Initial version

code/filesys/filehdr.cc

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+// filehdr.cc 
+//	Routines for managing the disk file header (in UNIX, this
+//	would be called the i-node).
+//
+//	The file header is used to locate where on disk the 
+//	file's data is stored.  We implement this as a fixed size
+//	table of pointers -- each entry in the table points to the 
+//	disk sector containing that portion of the file data
+//	(in other words, there are no indirect or doubly indirect 
+//	blocks). The table size is chosen so that the file header
+//	will be just big enough to fit in one disk sector, 
+//
+//      Unlike in a real system, we do not keep track of file permissions, 
+//	ownership, last modification date, etc., in the file header. 
+//
+//	A file header can be initialized in two ways:
+//	   for a new file, by modifying the in-memory data structure
+//	     to point to the newly allocated data blocks
+//	   for a file already on disk, by reading the file header from disk
+//
+// 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 "system.h"
+#include "filehdr.h"
+
+//----------------------------------------------------------------------
+// FileHeader::Allocate
+// 	Initialize a fresh file header for a newly created file.
+//	Allocate data blocks for the file out of the map of free disk blocks.
+//	Return FALSE if there are not enough free blocks to accomodate
+//	the new file.
+//
+//	"freeMap" is the bit map of free disk sectors
+//	"fileSize" is the bit map of free disk sectors
+//----------------------------------------------------------------------
+
+bool
+FileHeader::Allocate(BitMap *freeMap, int fileSize)
+{ 
+    numBytes = fileSize;
+    numSectors  = divRoundUp(fileSize, SectorSize);
+    if (freeMap->NumClear() < numSectors)
+	return FALSE;		// not enough space
+
+    for (int i = 0; i < numSectors; i++)
+	dataSectors[i] = freeMap->Find();
+    return TRUE;
+}
+
+//----------------------------------------------------------------------
+// FileHeader::Deallocate
+// 	De-allocate all the space allocated for data blocks for this file.
+//
+//	"freeMap" is the bit map of free disk sectors
+//----------------------------------------------------------------------
+
+void 
+FileHeader::Deallocate(BitMap *freeMap)
+{
+    for (int i = 0; i < numSectors; i++) {
+	ASSERT(freeMap->Test((int) dataSectors[i]));  // ought to be marked!
+	freeMap->Clear((int) dataSectors[i]);
+    }
+}
+
+//----------------------------------------------------------------------
+// FileHeader::FetchFrom
+// 	Fetch contents of file header from disk. 
+//
+//	"sector" is the disk sector containing the file header
+//----------------------------------------------------------------------
+
+void
+FileHeader::FetchFrom(int sector)
+{
+    synchDisk->ReadSector(sector, this);
+}
+
+//----------------------------------------------------------------------
+// FileHeader::WriteBack
+// 	Write the modified contents of the file header back to disk. 
+//
+//	"sector" is the disk sector to contain the file header
+//----------------------------------------------------------------------
+
+void
+FileHeader::WriteBack(int sector)
+{
+    synchDisk->WriteSector(sector, this); 
+}
+
+//----------------------------------------------------------------------
+// FileHeader::ByteToSector
+// 	Return which disk sector is storing a particular byte within the file.
+//      This is essentially a translation from a virtual address (the
+//	offset in the file) to a physical address (the sector where the
+//	data at the offset is stored).
+//
+//	"offset" is the location within the file of the byte in question
+//----------------------------------------------------------------------
+
+int
+FileHeader::ByteToSector(int offset)
+{
+    return(dataSectors[offset / SectorSize]);
+}
+
+//----------------------------------------------------------------------
+// FileHeader::FileLength
+// 	Return the number of bytes in the file.
+//----------------------------------------------------------------------
+
+int
+FileHeader::FileLength()
+{
+    return numBytes;
+}
+
+//----------------------------------------------------------------------
+// FileHeader::Print
+// 	Print the contents of the file header, and the contents of all
+//	the data blocks pointed to by the file header.
+//----------------------------------------------------------------------
+
+void
+FileHeader::Print()
+{
+    int i, j, k;
+    char *data = new char[SectorSize];
+
+    printf("FileHeader contents.  File size: %d.  File blocks:\n", numBytes);
+    for (i = 0; i < numSectors; i++)
+	printf("%d ", dataSectors[i]);
+    printf("\nFile contents:\n");
+    for (i = k = 0; i < numSectors; i++) {
+	synchDisk->ReadSector(dataSectors[i], data);
+        for (j = 0; (j < SectorSize) && (k < numBytes); j++, k++) {
+	    if ('\040' <= data[j] && data[j] <= '\176')   // isprint(data[j])
+		printf("%c", data[j]);
+            else
+		printf("\\%x", (unsigned char)data[j]);
+	}
+        printf("\n"); 
+    }
+    delete [] data;
+}