一个简单的时间片轮转多道程序内核操作系统工作流程

一.操作系统工作概述

1. 存储程序计算机工作模型，计算机系统最最基础性的逻辑结构；

2. 函数调用堆栈，高级语言得以运行的基础；

3. 中断，多道程序操作系统的基点。

二.代码分析

在上一篇博文《搭建OS kernel环境方法》的基础上进行时间片轮转多道程序的小os.

主要对mypcb.h,  mymain.c 和myinterrupt.c这三个文件进行分析。

<pre name="code" class="cpp"><span style="font-size:12px;">//mypcb.h</span>

<span style="font-size:12px;">#define MAX_TASK_NUM        4#define KERNEL_STACK_SIZE   1024*8/* CPU-specific state of this task */struct Thread {//给任务定义一个eip和esp    unsigned longip;    unsigned longsp;};typedef struct PCB{    int pid;//任务编号    volatile long state;/* -1 unrunnable, 0 runnable, >0 stopped */    char stack[KERNEL_STACK_SIZE];     //定义栈空间    /* CPU-specific state of this task */    struct Thread thread;       //定义进程的结构体thread, 其中有eip和esp    unsigned longtask_entry;//任务的函数起始处, 也就是任务第一次执行的起始位置    struct PCB *next;//一个任务链表, 指向下一个任务}tPCB;</span>

//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"    //引入其中两个结构体表示tPCB task[MAX_TASK_NUM];//定义两个数组tPCB * my_current_task = NULL;volatile int my_need_sched = 0;//定义是否调度, 1则调度, 0则不调度void my_process(void);void __init my_start_kernel(void)    //起始函数位置{    int pid = 0;    int i;    <strong>/* Initialize process 0*/</strong>    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];   <strong>//0号进程栈在最开始的位置</strong>    task[pid].next = &task[pid];       <strong> /*fork more process */</strong>    for(i=1;i<MAX_TASK_NUM;i++)    {        memcpy(&task[i],&task[0],sizeof(tPCB));//复制0号进程的结构形式        task[i].pid = i;        task[i].state = -1;//初始的任务(除0号进程外)都设置成未运行        task[i].thread.sp = (unsigned long)&task[i].stack[KERNEL_STACK_SIZE-1];        task[i].next = task[i-1].next;<strong>//新fork的进程加到进程链表的尾部,  该新建任务的next指向上一个任务的next,也就是自己（最后一个）</strong>        task[i-1].next = &task[i];  <strong>//配置上一个任务的next指向这时候新创建的任务</strong>    }    /* start process 0 by task[0] */    pid = 0;    my_current_task = &task[pid];//先让0号进程先执行  <strong>  asm volatile(      "movl %1,%%esp\n\t" /* set task[pid].thread.sp to esp */      "pushl %1\n\t"        /* push ebp ,当前esp=ebp*/      "pushl %0\n\t"        /* push task[pid].thread.ip */      "ret\n\t"            /* pop task[pid].thread.ip to eip */      "popl %%ebp\n\t"      :       : "c" (task[pid].thread.ip),"d" (task[pid].thread.sp)/* input c or d mean %ecx/%edx*/      );</strong>}   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)//判断是否调度；该值可有itnerrupt.c中的函数来配置            {                my_need_sched = 0;                my_schedule(); //主动调动的机制           }           printk(KERN_NOTICE "this is process %d +\n",my_current_task->pid);        }         }}

//myinterrupt.c#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)//时钟中断1000次的时候，调度一次, 配置调度值为1    {        printk(KERN_NOTICE ">>>my_timer_handler here<<<\n");        my_need_sched = 1;    }     time_count ++ ;  #endif    return;  }void my_schedule(void)     //<span style="color:#ff0000;">调度函数, 核心函数</span>{    tPCB * next;//定义两个指针    tPCB * prev;    if(my_current_task == NULL //当前进程和下一进程为空, 即没有任务, 返回        || my_current_task->next == NULL)    {      return;    }    printk(KERN_NOTICE ">>>my_schedule<<<\n");    <strong><span style="color:#ff0000;">/* 在调度函数中, next指向的是下一个将要被调度的任务, prev指向的是当前正在运行的任务*/</span></strong>    /* schedule */    next = my_current_task->next;//把当前进程的下一个进程赋值给next，当前进程赋值给prev    prev = my_current_task;    if(next->state == 0)/* -1 unrunnable, 0 runnable, >0 stopped */     {   //<strong>如果下一个任务不是第一次被调度, 则执行，下一个进程<span style="color:#ff0000;">有进程上下文</span></strong>      /* switch to next process */     <span style="color:#ff0000;">asm volatile(         "pushl %%ebp\n\t"       /* save 当前进程 ebp */       "movl %%esp,%0\n\t"     /* save 当前 esp 赋值到prev.thread.sp */        "movl %2,%%esp\n\t"     /* restore 下一个进程的sp到 esp */        "movl $1f,%1\n\t"       /*<strong> save 当前进程的 eip =[ 1：]处地址，即下一次从[ 1：]处开始继续执行</strong> */        /* 启动下一个进程*/"pushl %3\n\t"          /*保存下一个进程eip保存到栈里面*/        "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)      ); </span>      my_current_task = next;       printk(KERN_NOTICE ">>>switch %d to %d<<<\n",prev->pid,next->pid);       }    else    {  <strong> //下一个进程为第一次运行时,<span style="color:#ff0000;">没有进程上下文</span>, 则以下面这种方式来处理</strong>        next->state = 0;        my_current_task = next;        printk(KERN_NOTICE ">>>switch %d to %d<<<\n",prev->pid,next->pid);        /* switch to new process */    <span style="color:#ff0000;">asm volatile(         "pushl %%ebp\n\t"       /* save ebp */       "movl %%esp,%0\n\t"     /* save esp */x`        "movl %2,%%esp\n\t"     /* restore  esp */        "movl %2,%%ebp\n\t"     /* restore  ebp */        "movl $1f,%1\n\t"       /*<strong> save 当前进程的 eip =[ 1：]处地址，即下一次从[ 1：]处开始继续执行</strong> *//* 启动下一个进程*/        "pushl %3\n\t"         "ret\n\t"               /* restore  eip */        : "=m" (prev->thread.sp),"=m" (prev->thread.ip)        : "m" (next->thread.sp),"m" (next->thread.ip)          );          </span>    }       return;}

借用另一篇博文，以新任务切换为例进行堆栈变化分析：

 

author: 于凯

参考课程：《Linux内核分析》MOOC课程http://mooc.study.163.com/course/USTC-1000029000