docs: rewrite rip-recovery + drive-access for 0.13.6 single-shot model
Updates docs/ to reflect the recovery-loop strip: - rip-recovery.md: drops Phase 1/2/3 description, replaces with three-layer model (Disc::patch multi-pass / DiscStream batch halving / Drive::read single-shot). Notes that no SCSI resets fire from any retry path. - drive-access.md: removes SG_SCSI_RESET + STOP/START UNIT escalation references; SgIoTransport::reset is now kernel SG_IO flush + ALLOW MEDIUM REMOVAL only. - src/mux/disc.rs + tests/: cargo fmt cleanup.
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# Rip recovery — multi-pass architecture
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# Rip recovery — three-layer architecture
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`libfreemkv` supports a two-stage rip model for damaged or protection-bearing
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discs: a fast forward sweep that tolerates read failures, followed by targeted
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`libfreemkv` supports a multi-stage rip model for damaged or protection-bearing
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discs: a fast forward sweep that tolerates read failures, in-loop request-size
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adaptation that survives transient drive trouble without bailing, and targeted
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retry passes against a persistent bad-range map. The stream pipeline
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(`DiscStream` + `input`/`output`) operates against the resulting ISO image, so
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the mux stage never touches the drive.
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Three primitives compose the flow:
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Recovery is layered cleanly. Each layer has one responsibility and does not
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reach into the others.
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| Layer | Where it lives | What it does |
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|-------|---------------|--------------|
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| 1 — Bad-range retry | `Disc::patch` (multi-pass over the mapfile) | Re-reads non-`+` ranges with the long timeout. Idempotent; call N times. |
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| 2 — Single-shot primitive | `Drive::read` in `src/drive/mod.rs` | One CDB, one timeout, one result. No inline retries, no SCSI reset. |
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| 3 — In-loop request adaptation | `DiscStream::fill_extents` adaptive batch sizer | Halves the batch on failure, retries at the same LBA, walks back up on a clean-read streak. |
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The caller orchestrates layer 1. Autorip's `rip_disc` loops `copy` then
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N × `patch` per the `MAX_RETRIES` config, then hands the ISO off to the
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existing mux pipeline. Layer 3 runs inside any consumer of `DiscStream`
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(direct PES pipeline, ISO playback, etc.) without caller involvement.
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Three primitives compose the disc-side flow:
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| Primitive | What it does |
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|---------------------------|-----------------------------------------------------------------------|
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@@ -14,9 +29,6 @@ Three primitives compose the flow:
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| `Disc::patch` | Re-reads bad ranges from the drive. Idempotent; call N times. |
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| `DiscStream` (ISO source) | Reads sectors from the ISO, feeds decrypt → demux → codec → mux. |
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The caller orchestrates. Autorip's `rip_disc` loops `copy` then N × `patch` per
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the `MAX_RETRIES` config, then hands the ISO off to the existing mux pipeline.
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## Data model
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### Mapfile
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@@ -26,7 +38,7 @@ plain text, greppable, tool-interoperable. Flushed to disk on every `record()`
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so a crashed rip loses at most one block.
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```
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# Rescue Logfile. Created by libfreemkv v0.11.22
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# Rescue Logfile. Created by libfreemkv v0.13.6
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# Current pos / status / pass / pass_time
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0x000000000 ? 1 0
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# pos size status
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@@ -50,8 +62,8 @@ Position and size are hex byte offsets into the ISO.
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### `CopyOptions` and `PatchOptions`
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Defaults preserve pre-`0.11.21` behavior — full drive recovery on every read,
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abort on the first unreadable sector. Opt in to the recovery-friendly path:
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Defaults preserve pre-`0.11.21` behavior — abort on the first unreadable
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sector. Opt in to the recovery-friendly path:
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```rust
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CopyOptions {
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@@ -65,9 +77,10 @@ CopyOptions {
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## Algorithm
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### Pass 1 — fast sweep
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### Pass 1 — fast sweep (`Disc::copy`)
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1. Read 64 KB (32 sectors, one BD ECC block) at the current LBA.
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1. Read 64 KB (32 sectors, one BD ECC block) at the current LBA via
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`Drive::read(.., recovery=false)` — short 1.5 s timeout, single shot.
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2. On success: mark the range `+`, advance by one block.
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3. On failure (with `skip_on_error`): zero-fill the block in the ISO, mark
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it `*`, advance.
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@@ -80,12 +93,13 @@ CopyOptions {
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Pass 1 completes when every byte has terminal status (`+`, `-`, or the caller
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bails via the halt flag).
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### Pass 2+ — patch
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### Pass 2+ — patch (`Disc::patch`)
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`Disc::patch` reads the mapfile and iterates every non-`+` range. For each:
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1. Issue a drive read with full recovery enabled (SCSI-level retries,
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ECC recovery, the lot).
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1. Issue a drive read via `Drive::read(.., recovery=true)` — long 30 s
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timeout, still single shot. Drive firmware does its own ECC and retries
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inside that window; userspace does not pile on additional retries here.
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2. On success: write the good bytes into the ISO at the exact byte offset,
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mark `+`.
