Windows driver: overhaul IRP completion path in EncryptedIoQueue, add dual completion threads, precise byte accounting & safer UpdateBuffer
Major changes:
- Added pooled + elastic work item model with retry/backoff (MAX_WI_RETRIES). removed semaphore usage.
- Introduced two completion threads to reduce contention and latency under heavy IO.
- Added BytesCompleted (per IRP) and ActualBytes (per fragment) for correct short read/write accounting. total read/write stats now reflect real transferred bytes instead of requested length.
- Moved decryption of read fragments into IO thread. completion threads now only finalize IRPs (reduces race window and simplifies flow).
- Deferred final IRP completion via FinalizeOriginalIrp to avoid inline IoCompleteRequest re-entrancy. added safe OOM inline fallback.
- Implemented work item pool drain & orderly shutdown (ActiveWorkItems + NoActiveWorkItemsEvent) with robust stop protocol.
- Replaced semaphore-based work item acquisition with spin lock + free list + event (WorkItemAvailableEvent). added exponential backoff for transient exhaustion.
- Added elastic (on-demand) work item allocation with pool vs dynamic origin tracking (FromPool).
- Added FreeCompletionWorkItemPool() for symmetric cleanup; ensured all threads are explicitly awakened during stop.
- Added second completion thread replacing single CompletionThread.
- Hardened UpdateBuffer: fixed parameter name typo, added bounds/overflow checks using IntSafe (ULongLongAdd), validated Count, guarded sector end computation.
- Fixed GPT/system region write protection logic to pass correct length instead of end offset.
- Ensured ASSERTs use fragment‑relative bounds (cast + length) and avoided mixed 64/32 comparisons.
- Added MAX_WI_RETRIES constant. added WiRetryCount field in EncryptedIoRequest.
- Ensured RemoveLock is released only after all queue/accounting updates (OnItemCompleted).
- Reset/read-ahead logic preserved. read-ahead trigger now based on actual completion & zero pending fragment count.
- General refactoring, clearer separation of concerns (TryAcquireCompletionWorkItem / FinalizeOriginalIrp / HandleCompleteOriginalIrp).
Safety / correctness improvements:
- Accurate short read handling (STATUS_END_OF_FILE with true byte count).
- Eliminated risk of double free or premature RemoveLock release on completion paths.
- Prevented potential overflow in sector end arithmetic.
- Reduced contention and potential deadlock scenarios present with previous semaphore wait path.