Red Hat Training

A Red Hat training course is available for Red Hat Enterprise Linux

20.16.15. Guest Virtual Machine Interfaces

A character device presents itself to the guest virtual machine as one of the following types.
To set the parallel port, use a management tool to make the following change to the domain XML

...
  <devices>
    <parallel type='pty'>
      <source path='/dev/pts/2'/>
      <target port='0'/>
    </parallel>
  </devices>
  ...

Figure 20.60. Guest virtual machine interface Parallel Port

<target> can have a port attribute, which specifies the port number. Ports are numbered starting from 0. There are usually 0, 1 or 2 parallel ports.
To set the serial port use a management tool to make the following change to the domain XML:

  ...
  <devices>
    <serial type='pty'>
      <source path='/dev/pts/3'/>
      <target port='0'/>
    </serial>
  </devices>
  ...

Figure 20.61. Guest virtual machine interface serial port

<target> can have a port attribute, which specifies the port number. Ports are numbered starting from 0. There are usually 0, 1 or 2 serial ports. There is also an optional type attribute, which has two choices for its value, one is isa-serial, the other is usb-serial. If type is missing, isa-serial will be used by default. For usb-serial an optional sub-element <address> with type='usb' can tie the device to a particular controller, documented above.
The <console> element is used to represent interactive consoles. Depending on the type of guest virtual machine in use, the consoles might be paravirtualized devices, or they might be a clone of a serial device, according to the following rules:
  • If no targetType attribute is set, then the default device type is according to the hypervisor's rules. The default type will be added when re-querying the XML fed into libvirt. For fully virtualized guest virtual machines, the default device type will usually be a serial port.
  • If the targetType attribute is serial, and if no <serial> element exists, the console element will be copied to the <serial> element. If a <serial> element does already exist, the console element will be ignored.
  • If the targetType attribute is not serial, it will be treated normally.
  • Only the first <console> element may use a targetType of serial. Secondary consoles must all be paravirtualized.
  • On s390, the console element may use a targetType of sclp or sclplm (line mode). SCLP is the native console type for s390. There's no controller associated to SCLP consoles.
In the example below, a virtio console device is exposed in the guest virtual machine as /dev/hvc[0-7] (for more information, see http://fedoraproject.org/wiki/Features/VirtioSerial):

  ...
  <devices>
    <console type='pty'>
      <source path='/dev/pts/4'/>
      <target port='0'/>
    </console>

    <!-- KVM virtio console -->
    <console type='pty'>
      <source path='/dev/pts/5'/>
      <target type='virtio' port='0'/>
    </console>
  </devices>
  ...

  ...
  <devices>
    <!-- KVM s390 sclp console -->
    <console type='pty'>
      <source path='/dev/pts/1'/>
      <target type='sclp' port='0'/>
    </console>
  </devices>
  ...

Figure 20.62. Guest virtual machine interface - virtio console device

If the console is presented as a serial port, the <target> element has the same attributes as for a serial port. There is usually only one console.