feat: Phase 3 — performance tuning, iSCSI session refactor, store integration
Phase 3 delivers five checkpoints:
CP1 Engine Tuning: BlockVolConfig tunables, 256-shard DirtyMap, adaptive
group commit (low-watermark immediate flush), WAL pressure handling with
backpressure and ErrWALFull timeout.
CP2 iSCSI Session Refactor: RX/TX goroutine split with respCh (cap 64),
txLoop for serialized response writes, StatSN assignment modes. Login
phase stays single-goroutine; full-duplex after login.
CP3 Store Integration: BlockVolAdapter (iscsi.BlockDevice interface),
BlockVolumeStore management, BlockService in volume_server_block.go,
CLI flags (--block.listen/dir/iqn.prefix), sw-block-attach.sh helper.
CP5 Concurrency Hardening: WAL reuse guard (LSN validation in ReadLBA),
opsOutstanding counter with beginOp/endOp + Close drain, appendWithRetry
shared by WriteLBA and TrimLBA, flusher LSN guard in FlushOnce.
Bug fixes (P3-BUG-2–11): unbounded pending queue cap, Data-Out timeout,
flusher error logging, GroupCommitter panic recovery, Close vs concurrent
ops guard, target shutdown race, WAL-full retry vs Close, WRITE SAME(16)
for XFS, MODE SENSE(10) + VPD 0xB0/0xB2 for Linux kernel compatibility.
797 tests passing (517 engine + 280 iSCSI), go vet clean.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>