doc/devices: init

USB udev rules by @bct
<https://gist.github.com/bct/28d51ca86c91d3f06f9933cb21f32d32>

Author: astro

doc/src/SUMMARY.md

@@ -5,6 +5,7 @@
   - [Configuration options](./options.md)
   - [Network interfaces](./interfaces.md)
   - [Shared directories](./shares.md)
+  - [Device pass-through](./devices.md)
   - [CPU emulation](./cpu-emulation.md)
   - [Output options](./output-options.md)
   - [MicroVM options reference ⚙️](./microvm-options.md)

doc/src/devices.md

@@ -0,0 +1,53 @@
+# Device pass-through
+
+PCI and USB pass-through is supported on some hypervisors. Permission
+setup is automatic for declared `"pci'` devices, but manual for
+`"usb"` devices.
+
+## Example PCI pass-through
+
+Guest example:
+
+```nix
+microvm.devices = [ {
+  bus = "pci";
+  path = "0000:06:00.1";
+} {
+  bus = "pci";
+  path = "0000:06:10.4";
+} ];
+```
+
+Permission setup on the host is provided by systemd template unit
+`[email protected]`.
+
+## Example USB pass-through
+
+### In the guest
+
+```nix
+microvm.devices = [
+  # RTL2838UHIDIR
+  # Realtek Semiconductor Corp. RTL2838 DVB-T
+  { bus = "usb"; path = "vendorid=0x0bda,productid=0x2838"; }
+  # Sonoff Zigbee 3.0 USB Dongle Plus
+  # Silicon Labs CP210x UART Bridge
+  { bus = "usb"; path = "vendorid=0x10c4,productid=0xea60"; }
+];
+```
+
+### On the host
+
+USB device paths are not directly translatable to udev rules. Setup
+permissions yourself:
+
+```nix
+services.udev.extraRules = ''
+  # RTL2838UHIDIR
+  # Realtek Semiconductor Corp. RTL2838 DVB-T
+  SUBSYSTEM=="usb", ATTR{idVendor}=="0bda", ATTR{idProduct}=="2838", GROUP="kvm"
+  # Sonoff Zigbee 3.0 USB Dongle Plus
+  # Silicon Labs CP210x UART Bridge
+  SUBSYSTEM=="usb", ATTR{idVendor}=="10c4", ATTR{idProduct}=="ea60", GROUP="kvm"
+'';
+```