block.cpp

在Linux Red Hat下用C++设计并实现一个多用户多级目录结构的文件系统。

#include"block.h"
#include<iostream.h>
#include"fileflag.h"
#include<sys/types.h>
#include<sys/stat.h>
#include<fcntl.h>
#include<unistd.h>

block::block()
{
	char buf[bsize+1];
	if(vp==-1)		//当文件卷未建立时，创建新的文件卷，并将大小定在1M
	{
		vp=open("myfile",O_RDWR|O_CREAT,S_IRWXU|S_IRGRP|S_IXGRP|S_IROTH|S_IXOTH);
		lseek(vp,bsize*2047,0);
		write(vp,buf,512);
	}
	if(bread(0,buf)==BLKREADERR)	//读取的0＃块的信息
	{
		cout<<"BLOCK READ ERROR"<<endl;
		return;
	}
	if((int)buf[477]!=1)			//0＃的479字节非1，即系统第一次登陆
	{
		//将0＃的前479个字节存放名为icon.gif的图标
		int iflag=open("icon.gif",O_RDWR,S_IRWXU|S_IRGRP|S_IXGRP|S_IROTH|S_IXOTH);
		if(iflag!=-1)
		{
			char picture[318];
			lseek(iflag,0,0);
			read(iflag,picture,359);
			lseek(vp,0,0);
			write(vp,picture,359);
		}
		//初始化空闲块链，并存储在1＃~8＃块中
		unsigned short int k=1;
		unsigned short int byteno=0;
		for(unsigned short int freeblockno=9;freeblockno<2048;)
		{
			if(byteno%512==510)
			{
				buf[byteno%512]=char((k+1)/256);
				byteno++;
				buf[byteno%512]=char((k+1)%256);
				byteno++;
				buf[512]='\0';
				if(bwrite(k,buf)==BLKWRITEERR)
				{
					cout<<"BLOCK WRITE ERROR"<<endl;
					return;
				}
				k++;
			}
			else
			{
				buf[byteno%512]=char(freeblockno/256);
				byteno++;
				buf[byteno%512]=char(freeblockno%256);
				byteno++;
				freeblockno++;
			}
		}
		for(;;)
		{
			buf[byteno%512]=char(0/256);
			byteno++;
			buf[byteno%512]=char(0%256);
			if(byteno%512==511)
			{
				buf[512]='\0';
				if(bwrite(k,buf)==BLKWRITEERR)
				{
					cout<<"BLOCK WRITE ERROR"<<endl;
					return;
				}
				break;
			}
			byteno++;
		}
		bread(0,buf);
		buf[477]=(char)1;
		buf[478]=(char)(1/256);
		buf[479]=char(1%256);
		bwrite(0,buf);
	}
	point=-1;
}
//读指定的物理块的信息
int block::bread(int bno,char*buf)
{
    int nbyte;
    lseek(vp,bno*bsize,0);
    nbyte=read(vp,buf,bsize);
    if(nbyte!=bsize)
		return BLKREADERR;	//失败;
	else
    {
		buf[bsize]='\0';
		return nbyte;		//成功
    }
}
//将信息写到指定的物理块
int block::bwrite(int bno,char*buf)
{
	int nbyte;
    lseek(vp,bno*bsize,0);
    nbyte=write(vp,buf,bsize);
    if(nbyte!=bsize)
		return BLKWRITEERR;	//失败 
    else
		return nbyte;			//成功 
}
//分配块
int block::balloc()
{
	char buf[bsize+1];
	if(point==-1)
	{
		bread(0,buf);
		int phead=int((unsigned char)buf[478])*256+int((unsigned char)buf[479]);
		if(phead==0)
		{
			cout<<"NO SPACE!please exit the programme"<<endl;
			return NOSPACE;
		}
		if(bread(phead,buf)==BLKREADERR)
		{
			cout<<"BLOCK READ ERROR"<<endl;
			return BLOCKERR;
		}
		for(int num=0;num<256;num++)
		{
			freeblock[num]=int((unsigned char)buf[num*2])*256+int((unsigned char)buf[num*2+1]);
		}
		point=0;
		for(;;point++)
		{
			if(freeblock[point%256]==0)
				continue;
			else
				break;
		}
		return phead;
	}
	if(point%256==255&&freeblock[point%256]==0)  //到达空闲块号链的尾部，并且空闲块号栈中的空闲块号也用完
	{
		cout<<"not enough space\n";
		return NOSPACE;	//空间不足
	}
	else
		if(point%256==255)	//空闲块号栈中无空闲块
		{
			//从物理块中读出新的信息，并放到空闲块号栈中
			if(bread(freeblock[255],buf)==BLKREADERR)
			{
				cout<<"BLOCK READ ERROR\n";
				return BLOCKERR;
			}
			int temp=freeblock[255];
			for(int num=0;num<256;num++)
			{
				freeblock[num]=int((unsigned char)buf[num*2])*256+int((unsigned char)buf[num*2+1]);
			}
			point++;
			for(;;point++)
			{
				if(freeblock[point%256]==0)
					continue;
				else
					break;
			}
			return temp;
		}
	for(;;point++)  //分配空闲块，
	{
		if(freeblock[point%256]==0)
		{
			if(point%256==255)
			{
				cout<<"not enough space\n";
				return NOSPACE;
			}
			else
				continue;
		}
		point++;
		return freeblock[(point-1)%256];
	}
}
//回收空闲块
int block::brelse(int tofree)
{
 
