image-builder: test-recipe: Check fakemachine backend

The smoke test should retrieve the backend it's running and compare it
against the requested backend.

Signed-off-by: Christopher Obbard <chris.obbard@collabora.com>

image-builder/test-recipe.yaml

@@ -2,10 +2,26 @@
 {{- $mirror := or .mirror "https://repositories.apertis.org/apertis/" -}}
 {{- $suite := or .suite "v2021dev1" -}}
 {{- $osname := or .osname "apertis" -}}
+{{- $required_backend := or .required_backend "uml" -}}
 
 architecture: {{ $architecture }}
 
 actions:
+  - action: run
+    description: Check fakemachine backend
+    label: check-fakemachine-backend
+    command: |
+      BACKEND=$(systemd-detect-virt)
+
+      # workaround for https://github.com/systemd/systemd/issues/17754
+      # running fakemachine in uml mode inside gitlab runner we essentially run
+      # uml nested under kvm; systemd-detect-virt thinks we are running on kvm
+      grep -qP "^vendor_id\t: User Mode Linux" /proc/cpuinfo && BACKEND="uml"
+
+      echo "detected machine backend: ${BACKEND}"
+      echo "required machine backend: {{ $required_backend }}"
+      [ "${BACKEND}" = "{{ $required_backend }}" ]
+
   - action: debootstrap
     suite: {{ $suite }}
     components: