完成一个简单的时间片轮转多道程序内核代码

1 实验过程

使用实验楼的虚拟机打开 shell

输入如下代码

# 注意路径是区分大小的
$ cd ~/LinuxKernel/linux-3.9.4

$ rm -rf mykernel

$ patch -p1 < ../mykernel_for_linux3.9.4sc.patch

$ make allnoconfig

# 编译内核请耐心等待
$ make

$ qemu -kernel arch/x86/boot/bzImage

运行结果如图在这里插入图片描述

查看mymain.c和myinterrupt.c代码
main》c

2 mykernel时间片轮转代码分析

新增mypcb.h

#define MAX_TASK_NUM        4
#define KERNEL_STACK_SIZE   1024*8
 
/* CPU-specific state of this task */
struct Thread {
    unsigned long       ip;   //对应eip
    unsigned long       sp;   //对应esp
};
 
typedef struct PCB{
    int pid;                 //定义进程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;   //入口
    struct PCB *next; 
}tPCB;
 
void my_schedule(void); //声明调度函数

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];                /*pcb的数组*/
tPCB * my_current_task = NULL;
volatile int my_need_sched = 0;              /*是否需要调度的标志*/
void my_process(void)；
void __init my_start_kernel(void)            /*内核入口。初始化并启动0号进程*/
{
    int pid = 0;
    int i;
    /* Initialize process 0*/
    task[pid].pid = pid;
    task[pid].state = 0;                               /* -1 未运行, 0 正在运行, >0 停止运行 */
    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];
    task[pid].next = &task[pid];                  /*next指向自己*/
    /*fork more process */                         /*初始化更多进程*/
    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;             /*将创建的进程加到进程列表的尾部*/
        task[i-1].next = &task[i];
    }
    /* start process 0 by task[0] */
    pid = 0;                                                /*开始执行0号进程*/
    my_current_task = &task[pid];
    asm volatile(                                      
        "movl %1,%%esp\n\t"                       /*将ESP指向进程0的堆栈栈底，输出部分和输入部分从0开始编号，所以1%指task[pid].thread.sp*/
        "pushl %1\n\t"                                   /*将EBP的值入栈，因为是空栈，EBP=ESP，所以将task[pid].thread.sp入栈即可*/
        "pushl %0\n\t"                                   /*将EIP的值入栈，这里是初始化的值即my_process(void)的位置*/
        "ret\n\t"                                              /*将my_process(void)的位置放入EIP*/   
        "popl %%ebp\n\t"     
        : 
        : "c" (task[pid].thread.ip),"d" (task[pid].thread.sp)  
    );
} 

void my_process(void)
{    
    int i = 0;
    while(1)
    {
        i++;
        if(i%10000000 == 0)                        /*循环1000万次才有一次机会判断是否需要调度*/
        {
            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);
        }     
    }
}

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;

void my_timer_handler(void)      /*设置时间片大小，时间片用完时设置一下调度标志*/
{
#if 1
    if(time_count%1000 == 0 && my_need_sched != 1)
    {
        printk(KERN_NOTICE ">>>my_timer_handler here<<<\n");
        my_need_sched = 1;          /*调度执行my_schedule(void)*/
    } 
    time_count ++ ;  
#endif
    return;     
}

void my_schedule(void)              /*进程上下文的切换*/
{
    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)                  /* next对应进程曾经执行过 */
    { 
        asm volatile(   
            "pushl %%ebp\n\t"          /* 将当前进程的EBP入栈 */
            "movl %%esp,%0\n\t"     /* 将当前进程的ESP保存到PCB  */
            "movl %2,%%esp\n\t"     /* 将next进程的栈顶地址放入ESP */
            "movl $1f,%1\n\t"            /* 保存当前进程的EIP */
            "pushl %3\n\t"                /* 把即将进行的进程的代码位置标号1入栈 */ 
            "ret\n\t"                           /* 出栈标号1到EIP*/
            "1:\t"                               /* 标号1，next进程开始执行的位置 */
            "popl %%ebp\n\t"           /* 恢复EBP的值*/
            : "=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                                         /* next对应进程第一次被执行*/
    {
        next->state = 0;
        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"           /* 将当前进程的EBP入栈 */
            "movl %%esp,%0\n\t"      /* 将当前进程的ESP保存到PCB  */
            "movl %2,%%esp\n\t"      /* 将next进程的栈顶地址放入ESP */
            "movl %2,%%ebp\n\t"      /* 将next进程的栈底地址放入EBP */
            "movl $1f,%1\n\t"             /* 将当前EIP的值放入PCB */ 
            "pushl %3\n\t"                  /* 把即将进行的进程的代码入口地址入栈 */ 
            "ret\n\t"                             /* 把即将进行的进程的代码入口地址存入EIP */
            : "=m" (prev->thread.sp),"=m" (prev->thread.ip)
            : "m" (next->thread.sp),"m" (next->thread.ip)
        );          
    }   
    return; 
}