jasonsauntry / cs3650-ch3

Solution for CS 3650 Challenge 3 at NEU, to build a virtual filesystem with COW support.

COW Filesystem

This code is the solution to NEU's CS-3650 Challenge 3 for the Spring 2020 semester. The challenge was to implement a virtual filesystem implementing COW functionality, allowing a user to easily undo recent filesystem actions.

Design

File System Layout:

• 1MB = 256 pages (4k blocks)
• 4096 byte pages
• Page0: super block, including bitmaps
• Page1 - n: inodes
• Rest of pages: Data
• 256 inodes

COW:

• Add a thing in every inode that is a list of incoming hard links.
• Every inode has version number. On write, copy iff version number is older than global version number. Inc global version only on callback from Fuse.

Credit

Used throughout:

• Insights from [Geoff Kuenning](https://www.cs.hmc.edu/~geoff/classes/hmc.cs135.201001/homework/fuse/fuse_doc.html 3rd-party FUSE documentation)
• Linux Programmer's Manual