fix(raspberrypi): detect Raspberry Pi hardware in check mode (#719)

- set check_mode: false on the /proc/cpuinfo and /proc/device-tree/model
  probes, since ansible.builtin.command never executes under --check and
  returns rc 0 with "Command would have run if not in check mode"
- default a missing probe rc to 1 in the raspberry_pi gate so an undefined
  result cannot be read as "this host is a Raspberry Pi"
- add a structural regression test and hook it into pre-commit

Without this, site.yml --check marked every x86_64 host as a Raspberry Pi and
applied the distro specific setup tasks, failing on Ubuntu with
"Destination /boot/firmware/cmdline.txt does not exist".

.github/scripts/test-raspberrypi-detection.sh

@@ -0,0 +1,69 @@
+#!/usr/bin/env bash
+
+set -Eeuo pipefail
+
+repo_root="$(git rev-parse --show-toplevel)"
+tasks_file="$repo_root/roles/raspberrypi/tasks/main.yml"
+
+if [ ! -f "$tasks_file" ]; then
+  printf 'cannot find %s\n' "$tasks_file" >&2
+  exit 1
+fi
+
+# The role decides whether a host is a Raspberry Pi from the return code of two
+# ansible.builtin.command probes. The command module never executes under
+# --check: it returns rc 0 with "Command would have run if not in check mode".
+# Without check_mode: false on both probes every host looks like a Raspberry Pi
+# in a check run, so distro specific tasks (e.g. the Ubuntu cgroup
+# cmdline.txt edit) run against hosts that must not be touched.
+probe_count="$(grep -c -- 'check_mode: false' "$tasks_file" || true)"
+if [ "$probe_count" -lt 2 ]; then
+  printf 'raspberrypi detection probes must set check_mode: false (found %s, expected 2)\n' \
+    "$probe_count" >&2
+  exit 1
+fi
+
+# Both probes must be the detection greps, not some other task.
+for probe in \
+  'grep -E "Raspberry Pi|BCM2708|BCM2709|BCM2835|BCM2836" /proc/cpuinfo' \
+  'grep -E "Raspberry Pi" /proc/device-tree/model'; do
+  grep -Fq -- "$probe" "$tasks_file" || {
+    printf 'missing raspberry pi detection probe: %s\n' "$probe" >&2
+    exit 1
+  }
+done
+
+# The probes must stay registered under the names the gate consumes.
+for var in grep_cpuinfo_raspberrypi grep_device_tree_model_raspberrypi; do
+  grep -Fq -- "register: $var" "$tasks_file" || {
+    printf 'detection probe is not registered as %s\n' "$var" >&2
+    exit 1
+  }
+done
+
+# The gate must keep keying on rc 0 and must tolerate a missing rc so an
+# undefined result cannot be read as "this host is a Raspberry Pi".
+grep -Eq -- 'when:.*grep_cpuinfo_raspberrypi\.rc.*== 0.*grep_device_tree_model_raspberrypi\.rc.*== 0' \
+  "$tasks_file" || {
+  printf 'raspberry_pi gate no longer tests both probe return codes for 0\n' >&2
+  exit 1
+}
+
+grep -Eq -- 'grep_cpuinfo_raspberrypi\.rc \| default\(1\)' "$tasks_file" || {
+  printf 'raspberry_pi gate does not default the /proc/cpuinfo probe rc\n' >&2
+  exit 1
+}
+
+grep -Eq -- 'grep_device_tree_model_raspberrypi\.rc \| default\(1\)' "$tasks_file" || {
+  printf 'raspberry_pi gate does not default the /proc/device-tree probe rc\n' >&2
+  exit 1
+}
+
+# The distro specific include must remain gated on the detection result so a
+# non Raspberry Pi host skips setup/ and teardown/ entirely.
+grep -Eq -- 'raspberry_pi\|default\(false\)' "$tasks_file" || {
+  printf 'OS specific tasks are no longer gated on raspberry_pi\n' >&2
+  exit 1
+}
+
+printf 'Raspberry Pi detection regression test passed\n'

.pre-commit-config.yaml

@@ -76,6 +76,12 @@ repos:
         language: system
         pass_filenames: false
         files: ^roles/prereq/(tasks/main|defaults/main)\.yml$|^\.github/scripts/test-disable-swap\.sh$
+      - id: raspberrypi-detection-test
+        name: Raspberry Pi detection test
+        entry: .github/scripts/test-raspberrypi-detection.sh
+        language: system
+        pass_filenames: false
+        files: ^roles/raspberrypi/(tasks/main|defaults/main)\.yml$|^\.github/scripts/test-raspberrypi-detection\.sh$
       - id: cilium-bgp-manifest-test
         name: Cilium BGP manifest test
         entry: python3 .github/scripts/test-cilium-bgp-manifest.py

roles/raspberrypi/tasks/main.yml

@@ -1,20 +1,27 @@
 ---
+# The probes below must run in check mode as well. The command module does not
+# execute under --check, it returns rc 0 with "Command would have run if not in
+# check mode", which would otherwise mark every host as a Raspberry Pi and make
+# check runs apply the distro specific tasks. The rc values mean: 0 matched, 1 no
+# match, 2 the file is absent (no /proc/device-tree on non ARM systems).
 - name: Test for raspberry pi /proc/cpuinfo
   ansible.builtin.command: grep -E "Raspberry Pi|BCM2708|BCM2709|BCM2835|BCM2836" /proc/cpuinfo
   register: grep_cpuinfo_raspberrypi
   failed_when: false
   changed_when: false
+  check_mode: false
 
 - name: Test for raspberry pi /proc/device-tree/model
   ansible.builtin.command: grep -E "Raspberry Pi" /proc/device-tree/model
   register: grep_device_tree_model_raspberrypi
   failed_when: false
   changed_when: false
+  check_mode: false
 
 - name: Set raspberry_pi fact to true
   ansible.builtin.set_fact:
     raspberry_pi: true
-  when: grep_cpuinfo_raspberrypi.rc == 0 or grep_device_tree_model_raspberrypi.rc == 0
+  when: (grep_cpuinfo_raspberrypi.rc | default(1)) == 0 or (grep_device_tree_model_raspberrypi.rc | default(1)) == 0
 
 - name: Set detected_distribution to Raspbian (ARM64 on Raspbian, Debian Buster/Bullseye/Bookworm)
   ansible.builtin.set_fact: