// openfile.cc //	Routines to manage an open Nachos file.  As in UNIX, a//	file must be open before we can read or write to it.//	Once we're all done, we can close it (in Nachos, by deleting//	the OpenFile data structure).////	Also as in UNIX, for convenience, we keep the file header in//	memory while the file is open.//// 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 "filehdr.h"#include "openfile.h"#include "system.h"#ifdef HOST_SPARC#include <strings.h>#endif//----------------------------------------------------------------------// OpenFile::OpenFile// 	Open a Nachos file for reading and writing.  Bring the file header//	into memory while the file is open.////	"sector" -- the location on disk of the file header for this file//----------------------------------------------------------------------OpenFile::OpenFile(int sector){     hdr = new FileHeader;    hdr->FetchFrom(sector);    seekPosition = 0;}//----------------------------------------------------------------------// OpenFile::~OpenFile// 	Close a Nachos file, de-allocating any in-memory data structures.//----------------------------------------------------------------------OpenFile::~OpenFile(){    delete hdr;}//----------------------------------------------------------------------// OpenFile::Seek// 	Change the current location within the open file -- the point at//	which the next Read or Write will start from.////	"position" -- the location within the file for the next Read/Write//----------------------------------------------------------------------voidOpenFile::Seek(int position){    seekPosition = position;}	//----------------------------------------------------------------------// OpenFile::Read/Write// 	Read/write a portion of a file, starting from seekPosition.//	Return the number of bytes actually written or read, and as a//	side effect, increment the current position within the file.////	Implemented using the more primitive ReadAt/WriteAt.////	"into" -- the buffer to contain the data to be read from disk //	"from" -- the buffer containing the data to be written to disk //	"numBytes" -- the number of bytes to transfer//----------------------------------------------------------------------intOpenFile::Read(char *into, int numBytes){   int result = ReadAt(into, numBytes, seekPosition);   seekPosition += result;   return result;}intOpenFile::Write(char *into, int numBytes){   int result = WriteAt(into, numBytes, seekPosition);   seekPosition += result;   return result;}//----------------------------------------------------------------------// OpenFile::ReadAt/WriteAt// 	Read/write a portion of a file, starting at "position".//	Return the number of bytes actually written or read, but has//	no side effects (except that Write modifies the file, of course).////	There is no guarantee the request starts or ends on an even disk sector//	boundary; however the disk only knows how to read/write a whole disk//	sector at a time.  Thus:////	For ReadAt://	   We read in all of the full or partial sectors that are part of the//	   request, but we only copy the part we are interested in.//	For WriteAt://	   We must first read in any sectors that will be partially written,//	   so that we don't overwrite the unmodified portion.  We then copy//	   in the data that will be modified, and write back all the full//	   or partial sectors that are part of the request.////	"into" -- the buffer to contain the data to be read from disk //	"from" -- the buffer containing the data to be written to disk //	"numBytes" -- the number of bytes to transfer//	"position" -- the offset within the file of the first byte to be//			read/written//----------------------------------------------------------------------intOpenFile::ReadAt(char *into, int numBytes, int position){    int fileLength = hdr->FileLength();    int i, firstSector, lastSector, numSectors;    char *buf;    if ((numBytes <= 0) || (position >= fileLength))    	return 0; 				// check request    if ((position + numBytes) > fileLength)			numBytes = fileLength - position;    DEBUG('f', "Reading %d bytes at %d, from file of length %d.\n", 				numBytes, position, fileLength);    firstSector = divRoundDown(position, SectorSize);    lastSector = divRoundDown(position + numBytes - 1, SectorSize);    numSectors = 1 + lastSector - firstSector;    // read in all the full and partial sectors that we need    buf = new char[numSectors * SectorSize];    for (i = firstSector; i <= lastSector; i++)	        synchDisk->ReadSector(hdr->ByteToSector(i * SectorSize), 					&buf[(i - firstSector) * SectorSize]);    // copy the part we want    bcopy(&buf[position - (firstSector * SectorSize)], into, numBytes);    delete [] buf;    return numBytes;}intOpenFile::WriteAt(char *from, int numBytes, int position){    int fileLength = hdr->FileLength();    int i, firstSector, lastSector, numSectors;    bool firstAligned, lastAligned;    char *buf;    if ((numBytes <= 0) || (position >= fileLength))	return 0;				// check request    if ((position + numBytes) > fileLength)	numBytes = fileLength - position;    DEBUG('f', "Writing %d bytes at %d, from file of length %d.\n", 				numBytes, position, fileLength);    firstSector = divRoundDown(position, SectorSize);    lastSector = divRoundDown(position + numBytes - 1, SectorSize);    numSectors = 1 + lastSector - firstSector;    buf = new char[numSectors * SectorSize];    firstAligned = (position == (firstSector * SectorSize));    lastAligned = ((position + numBytes) == ((lastSector + 1) * SectorSize));// read in first and last sector, if they are to be partially modified    if (!firstAligned)        ReadAt(buf, SectorSize, firstSector * SectorSize);	    if (!lastAligned && ((firstSector != lastSector) || firstAligned))        ReadAt(&buf[(lastSector - firstSector) * SectorSize], 				SectorSize, lastSector * SectorSize);	// copy in the bytes we want to change     bcopy(from, &buf[position - (firstSector * SectorSize)], numBytes);// write modified sectors back    for (i = firstSector; i <= lastSector; i++)	        synchDisk->WriteSector(hdr->ByteToSector(i * SectorSize), 					&buf[(i - firstSector) * SectorSize]);    delete [] buf;    return numBytes;}//----------------------------------------------------------------------// OpenFile::Length// 	Return the number of bytes in the file.//----------------------------------------------------------------------intOpenFile::Length() {     return hdr->FileLength(); }