2019-2020-1 20209329《Linux内核原理与分析》第三周作业

《Linux内核原理与分析》第三周作业

目录

• 《Linux内核原理与分析》第三周作业
  • 1.mykernel实验
  • 2.编写一个简单的时间片轮转多道程序内核
  • 3.运行结果
  • 4.学习感受

1.mykernel实验

实验楼的虚拟机的环境配置已经搭载好，输入以下命令，可以直观地感受到cpu的中断机制。

cd ~/LinuxKernel/linux-3.9.4
rm -rf mykernel
patch -p1 < ../mykernel_for_linux3.9.4sc.patch
make allnoconfig      
make
qemu -kernel arch/x86/boot/bzImage

运行结果如下：

在mykernel目录下查看mymain.c和myinterrupt.c源代码，可以发现qemu窗口输出是mymain.c里的printk语句，并周期性的输出myinterrupt.c里的printk语句。
其中每隔一段时间，发生一次时钟中断，能够触发myinterrupt.c中的代码。
在此基础上，可以在mymain.c写入进程描述PCB和进程链表管理等代码，在myinterrupt.c写入进程切换代码。这样就完成了一个简单的时间片轮转多道程序内核。

2.编写一个简单的时间片轮转多道程序内核

2.1编写mypcb.h头文件

#define MAX_TASK_NUM        4
#define KERNEL_STACK_SIZE   1024*8                 //进程控制块

/* CPU-specific state of this task */
struct Thread {                        //存储ip,sp
    unsigned long        ip;
    unsigned long        sp;
};

typedef struct PCB{
    int pid;                        //进程的id
    volatile long state;    /* -1 unrunnable, 0 runnable, >0 stopped */
    char stack[KERNEL_STACK_SIZE];            //内核堆栈
    /* CPU-specific state of this task */
    struct Thread thread;
    unsigned long    task_entry;            //指定的入口，平时入口为main函数
    struct PCB *next;                    //进程用链表连接
}tPCB;

void my_schedule(void);                    //函数，调度器

该头文件包含了对结构体PCB的定义，用来存放进程的各种信息。

2.2修改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"

tPCB task[MAX_TASK_NUM];               //声明tPCB类型的数组
tPCB * my_current_task = NULL;           //声明当前task的指针
volatile int my_need_sched = 0;        //是否需要调度

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0号进程
    task[pid].state = 0;/* -1 unrunnable, 0 runnable, >0 stopped ，状态正在运行*/
    task[pid].task_entry = task[pid].thread.ip = (unsigned long)my_process;    //入口
    task[pid].thread.sp = (unsigned long)&task[pid].stack[KERNEL_STACK_SIZE-1];//
    task[pid].next = &task[pid];    //指向自己，系统启动只有0号进程
    /*fork more process */
    for(i=1;i<MAX_TASK_NUM;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;  //新进程加到进程链表尾部
        task[i-1].next = &task[i];
    }
    /* start process 0 by task[0] */
    pid = 0;
    my_current_task = &task[pid];
    asm volatile(
        "movl %1,%%esp
	"     /* set task[pid].thread.sp（%1） to esp */
        "pushl %1
	"             /* push ebp */
        "pushl %0
	"             /* push task[pid].thread.ip */
        "ret
	"             /* pop task[pid].thread.ip to eip ，ret之后0号进程正式启动*/
        "popl %%ebp
	"
        : 
        : "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)        //循环1000万次判断是否需要调度
        {
            printk(KERN_NOTICE "this is process %d -
",my_current_task->pid);
            if(my_need_sched == 1)
            {
                my_need_sched = 0;
                my_schedule();
            }
            printk(KERN_NOTICE "this is process %d +
",my_current_task->pid);
        }     
    }
}

mymain.c文件首先对0号进程进行了描述，然后建立了多个进程，进程间组成一个环形链表。my_process函数是一个死循环，不断的判断my_need_sched是否为1（是否需要调度）
值得关注的是对0号进程的启动

    /* start process 0 by task[0] */
    pid = 0;
    my_current_task = &task[pid];
    asm volatile(
        "movl %1,%%esp
	"     /* set task[pid].thread.sp（%1） to esp，将0号进程的堆栈指针赋予esp */
        "pushl %1
	"             /* push ebp ，把0号进程的堆栈指针压进0号进程的堆栈 */
        "pushl %0
	"             /* push task[pid].thread.ip ，把0号进程的ip指针（my_process函数的地址）压进0号进程的堆栈 */
        "ret
	"             /* pop task[pid].thread.ip to eip ，ret之后0号进程正式启， 把堆栈中的ip指针弹出给eip，开始进入my_process函数 */
        "popl %%ebp
	"
        : 
        : "c" (task[pid].thread.ip),"d" (task[pid].thread.sp)    /* input c or d mean %ecx/%edx*/
    );

