Three changes targeting 0.20.9's "muxer never read-stalls on NFS read
latency" invariant:
A. FileSectorSource gets a 32 MiB internal read-ahead buffer
(READAHEAD_BUF_BYTES). Splits out from src/sector/file.rs into
src/io/file_sector_source/ with per-OS open hints (Linux
posix_fadvise(SEQUENTIAL), macOS fcntl(F_RDADVISE) with 64 MiB
cap, Windows TODO stub, BSD/illumos no-op). Backward seeks
rebuffer; partial reads at EOF return only the bytes that exist;
oversize-request bypass for count > BUF_SECTORS.
B. WritebackFile inline #[cfg(target_os = "linux")] blocks split
into per-OS files under src/io/writeback_file/. Linux unchanged
(fallocate KEEP_SIZE, fsync via bounded_syscall). macOS gets a
real F_PREALLOCATE + F_FULLFSYNC impl (was a "skipped (non-linux)"
debug log before). Windows is a stub (FlushFileBuffers via
std sync_all; TODO for SetFileValidData). BSDs/illumos fall back
to std sync_all.
C. New byte_channel module — byte-bounded producer/consumer wrapping
std sync_channel with Mutex/Condvar byte accounting. Sender blocks
when used_bytes + item.byte_size() > capacity. HasByteSize impl
for PesFrame. Default cap BYTE_CHANNEL_DEFAULT_CAPACITY = 64 MiB,
sized to absorb worst-case NFS read p99 (~2 s × UHD peak compressed
~15 MB/s). The mux call site lives in autorip (out of scope here);
this lands the primitive in libfreemkv for autorip to adopt.
Test counts: byte_channel +6, file_sector_source +5, sector::file
round-trip suite (3) preserved. passn_handler_ab.rs A/B fixture
(8 profiles) still green.
precommit.sh libfreemkv: fmt + clippy + test all green on Rust 1.86.
No version bump; no Cargo.lock changes; no forbidden-file edits
(disc/patch.rs, disc/read_error.rs, io/pipeline.rs,
tests/passn_handler_ab.rs).
Four targeted changes to maximize mux throughput regardless of storage
backend (local SSD, local HDD, NFS, network share) and surface enough
log data to diagnose 'mux slow' reports without a re-rip:
1. POSIX_FADV_SEQUENTIAL on FileSectorSource::open (Linux only).
Widens the kernel readahead window for sequential ISO reads. One
syscall at open, free on every storage type.
2. POSIX_FADV_DONTNEED on the ISO read side after every 32 MiB chunk.
Mirrors the writeback DONTNEED that already runs on the write
side. Keeps the read-side page cache bounded during multi-GB ISO
reads — eliminates the OOM-pressure / eviction-storm risk on
long mux runs. Linux only; per-drop trace at target="mux".
3. WritebackFile::create_with_size_hint(path, size_bytes) calls
fallocate(FALLOC_FL_KEEP_SIZE) on Linux to pre-reserve extents
for the output. Reported file size stays 0 (writes grow it
naturally) but the on-disk extent allocation is contiguous —
reduces extent fragmentation for big sequential muxes. Wired
into mkv:// and m2ts:// output paths via DiscTitle::size_bytes.
No-op on macOS/Windows; old create() kept with #[allow(dead_code)]
for callers without a size hint.
4. Adaptive WRITEBACK_CHUNK_BYTES in the Linux writeback pipeline.
Tracks sync_file_range(WAIT_AFTER) elapsed_ms in a rolling
16-sample window. p95 > 200 ms → double chunk size (cap 256 MiB).
p95 < 20 ms → halve (floor 4 MiB). One algorithm, both
fast-storage (small chunks, responsive) and slow-storage (big
chunks, fewer commit round-trips) optimized. Per-chunk trace +
per-32-chunk debug snapshot + info-on-resize so an operator can
see where the autoscaler settled.
All four are universal — no storage-type detection, no env vars to
flip, no per-deploy tuning required. Total +201/-6 across four files.
WO-2 (delete SectorReader trait):
- The 0.18 trait split into SectorSource (read-only) and SectorSink
(write-only) is final; the legacy SectorReader alias was a bridge.
- Renames every internal &mut dyn SectorReader (~25 sites) to
&mut dyn SectorSource. The trait method capacity() becomes
capacity_sectors() with a default of 0 (preserves SectorReader's
default-0 behavior).
