基于mykernel 2.0编写一个操作系统内核

一、按照https://github.com/mengning/mykernel 的说明配置mykernel 2.0，熟悉Linux内核的编译

　　实验环境

　　　Ubantu16.04 运行于VMware15.1上

　　　依次执行以下命令

wget https://raw.github.com/mengning/mykernel/master/mykernel-2.0_for_linux-5.3.34.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
cd linux-5.4.34
patch -p1 < ../mykernel-2.0_for_linux-5.3.34.patch
sudo apt install build-essential gcc-multilib
sudo apt install qemu # install QEMU
sudo apt install libncurses5-dev bison flex libssl-dev libelf-dev
make defconfig # Default configuration is based on 'x86_64_defconfig'
make -j$(nproc)
qemu-system-x86_64 -kernel arch/x86/boot/bzImage

　　　其中  wget https://raw.github.com/mengning/mykernel/master/mykernel-2.0_for_linux-5.3.34.patch 出现连接失败的提示，于是使用了群内下载完成的文件

　　　编译内核

　　　

　　　用 mykernel-2.0_for_linux-5.4.34.patch 对 内核文件进行更新

　　　

　　　使用make -j4命令编译时间10分钟

　　　编译完成后可以在qmeu窗口观察到如下：

　　　

二、基于mykernel 2.0编写一个操作系统内核，参照https://github.com/mengning/mykernel 提供的范例代码

　　1.在mykernel目录下增加一个mypcb.h 头文件，用来定义进程控制块（Process Control Block），也就是进程结构体。

/*
 *  linux/mykernel/mypcb.h
 */

#define MAX_TASK_NUM        4
#define KERNEL_STACK_SIZE   1024*8


/* 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 */
    char stack[KERNEL_STACK_SIZE];
    /* CPU-specific state of this task */
    struct Thread thread;
    unsigned long   task_entry;
    struct PCB *next;
}tPCB;

//调度函数
void my_schedule(void);

　　2.对mymain.c进行修改，为进程的代码模拟一个个进程，时间片轮转调度。

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].state = -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] */
    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*/
    );
}

void my_process(void)
{
    int i = 0;
    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.对myinterrupt.c进行修改，my_timer_handler用来记录时间片，时间片消耗完之后完成调度。

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.
 */
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;
}

　　4.重新编译后运行qemu

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

　　

三、简要分析操作系统内核核心功能及运行工作机制

　　1.系统启动后，运行mymain.c中的my_start_kernal， 进程0首先初始化，再初始化其他的进程。

　　2.myinterrupt.c中的my_timer_handler 函数每调用1000次，就去将全局变量my_need_sched的值修改为1

　　3.my_start_kernel中的while循环发现my_need_sched值变为1后，就进行进程的调度，完成进程的切换，以此实现进程切换。