readwe.c

设计并实现一个多用户多级目录结构的文件系统

/************************************************/
/*												*/
/*					readwrite.c					*/
/*												*/
/************************************************/

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

int read( int fh, char * buf, unsigned int nbyte )
{
	unsigned long off;
	int block, block_off, i, sys_ip;
	struct inode * inode;
//	char * temp_buf;

	sys_ip = user[user_id].u_ofile[fh];
	inode = sys_ofile[sys_ip].f_inode;

	if( !( sys_ofile[sys_ip].f_flag & O_RDONLY ))
	{
		printf( "The file is not opened for read\n" );
		return -1;
	}


	off = sys_ofile[sys_ip].f_off;

	block = off / BLOCKSIZ;					/* 从inode->i_addr[block]号盘块读起 */
	block_off = off % BLOCKSIZ;				/* block_off是在block号盘块中的偏移量 */

	/* 读写指针在文件末尾，读出字数为0 */
	if( off == inode->i_size )
		return 0;

	/* 读文件不用跨越盘块，即在一盘块中就可读出nbyte字 */
	if( block_off + nbyte < BLOCKSIZ )
	{
		fseek( fd, 
			DATASTART + inode->i_addr[block] * BLOCKSIZ + block_off, 
			SEEK_SET );
		fread( buf, 1, nbyte, fd );
//		free( temp_buf );
		return nbyte;
	}

	/* 读文件跨越盘块，即所读的文件有多个盘块 */

	/* 先读block盘块 */
	fseek( fd, 
		DATASTART + inode->i_addr[block] * BLOCKSIZ + block_off, 
		SEEK_SET );
	fread( buf, 1, BLOCKSIZ - block_off, fd );
	buf += BLOCKSIZ - block_off;

	block++;
	/* 所读的文件没有到末尾 */
	if( nbyte + off < inode->i_size )
	{
		for( i = 0; i < ( nbyte - block_off ) / BLOCKSIZ; i++ )
		{
			fseek( fd, 
				DATASTART + inode->i_addr[i + block] * BLOCKSIZ, 
				SEEK_SET );
			fread( buf, 1, BLOCKSIZ, fd );
			buf += BLOCKSIZ;
		}
//		block_off = ( nbyte - block_off ) % BLOCKSIZ;
//		block = inode->i_addr[off + nbyte / BLOCKSIZ + 1];
		fseek( fd, DATASTART + inode->i_addr[i + block] * BLOCKSIZ, SEEK_SET );
		fread( buf, 1, ( nbyte - block_off ) % BLOCKSIZ, fd );
		
		/* 置文件读/写指针位置 */
		sys_ofile[sys_ip].f_off += nbyte;

		return nbyte;
	}
	/* 所读的文件到末尾 */
	for( i = block; i < inode->i_size / BLOCKSIZ; i++ )
	{
		fseek( fd, 
			DATASTART + inode->i_addr[i] * BLOCKSIZ, 
			SEEK_SET );
		fread( buf, 1, BLOCKSIZ, fd );
		buf += BLOCKSIZ;
	}
	fseek( fd, DATASTART + inode->i_addr[i] * BLOCKSIZ, SEEK_SET );
	fread( buf, 1, inode->i_size % BLOCKSIZ, fd );
	sys_ofile[sys_ip].f_off = inode->i_size;
	return ( inode->i_size - off );
}

int write( int fh, char * buf, unsigned int nbyte )
{
	unsigned long off;
	int block, block_off, i, sys_ip;
	struct inode * inode;
	char * temp_buf;

	sys_ip = user[user_id].u_ofile[fh];
	inode = sys_ofile[sys_ip].f_inode;

	if( !( sys_ofile[sys_ip].f_flag & O_WRONLY ))
	{
		printf( "The file is not opened for write\n" );
		return -1;
	}

	off = sys_ofile[sys_ip].f_off;

	block = off / BLOCKSIZ;					/* 从inode->i_addr[block]号盘块起开始写 */
	block_off = off % BLOCKSIZ;				/* block_off是在block号盘块中的偏移量 */

//	temp_buf = buf;

	/* 写文件不用跨越盘块，即在一盘块中就可写入nbyte字 */
	if( block_off + nbyte < BLOCKSIZ )
	{
		fseek( fd, 
			DATASTART + inode->i_addr[block] * BLOCKSIZ + block_off, 
			SEEK_SET );
		fwrite( buf, 1, nbyte, fd );
		if( inode->i_size < nbyte )
			inode->i_size = nbyte;
		return nbyte;
	}

	/* 写文件跨越盘块，即所写的文件有多个盘块 */

	/* 先往block盘块写入 */
	fseek( fd, 
		DATASTART + inode->i_addr[block] * BLOCKSIZ + block_off, 
		SEEK_SET );
	fwrite( temp_buf, 1, BLOCKSIZ - block_off, fd );

	buf += BLOCKSIZ - block_off;

	/* 所写的文件没有到末尾 */
	if( nbyte + off < inode->i_size )
	{
		for( i = 0; i < ( nbyte - block_off ) / BLOCKSIZ; i++ )
		{
			fseek( fd, 
				DATASTART + inode->i_addr[i + block] * BLOCKSIZ, 
				SEEK_SET );
			fwrite( buf, 1, BLOCKSIZ, fd );
			buf += BLOCKSIZ;
		}
//		block_off = ( nbyte - block_off ) % BLOCKSIZ;
//		block = inode->i_addr[off + nbyte / BLOCKSIZ + 1];
		fseek( fd, DATASTART + inode->i_addr[i + block] * BLOCKSIZ, SEEK_SET );
		fwrite( buf, 1, ( nbyte - block_off ) % BLOCKSIZ, fd );
		
		/* 置文件读/写指针位置 */
		sys_ofile[sys_ip].f_off += nbyte;

		if( inode->i_size < nbyte )
			inode->i_size = nbyte;

		return nbyte;
	}
	/* 所读的文件到末尾 */

	/* 写到文件尾 */
	for( i = block; i < inode->i_size / BLOCKSIZ; i++ )
	{
		fseek( fd, 
			DATASTART + inode->i_addr[i] * BLOCKSIZ, 
			SEEK_SET );
		fwrite( buf, 1, BLOCKSIZ, fd );
		buf += BLOCKSIZ;
	}

	/* 申请空间再写 */
	for( ; i < ( nbyte + off ) / BLOCKSIZ; i++ )
	{
		inode->i_addr[i] = balloc();
		fseek( fd, 
			DATASTART + inode->i_addr[i] * BLOCKSIZ, 
			SEEK_SET );
		fwrite( temp_buf, 1, BLOCKSIZ, fd );
		buf += BLOCKSIZ;
	}
	fseek( fd, DATASTART + inode->i_addr[i] * BLOCKSIZ, SEEK_SET );
	fwrite( buf, 1, ( nbyte + off ) % BLOCKSIZ, fd );
	inode->i_size = nbyte + off;
	sys_ofile[sys_ip].f_off = inode->i_size;

	if( inode->i_size < nbyte )
			inode->i_size = nbyte;

	return nbyte;


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

	block_off = ( nbyte - block_off ) % BLOCKSIZ;
	block = inode->i_addr[off+nbyte / BLOCKSIZ + 1] = balloc();
	fseek( fd, DATASTART + block * BLOCKSIZ, SEEK_SET );
	fwrite( buf, 1, block_off, fd );

	sys_ofile[user[user_id].u_ofile[fh]].f_off += nbyte;

	return nbyte;*/
}