Module ledger 

VRAM Reservation Ledger (GPU-SHARE-001).

Uses flock for mutual exclusion and atomic write (write-to-temp, rename) for crash safety.

Contract C-VRAM-001

CudaTrainer::new() MUST NOT allocate if ledger.total_reserved() + budget > total_mb × reserve_factor.

Protocol

1. Acquire flock(LOCK_EX) on ledger file
2. Read reservations, prune dead PIDs + expired leases
3. Check capacity: sum(active.budget_mb) + my_budget <= total_mb × reserve_factor
4. Write reservation via atomic rename (write tmp → rename)
5. Release lock (close fd / drop)
6. On exit: best-effort cleanup via Drop

Structs

Reservation

A single VRAM reservation.

VramLedger

VRAM reservation ledger with flock-based mutual exclusion.

Enums

MemoryType

GPU memory type.

Constants

DEFAULT_LEASE_HOURS

Default lease duration (24 hours).

RESERVE_FACTOR_DISCRETE

Reserve factor for discrete GPUs (15% headroom).

RESERVE_FACTOR_UNIFIED

Reserve factor for unified memory (40% headroom for OS).

Functions

auto_ledger

Create a ledger auto-detecting GPU properties.

detect_gpu_uuid

Detect GPU UUID by shelling out to nvidia-smi -L.

detect_memory_type

Detect whether GPU has unified memory (Jetson) vs discrete.

detect_total_memory_mb

Detect total GPU memory in MB via nvidia-smi.

gpu_status_display

Human-readable GPU status display.