Reference no: EM13906328 , Length: 17

Project - Implementation of TRU File System (TFS)

File system is one of the important portions of an OS that is used by all applications. File systems come in different forms. Simple devices such as digital cameras and MP3 plays have simple file systems that have limited functionality. Other extremes are the file systems that run on networked machines. This project aims to introduce to you a simple file system. By designing and implementing a simple file system, called the TRU file system (TFS), you will obtain much deeper understanding of the file system internals. Because of the significance of a file system, you receive significant insight into the operation of the OS by doing this project.

In this project TFS will be created in one real file in your system.

As part of project, you are expected to design and implement TFS. It is a file system that can be used on a standalone machine. There are several simplifying assumptions such as a single application is accessing the file system at any given time. Although this assumption is quite dramatic, it leaves the file system usable in single-tasking embedded system environment such as digital cameras. Also, we will implement a simplified interface to the file system with notable restrictions such as:
• Limited length filenames - 15 bytes
• A few file attributes - file or directory, file/directory name, size, ...
• There is no concept of the current working directory - every file/directory name is given as a full path from the root "/"
• Block size - 128 bytes
• Maximum file size - 65535 bytes
• The disk system will be emulated on a real Java file - TFSDiskFile

3. Overall diagram

User

Shell

ß

main

Commands - mkfs; ls; print; ...

TFS API

TFS

ß

Disk I/O API

Disk (In this project, this is a real regular file.)

ß

JVM

4. Objectives in detail

Shell commands:

You should implement some basic commands that would run from a shell program (public class TFSShell extends Thread) that will be given. The commands should print proper results and error messages as well.

$ mkfs
- Make a file system - Make new PCB and FAT in the file system
$ mount -
- Mount a file system - Copy PCB and FAT in the file system into the main memory
$ sync
- Synchronize the file system - Copy PCB and FAT in the main memory back to the file system on the disk
$ prrfs
- Print PCB and FAT in the file system
$ prmfs
- Print PCB and FAT in the main memory

$ mkdir directory
- Make a directory if it does not exist
$ rmdir directory
- Remove a directory if it is empty
$ ls directory
- List file or directory names in the directory, with size
$ create file
- Create an empty file if it does not exist
$ rm file
- Remove a file
$ print file position number
- Print number characters from the position in the file file
$ append file number
- Append any number characters at the end of the file if it exits
$ cp source_file destination_directory
- Copy a file into a directory if they exit and source_file does not exist under destination_directory
$ rename source_file destination_file
- Rename a file if source_file exists and destination_file does not exit

$ exit
- Exit from the shell, i.e., shutdown the system

TFS APIs:

Your TFS should implement the following application programming interface (API) in public class TFSFileSystem. The methods should return appropriate return values, including errors (negative numbers).

public static int tfs_mkfs()
- Create the file system on the hard disk
public static int tfs_mount()
- Mount the file system
public static int tfs_umount()
- Unmount the file system
public static int tfs_sync()
- Synchronize the file system
public static String tfs_prrfs()
- Print PCB and FAT in the file system
public static String tfs_prmfs()
- Print PCB and FAT in the main memory
public static String tfs_exit()
- Unmount the file system, and call tfs_dio_close()

public static int tfs_open(byte[] name, int nlength)
- Open the given file
public static int tfs_read(int file_id, byte[] buf, int blength)
- Read bytes from disk into buf
public static int tfs_write(int file_id, byte[] buf, int blength)
- Write bytes from buf into disk
public static int tfs_seek(int file_id, int position)
- Set the new file pointer
public static void tfs_close(int file_id)
- Close the given file

public static int tfs_create(byte[] name, int nlength)
- Create the given file
public static int tfs_delete(byte[] name, int nlength)
- Delete the given file

public static int tfs_create_dir(byte[] name, int nlength)
- Create a directory
public static int tfs_delete_dir(byte[] name, int nlength)
- Delete a directory

Disk I/O APIs:

You should implement the following API for the emulation of disk input/output in public class TFSDiskInputOutput. The methods should return appropriate return values, including errors (negative numbers).

public static int tfs_dio_create(byte[] name, int nlength, int size)
- Create a disk file of size blocks. The disk file is a real file in your system, in which TFS is implemented.
- Return 0 if there is no error.
public static int tfs_dio_open(byte[] name, int nlength)
- Open a disk file
- Return 0 if there is no error.
public static int tfs_dio_get_size()
- ReturnGet the total # of blocks of the disk file
- Return -10 if there is anno error.
public static int tfs_dio_read_block(int block_no, byte[] buf)
- Read a block from the disk file
- Return 0 if there is no error.
public static int tfs_dio_write_block(int block_no, byte[] buf)
- Write a block into the disk file
- Return 0 if there is no error.
public static int tfs_dio_close()
- Close the disk file
- Return 0 if there is no error.