	char buf[bsize+1];
	if(point==-1)
	{
		bread(0,buf);
		int phead=int((unsigned char)buf[478])*256+int((unsigned char)buf[479]);
		if(phead==0)
		{
			cout<<"NO SPACE!please exit the programme"<<endl;
			return NOSPACE;
		}
		if(bread(phead,buf)==BLKREADERR)
		{
			cout<<"BLOCK READ ERROR"<<endl;
			return BLOCKERR;
		}
		for(int num=0;num<256;num++)
		{
			freeblock[num]=int((unsigned char)buf[num*2])*256+int((unsigned char)buf[num*2+1]);
		}
		point=0;
		for(;;point++)
		{
			if(freeblock[point%256]==0)
				continue;
			else
				break;
		}
		return brelse(phead);
	}
	if(point%256==0)  //空闲块栈满，则将该栈中的信息存储到物理块中
	{
		char buf[bsize+1];
		for(int ppoint=0;ppoint<256;ppoint++)
		{
			buf[ppoint*2]=(char)(freeblock[ppoint]/256);
			buf[ppoint*2+1]=(char)(freeblock[ppoint]%256);
		}
		buf[512]='\0';
		if(bwrite(tofree,buf)==BLKWRITEERR)
		{
			cout<<"BLOCK WRITE ERROR\n";
			return BLOCKERR;
		}
		point--;
		freeblock[point%256]=tofree;
		return tofree;
	}
	else  //未满，则分配空闲块
	{
		point--;
		freeblock[point%256]=tofree;
		return tofree;
	}    
}
block::~block()
{
	//将空闲块栈，用0填充满，再将其信息存储到物理块中
	if(point!=-1)
	{
		char buf[bsize+1];
		if(point%256==255&&freeblock[point%256]==0)
		{
			bread(0,buf);
			buf[478]=char(0/256);
			buf[479]=char(0%256);
			bwrite(0,buf);
			return;
		}    
		int one=balloc();
		if(point%256!=0)
		{
			point--;
			for(;;point--)
			{
				if(point%256==255||point==-1)
					break;
				freeblock[point%256]=0;
			}
		}
		for(int ppoint=0;ppoint<256;ppoint++)
		{
			buf[ppoint*2]=(char)(freeblock[ppoint]/256);
			buf[ppoint*2+1]=(char)(freeblock[ppoint]%256);
		}
		buf[512]='\0';
		if(bwrite(one,buf)==BLKWRITEERR)
		{
			cout<<"BLOCK WRITE ERROR\n";
			return;
		}
		bread(0,buf);
		buf[478]=char(one/256);
		buf[479]=char(one%256);
		bwrite(0,buf);
	}
}