Support configuration of engine, emulator and CPU arch

For the engine and emulator configuration, some level of autodetection
is supported - if KVM is supported, this will be used, otherwise QEMU
will be used.

Much of the logic added here has been adapted from the ironic devstack
plugin's tooling.

Author: markgoddard

README.md

@@ -21,6 +21,14 @@ Defaults to `present`.
 
 `libvirt_vm_vcpus`: the number of VCPU cores to assign to the VM.
 
+`libvirt_vm_engine`: virtualisation engine. If not set, the role will attempt
+to auto-detect the optimal engine to use.
+
+`libvirt_vm_emulator`: path to emulator binary. If not set, the role will
+attempt to auto-detect the correct emulator to use.
+
+`libvirt_vm_arch`: CPU architecture, default is `x86_64`.
+
 `libvirt_vm_volumes`: a list of volumes to attach to the VM.  Each volume is
 defined with the following dict:
 - `name`: Name to associate with the volume being created.

defaults/main.yml

@@ -11,6 +11,17 @@ libvirt_vm_memory_mb:
 # Number of vCPUs.
 libvirt_vm_vcpus:
 
+# Virtualisation engine. If not set, the role will attempt to auto-detect the
+# optimal engine to use.
+libvirt_vm_engine:
+
+# Path to emulator binary. If not set, the role will attempt to auto-detect the
+# correct emulator to use.
+libvirt_vm_emulator:
+
+# CPU architecture.
+libvirt_vm_arch: x86_64
+
 # List of volumes.
 libvirt_vm_volumes: []
 

tasks/autodetect.yml

@@ -0,0 +1,53 @@
+---
+- name: Detect the virtualisation engine
+  block:
+    - name: Load the kvm kernel module
+      modprobe:
+        name: kvm
+      become: true
+      failed_when: false
+
+    - name: Check for the KVM device
+      stat:
+        path: /dev/kvm
+      register: stat_kvm
+
+    - name: Set a fact containing the virtualisation engine
+      set_fact:
+        libvirt_vm_engine: "{% if stat_kvm.stat.exists %}kvm{% else %}qemu{% endif %}"
+  when: libvirt_vm_engine is none
+
+- name: Detect the virtualisation emulator
+  block:
+    - block:
+        - name: Detect the KVM emulator binary path
+          stat:
+            path: "{{ item }}"
+          register: kvm_emulator_result
+          with_items:
+            - /usr/bin/kvm
+            - /usr/bin/qemu-kvm
+            - /usr/libexec/qemu-kvm
+
+        - name: Set a fact containing the KVM emulator binary path
+          set_fact:
+            libvirt_vm_emulator: "{{ item.item }}"
+          with_items: "{{ kvm_emulator_result.results }}"
+          when: item.stat.exists
+      when: libvirt_vm_engine == 'kvm'
+
+    - block:
+        - name: Detect the QEMU emulator binary path
+          shell: which qemu-system-{{ libvirt_vm_arch }}
+          register: qemu_emulator_result
+
+        - name: Set a fact containing the QEMU emulator binary path
+          set_fact:
+            libvirt_vm_emulator: "{{ qemu_emulator_result.stdout }}"
+      when: libvirt_vm_engine == 'qemu'
+
+    - name: Fail if unable to detect the emulator
+      fail:
+        msg: Unable to detect emulator for engine {{ libvirt_vm_engine }}.
+      when: libvirt_vm_emulator is none
+  when: libvirt_vm_emulator is none

tasks/main.yml

@@ -1,5 +1,6 @@
 ---
 - block:
+    - include: autodetect.yml
     - include: volumes.yml
     - include: vm.yml
   when: libvirt_vm_state == 'present'

templates/vm.xml.j2

@@ -1,12 +1,16 @@
-<domain type='kvm'>
+<domain type='{{ libvirt_vm_engine }}'>
   <name>{{ libvirt_vm_name }}</name>
   <memory>{{ libvirt_vm_memory_mb | int * 1024 }}</memory>
   <vcpu>{{ libvirt_vm_vcpus }}</vcpu>
   <clock sync="localtime"/>
   <os>
-    <type arch='x86_64'>hvm</type>
+    <type arch='{{ libvirt_vm_arch }}'>hvm</type>
   </os>
+  {% if libvirt_vm_engine == 'kvm' %}
+  <cpu mode='host-passthrough'/>
+  {% endif %}
   <devices>
+    <emulator>{{ libvirt_vm_emulator }}</emulator>
 {% for volume in libvirt_vm_volumes %}
     <disk type='volume' device='{{ volume.device | default('disk') }}'>
       <driver name='qemu' type='{{ volume.format }}'/>