matthew
b69495e759
- Fix unwrap in disc/mod.rs sweep() hot path using pattern matching - Patch pass excludes Unreadable sectors from work list - Expose bytes_bad_in_title for accurate UI reporting - All 256 tests pass, cargo clippy clean with -D warnings
79 lines
5.7 KiB
Markdown
79 lines
5.7 KiB
Markdown
# libfreemkv — Rules
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## No English in library code
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The library contains ZERO user-facing English text. All errors use numeric codes from `error.rs`. Applications (CLI, GUI, server) handle i18n.
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- `io::Error::new(kind, "english string")` — NEVER. Use `Error::VariantName.into()`.
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- If you need a new error, add a variant to `error.rs` with a code, not a string.
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- Acceptable strings: debug/trace logging, test assertions, comments, data format strings (paths, codec IDs).
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- `Error` implements `From<Error> for io::Error` — use `?` or `.into()` anywhere an `io::Error` is expected.
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## Architecture
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- **Streams are PES.** Every stream reads its format → PES frames out, or PES frames in → writes its format. One type per format.
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- **Disc::copy() for sector dumps.** disc→ISO is NOT a stream. It's `Disc::copy()`.
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- **DiscStream = any disc.** Physical drive or ISO file. Same type, different SectorReader.
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- **No IOStream.** Deleted. No byte-level Read/Write on streams.
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- **Streams don't know their size.** Progress/file_size is a CLI concern.
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- **One method per action.** No `foo_with_X` variants. Use `Option<T>` params.
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- **Streams impl Read only (conceptually).** No Seek, no File backing.
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- **Functions return errors, only main() exits.** No `process::exit` in library code.
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## Device rules
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- Always use `/dev/sg*` not `/dev/sr*` for SCSI.
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- `--raw` only skips decryption. Init/probe/speed still run.
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- Each function does one thing. One runner orchestrates the sequence.
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## macOS IOKit transport
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The macOS SCSI transport uses exclusive IOKit access, not hybrid MMC+pread.
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- **C shim** (`src/scsi/macos_shim.c`):
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- `shim_open_exclusive(bsd_name)`: `diskutil unmountDisk force` on target device only → find `IOBDServices` matching BSD name via IOKit registry walk → MMCDeviceInterface → SCSITaskDeviceInterface → `ObtainExclusiveAccess` → raw CDB dispatch.
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- `shim_list_drives()`: registry-based enumeration. Walks all `IOBDServices` entries, reads `"Device Characteristics"` for vendor/model/firmware, walks child chain to `IOMedia` for BSD name. Zero SCSI, zero exclusive access, zero unmounts.
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- `shim_execute()` / `shim_close()`: raw CDB dispatch and cleanup.
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- **Build** (`build.rs`): compiles shim via `cc` into static lib, linked by Cargo. NOT the `cc` crate (produces object code that breaks IOKit exclusive access).
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- **Rust** (`src/scsi/macos.rs`): FFI to `shim_open_exclusive`, `shim_close`, `shim_execute`, `shim_list_drives`. `list_drives()` uses registry-based enumeration. `MacScsiTransport::open()` uses exclusive access only when ripping a specific device.
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- **IOBDServices parent chain**: IOSCSIPeripheralDeviceType05 → IOBDServices → IOBDBlockStorageDriver → IOMedia (has `"BSD Name"`). The shim walks this chain to match BSD name to IOBDServices.
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- **IOKit lookup order**: (1) iterate all IOBDServices → match child IOMedia BSD name, (2) fallback: find IOMedia by BSD name → walk parent chain to IOBDServices, (3) fallback: first IOBDServices (single-drive systems).
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- **Test disc**: DUNE_PART_TWO UHD, `/dev/disk6`, ~84.6 GB.
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## Bad-sector handling (BU40N + Initio INIC-1618L)
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Three failure modes on this USB bridge:
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1. **NOT READY** (sense_key=2, ASC=0x04, ASCQ=0x3E) — most common on BU40N for bad sectors. Pause 3s, retry up to 3x, then mark NonTrimmed.
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2. **Transport failure** (status=0xFF) — bridge crash, auto-recovers ~15s. Aborts copy.
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3. **INCOMPATIBLE FORMAT** (ASC=0x30) wedge — ALL sectors fail, requires power cycle.
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### Damage-jump algorithm (Pass 1 sweep)
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When `skip_on_error=true` (multipass mode):
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- Read each ECC block sequentially. Track a sliding window of the last 16 ECC block results.
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- On error: zero-fill, mark NonTrimmed, push `false` to window.
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- On success: write data, mark Finished, push `true` to window. Track consecutive good count.
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- When ≥12% of the 16-block window are failures → **jump** ahead by `256×batch×multiplier` sectors (8 MB base for UHD). Zero-fill the gap as NonTrimmed. Double the multiplier (8→16→32→64 MB...).
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- When 16 consecutive good reads → reset multiplier to 1, restore max read speed.
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- Only transport failures (bridge crash) abort the pass.
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Tuning knobs: `DAMAGE_WINDOW=16` and `DAMAGE_THRESHOLD_PCT=12%`. Calibrated from live BU40N data: old 50/25% was too diluted by good reads between sparse failures; 16/12% triggers on the 2nd scattered failure (2/16 = 12.5% ≥ 12%).
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### Patch (Pass N) — `disc/mod.rs:1910`
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- Default: **reverse** mode. Walks bad ranges from highest LBA to lowest, and within each range from end to start. Rationale: sweep jumps forward with escalating gaps, so NonTrimmed ranges have good data at their tail (where the jump landed). Reverse hits good data first, converges on actual bad block boundaries.
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- Single-sector reads with 60 s timeout (`READ_RECOVERY_TIMEOUT_MS`).
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- NOT_READY (sense=2, ASC ∈ {0x02, 0x03, 0x04}): 15 s pause, retry without immediate Unreadable mark.
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- Non-marginal SCSI sense → mark Unreadable and continue.
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- Skip escalation: damage window 16/12 %, skip `64 << escalation` sectors capped at 4096; max 10 skips per range, then mark range Unreadable.
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- Wedge exit: 50 consecutive failures **and** ≥ 2 ranges attempted (single-range stalls don't kill the pass).
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- Whole-pass watchdog: `STALL_SECS = 3600` on `bytes_good`. Per-range watchdog: `MAX_RANGE_SECS = 180`.
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Constants live at `disc/mod.rs:1974-1985` (PASSN_*, STALL_SECS, MAX_RANGE_SECS, MAX_SKIPS_PER_RANGE). The full algorithm is documented in `freemkv-private/memory/project_recovery_v0_16.md`.
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## Public repo rules
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- **No internal docs.** Audit reports, test plans, roadmaps, TODOs go in freemkv-private, never here.
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- **No Co-Authored-By** in commit messages. One contributor: MattJackson.
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- **No private references.** No Gitea URLs, no /data/code paths, no internal IPs in code.
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