通过ls命令我们可以发现主要的代码文件为mymain.c与myinterrupt.c文件。
//mymain.c
void __init my_start_kernel(void)
{
int i = 0;
while(1)
{
i++;
//无限递增i，当i为100000的整除时打印i与字符。
if(i%100000 == 0)
printk(KERN_NOTICE "my_start_kernel here %d \n",i);
}
}
//myinterrupt.c
/*
* Called by timer interrupt.
*/
void my_timer_handler(void)
{
//周期性的打印字符
printk(KERN_NOTICE "\n>>>>>>>>>>>>>>>>>my_timer_handler here<<<<<<<<<<<<<<<<<<\n\n");
}
通过对代码与实验结果的分析，我们发现只要能利用好时钟中断程序，我们就可以开始做我们的简易多道程序的轮换了！
4.简单的时间片轮转多道程序
4.1 实验准备
首先要感谢孟宁老师发布的代码，我们需要首先将代码部署到我们的实验环境下，通过git clone获取代码。
git clone https://github.com/mengning/mykernel.git
获取代码后我们将其中主要的三个文件mymain.c，myinterrupt.c，mypcb.h覆盖到目录下，并重新编译：
make allnoconfig
make
qemu -kernel arch/x86/boot/bzImage
4.2 实验结果分析
我们可以看到在我们的程序下四个进程来回占用时间片。
4.3 程序代码分析
/*
* linux/mykernel/mymain.c
*
* Kernel internal my_start_kernel
*
* Copyright (C) 2013 Mengning
*
*/
#include <linux/types.h>
#include <linux/string.h>
#include <linux/ctype.h>
#include <linux/tty.h>
#include <linux/vmalloc.h>
#include "mypcb.h"
/*先声明了一个程序队列与当前占用程序的程序，初始当前程序无*/
tPCB task[MAX_TASK_NUM];
tPCB * my_current_task = NULL;
volatile int my_need_sched = 0;
void my_process(void);
void __init my_start_kernel(void)
{
int pid = 0;
int i;
/* Initialize process 0*/
/*初始化进程，初始进程的pid为0*/
task[pid].pid = pid;
task[pid].state = 0;/* -1 unrunnable, 0 runnable, >0 stopped */
task[pid].task_entry = task[pid].thread.ip = (unsigned long)my_process;
task[pid].thread.sp = (unsigned long)&task[pid].stack[KERNEL_STACK_SIZE-1];
task[pid].next = &task[pid];
/*fork more process */
/*初始化几个进程，先通过memcpy函数为新进程准备空间，为其赋予pid，并将其链接成单循环队列*/
for(i=1;i<MAX_TASK_NUM;i++)
{
memcpy(&task[i],&task[0],sizeof(tPCB));
task[i].pid = i;
//*(&task[i].stack[KERNEL_STACK_SIZE-1] - 1) = (unsigned long)&task[i].stack[KERNEL_STACK_SIZE-1];
task[i].thread.sp = (unsigned long)(&task[i].stack[KERNEL_STACK_SIZE-1]);
task[i].next = task[i-1].next;
task[i-1].next = &task[i];
}
/* start process 0 by task[0] */
//开始task[0]
pid = 0;
my_current_task = &task[pid];
asm volatile(
"movl %1,%%esp\n\t" /* set task[pid].thread.sp to esp */
"pushl %1\n\t" /* push ebp */
"pushl %0\n\t" /* push task[pid].thread.ip */
"ret\n\t" /* pop task[pid].thread.ip to eip */
:
: "c" (task[pid].thread.ip),"d" (task[pid].thread.sp) /* input c or d mean %ecx/%edx*/
);
}
int i = 0;
//循环进程
void my_process(void)
{
while(1)
{
i++;
if(i%10000000 == 0)//当i为1000000的倍数的切换时间片
{
printk(KERN_NOTICE "this is process %d -\n",my_current_task->pid);
if(my_need_sched == 1)
{
my_need_sched = 0;
my_schedule();
}
printk(KERN_NOTICE "this is process %d +\n",my_current_task->pid);
}
}
}
/*
* linux/mykernel/mypcb.h
*
* Kernel internal PCB types
*
* Copyright (C) 2013 Mengning
*
*/
/*定义了程序的数量*/
#define MAX_TASK_NUM 4
#define KERNEL_STACK_SIZE 1024*2
/* CPU-specific state of this task */
/**/
/*线程的数据结构，规定了线程的ip与sp*/
struct Thread {
unsigned long ip;
unsigned long sp;
};
/*PCB的数据结构，定义了pid，进程状态，程序堆栈，程序入口与程序队列*/
typedef struct PCB{
int pid;
volatile long state; /* -1 unrunnable, 0 runnable, >0 stopped */
unsigned long stack[KERNEL_STACK_SIZE];
/* CPU-specific state of this task */
struct Thread thread;
unsigned long task_entry;
struct PCB *next;
}tPCB;
void my_schedule(void);
*
* linux/mykernel/myinterrupt.c
*
* Kernel internal my_timer_handler
*
* Copyright (C) 2013 Mengning
*
*/
#include <linux/types.h>
#include <linux/string.h>
#include <linux/ctype.h>
#include <linux/tty.h>
#include <linux/vmalloc.h>
#include "mypcb.h"
extern tPCB task[MAX_TASK_NUM];
extern tPCB * my_current_task;
extern volatile int my_need_sched;
volatile int time_count = 0;
/*
* Called by timer interrupt.
* it runs in the name of current running process,
* so it use kernel stack of current running process
*/
void my_timer_handler(void)
{
#if 1
if(time_count%1000 == 0 && my_need_sched != 1)
{
printk(KERN_NOTICE ">>>my_timer_handler here<<<\n");
my_need_sched = 1;
}
time_count ++ ;
#endif
return;
}
void my_schedule(void)
{
tPCB * next;
tPCB * prev;
//如果当前没有进程或进程队列结束
if(my_current_task == NULL
|| my_current_task->next == NULL)
{
return;
}
printk(KERN_NOTICE ">>>my_schedule<<<\n");
/* schedule */
next = my_current_task->next;//切换进程
prev = my_current_task;
//如果下个进程状态为可运行状态的话，则切换进程
if(next->state == 0)/* -1 unrunnable, 0 runnable, >0 stopped */
{
my_current_task = next;
printk(KERN_NOTICE ">>>switch %d to %d<<<\n",prev->pid,next->pid);
/* switch to next process */
asm volatile(
"pushl %%ebp\n\t" /* save ebp */
"movl %%esp,%0\n\t" /* save esp */
"movl %2,%%esp\n\t" /* restore esp */
"movl $1f,%1\n\t" /* save eip */
"pushl %3\n\t"
"ret\n\t" /* restore eip */
"1:\t" /* next process start here */
"popl %%ebp\n\t"
: "=m" (prev->thread.sp),"=m" (prev->thread.ip)
: "m" (next->thread.sp),"m" (next->thread.ip)
);
}
return;
}
总的来说，mypcb定义了进程的数据结构，myinterrupt负责时钟切换程序与程序的交替，mymain是入口，负责对进程进行初始化，包括初始化PCB与启动0号进程等。
5 总结
通过这次手动模拟操作系统进程的切换过程让我加深了对操作系统原理的理解，同时观看汇编代码加深了我对CPU寄存器，函数堆栈，汇编代码等理解，感谢孟老师提供的机会与代码，让我受益匪浅。