p11-file-layer: Integration fixes for constants and eliminate warnings

[Yash-Rawat-IIT-D]

Overview

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Integrated p11-file-layer file descriptor and file operations functionality from PR #13. Applied integration fixes for constants organization, module integration, and Rust 2024 compatibility. Built on p10-write-fs (PR #20 submitted).

Credit: Original p11-file-layer implementation by Anoop Singh (greninja1947, PR #13: #13)
This PR: Integration fixes only (constants imports, static mut warnings)

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Changes Made (Integration Work)

1. Constants Organization

Files: src/file.rs, src/fs.rs

• Imported constants from constants.rs: T_DIR, T_FILE, DIRSIZ, DIRENT_SIZE
• Imported parameters from param.rs: MAXOPBLOCKS, NFILE
• Ensures single source of truth, matches C header pattern

2. Rust Compatibility

File: src/fs.rs

• Fixed static mut references using raw const pointer pattern
• Changed &SB → &*(&raw const SB) in multiple functions
• Applied to: readsb(), bfree(), ialloc(), iupdate(), bmap()
• Eliminates static_mut_refs warnings and undefined behavior

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Expected Behavior

On boot:

• Creates /foo/hello.txt with content "hello"
• Reads and prints file contents
• Deletes /foo/hello.txt
• Verifies /foo is empty
• Reads and prints /welcome.txt contents (ASCII Banner)

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Testing

Testing Environment: WSL (Windows Subsystem for Linux) with nightly compiler (no_std)

[PASS] Build: make kernel completes with 0 warnings, 0 errors
[PASS] Build: make xv6.img generates filesystem image correctly
[PASS] Runtime: make qemu shows expected behavior:
       - File create: /foo/hello.txt created successfully
       - File write: Content written correctly
       - File read: Content matches written data
       - File unlink: File deleted, directory emptied
       - Welcome text: /welcome.txt read and displayed
       - Filesystem operations: All file I/O operations working correctly

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Files Modified

• src/file.rs - Constants imported from constants.rs, param.rs
• src/fs.rs - Static mut warnings fixed with raw const pointers
• src/constants.rs - Removed duplicate KSTACKSIZE and NCPU constants (already in param.rs)
• src/proc.rs - Updated imports for NCPU from constants.rs

Constraints Met

• Semantic equivalence with C implementation
• Zero compilation warnings/errors
• Proper constants organization with single source of truth