一個簡單的時間片輪轉多道程序內核操作系統工作流程
阿新 • • 發佈：2017-05-22
gson star 高級 time author family num 個數 count
一.操作系統工作概述
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存儲程序計算機工作模型，計算機系統最最基礎性的邏輯結構；
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函數調用堆棧，高級語言得以執行的基礎；
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中斷。多道程序操作系統的基點。
二.代碼分析
在上一篇博文《搭建OS kernel環境方法》的基礎上進行時間片輪轉多道程序的小os.
主要對mypcb.h, mymain.c 和myinterrupt.c這三個文件進行分析。
<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 {//給任務定義一個eip和esp
unsigned longip;
unsigned longsp;
};
typedef struct PCB{
int pid;//任務編號
volatile long state;/* -1 unrunnable, 0 runnable, >0 stopped */
char stack[KERNEL_STACK_SIZE]; //定義棧空間
/* CPU-specific state of this task */
struct Thread thread; //定義進程的結構體thread, 當中有eip和esp
unsigned longtask_entry;//任務的函數起始處, 也就是任務第一次運行的起始位置
struct PCB *next;//一個任務鏈表, 指向下一個任務
}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" //引入當中兩個結構體表示
tPCB task[MAX_TASK_NUM];//定義兩個數組
tPCB * my_current_task = NULL;
volatile int my_need_sched = 0;//定義是否調度, 1則調度, 0則不調度
void my_process(void);
void __init my_start_kernel(void) //起始函數位置
{
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號進程棧在最開始的位置</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));//復制0號進程的結構形式
task[i].pid = i;
task[i].state = -1;//初始的任務(除0號進程外)都設置成未運行
task[i].thread.sp = (unsigned long)&task[i].stack[KERNEL_STACK_SIZE-1];
task[i].next = task[i-1].next;<strong>//新fork的進程加到進程鏈表的尾部, 該新建任務的next指向上一個任務的next,也就是自己（最後一個）</strong>
task[i-1].next = &task[i]; <strong>//配置上一個任務的next指向這時候新創建的任務</strong>
}
/* start process 0 by task[0] */
pid = 0;
my_current_task = &task[pid];//先讓0號進程先運行
<strong> asm volatile(
"movl %1,%%esp\n\t" /* set task[pid].thread.sp to esp */
"pushl %1\n\t" /* push ebp ,當前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)//推斷是否調度。該值可有itnerrupt.c中的函數來配置
{
my_need_sched = 0;
my_schedule(); //主動調動的機制
}
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)//時鐘中斷1000次的時候，調度一次, 配置調度值為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;">調度函數, 核心函數</span>
{
tPCB * next;//定義兩個指針
tPCB * prev;
if(my_current_task == NULL //當前進程和下一進程為空, 即沒有任務, 返回
|| my_current_task->next == NULL)
{
return;
}
printk(KERN_NOTICE ">>>my_schedule<<<\n");
<strong><span style="color:#ff0000;">/* 在調度函數中, next指向的是下一個將要被調度的任務, prev指向的是當前正在運行的任務*/</span></strong>
/* schedule */
next = my_current_task->next;//把當前進程的下一個進程賦值給next。當前進程賦值給prev
prev = my_current_task;
if(next->state == 0)/* -1 unrunnable, 0 runnable, >0 stopped */
{ //<strong>假設下一個任務不是第一次被調度, 則運行，下一個進程<span style="color:#ff0000;">有進程上下文</span></strong>
/* switch to next process */
<span style="color:#ff0000;">asm volatile(
"pushl %%ebp\n\t" /* save 當前進程 ebp */
"movl %%esp,%0\n\t" /* save 當前 esp 賦值到prev.thread.sp */
"movl %2,%%esp\n\t" /* restore 下一個進程的sp到 esp */
"movl $1f,%1\n\t" /*<strong> save 當前進程的 eip =[ 1：]處地址，即下一次從[ 1：]處開始繼續運行</strong> */
/* 啟動下一個進程*/
"pushl %3\n\t" /*保存下一個進程eip保存到棧裏面*/
"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> //下一個進程為第一次運行時,<span style="color:#ff0000;">沒有進程上下文</span>, 則以以下這樣的方式來處理</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 當前進程的 eip =[ 1：]處地址，即下一次從[ 1：]處開始繼續運行</strong> */
/* 啟動下一個進程*/
"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;
}
author: 於凱
參考課程：《Linux內核分析》MOOC課程http://mooc.study.163.com/course/USTC-1000029000
一個簡單的時間片輪轉多道程序內核操作系統工作流程