vm-manager/docs/book/architecture/backends.html
Till Wegmueller b37beea0f5
Add mdbook documentation for vmctl and vm-manager
Comprehensive docs covering CLI reference, VMFile.kdl format,
architecture, library API, tutorials, and advanced topics.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
2026-02-15 13:37:22 +01:00

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<h1 id="hypervisor-backends"><a class="header" href="#hypervisor-backends">Hypervisor Backends</a></h1>
<h2 id="the-hypervisor-trait"><a class="header" href="#the-hypervisor-trait">The Hypervisor Trait</a></h2>
<p>All backends implement the <code>Hypervisor</code> trait defined in <code>crates/vm-manager/src/traits.rs</code>:</p>
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>pub trait Hypervisor: Send + Sync {
fn prepare(&amp;self, spec: &amp;VmSpec) -&gt; impl Future&lt;Output = Result&lt;VmHandle&gt;&gt;;
fn start(&amp;self, vm: &amp;VmHandle) -&gt; impl Future&lt;Output = Result&lt;VmHandle&gt;&gt;;
fn stop(&amp;self, vm: &amp;VmHandle, timeout: Duration) -&gt; impl Future&lt;Output = Result&lt;VmHandle&gt;&gt;;
fn suspend(&amp;self, vm: &amp;VmHandle) -&gt; impl Future&lt;Output = Result&lt;VmHandle&gt;&gt;;
fn resume(&amp;self, vm: &amp;VmHandle) -&gt; impl Future&lt;Output = Result&lt;VmHandle&gt;&gt;;
fn destroy(&amp;self, vm: VmHandle) -&gt; impl Future&lt;Output = Result&lt;()&gt;&gt;;
fn state(&amp;self, vm: &amp;VmHandle) -&gt; impl Future&lt;Output = Result&lt;VmState&gt;&gt;;
fn guest_ip(&amp;self, vm: &amp;VmHandle) -&gt; impl Future&lt;Output = Result&lt;String&gt;&gt;;
fn console_endpoint(&amp;self, vm: &amp;VmHandle) -&gt; Result&lt;ConsoleEndpoint&gt;;
}
<span class="boring">}</span></code></pre></pre>
<h2 id="qemu-backend-linux"><a class="header" href="#qemu-backend-linux">QEMU Backend (Linux)</a></h2>
<p>Located in <code>crates/vm-manager/src/backends/qemu.rs</code>.</p>
<p><strong>Prepare:</strong></p>
<ul>
<li>Creates work directory under <code>~/.local/share/vmctl/vms/&lt;name&gt;/</code>.</li>
<li>Creates QCOW2 overlay on top of the base image.</li>
<li>Generates cloud-init seed ISO (if configured).</li>
<li>Allocates a deterministic SSH port (10022-10122 range, hash-based).</li>
<li>Generates a locally-administered MAC address.</li>
</ul>
<p><strong>Start:</strong></p>
<ul>
<li>Launches <code>qemu-system-x86_64</code> with KVM acceleration.</li>
<li>CPU type: <code>host</code> (passthrough).</li>
<li>Machine type: <code>q35,accel=kvm</code>.</li>
<li>Devices: virtio-blk for disk, virtio-rng for entropy.</li>
<li>Console: Unix socket + log file.</li>
<li>VNC: localhost, auto-port.</li>
<li>Networking: User-mode (SLIRP with port forwarding) or TAP (bridged).</li>
<li>Daemonizes with PID file.</li>
<li>Connects via QMP to verify startup and retrieve VNC address.</li>
</ul>
<p><strong>Stop:</strong></p>
<ol>
<li>ACPI power-down via QMP (<code>system_powerdown</code>).</li>
<li>Poll for process exit (500ms intervals) up to timeout.</li>
<li>SIGTERM if timeout exceeded.</li>
<li>SIGKILL as last resort.</li>
</ol>
<p><strong>IP Discovery:</strong></p>
<ul>
<li>User-mode: returns <code>127.0.0.1</code> (SSH via forwarded port).</li>
<li>TAP: parses ARP table (<code>ip neigh show</code>), falls back to dnsmasq lease files by MAC address.</li>
</ul>
<h2 id="qmp-client"><a class="header" href="#qmp-client">QMP Client</a></h2>
<p>Located in <code>crates/vm-manager/src/backends/qmp.rs</code>. Async JSON-over-Unix-socket client implementing the QEMU Machine Protocol.</p>
<p>Commands: <code>system_powerdown</code>, <code>quit</code>, <code>stop</code>, <code>cont</code>, <code>query_status</code>, <code>query_vnc</code>.</p>
<h2 id="propolis-backend-illumos"><a class="header" href="#propolis-backend-illumos">Propolis Backend (illumos)</a></h2>
<p>Located in <code>crates/vm-manager/src/backends/propolis.rs</code>.</p>
<ul>
<li>Uses ZFS clones for VM disks.</li>
<li>Manages zones with the <code>nebula-vm</code> brand.</li>
<li>Communicates with <code>propolis-server</code> via REST API.</li>
<li>Networking via illumos VNICs.</li>
<li>Suspend/resume not yet implemented.</li>
</ul>
<h2 id="noop-backend"><a class="header" href="#noop-backend">Noop Backend</a></h2>
<p>Located in <code>crates/vm-manager/src/backends/noop.rs</code>. All operations succeed immediately. Used for testing.</p>
<h2 id="routerhypervisor"><a class="header" href="#routerhypervisor">RouterHypervisor</a></h2>
<p>Located in <code>crates/vm-manager/src/backends/mod.rs</code>. Dispatches <code>Hypervisor</code> trait calls to the correct backend based on the <code>VmHandle</code>'s <code>BackendTag</code>.</p>
<p>Construction:</p>
<ul>
<li><code>RouterHypervisor::new(bridge, zfs_pool)</code> - Platform-aware, creates the appropriate backend.</li>
<li><code>RouterHypervisor::noop_only()</code> - Testing mode.</li>
</ul>
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