// filesys.h //	Data structures to represent the Nachos file system.////	A file system is a set of files stored on disk, organized//	into directories.  Operations on the file system have to//	do with "naming" -- creating, opening, and deleting files,//	given a textual file name.  Operations on an individual//	"open" file (read, write, close) are to be found in the OpenFile//	class (openfile.h).////	We define two separate implementations of the file system. //	The "STUB" version just re-defines the Nachos file system //	operations as operations on the native UNIX file system on the machine//	running the Nachos simulation.  This is provided in case the//	multiprogramming and virtual memory assignments (which make use//	of the file system) are done before the file system assignment.////	The other version is a "real" file system, built on top of //	a disk simulator.  The disk is simulated using the native UNIX //	file system (in a file named "DISK"). ////	In the "real" implementation, there are two key data structures used //	in the file system.  There is a single "root" directory, listing//	all of the files in the file system; unlike UNIX, the baseline//	system does not provide a hierarchical directory structure.  //	In addition, there is a bitmap for allocating//	disk sectors.  Both the root directory and the bitmap are themselves//	stored as files in the Nachos file system -- this causes an interesting//	bootstrap problem when the simulated disk is initialized. //// 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.#ifndef FS_H#define FS_H#include "copyright.h"#include "openfile.h"#ifdef FILESYS_STUB 		// Temporarily implement file system calls as 				// calls to UNIX, until the real file system				// implementation is availableclass FileSystem {  public:    FileSystem(bool format) {}    bool Create(char *name, int initialSize) { 	int fileDescriptor = OpenForWrite(name);	if (fileDescriptor == -1) return FALSE;	Close(fileDescriptor); 	return TRUE; 	}    OpenFile* Open(char *name) {	  int fileDescriptor = OpenForReadWrite(name, FALSE);	  if (fileDescriptor == -1) return NULL;	  return new OpenFile(fileDescriptor);      }    bool Remove(char *name) { return Unlink(name) == 0; }};#else // FILESYSclass FileSystem {  public:    FileSystem(bool format);		// Initialize the file system.					// Must be called *after* "synchDisk" 					// has been initialized.    					// If "format", there is nothing on					// the disk, so initialize the directory    					// and the bitmap of free blocks.    bool Create(char *name, int initialSize);  						// Create a file (UNIX creat)    OpenFile* Open(char *name); 	// Open a file (UNIX open)    bool Remove(char *name);  		// Delete a file (UNIX unlink)    void List();			// List all the files in the file system    void Print();			// List all the files and their contents  private:   OpenFile* freeMapFile;		// Bit map of free disk blocks,					// represented as a file   OpenFile* directoryFile;		// "Root" directory -- list of 					// file names, represented as a file};#endif // FILESYS#endif // FS_H