5. Implementation strategies

• Structure of TFS on a hard disk (being emulated on a real Java file)

o Directory structure - Linear list; it contains file attributes as well
o Allocation method - FAT
o Free space management - Linked list
o PCB (Partition Control Block)
- Two pointers to the root directory and the first free block
- Size of FAT
- Number of data blocks

• In-memory data structures
o PCB
o FAT
o System-wide file descriptor table (FDT)
- Combination of file descriptor table, open file table and inode table in the lecture slides of the chapter 11
- Name
- Directory or not
- Starting block number
- File pointer - Offset where the process reads from or writes to
- Total size in bytes

• TFSFileSystem
o tfs_mkfs()
- Initialize PCB and FAT in disk
- PCB in disk -> memory
- FAT in disk -> memory
• tfs_mount()
- PCB in disk -> memory
- FAT in disk -> memory
• tfs_umount(); tfs_sync()
- PCB in memory -> disk
- FAT in memory -> disk
• tfs_exit()
- tfs_umount()
- tfs_dio_close()
• tfs_open()
- Search the first block number: PCB in memory -> FAT in memory
- Create a new entry in FDT
o tfs_read(); tfs_write()
- File descriptor -> FDT -> FAT in memory -> Disk
• tfs_close()
- Delete the entry in FDT

6. Implementation steps

• Stage I:
o When this stage starts, TFSDiskInputOutput.java, TFSFileSystem.java, and TFSShell.java will be given to students. They include method definitions.
o First, you should decide data structures for PCB, FAT and directory. The detail explanation about them should be included in TFSFileSystem.java.
o Second, you should implement the next methods.
- TFSDiskInputOutput
- All methods, i.e., Disk I/O APIs.
- TFSFileSystem
- tfs_mkfs()
- tfs_prrfs()
- tfs_exit()
- TFSShell
- mkfs()
- prrfs()
- exit()

• Stage II:
o When this stage starts, a solution for the stage I will be given to the students who could not complete the stage I. If you are confident with your code in the stage I, then you can use your code for this stage.
o TFSFileSystem.java includes the code of the next private TFS APIs. These private TFS APIs could be used for the implementation of public TFS APIs.
- Disk related utilities
- int _tfs_read_block(int block_no, byte buf[])
- int _tfs_write_block(int block_no, byte buf[])
- FDT related utilities
- int _tfs_open_fd(byte name[], int nlength, int first_block_no, int file_size): Create a new entry in FDT for a file or directory; return the file descriptor
- int _tfs_seek_fd(int fd, int offset): Change the file pointer to offset
- void _tfs_close_fd(int fd): Remove the file descriptor from FDT
- int _tfs_read_bytes_fd(int fd, byte buf[], int length)
- int _tfs_write_bytes_fd(int fd, byte buf[], int length)
- int _tfs_get_block_no_fd(int fd, int offset): Find the block number for the offset in the file represented by fd
- int _tfs_read_directory_fd(int fd, byte[] is_directory,
- byte[] nlength, byte[][] name, int[] first_block_no,
- int[] file_size): byte[][16] name; Read a directory into the main memory from the file system; It returns a negative number if there is an error, otherwise the number of files and subdirectories under the directory
- PCB related utilities
- void _tfs_write_pcb(): Write PCB back into the disk
- void _tfs_read_pcb(): Read PCB from the disk into memory
- FAT related utilities
- void _fts_read_fat(): Read FAT from the disk into memory
- int _tfs_get_block_fat(): Get a free block
- void _tfs_return_block_fat(int block_no): Return a free block
- int _tfs_attach_block_fat(int start_block_no, int new_block_no): Attach a block at the end of a file having the start_block_no
- Block handling utilities
- int _tfs_get_int_block(byte[] block, int offset): Get an integer from a block
- void _tfs_put_int_block(byte[] block, int offset, int data): Put an integer into a block
- byte _tfs_get_byte_block(byte[] block, int offset): Get a byte from a block
- void _tfs_put_byte_block(byte[] block, int offset, byte data): Put a byte into a block
- byte[] _tfs_get_bytes_block(byte[] block, int offset, int length): Get bytes from a block
- void _tfs_put_bytes_block(byte[] block, int offset, byte[] buf, int length): Put bytes into a block
o First, you may need to include additional routines to handle in-memory data structures, such as PCB, FAT, FDT. The detail explanation about FDT should be included in TFSFileSystem.
o Second, you should
- Create PCB, FAT and FDT in the main memory in TFSFileSystem(), when the file system is mounted.
- Create the root directory (initially empty) within tfs_mkfs()
o Third, you should implement the next methods.
- TFSFileSystem
- tfs_mount()
- tfs_umount()
- tfs_sync()
- tfs_prmfs()
- TFSShell
- mount()
- umount()
- sync()
- prmfs()

