基于mykernel 2.0编写一个操作系统内核

配置mykernel 2.0，熟悉Linux内核的编译

1.下载补丁和内核源码，解压内核源码

wget https://raw.github.com/mengning/mykernel/master/mykernel-2.0_for_linux-5.4.34.patch
sudo apt install axel
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

 

2.进入内核文件夹linux-5.4.34，在内核中打补丁

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

 

3.安装编译工具和qemu虚拟机

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

 

4.配置编译内核生成bzImage文件

make defconfig
make -j4

 

5.虚拟机启动内核

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

 

基于mykernel 2.0编写一个操作系统内核

1.在mykernel目录下增加一个mypcb.h 头文件，定义进程控制块PCB结构体

#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.修改mymain.c中的my_start_kernel函数。添加my_process函数，此函数相当于一个进程，它的工作就是输出正在执行的进程的编号，并判断时间片是否用完来控制进程的调度。

#include 
#include string.h>
#include 
#include 
#include 


#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)
    {
        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);
        }     
    }
}

 

3.修改myinterupt.c ，使用my_timer_handler模拟时间片，连续被调用1000次就是一个时间片。使用my_schedule函数完成上下文切换，my_schedule函数中的汇编代码是进程上下文切换的关键代码。

#include 
#include string.h>
#include 
#include 
#include 

#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;    
}

 

重新编译运行，可以看到一个时间片用完后进行进程的切换

 

简要分析操作系统内核核心功能及运行工作机制

系统启动执行mymain.c中的my_start_kernal函数， 先初始化进程0，再初始化其他的进程，启动进程0。

mymain.c中的my_process函数里面有一个while(1)循环，会不停地执行，每循环一次i值加1，当i是10000000的整数倍时，对my_need_sched值进行判断，若my_need_sched为1，那么执行my_schedule函数进行进程切换。

my_need_sched的值由myinterrupt.c中的my_timer_handler函数控制，内核周期性地调用my_timer_handler函数，每调用一次time_cout加1，当time_cout的值是1000的整数倍，就将my_need_sched置为1，相当于一个时间片结束。