[libvirt-users] can someone explain why the domain, function bus, slot function is used in this xml

[lei yang]

I don't understand the domain bus slot fuction in below xml,becase,
this is used when deal with management of host devices that can be
handed to guests via passthrough as <hostdev> elements in the domain
XML.( from http://libvirt.org/formatnode.html)

I don't see it use passthrough feature, why it has "domain" bus" slot"
and function here


<disk type='file' device='disk'>
<driver name='qemu' type='raw'/>
<source file='/kvm/images/disk/vmname_boot.img'/>
<target dev='vda' bus='virtio'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
</disk>

<interface type='bridge'>
<mac address='52:54:00:07:ab:b0'/>
<source bridge='br0'/>
<model type='virtio'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
</interface>

which originally comes from this blog:
http://blog.allanglesit.com/2011/03/kvm-guests-manipulating-libvirt-xml-for-guest-creation/

Any point?