FileHeader Class Reference

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. More...

#include <filehdr.h>

Public Member Functions
bool	Allocate (BitMap *bitMap, int fileSize)
	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. More...
void	Deallocate (BitMap *bitMap)
	FileHeader::Deallocate De-allocate all the space allocated for data blocks for this file. More...
void	FetchFrom (int sectorNumber)
	FileHeader::FetchFrom Fetch contents of file header from disk. More...
void	WriteBack (int sectorNumber)
	FileHeader::WriteBack Write the modified contents of the file header back to disk. More...
int	ByteToSector (int offset)
	FileHeader::ByteToSector. More...
int	FileLength ()
	FileHeader::FileLength. More...
void	Print ()
	FileHeader::Print Print the contents of the file header, and the contents of all the data blocks pointed to by the file header.
void	test ()
int	get_sector (int id_sector)
void	set_sector (int id_sector, int sector)

Public Attributes
File_type	type

Detailed Description

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.

Member Function Documentation

bool FileHeader::Allocate	(	BitMap *	freeMap,
		int	fileSize
	)

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.

Returns

Return FALSE if there are not enough free blocks to accomodate the new file.

Parameters

freeMap	is the bit map of free disk sectors
fileSize	is the bit map of free disk sectors

int FileHeader::ByteToSector

(

int

offset

)

FileHeader::ByteToSector.

Returns

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).

Parameters

offset

is the location within the file of the byte in question

void FileHeader::Deallocate

(

BitMap *

freeMap

)

FileHeader::Deallocate De-allocate all the space allocated for data blocks for this file.

Parameters

freeMap

is the bit map of free disk sectors

void FileHeader::FetchFrom

(

int

sector

)

FileHeader::FetchFrom Fetch contents of file header from disk.

Parameters

sector

is the disk sector containing the file header

int FileHeader::FileLength

(

)

FileHeader::FileLength.

Returns

Return the number of bytes in the file.

void FileHeader::WriteBack

(

int

sector

)

FileHeader::WriteBack Write the modified contents of the file header back to disk.

Parameters

sector

is the disk sector to contain the file header

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The documentation for this class was generated from the following files:

• code/filesys/filehdr.h
• code/filesys/filehdr.cc