virt: Merge changes from master to resolve conflict

diff --combined src/collectd.conf.pod
index 8960597,2f3322f..ae52bee
--- 1/src/collectd.conf.pod
--- 2/src/collectd.conf.pod
+++ b/src/collectd.conf.pod
@@@ -9287,7 -9287,7 +9287,7 @@@ be set to C<var_lib_libvirt_images_imag
  Setting C<BlockDeviceFormatBasename true> will cause the I<type instance> to be
  set to C<image1.qcow2>.
  
 -=item B<HostnameFormat> B<name|uuid|hostname|...>
 +=item B<HostnameFormat> B<name|uuid|hostname|metadata...>
  
  When the virt plugin logs data, it sets the hostname of the collected data
  according to this setting. The default is to use the guest name as provided by
@@@ -9300,9 -9300,6 +9300,9 @@@ B<hostname> means to use the global B<H
  useful on its own because all guests will appear to have the same name. This is
  useful in conjunction with B<PluginInstanceFormat> though.
  
 +B<metadata> means use information from guest's metadata. Use
 +B<HostnameMetadataNS> and B<HostnameMetadataXPath> to localize this information.
 +
  You can also specify combinations of these fields. For example B<name uuid>
  means to concatenate the guest name and UUID (with a literal colon character
  between, thus I<"foo:1234-1234-1234-1234">).
@@@ -9321,37 -9318,18 +9321,37 @@@ setting B<name>
  B<address> means use the interface's mac address. This is useful since the
  interface path might change between reboots of a guest or across migrations.
  
 -=item B<PluginInstanceFormat> B<name|uuid|none>
 +=item B<PluginInstanceFormat> B<name|uuid|metadata|none>
  
  When the virt plugin logs data, it sets the plugin_instance of the collected
  data according to this setting. The default is to not set the plugin_instance.
  
  B<name> means use the guest's name as provided by the hypervisor.
  B<uuid> means use the guest's UUID.
 +B<metadata> means use information from guest's metadata.
  
  You can also specify combinations of the B<name> and B<uuid> fields.
  For example B<name uuid> means to concatenate the guest name and UUID
  (with a literal colon character between, thus I<"foo:1234-1234-1234-1234">).
  
 +=item B<HostnameMetadataNS> B<string>
 +
 +When B<metadata> is used in B<HostnameFormat> or B<PluginInstanceFormat>, this
 +selects in which metadata namespace we will pick the hostname. The default is
 +I<http://openstack.org/xmlns/libvirt/nova/1.0>.
 +
 +=item B<HostnameMetadataXPath> B<string>
 +
 +When B<metadata> is used in B<HostnameFormat> or B<PluginInstanceFormat>, this
 +describes where the hostname is located in the libvirt metadata. The default is
 +I</instance/name/text()>.
 +
 +=item B<Instances> B<integer>
 +
 +How many read instances you want to use for this plugin. The default is one,
 +and the sensible setting is a multiple of the B<ReadThreads> value.
 +If you are not sure, just use the default setting.
 +
  =item B<ExtraStats> B<string>
  
  Report additional extra statistics. The default is no extra statistics, preserving
@@@ -9402,11 -9380,38 +9402,38 @@@ B<Note>: I<perf> metrics can't be colle
  =back
  
  =item B<PersistentNotification> B<true>|B<false>
+ 
  Override default configuration to only send notifications when there is a change
  in the lifecycle state of a domain. When set to true notifications will be sent
  for every read cycle. Default is false. Does not affect the stats being
  dispatched.
  
+ =item B<Instances> B<integer>
+ 
+ How many read instances you want to use for this plugin. The default is one,
+ and the sensible setting is a multiple of the B<ReadThreads> value.
+ 
+ This option is only useful then domains are specially tagged.
+ If you are not sure, just use the default setting.
+ 
+ The reader instance will only query the domains with attached a matching tag.
+ Tags should have the form of 'virt-X' where X is reader instance number,
+ starting from 0.
+ 
+ The special-purpose reader instance #0, guaranteed to be always present,
+ will query all the domains with missing or unrecognized tag, so no domain will
+ ever left out.
+ 
+ Domain tagging is done with custom attribute in the libvirt domain metadata
+ section. Value is taken by XPath I</domain/metadata/ovirtmap/tag/text()>
+ expression in I<http://ovirt.org/ovirtmap/tag/1.0> namespace.
+ (XPath and namespace values are not configurable yet).
+ 
+ Tagging could be used by management application to evenly spread the
+ load among the reader threads, or to pin on the same threads all
+ the libvirt domains which use the same shared storage, to minimize
+ the disruption in presence of storage outages.
+ 
  =back
  
  =head2 Plugin C<vmem>