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filesys.h

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// 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 available
class 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 // FILESYS
class 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

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