• Stage III:
o When this stage starts, a solution for the stage II will be given to the students who could not complete the stage II. If you are confident with your code in the stage II, then you can use your code for this stage.
o We will use the next directory structure. However you can use your own directory structure if you want.
// the total number of entries
int noEntries; // it has meaning only in the first block
int parentBlockNo; // the first block number of the parent dir
// each entry has
byte isDirectory; // 0: subdirectory, 1: file
byte nLength; // name length
byte reserved1; // reserved
byte reserved2; // reserved
byte[16] name; // not a full path
int firstBlockNo; // the first block number
int size; // the size of the file or subdirectory
// the size of each entry is 4 + 16 + 4 +4 = 28 bytes
// 128 % 28 = 4 => one block can hold maximum 4 entries
o First, you should update the next method in TFSFileSystem.
- _tfs_close_fd(int fd)
- Update the entry for the file or directory in the parent directory, if there is a change
- Destroy the entry of fd from FDT
o Second, you should implement the next directory related utilities in TFSFileSystem.
- _tfs_search_dir(byte[] name, int nlength)
- Return the first block number of the parent directory in which name exists
- name contains a full path
- _tfs_get_entry_dir(int block_no, byte[] name, byte nlength, byte[] is_directory, int[] fbn, int[] size)
- Get the entry for name from the directory of which the first block number is block_no
- name is not a full path
- isDirectory, fbn and size are arrays of one element
- Return a negative number if name does not exist in the directory
- _tfs_create_entry_dir(int block_no, byte[] name, byte nlength, byte is_directory, int fbn, int size)
- Create an entry for name in the directory of which the first block number is block_no
- name is not a full path
- The whole size of the directory might be changed
- _tfs_delete_entry_dir(int block_no, byte[] name, byte nlength)
- Delete the entry for name from the directory of which the first block number is block_no
- name is not a full path
- The whole size of the directory might be changed
- _tfs_update_entry_dir(int block_no, byte[] name, byte nlength, byte is_directory, int fbn, int size)
- Update the entry for name in the directory of which the first block number is block_no
- name is not a full path
o Third, you should implement the next TFS APIs.
- tfs_open(byte[] name, int nlength)
- Return file descriptor for the file or directory
- name has a full path for the file or directory
- Need to search name from the root directory
- tfs_read(int fd, byte[] buf, int blength)
- Read blength bytes in buf from fd
- Return the number of bytes read
- tfs_read_dir(int fd, byte[] is_directory, byte[] nlength, byte[][] name, int[] first_block_no, int[] file_size)
- Read all entries in the directory fd into arrays
- Return the number of entries
- tfs_write(int fd, byte[] buf, int blength)
- Return the number of bytes written into the file or directory
- tfs_seek(int fd, int offset)
- Return the new file pointer
- tfs_close(int fd)
- tfs_create(byte[] name, int nlength)
- Create a file
- name contains a full path
- tfs_delete(byte[] name, int nlength)
- Delete a file
- name contains a full path
- tfs_create_dir(byte[] name, int nlength)
- Create a directory
- name contains a full path
- tfs_delete_dir(byte[] name, int nlength)
- Delete a directory
- name contains a full path
o Fourth, you should implement all other commands in TFSShell.