基于mykernel 2.0编写一个操作系统内核

mykernel2.0基于linux-5.4.34版本，来源https://github.com/mengning/mykernel，在本实验中首先配置并编译了mykernel2.0，其次进程切换作为操作系统内核最核心的功能，在本实验中，实现了基于时间片轮转调度算法的进程切换功能。

1. 配置并编译mykernel 2.0

1.1 安装开发工具

sudo apt install build-essential gcc-multilib

sudo apt install qemu #一种模拟器

sudo apt install libncurses5-dev bison flex libssl-dev libelf-dev

1.2 下载内核源码

sudo apt install axel#一种多线程下载工具
axel -n 20 https://mirrors.edge.kernel.org/pub/linux/kernel/v5.x/linux-5.4.34.tar.xz
xz -d linux-5.4.34.tar.xz 
tar -xvf linux-5.4.34.tar 
cd linux-5.4.34
wget https://raw.github.com/mengning/mykernel/master/mykernel-2.0_for_linux-5.4.34.patch#打补丁
patch -p1 < ../mykernel-2.0_for_linux-5.4.34.patch

1.3 配置内核

make defconfig # 默认的配置基于'x86_64_defconfig' 
make menuconfig #图形化界面配置

 

1.4 编译和运行内核

make -j$(nproc)
qemu-system-x86_64 -kernel arch/x86/boot/bzImage

因为在mykernel目录下，已有mymain.c和myinterrupt.c文件，所以在虚拟机上运行时会出现如下界面，说明mykernel配置完成并正常运行。

 

 

1.5制作内存跟文件系统

mkdir rootfs
cd rootfs
cp ../busybox-1.31.1/_install/* ./ -rf
mkdir dev proc sys home
sudo cp -a /dev/{null,console,tty,tty1,tty2,tty3,tty4} dev/

准备init文件：

#!/bin/sh
mount -t proc none /proc mount -t sysfs none /sys
echo "Wellcome MengningOS!" echo "--------------------"
cd home
/bin/sh

chmod +x init #添加权限

find . -print0 | cpio --null -ov --format=newc | gzip -9 > ../rootfs.cpio.gz#打包成内存根文件系统镜像

2. 编写基于时间片轮转算法的进程切换程序

2.1 编写mypcb.h文件如下：

#define MAX_TASK_NUM        4
#define KERNEL_STACK_SIZE   1024*2
/* CPU-specific state of this task */
struct Thread {
    unsigned long        ip;
    unsigned long        sp;
};

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);

2.2 编写mymain.c文件如下：

#include <linux/types.h>
#include <linux/string.h>
#include <linux/ctype.h>
#include <linux/tty.h>
#include <linux/vmalloc.h>


#include "mypcb.h"

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*/
    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 */
    for(i=1;i<MAX_TASK_NUM;i++)
    {
        memcpy(&task[i],&task[0],sizeof(tPCB));
        task[i].pid = i;
        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] */
    pid = 0;
    my_current_task = &task[pid];
    asm volatile(
        "movq %1,%%rsp\n\t"     /* set task[pid].thread.sp to rsp */
        "pushq %1\n\t"             /* push rbp */
        "pushq %0\n\t"             /* push task[pid].thread.ip */
        "ret\n\t"                 /* pop task[pid].thread.ip to rip */
        : 
        : "c" (task[pid].thread.ip),"d" (task[pid].thread.sp)    /* input c or d mean %ecx/%edx*/
    );
} 

int i = 0;

void my_process(void)
{    
    while(1)
    {
        i++;
        if(i%10000000 == 0)
        {
            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);
        }     
    }
}

2.3 编写myinterrupt.c文件如下：

#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(time_count%1000 == 0 && my_need_sched != 1)
    {
        printk(KERN_NOTICE ">>>my_timer_handler here<<<\n");
        my_need_sched = 1;
    } 
    time_count ++ ;  
    return;      
}

void my_schedule(void)
{
    tPCB * next;
    tPCB * prev;

    if(my_current_task == NULL 
        || my_current_task->next == NULL)
    {
        return;
    }
    printk(KERN_NOTICE ">>>my_schedule<<<\n");
    /* schedule */
    next = my_current_task->next;
    prev = my_current_task;
    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(    
            "pushq %%rbp\n\t"         /* save rbp of prev */
            "movq %%rsp,%0\n\t"     /* save rsp of prev */
            "movq %2,%%rsp\n\t"     /* restore  rsp of next */
            "movq $1f,%1\n\t"       /* save rip of prev */    
            "pushq %3\n\t" 
            "ret\n\t"                 /* restore  rip of next */
            "1:\t"                  /* next process start here */
            "popq %%rbp\n\t"
            : "=m" (prev->thread.sp),"=m" (prev->thread.ip)
            : "m" (next->thread.sp),"m" (next->thread.ip)
        ); 
    }  
    return;    
}

重新编译内核后，运行qemu，界面如下：

 

 

 3. 简要分析操作系统内核核心功能及运行工作机制

进程切换基于的时间片轮转算法，当一个进程执行时的时间片耗完，会出发一次时钟中断，cpu会切换到就绪队列中的下一个进程开始执行。

进程切换的过程如下：

1. 当前进程栈基址寄存器 rbp 入栈

2、下一个进程的sp赋值到栈顶寄存器 rsp 

3. 将eip寄存器的值入栈保存。

4. 将下一个进程的ip赋值到eip寄存器中。

结尾附上孟老师的讲解视频：自己手写一个操作系统内核

标签：task,process,pid,next,include,内核,mykernel,2.0,my
来源： https://www.cnblogs.com/Luck-365/p/12885179.html