完成一个简单的时间片轮转多道程序内核代码

2019-11-06 07:10:30

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实验截图

使用实验楼的虚拟机打开shell ，输入指令 1.cd LinuxKernel/linux-3.9.4 2.qemu -kernel arch/x86/boot/bzImage 然后cd mykernel 可以看到qemu窗口输出的内容的代码mymain.c和myinterrupt.c

mymain.c：内核从这里启动，从这个函数开始运行并无限循环

void __init my_start_kernel(void){ int i = 0; while(1) { i++; if(i%100000 == 0) PRintk(KERN_NOTICE "my_start_kernel here %d /n",i); }}

myinterrupt.c：由内核周期性调用，从而产生一个周期性的中断机制

void my_timer_handler(void){ printk(KERN_NOTICE "/n>>>>>>>>>>>>>>>>>my_timer_handler here<<<<<<<<<<<<<<<<<</n/n");}

然后修改内核代码，使之成为一个简单的时间片轮转多道程序内核，然后重新编译运行，从https://github.com/mengning/mykernel下载代码替换mykernel中的mymain.c和myinterrupt.c，mypuc.h也放在该文件夹下。接下来在shell中将工作目录退回到home/shiyanlou/LinuxKernel/linux-3.9.4/ 然后执行make，重新编译

这里写图片描述

然后再次输入：qemu -kernel arch/x86/boot/bzImage 启动内核执行结果如下这里写图片描述从上图中可以看到进程的切换过程：在0号进程运行过程中，先是my_timer_handler()被执行，然后执行myschedule(），myschedule()在运行过程中输出switch 0（被切换出去的进程号） to 1（切换到的进程号）。然后就跳到新的进程1继续执行。

代码分析

mypcb.h

/* * linux/mykernel/mypcb.h * * Kernel internal PCB types * * Copyright (C) 2013 Mengning * */#define MAX_TASK_NUM 4 //最大进程数#define KERNEL_STACK_SIZE 1024*2 # unsigned long/* CPU-specific state of this task */struct Thread { unsigned long ip;//进程的eip unsigned long sp;//进程的esp};typedef struct PCB{ int pid;//进程id volatile long state; /* -1 unrunnable, 0 runnable, >0 stopped */ //进程的状态 unsigned long stack[KERNEL_STACK_SIZE];//进程的栈 /* CPU-specific state of this task */ struct Thread thread;//每个进程只有一个线程 unsigned long task_entry;//进程起始入口地址 struct PCB *next;//指向下一个进程的指针}tPCB;void my_schedule(void);

mymain.c

/* * linux/mykernel/mymain.c * * Kernel internal my_start_kernel * * Copyright (C) 2013 Mengning * */#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];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;//0号进程的入口地址为my_process() task[pid].thread.sp = (unsigned long)&task[pid].stack[KERNEL_STACK_SIZE-1];//0号进程的栈顶为stack[]数组的最后一个元素 task[pid].next = &task[pid];//next指针指向自己 /*fork more process */ for(i=1;i<MAX_TASK_NUM;i++)//产生几个编号不同的进程 { 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].thread.sp - 1) = task[i].thread.sp; task[i].thread.sp -= 1; task[i].next = task[i-1].next;新建的进程next指针指向0号进程首地址 task[i-1].next = &task[i];//前一个进程的next指向新创建的进程首地址，形成一个循环链表 } /* start process 0 by task[0] */ pid = 0; my_current_task = &task[pid];//当前运行的进程设置为0号进程 asm volatile( "movl %1,%%esp/n/t" /* set task[pid].thread.sp to esp */ "pushl %1/n/t" /* push 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*/ );} 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); } }}

myinterrupt.c

/* * linux/mykernel/myinterrupt.c * * Kernel internal my_timer_handler * * Copyright (C) 2013 Mengning * */#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) { printk(KERN_NOTICE ">>>my_timer_handler here<<</n"); my_need_sched = 1; } time_count ++ ; #endif 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( "pushl %%ebp/n/t" /* save ebp 保存当前进程的ebp*/ "movl %%esp,%0/n/t" /* save esp 保存当前进程的esp*/ "movl %2,%%esp/n/t" /* restore esp 由next->thread.sp存入下一个进程的esp*/ "movl $1f,%1/n/t" /* save eip 下一个进程的eip设置为1f，$1f指标号1：的代码在内存中的地址*/ "pushl %3/n/t" /* 将next->thread.ip压入当前进程的栈*/ "ret/n/t" /* restore eip 弹出上一进程的eip进行进程切换*/ "1:/t" /* next process start here 即$1f指向的地址*/ "popl %%ebp/n/t" /* ebp出栈*/ : "=m" (prev->thread.sp),"=m" (prev->thread.ip) : "m" (next->thread.sp),"m" (next->thread.ip) ); } return; }