changMN.c

/*
 * Disclaimer: Possible loss of data!! This code was written by the students
 * who took the Operating System module at Zhejiang University. Use it at
 * your own will and risk! If you do not know what the code does, please try
 * not to use it.
 */

#include <stdio.h>
main()
{
	int ret;
	FILE *fp_read;
	FILE *fp_write;
	unsigned char buf[2048];
	
	fp_read=fopen("./myfs","rb");

	if(fp_read == NULL)
	{
		printf("open myfs failed!\n");
		return 1;
	}

	fp_write=fopen("./fs.new","wb");

	if(fp_write==NULL)
	{
		printf("open fs.new failed!\n");
		return 2;
	}

	ret=fread(buf,sizeof(unsigned char),2048,fp_read);

	printf("previous magic number is 0x%x%x\n",buf[0x438],buf[0x439]);

	buf[0x438]=0x66;
	buf[0x439]=0x66;

	fwrite(buf,sizeof(unsigned char),2048,fp_write);

	printf("current magic number is 0x%x%x\n",buf[0x438],buf[0x439]);

	while(ret == 2048)
	{
		ret=fread(buf,sizeof(unsigned char),2048,fp_read);
		fwrite(buf,sizeof(unsigned char),ret,fp_write);
	}

	if(ret < 2048 && feof(fp_read))
	{
		printf("change magic number ok!\n");
	}

	fclose(fp_read);
	fclose(fp_write);

	return 0;
}