实验:基于kernel的简单的时间片轮转多道程序内核
1、实验要求
- 完成一个简单的时间片轮转多道程序内核代码
2、实验过程
- 进入实验楼的linux环境,打开shell,输入以下代码:
cd LinuxKernel/linux-3.9.4
rm -rf mykernel
patch -p1 < ../mykernel_for_linux3.9.4sc.patch
make allnoconfig
make #编译内核请耐心等待
qemu -kernel arch/x86/boot/bzImage
执行的效果如下:
- 在mykernel的基础上添加mypcb.h,修改mymain.c和myinterrupt.c文件,实现一个简单的操作系统内核,实现效果如下:
3、mykernel时间片轮转代码分析
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
本mypcb.h头文件主要定义了程序控制块PCB,包括:
pid:定义进程id
state:进程状态标记,-1是未运行,0为运行,>0为终止
stack:定义使用的堆栈
thread:定义线程
task_entry:进程入口
next:链表指向下一个PCB
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引用全局变量
extern tPCB * my_current_task;
extern volatile int my_need_sched;
volatile int time_count = 0;
void my_timer_handler(void) //时钟中断触发本函数
{
#if 1
if(time_count%100 == 0 && my_need_sched != 1) //当时钟中断发生100次,并且my_need_sched不为1时,赋值为1
{
printk(KERN_NOTICE ">>>my_timer_handler here<<<
");
my_need_sched = 1;
}
time_count ++ ;
#endif
return;
}
void my_schedule(void)
{
tPCB * next; //下一进程
tPCB * prev; //当前进程
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 */ //下一个进程可运行,执行进程切换
{
my_current_task = next;
printk(KERN_NOTICE ">>>switch %d to %d<<<
",prev->pid,next->pid);
/* 切换进程 */
asm volatile(
"pushl %%ebp
" /* save ebp */
"movl %%esp,%0
" /* save esp */
"movl %2,%%esp
" /* restore esp */
"movl $1f,%1
" /* save eip */
"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;
}
本c文件中,定义了my_timer_handler和my_schedule两个函数调用,前者是当时钟中断发生100次,并且my_need_sched不为1时,赋值为1,是mymain.c中my_process函数判定主动调度的标志;后者是执行调度的具体过程,下面对切换进程的汇编代码进行分析:
"pushl %%ebp
" /* save ebp / ebp入栈
"movl %%esp,%0
" / save esp / 保存当前esp到进程的sp中
"movl %2,%%esp
" / restore esp / esp指向下一进程
"movl $1f,%1
" / save eip / 将1f存储到进程的ip中,$1f是标号“1: ”处,再次调度到该进程时就会从1:开始执行
"pushl %3
" 下一进程的ip入栈
"ret
" / restore eip / eip指向下一进程的起始地址
"1: " / next process start here */ 下一进程从此处开始执行
"popl %%ebp
" 执行完后出栈释放空间
: "=m" (prev->thread.sp),"=m" (prev->thread.ip) 分别对于上面的%0,%1
: "m" (next->thread.sp),"m" (next->thread.ip) 分别对应上面的%2,%3
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task
tPCB * my_current_task = NULL; //当前task指针
volatile int my_need_sched = 0; //是否需要调度
void my_process(void); //my_process函数声明
void __init my_start_kernel(void) //mykernel内核代码的入口
{
int pid = 0;
int i;
/* 初始化0号进程*/
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其他进程 */
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;
task[i-1].next = &task[i];
}
/* 用task[0]开始0号进程 */
pid = 0;
my_current_task = &task[pid];
asm volatile(
"movl %1,%%esp
" /* set task[pid].thread.sp to esp */
"pushl %1
" /* push ebp */
"pushl %0
" /* push task[pid].thread.ip */
"ret
" /* pop task[pid].thread.ip to eip */
"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)
{
printk(KERN_NOTICE "this is process %d -
",my_current_task->pid);
if(my_need_sched == 1) //判断是否需要调度
{
my_need_sched = 0;
my_schedule(); //这是一个主动调度
}
printk(KERN_NOTICE "this is process %d +
",my_current_task->pid);
}
}
}
本c文件中,有my_start_kernel和my_process两个函数,其中,前者为mykernel内核代码的入口函数,后者为进程的入口函数,进程在运行中输出当前进程号,并通过my_need_sched变量判断是否需要调度。
其中对0号进程的启动汇编代码进行分析:
"movl %1,%%esp
" /* set task[pid].thread.sp to esp / 将当前进程0的sp赋给esp
"pushl %1
" / push ebp / 进程0的sp入栈
"pushl %0
" / push task[pid].thread.ip / 进程0的ip入栈
"ret
" / pop task[pid].thread.ip to eip / 将进程0的ip赋给eip
"popl %%ebp
" 执行完其他进程,回到0号进程,出栈
:
: "c" (task[pid].thread.ip),"d" (task[pid].thread.sp) / input c or d mean %ecx/%edx*/ 输入,将0号进程的ip、sp值分别存入ecx、edx寄存器中,分别对应上面的%0,%1
4、问题与总结
本次实验没有遇到什么重大的问题,但是小毛病犯了一堆,比如在将代码拷入实验楼linux环境的vim中时,实验楼的粘贴板不知为何复制粘贴会缺失一段代码,后在编译c文件的时候总是报错,这个问题找了好久,后来发现是粘贴板粘贴的代码缺失。还有一个是在make时找不到文件,后来发现修改代码是在/mykernel目录下进行修改的,make编译内核需要在LinuxKernel/linux-3.9.4目录下进行,需要返回上一级菜单进行make。
总共来讲,本周各种事情比较多,学习的计划一拖再拖,推迟了好久才完成,以后一定要合理分配时间,这一点尤为重要。
还有,学习要认真仔细,尽量避免因为犯低级错误而白白消耗大量学习时间。