block.c~

模拟linux的ext3文件系统。采用位图法。用一个文件模拟硬盘。实现创建、删除目录、文件。读、写文件

#include"structure.h"
int load_block_entry(u8 *buffer, u16 block_num)
{
 u32 block_addr;
 block_addr=DATA_BLOCK+block_num*512;
 fseek(FS,block_addr,SEEK_SET);
 fread(buffer,sizeof(u8),512,FS);
 return 1;
}

int update_block_entry(u8 *buffer,u16 block_num)
{
 u32 block_addr;
 block_addr=DATA_BLOCK+block_num*512;
 fseek(FS,block_addr,SEEK_SET);
 fwrite(buffer,sizeof(u8),512,FS);
 fclose(FS);
 FS=fopen("FS","r+");
 return 1;
}
int pow(int x,int y)
{
 int i;
 int ret=1;
 for (i=0; i<y;i++)
     ret=ret*x;
 return ret;
}
u16 new_block()
{
 u16 ret;
 u8 i,j;
 u8 a,b;
 u8 buffer[512];
 fseek(FS,BLOCK_BITMAP,SEEK_SET);
 fread(buffer,sizeof(u8),512,FS);
 b=0;
 for(i=0;i<512;i++){
	a=b^buffer[i];
	if(a!=0xff)  break;
	}
 if(i==512)   ret=0;
 else{
        for(j=0;j<8;j++){ 
		a=pow(2,(7-j));
	        b=a|buffer[i]; 
	        if(b!=buffer[i]) break;
	 }
	 buffer[i]=b;
	 fseek(FS,BLOCK_BITMAP,SEEK_SET);
	 fwrite(buffer,sizeof(u8),512,FS);
         fclose(FS);
         FS=fopen("FS","r+");
         ret=i*8+j;
 }	 
 return ret;
}
void free_block(u16 inode_num)
{
 u8 i,j,temp;
 u8 buffer[512];
 fseek(FS,BLOCK_BITMAP,SEEK_SET);
 fread(buffer,sizeof(u8),512,FS);
 i=inode_num/8;
 j=inode_num%8;
 temp=pow(2,(7-j));
 buffer[i]=temp^buffer[i];
 fseek(FS,BLOCK_BITMAP,SEEK_SET);
 fwrite(buffer,sizeof(u8),512,FS);
 fclose(FS);
 FS=fopen("FS","r+");
}
u16 test_block(u16 block)
{
 u8 i,j,a,b;
 u8 buffer[512];
 fseek(FS,BLOCK_BITMAP,SEEK_SET);
 fread(buffer,sizeof(u8),512,FS);
 i=block/8;
 j=block%8;
 a=pow(2,(7-j));
 b=a|buffer[i];
 if(b!=buffer[i])  return 0;
 return 1;
}