基于mykernel 2.0编写一个操作系统内核
作者:互联网
- 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
一、实验环境配置-mykernel 2.0
(1)本机环境:VMware® Workstation 15 Pro + Ubuntu18.04.2 LTS
(2)下载mykernel文件:
wget https://raw.github.com/mengning/mykernel/master/mykernel-2.0_for_linux-5.4.34.patch ##这句不行
发现连接不能用,于是:
git clone https://github.com/mengning/mykernel ##clone整个文件
(3)安装axel:
sudo apt install axel
(4)通过axel下载对应的kernel压缩文件:
axel -n 20 https://mirrors.edge.kernel.org/pub/linux/kernel/v5.x/linux-5.4.34.tar.xz
下载连续失败:
于是手动从网站下载Linux内核文件:
(5)解压缩下载好的kernel文件:
xz -d linux-5.4.34.tar.xz
然后打包:
tar -xvf linux-5.4.34.tar
(6)利用mykernel,修补kernel文件
cd linux-5.4.34 patch -p1 < ../mykernel-2.0_for_linux-5.4.34.patch
(7)安装必须的库:
sudo apt install build-essential libncurses-dev bison flex libssl-dev libelf-dev
(8)生成内核编译:
make defconfig
(9)编译内核kernel:
make -j$(nproc) # 编译的时间不算太长,只用了8min
(10)安装qemu:
sudo apt install qemu
现在就完成了实验环境的配置啦!
二、实验过程
(1)查看当前的kernel运行状态
qemu-system-x86_64 -kernel arch/x86/boot/bzImage
从qemu窗口中可以看到my_start_kernel在执行,同时my_timer_handler时钟中断处理程序可以执行:
(2)查看mykernel关键代码
进入mykernel目录:
上图可以看到qemu窗口输出的内容的代码 mymain.c 和 myinterrupt.c
cat mymain.c
cat myinterrupt.c
从中可知:刚刚的QEMU窗口中的结果正是这两个文件中的程序执行结果。
(3)基于mykernel 2.0编写一个操作系统内核并进行分析
1.对mypcb.h文件注释分析:
#define MAX_TASK_NUM 4 #define KERNEL_STACK_SIZE 1024*2 /* CPU-specific state of this task */ // 存储当前进程中正在执行线程的ip和sp struct Thread { unsigned long ip; unsigned long sp; }; // PCB 模拟进程控制块 typedef struct PCB{ int pid; // 进程号 volatile long state; /* -1 unrunnable阻塞态, 0 runnable可运行态, >0 stopped暂停态 */ unsigned long stack[KERNEL_STACK_SIZE]; // 进程使用的堆栈 /* CPU-specific state of this task */ struct Thread thread; // 当前正在执行的线程信息 unsigned long task_entry; // 存储进程入口函数地址(本实验中为my_process函数) struct PCB *next; // 指向下一个PCB }tPCB; void my_schedule(void); // 函数的声明 my_schedule,它的实现在my_interrupt.c中, //在mymain.c中的各个进程函数会根据一个全局变量的状态来决定是否调用它,从而实现主动调度。
2.修改mymain.c中的my_start_kernel函数,并在其中实现了my_process函数,作为进程的代码模拟一个个进程,时间片轮转调度:
#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); } } }
void __init my_start_kernel(void)函数是mykernel内核代码的入口,负责初始化内核的各个组成部分。
在Linux内核源代码中,实际的内核⼊⼝是init/main.c中的start_kernel(void)函数。
my_process函数的while循环可见,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,就需要发生进程调度,全局变量my_need_sched重新置为0,执行my_schedule()函数进行进程切换。
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(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:
make clean make allnoconfig make
然后运行QEMU:
qemu -kernel arch/x86/boot/bzImage
看到运行结果出现了变化:
标签:kernel,task,process,pid,内核,mykernel,2.0,my 来源: https://www.cnblogs.com/qyf2199/p/12807451.html