基于mykernel 2.0编写一个操作系统内核

1.下载linux-5.4.34和mykernel

在kernel.org下载内核速度特别慢,推荐在USTC开源镜像站下载,速度飞起.linux-5.4.34的下载地址是

https://mirrors.ustc.edu.cn/kernel.org/linux/kernel/v5.x/linux-5.4.34.tar.xz

mykernel的代码直接通过git clone即可

git clone https://github.com/mengning/mykernel.git

通过下面的命令将下载的内核进行解压

xz -d linux-5.4.34.tar.xz
tar -xvf linux-5.4.34.tar

最后的目录结构如下

2. 将patch整合到内核代码中

cd linux-5.4.34
patch -p1 < ../mykernel/mykernel-2.0_for_linux-5.4.34.patch

3. 安装编译内核所需的库

sudo apt install build-essential libncurses-dev bison flex libssl-dev libelf-dev

我的机器上之前已经安装过

 4. 编译内核(时间较长)

make defconfig # Default configuration is based on 'x86_64_defconfig'
make -j$(nproc) # 编译的时间比较久哦 

5. 安装QEMU虚拟机并加载内核运行

在终端运行以下代码(我的机器之前已经安装过)

sudo apt install qemu

通过下面的代码加载内核

qemu-system-x86_64 -kernel arch/x86/boot/bzImage

从qemu窗口中您可以看到my_start_kernel在执行，同时my_timer_handler时钟中断处理程序周期性执行。这样我们就模拟了⼀个具有时钟中断和C代码执⾏环境的硬件平台

6. 将自己的程序以及进程调度模块整合进内核

切换到内核目录下的mykernel文件夹,将github中的myinterrupt.c,mymain.c,mypcb.h文件复制到该文件夹中,然后重新编译内核.再将内核加载到QEMU中运行.

通过下面的截图我们看到了中断发生后进程调度模块工作,进程1和进程2发生切换.

7. 代码分析(见注释)

7.1 mypcb.c

#define MAX_TASK_NUM        4       //最大进程个数
#define KERNEL_STACK_SIZE   1024*2  //每个进程内核栈的大小
/* CPU-specific state of this task */
struct Thread {
    unsigned long        ip;
    unsigned long        sp;
};

/* 
    进程有唯一的pid标识
    进程共有三个状态(与操作系统原理中不同)
    每个进程有自己的栈,大小为2KB
    每个进程有一个线程用于抢占物理CPU时间
    进程有自己任务入口
    多个进程通过循环链表进行组织,所以当前进程还有指向下一个进程的指针
*/
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;
// 声明了进程调度函数
void my_schedule(void);

7.2 myinterrupt.c

#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; //进程调度
    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"     /* 保存rsp的值到当前进程PCB的thread.sp*/
            "movq %2,%%rsp\n\t"     /* 设置rsp为scheduler选中的下一个进程的sp*/
            "movq $1f,%1\n\t"       /* $1f指向label1代码段的位置 */    
            "pushq %3\n\t"          
            "ret\n\t"                 /* 64,65l两行共同完成设置rip的值为next.thread.ip*/
            "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;    
}

7.3 mymain.c

#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]; //创建4个PCB
tPCB * my_current_task = NULL;
volatile int my_need_sched = 0;

void my_process(void);

void __init my_start_kernel(void)
{
    int pid = 0; //进程id从0开始增长
    int i;
    /* Initialize process 0*/
    task[pid].pid = pid;
    task[pid].state = 0;/* -1 unrunnable, 0 runnable, >0 stopped */
    // 进程初始化时thread.ip和task_entry相同,都是指向my_process的程序入口
    task[pid].task_entry = task[pid].thread.ip = (unsigned long)my_process;
    // 将进程栈的高地址赋给0号进程的thread.sp
    task[pid].thread.sp = (unsigned long)&task[pid].stack[KERNEL_STACK_SIZE-1];
    // 0号进程的next指针指向自己(循环链表的边界情况)
    task[pid].next = &task[pid];
    /*fork more process */
    for(i=1;i<MAX_TASK_NUM;i++)
    {
        memcpy(&task[i],&task[0],sizeof(tPCB));
        // fork后的进程state不用修改, 或者说进程创建时默认状态就是runnable
        // 这里task_entry也没有修改,因为四个进程的代码块都是同一个my_process
        task[i].pid = i;
        task[i].thread.sp = (unsigned long)(&task[i].stack[KERNEL_STACK_SIZE-1]);
        // 构成循环链表(自己手动验证)
        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;

// 进程执需要执行的代码
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);
        }     
    }
}