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3. On failure: mark `-`.
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@@ -95,21 +109,61 @@ Idempotent. Call `patch` N times for N retry attempts; typically the caller
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stops early if a pass recovers zero bytes (structure-protected sectors will
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never yield).
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### In-stream — adaptive batch halving (`DiscStream::fill_extents`)
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When a consumer reads a `DiscStream` directly (no ISO intermediate),
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`fill_extents` runs an adaptive sizer in front of `Drive::read`:
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1. Try the current preferred batch size (e.g. 32 sectors, one BD ECC block).
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2. On failure: halve the batch and retry at the same LBA. Emit
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`EventKind::BatchSizeChanged { reason: Shrunk }`.
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3. On a clean-read streak: probe back up toward the preferred size. Emit
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`EventKind::BatchSizeChanged { reason: Probed }`.
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4. If a single-sector read fails: skip (zero-fill, emit
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`EventKind::SectorSkipped`) when `skip_errors` is set, otherwise return
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`Err(DiscRead)`.
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This is layer 3. It exists so a transient single-sector glitch in a 32-sector
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batch can be isolated and read individually without the caller needing to
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implement retry logic.
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## Design choices
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**`Drive::read` is single-shot.** No inline retry phases, no SCSI reset,
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no eject cycle. The `recovery` flag controls only the per-CDB timeout
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(1.5 s vs. 30 s); on any failure it returns `Err(DiscRead)` immediately.
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Inline recovery (5× gentle retry → close + SCSI reset + reopen → 5× more)
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was removed in 0.13.6. See `freemkv-private/postmortems/2026-04-25-stop-wedge-and-zero-kbs.md`
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for rationale: the inline reset on the LG BU40N (Initio USB-SATA bridge)
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wedged drive firmware below the bridge without ever recovering a sector,
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and the gentle-retry phase produced long stretches of 0 KB/s with no
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recoveries to show for it. Recovery responsibility is now layered: layer 1
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handles ranges, layer 3 handles request size, neither touches the
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wedge-prone reset path.
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**No `MODE SELECT` to disable drive retries.** Research showed neither ddrescue
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nor MakeMKV does this. Drive firmware has access to raw analog signal, laser
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power control, and drive-specific ECC tuning that userspace can't replicate —
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disabling it throws away recovery headroom on marginal sectors. We fail fast
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via short SG_IO timeouts instead, and we avoid per-sector probing on first
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contact by using large blocks + skip-forward.
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via short SG_IO timeouts in pass 1 and let the firmware work the long timeout
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in pass 2 / patch.
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**No SCSI reset from any retry path.** `SgIoTransport::reset` (Linux) is
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trimmed to a kernel SG_IO state flush plus ALLOW MEDIUM REMOVAL — the
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`SG_SCSI_RESET` ioctl and STOP/START UNIT escalation were removed in 0.13.6.
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The macOS reset (which had been a no-op) was removed entirely. The top-level
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`scsi::reset()` / `reset_with_timeout()` / `reset_blocking()` wrappers were
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also removed (no callers). The remaining `Drive::reset()` is only invoked
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explicitly by callers that need an eject-cycle escape hatch — it is never
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reached from a read path.
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**ISO intermediate, even for single-pass.** Pass 1 always writes an ISO. The
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mux stage reads the ISO via `IsoSectorReader`. For single-pass (no retries),
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this adds ~2-3 min (local disk mux) but gains resumability across crashes,
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re-muxability without re-ripping, and a persistent forensic artifact. Callers
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who need pure speed can bypass and use `DiscStream::new(Box::new(drive), …)`
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directly — the lib doesn't forbid it.
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directly — the lib doesn't forbid it, and layer 3 (adaptive batch halving)
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still applies there.
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**Mapfile in ddrescue format.** Plain text so users can `less` it, `diff` it,
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or feed it to ddrescue's own tooling. Crash-safe (flush-per-record). Entries
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@@ -117,11 +171,11 @@ coalesce on adjacent same-status ranges so files stay small.
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**Patches target `-`, `*`, `/`, and `?` alike.** The status state machine is
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ddrescue's but `patch` collapses the distinction — it just tries every
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non-finished range with full recovery. Future work can specialize (trim vs.
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non-finished range with the long timeout. Future work can specialize (trim vs.
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scrape vs. retry with direction reversal) if there's measured benefit.
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## References
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- [ddrescue manual, Algorithm chapter](https://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html)
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- [ddrescue optical media notes](https://www.electric-spoon.com/doc/gddrescue/html/Optical-media.html)
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- Source: [`src/disc/mapfile.rs`](../src/disc/mapfile.rs), [`src/disc/mod.rs`](../src/disc/mod.rs) (`Disc::copy`, `Disc::patch`)
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- Source: [`src/disc/mapfile.rs`](../src/disc/mapfile.rs), [`src/disc/mod.rs`](../src/disc/mod.rs) (`Disc::copy`, `Disc::patch`), [`src/drive/mod.rs`](../src/drive/mod.rs) (`Drive::read`), [`src/mux/disc.rs`](../src/mux/disc.rs) (`DiscStream::fill_extents`).
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