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openfile.h

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// openfile.h 
//      Data structures for opening, closing, reading and writing to 
//      individual files.  The operations supported are similar to
//      the UNIX ones -- type 'man open' to the UNIX prompt.
//
//      There are two implementations.  One is a "STUB" that directly
//      turns the file operations into the underlying UNIX operations.
//      (cf. comment in filesys.h).
//
//      The other is the "real" implementation, that turns these
//      operations into read and write disk sector requests. 
//      In this baseline implementation of the file system, we don't 
//      worry about concurrent accesses to the file system
//      by different threads -- this is part of the assignment.
//
// 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 OPENFILE_H
#define OPENFILE_H

#include "copyright.h"
#include "utility.h"

#ifdef FILESYS_STUB                     // Temporarily implement calls to 
                                        // Nachos file system as calls to UNIX!
                                        // See definitions listed under #else
class OpenFile {
  public:
    OpenFile(int f) { file = f; currentOffset = 0; }    // open the file
    ~OpenFile() { Close(file); }                        // close the file

    int ReadAt(char *into, int numBytes, int position) { 
                Lseek(file, position, 0); 
                return ReadPartial(file, into, numBytes); 
                }       
    int WriteAt(char *from, int numBytes, int position) { 
                Lseek(file, position, 0); 
                WriteFile(file, from, numBytes); 
                return numBytes;
                }       
    int Read(char *into, int numBytes) {
                int numRead = ReadAt(into, numBytes, currentOffset); 
                currentOffset += numRead;
                return numRead;
                }
    int Write(char *from, int numBytes) {
                int numWritten = WriteAt(from, numBytes, currentOffset); 
                currentOffset += numWritten;
                return numWritten;
                }

    int Length() { Lseek(file, 0, 2); return Tell(file); }
    
  private:
    int file;
    int currentOffset;
};

#else // FILESYS
class FileHeader;

class OpenFile {
  public:
    OpenFile(int sector);               // Open a file whose header is located
                                        // at "sector" on the disk
    ~OpenFile();                        // Close the file

    void Seek(int position);            // Set the position from which to 
                                        // start reading/writing -- UNIX lseek

    int Read(char *into, int numBytes); // Read/write bytes from the file,
                                        // starting at the implicit position.
                                        // Return the # actually read/written,
                                        // and increment position in file.
    int Write(char *from, int numBytes);

    int ReadAt(char *into, int numBytes, int position);
                                        // Read/write bytes from the file,
                                        // bypassing the implicit position.
    int WriteAt(char *from, int numBytes, int position);

    int Length();                       // Return the number of bytes in the
                                        // file (this interface is simpler 
                                        // than the UNIX idiom -- lseek to 
                                        // end of file, tell, lseek back 
    
  private:
    FileHeader *hdr;                    // Header for this file 
    int seekPosition;                   // Current position within the file
};

#endif // FILESYS

#endif // OPENFILE_H

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