from http://blog.csdn.net/ustc_dylan/article/details/7685259

libvirt_sample.xml

<domain type='kvm'>
    <name>test_ubuntu</name>
    <memory>1048576</memory>
    <vcpu>8</vcpu>
    <os>
        <type arch='x86_64' machine='pc'>hvm</type>
        <boot dev='cdrom'/>
    </os>
    <features>
        <acpi/>
        <apic/>
        <pae/>
    </features>
    <clock offset='localtime'/>
    <on_poweroff>destroy</on_poweroff>
    <on_reboot>restart</on_reboot>
    <on_crash>destroy</on_crash>
    <devices>
        <emulator>/usr/libexec/qemu-kvm</emulator>
        <disk type='file' device='disk'>
            <driver name='qemu' type='qcow2'/>
            <source file='/var/lib/libvirt/images/test.qcow2'/>
            <target dev='hda' bus='ide'/>
        </disk>
        <disk type='file' device='cdrom'>
            <source file='/var/lib/libvirt/images/ubuntu.iso'/>
            <target dev='hdb' bus='ide'/>
        </disk>
        <interface type='bridge'>
            <source bridge='kvmbr0'/>
            <mac address="00:16:3e:5d:aa:a8"/>
        </interface>
        <input type='mouse' bus='ps2'/>
        <graphics type='vnc' port='-1' autoport='yes' listen = '0.0.0.0' keymap='en-us'/>
    </devices>
</domain>