Initial version

code/filesys/filehdr.h

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+// filehdr.h 
+//	Data structures for managing a disk file header.  
+//
+//	A file header describes where on disk to find the data in a file,
+//	along with other information about the file (for instance, its
+//	length, owner, etc.)
+//
+// 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"
+
+#ifndef FILEHDR_H
+#define FILEHDR_H
+
+#include "disk.h"
+#include "bitmap.h"
+
+#define NumDirect 	((SectorSize - 2 * sizeof(int)) / sizeof(int))
+#define MaxFileSize 	(NumDirect * SectorSize)
+
+// The following class defines the Nachos "file header" (in UNIX terms,  
+// the "i-node"), describing where on disk to find all of the data in the file.
+// The file header is organized as a simple table of pointers to
+// data blocks. 
+//
+// The file header data structure can be stored in memory or on disk.
+// When it is on disk, it is stored in a single sector -- this means
+// that we assume the size of this data structure to be the same
+// as one disk sector.  Without indirect addressing, this
+// limits the maximum file length to just under 4K bytes.
+//
+// There is no constructor; rather the file header can be initialized
+// by allocating blocks for the file (if it is a new file), or by
+// reading it from disk.
+
+class FileHeader {
+  public:
+    bool Allocate(BitMap *bitMap, int fileSize);// Initialize a file header, 
+						//  including allocating space 
+						//  on disk for the file data
+    void Deallocate(BitMap *bitMap);  		// De-allocate this file's 
+						//  data blocks
+
+    void FetchFrom(int sectorNumber); 	// Initialize file header from disk
+    void WriteBack(int sectorNumber); 	// Write modifications to file header
+					//  back to disk
+
+    int ByteToSector(int offset);	// Convert a byte offset into the file
+					// to the disk sector containing
+					// the byte
+
+    int FileLength();			// Return the length of the file 
+					// in bytes
+
+    void Print();			// Print the contents of the file.
+
+  private:
+    int numBytes;			// Number of bytes in the file
+    int numSectors;			// Number of data sectors in the file
+    int dataSectors[NumDirect];		// Disk sector numbers for each data 
+					// block in the file
+};
+
+#endif // FILEHDR_H