操作系统开发之实现多系统引导
一. 一点说明
一直都想写一个属于自己的操作系统，可是总是由于这样或那样的原因，一直没有集中精力去搞下来。作为一个非计算机专业的大五学生，现在忙于补修本职专业课（挂了些课）和找IT方面工作，暂时也没时间继续了。现公布一点自己些的垃圾，写得不好，请大家不要抛砖头砸我
二.设计与实现
硬盘多系统引导功能基本有两部分组成,包括引导启动代码安装和导启动代码. 考虑到测试的环境和处理问题的方便性, 安装程序为没有使用TASM来写。就拿从硬盘定位一个引导文件来说吧, 就得考虑该分区的文件系统类型是VFAT还是NTFS或是EXT2之类情况。由于我们的主要目的是实现多系统引导, 为了不喧宾夺主就将主要精力花在引导的设计上，至于文件系统的设计与处理，等以后有机会在于大家探讨
安装部分必须完成的任务有：保存原MBR内容，修改分区类型，恢复MBR内容，修改MBR启动代码，其他的可以安自己需要添加。
对于多系统引导的设计与处理，考虑到代码可移植性与稳定性，没有采用默认开始执行的IP为0000:7c00，而是选择程序自己动态调整；另外为了便于测试和改进代码应该具有重定位功能，在
非引导环境下也应当能够执行（不然你没法DEBUG ）
三.具体代码
每个部分都有详细的注释,相信大家都该能够看明白.
代码:
/* MDISK.C 功能简介:
1.)保存MBR内容
2.)修改分区类型
3.)删除分区
4.)恢复MBR内容
5.)修改MBR启动代码
*/
#include <stdio.h>
#include <conio.h>
#include <bios.h>
void main(void)
{
FILE *fp;
unsigned char buff[512];
int x,y,z,ch,i,s;
/* read MBR
int biosdisk(int cmd,int drive,int head,int track,int sector,int nsects,void *buffer)
*/
/*读取MBR并检测是否改动*/
biosdisk(2,0x80,0,0,1,1,buff);
if(buff[3]=='H'&&buff[4]=='S'&&buff[5]=='Q')
{
printf("\n MBR had been modifled by HSQ ");
printf("\n Do you want to Overlay MBR (y/n) :");
for(ch='*';ch!='y'&&ch!='n';)ch=getchar();
if(ch=='y')
{
printf("\n Enter (1-9) sector index to be read :"); /* 49-57*/
for(x='*';x<'1'||x>'9';)x=getchar();
biosdisk(2,0x80,0,0,x-48+10,1,buff); /* 2-10 */
biosdisk(3,0x80,0,0,1,1,buff);
printf("\n Overlay Complete !");
}
}
else
{ /*在处理原始MBR前,必须备份*/
printf("\n Save MBR to (1-9) sector index :");
for(x='*';x<'1'||x>'9';)x=getchar();
biosdisk(3,0x80,0,0,x-48+10,1,buff);
printf("\n Save MBR Complete !");
}
/*显示操作菜单*/
while(1)
{
clrscr();
printf("\n\n Disk Partition type information :");
for(x=0x1c2;x<=0x1f2;x+=16)printf("%02x",buff[x]);
printf("\n\n *************** Menu Title ******************");
printf("\n * *");
printf("\n * 1--> Change partition type *");
printf("\n * *");
printf("\n * 2--> Delete partition *");
printf("\n * *");
printf("\n * 3--> Recover MBR *");
printf("\n * *");
printf("\n * 4--> Load LDMBR File *");
printf("\n * *");
printf("\n * 5--> Load BOOT File *");
printf("\n * *");
printf("\n * 0--> Quit this Program *");
printf("\n * *");
printf("\n * MDISK v1.23 by Huang Shiquan 2007-10-06 *");
printf("\n * *");
printf("\n *********************************************");
printf("\n Enter your choice :");
for(ch='*';ch<'0'||ch>'5';)ch=getchar();
if(ch=='0')break;
if(ch=='1')
{
printf("\n Partition do you want to change (1-4) :");
for(x='*';x<'1'||x>'4';)x=getchar();
printf("\n Current partition type is %02x",buff[0x1c2+(x-49)*16]);
printf("\n Enter new partition type :");
scanf("%02x",&y);
buff[0x1c2+(x-49)*16]=y;
biosdisk(3,0x80,0,0,1,1,buff);
printf("\n Change Complete !");
getch();
}
if(ch=='2')
{
printf("\n Partition do you want to delete (1-4) :");
for(x='*';x<'1'||x>'4';)x=getchar();
for(x-=49,y=0;y<(3-x)*16;y++)
{
z=0x1be+x*16+y;
buff[z]=buff[z+16];
}
for(y=0;y<16;y++)buff[0x1ee+y]=0;
biosdisk(3,0x80,0,0,1,1,buff);
printf("\n Delete Complete !");
getch();
}
if(ch=='3') /*调用备份扇区覆盖启动扇区*/
{
printf("\n Enter (1-9) sector index to read be :");
for(x='*';x<'1'||x>'9';)x=getchar();/*HEX: 31 - DEC: 49 - ASCII: 1*/
biosdisk(2,0x80,0,0,x-48+10,1,buff);
biosdisk(3,0x80,0,0,1,1,buff);
printf("\n Recover Complete !");
getch();
}
if(ch=='4') /*装载启动扇区文件*/
{
s=1;
if((fp=fopen("LDMBR.COM","rb")) == NULL)
{
printf("\n Open file LDMBR.COM error !\n");
break;
}
for(i=2;i<=10;i++) /*执行前检查被覆盖分区是否含有MBR信息*/
{
biosdisk(2,0x80,0,0,i,1,buff);
if(buff[0x1fe]==0x55&&buff[0x1ff]==0xaa)
{
printf("\n Warming : The [%d] sector have MBR information!",i);
printf("\n Are you sure to continue work (y/n) :");
for(ch='*';ch!='y'&&ch!='n';)ch=getchar();
if(ch=='n')
{
s=0;break;
}
}
}
for(i=1;s==1&&i<=10;i++) /*读入10个扇区大小的文件*/
{
for(x=0;x<0x200;x++)buff[x]=0; /*初始化缓冲区*/
fread(buff,0x200,1,fp);
biosdisk(3,0x80,0,0,i,1,buff);
}
if(s==1)printf("\n Modify Complete !");
fclose(fp);
getch();
}
if(ch=='5') /*装载启动扇区文件*/
{
s=1;
if((fp=fopen("Boot.bin","rb")) == NULL)
{
printf("\n Open file Boot.BIN error !\n");
break;
}
for(i=1;s==1&&i<=1;i++) /*最多读入1个扇区大小的文件*/
{
for(x=0;x<0x200;x++)buff[x]=0; /*初始化缓冲区*/
fread(buff,0x200,1,fp);
biosdisk(3,0x80,0,0,i,1,buff);
}
if(s==1)printf("\n Modify Boot Complete !");
fclose(fp);
getch();
}
}
return;
}