[root@node4 ~]# cat /etc/libvirt/qemu/centos6-64-base.xml
<!--
WARNING: THIS IS AN AUTO-GENERATED FILE. CHANGES TO IT ARE LIKELY TO BE
OVERWRITTEN AND LOST. Changes to this xml configuration should be made using:
  virsh edit centos6-64-base
or other application using the libvirt API.
-->

<domain type='kvm'>
  <name>centos6-64-base</name>
  <uuid>10218392-7792-1f09-7c39-8652a82f1bb0</uuid>
  <memory>1048576</memory>
  <currentMemory>1048576</currentMemory>
  <vcpu>1</vcpu>
  <os>
    <type arch='x86_64' machine='pc-0.14'>hvm</type>
    <boot dev='hd'/>
  </os>
  <features>
    <acpi/>
    <apic/>
    <pae/>
  </features>
  <clock offset='utc'/>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>restart</on_crash>
  <devices>
    <emulator>/usr/bin/qemu-kvm</emulator>
    <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2'/>
      <source file='/var/lib/libvirt/images/centos-64-base-disk0.qcow2'/>
      <target dev='vda' bus='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
    </disk>
    <interface type='bridge'>
      <mac address='52:54:00:17:db:5d'/>
      <source bridge='br0'/>
      <model type='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    </interface>
    <serial type='pty'>
      <target port='0'/>
    </serial>
    <console type='pty'>
      <target type='serial' port='0'/>
    </console>
    <input type='tablet' bus='usb'/>
    <input type='mouse' bus='ps2'/>
    <graphics type='vnc' port='-1' autoport='yes'/>
    <video>
      <model type='cirrus' vram='9216' heads='1'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
    </video>
    <memballoon model='virtio'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/>
    </memballoon>
  </devices>
</domain>

[root@node4 ~]# brctl show
bridge name	bridge id		STP enabled	interfaces
br0		8000.0025906239b4	no		bond0
							vnet0
							vnet1
virbr0		8000.5254007f5d9e	yes		virbr0-nic


qemu cmd:

LC_ALL=C PATH=/sbin:/usr/sbin:/bin:/usr/bin QEMU_AUDIO_DRV=none /usr/bin/qemu-kvm -S -M pc-0.14 -enable-kvm -m 1024 -smp 1,sockets=1,cores=1,threads=1 -name centos6-64-base -uuid 10218392-7792-1f09-7c39-8652a82f1bb0 -nodefconfig -nodefaults -chardev socket,id=charmonitor,path=/var/lib/libvirt/qemu/centos6-64-base.monitor,server,nowait -mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc -no-reboot -kernel /var/lib/libvirt/boot/virtinst-vmlinuz.pf_6MA -initrd /var/lib/libvirt/boot/virtinst-initrd.img.zDkPZo -append method=http://centos2.cpanel.net/centos-6/6.0/os/x86_64/ -drive file=/var/lib/libvirt/images/centos-64-base-disk0.qcow2,if=none,id=drive-virtio-disk0,format=qcow2 -device virtio-blk-pci,bus=pci.0,addr=0x4,drive=drive-virtio-disk0,id=virtio-disk0 -netdev tap,fd=26,id=hostnet0 -device virtio-net-pci,netdev=hostnet0,id=net0,mac=52:54:00:17:db:5d,bus=pci.0,addr=0x3 -chardev pty,id=charserial0 -device isa-serial,chardev=charserial0,id=serial0 -usb -device usb-tablet,id=input0 -vnc 127.0.0.1:0 -vga cirrus -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x5
char device redirected to /dev/pts/2