Thread: help on boot sector plzzzzz

here is the code:

Code:

/* ===== SharedDisk.h ===== */

#ifndef __SHAREDISK__
#define __SHAREDISK__


typedef struct
{
	unsigned short	Jump;
		char 	Manufacturer[ 9 ];
	unsigned short 	BytesPerSector;
	unsigned char 	SectorsPerCluster;
	unsigned short 	ReservedSectors;
	unsigned char	FATs;
	unsigned short	RootDirectoryEntries;
	unsigned short	LogicalSectors;
	unsigned char	MediaDescriptorByte;
	unsigned short	SectorsPerFAT;
	unsigned short	SectorsPerTrack;
	unsigned short	Surfaces;
	unsigned short	HiddenSectors;
} Disk;

#endif

/* ===== FDisk.c ===== */

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <ctype.h>
#include <string.h>
#include "SharedDisk.h"
#include "FDisk.h"


int DiskOpen( Disk *theDisk )
{
	int 	fd;
	int 	len;
	char	buffer[SIZE]; 

	
	// ===== Initialize theDisk ===== //
	memset( theDisk, '\0', sizeof( Disk ) );
	
	// ===== Open the file ===== //
	fd = open ( "disk.img", O_RDONLY );
	
	// ===== Read boot sector information in the file to array buffer ===== //
    	len = read ( fd, buffer, 512 );

	// ===== Check if it reads file sucessful ===== //
	if ( len == -1 )
	{
		printf( "Unable to read file.\n" );
	 }


===== i have problem from here it is not correct ===== 
===== i do not know how to put each inforamtion to each member of the struct Disk. =====

	// ===== Copy the information to each member of the Disk ===== //
	memcpy( theDisk->Jump, &buffer[ 0 ], 3 );
	memcpy( theDisk->Manufacturer, &buffer[ 3 ], 8 );
	memcpy( theDisk->BytesPerSector, &buffer[ 11 ], 2 );
	memcpy( theDisk->SectorsPerCluster, &buffer[ 13 ], 1 );
	memcpy( theDisk->ReservedSectors, &buffer[ 14 ], 2 );
	memcpy( theDisk->FATs, &buffer[ 16 ], 1 );
	memcpy( theDisk->RootDirectoryEntries, &buffer[ 17 ], 2 );
	memcpy( theDisk->LogicalSectors, &buffer[ 19 ], 2 );
	memcpy( theDisk->MediaDescriptorByte, &buffer[ 21 ], 1 );
	memcpy( theDisk->SectorsPerFAT, &buffer[ 22 ], 2 );
	memcpy( theDisk->SectorsPerTrack, &buffer[ 24 ], 2 );
	memcpy( theDisk->Surfaces, &buffer[ 26 ], 2 );
	memcpy( theDisk->HiddenSectors, &buffer[ 28 ], 2 );

	return	fd;
}

after i have read all information on the boot sector to buffer,
how do i put each information to each member of the struct Disk?

i have heard that i have to deal with offset bytes to get each information like shifting byte left.
i do not know how.

can some one tell me how?

if u need more information, please tell me.
i will provide more information.

thx a lot

How was the data in "disk.img" written, as a structure identical to "Disk"? If yes, you don't need to:

Code:

len = read ( fd, buffer, 512 );

Instead:

Code:

len = read ( fd, theDisk, sizeof(Disk) );

>fd = open ( "disk.img", O_RDONLY );
One more thing, what if open() failed?

the data in "disk.img" is written, as a structure identical to "Disk".
this file is made from the floopy disk.
floppy disks have a logical sector size of 512 bytes.
that is why 512 is there.
buffer only stores one sector at a time.
read the Boot Sector and fill in the appropriate structures in theDisk.
display a human readable summary of the disk information read from the boot sector on stdout.

Then the best solution is:

Code:

len = read ( fd, theDisk, sizeof(Disk) );

But ofcourse, make sure to allocate enough memory for 'theDisk'. And keep reading that way until 512 bytes have been read (512 / sizeof(Disk) times)