20.16.16. Channel

This represents a private communication channel between the host physical machine and the guest virtual machine and is manipulated by making changes to your guest virtual machine virtual machine using a management tool that results in changes made to the following section of the domain xml 

  ...
  <devices>
    <channel type='unix'>
      <source mode='bind' path='/tmp/guestfwd'/>
      <target type='guestfwd' address='10.0.2.1' port='4600'/>
    </channel>

    <!-- KVM virtio channel -->
    <channel type='pty'>
      <target type='virtio' name='arbitrary.virtio.serial.port.name'/>
    </channel>
    <channel type='unix'>
      <source mode='bind' path='/var/lib/libvirt/qemu/f16x86_64.agent'/>
      <target type='virtio' name='org.qemu.guest_agent.0'/>
    </channel>
    <channel type='spicevmc'>
      <target type='virtio' name='com.redhat.spice.0'/>
    </channel>
  </devices>
  ...

Figure 20.63. Channel

This can be implemented in a variety of ways. The specific type of <channel> is given in the type attribute of the <target> element. Different channel types have different target attributes as follows:
  • guestfwd - Dictates that TCP traffic sent by the guest virtual machine to a given IP address and port is forwarded to the channel device on the host physical machine. The target element must have address and port attributes.
  • virtio - Paravirtualized virtio channel. <channel> is exposed in the guest virtual machine under /dev/vport*, and if the optional element nameis specified, /dev/virtio-ports/$name (for more info, see http://fedoraproject.org/wiki/Features/VirtioSerial). The optional element address can tie the channel to a particular type='virtio-serial' controller, documented above. With QEMU, if name is "org.qemu.guest_agent.0", then libvirt can interact with a guest virtual machine agent installed in the guest virtual machine, for actions such as guest virtual machine shutdown or file system quiescing.
  • spicevmc - Paravirtualized SPICE channel. The domain must also have a SPICE server as a graphics device, at which point the host physical machine piggy-backs messages across the main channel. The target element must be present, with attribute type='virtio'; an optional attribute name controls how the guest virtual machine will have access to the channel, and defaults to name='com.redhat.spice.0'. The optional <address> element can tie the channel to a particular type='virtio-serial' controller.