// filehdr.cc //	Routines for managing the disk file header (in UNIX, this//	would be called the i-node).////	The file header is used to locate where on disk the //	file's data is stored.  We implement this as a fixed size//	table of pointers -- each entry in the table points to the //	disk sector containing that portion of the file data//	(in other words, there are no indirect or doubly indirect //	blocks). The table size is chosen so that the file header//	will be just big enough to fit in one disk sector, ////      Unlike in a real system, we do not keep track of file permissions, //	ownership, last modification date, etc., in the file header. ////	A file header can be initialized in two ways://	   for a new file, by modifying the in-memory data structure//	     to point to the newly allocated data blocks//	   for a file already on disk, by reading the file header from disk//// Copyright (c) 1992-1993 The Regents of the University of California.// All rights reserved.  See copyright.h for copyright notice and limitation // of liability and disclaimer of warranty provisions.#include "copyright.h"#include "system.h"#include "filehdr.h"//----------------------------------------------------------------------// FileHeader::Allocate// 	Initialize a fresh file header for a newly created file.//	Allocate data blocks for the file out of the map of free disk blocks.//	Return FALSE if there are not enough free blocks to accomodate//	the new file.////	"freeMap" is the bit map of free disk sectors//	"fileSize" is the bit map of free disk sectors//----------------------------------------------------------------------boolFileHeader::Allocate(BitMap *freeMap, int fileSize){     numBytes = fileSize;    numSectors  = divRoundUp(fileSize, SectorSize);    if (freeMap->NumClear() < numSectors)	return FALSE;		// not enough space    for (int i = 0; i < numSectors; i++)	dataSectors[i] = freeMap->Find();    return TRUE;}//----------------------------------------------------------------------// FileHeader::Deallocate// 	De-allocate all the space allocated for data blocks for this file.////	"freeMap" is the bit map of free disk sectors//----------------------------------------------------------------------void FileHeader::Deallocate(BitMap *freeMap){    for (int i = 0; i < numSectors; i++) {	ASSERT(freeMap->Test((int) dataSectors[i]));  // ought to be marked!	freeMap->Clear((int) dataSectors[i]);    }}//----------------------------------------------------------------------// FileHeader::FetchFrom// 	Fetch contents of file header from disk. ////	"sector" is the disk sector containing the file header//----------------------------------------------------------------------voidFileHeader::FetchFrom(int sector){    synchDisk->ReadSector(sector, (char *)this);}//----------------------------------------------------------------------// FileHeader::WriteBack// 	Write the modified contents of the file header back to disk. ////	"sector" is the disk sector to contain the file header//----------------------------------------------------------------------voidFileHeader::WriteBack(int sector){    synchDisk->WriteSector(sector, (char *)this); }//----------------------------------------------------------------------// FileHeader::ByteToSector// 	Return which disk sector is storing a particular byte within the file.//      This is essentially a translation from a virtual address (the//	offset in the file) to a physical address (the sector where the//	data at the offset is stored).////	"offset" is the location within the file of the byte in question//----------------------------------------------------------------------intFileHeader::ByteToSector(int offset){    return(dataSectors[offset / SectorSize]);}//----------------------------------------------------------------------// FileHeader::FileLength// 	Return the number of bytes in the file.//----------------------------------------------------------------------intFileHeader::FileLength(){    return numBytes;}//----------------------------------------------------------------------// FileHeader::Print// 	Print the contents of the file header, and the contents of all//	the data blocks pointed to by the file header.//----------------------------------------------------------------------voidFileHeader::Print(){    int i, j, k;    char *data = new char[SectorSize];    printf("FileHeader contents.  File size: %d.  File blocks:\n", numBytes);    for (i = 0; i < numSectors; i++)	printf("%d ", dataSectors[i]);    printf("\nFile contents:\n");    for (i = k = 0; i < numSectors; i++) {	synchDisk->ReadSector(dataSectors[i], data);        for (j = 0; (j < SectorSize) && (k < numBytes); j++, k++) {	    if ('\040' <= data[j] && data[j] <= '\176')   // isprint(data[j])		printf("%c", data[j]);            else		printf("\\%x", (unsigned char)data[j]);	}        printf("\n");     }    delete [] data;}