- Deletes the SectorReader trait, its blanket-to-Source bridge, and
the FileSectorReader type alias. Adds explicit forwarding impls
for Box<dyn SectorSource> and &mut dyn SectorSource so generic
decorators like DecryptingSectorSource<S: SectorSource> compose.
WO-3a (extract Disc::patch):
- Moves Disc::patch (1230 lines) and bytes_bad_in_title from
disc/mod.rs into disc/patch.rs as a split inherent impl. Zero
behavior change — pure mechanical relocation. disc/mod.rs drops
from 3,945 to 2,714 LOC.
WO-6 (partial):
- Deletes src/labels/png_filenames.rs — was a 72-LOC stub with
detect() returning false, never wired into the PARSERS registry.
CLAUDE.md doc drift fixes (audited 2026-05-13):
- JUMP_BASE_SECTORS: 256→1024 (64 MB base for UHD, not 8 MB)
- PASSN_DAMAGE_THRESHOLD_PCT: 12→6
- PASSN_SKIP_SECTORS_BASE: 64→32
- MAX_RANGE_SECS=180: replaced by proportional range_sectors × 25,
capped at RANGE_BUDGET_CAP_SECS=1800.
existing call sites — sweep producer and DiscStream demux
Round 1 shipped the DecryptingSectorSource decorator
(libfreemkv/src/sector/decrypting.rs) but the existing decrypt
sites kept calling crate::decrypt::decrypt_sectors inline. This
commit migrates both:
- Disc::sweep (disc/mod.rs): producer wraps the input reader
in DecryptingSectorSource::new(reader, keys) before the read loop.
The inline decrypt_sectors call goes away — read_sectors yields
plaintext directly.
- DiscStream (mux/disc.rs): constructor wraps the underlying
Box<dyn SectorReader> in DecryptingSectorSource so the internal
fill_extents / read path sees plaintext bytes. The DecryptKeys
field stays on DiscStream for metadata-side use; it just no
longer drives decryption.
Disc::patch carried the same inline decrypt step at three call
sites (main read, backtrack read, non-NOT_READY retry read). All
three migrated onto the same wrapping for a single audit surface.
Two small support changes carry the migration without touching
the round-1 decorator shape:
- sector/mod.rs gains specific SectorSource impls for
&mut dyn SectorReader and Box<dyn SectorReader>, mirroring
std's Read forwarding pattern. Generic blankets would conflict
with the existing SectorReader → SectorSource blanket under the
orphan rule (downstream could impl SectorReader for &mut U), so
the impls are scoped to the dyn-trait shape we actually consume.
- sector/decrypting.rs gains DecryptingSectorSource::set_keys so
DiscStream::set_raw() can flip the wrapped reader to a
DecryptKeys::None pass-through without rebuilding the decorator
(which would require moving the inner Box out from behind &mut self).
After this commit, grep `decrypt_sectors` in src/ shows the
function definition, its single use inside DecryptingSectorSource,
plus comments only. One audit surface for AACS / CSS / passthrough
correctness.
Behaviour-preserving: same plaintext bytes flow through; the only
difference is which type owns the decrypt step.
See freemkv-private/memory/0_18_redesign.md.
Single contributor: MattJackson.
The SectorSource/Sink agent and the WritebackFile-rename agent both
branched from main concurrently; the sector branch wrote against the
0.17 Writer name and only the rename branch knew about WritebackFile.
This integration commit reconciles the two: FileSectorSink::create /
::open / the inner-field type all use WritebackFile directly, and the
module-level + struct-level docs are corrected.
Splits the unidirectional read trait from a (planned) write trait at
the sector level, eliminating runtime "wrong direction" potential.
Keeps SectorReader alive as a pre-deprecation alias via blanket impl
so existing callers compile unchanged through the migration window.
Adds DecryptingSectorSource decorator: wrap any SectorSource in this
to get plaintext sectors out. Replaces the duplicate decrypt code
paths in sweep_pipeline and DiscStream (those migrations are
follow-up commits).
The formal #[deprecated] attribute on SectorReader is held back to a
follow-up commit because internal call sites in disc/, udf/, mux/,
and verify/ still go through the legacy trait, and the CI gauntlet
treats deprecation lints as errors. Behavioural intent — "this trait
is going away" — is documented on the trait itself.
See freemkv-private/memory/0_18_redesign.md.
Single contributor: MattJackson.
matthew