Parameterize disk_cachemodes

The current manifests don't expose a way for end users to set
the disk_cachemodes directive in nova.conf, which can be useful
for improving disk performance.  This patch adds a parameter
allowing users to specify a list of values to be written in
to the disk_cachemodes setting.  The default value is an empty
list, which will cause the disk_cachemodes setting to be removed
entirely from nova.conf (thus matching the Nova default and
current behavior).

This patch is based on 0a5d6568f070d193b604513f194c966cc224a86b
but is slightly modified to account for a change in how the
nova.conf file is organized between Havana and Icehouse
(some libvirt params were moved from the [DEFAULT] section
to the new [libvirt] section in Icehouse).

Change-Id: I9173ef79e4e573515f290734535907794dda7dbf
(cherry picked from commit 0a5d6568f070d193b604513f194c966cc224a86b)

manifests/compute/libvirt.pp

@@ -23,11 +23,20 @@
 #   Defaults to 'host-model' if libvirt_type is set to either
 #   kvm or qemu, otherwise defaults to 'None'.
 #
+# [*libvirt_disk_cachemodes*]
+#   (optional) A list of cachemodes for different disk types, e.g.
+#   ["file=directsync", "block=none"]
+#   If an empty list is specified, the disk_cachemodes directive
+#   will be removed from nova.conf completely.
+#   Defaults to an empty list
+#
+
 class nova::compute::libvirt (
-  $libvirt_type      = 'kvm',
-  $vncserver_listen  = '127.0.0.1',
-  $migration_support = false,
-  $libvirt_cpu_mode  = false,
+  $libvirt_type            = 'kvm',
+  $vncserver_listen        = '127.0.0.1',
+  $migration_support       = false,
+  $libvirt_cpu_mode        = false,
+  $libvirt_disk_cachemodes = [],
 ) {
 
   include nova::params
@@ -93,4 +102,14 @@
     'DEFAULT/vncserver_listen': value => $vncserver_listen;
     'DEFAULT/libvirt_cpu_mode': value => $libvirt_cpu_mode_real;
   }
+
+  if size($libvirt_disk_cachemodes) > 0 {
+    nova_config {
+      'DEFAULT/disk_cachemodes': value => join($libvirt_disk_cachemodes, ',');
+    }
+  } else {
+    nova_config {
+      'DEFAULT/disk_cachemodes': ensure => absent;
+    }
+  }
 }

spec/classes/nova_compute_libvirt_spec.rb

@@ -38,19 +38,22 @@
       it { should contain_nova_config('DEFAULT/connection_type').with_value('libvirt')}
       it { should contain_nova_config('DEFAULT/vncserver_listen').with_value('127.0.0.1')}
       it { should contain_nova_config('DEFAULT/libvirt_cpu_mode').with_value('host-model')}
+      it { should contain_nova_config('DEFAULT/disk_cachemodes').with_ensure('absent')}
     end
 
     describe 'with params' do
       let :params do
         { :libvirt_type     => 'qemu',
           :vncserver_listen => '0.0.0.0',
-          :libvirt_cpu_mode => 'host-passthrough'
+          :libvirt_cpu_mode => 'host-passthrough',
+          :libvirt_disk_cachemodes => ['file=directsync','block=none']
         }
       end
 
       it { should contain_nova_config('DEFAULT/libvirt_type').with_value('qemu')}
       it { should contain_nova_config('DEFAULT/vncserver_listen').with_value('0.0.0.0')}
       it { should contain_nova_config('DEFAULT/libvirt_cpu_mode').with_value('host-passthrough')}
+      it { should contain_nova_config('DEFAULT/disk_cachemodes').with_value('file=directsync,block=none')}
     end
 
     describe 'with migration_support enabled' do