Process Checkpointing and Restoration Mechanism in xv6

What is xv6?

Xv6 is a teaching operating system developed in the summer of 2006 for MIT’s operating systems course.

Abstract

This project implements a process checkpointing and restoration mechanism within the MIT xv6 operating system. The system allows the kernel to serialize the memory state and CPU context of a running process into a persistent disk file. A restoration mechanism allows the kernel to reconstruct the process from this file, resuming execution from the exact point of interruption.

Key features include support for both self-checkpointing and external process target- ing, a custom binary file format with id validation, incremental disk writing to bypass file system journal limitations, and open file detection. The implementation required mod- ifications to the kernel’s memory management subsystem, system call interface and file system.

What is process Checkpointing?

Process fault tolerance is a critical feature in an operating systems. Checkpointing is the ability to save the state of a running process to disk storage, allowing it to be resumed later, even after a system reboot.

Goal of the project

The goal of this project was to extend the minimal xv6 kernel to support this functionality. This required an understanding of:

• Virtual Memory: Translating user virtual addresses to physical addresses for serializa- tion.

• Context Switching: Capturing the exact state of CPU registers (trapframe).

• File System Internals: Writing large binary blobs from kernel space without violating transaction log limits.

(This was a project done for the Operating systems course during my B.Tech studies.)