使用网桥br0 xml片断
<interface type='bridge'>
<mac address='00:11:22:33:44:55'/>
<source bridge='br0'/>
</interface>
使用virtio片段并禁用cache
<disk type='file' device='disk'>
<driver name='qemu' type='qcow2' cache='none'/>
<source file='/vmstore/images/centos_test0_preallc.qcow2'/>
<target dev='vda' bus='virtio'/>
<address type='drive' controller='0' bus='0' unit='0'/>
</disk>
不太懂得地方：
<domain type='xen' id='3'>
<name>fv0</name>
<uuid>4dea22b31d52d8f32516782e98ab3fa0</uuid>
<title>A short description - title - of the domain</title>
<description>Some human readable description</description>
<metadata>
<app1:foo xmlns:app1="http://app1.org/app1/">..</app1:foo>
<app2:bar xmlns:app2="http://app1.org/app2/">..</app2:bar>
</metadata>
metadata 是为应用程序自定义的元数据，是什么地方/怎么用的？