/projects/haiku-rewind

Copy-on-Write filesystem snapshots for Haiku's BFS. Point-in-time captures of your filesystem state - think Time Machine for Haiku, or ZFS/Btrfs snapshots.

Architecture

┌─────────────────────────────────────────────────────┐
│                  User Space                         │
│  ┌──────────────┐      ┌──────────────┐            │
│  │  CLI Tool    │      │   GUI Tool   │  (Future)  │
│  └──────┬───────┘      └──────┬───────┘            │
│         └─────────┬───────────┘                     │
│                   │ ioctl()                         │
├───────────────────┼─────────────────────────────────┤
│              Kernel Space                           │
│         ┌─────────▼──────────┐                      │
│         │ SnapshotManager    │  Lifecycle & Control │
│         └─────────┬──────────┘                      │
│         ┌─────────▼──────────┐                      │
│         │     Snapshot       │  Block Tracking      │
│         │  - COW Logic       │                      │
│         └─────────┬──────────┘                      │
│    ┌──────────────┼──────────────┐                  │
│  ┌─▼────┐    ┌───▼────┐    ┌───▼─────┐            │
│  │Volume│    │ Inode  │    │  Block  │            │
│  └──────┘    └────────┘    │Allocator│            │
│              BFS Core      └─────────┘            │
└─────────────────────────────────────────────────────┘

Key Features

Copy-on-Write

Block-level COW mechanism
Automatic duplication on write
Efficient block mapping
BFS BlockAllocator integration

Snapshot Management

Up to 64 simultaneous snapshots
Thread-safe operations
Transaction integration
Graceful init/shutdown

Implementation Status

Core:

100%

BFS Hooks:

100%

Build:

100%

Testing:

30%

CLI Tool:

Progress Tracker

Done

~1,000 lines C++ implementation
Volume/Inode/Superblock hooks
Docker + Linux build system
Cross-compiler toolchain

In Progress

VM testing (Phase 1-2)
Stability verification
Documentation

Planned

CLI tool (create/list/restore)
Metadata persistence
GUI snapshot browser

COW Write Flow

Application writes to file
Inode::WriteAt() intercepts the write
SnapshotManager::CheckCOWRequirement() called
For each modified block:
- Check if block already copied
- Allocate new COW block if needed
- Copy original → COW block
- Record mapping (original → COW)
Allow write to proceed to original block
Snapshot preserves old data in COW block