rdwt.c

基于UNIX6的文件系统模拟程序

#include <stdio.h>
#include "filesys.h"


unsigned int read(fileid,buf,size)
int fileid;
char *buf;
unsigned int size;
{
	unsigned long off;
	int block,block_off,i,j;
	struct inode *inode;
	char *temp_buf;

	inode=sys_ofile[user[user_id].u_ofile[fileid]].f_inode;
	if(!(sys_ofile[user[user_id].u_ofile[fileid]].f_flag&FREAD))
	{
		printf("\nthe file is not opened for read\n");
		return 0;
	}


	temp_buf = buf;

	off = sys_ofile[user[user_id].u_ofile[fileid]].f_off;
	if((off+size)>inode->di_size)
		size=inode->di_size-off;

	block_off=off%BLOCKSIZ;
	block=off/BLOCKSIZ;

	if(block_off+size < BLOCKSIZ)
	{
		fseek(fd,DATASTART+inode->di_addr[block]*BLOCKSIZ+block_off,SEEK_SET);
		fread(buf,1,size,fd);
		return size;
	}

	fseek(fd,DATASTART+inode->di_addr[block]*BLOCKSIZ+block_off,SEEK_SET);
	fread(temp_buf,1,BLOCKSIZ-block_off,fd);

	temp_buf += BLOCKSIZ-block_off;
	j=(inode->di_size-off-block_off)/BLOCKSIZ;
	for(i=0;i<(size-block_off)/BLOCKSIZ;i++)
	{
		fseek(fd,DATASTART+inode->di_addr[j+i]*BLOCKSIZ,SEEK_SET);
		fread(temp_buf,1,BLOCKSIZ,fd);
		temp_buf += BLOCKSIZ;
	}

	block_off=(size-block_off)%BLOCKSIZ;
	block=inode->di_addr[off+size/BLOCKSIZ+1];
	fseek(fd,DATASTART+block*BLOCKSIZ,SEEK_SET);
	fread(temp_buf,1,BLOCKSIZ,fd);
	
	sys_ofile[user[user_id].u_ofile[fileid]].f_off += size;

	return size;
}



unsigned int write(fileid,buf,size)
int fileid;
char * buf;
unsigned int size;
{
	unsigned long off;
	int block,block_off,i,j;
	struct inode *inode;
	char *temp_buf,*a;

	inode = sys_ofile[user[user_id].u_ofile[fileid]].f_inode;


//	printf("in write mode%d",inode->di_mode);

	if(!sys_ofile[user[user_id].u_ofile[fileid]].f_flag&FWRITE)
	{
		printf("\nthe file is not opened for write\n");
		return 0;
	}
	temp_buf = buf;

	off= sys_ofile[user[user_id].u_ofile[fileid]].f_off;
	block_off=off%BLOCKSIZ;
	block=off/BLOCKSIZ;

	if(0 == off&&inode->di_size==0)
		inode->di_addr[0] = balloc();

	if(block_off+size<BLOCKSIZ)
	{
		fseek(fd,DATASTART+inode->di_addr[block]*BLOCKSIZ+block_off,SEEK_SET);
		fwrite(temp_buf,1,size,fd);
		//the below is just for debug
		//fseek(fd,DATASTART+inode->di_addr[block]*BLOCKSIZ+block_off,SEEK_SET);
		//a = malloc(20);
		//fread(a,1,size,fd);
		//printf("fffffffff:%s",a);
		inode->di_size += size;
		sys_ofile[user[user_id].u_ofile[fileid]].f_off += size;//
		return size;
	}

	fseek(fd,DATASTART+inode->di_addr[block]*BLOCKSIZ+block_off,SEEK_SET);
	fwrite(temp_buf,1,BLOCKSIZ-block_off,fd);

	temp_buf+=BLOCKSIZ-block_off;
	for(i=0;i<(size-BLOCKSIZ+block_off)/BLOCKSIZ;i++)//size-block_off
	{
		inode->di_addr[block+1+i]=balloc();
		fseek(fd,DATASTART+inode->di_addr[block+1+i]*BLOCKSIZ,SEEK_SET);
		fwrite(temp_buf,1,BLOCKSIZ,fd);
		temp_buf += BLOCKSIZ;
	}

	block_off = (size-BLOCKSIZ+block_off)%BLOCKSIZ;
	block=inode->di_addr[(off+size)/BLOCKSIZ+1]=balloc();
	fseek(fd,DATASTART+block*BLOCKSIZ,SEEK_SET);
	fwrite(temp_buf,1,block_off,fd);
	
	inode->di_size += size;
	sys_ofile[user[user_id].u_ofile[fileid]].f_off += size;//

	return size;
}
	
/**/	
int seek(fileid,offset,origin)
unsigned int fileid;
long offset;
int origin;
{
	struct inode *inode;
	inode = sys_ofile[user[user_id].u_ofile[fileid]].f_inode;
	switch(origin)
	{
		/* 0 is from the head,2 is from the end,1 is from the current position*/
	case 0:
		{
			if(offset>inode->di_size)
				sys_ofile[user[user_id].u_ofile[fileid]].f_off = inode->di_size;
			else
				sys_ofile[user[user_id].u_ofile[fileid]].f_off = offset;
			break;
		}
	case 1:
		{
			if(offset+offset>inode->di_size)
				sys_ofile[user[user_id].u_ofile[fileid]].f_off = inode->di_size;
			else
				sys_ofile[user[user_id].u_ofile[fileid]].f_off = offset+offset;
			break;
		}
	case 2:
		{
			if(offset>inode->di_size)
				sys_ofile[user[user_id].u_ofile[fileid]].f_off = 0;
			else
				sys_ofile[user[user_id].u_ofile[fileid]].f_off = inode->di_size-offset;
			break;
		}
	default:
		break;
	}
}