p8-read-fs: Filesystem Reading Integration with Constants Deduplication

[Yash-Rawat-IIT-D]

Overview:
Integrated p8-read-fs functionality from PR #6 (Amber-Agarwal/rem-amber) on top of unmerged p7-mkfs changes from PR #17. Applied compatibility fixes for constants deduplication and Rust 2024 edition.

Credit: Original p8-read-fs implementation by Amber-Agarwal (PR #6)

Changes Made:

1. Filesystem Integration (src/fs.rs)

   • Added inode cache with ICACHE static (50 in-memory inodes)
   • Implemented core functions: iinit(), iget(), iread(), stati(), readi()
   • Added bmap() for block mapping (direct + indirect blocks)
   • Added parse_dirent() helper for directory entry parsing
   • Proper buffer release in bmap() (fixes C version leak)

2. Constants Deduplication

   • Removed duplicate definitions: ROOTINO, NDIRECT, NINDIRECT, DIRSIZ, DINODE_SIZE, IPB
   • Imported from constants.rs (single source of truth)
   • Fixed type compatibility: IPB usage with explicit casts

3. Rust Compatibility

   • Replaced mutable static references with raw pointers
   • Used &raw mut and &raw const patterns in iinit() and iread()
   • Eliminates undefined behavior from static aliasing

Constraints Met:

• Semantic equivalence with C implementation
• Zero compilation warnings
• Proper error handling and bounds checking

Validation:

• Platform: WSL (Windows Subsystem for Linux)
• Toolchain: Rust nightly with build-std
• Build: make clean && make completes with 0 warnings, 0 errors
• Runtime: make qemu displays:
  • Superblock fields (size, nblocks, ninodes, logstart, inodestart, bmapstart)
  • Root directory entries (., .., welcome.txt)
  • welcome.txt stats (device, inode number, type, links, size)
  • welcome.txt contents (ASCII art banner)

[codenet]

I have manually merged this branch. I dislike the significant copy-pasting of code that has happened in mkfs.rs. Can you kindly remove it? Maybe create some common fs_h.rs or something? We can discuss here: https://discord.com/channels/1482638649144119376/1499695428898258977

[codenet]

fs_h was merged manually. closing this too.