Hypervisor Backends

The Hypervisor Trait

All backends implement the Hypervisor trait defined in crates/vm-manager/src/traits.rs:

#![allow(unused)]
fn main() {
pub trait Hypervisor: Send + Sync {
    fn prepare(&self, spec: &VmSpec) -> impl Future<Output = Result<VmHandle>>;
    fn start(&self, vm: &VmHandle) -> impl Future<Output = Result<VmHandle>>;
    fn stop(&self, vm: &VmHandle, timeout: Duration) -> impl Future<Output = Result<VmHandle>>;
    fn suspend(&self, vm: &VmHandle) -> impl Future<Output = Result<VmHandle>>;
    fn resume(&self, vm: &VmHandle) -> impl Future<Output = Result<VmHandle>>;
    fn destroy(&self, vm: VmHandle) -> impl Future<Output = Result<()>>;
    fn state(&self, vm: &VmHandle) -> impl Future<Output = Result<VmState>>;
    fn guest_ip(&self, vm: &VmHandle) -> impl Future<Output = Result<String>>;
    fn console_endpoint(&self, vm: &VmHandle) -> Result<ConsoleEndpoint>;
}
}

QEMU Backend (Linux)

Located in crates/vm-manager/src/backends/qemu.rs.

Prepare:

Creates work directory under ~/.local/share/vmctl/vms/<name>/.
Creates QCOW2 overlay on top of the base image.
Generates cloud-init seed ISO (if configured).
Allocates a deterministic SSH port (10022-10122 range, hash-based).
Generates a locally-administered MAC address.

Start:

Launches qemu-system-x86_64 with KVM acceleration.
CPU type: host (passthrough).
Machine type: q35,accel=kvm.
Devices: virtio-blk for disk, virtio-rng for entropy.
Console: Unix socket + log file.
VNC: localhost, auto-port.
Networking: User-mode (SLIRP with port forwarding) or TAP (bridged).
Daemonizes with PID file.
Connects via QMP to verify startup and retrieve VNC address.

Stop:

ACPI power-down via QMP (system_powerdown).
Poll for process exit (500ms intervals) up to timeout.
SIGTERM if timeout exceeded.
SIGKILL as last resort.

IP Discovery:

User-mode: returns 127.0.0.1 (SSH via forwarded port).
TAP: parses ARP table (ip neigh show), falls back to dnsmasq lease files by MAC address.

QMP Client

Located in crates/vm-manager/src/backends/qmp.rs. Async JSON-over-Unix-socket client implementing the QEMU Machine Protocol.

Commands: system_powerdown, quit, stop, cont, query_status, query_vnc.

Propolis Backend (illumos)

Located in crates/vm-manager/src/backends/propolis.rs.

Uses ZFS clones for VM disks.
Manages zones with the nebula-vm brand.
Communicates with propolis-server via REST API.
Networking via illumos VNICs.
Suspend/resume not yet implemented.

Noop Backend

Located in crates/vm-manager/src/backends/noop.rs. All operations succeed immediately. Used for testing.

RouterHypervisor

Located in crates/vm-manager/src/backends/mod.rs. Dispatches Hypervisor trait calls to the correct backend based on the VmHandle's BackendTag.

Construction:

RouterHypervisor::new(bridge, zfs_pool) - Platform-aware, creates the appropriate backend.
RouterHypervisor::noop_only() - Testing mode.

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