packfs/CHANGELOG.md

Changelog

All notable changes to this project are documented in this file, in the style of Keep a Changelog. This project follows Semantic Versioning; see PACKFS_VERSION_STRING in include/packfs.h for the authoritative current version (packfs.pc, generated by make install, is derived from it, not maintained separately).

This project is pre-release (0.x, an initial, partial implementation of concept.md, not a completed one; see README.md's "Status"). v0.1.0 is tagged locally in this repository's own git history but has not been pushed to any remote — there is no public release yet, only a local one.

[0.1.0] - 2026-09-14

Added

• Initial implementation of concept.md: vfs_* core, mem/dir/pack backends, the copy-on-write overlay (copy-up, whiteouts, compaction, an append journal), path containment (openat2/Landlock on Linux 5.6+/5.13+, a documented weaker fallback elsewhere), and pack integrity validation.
• tests/test_*.c covering each backend, concurrency, and randomized structural-index stress testing against an independent reference model.
• bench/bench.c (make bench) and BENCH.md, comparing PackFS against the host filesystem across metadata operations, large sequential I/O, random-access pack reads, mount-table scaling, and concurrent workloads.
• PACKFS_VERSION_MAJOR/MINOR/PATCH/STRING and pfs_version() for compile-time and runtime version/ABI checks.
• packfs.pc (pkg-config), generated by make install from packfs.pc.in, version always derived from include/packfs.h.
• SPDX-License-Identifier: MIT on every file under src/ and include/.

Fixed

• Bulk sequential create/unlink/mkdir on mem/dir was O(n²) in file count. The index (UpperSnapshot) was a flat sorted array copied in full on every structural write; rewritten as a persistent treap (src/upper.c), reducing a structural write to the O(log n) nodes on the path to the change. See BENCH.md's "Resolution" for the full before/after measurement and complexity-class confirmation.
• pack_write's compaction-time exact-duplicate elimination (Section 9.2) was O(n²) in entry count, and trusted a hash match without comparing actual bytes (a latent correctness bug: FNV-1a64 is explicitly not collision-resistant). Rewritten as an open-addressing hash table with a memcmp verification before ever reusing a data_off, fixing both at once. See BENCH.md's "Resolution #2".
• backend_pack_new was declared in include/packfs.h but never implemented — any program calling it failed at link time. Implemented as a standalone, read-only pack Backend.
• .github/workflows/ci.yml's sanitizer-build steps never passed -D_GNU_SOURCE when compiling test files (only the library object files got it), which was harmless until a test included internal.h (needed for pthread_rwlock_t) and became a link failure.

Documented

• vfs.c's mount table (MountSnapshot) is O(n²) in mount count, the same pattern the file index used to have — confirmed, and deliberately left unfixed. Mount counts are bounded by a program's own source code, not workload-driven, so they do not reach the scale that made the file index's O(n²) a real problem. See BENCH.md's "Finding: mount table scaling" for the numbers and reasoning.
• A ThreadSanitizer environment limitation (some sandboxes block the personality(ADDR_NO_RANDOMIZE) syscall TSan needs) and a related ASan/UBSan sandbox startup flake (AddressSanitizer:DEADLYSIGNAL), both in CONTRIBUTING.md and CLAUDE.md, with the confirming tests and the required mitigation (timeout-wrapped sanitizer runs).