linux 进程调度程序分析 基于Mykernel

由于时间仓促，难免有遗漏 错误地方 敬请指出！

实验环境;虚拟机kali linux 3.18

编译器：gcc

linux源代码：C语言 汇编

编辑器：vim

首先贴出mykernel的源码 以下会对一些源码做出解释 一共三个文件mymain.c myintterrupt.c mypcb.h

<pre name="code" class="cpp">/* *  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;    task[pid].thread.sp = (unsigned long)&task[pid].stack[KERNEL_STACK_SIZE-1];    task[pid].next = &task[pid];    /*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;        task[i-1].next = &task[i];    }    /* start process 0 by task[0] */    pid = 0;    my_current_task = &task[pid];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);        }         }}

/*
 *  linux/mykernel/mypcb.h
 *
 *  Kernel internal PCB types
 *
 *  Copyright (C) 2013  Mengning
 *
 */


#define MAX_TASK_NUM        4
#define KERNEL_STACK_SIZE   1024*8


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


typedef struct PCB{
    int pid;
    volatile long state; /* -1 unrunnable, 0 runnable, >0 stopped */
    char stack[KERNEL_STACK_SIZE];
    /* CPU-specific state of this task */
    struct Thread thread;
    unsigned long task_entry;
    struct PCB *next;
}tPCB;

void my_schedule(void);

</pre><pre name="code" class="cpp"><pre name="code" class="cpp">/* *  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 */    {    /* switch to next process */    asm volatile(        "pushl %%ebp\n\t"     /* save ebp */        "movl %%esp,%0\n\t" /* save esp */        "movl %2,%%esp\n\t"     /* restore  esp */        "movl $1f,%1\n\t"       /* save eip */        "pushl %3\n\t"         "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)    );     my_current_task = next;     printk(KERN_NOTICE ">>>switch %d to %d<<<\n",prev->pid,next->pid);       }    else    {        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"     /* 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"         "ret\n\t"             /* restore  eip */        : "=m" (prev->thread.sp),"=m" (prev->thread.ip)        : "m" (next->thread.sp),"m" (next->thread.ip)    );              }       return;}

mykernel，它是提供初始化好的CPU从my_start_kernel开始执行，并提供了时钟中断机制周期性性执行my_time_handler中断处理程序，执行完后中断返回总是可以回到my_start_kernel中断的位置继续执行。以上是需要知道的前提知识 这点对于理解代码至关重要。 让我们首先从my_start_kernel函数开始分析。首先创建了一个tPCB类型链表 task，然后用了my_current_task指定当前进程。（tPCB内各个元素含义详见 mypcb.h）task[pid].task_entry = task[pid].thread.ip = (unsigned long)my_process; 中的myprocess需要知道代表的是函数内存地址。 for循环并不是很难，也就是通过memcpy()把task[0]进程复制到各个进程 进程总个数由MAX_TASK_NUM决定。my_current_task = &task[pid];这句话和刚才一样，就不解释了。而mymain.c中的内嵌汇编也就是保存当前上下文。为后面进程切换做好准备。而myinterrupt.c是由time interrupt调用，所以我们在mymain.c中未见有调用myinterrupt.c的代码. 而其中的两段内联汇编仔细一看 也是一样的 所以也没有继续分析的必要 通过这个 我们就成功的实现了一个进程调度程序。

---张振海 MOOC