基于mykernel 2.0编写一个操作系统内核
实验一 基于mykernel 2.0编写一个操作系统内核
一、实验内容
基于mykernel 2.0编写一个操作系统内核
- 按照https://github.com/mengning/mykernel 的说明配置mykernel 2.0，熟悉Linux内核的编译；
- 基于mykernel 2.0编写一个操作系统内核，参照https://github.com/mengning/mykernel 提供的范例代码
- 简要分析操作系统内核核心功能及运行工作机制
二、实验过程
1.安装Ubuntu 18.0.4虚拟机
2.配置mykernel，具体步骤如下
wget https://raw.github.com/mengning/mykernel/master/mykernel-2.0_for_linux-5.4.34.patch sudo apt install axel axel -n 20 https://mirrors.edge.kernel.org/pub/linux/kernel/v5.x/linux-5.4.34.tar.xz xz -d linux-5.4.34.tar.xz tar -xvf linux-5.4.34.tar cd linux-5.4.34 patch -p1 < ../mykernel-2.0_for_linux-5.4.34.patch sudo apt install build-essential libncurses-dev bison flex libssl-dev libelf-dev make defconfig # Default configuration is based on 'x86_64_defconfig' # 使用allnoconfig编译出来qemu无法加载启动，不知道为什么？有明白的告诉我，完整编译太慢了，消耗的资源也多。 make -j$(nproc) # 编译的时间比较久哦 sudo apt install qemu # install QEMU qemu-system-x86_64 -kernel arch/x86/boot/bzImage
配置过程中出现如下问题：
使用以下两条语句解决：
首先运行下面的命令来移除 /var/lib/dpkg/ 文件夹下的锁定文件，之后像下面这样强制重新配置软件包
sudo rm /var/lib/dpkg/lock sudo dpkg --configure -a
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3 基于mykernel 2.0编写操作系统内核
1）在mykernel目录中添加 mypcb.h
结构体Thread ：用于存储当前进程中正在执行的线程的ip和sp
结构体PCB：主要包含进程号\进程状态\进程使用的堆栈\当前正在执行的Thread信息、入口函数地址以及下一个pcb
#define MAX_TASK_NUM 4 #define KERNEL_STACK_SIZE 1024*2 /* 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 */ unsigned long 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);
2）修改mymain.c
mykernel内核代码的⼊⼝，负责初始化内核的各个组成部分。my_process通过while循环不断检测全局变量my_need_sched的值，当my_need_sched的值从0变成1的时候，意味着需要发生进程调度，全局变量my_need_sched重新置为0，调用my_schedule()函数进行进程切换。
#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].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( "movq %1,%%rsp\n\t" /* set task[pid].thread.sp to rsp */ "pushq %1\n\t" /* push rbp */ "pushq %0\n\t" /* push task[pid].thread.ip */ "ret\n\t" /* pop task[pid].thread.ip to rip */ : : "c" (task[pid].thread.ip),"d" (task[pid].thread.sp) /* input c or d mean %ecx/%edx*/ ); } int i = 0; void my_process(void) { 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); } } }
3）修改myinerrupt.c
通过my_timer_handler来记录时间片，每循环1000次，设置标志位触发函数 my_schedule的调度，从而达到了根据时间片进行调度的目的。
#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(time_count%1000 == 0 && my_need_sched != 1) { printk(KERN_NOTICE ">>>my_timer_handler here<<<\n"); my_need_sched = 1; } time_count ++ ; 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 */ { my_current_task = next; printk(KERN_NOTICE ">>>switch %d to %d<<<\n",prev->pid,next->pid); /* switch to next process */ asm volatile( "pushq %%rbp\n\t" /* save rbp of prev */ "movq %%rsp,%0\n\t" /* save rsp of prev */ "movq %2,%%rsp\n\t" /* restore rsp of next */ "movq $1f,%1\n\t" /* save rip of prev */ "pushq %3\n\t" "ret\n\t" /* restore rip of next */ "1:\t" /* next process start here */ "popq %%rbp\n\t" : "=m" (prev->thread.sp),"=m" (prev->thread.ip) : "m" (next->thread.sp),"m" (next->thread.ip) ); } return; }
重新编译后运行如下：
三、分析与总结
进程切换部分代码分析如下
asm volatile( "pushq %%rbp\n\t" /* 保存上一个进程的rbp*/ "movq %%rsp,%0\n\t" /*当前rsp寄存器的值到prev->thread.sp*/ "movq %2,%%rsp\n\t" /* 将next进程的栈顶地址放入rsp寄存器，切换堆栈 */ "movq $1f,%1\n\t" "pushq %3\n\t" /*把即将执行的next进程的指令地址next->thread.ip入栈*/ "ret\n\t" /* next进程的rip出栈 */ "1:\t" "popq %%rbp\n\t" /*弹出next进程的rbp */ : "=m" (prev->thread.sp),"=m" (prev->thread.ip) : "m" (next->thread.sp),"m" (next->thread.ip) );
实现了基于时间片的进程轮换。进程在执⾏过程中，当时间⽚⽤完需要进⾏进程切换时，首先保存当前的进程上下⽂环境，下次进程被调度执⾏时，需要恢复进程上下⽂环境，了多道程序在同⼀个物理CPU上并发执⾏。通过此次实验，对于进程调度有了进一步的认识。
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