Introduces the SequentialSink / RandomAccessSink trait pair under
io::sink and an open_for_mkv dispatch helper that picks WritebackFile
on Linux+NFS and LocalFileSink everywhere else. LocalFileSink wraps
BufWriter<File> with a 4 MiB buffer and exposes a per-OS preallocate
path (fallocate on Linux, F_PREALLOCATE on macOS, no-op fallback).
Adds platform::fs_type::detect with a per-OS split (statfs on Linux /
macOS, UNC heuristic on Windows, Unknown elsewhere) so construction-
site dispatch has a single primitive to call.
Blanket impls cover the common shapes: any Write+Send is a
SequentialSink, and any SequentialSink+Seek is a RandomAccessSink.
WritebackFile satisfies the random-access trait via the blanket impl
without needing an explicit per-type impl. No callers wired yet — the
mux::resolve construction sites stay on WritebackFile pending Phase 3.
Tests: 5 new sink/preallocate tests + 3 fs_type tests (1 ignored,
needs a real NFS mount). cargo +1.86 fmt + clippy + tests all green.
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).
Generalizes 0.20.5's hand-written wait_after_with_timeout into a
reusable primitive. After this change, every blocking syscall in the
recovery + mux paths is wrapped, so cooperative Halt has bounded
~250 ms latency reach even into kernel-owned thread states.
New module src/io/bounded.rs:
- BoundedError { Halted, Timeout, WorkerLost }
- bounded_syscall<F, R>(halt: Option<&Halt>, timeout, op) -> Result<R, BoundedError>
- Worker thread runs op; main thread recv_timeouts on a rendezvous
channel in 250 ms slices, polling halt between slices.
- Worker is intentionally leaked on timeout/halt — kernel reaps when
the syscall finally returns or at process exit. Calling thread is
NEVER trapped inside a kernel call.
- 6 unit tests cover the happy path + each error variant.
Refactored callsites:
- src/io/writeback/linux.rs::wait_after_with_timeout now delegates
to bounded_syscall. ~30 LOC of duplicated channel/thread plumbing
deleted. Same semantics, cleaner.
- src/io/writeback_file.rs::WritebackFile::sync_all now wraps the
final libc::fsync(fd) with bounded_syscall (60 s deadline). On
timeout: log error at target=mux and return Ok — kernel will flush
on close, best-effort but bounded. Covers FileSectorSink::finish,
PatchSink::close, SweepSink::close, and the mux MKV finalize path
(they all sync through WritebackFile).
What still hangs (deliberately not wrapped — too hot a path):
- File::write itself. Per-frame write on a wedged NFS could still
block; but back-pressure from a stuck consumer means the producer
notices within seconds, not minutes — different failure mode than
the WAIT_AFTER hang 0.20.5/0.20.6 fix.
Sweep was the original producer/consumer split that motivated the
generic Pipeline primitive (round 1, commit 500894e). Now that
Pipeline + Sink exist, sweep stops shipping its own bespoke
threading.
- New SweepSink: Sink<WorkItem> impl in src/disc/sweep.rs. Owns
WritebackFile + Mapfile + ProgressSnapshot back-channel. apply()
carries the file-write + mapfile.record per WorkItem; close()
drains writeback, fsyncs, flushes mapfile.
- Disc::sweep: constructs SweepSink, calls Pipeline::spawn_named
(so the consumer thread keeps showing up as
freemkv-sweep-consumer), sends WorkItems, calls pipe.finish().
The producer-side ReadCtx state machine, decrypt, set_speed,
halt — all unchanged.
- Pipeline gains spawn_named(name, depth, sink) so callers can
preserve identifiable thread names without the primitive baking
one in. Also adds Pipeline::try_send for the throttled
StatsRequest path that must not block the producer.
- Deleted src/disc/sweep_pipeline.rs entirely. WorkItem,
ProgressSnapshot, ConsumerSummary moved into disc/sweep.rs as
module-private types. WorkItem::Finish dropped — dropping the
channel is the end-of-stream signal Pipeline already uses.
Behaviour-preserving: the sweep algorithm, mapfile invariants,
back-pressure via channel depth (DEFAULT_PIPELINE_DEPTH = 4) all
match the 0.17.13 implementation. New synthetic regression test
(sweep_pipeline_full_good_100_batches) exercises ~100 batches of
clean reads end-to-end through the new Pipeline path and verifies
bytes_good and ISO file size.
See freemkv-private/memory/0_18_redesign.md.
Patch was strictly serial (per-sector recovery: read → seek+write
→ mapfile.record → next). Lifting the write+record onto a consumer
thread lets the drive issue the next per-sector retry while the
previous block's recovered bytes are being committed — small but
real win on damaged discs with many bad sectors, and uniform with
sweep's threading model.
- New PatchSink: Sink<PatchItem> impl in src/disc/patch.rs. Owns
WritebackFile + Mapfile. apply() seeks+writes recovered bytes
and records mapfile state per item; close() runs sync_all and
mapfile.flush.
- Channel depth: WRITE_THROUGH_DEPTH (1). Patch wants minimum
buffering — back-pressure should kick in immediately so the
drive's per-sector retry budget isn't ahead of the writer.
- Disc::patch: keeps every existing recovery decision on the
producer (reverse walk, damage-window skip, NOT_READY pauses,
bridge-degradation handling, wedge exit, range watchdog).
WritebackFile ownership moves to the sink.
Behaviour-preserving: per-sector single-shot read budget unchanged
(BU40N+Initio bridge wedge concern still respected); recovery
algorithm bit-identical.
See freemkv-private/memory/0_18_redesign.md.
Single contributor: MattJackson.
Generic bounded producer/consumer pipeline. The same shape applies to
sweep, patch, and mux today via three near-duplicate implementations
(or, in patch's and mux's case, no implementation at all). 0.18
collapses them onto one primitive. See
freemkv-private/memory/0_18_redesign.md for full context.
Single contributor: MattJackson.
The type's job is the bounded-cache writeback pipeline (sync_file_range
+ posix_fadvise(DONTNEED)) — not generic writing. The 0.17 name was
ambiguous; reading `Writer::new(file)` gave no hint about what was
special. New name makes the role obvious at every call site.
Adds `WritebackFile::create(path)` and `WritebackFile::open(path)`
constructors so callers don't have to assemble a `File` first.
No alias kept; this is a clean 0.18 rename. See
freemkv-private/memory/0_18_redesign.md.
Single contributor: MattJackson.
Pass 1 sweep speed on a healthy disc previously dipped from ~15 MB/s
to ~1 MB/s every ~30 s on a host with default Linux dirty-page
settings. Empirical cause: the kernel's vm.dirty_ratio (~20% of RAM)
lets hundreds of MB of dirty pages accumulate, then bursts a flush at
99% disk utilisation that blocks app writes for ~1 s. Confirmed on
the BU40N test bed — dirty pages grew 112 → 563 MB between bursts;
lowering vm.dirty_bytes to 64 MB at the host sysctl level eliminated
the dips. Shipping the equivalent inside libfreemkv so users do not
need to tune the host kernel.
- New crate::io::Writer: drop-in File wrapper (impl Write + Seek).
Wraps a per-platform WritebackPipeline that on Linux schedules
sync_file_range(WRITE) + lagging sync_file_range(WAIT_AFTER) +
posix_fadvise(DONTNEED) in 32 MB chunks, bounding dirty cache at
~64 MB. macOS and Windows ship a no-op stub.
- Disc::sweep wraps its output File in Writer. Loop body unchanged.
- Module is purpose-built so any large sequential output (patch,
mux) can adopt the same wrapper as a one-line change later.
matthew