16.6. Random Number Generator Device

Procedure 16.11. Implementing virtio-rng using the Virtual Machine Manager

1. Shut down the guest virtual machine.
2. Select the guest virtual machine and from the Edit menu, select Virtual Machine Details, to open the Details window for the specified guest virtual machine.
3. Click the Add Hardware button.
4. In the Add New Virtual Hardware window, select RNG to open the Random Number Generator window.
   

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   Figure 16.20. Random Number Generator window

   Enter the intended parameters and click Finish when done. The parameters are explained in virtio-rng elements.

Procedure 16.12. Implementing virtio-rng using command-line tools

1. Shut down the guest virtual machine.
2. Using the virsh edit domain-name command, open the XML file for the intended guest virtual machine.
3. Edit the <devices> element to include the following:

     ...
     <devices>
       <rng model='virtio'>
         <rate period='2000' bytes='1234'/>
         <backend model='random'>/dev/random</backend>
         <!-- OR -->
         <backend model='egd' type='udp'>
           <source mode='bind' service='1234'/>
           <source mode='connect' host='1.2.3.4' service='1234'/>
         </backend>
       </rng>
     </devices>
     ...

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   Figure 16.21. Random number generator device

   The random number generator device allows the following XML attributes and elements:

   virtio-rng elements

   • <model> - The required model attribute specifies what type of RNG device is provided.
   • <backend model> - The <backend> element specifies the source of entropy to be used for the guest. The source model is configured using the model attribute. Supported source models include 'random' and 'egd' .
     • <backend model='random'> - This <backend> type expects a non-blocking character device as input. Examples of such devices are /dev/random and /dev/urandom. The file name is specified as contents of the <backend> element. When no file name is specified the hypervisor default is used.
     • <backend model='egd'> - This back end connects to a source using the EGD protocol. The source is specified as a character device. See character device host physical machine interface for more information.