# Volt VMM

A lightweight, secure Virtual Machine Monitor (VMM) built on KVM. Volt is designed as a Firecracker alternative for running microVMs with minimal overhead and maximum security.

## Features

- **Lightweight**: Minimal footprint, fast boot times
- **Secure**: Strong isolation using KVM hardware virtualization
- **Simple API**: REST API over Unix socket for VM management
- **Async**: Built on Tokio for efficient I/O handling
- **VirtIO Devices**: Block and network devices using VirtIO
- **Serial Console**: 8250 UART emulation for guest console access

## Architecture

```
volt-vmm/
├── src/
│   ├── main.rs         # Entry point and CLI
│   ├── vmm/            # Core VMM logic
│   │   └── mod.rs      # VM lifecycle management
│   ├── kvm/            # KVM interface
│   │   └── mod.rs      # KVM ioctls wrapper
│   ├── devices/        # Device emulation
│   │   ├── mod.rs      # Device manager
│   │   ├── serial.rs   # 8250 UART
│   │   ├── virtio_block.rs
│   │   └── virtio_net.rs
│   ├── api/            # HTTP API
│   │   └── mod.rs      # REST endpoints
│   └── config/         # Configuration
│       └── mod.rs      # VM config parsing
└── Cargo.toml
```

## Building

```bash
cargo build --release
```

## Usage

### Command Line

```bash
# Start a VM with explicit options
volt-vmm \
  --kernel /path/to/vmlinux \
  --initrd /path/to/initrd.img \
  --rootfs /path/to/rootfs.ext4 \
  --vcpus 2 \
  --memory 256

# Start a VM from config file
volt-vmm --config vm-config.json
```

### Configuration File

```json
{
  "vcpus": 2,
  "memory_mib": 256,
  "kernel": "/path/to/vmlinux",
  "cmdline": "console=ttyS0 reboot=k panic=1 pci=off",
  "initrd": "/path/to/initrd.img",
  "rootfs": {
    "path": "/path/to/rootfs.ext4",
    "read_only": false
  },
  "network": [
    {
      "id": "eth0",
      "tap": "tap0"
    }
  ],
  "drives": [
    {
      "id": "data",
      "path": "/path/to/data.img",
      "read_only": false
    }
  ]
}
```

### API

The API is exposed over a Unix socket (default: `/tmp/volt-vmm.sock`).

```bash
# Get VM info
curl --unix-socket /tmp/volt-vmm.sock http://localhost/vm

# Pause VM
curl --unix-socket /tmp/volt-vmm.sock \
  -X PUT -H "Content-Type: application/json" \
  -d '{"action": "pause"}' \
  http://localhost/vm/actions

# Resume VM
curl --unix-socket /tmp/volt-vmm.sock \
  -X PUT -H "Content-Type: application/json" \
  -d '{"action": "resume"}' \
  http://localhost/vm/actions

# Stop VM
curl --unix-socket /tmp/volt-vmm.sock \
  -X PUT -H "Content-Type: application/json" \
  -d '{"action": "stop"}' \
  http://localhost/vm/actions
```

## Dependencies

Volt leverages the excellent [rust-vmm](https://github.com/rust-vmm) project:

- `kvm-ioctls` / `kvm-bindings` - KVM interface
- `vm-memory` - Guest memory management
- `virtio-queue` / `virtio-bindings` - VirtIO device support
- `linux-loader` - Kernel/initrd loading

## Roadmap

- [x] Project structure
- [ ] KVM VM creation
- [ ] Guest memory setup
- [ ] vCPU initialization
- [ ] Kernel loading (bzImage, ELF)
- [ ] Serial console
- [ ] VirtIO block device
- [ ] VirtIO network device
- [ ] Snapshot/restore
- [ ] Live migration

## License

Apache-2.0