2.3修改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)   //设置时间片的大小，时间片用完时设置调度的标志
    {
        printk(KERN_NOTICE ">>>my_timer_handler here<<<
");
        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<<<
");
    /* 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<<<
",prev->pid,next->pid);  
        /* switch to next process */
        asm volatile(    
            "pushl %%ebp
	"     /* save ebp */
            "movl %%esp,%0
	"     /* save esp */
            "movl %2,%%esp
	"     /* restore  esp */
            "movl $1f,%1
	"       /* save eip，%1f指接下来的标号为1的位置 */    
            "pushl %3
	" 
            "ret
	"                 /* restore  eip */
            "1:	"                  /* next process start here */
            "popl %%ebp
	"
            : "=m" (prev->thread.sp),"=m" (prev->thread.ip)
            : "m" (next->thread.sp),"m" (next->thread.ip)
        ); 
     
    }
    else
    {
        next->state = 0;
        my_current_task = next;
        printk(KERN_NOTICE ">>>switch %d to %d<<<
",prev->pid,next->pid);
        /* switch to new process */
        asm volatile(    
            "pushl %%ebp
	"      /* save ebp */
            "movl %%esp,%0
	"     /* save esp */
            "movl %2,%%esp
	"     /* restore  esp */
            "movl %2,%%ebp
	"     /* restore  ebp */
            "movl $1f,%1
	"       /* save eip */    
            "pushl %3
	" 
            "ret
	"                 /* restore  eip */
            : "=m" (prev->thread.sp),"=m" (prev->thread.ip)
            : "m" (next->thread.sp),"m" (next->thread.ip)
        );          
    }   
    return;    
}

myinterrupt.c中my_timer_hander函数实现了对时间片大小的设置，时间片用完时设置调度的标志（修改my_need_sched）。当执行中断程序myinterrupt.c修改了my_need_sched后，回到mymain.c中的my_process函数，触发调度，转到my_schedule()函数。
在my_schedule()函数中，实现了进程的调度。

void my_schedule(void)
{
    tPCB * next;
    tPCB * prev;

    if(my_current_task == NULL 
        || my_current_task->next == NULL)
    {
        return;
    }
    printk(KERN_NOTICE ">>>my_schedule<<<
");
    /* 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<<<
",prev->pid,next->pid);  
        /* switch to next process */
        asm volatile(    
            "pushl %%ebp
	"     /* save ebp ，将当前的ebp压进栈*/
            "movl %%esp,%0
	"     /* save esp，将当前的esp压进当前进程的堆栈 */
            "movl %2,%%esp
	"     /* restore  esp ，将下一个进程的sp移动到esp*/
            "movl $1f,%1
	"       /* save eip，%1f指接下来的标号为1的位置 ，将$1f保存到prev->thread.ip*/    
            "pushl %3
	"          /* 将下一个进程的ip压进下一个进程的堆栈 */
            "ret
	"                 /* restore  eip ，将堆栈的ip弹出给eip */
            "1:	"                  /* next process start here */
            "popl %%ebp
	"
            : "=m" (prev->thread.sp),"=m" (prev->thread.ip)
            : "m" (next->thread.sp),"m" (next->thread.ip)
        ); 
     
    }
    else
    {
        next->state = 0;
        my_current_task = next;
        printk(KERN_NOTICE ">>>switch %d to %d<<<
",prev->pid,next->pid);
        /* switch to new process */
        asm volatile(    
            "pushl %%ebp
	"      /* save ebp ，将当前的epb压进栈*/
            "movl %%esp,%0
	"     /* save esp ，将当前esp压进pre->thread.sp*/
            "movl %2,%%esp
	"     /* restore  esp ，将next->thread.sp移动到esp*/
            "movl %2,%%ebp
	"     /* restore  ebp ，将next->thread.sp移动到ebp*/
            "movl $1f,%1
	"       /* save eip ，将$1f保存到prev->thread.ip*/    
            "pushl %3
	"          /* 将下一个进程的ip压进下一个进程的堆栈 */
            "ret
	"                 /* restore  eip ，将堆栈的ip弹出给eip */
            : "=m" (prev->thread.sp),"=m" (prev->thread.ip)
            : "m" (next->thread.sp),"m" (next->thread.ip)
        );          
    }   
    return;    
}

3.运行结果

4.学习感受

通过这次对一个简单的操作系统内核的分析，我对中断服务程序有了更加直观的感受，并对时间片的应用、进程间的调度有了解，不由得感叹操作系统代码实现的巧妙。另外有一些深入的问题还不了解，比如mymain.c和myinterrupt.c是如何交替运行的，中断信号为什么能够触发myinterrupt.c，为什么中断信号发生后只执行my_timer_handler函数。