linux内核分析第二周作业

实验截图

实验代码分析

mypcb.h

#define MAX_TASK_NUM        4           // 最大进程数
#define KERNEL_STACK_SIZE   1024*8      //内核堆栈大小

/* CPU-specific state of this task */
struct Thread {
    unsigned long       ip; //定义eip
    unsigned long       sp; //定义esp
};

typedef struct PCB{
    int pid;                //定义进程标识符（进程号）  
    volatile long state;      //定义进程状态：-1不运行，0运行，>0停止
    char stack[KERNEL_STACK_SIZE];  //定义内核堆栈
    
    struct Thread thread;   //定义一个Thread(eip,esp)
    unsigned long   task_entry; //定义进程入口
    struct PCB *next;       //定义进程链表指针  
}tPCB;

void my_schedule(void);   //定义进程调度器

mymain.c

#include 
#include 
#include 
#include 
#include 


#include "mypcb.h"

tPCB task[MAX_TASK_NUM];           //声明一个task数组
tPCB * my_current_task = NULL;     //声明一个进程控制块指针
volatile int my_need_sched = 0;    //设置调度标识符

void my_process(void);           


void __init my_start_kernel(void)
{
    int pid = 0;  
    int i;
    /* Initialize process 0*/
    task[pid].pid = pid;     //初始化进程pid为0.
    task[pid].state = 0;     //初始化0号进程状态为运行
    task[pid].task_entry = task[pid].thread.ip = (unsigned long)my_process;             //初始化程序入口为，my_process
    task[pid].thread.sp = (unsigned long)&task[pid].stack[KERNEL_STACK_SIZE-1]; //初始化堆栈栈顶，esp指向栈顶。
    task[pid].next = &task[pid];  //初始时系统只有一个进程，所以自己指向自己。
    /*创建更多的进程*/
    for(i=1;ipid);
            if(my_need_sched == 1)  
            {
                my_need_sched = 0;  //将进程调度标识符置0
                my_schedule();     //调度下一个进程
            }
            printk(KERN_NOTICE "this is process %d +\n",my_current_task->pid);
        }     
    }
}

myinterrupt.c

#include 
#include 
#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;   //时钟计数

/*
 * 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)//时钟终端1000次，且调度标识符不为1时输出提示，且将调度标识符变为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)//当当前进程为空或当前下一个进程为空则返回。
    {
        return;
    }
    printk(KERN_NOTICE ">>>my_schedule<<<\n");
    /* schedule */
    next = my_current_task->next;
    prev = my_current_task;
    if(next->state == 0)//判断下一个进程是否为正在执行状态
    {
        /* switch to next process */
        asm volatile(   
            "pushl %%ebp\n\t"       //保存当前进程的ebp
            "movl %%esp,%0\n\t"     //将当前进程的esp保存在prev->thread.sp中
            "movl %2,%%esp\n\t"     //将下一个进程的esp（next->thread.sp）放在esp中
            "movl $1f,%1\n\t"       //将1:标志处的内存地址保存在prev->thread.ip中
            "pushl %3\n\t"        //将下一个进程的eip放入栈中
            "ret\n\t"               //释放下一个进程的eip，下一个进程开始执行 
            "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)
        ); 
        my_current_task = next; 
        printk(KERN_NOTICE ">>>switch %d to %d<<<\n",prev->pid,next->pid);      
    }
    else    //对于还没有执行过的进程的处理
    {
        next->state = 0;  //将进程状态转为执行状态
        my_current_task = next;   
        printk(KERN_NOTICE ">>>switch %d to %d<<<\n",prev->pid,next->pid);
        /* switch to new process */
        asm volatile(   
            "pushl %%ebp\n\t"       /* save ebp */
            "movl %%esp,%0\n\t"     /* save esp */
            "movl %2,%%esp\n\t"     /* restore  esp */
            "movl %2,%%ebp\n\t"     /* restore  ebp */
            "movl $1f,%1\n\t"       /* save eip */  
            "pushl %3\n\t"      //保存将当前进程的入口
            "ret\n\t"               /* restore  eip */
            : "=m" (prev->thread.sp),"=m" (prev->thread.ip)
            : "m" (next->thread.sp),"m" (next->thread.ip)
        );          
    }   
    return; 
}

总结

操作系统通过在某种时间片轮转算法下，通过中断和调度机制，不断切换处理各个进程已达到高效处理系统工作任务的目的。

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