Custom Virtual File System (CVFS)

Description

This project is a C++ implementation of a Custom Virtual File System (CVFS). It simulates the core functionalities of a file system entirely in memory, providing a hands-on understanding of concepts like Inodes, Superblocks, File Descriptor Tables, and system calls for file manipulation. The program features its own custom command-line shell that allows users to create, read, write, and delete files within this virtual environment.

Features

• Custom Shell: An interactive shell to accept and process file system commands.
• In-Memory Simulation: All file system components (Inodes, data blocks, etc.) are managed in memory using C++ data structures.
• File Management: Supports creation, deletion, and statistical display of files.
• I/O Operations: Implements write and read functionalities for files using file descriptors.
• Permission Control: Basic read/write permissions are associated with each file upon creation.
• Built-in Help System: Includes help and man commands to provide command information and usage details.
• Structured Data Management: Utilizes key file system data structures like Inode, SuperBlock, FileTable, and UAREA to mimic a real file system architecture.

Core Data Structures

• BootBlock: Contains information to boot the virtual operating system.
• SuperBlock: Holds metadata about the file system, such as the total number of inodes and the number of free inodes.
• Inode: Represents a file and stores its metadata, including file name, size, type, permissions, and a pointer to its data buffer. All inodes are managed in a singly linked list (DILB - Disk Inode List Block).
• FileTable: An entry in the User File Descriptor Table that stores runtime information about an opened file, such as read/write offsets and a pointer to its inode.
• UAREA: The User Area structure, which contains the User File Descriptor Table (UFDT), an array of pointers to FileTable entries for all opened files.

Available Commands

The following table lists the commands available in the CVFS shell.

Command	Syntax	Description
creat	creat <file_name> <permission>	Creates a new regular file. Permissions: 1 (Read), 2 (Write), 3 (Read+Write).
unlink	unlink <file_name>	Deletes an existing file from the file system.
write	write <fd>	Writes data to a file specified by its file descriptor (fd).
read	read <fd> <size>	Reads a specified number of bytes from a file.
ls	ls	Lists all files currently existing in the file system.
stat	stat <file_name>	Displays statistical information about a specific file.
man	man <command_name>	Shows the manual page with usage details for a specific command.
help	help	Displays a list of all available commands.
clear	clear	Clears the terminal screen.
exit	exit	Terminates the CVFS shell and deallocates resources.

How to Compile and Run

1. Save the code as a .cpp file (e.g., cvfs.cpp).
2. Open a terminal and compile the file using a C++ compiler like g++.

   g++ cvfs.cpp -o cvfs
   

3. Run the resulting executable.

   ./cvfs
   

4. The "Mangesh/CVFS > " shell will start, ready to accept commands.

Example Usage

Here is a sample session demonstrating how to use the CVFS shell:

The shell prompt appears
Mangesh/CVFS > creat myFile.txt 3
File is succesfully created with FD : 0

Mangesh/CVFS > write 0
Please enter the data that you want to write into the file :
Hello World
11 bytes gets succesfully written into the file
Data from file is : Hello World

Mangesh/CVFS > ls
myFile.txt

Mangesh/CVFS > stat myFile.txt
------------ Statistical Information of file -----------
File name : myFile.txt
File size on Disk : 100
Actual File size : 11
Link count : 1
File permission : Read + Write
File type : Regular file
Mangesh/CVFS > read 0 5
Read operation is successfull
Data from file is : Hello

Mangesh/CVFS > unlink myFile.txt
Unlink Opertaion is succesfully performed

Mangesh/CVFS > ls

(no output, as the file has been deleted)
CVFS > exit
Thank you for using CVFS
Deallocating all resources...

Core Functions

This table provides an overview of the key C++ functions that implement the logic for the Custom Virtual File System.

Function Signature	Description
int main()	The main entry point and command-line shell loop. It reads user input, parses commands, and calls the appropriate handler functions.
void StartAuxilaryDataInitialisation()	A high-level initialization function that orchestrates the setup of the entire file system by calling the InitialiseSuperblock, CreateDILB, and InitialiseUAREA functions.
void InitialiseSuperblock()	Initializes the superobj global variable, setting the total and free inode counts based on the MAXINODE macro.
void CreateDILB()	"Creates the Disk Inode List Block" by allocating a singly linked list of INODE structures, which serves as the Inode Table.
void InitialiseUAREA()	Initializes the User Area (uareaobj) by setting the process name and preparing the User File Descriptor Table (UFDT) with NULL entries.
void DisplayHelp()	Prints a formatted list of all available commands and their brief descriptions to the console.
void ManPage(char *name)	Displays detailed usage information for a specific command, including its purpose, syntax, and arguments.
bool IsFileExists(char *name)	Traverses the inode linked list to check if a file with the given name already exists.
int CreateFile(char *name, int permission)	Handles the logic for creating a new file. It finds a free inode, allocates a file table entry in the UFDT, initializes file metadata, and returns a file descriptor.
int UnlinkFile(char *name)	Deletes a file by deallocating its data buffer and resetting its inode, making it available for reuse.
void ls_file()	Lists all existing files by traversing the inode linked list and printing the FileName of each active inode.
int stat_file(char *name)	Displays detailed metadata for a given file, including its inode number, file size, link count, and permissions.
int write_file(int fd, char *data, int size)	Writes data from a character buffer into the file's in-memory data block, updating the write offset and actual file size.
int read_file(int fd, char *data, int size)	Reads data from a file's in-memory data block into a specified buffer, advancing the read offset.

Author

• Mangesh Ashok Bedre