packfs/CHANGELOG.md

# Changelog

All notable changes to this project are documented in this file, in the
style of [Keep a Changelog](https://keepachangelog.com/en/1.1.0/). This
project follows [Semantic Versioning](https://semver.org/); 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`.
- The CI config's (`.gitea/workflows/ci.yml`) 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.

### Changed
- CI moved from a GitHub-Actions-convention config (`.github/workflows/`)
  to Gitea Actions (`.gitea/workflows/`) — this project is hosted on
  Gitea, not GitHub, and was never actually hosted on GitHub; only the
  scaffolding's starting convention changed. `SECURITY.md`, `CLAUDE.md`,
  `CONTRIBUTING.md`, and `README.md` updated to match.

### 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).

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