OpenFile Class Reference

Public Member Functions
	OpenFile (int sector)
	OpenFileTable::OpenFileTable Open a Nachos file for reading and writing. Bring the file header into memory while the file is open. More...
	~OpenFile ()
	OpenFileTable::~OpenFileTable Close a Nachos file, de-allocating any in-memory data structures.
void	Seek (int position, unsigned int tid=0)
	OpenFileTable::Seek Change the current location within the open file – the point at which the next Read or Write will start from. More...
int	Read (char *into, int numBytes, unsigned int tid=0)
	OpenFileTable::Read/Write Read/write a portion of a file, starting from seekPosition. More...
int	Write (const char *from, int numBytes, unsigned int tid=0)
	OpenFileTable::Write into a file. More...
int	ReadAt (char *into, int numBytes, int position)
	OpenFileTable::ReadAt/WriteAt Read/write a portion of a file, starting at "position". Return the number of bytes actually written or read, but has no side effects (except that Write modifies the file, of course). More...
int	WriteAt (const char *from, int numBytes, int position)
int	Length ()
	OpenFileTable::Length. More...
int	get_sector ()
void	add_seek (unsigned int tid)
	OpenFileTable::add_seek add a seek to a openfile Allow multi threads to access to the same openfile with separated pointer. More...
bool	remove_seek (unsigned int tid)
	OpenFileTable::remove_seek remove a seek to a openfile Allow multi threads to access to the same openfile with separated pointer. More...
bool	isOpenByOthers ()
bool	isdir ()

Constructor & Destructor Documentation

OpenFile::OpenFile

(

int

sector

)

OpenFileTable::OpenFileTable Open a Nachos file for reading and writing. Bring the file header into memory while the file is open.

Parameters

sector

– the location on disk of the file header for this file

Member Function Documentation

void OpenFile::add_seek

(

unsigned int

tid

)

OpenFileTable::add_seek add a seek to a openfile Allow multi threads to access to the same openfile with separated pointer.

Parameters

tid	the thread tid

int OpenFile::Length

(

)

OpenFileTable::Length.

Returns

Return the number of bytes in the file.

int OpenFile::Read	(	char *	into,
		int	numBytes,
		unsigned int	tid = 0
	)

OpenFileTable::Read/Write Read/write a portion of a file, starting from seekPosition.

Returns

Return the number of bytes actually written or read, and as a side effect, increment the current position within the file.

Implemented using the more primitive ReadAt/WriteAt.

Parameters

into	– the buffer to contain the data to be read from disk
from	– the buffer containing the data to be written to disk
numBytes	– the number of bytes to transfer

int OpenFile::ReadAt	(	char *	into,
		int	numBytes,
		int	position
	)

OpenFileTable::ReadAt/WriteAt Read/write a portion of a file, starting at "position". Return the number of bytes actually written or read, but has no side effects (except that Write modifies the file, of course).

There is no guarantee the request starts or ends on an even disk sector boundary; however the disk only knows how to read/write a whole disk sector at a time. Thus:

For ReadAt: We read in all of the full or partial sectors that are part of the request, but we only copy the part we are interested in. For WriteAt: We must first read in any sectors that will be partially written, so that we don't overwrite the unmodified portion. We then copy in the data that will be modified, and write back all the full or partial sectors that are part of the request.

Parameters

into	– the buffer to contain the data to be read from disk
from	– the buffer containing the data to be written to disk
numBytes	– the number of bytes to transfer
position	– the offset within the file of the first byte to be read/written

bool OpenFile::remove_seek

(

unsigned int

tid

)

OpenFileTable::remove_seek remove a seek to a openfile Allow multi threads to access to the same openfile with separated pointer.

Parameters

tid	the thread tid

void OpenFile::Seek	(	int	position,
		unsigned int	tid = 0
	)

OpenFileTable::Seek Change the current location within the open file – the point at which the next Read or Write will start from.

Parameters

position

– the location within the file for the next Read/Write

int OpenFile::Write	(	const char *	into,
		int	numBytes,
		unsigned int	tid = 0
	)

OpenFileTable::Write into a file.

Parameters

into
numBytes
tid

Returns

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

• code/filesys/openfile.h
• code/filesys/openfile.cc