Operating Systems Lab 7 - File Server

0. Group Members

• M.Abdullah Iftikhar (BSCS-23070)
• Waqas Sohaib (BSCS-23173)
• Abdul Moiz (BSCS-23118)

1. Design Report

System Architecture

1.1 Thread Structure

• Main Thread

  • Initializes server components and thread pools
  • Listens for incoming client connections
  • Distributes client connections to the client thread pool
  • Handles graceful shutdown procedures

• Client Thread Pool (4 threads by default)

  • Each thread manages multiple client connections
  • Parses incoming commands into Task structures
  • Manages client state and authentication
  • Handles response delivery back to clients

• Worker Thread Pool (4 threads by default)

  • Processes tasks from the global task queue
  • Executes filesystem operations (read/write/delete)
  • Manages user authentication and file operations
  • Sends responses back through the response queue system

1.2 Data Structures

• Task Queue

  • Thread-safe FIFO queue for pending operations
  • Shared between client and worker threads
  • Implements producer-consumer pattern with condition variables

• Response Queues

  • Per-client response queues for command results
  • Ensures ordered response delivery
  • Implements timeout and error handling

• User Store

  • Manages user authentication and file permissions
  • Implements thread-safe user session management
  • Handles user home directory structure

1.3 File System Layer

• Virtual File System
  • Abstracts physical file operations
  • Implements user quota management
  • Handles concurrent access to shared resources
  • Provides atomic operations for file modifications

Key Features

2.1 Concurrency Control

• Fine-grained locking strategy
• Deadlock prevention mechanisms
• Thread-safe memory management
• Non-blocking I/O operations where applicable

2.2 Error Handling

• Comprehensive error reporting
• Graceful degradation under load
• Resource cleanup on error conditions
• Client disconnection handling

2.3 Security

• Secure password hashing
• File permission enforcement
• Input validation and sanitization
• Protection against path traversal attacks

2.4 Performance

• Configurable thread pool sizes
• Efficient memory management
• Minimized critical sections
• Asynchronous I/O operations

2. Communication Mechanism

Between Worker Thread Pool and Client Thread Pool

The system uses a thread-safe queue implementation for communication between components. The communication flow is as follows:

1. Client Threads (in client_thread_main):

   • Accept client connections and parse commands
   • Create Task objects for each client request
   • Push tasks to the global task_queue using queue_push()
   • Wait for responses on a per-client response queue

2. Worker Threads (in worker_thread_main):

   • Continuously wait for tasks using queue_pop() on the shared task_queue
   • Process different command types (SIGNUP, LOGIN, UPLOAD, DOWNLOAD, etc.)
   • Send responses back through the response queue system

3. Queue Implementation (in queue.h):

   • Uses pthread_mutex_t for thread safety
   • Implements pthread_cond_t for efficient waiting on empty queues
   • Supports thread-safe operations: queue_push(), queue_pop(), queue_init(), queue_destroy()
   • Handles proper cleanup on shutdown with queue_close()

4. Response Handling:

   • Each client has a dedicated response queue entry
   • Worker threads send responses using send_response()
   • Client threads block on their response queue until a response is available

This design provides:

• Thread Safety: Proper synchronization with mutexes and condition variables
• Efficiency: Non-blocking operations where possible
• Scalability: Configurable number of client and worker threads
• Clean Shutdown: Proper cleanup of resources on server shutdown

3. Build and Run Instructions

Prerequisites

• POSIX-compliant system (Linux/macOS) or Windows with WSL/MSYS2
• GCC or Clang compiler
• GNU Make

Building the Project

make

Running the Server

./server <port>

Running the Client

./client <host> <port>

4. Testing

Memory Leaks

./testing/run_valgrind_simple.sh

Race Conditions

./testing/run_tsan_simple.sh

Test Reports

All test reports are saved in the reports/ directory.

5. GitHub Repository

GitHub Repository Link

Important Note: Any commits made after Thursday 11:59 PM will not be accepted. Please ensure all your work is committed and pushed before the deadline.

6. Protocol

The server supports the following commands:

• SIGNUP <user> <pass> - Create a new user account
• LOGIN <user> <pass> - Authenticate a user
• UPLOAD <user> <relpath> <size> <tmp_src_path> - Upload a file
• DOWNLOAD <user> <relpath> - Download a file
• DELETE <user> <relpath> - Delete a file
• LIST <user> - List user's files

For detailed client usage, see CLIENT_README.md.